U.S. patent number RE48,024 [Application Number 14/681,764] was granted by the patent office on 2020-06-02 for obstructive sleep apnea treatment devices, systems and methods.
This patent grant is currently assigned to LivaNova USA, Inc.. The grantee listed for this patent is LivaNova USA, Inc.. Invention is credited to Robert E. Atkinson, Stephen L. Bolea, Sidney F. Hauschild, Thomas B. Hoegh, Keith E. Jasperson, Paula M. Kaplan, Brian D. Kuhnley, Bruce J. Persson, Wondimeneh Tesfayesus, Christopher K. Thorp.
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United States Patent |
RE48,024 |
Bolea , et al. |
June 2, 2020 |
Obstructive sleep apnea treatment devices, systems and methods
Abstract
Devices, systems and methods for nerve stimulation for OSA
therapy.
Inventors: |
Bolea; Stephen L. (Watertown,
MN), Hoegh; Thomas B. (Edina, MN), Persson; Bruce J.
(Dresser, WI), Atkinson; Robert E. (Elmo, MN), Hauschild;
Sidney F. (St. Paul, MN), Kaplan; Paula M. (St. Paul,
MN), Kuhnley; Brian D. (Maple Grove, MN), Jasperson;
Keith E. (Andover, MN), Tesfayesus; Wondimeneh (St.
Paul, MN), Thorp; Christopher K. (Chanhassen, MN) |
Applicant: |
Name |
City |
State |
Country |
Type |
LivaNova USA, Inc. |
Houston |
TX |
US |
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|
Assignee: |
LivaNova USA, Inc. (Houston,
TX)
|
Family
ID: |
39185965 |
Appl.
No.: |
14/681,764 |
Filed: |
April 8, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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60851386 |
Oct 13, 2006 |
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60918257 |
Mar 14, 2007 |
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Reissue of: |
11907533 |
Oct 12, 2007 |
8417343 |
Apr 9, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N
1/3606 (20130101); A61N 1/0558 (20130101); A61N
1/0556 (20130101); A61N 1/37229 (20130101); A61N
1/3601 (20130101); A61N 1/0558 (20130101); A61N
1/3606 (20130101); A61N 1/37229 (20130101); A61N
1/0556 (20130101); A61N 1/3601 (20130101); A61B
5/7239 (20130101); A61B 5/0809 (20130101); A61B
5/4818 (20130101); A61B 5/0809 (20130101); A61B
5/7239 (20130101); A61B 5/4818 (20130101) |
Current International
Class: |
A61N
1/36 (20060101); A61N 1/372 (20060101); A61N
1/05 (20060101); A61B 5/08 (20060101); A61B
5/00 (20060101) |
References Cited
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|
Primary Examiner: Williams; Catherine S
Attorney, Agent or Firm: Foley & Lardner LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This .[.patent.]. application .Iadd.is a reissue application of
U.S. Pat. No. 8,417,343 B2, which issued on Apr. 9, 2013, from U.S.
patent application Ser. No. 11/907,533, filed on Oct. 12, 2007,
which .Iaddend.claims the benefits of priority under 35 U.S.C.
.sctn..sctn.119 and 120 to U.S. Provisional Patent Application Nos.
60/851,386 and 60/918,257, filed on Oct. 13, 2006, and Mar. 14,
2007, respectively.Iadd., the disclosures of which are expressly
incorporated by reference herein.Iaddend.. .[.The entire contents
of these provisional applications are incorporated herein by
reference..]. .Iadd.This application is related to reissue
application Ser. No. 14/693,836, filed on Apr. 22, 2015..Iaddend.
Claims
What is claimed is:
1. A method of treating obstructive sleep apnea, the method
comprising: chronically implanting an electrode on a nerve
innervating an upper airway dilator muscle; sensing a measure of
respiration; analyzing the measure of respiration to identify
onsets of expiration; calculating a respiratory period from the
onsets of expiration; predicting the onset of a future expiratory
phase; and beginning stimulation of the nerve a fraction of the
calculated respiratory period before the onset of the future
expiratory phase, and continuing stimulation of the nerve during an
entire inspiratory phase, wherein the method is performed without
identifying an onset of the inspiratory phase.
2. The method of claim 1, wherein the fraction ranges between
30/100 and 50/100.
3. The method of claim 1, wherein the fraction is selectively
adjustable.
4. The method of claim 1, wherein the measure of respiration is
bio-impedance.
5. The method of claim 1, wherein the electrode is disposed on a
nerve cuff operably connected to a first end of a stimulation
lead.
6. The method of claim 5, wherein a second end of the stimulation
lead is operably connected to a neurostimulator.
7. The method of claim 6, wherein the neurostimulator is operably
connected to a respiration sensing lead having a proximal end and a
distal portion, wherein the distal portion is connected to a
respiration sensor.
8. The method of claim 6, wherein the neurostimulator includes
electronics containing an algorithm.
9. The method of claim 8, wherein the algorithm triggers the
delivery of the stimulation via the stimulation lead.
10. The method of claim 5, wherein the stimulation lead includes a
sigmoid-shaped section.
11. The method of claim 5, wherein the nerve cuff is cylindrical
and includes a first semi-cylindrical portion connected to a second
semi-cylindrical portion.
12. The method of claim 11, wherein the first semi-cylindrical
portion is shorter in length than the second semi-cylindrical
portion.
13. The method of claim 5, wherein the nerve cuff is cylindrical
and includes a semi-cylindrical portion having a plurality of
extending semi-cylindrical arms having free ends.
14. The method of claim 5, wherein the nerve cuff includes a
plurality of electrodes configured to steer an electrical
field.
15. A method of treating obstructive sleep apnea, the method
comprising: obtaining a respiration waveform; analyzing the
respiration waveform to identify onsets of expiration; calculating
a respiratory period from the onsets of expiration; predicting the
onset of a future expiratory phase; and stimulating a nerve to
cause dilation of a patient's upper airway, wherein stimulation of
the nerve begins a fraction of the calculated respiratory period
before the onset of the future expiratory phase, and continuing
stimulation of the nerve during an entire inspiratory phase,
wherein the method is performed without identifying an onset of the
inspiratory phase.
16. The method of claim 15, wherein the fraction is selectively
adjustable.
17. The method of claim 15, wherein analyzing the respiration
waveform to identify onsets of expiration includes identifying a
peak of the respiration waveform.
.Iadd.18. A method of treating obstructive sleep apnea with an
electrode implanted on a nerve innervating an upper airway dilator
muscle, the method comprising: sensing a measure of respiration to
generate a respiration waveform; analyzing the respiration waveform
to identify onsets of expiration; calculating a respiratory period
from the onsets of expiration identified in the respiration
waveform; and beginning stimulation of the nerve a fraction of the
calculated respiratory period before an onset of a subsequent
expiratory phase, and continuing stimulation of the nerve during an
entire inspiratory phase, wherein the method is performed without
identifying an onset of the inspiratory phase..Iaddend.
.Iadd.19. The method of claim 18, wherein the fraction ranges
between 30/100 and 50/100..Iaddend.
.Iadd.20. The method of claim 18, wherein the fraction is
selectively adjustable..Iaddend.
.Iadd.21. The method of claim 18, wherein the fraction of the
calculated respiratory period is a predetermined amount of
time..Iaddend.
.Iadd.22. The method of claim 18, wherein the measure of
respiration is bio-impedance..Iaddend.
.Iadd.23. The method of claim 18, wherein the electrode is disposed
on a nerve cuff operably connected to a first end of a stimulation
lead including a first sigmoid section..Iaddend.
.Iadd.24. The method of claim 23, wherein the stimulation lead
includes an anchor device disposed between the first sigmoid
section and a second sigmoid section..Iaddend.
.Iadd.25. The method of claim 23, wherein a second end of the
stimulation lead is operably connected to a
neurostimulator..Iaddend.
.Iadd.26. The method of claim 25, wherein the neurostimulator is
operably connected to a respiration sensing lead having a proximal
end and a distal portion, wherein the distal portion is connected
to a respiration sensor..Iaddend.
.Iadd.27. The method of claim 23, wherein the nerve cuff is
cylindrical and includes a first semi-cylindrical portion connected
to a second semi-cylindrical portion..Iaddend.
.Iadd.28. The method of claim 27, wherein the first
semi-cylindrical portion is shorter in length than the second
semi-cylindrical portion..Iaddend.
.Iadd.29. The method of claim 23, wherein the nerve cuff is
cylindrical and includes a semi-cylindrical portion having a
plurality of semi-cylindrical arms extending therefrom, the
plurality of semi-cylindrical arms having free ends..Iaddend.
.Iadd.30. The method of claim 23, wherein the nerve cuff includes a
plurality of electrodes configured to steer an electrical
field..Iaddend.
.Iadd.31. The method of claim 18, wherein the onsets of expiration
are identified without identifying an onset of an inspiratory
phase..Iaddend.
.Iadd.32. A method of treating obstructive sleep apnea the method
comprising: obtaining a respiration waveform; analyzing the
respiration waveform to identify onsets of expiration; calculating
a respiratory period from the identified onsets of expiration;
stimulating a nerve to cause dilation of a patient's upper airway,
wherein stimulation of the nerve begins a fraction of the
calculated respiratory period before an onset of an expiratory
phase; and continuing stimulation of the nerve during an entire
inspiratory phase, wherein the step of stimulating the nerve is
performed without identifying an onset of the inspiratory phase,
and wherein the stimulation is delivered to the nerve via an
electrode cuff positioned on the nerve and disposed on a distal end
of a stimulation lead having a sigmoid section..Iaddend.
.Iadd.33. The method of claim 32, wherein analyzing the respiration
waveform to identify onsets of expiration includes identifying a
peak of the respiration waveform..Iaddend.
.Iadd.34. The method of claim 32, wherein the onsets of expiration
are identified without identifying an onset of an inspiratory
phase..Iaddend.
.Iadd.35. A method of treating obstructive sleep apnea using an
electrode implanted on a nerve innervating an upper airway dilator
muscle, the method comprising: sensing a biological parameter to
generate a respiration waveform; analyzing the respiration waveform
to identify at least a first onset of expiration and a second onset
of expiration; calculating a respiratory period from the identified
first and second onsets of expiration; and beginning stimulation of
the nerve a fraction of the calculated respiratory period after the
identified second onset of expiration, and continuing stimulation
of the nerve during an entire inspiratory phase subsequent to the
identified second onset of expiration, wherein the step of
beginning stimulation is performed without identifying an onset of
the subsequent inspiratory phase..Iaddend.
.Iadd.36. The method of claim 35, wherein the fraction ranges
between 50/100 to 70/100..Iaddend.
.Iadd.37. The method of claim 35, wherein the electrode is disposed
on a nerve cuff operably connected to a first end of a stimulation
lead including a first sigmoid section..Iaddend.
.Iadd.38. The method of claim 37, wherein the stimulation lead
includes an anchor disposed between the first sigmoid section and a
second sigmoid section..Iaddend.
.Iadd.39. The method of claim 35, wherein the first and second
onsets of expiration are identified without identifying an onset of
an inspiratory phase..Iaddend.
.Iadd.40. A method of treating obstructive sleep apnea with an
electrode implanted on a nerve innervating an upper airway dilator
muscle, the method comprising: sensing a measure of respiration;
analyzing the measure of respiration to identify onsets of
expiration; calculating a respiratory period from the onsets of
expiration; and beginning stimulation of the nerve a fraction of
the calculated respiratory period before an onset of an expiratory
phase, and continuing stimulation of the nerve during an entire
inspiratory phase, wherein the method is performed without
identifying an onset of the inspiratory phase..Iaddend.
.Iadd.41. The method of claim 40, wherein the electrode is disposed
on a nerve cuff operably connected to a first end of a stimulation
lead including a first sigmoid section..Iaddend.
.Iadd.42. The method of claim 41, wherein the stimulation lead
includes an anchor disposed between the first sigmoid section and a
second sigmoid section..Iaddend.
.Iadd.43. A method of treating obstructive sleep apnea using an
electrode implanted on a nerve innervating an upper airway dilator
muscle, the method comprising: sensing a measure of respiration;
analyzing the measure of respiration to identify onsets of
expiration; calculating a respiratory period from the onsets of
expiration; and beginning stimulation of the nerve a predetermined
amount of time after the onset of an expiratory phase, and
continuing stimulation of the nerve during an entire subsequent
inspiratory phase, wherein the method is performed without
identifying an onset of the subsequent inspiratory
phase..Iaddend.
.Iadd.44. The method of claim 43, wherein the electrode is disposed
on a nerve cuff operably connected to a first end of a stimulation
lead including a first sigmoid section..Iaddend.
.Iadd.45. The method of claim 44, wherein the stimulation lead
includes an anchor disposed between the first sigmoid section and a
second sigmoid section..Iaddend.
.Iadd.46. A method of treating obstructive sleep apnea with an
electrode implanted on a nerve innervating an upper airway dilator
muscle, the method comprising: sensing a measure of respiration;
analyzing the measure of respiration to identify onsets of
expiration; calculating a respiratory period from the identified
onsets of expiration; and beginning stimulation of the nerve a
fraction of the calculated respiratory period before an onset of a
subsequent expiratory phase, and continuing stimulation of the
nerve during an entire inspiratory phase prior to the subsequent
expiratory phase, wherein the step of beginning stimulation is
performed without identifying an onset of the inspiratory
phase..Iaddend.
.Iadd.47. The method of claim 46, wherein the fraction ranges
between 30/100 and 50/100..Iaddend.
.Iadd.48. The method of claim 46, wherein the onsets of expiration
are identified without identifying an onset of an inspiratory
phase..Iaddend.
.Iadd.49. A method of treating obstructive sleep apnea with an
electrode implanted on a nerve innervating an upper airway dilator
muscle of a subject having a breathing pattern, the method
comprising: identifying onsets of expiration by analyzing portions
of the breathing pattern; calculating a respiratory period from the
identified onsets of expiration; and beginning stimulation of the
nerve a fraction of the calculated respiratory period before an
onset of a subsequent expiratory phase, and continuing stimulation
of the nerve during an entire inspiratory phase prior to the
subsequent expiratory phase, wherein the step of beginning
stimulation is performed without identifying an onset of the
inspiratory phase..Iaddend.
.Iadd.50. The method of claim 49, wherein the fraction ranges
between 30/100 and 50/100..Iaddend.
.Iadd.51. The method of claim 49, wherein the onsets of expiration
are identified without identifying an onset of an inspiratory
phase..Iaddend.
Description
FIELD OF THE INVENTION
The inventions described herein relate to devices, systems and
associated methods for treating sleeping disorders. More
particularly, the inventions described herein relate to devices,
systems and methods for treating obstructive sleep apnea.
BACKGROUND OF THE INVENTION
Obstructive sleep apnea (OSA) is highly prevalent, affecting one in
five adults in the United States. One in fifteen adults has
moderate to severe OSA requiring treatment. Untreated OSA results
in reduced quality of life measures and increased risk of disease
including hypertension, stroke, heart disease, etc.
Continuous positive airway pressure (CPAP) is a standard treatment
for OSA. While CPAP is non-invasive and highly effective, it is not
well tolerated by patients. Patient compliance for CPAP is often
reported to be between 40% and 60%.
Surgical treatment options for OSA are available too. However, they
tend to be highly invasive (result in structural changes),
irreversible, and have poor and/or inconsistent efficacy. Even the
more effective surgical procedures are undesirable because they
usually require multiple invasive and irreversible operations, they
may alter a patient's appearance (e.g., maxillo-mandibulary
advancement), and/or they may be socially stigmatic (e.g.,
tracheostomy).
U.S. Pat. No. 4,830,008 to Meer proposes hypoglossal nerve
stimulation as an alternative treatment for OSA. An example of an
implanted hypoglossal nerve stimulator for OSA treatment is the
Inspire.TM. technology developed by Medtronic, Inc. (Fridely,
Minn.). The Inspire device is not FDA approved and is not for
commercial sale. The Inspire device includes an implanted
neurostimulator, an implanted nerve cuff electrode connected to the
neurostimulator by a lead, and an implanted intra-thoracic pressure
sensor for respiratory feedback and stimulus trigger. The Inspire
device was shown to be efficacious (approximately 75% response rate
as defined by a 50% or more reduction in RDI and a post RDI of
.ltoreq.20) in an eight patient human clinical study, the results
of which were published by Schwartz et al. and Eisele et al.
However, both authors reported that only three of eight patients
remained free from device malfunction, thus demonstrating the need
for improvements.
SUMMARY OF THE INVENTION
To address this and other unmet needs, the present invention
provides, in exemplary non-limiting embodiments, devices, systems
and methods for nerve stimulation for OSA therapy as described in
the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
It is to be understood that both the foregoing summary and the
following detailed description are exemplary. Together with the
following detailed description, the drawings illustrate exemplary
embodiments and serve to explain certain principles. In the
drawings:
FIG. 1 is a schematic diagram showing a fully implanted
neurostimulator system with associated physician programmer and
patient controller for treating obstructive sleep apnea;
FIG. 2 is a schematic diagram showing the implantable components of
FIG. 1 implanted in a patient;
FIG. 3 is a perspective view of the implantable components shown in
FIG. 1;
FIG. 4 is a detailed perspective view of the implantable
neurostimulator (INS) shown in FIG. 3;
FIG. 5 is a detailed perspective view of the nerve cuff electrode
and lead body shown in FIG. 3;
FIG. 5a is an illustration of exemplary movements a lead body may
be configured to withstand;
FIG. 6 is a close-up detailed perspective view of the nerve cuff
electrode shown in FIG. 3;
FIG. 7 is a detailed perspective view of the internal components of
the nerve cuff electrode shown in FIG. 6;
FIG. 8 shows side and end views of an electrode contact of the
nerve cuff electrode shown in FIG. 7;
FIGS. 9A and 9B are perspective views of the respiration sensing
lead shown in FIG. 3;
FIG. 10 schematically illustrates surgical access and tunneling
sites for implanting the system illustrated in FIG. 2;
FIGS. 11A and 11B schematically illustrate dissection to a
hypoglossal nerve;
FIGS. 12 and 12A-12D schematically illustrate various possible
nerve stimulation sites for activating muscles controlling the
upper airway;
FIGS. 13-22 and 22A-22D are schematic illustrations of various
stimulation lead body and electrode designs for use in a
neurostimulator system;
FIGS. 23-24 schematically illustrate alternative implant procedures
and associated tools for the stimulation lead;
FIG. 25 schematically illustrates an alternative bifurcated lead
body design;
FIGS. 26A-26B schematically illustrate alternative fixation
techniques for the stimulation lead and electrode cuff;
FIG. 26C schematically illustrates an alternative embodiment of a
stimulation lead having a fixation mechanism;
FIGS. 27A-27H schematically illustrate field steering
embodiments;
FIGS. 27I-27Q schematically illustrate alternative embodiments of
nerve cuff electrodes with selective fiber stimulation
mechanisms;
FIGS. 28-33B schematically illustrate alternative fixation
techniques for the respiration sensing lead;
FIG. 34 schematically illustrates the distal portion of an
exemplary respiration sensing lead
FIGS. 35A-35E and 36 schematically illustrate alternative electrode
arrangements on the respiration sensing lead;
FIGS. 37A-37C schematically illustrate various anatomical positions
or bio-Z vectors for the electrodes on the respiration sensing
lead;
FIG. 38A illustrates an exemplary method of sampling a plurality of
vector signals;
FIGS. 38B-46 schematically illustrate alternative respiration
signal processing techniques;
FIG. 47 schematically illustrates an alternative respiration
detection technique;
FIGS. 47A-47D illustrate an exemplary stimulation trigger
algorithm;
FIGS. 48-50 schematically illustrate alternative stimulation
trigger algorithms;
FIG. 50A illustrates an exemplary waveform of a patient's
respiratory cycle;
FIG. 50B illustrates an exemplary stimulation waveform;
FIGS. 51A-51M are schematic illustrations of various external
(partially implanted) neurostimulation systems for treating
obstructive sleep apnea;
FIGS. 52A-52G are schematic illustrations of a specific embodiment
of an external (partially implanted) neurostimulation system;
FIGS. 53-56 schematically illustrate alternative screening tools;
and
FIGS. 57A-58B schematically illustrate alternative intra-operative
tools.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following detailed description should be read with reference to
the drawings in which similar elements in different drawings are
numbered the same. The drawings, which are not necessarily to
scale, depict illustrative embodiments and are not intended to
limit the scope of the invention.
Description of Fully Implanted Neurostimulator System
With reference to FIG. 1, a neurostimulator system 10 including
implanted components 20, physician programmer 30 and patient
controller 40 is shown schematically. The implanted components of
the system 10 may generally include an implanted neurostimulator
(INS) 50 (a.k.a., implanted pulse generator (IPG)), an implanted
stimulation lead (or leads) 60, and an implanted respiration
sensing lead (or leads) 70. The INS 50 generally includes a header
52 for connection of the leads 60/70, and a hermetically sealed
housing 54 for the associated electronics and long-life or
rechargeable battery (not visible). The stimulation lead 60
generally includes a lead body 62 with a proximal connector and a
distal nerve electrode cuff 64. The respiration sensing lead 70
generally includes a lead body 72 with a proximal connector and one
or more sensors 74 disposed on or along a distal portion thereof.
Suitable designs of the INS 50, stimulation lead 60 and respiration
sensing lead 70 are described in more detail hereinafter.
As shown in FIG. 2, and by way of example, not limitation, the
implanted components 20 (shown faded) of the neurostimulator system
10 are implanted in a patient P with the INS 50 disposed in a
subcutaneous pocket, the stimulation lead body 62 disposed in a
subcutaneous tunnel, the nerve cuff electrode 64 disposed on a
nerve (e.g., hypoglossal nerve (HGN)) innervating a muscle (e.g.,
genioglossus muscle, not shown) controlling the upper airway, the
respiration sensing lead body 72 disposed in a subcutaneous tunnel,
and the respiration sensors 74 disposed adjacent lung tissue and/or
intercostal muscles outside the pleural space.
Generally, electrical stimulus is delivered by the INS 50 via the
stimulation lead 60 to a nerve innervating a muscle controlling
upper airway patency to mitigate obstruction thereof. To reduce
nerve and muscle fatigue, the stimulus may be delivered for only a
portion of the respiratory cycle, such as during inspiration which
corresponds to negative pressure in the upper airway. Stimulation
may be thus triggered as a function of respiration as detected by
respiration sensing lead 70 in a closed-loop feedback system. By
way of example, the stimulus may be triggered to turn on at the end
of expiration (or at the beginning of inspiration), and triggered
to turn off at the beginning of expiration (or at the end of
inspiration). Triggering the stimulus as a function of expiration
improves capture of the entire inspiratory phase, including a brief
pre-inspiratory phase of about 300 milliseconds, thus more closely
mimicking normal activation of upper airway dilator muscles.
Over-stimulation may cause nerve and/or muscle fatigue, but a 40%
to 50% duty cycle may be safely tolerated, thus enabling limited
over-stimulation. As an alternative, stimulus may be delivered
independent of actual respiration wherein the stimulus duty cycle
is set for an average inspiratory duration at a frequency
approximately equal to an average respiratory cycle.
Stimulus may be delivered to one or more of a variety of nerve
sites to activate one muscle or muscle groups controlling patency
of the upper airway. For example, stimulation of the genioglossus
muscle via the hypoglossal nerve moves or otherwise stiffens the
anterior portion of the upper airway, thereby decreasing the
critical pressure at which the upper airway collapses during
inspiration and reducing the likelihood of an apnea or hypopnea
event occurring during sleep. Because the systems described herein
work at the level of the tongue, it may be desirable to combine
this therapy with a therapy (e.g., UPPP or palatal implant) that
work at the level of the soft palate, thus increasing efficacy for
a broader range of patients.
With reference back to FIG. 1, the physician programmer 30 may
comprise a computer 32 configured to control and program the INS 50
via a wireless link to a programming wand 34. The physician
programmer 30 may be resident in a sleep lab where the patient
undergoes a polysomnographic (PSG) study during which the patient
sleeps while the INS 50 is programmed to optimize therapy.
The patient controller 40 may comprise control circuitry and
associated user interface to allow the patient to control the
system via a wireless telemetry link while at home, for example.
The patient controller 40 may include a power switch 42 to turn the
system on and slowly ramp up when the patient goes to sleep at
night, and turn it off when the patient wakes in the morning. A
snooze switch 44 may be used to temporarily put the INS 50 in
standby mode during which electrical stimulus is paused for a
preprogrammed period of time to allow the patient to temporarily
wake, after which the INS 50 turns back on and ramps up to the
desired stimulus level. A display 46 may be provided to indicate
the status of the INS 50 (e.g., on, off or standby), to indicate
satisfactory wireless telemetry link to the INS 50, to indicate
remaining battery life of the INS 50, to indicate normal operation
of the INS 50, and/or to indicate the need for patient action etc.
Display 46 may be configured to be a dash-board-like display, and
may be any suitable display available to those of ordinary skill in
the art, such as, for example, an LED or LCD display. Furthermore,
information may be communicated to the patient controller 40 for
display purposes by any suitable means known to those of ordinary
skill in the art. For example, communication of information may be
achieved through inductively coupled or radio frequency telemetry.
The patient controller 40 may also have programmability to adjust
stimulus parameters (e.g., amplitude) within a pre-set range
determined by the physician in order to improve efficacy and/or to
reduce sensory perception, for example. Optionally, the patient
controller 40 may be configured to function as the programming wand
34 of the physician programmer 30.
Furthermore, the patient controller 40 may be provided with one or
more mechanisms for improving patient compliance. For example,
patient controller 40 may be provided with a time-keeping mechanism
having the capabilities of a conventional alarm clock. In certain
embodiments, controller 40 may be programmed by the user and/or the
physician to alert the user when action, such as, for example,
turning the system 10 on or off, is required by the user.
Controller 40 may be configured to alert the user by any suitable
means known in the art. For example, controller 40 may emit an
audible alarm at programmed time intervals. In other embodiments,
the patient controller 40 may be used to monitor a patient. For
example, the patient controller 40 may be programmed to
periodically send reports of patient actions, patient compliance,
system status, etc., to a clinician or caregiver via a telephone or
computer network.
With reference to FIG. 3, the implanted components 20 are shown
schematically with more detail. The implanted components include
INS 50, stimulation lead 60, and respiration sensing lead 70. The
INS 50 includes header 52 and housing 54. The stimulation lead 60
includes lead body 62 and nerve cuff electrode 64. The respiration
sensing lead 70 includes lead body 72 and respiration sensors 74
(e.g., impedance sensing electrodes).
With reference to FIG. 4, the INS 50 is shown schematically in more
detail. The INS 50 includes header 52 that may be formed using
conventional molding or casting techniques and may comprise
conventional materials such as epoxy or polyurethane (e.g.,
Tecothane brand polyurethane). The housing 54 may be formed using
conventional stamping or forming techniques and may comprise
conventional materials such as titanium or ceramic. The housing 54
may include one or more isolated electrodes, and/or if a conductive
material is used for the housing 54, the housing 54 may comprise an
electrode, which may be used for respiratory sensing, for example.
The housing 54 may be hermetically sealed to the header 52 using
conventional techniques. The header 52 may include two or more
receptacles for receiving the proximal connectors 66/76 of the
stimulation lead body 62 and respiration sensing lead body 72. The
connectors 66/76 may comprise a conventional design such as IS1 or
other in-line designs. The header 52 may also include set screw
seals and blocks 56 for receiving set screws (not shown) that
establish electrical contact between the INS 50 and the conductors
of the leads 60/70 via connectors 66/76, and that establish
mechanical fixation thereto. Some electrical contact may be
achieved through spring type or cam-locked mechanisms. As shown,
two set screw arrangements 56 are shown for the stimulation lead 60
and four set screw arrangements 56 are shown for the respiration
sensing lead 70, but the number may be adjusted for the number of
conductors in each lead. A hole 58 may be provided in the header 52
for securing the INS 50 to subcutaneous tissue using a suture at
the time of implantation.
The INS 50 may comprise a conventional implanted neurostimulator
design used in neurostimulation applications, such as those
available from Texcel (US), CCC (Uruguay) and NeuroTECH (Belgium),
but modified for the present clinical application in terms of
stimulation signal parameters, respiratory signal processing,
trigger algorithm, patient control, physician programming, etc. The
INS may contain a microprocessor and memory for storing and
processing data and algorithms. Algorithms may be in the form of
software and/or firmware, for example. One of several different
embodiments of the neurostimulator may be implemented. For example,
the neurostimulator may be an internal/implanted neurostimulator
(INS) powered by a long-life primary battery or rechargeable
battery, or an external neurostimulator (ENS) wirelessly linked
(e.g., inductive) to an implanted receiver unit connected to the
leads. The INS (or the receiver, unit of the ENS) may be implanted
and optionally anchored in a number of different locations
including a subcutaneous pocket in the pectoral region, the dorsal
neck region, or cranial region behind the ear, for example.
The INS 50 may include any suitable circuitry and programming in
accordance with the principles of the present disclosure. In one
embodiment, INS 50 may include an activity sensor (not shown) for
sensing the activity of a patient, including the amount of activity
of the patient. The activity sensor may detect motion of a patient
by any suitable means available to those of ordinary skill in the
art. For example, a patient's motion may be detected by, for
example, using an internal accelerometer and/or measuring the
impedance of the patient's torso with, for example, the built-in
respiration sensor discussed below, and/or measuring a tissue
pressure on the surface of the implanted INS 50.
The data corresponding to a patient's detected motion may be
stored, evaluated, and utilized in any of a number of various ways.
In one embodiment, data corresponding to a patient's motion may be
used to determine whether a patient is sleeping or awake. For
example, when a patient's activity level falls below a
predetermined threshold, it may be assumed that the patient is
sleeping. Conversely, when the patient's activity level rises above
the pre-determined threshold, it may be assumed that the patient is
awake. The activity sensor therefore may be used to facilitate
selectively applying treatment when the patient is detected to be
sleeping and/or inhibiting treatment when the patient is detected
to be awake. Alternatively, data corresponding to a patient's
motion may be evaluated over a long period of time, such as, for
example, the first few months of treatment, for indications of
improvement in a patient's quality of life. It is contemplated that
increases in a patient's average level of daily activity will
correspond to successful treatment of OSA. This, in turn, may
correspond to improvements in the patient's quality of life.
Moreover, the INS 50 may include a long-life battery (not shown)
which requires periodic replacement after years of service.
Alternatively, the INS may include a rechargeable power source such
as a rechargeable battery or super capacitor that is used instead
of the long-life battery. To facilitate recharging, the INS may
include a receiver coil inductively linked to a transmitter coil
that is connected to a recharging unit powered by a larger battery
or line power. Because the patient is stationary while sleeping,
recharging may be scheduled to occur sometime during sleep to
eliminate the need to carry the recharging unit during daily
activities. The transmitter coil and the receiver coil may be
arranged coaxially in parallel planes to maximize energy transfer
efficiency, and may be held in proximity to each other by a patch,
garment, or other means as described with reference to the external
neurostimulator embodiments. Other examples of neurostimulator
designs will be described in more detail hereinafter.
With reference to FIG. 5, the stimulation lead 60 may comprise a
variety of different design embodiments and may be positioned at
different anatomical sites. For example, a nerve cuff electrode(s)
64 may be attached to a nerve(s) innervating musculature affecting
patency of the upper airway. As an alternative or in addition, the
nerve cuff electrode 64 may be replaced with an intramuscular
electrode and placed directly in the musculature affecting patency
of the upper airway. The nerve electrode 64 may be attached to a
specific branch of a nerve innervating the desired muscle(s), or
may be attached to a proximal trunk of the nerve in which a
specific fascicle innervating the desired muscle(s) is targeted by
steering the stimulus with multiple electrodes. One or more
electrodes may be used for attachment to one or more portions of
nerves on one side (unilateral) of the body, or one or more
electrodes may be used for attachment to one or more portions of
nerves on both sides (bilateral) of the body. Variations in lead
body 62 and electrode 64 design as well as variations in the target
stimulation site or sites will be described in more detail
hereinafter.
With continued reference to FIG. 5, the lead body 62 may be sigmoid
shaped, for example, to reduce strain applied to the cuff electrode
64 when the lead body 62 is subject to movement. The sigmoid shape,
which may alternatively comprise a variety of other waveform
shapes, may have a wavelength of approximately 1.0 to 1.5 cm, and
an amplitude of approximately 0.75 to 1.5 cm, for example. The lead
body 62 may comprise a tubular jacket with electrical conductors 68
extending therein. The tubular jacket may comprise extruded
silicone having an outside diameter of approximately 0.047 inches
and an inside diameter of approximately 0.023 inches, for example.
The tubular jacket may optionally have a covering of co-extruded
polyurethane, for example, to improve durability. The conductors
68, shown in a transparent window in the jacket for purposes of
illustration only, may comprise a bifilar coil of insulated (e.g.,
ETFE) braided stranded wire (BSW) of MP35NLT material. The number
of conductors 68 is shown as two, but may be adjusted depending on
the desired number of independent electrodes used.
The various embodiments of stimulation leads, for example,
stimulation lead 60, disclosed herein may be fabricated by any
suitable means known to those having ordinary skill in the art, and
may be made from any suitable material. For example, the discussed
sigmoid shape of the tubular jacket of lead body 62 may be formed
by first extruding silicone in a semi-cured or semi cross-linked
state. Next, the semi cross-linked extruded tubular jacket may be
placed in a sigmoid mold and then allowed to become fully
cross-linked. In particular, the semi cross-linked extruded tubular
jacket may be placed in an oven and heated to convert the semi
cross-linked silicone of the extruded tubular jacket to fully
cross-linked silicone. Additionally, a lumen within the tubular
jacket may be created along a longitudinal axis of the tubular
jacket by any suitable means.
Furthermore, in accordance with the principles of the present
disclosure, it is contemplated that one or more of the various
embodiments of stimulation leads disclosed herein may be implanted
in or near highly mobile portions of the body. For example,
embodiments of the disclosed stimulation leads may be implanted in
the ventral neck, for example, along a path between the clavicle
and mandible of a patient. Additionally, although mastication,
deglutition, and speech may result in mechanical loading on an
implanted stimulation lead, it has been found that gross movement
of the head and neck may create high mechanical stresses in the
conductors of the lead body, lead jacket, and the junction between
the conductor wires and the anchor points, such as, for example,
the electrodes. Accordingly, it may be desirable to configure the
various embodiments of stimulation leads to withstand certain
predetermined amounts of fatigue and/or stresses, which may result
from mechanical loading on a lead body due to gross movements of a
patient's neck and head.
In particular, research has revealed that approximately 98% of the
population may experience a 38.5% elongation or less in the
distance between the clavicle and angle of the mandible (e.g.,
adjacent a contemplated area of implantation for a stimulation lead
in accordance with the principles of this disclosure). It has also
been found that the angular range of motion of the cervical spine
between adjacent vertebrae may be approximately 12 degrees, thereby
flexing the lead through this angle with a bend radius assumed to
be approximately 1.0 centimeter. See Augustus A. White III et al.,
Clinical Biomechanics of the Spine, pp. 84, 356, and 373 (1978).
Furthermore, the frequency of gross head movement through the range
of motion in the contemplated area of implantation has been
estimated to be approximately 300,000 cycles per year, or on the
average approximately 50 times per waking hour.
Thus, it may be desirable to design a lead body that is capable of
withstanding, among other things, the stresses imparted by the
above-noted head and neck movements for an extended amount of time,
such as, for example, ten years. In particular, in order to design
a lead body that may remain functional for the exemplary ten year
implanted life, it may be desirable to configure the lead bodies
disclosed herein to withstand at least the above noted elongation
and ranges of motion. For example, since implanted lead bodies are
likely to be elongated by at least 38.5%, it may be desirable to
design lead bodies to withstand being elongated by a predetermined
distance Y, such as, for example, approximately 40% (+/-2%) from an
initial unstressed state, for a minimum of 3.0 million cycles
without failure, as depicted in FIG. 5A. In addition, since it is
likely that an implanted lead body may experience an angular range
of motion of at least 12 degrees, with a bend radius of
approximately 1.0 centimeter, it may be desirable to configure the
lead bodies to withstand being flexed around a predetermined radius
X, such as, for example, 1.0 centimeter (+/-0.05 centimeters), for
a predetermined amount of rotation W, such as, for example, from
approximately 0 degrees to approximately 15 degrees (+/-3 degrees),
such that the 15 degree maximum deflection occurs coincidentally
with the maximum elongation of the lead body.
With reference to FIG. 6, the nerve cuff electrode 64 may comprise
a cuff body 80 having a lateral (or superficial) side 82 and a
medial (or contralateral, or deep) side 84. The medial side 84 is
narrower or shorter in length than the lateral side 82 to
facilitate insertion of the medial side 84 around a nerve such that
the medial side is on the deep side of the nerve and the lateral
side is on the superficial side of the nerve. This configuration
reduces the dissection of nerve branches and vascular supply
required to get the cuff around a nerve. For the nerve cuff implant
sites discussed herein, the medial side 84 may have a length of
less than 6 mm, and preferably in the range of approximately 3 to 5
mm, for example. The lateral side 82 may have a length of more than
6 mm, and preferably in the range of approximately 7 to 8 mm, for
example. The cuff body 80 may be compliant and may be available in
different sizes with an inside diameter of approximately 2.5 to 3.0
mm or 3.0 to 3.5 mm, for example. The cuff size may also be
adjusted depending on the nominal diameter of the nerve at the site
of implantation. The cuff body 80 may have a wall thickness of
approximately 1.0 mm and may be formed of molded silicone, for
example, and may be reinforced with imbedded fibers or fabrics. An
integral tow strap 86 may be used to facilitate wrapping the cuff
around a nerve by first inserting the strap 86 under and around the
deep side of the nerve and subsequently pulling the strap to bring
the medial side 84 in position on the deep side of the nerve and
the lateral side 82 on the superficial side of the nerve.
With continued reference to FIG. 6, the nerve cuff electrode 64
includes electrode contacts 90A, 90B, and 90C imbedded in the body
80 of the cuff, with their inside surface facing exposed to
establish electrical contact with a nerve disposed therein. A
transverse guarded tri-polar electrode arrangement is shown by way
of example, not limitation, wherein electrode contacts 90A and 90B
comprise anodes transversely guarding electrode contact 90C which
comprises a cathode.
With this arrangement, the anode electrodes 90A and 90B are
connected to a common conductor 68A imbedded in the body 80, and
the cathode electrode 90C is connected to an independent conductor
68B extending from the lateral side 82 to the medial side 84 and
imbedded in the body 80. By using the conductors 68 to make
connections within the body 80 of the cuff 64, fatigue stresses are
imposed on the conductors rather than the electrode contacts 90A,
90B and 90C.
With additional reference to FIGS. 7 and 8, the electrode contacts
90A, 90B and 90C may thus be semi-circular shaped having an arc
length of less than 180 degrees, and preferably an arc length of
approximately 120 degrees, for example. Each electrode 90 may have
two reverse bends (e.g., hooked or curled) portions 92 to provide
mechanical fixation to the body 80 when imbedded therein. Each
electrode 90 may also have two crimp tabs 94 defining grooves
thereunder for crimping to the conductors 68 or for providing a
pass-through. As shown in FIG. 7, conductor 68A passes through the
grooves under the lower crimp tabs 94 of electrodes 90B and 90A,
loops 98 around through the grooves under the upper crimp tabs 94
of electrodes 90A and 90B, is crimped 96 by the upper tabs 94 of
electrodes 90A and 90B to provide mechanical and electrical
connection, is looped again back between the crimp tabs 94 on the
outside of the electrode contact 90, and is resistance spot welded
95 to provide redundancy in mechanical and electrical connection.
Also as shown in FIG. 7, conductor 68B passes through the groove
under the lower crimp tab 94 of electrode 90C, loops around through
the groove under the upper crimp tab 94 of electrode 90C, and is
crimped by the upper tab 94 of electrode 90C to provide mechanical
and electrical connection. This arrangement avoids off-axis tensile
loading at the crimp sites 96 which may otherwise fail due to
stress concentration, and the looped portion 98 provides additional
strain relief.
FIG. 8 provides example dimensions (inches) of an electrode contact
90 for a 2.5 mm inside diameter cuff, wherein the electrode is
formed of 90/10 or 80/20 platinum iridium alloy formed by wire EDM,
for example. As illustrated, and as exemplary and approximate
dimensions, electrode contact 90 may include a surface A having a
full radius, a dimension B of 0.079 inches from tangent to tangent,
a dimension C of 0.020 inches (3.times.), a radius of curvature D
of 0.049 R with a 16 micro-inch RMS, a dimension E of 0.008 inches
(2.times.), a dimension F of 0.0065 inches (+/-0.001 inches)
(2.times.), a dimension G of 0.006 inches (+0.002 inches, -0.001
inches) (2.times.), a dimension H of 0.014 inches (2.times.), a
dimension I of 0.010 inches (2.times.), a dimension J of 0.010
inches (2.times.), and a dimension K of 0.006 inches (+/-0.001
inches).
With reference to FIGS. 9A and 9B, a distal portion of the
respiration sensing lead 70 and a distal detail of the sensing lead
70, respectively, are shown schematically. In the illustrated
embodiment, the respiration sensing lead 70 and associated sensors
74 are implanted as shown in FIG. 2. However, the respiration
sensor(s) may comprise a variety of different design embodiments,
both implanted and external, and may be positioned at different
anatomical sites. Generally, the respiratory sensor(s) may be
internal/implanted or external, and may be connected to the
neurostimulator via a wired or wireless link. The respiratory
sensor(s) may detect respiration directly or a surrogate thereof.
The respiratory sensor(s) may measure, for example, respiratory
airflow, respiratory effort (e.g., diaphragmatic or thoracic
movement), intra-pleural pressure, lung impedance, respiratory
drive, upper airway EMG, changes in tissue impedance in and around
the lung(s) including the lungs, diaphragm and/or liver, acoustic
airflow or any of a number other parameters indicative of
respiration. Detailed examples of suitable respiration sensing
leads and sensors will be described in more detail hereinafter.
With continued reference to FIGS. 9A and 9B, the respiration
sensing lead 70 includes a lead body 72 and a plurality of
respiration sensors 74A-74D comprising ring electrodes for sensing
bio-impedance. The lead body 72 of the respiration sensing lead 70
may include a jacket cover comprising an extruded silicone tube
optionally including a polyurethane cover (80A durometer), or may
comprise an extruded polyurethane tube (55D durometer). The ring
electrodes 74A-74D may comprise 90/10 or 80/20 platinum iridium
alloy tubes having an outside diameter of 0.050 inches and a length
of 5 mm, and secured to the jacket cover by laser welding and/or
adhesive bonding, for example. The lead body 72 may include a
plurality of conductors 78 as seen in the transparent window in the
jacket cover, which is shown for purposes of illustration only. The
conductors 78 may comprise insulated and coiled BSW or solid wire
(optionally DFT silver core wire) disposed in the tubular jacket,
with one conductor provided for each ring electrode 74A-74D
requiring independent control. Generally, the impedance electrodes
74A-74D may comprise current emitting electrodes and voltage
sensing electrodes for detecting respiration by changes in
bio-impedance. The number, spacing, anatomical location and
function of the impedance electrodes will be described in more
detail hereinafter.
System 10 may also include a plurality of diagnostic mechanisms
(e.g., circuitry and/or programming) for monitoring and/or
determining the functionality of certain components, such as, for
example, stimulation lead 60. In particular, system 10 may include
one or more switching circuits (not shown) that facilitate
connection of the respiratory/trans-thoracic impedance sensing
circuits of the present disclosure (discussed in greater detail
below) to stimulation lead 60 for measuring the impedance of lead
60. In some embodiments, the impedance sensing circuit may be
connected to each electrode pair. In other embodiments, the
impedance sensing circuit may be connected between the case of the
implanted INS 50 and each conductor 68 within the lead 60. While
those having ordinary skill in the art will readily recognize that
any suitable impedance sensing method may be utilized to monitor
and/or determine the functionality of lead 60, the
respiratory/trans-thoracic impedance sensing circuit of the present
disclosure may be preferred, since this circuit may be capable of
identifying small changes in impedance rather than the large
changes detectable by standard methods.
As alluded to above, sensing the impedance of lead 60 may provide
for monitoring and/or determining the functionality of lead 60.
Specifically, sensing the impedance of lead 60 may facilitate
diagnosing and distinguishing between differing types of failures
of lead 60. In particular, research has revealed that changes in
the impedance of lead 60 may be indicative of certain types of
failures, including, but not limited to, corrosion, high contact
resistance, breakage, and/or shorting. For example, a broken wire
inside the lead could be identified by an excessively high lead
impedance value. Corrosion of an electrode with its resultant
decrease in effective electrode surface area could be identified by
a smaller increase in impedance of that electrode. Similarly, an
abnormally low value could correspond with a short between
conductors in the lead, or an abrasion of the lead body that
exposed a conductor to the tissue. Measuring from the case of the
INS to each electrode allows independent identification of the
integrity of each wire/electrode in the lead. In addition, sensing
the impedance of lead 60 may facilitate periodic, automated
adjustment of stimulation pulse amplitude so as to maintain
constant current, energy, and/or charge delivery using a simpler
voltage mode delivery circuit. Such automated adjustment may
facilitate ensuring safety and effectiveness by consistently
delivering the prescribed current, energy, or charge in the
presence of tissue/electrode impedance variations. By consistently
controlling the delivery of only the minimally required energy
necessary for stimulation of the nerve, the stimulation amplitude
may be programmed closer to the actual stimulation threshold rather
than programming a wide margin to ensure continued effectiveness.
This enhances safety and reduces power consumption. Moreover,
sensing the impedance of lead 60 may allow monitoring of certain
system dynamics, such as, for example, doses actually delivered to
a patient.
Description of Implant Procedure
With reference to FIG. 10, surgical access sites are schematically
shown for implanting the internal neurostimulator components 20
shown in FIG. 1. The internal neurostimulator components 20 may be
surgically implanted in a patient on the right or left side. The
right side may be preferred because it leaves the left side
available for implantation of a pacemaker, defibrillator, etc.,
which are traditionally implanted on the left side. The right side
may also be preferred because it lends itself to a clean
respiratory signal less susceptible to cardiac artifact and also
offers placement of respiratory sensors across the interface
between the lung, diaphragm and liver for better detection of
impedance changes during respiration.
With continued reference to FIG. 10, the INS (not shown) may be
implanted in a subcutaneous pocket 102 in the pectoral region, for
example. The stimulation lead (not shown) may be implanted in a
subcutaneous tunnel 104 along (e.g., over or under) the platysma
muscle in the neck region. The respiration sensing lead (not shown)
may be implanted in a subcutaneous tunnel 106 extending adjacent
the ribcage to an area adjacent lung tissue and/or intercostal
muscles outside the pleural space. The nerve cuff electrode (not
shown) may be attached to a nerve by surgical dissection at a
surgical access site 110 proximate the targeted stimulation site.
In the illustrated example, the target nerve is the right
hypoglossal nerve and the surgical access site is in the
submandibular region.
With reference to FIGS. 11A and 11B, a surgical dissection 110 to
the hypoglossal nerve is shown schematically. A uni-lateral
dissection is shown, but a bilateral approach for bilateral
stimulation may also be employed. Conventional surgical dissection
techniques may be employed. The branch of the hypoglossal nerve
(usually a medial or distal branch) leading to the genioglossus
muscle may be identified by stimulating the hypoglossal nerve at
different locations and observing the tongue for protrusion.
Because elongation and/or flexion may be mistaken for protrusion,
it may be desirable to observe the upper airway using a flexible
fiber optic scope (e.g., nasopharyngoscope) inserted into the
patient's nose, through the nasal passages, past the nasopharynx
and velopharynx to view of the oropharynx and hypopharynx and
visually confirm an increase in airway caliber by anterior
displacement (protrusion) of the tongue base when the nerve branch
is stimulated.
The implant procedure may be performed with the patient under
general anesthesia in a hospital setting on an out-patient basis.
Alternatively, local anesthesia (at the surgical access sites and
along the subcutaneous tunnels) may be used together with a
sedative in a surgical center or physician office setting. As a
further alternative, a facial nerve block may be employed. After a
post-surgical healing period of about several weeks, the patient
may return for a polysomnographic (PSG) test or sleep study at a
sleep center for programming the system and titrating the therapy.
A trialing period may be employed prior to full implantation
wherein the hypoglossal nerve or the genioglossus muscle is
stimulated with fine wire electrodes in a sleep study and the
efficacy of delivering stimulus to the hypoglossal nerve or
directly to the genioglossus muscle is observed and measured by
reduction in apnea hypopnea index, for example.
Other nerve target sites are described elsewhere herein and may be
accessed by similar surgical access techniques. As an alternative
to surgical dissection, less invasive approaches such as
percutaneous or laparoscopic access techniques may be utilized,
making use of associated tools such as tubular sheaths, trocars,
etc.
Description of Alternative Stimulation Target Sites
With reference to FIG. 12, various possible nerve and/or direct
muscle stimulation sites are shown for stimulating muscles
controlling patency of the upper airway. In addition to the upper
airway which generally includes the pharyngeal space, other nerves
and dilator muscles of the nasal passage and nasopharyngeal space
may be selectively targeted for stimulation. A general description
of the muscles and nerves suitable for stimulation follows, of
which the pharyngeal nerves and muscles are shown in detail in FIG.
12.
Airway dilator muscles and associated nerves suitable for
activation include are described in the following text and
associated drawings. The dilator naris muscle functions to widen
the anterior nasal aperture (i.e., flares nostrils) and is
innervated by the buccal branch of the facial nerve (cranial nerve
VII). The tensor veli palatine muscle functions to stiffen the soft
palate and is innervated by the medial (or internal) pterygoid
branch of the mandibular nerve MN. The genioglossus muscle is an
extrinsic pharyngeal muscle connecting the base of the tongue to
the chin and functions to protrude the tongue. The genioglossus
muscle is typically innervated by a distal or medial branch (or
braches) of the right and left hypoglossal nerve. The geniohyoid
muscle connects the hyoid bone to the chin and the sternohyoid
muscle attaches the hyoid bone to the sternum. The geniohyoid
muscle functions to pull the hyoid bone anterosuperiorly, the
sternohyoid muscle functions to pull hyoid bone inferiorly, and
collectively (i.e., co-activation) they function to pull the hyoid
bone anteriorly. The geniohyoid muscle is innervated by the
hypoglossal nerve, and the sternohyoid muscle is innervated by the
ansa cervicalis nerve.
By way of example, a nerve electrode may be attached to a specific
branch of the hypoglossal nerve innervating the genioglossus muscle
(tongue protruder), or may be attached to a more proximal portion
(e.g., trunk) of the hypoglossal nerve in which a specific fascicle
innervating the genioglossus muscle is targeted by steering the
stimulus using an electrode array. Activating the genioglossus
muscle causes the tongue to protrude thus increasing the size of
anterior aspect of the upper airway or otherwise resisting collapse
during inspiration.
As an alternative to activation of any or a combination of the
airway dilator muscles, co-activation of airway dilator and airway
restrictor or retruder muscles may be used to stiffen the airway
and maintain patency. By way of example, a nerve electrode may be
attached to specific branches of the hypoglossal nerve innervating
the genioglossus muscle (tongue protruder), in addition to the
hyoglossus and styloglossus muscles (tongue retruders), or may be
attached to a more proximal portion (e.g., trunk) of the
hypoglossal nerve in which specific fascicles innervating the
genioglossus, hyoglossus and styloglossus muscles are targeted by
steering the stimulus using an electrode array. Activating the
hyoglossus and styloglossus muscles causes the tongue to retract,
and when co-activated with the genioglossus, causes the tongue to
stiffen thus supporting the anterior aspect of the upper airway and
resisting collapse during inspiration. Because the tongue retruder
muscles may overbear the tongue protruder muscle under equal
co-activation, unbalanced co-activation may be desired. Thus, a
greater stimulus (e.g., longer stimulation period, larger
stimulation amplitude, higher stimulation frequency, etc.) or an
earlier initiated stimulus may be delivered to the portion(s) of
the hypoglossal nerve innervating the genioglossus muscle than to
the portion(s) of the hypoglossal nerve innervating the hyoglossus
and styloglossus muscles.
With continued reference to FIG. 12, examples of suitable nerve
stimulation sites include B; A+C; A+C+D; B+D; C+D; and E. Sites B
and E may benefit from selective activation by field steering using
an electrode array. As mentioned before, nerve electrodes may be
placed at these target nerve(s) and/or intramuscular electrodes may
be placed directly in the muscle(s) innervated by the target
nerve(s).
Site A is a distal or medial branch of the hypoglossal nerve
proximal of a branch innervating the genioglossus muscle and distal
of a branch innervating the geniohyoid muscle. Site B is a more
proximal portion of the hypoglossal nerve proximal of the branches
innervating the genioglossus muscle and the geniohyoid muscle, and
distal of the branches innervating the hyoglossus muscle and the
styloglossus muscle. Site C is a medial branch of the hypoglossal
nerve proximal of a branch innervating the geniohyoid muscle and
distal of branches innervating the hyoglossus muscle and the
styloglossus muscle. Site D is a branch of the ansa cervicalis
nerve distal of the nerve root and innervating the sternohyoid.
Site E is a very proximal portion (trunk) of the hypoglossal nerve
proximal of the branches innervating the genioglossus, hyoglossus
and styloglossus muscles.
Activating site B involves implanting an electrode on a hypoglossal
nerve proximal of the branches innervating the genioglossus muscle
and the geniohyoid muscle, and distal of the branches innervating
the hyoglossus muscle and the styloglossus muscle.
Co-activating sites A+C involves implanting a first electrode on a
hypoglossal nerve proximal of a branch innervating the genioglossus
muscle and distal of a branch innervating the geniohyoid muscle,
and implanting a second electrode on the hypoglossal nerve proximal
of a branch innervating the geniohyoid muscle and distal of
branches innervating the hyoglossus muscle and the styloglossus
muscle.
Co-activating sites A+C+D involves implanting a first electrode on
a hypoglossal nerve proximal of a branch innervating the
genioglossus muscle and distal of a branch innervating the
geniohyoid muscle; implanting a second electrode on the hypoglossal
nerve proximal of a branch innervating the geniohyoid muscle and
distal of branches innervating the hyoglossus muscle and the
styloglossus muscle; and implanting a third electrode on a branch
of an ansa cervicalis nerve distal of the nerve root and
innervating the sternohyoid.
Co-activating sites B+D involves implanting a first electrode on a
hypoglossal nerve proximal of branches innervating the genioglossus
muscle and the geniohyoid muscle, and distal of branches
innervating the hyoglossus muscle and the styloglossus muscle; and
implanting a second electrode on a branch of an ansa cervicalis
nerve distal of the nerve root and innervating the sternohyoid.
Co-activating sites C+D involves implanting a first electrode on a
hypoglossal nerve proximal of a branch innervating the geniohyoid
muscle, and distal of branches innervating the hyoglossus muscle
and the styloglossus muscle and implanting a second electrode on a
branch of an ansa cervicalis nerve distal of the nerve root and
innervating the sternohyoid.
Activating site E involves implanting an electrode on a hypoglossal
nerve proximal of the branches innervating the genioglossus,
hyoglossus and styloglossus muscles; and selectively activating
(e.g., by field steering) the genioglossus muscle before or more
than the hyoglossus and styloglossus muscles.
With reference now to FIGS. 12A-12D, additional possible nerve
stimulation sites are shown for effecting muscles controlling
patency of the upper airway. For example, the cranial root of the
accessory nerve AN (cranial nerve XI) innervates the levator veli
palatini muscle of the soft palate, which elevates the soft palate.
The cranial root of the accessory nerve AN also innervates the
palatoglossal muscle, which functions to pull the soft palate
inferiorly when the genioglossus is co-activated via the
hypoglossal nerve (HGN). Moreover, because the cranial root of the
accessory nerve AN also innervates various other muscles including,
but not limited to, the palatopharyngeus, specific fibers in the
accessory nerve AN may be selectively stimulated with one or more
of the fiber selective stimulation means described in greater
detail below, in order to only activate desired fibers of the
nerve. The glossopharyngeal nerve GN. (cranial nerve IX) innervates
the stylopharyngeus, which functions to dilate the lateral walls of
the pharynx. However, since the glossopharyngeal nerve GN is a
multi-function nerve with both afferent and efferent fibers, one or
more of the fiber selective stimulation means described in greater
detail below may be used to facilitate targeting the fibers that
innervate only the stylopharyngeus. The cranial root of the
accessory nerve AN and the glossopharyngeal nerve GN may be
singularly activated, or these nerves may be co-activated with
other nerve sites, such as, for example, the hypoglossal nerve, for
increased efficacy.
Another possible nerve stimulation site may include the superior
laryngeal nerve SLN. The superior laryngeal nerve SLN descends
posterior and medial from the internal carotid artery and divides
into the internal laryngeal nerve ILN and external laryngeal nerve
ELN. While the external laryngeal nerve ELN descends behind the
sternohyoid with the superior thyroid artery, the internal
laryngeal nerve ILN descends near the superior laryngeal artery.
The internal laryngeal nerve ILN contains sensory (afferent) fibers
that are connected to receptors in the larynx. Some of these
receptors include, but are not limited to, mechanoreceptors which
detect pressure changes in a patient's upper airway associated with
its collapse and institute a physiological response to re-open the
patient's upper airway. Therefore, stimulation of specific afferent
fibers inside the ILN nerve may result in triggering a reflex
response that causes upper airway dilation by activating several
muscles groups.
As discussed below, the superior laryngeal nerve SLN, in addition
to being a sensory nerve, is also a motor nerve. Therefore, it is
contemplated that one or more of the fiber selective stimulation
means described in greater detail below may be utilized to
facilitate only stimulating the sensory or afferent fibers of the
nerve.
Description of Alternative Nerve Electrodes
Any of the alternative nerve electrode designs described
hereinafter may be employed in the systems described herein, with
modifications to position, orientation, arrangement, integration,
etc. made as dictated by the particular embodiment employed.
Examples of other nerve electrode designs are described in U.S.
Pat. No. 5,531,778, to Maschino et al., U.S. Pat. No. 4,979,511 to
Terry, Jr., and U.S. Pat. No. 4,573,481 to Bullara, the entire
disclosures of which are incorporated herein by reference.
With reference to the following figures, various alternative
electrode designs for use in the systems described above are
schematically illustrated. In each of the embodiments, by way of
example, not limitation, the lead body and electrode cuff may
comprise the same or similar materials formed in the same or
similar manner as described previously. For example, the lead body
may comprise a polymeric jacket formed of silicone, polyurethane,
or a co-extrusion thereof. The jacket may contain insulated wire
conductors made from BSW or solid wire comprising MP35N, MP35N with
Ag core, stainless steel or Tantalum, among others. The lead body
may be sigmoid shaped to accommodate neck and mandibular movement.
Also, a guarded cathode tri-polar electrode arrangement (e.g.,
anode-cathode-anode) may be used, with the electrodes made of 90/10
or 80/20 PtIr alloy with silicone or polyurethane backing.
With specific reference to FIGS. 13A and 13B, a self-sizing and
expandable design is shown to accommodate nerve swelling and/or
over-tightening. FIG. 13A shows a perspective view of a nerve
electrode cuff 130 on a nerve such as a hypoglossal nerve, and FIG.
13B shows a cross-sectional view of the nerve cuff electrode 130 on
the nerve. In this embodiment, the implantable nerve cuff electrode
130 comprises a compliant sheet wrap 132 configured to be wrapped
about a nerve and secured thereto by connecting opposite portions
of the sheet by sutures 138, for example. The sheet 132 includes a
plurality of radially and longitudinally distributed fenestrations
134 to allow expansion of the sheet 132 to accommodate nerve
swelling and/or over tightening. Electrode contacts 136 comprising
a coil, foil strip, conductive elastomer or individual solid
conductors may be carried by the sheet 132 with an exposed inside
surface to establish electrical contact with the nerve.
With specific reference to FIGS. 14A-14C, another self-sizing and
expandable design is shown to accommodate nerve swelling and/or
over-tightening. FIG. 14A shows a perspective view of a nerve
electrode cuff 140 on a nerve such as a hypoglossal nerve, and FIG.
14B shows a cross-sectional view of the nerve cuff electrode 140 on
the nerve. In this embodiment, the implantable nerve cuff electrode
140 comprises a compliant sheet wrap 142 configured to be wrapped
about a nerve and secured thereto by connecting opposite portions
of the sheet by sutures 148A, or by a buckle 148B as shown in FIG.
14C, for example. The opposite portions of the sheet 142 comprise
one or more narrow strips 144 integral with the sheet 142 to allow
expansion and to accommodate nerve swelling and/or over tightening.
Electrode contacts 146 comprising a coil, foil strip, conductive
elastomer or individual solid conductors may be carried by the
sheet 142 with an exposed inside surface to establish electrical
contact with the nerve.
With specific reference to FIGS. 15A-15C, another self-sizing and
expandable design is shown to accommodate nerve swelling and/or
over-tightening. FIG. 15A shows a perspective view of a nerve
electrode cuff 150 on a nerve such as a hypoglossal nerve, and FIG.
15B shows a cross-sectional view of the nerve cuff electrode 150 on
the nerve. In this embodiment, the implantable nerve cuff electrode
150 comprises a compliant sheet wrap 152 configured to be wrapped
about a nerve and secured thereto by connecting opposite portions
of the sheet 152 by sutures 158, for example. The opposite portions
of the sheet 152 are offset from the nerve and a thickened portion
of the sheet 152 fills the offset space. The offset distance
reduces the amount of compressive force that the electrode cuff can
exert on the nerve. To further reduce the pressure on the nerve,
the sheet 152 includes a plurality of radially distributed slits
154 extending partly through the thickness of the sheet 152 to
allow expansion and to accommodate nerve swelling and/or over
tightening.
With specific reference to FIGS. 16A and 16B, another self-sizing
and expandable design is shown to accommodate nerve swelling and/or
over-tightening. FIG. 16A shows a perspective view of a nerve
electrode cuff 160 on a nerve such as a hypoglossal nerve, and FIG.
16B shows a cross-sectional view of the nerve cuff electrode 160 on
the nerve. In this embodiment, the implantable nerve cuff electrode
160 comprises a compliant sheet wrap 162 configured to be wrapped
about a nerve and secured thereto by connecting opposite portions
of the sheet 162 by sutures 168, for example. The sheet 162
includes a plurality of radially distributed and longitudinally
extending convolutions 164 that may comprise alternative thick 164A
and thin 164B portions in the sheet 162 and/or overlapping portions
164C of the sheet 162 to allow expansion and to accommodate nerve
swelling and/or over tightening. Electrode contacts 166 comprising
a coil, foil strip, conductive elastomer or individual solid
conductors may be carried by the sheet 162 with an exposed inside
surface to establish electrical contact with the nerve. Nerve cuff
electrode 160 may accommodate one or two lead bodies 62A, 62B for
connection to the electrode contacts 166 on the same or opposite
sides of the nerve.
Turning now to FIGS. 16C-16D, additional self-sizing and expandable
designs are shown to accommodate nerve swelling and/or
over-tightening. With specific reference to FIG. 16C, there is
depicted a nerve cuff electrode 1600 having a cuff body with a
relatively wide semi-cylindrical lateral side 1601 and a plurality
of opposing arms 1602 extending thereform for placement on the deep
(contralateral) side of the nerve. Although the embodiment depicted
in FIG. 16C includes two such opposing arms 1602, nerve cuff
electrode 1600 may include any suitable number of opposing arms
1602. Lateral side 1601 may include an array of electrode contacts
1603. For example, in the depicted embodiment, lateral side may
include three electrode contacts 1603. The three electrode contacts
1603 may include one cathode electrode contact 1603 disposed
between two anode electrode contacts 1603, as shown.
Arms 1602 may be secured around a nerve (not shown) by any suitable
means. For example, it is contemplated that arms 1602 may be
elastic in nature, so as to gently grasp the nerve on its deep
(contralateral) side. Alternatively, arms 1602 may be actively
secured about a nerve by, for example, suturing an end portion of
arms 1602 to, e.g., a portion of lateral side 1601. In embodiments
where arms 1602 may be actively secured about a nerve, arms 1602
may be provided with a safety mechanism (not shown) that permits
nerve cuff electrode 1600 to become disengaged from a nerve it is
secured about upon the application of a predetermined amount of
force. This predetermined force will be established at a level that
is below that which can cause damage to the nerve.
As shown in FIG. 16D, opposing arms 1602 may be configured to
expand and/or deform as necessary, in order to accommodate nerve
swelling caused by, for example, localized trauma inflicted upon
the nerve during cuff implantation. For example, each of opposing
arms 1602 may have an unattached terminal end 1602a. In order to
facilitate expansion, opposing arms 1602 may be also made from any
suitable material known to those having ordinary skill in the art.
For example, arms 1602 may be made from an elastomer, such as, for
example, silicone or polyurethane. Additionally, one or both of
arms 1602 may be provided with one or more limiting mechanisms (not
shown) to limit the amount of expansion arms 1602 may undergo as a
result of, for example, nerve swelling. Such limiting mechanisms
may include any suitable mechanism, including, but not limited to,
flanges, barbs, and/or sutures.
With reference to FIG. 16E, there is depicted another design of a
self-sizing and expandable nerve cuff electrode 1610. For the
purposes of this disclosure, nerve cuff electrode 1610 may be
substantially similar to nerve cuff electrode 1600 depicted in
FIGS. 16C-16D. Nerve cuff electrode 1610, however, may differ from
nerve cuff electrode 1600 in at least two significant ways. First,
for example, lateral side 1611 of nerve cuff electrode 1610 may
carry two anode electrode contacts 1613 and the medial side 1612
may carry one cathode electrode contact 1613 in an arrangement that
may be referred to as transverse guarded tri-polar. Second, for
example, nerve cuff electrode 1610 may include three arms 1614-1616
extending from lateral side 1611. In the depicted embodiment, arms
1614 and 1616 may be configured to extend substantially in the same
direction from the same edge 1611a of lateral side 1611, while arm
1615 may be configured to extend in substantially the opposing
direction from an opposing edge 1611b of lateral side 1611. In the
depicted embodiment, arm 1615 may be disposed between arms 1614 and
1616, and may be configured to carry the cathode electrode contact
1613, as mentioned above. However, any suitable arrangement of arms
1614-1616 and/or electrode contacts 1613 may be utilized within the
principles of this disclosure.
As shown in FIG. 16F, certain embodiments of nerve curve electrode
1600 and/or nerve cuff electrode 1610 may include one or more
elongated arms 1617. Arms 1617 may include any suitable length, so
as to allow arms 1617 to wrap around a body portion of the cuff
electrode one or more times in a spiral-like fashion, when the cuff
electrode is mounted about an un-swollen nerve. However, arms 1617
may allow the cuff electrode to remain mounted on the nerve as it
accommodates large amounts of nerve swelling by unraveling and/or
unwrapping as the nerve swells. For example, each of the arms 1617
may overlap lateral side 1601 or 1611 to accommodate larger amounts
of nerve swelling without allowing the cuff to become detached from
the nerve. The elongated arms 1617 may extend around the body of
the cuff electrode to form a spiral when the nerve is in a
substantially un-swollen state, as shown.
With reference to FIG. 17, a modular nerve electrode cuff 170 is
shown that includes a semi-cylindrical body portion 172 with an
array of electrode contacts 176 with separate insulative strips 174
for placement on the deep (contralateral side) of the nerve, which
typically has more nerve branches and connecting blood vessels. In
this embodiment, independent placement of the electrode body 172 on
the superficial (lateral) side of the nerve and placement of the
insulative strips 174 on the deep (contralateral) side of the nerve
minimizes dissection. The strips 174 may be connected to the
electrode body 172 by sutures or buckles as described previously.
This embodiment is also self-sizing to accommodate nerve swelling
and/or over-tightening.
With reference to FIG. 18, a nerve cuff electrode 180 is shown that
has a cuff body with a relatively wide semi-cylindrical lateral
side 182 and a relatively narrow semi-cylindrical medial side 184
that may extend through a small fenestration around the deep
(contralateral) side of a nerve to securely and gently grasp the
nerve while minimizing dissection. In the illustrated example, the
lateral side 182 carries two anode electrode contacts 186 and the
medial side 184 carries one cathode electrode contact 186 in an
arrangement that may be referred to as transverse guarded
tri-polar. A tow strap 188 is provided for inserting the medial
side 184 around the deep side of the nerve. The tow strap 188 may
be integrally formed with the medial side 184 of the cuff body, and
may include a reinforced tip 188A with a serrated or marked cut
line 188B.
With reference to FIGS. 19A and 19B, a nerve cuff electrode 190 is
shown that has a cuff body with a relatively wide semi-cylindrical
lateral side 192 and a relatively narrow semi-cylindrical medial
side 194 that may extend through a small fenestration around the
deep (contralateral) side of a nerve to securely and gently grasp
the nerve while minimizing dissection. In the illustrated example,
the lateral side 192 carries one cathode electrode contact 196C and
two guarding anode electrode contacts 196B and 196D, and the medial
side 194 carries one anode electrode contact 196A in an arrangement
that may be referred to as transverse and longitudinal guarded
quad-polar. The provision of guarding electrode contacts 196B and
196C reduces extrinsic stimulation due to the lack of insulative
material on the medial side 194. The embodiments of FIGS. 18, 19A
and 19B illustrate two different electrode contact arrangements,
but the number and arrangement may be modified to suit the
particular application.
With reference to FIG. 20, a nerve cuff electrode array 200 is
shown that utilizes a series of relatively narrow independent cuffs
200A, 200B and 200C with corresponding independent lead bodies 62.
Providing a series of relatively narrow independent cuffs 200A,
200B and 200C minimizes the required dissection around the nerve
for implantation thereof. Also, the series of independent cuffs
200A, 200B and 200C allows more selectivity in electrode placement
to adjust for anatomical variation or multiple target stimulation
sites, for example. Providing multiple independent lead bodies 62
allows for more options in routing and placement of the individual
lead bodies 62 (e.g., alternate placement of lead body 62A) and
also prevents tissue encapsulation around the lead bodies 62 from
collectively affecting encapsulation of the nerve cuffs 200. Each
of the cuffs 200A, 200B and 200C may include a cuff body 202 with
one or more imbedded electrode contacts (not shown) and a tow strap
204 as described before. Also, each of the cuffs 200A, 200B and
200C may include suture 208 or a buckle 206 to lock onto the tow
strap 204 for connecting opposite ends of the body 202 around the
nerve.
With reference to FIGS. 21A and 21B, a nerve cuff electrode 210 is
shown with multiple electrode contacts 216 radially spaced around
the inside surface of a compliant split cuff body 212 to establish
multiple electrical contact points around the circumference of the
nerve. Each of the electrode contacts 216 may be connected to
independent conductors in the lead body 62 via axially extending
wires 217. This arrangement allows for field steering as discussed
herein. The compliant split cuff body 212 together with axially
extending wires 217 allows for self-sizing to accommodate nerve
swelling and/or over-tightening. One or more pairs of tabs 214
extending from opposite end portions of the cuff body 212 may be
connected by a suture (not shown) as described herein. As shown in
FIG. 21B, the proximal and distal ends of the cuff body 212 may
have tapered thickness extensions 218 to provide strain relief and
reduce mechanical irritation of the nerve due to contact with the
edge of the cuff.
With reference to FIG. 22, a nerve cuff electrode 220 is shown with
a separable lead 62 in what may be referred to as a modular design.
In this embodiment, the nerve cuff electrode 220 includes a
semi-circular flexible cuff body (or housing) 222 with a receptacle
224 configured to accommodate a distal end of a lead body 62
therein. The receptacle 224 may provide a releasable mechanical
lock to the lead body 52 as by a press fit, mating detents, etc.
The distal end of the lead body 62 carries an array of ring
electrodes 65, with windows 226 provided in the cuff body 222
configured to align with the ring electrodes 65 and permit exposure
of the ring electrodes 65 to the nerve to establish electrical
connection therebetween. The cuff body 222 may be attached to the
nerve or simply placed adjacent the nerve. Any of the cuff designs
described herein may be provided with a receptacle to accommodate a
removable lead body. This embodiment allows postoperative removal
of the lead body 62 without removal of the cuff 220, which may be
beneficial in revision operations, for example.
Turning now to FIG. 22A, there is depicted another design for a
nerve cuff electrode 2000 where a substantially cylindrical distal
portion 62' of lead body 62 carries an array of electrodes 2001.
Electrodes 2001 may include ring electrodes that extend completely
around the circumference of lead body 62, or, alternatively, may
include generally semi-circular electrodes that extend partially
around the circumference of lead body 62. The electrode may be
selectively insulated on any portion of its surface to allow
directional stimulation. Nerve cuff electrode 2000 may further
include a nerve securing mechanism for securing lead body 62 to a
nerve, such as, for example, a hypoglossal nerve. The nerve
securing mechanism may include, for example, a compliant sheet wrap
2002 that is attached on one end to a distal portion of lead body
62, and unattached on the other opposing end. Compliant sheet wrap
2002 may be attached to lead body 62 by any suitable means.
As shown in FIG. 22B, compliant sheet wrap 2002 may be configured
to be wrapped around a nerve and secured thereto by, for example,
connecting opposite portions of the sheet wrap 2002 together. Sheet
wrap 2002 may be provided with one or more features to facilitate
such connections. For example, it is contemplated that a portion
2002b of sheet wrap 2002 that is closest to lead body 62 may be
provided with a projection 2002c that is configured for insertion
into a corresponding opening 2002e provided on a portion 2002d of
sheet wrap 2002 that is opposite portion 2002b. Opening 2002e may
be configured to retain projection 2002c despite the forces exerted
on sheet wrap 2002 during normal nerve swelling. However, opening
2002e may be configured to release projection 2002c when forces
greater than a predetermined threshold are exerted on sheet wrap
2002, so as to prevent injury to the nerve. As shown in FIG. 22C,
in some embodiments, opening 2002e may be provided as a slot,
which, in addition to securing projection 2002c, may allow
projection 2002c to slide within the opening 2002e, thereby
allowing expansion of the sheet wrap 2002 to accommodate nerve
swelling and/or over tightening of the sheet wrap 2002.
Additionally, both portions 2002b and 2002d may be provided with
suitable openings to facilitate the insertion of sutures (not
shown) or other suitable fastening mechanisms. Sheet wrap 2002 may
have any desired width. For example, sheet wrap 2002 may have a
substantially tapered width, in order to securely wrap the nerve
while minimizing dissection.
Compliant sheet wrap 2002 may be provided with any of a number of
means that allow sheet wrap 2002 to expand, in order to accommodate
nerve swelling and/or over tightening. For example, in one
embodiment, sheet wrap 2002 may be provided with a plurality of
radially and/or longitudinally distributed fenestrations (not
shown). In other embodiments, sheet wrap 2002 may be provided with
a plurality of undulations 2002a, such as, for example, sigmoid
undulations, which may allow for expansion of sheet wrap 2002.
With reference now to FIG. 22D, there is depicted another design
for a nerve cuff electrode 2200 where a distal portion 62'' of lead
body 62 carries an array of electrodes 2201. For the purposes of
this disclosure, nerve cuff electrode 2200 may include
substantially the same features as nerve cuff electrode 2000
depicted in FIGS. 22A-22C. Nerve cuff electrode 2200, however, may
differ from nerve cuff electrode 2000 in that distal portion 62''
may be substantially flat or paddle-shaped. Furthermore, electrode
contacts 2201, rather than being circular or semi-circular in
configuration, may be substantially, flat in configuration. In
certain procedures, it is contemplated that the paddle-shaped
distal portion 62'', along with the substantially flat electrode
contacts 2201, may promote greater contact between electrode
contacts 2201 and the nerve they are mounted upon.
Description of Alternative Implant Procedure for the Stimulation
Lead
With reference to FIGS. 23A-23C, an insertable paddle-shaped lead
230 design is shown. The insertable lead 230 may have a
paddle-shape (rectangular) cross-section with a tubular jacket 232
and one or more conductors 234 extending therethrough to one or
more distally placed electrode contact(s) 236. The electrode
contact(s) 236 may be imbedded in a molded distal end of the jacket
232 such that the electrode contact 236 has an exposed surface to
face the nerve when implanted as shown in FIG. 23B. The space
between the nerve and electrode is shown for purposes of
illustration only, as the electrodes may be placed in direct
contact with the nerve. Soft tines 238 may be integrally formed at
the distal end of the tubular jacket 232 for purposes of mild
fixation to tissue when implanted. The insertable lead 230 is
configured to be placed adjacent to the nerve (thereby negating the
need for a cuff) by inserting the lead 230 at the surgical access
site 110 and following the nerve distally until the electrode
contacts 236 are placed adjacent the target stimulation site. The
insertable lead 232 may be used alone or in conjunction with
another lead as shown in FIGS. 23B and 23C. In the illustrated
example, a first lead 230A is inserted along a superficial side of
the nerve and a second lead 230B is inserted along a deep side of
the nerve.
A method of implanting lead 230 may generally comprise accessing a
proximal extent of the nerve by minimal surgical dissection and
retraction of the mylohyoid muscle as shown in FIG. 23C. Special
tools may alternatively be employed for percutaneous or
laparoscopic access as shown and described with reference to FIGS.
24A-24C. Subsequently, two paddle-shaped leads 230 with distal
electrode contacts 236 may be inserted into the surgical access
site and advanced beyond the access site along a distal aspect of
the nerve to the desired stimulation site on either side of the
nerve. These techniques minimize trauma and facilitate rapid
recovery.
A less invasive method of implanting a paddle-shaped lead 230 is
shown in FIGS. 24A-24C. In this embodiment, a rectangular tubular
trocar 240 with a sharpened curved tip is placed through a
percutaneous access site 111 until a distal end thereof is adjacent
the superficial side of the nerve. A paddle-shaped lead 230 is
inserted through the lumen of the trocar 240 and advanced distally
beyond the distal end of the trocar 240 along the nerve, until the
electrode contacts 236 are positioned at the target stimulation
site. As shown in FIG. 24B, which is a view taken along line A-A in
FIG. 24A, the insertable lead 230 includes multiple electrode
contacts 236 in an anode-cathode-anode arrangement, for example, on
one side thereof to face the nerve when implanted. In this
embodiment, tines are omitted to facilitate smooth passage of the
lead 230 through the trocar. To establish fixation around the nerve
and to provide electrical insulation, a backer strap 242 of
insulative material may be placed around the deep side of the
nerve. To facilitate percutaneous insertion of the backer 242, a
curved tip needle 244 may be inserted through a percutaneous access
site until the tip is adjacent the nerve near the target
stimulation site. A guide wire 246 with a J-shaped tip may then be
inserted through the needle 244 and around the nerve. The backer
242 may then be towed around using the guide wire 246 as a leader,
and secured in place by a buckle (not shown), for example.
With reference to FIG. 25, a bifurcated lead 250 is shown to
facilitate separate attachment of electrode cuffs 64 to different
branches of the same nerve or different nerves for purposes
described previously. Any of the nerve cuff electrode or
intramuscular electrode designs described herein may be used with
the bifurcated lead 250 as shown. In the illustrated example, a
first lead furcation 252 and a second lead furcation 254 are shown
merging into a common lead body 62. Each furcation 252 and 254 may
be the same or similar construction as the lead body 62, with
modification in the number of conductors. More than two electrode
cuffs 64 may be utilized with corresponding number of lead
furcations.
Description of Stimulation Lead Anchoring Alternatives
With reference to FIGS. 26A and 26B, an elastic tether 264 with a
limited length is utilized to prevent high levels of traction on
the electrode cuff 64 around the hypoglossal nerve (or other nerve
in the area) resulting from gross head movement. In other words,
tether 264 relieves stress applied to the electrode cuff 64 by the
lead body 62. FIGS. 26A and 26B are detailed views of the area
around the dissection to the hypoglossal nerve, showing alternative
embodiments of attachment of the tether 264. The proximal end of
the tether 264 may be attached to the lead body 62 as shown in FIG.
26A or attached to the electrode cuff 64 as shown in FIG. 26B. The
distal end of the tether 264 may be attached to the fibrous loop
carrying the digastrics tendon as shown in FIG. 26A or attached to
adjacent musculature as shown in FIG. 26B.
By way of example, not limitation, and as shown in FIG. 26A, a
tubular collar 262 is disposed on the lead body 62 to provide
connection of the tether 264 to the lead body 62 such that the lead
body 62 is effectively attached via suture 266 and tether 264 to
the fibrous loop surrounding the digastrics tendon. The tether 264
allows movement of the attachment point to the lead body 62 (i.e.,
at collar 262) until the tether 264 is straight. At this point, any
significant tensile load in the caudal direction will be borne on
the fibrous loop and not on the electrode cuff 64 or nerve. This is
especially advantageous during healing before a fibrous sheath has
formed around the lead body 62 and electrode cuff 64, thus ensuring
that the cuff 64 will not be pulled off of the nerve. It should be
noted that the length of the tether 262 may be less than the length
of the lead body 62 between the attachment point (i.e., at collar
262) and the cuff 64 when the tensile load builds significantly due
to elongation of this section of lead body 62.
The tether 264 may be formed from a sigmoid length of braided
permanent suture coated with an elastomer (such as silicone or
polyurethane) to maintain the sigmoid shape when in the unloaded
state. The tether 264 may also be made from a monofilament suture
thermoformed or molded into a sigmoid shape. The distal end of the
tether 264 may be attached to the fibrous loop using a suture 266
or staple or other secure means. Note that the tether 264 may be
made from a biodegradable suture that will remain in place only
during healing.
Also by way of example, not limitation, an alternative is shown in
FIG. 26B wherein the tether 264 is attached to the electrode cuff
64. The distal end of the tether 264 may be attached to the
adjacent musculature by suture 266 such the musculature innervated
by branches of the hypoglossal nerve or other musculature in the
area where the electrode cuff 64 is attached to the nerve. The
tether 264 ensures that the electrode cuff 64 and the hypoglossal
nerve are free to move relative to the adjacent musculature (e.g.,
hyoglossal). As significant tensile load is applied to the lead
body 62 due to gross head movement, the tether 264 will straighten,
transmitting load to the muscle rather then to the nerve or
electrode cuff 64.
As alluded to above, stimulation lead 60 may comprise a number of
differing design embodiments. One such embodiment has been
discussed above with respect to FIG. 5. Another such embodiment is
depicted in FIG. 26C, which illustrates a stimulation lead 2600.
Stimulation lead 2600 may be substantially similar to and/or may
include one or more of the features described in connection with
stimulation lead 60. As shown in FIG. 26C, stimulation lead 2600
may include a lead body 2662 having a first, proximal lead body
portion 2663. First lead body portion 2663 may be substantially
similar to lead body 62. For example, first lead body portion 2663
may include a similar flexibility as lead body 62. Lead body 2662
may further include a second, distal lead body portion 2664 leading
to the distal end of lead body 2662 at the nerve cuff electrode.
Second lead body portion 2664 may include a material property that
is different than lead body portion 2663, such as, for example, a
greater flexibility, in order to accommodate stresses imparted upon
lead body 2662 by a nerve cuff electrode and movement of the
patient's head, neck, and other neighboring body portions. The
highly flexible distal portion 2664 reduces the stress (torque and
tension) imparted by lead body 2662 on the electrode cuff, thereby
reducing the likelihood that the cuff will be detached from the
nerve or damage the nerve.
Lead body portion 2664 may be made more flexible than lead body
portion 2663 by any of a variety of ways. For example, lead body
portion 2664 may be made from a material having differing
flexibility. Alternatively, the diameters of the braided stranded
wires (BSW) and/or wire insulation that make up the lead body
portion 2664 may be reduced when possible.
With continuing reference to FIG. 26C, stimulation lead 2600 may
further include an anchor 2665 operably connected to lead body
2662. Although anchor 2665 in the illustrated embodiment is
depicted as being disposed in between lead body portions 2663 and
2664, anchor 2665 may be disposed at any suitable location along
the length of lead body 2662. Furthermore, anchor 2665 may be
fixedly or movably connected to lead body 2662.
Anchor 2665 may include any suitable configuration known in the
art. For example, anchor 2665 may include a substantially flat body
portion 2666. Body portion 2666 may be configured to be secured to
tissue, such as, for example, tissue proximate a treatment site, by
any suitable means available in the art. For example, body portion
2666 may be provided with openings 2667 to facilitate, for example,
suturing anchor 2665 to nearby tissue. Anchor 2665 can thereby
isolate stress (tension) to one portion of lead body 2662, and
particularly portion 2663, caused by gross head and neck
movement.
Description of Field Steering Alternatives
With reference to FIGS. 27A-27G, a field steering nerve cuff
electrode 64 is shown schematically. As seen in FIG. 27A, the nerve
cuff electrode 64 may include four electrode contacts 90A-90D to
enable field steering, and various arrangements of the electrode
contacts 90A-90D are shown in FIGS. 27B-27G. Each of FIGS. 27B-27G
includes a top view of the cuff 64 to schematically illustrate the
electrical field (activating function) and an end view of the cuff
64 to schematically illustrate the area of the nerve effectively
stimulated. With this approach, electrical field steering may be
used to stimulate a select area or fascicle(s) within a nerve or
nerve bundle to activate select muscle groups as described
herein.
With specific reference to FIG. 27A, the nerve cuff electrode 64
may comprise a cuff body having a lateral (or superficial) side 82
and a medial (or contralateral, or deep) side 84. The medial side
84 is narrower or shorter in length than the lateral side 82 to
facilitate insertion of the medial side 84 around a nerve such that
the medial side is on the deep side of the nerve and the lateral
side is on the superficial side of the nerve. An integral tow strap
86 may be used to facilitate wrapping the cuff around a nerve. The
nerve cuff electrode 64 includes electrode contacts 90A, 90B, 90C
and 90D imbedded in the body of the cuff, with their inside surface
facing exposed to establish electrical contact with a nerve
disposed therein. Electrode contacts 90A and 90B are longitudinally
and radially spaced from each other. Electrode contacts 90C and 90D
are radially spaced from each other and positioned longitudinally
between electrode contacts 90A and 90B. Each of the four electrode
contacts may be operated independently via four separate conductors
(four filar) in the lead body 62.
With specific reference to FIGS. 27B-27G, each includes a top view
(left side) to schematically illustrate the electrical field or
activating function (labeled E), and an end view (right side) to
schematically illustrate the area of the nerve effectively
stimulated (labeled S) and the area of the nerve effectively not
stimulated (labeled NS). Electrodes 90A-90D are labeled A-D for
sake of simplicity only. The polarity of the electrodes is also
indicated, with each of the cathodes designated with a negative
sign (-) and each of the anodes designated with a positive sign
(+).
With reference to FIG. 27B, a tripolar transverse guarded cathode
arrangement is shown with electrodes C and D comprising cathodes
and electrodes A and B comprising anodes, thus stimulating the
entire cross-section of the nerve.
With reference to FIG. 27C, a bipolar diagonal arrangement is shown
with electrode C comprising a cathode and electrode A comprising an
anode, wherein the fascicles that are stimulated may comprise
superior fascicles of the hypoglossal nerve, and the fascicles that
are not stimulated may comprise inferior fascicles of the
hypoglossal nerve (e.g., fascicles that innervate the intrinsic
muscles of the tongue).
With reference to FIG. 27D, another bipolar diagonal arrangement is
shown with electrode D comprising a cathode and electrode B
comprising an anode, wherein the fascicles that are stimulated may
comprise inferior fascicles of the hypoglossal nerve.
With reference to FIG. 27E, a bipolar axial arrangement is shown
with electrode A comprising a cathode and electrode B comprising an
anode, wherein the fascicles that are stimulated may comprise
lateral fascicles of the hypoglossal nerve.
With reference to FIG. 27F, a bipolar transverse arrangement is
shown with electrode C comprising a cathode and electrode D
comprising an anode, wherein the fascicles that are stimulated may
comprise medial fascicles of the hypoglossal nerve.
With reference to FIG. 27G, a modified tripolar transverse guarded
cathode arrangement is shown with electrode C comprising a cathode
and electrodes A and B comprising anodes, thus stimulating the
entire cross-section of the nerve with the exception of the
inferior medial fascicles.
Nerves like the hypoglossal nerve or superior laryngeal nerve
typically include a plurality of fibers having relatively larger
diameters and a plurality of fibers having relatively smaller
diameters. In the case of single function nerves, such as, for
example, the hypoglossal nerve HGN, all of the nerve fibers may
either be sensory or motor in function. However, in the case of
multi-function nerves, such as, for example, the superior laryngeal
nerve SLN, the fibers having relatively larger diameters are
typically motor (efferent) fibers, and the fibers having relatively
smaller diameters are typically sensory (afferent) fibers.
Accordingly, there may be a need to selectively stimulate the
differing diameter fibers in a nerve.
Turning now to FIG. 27H, there is depicted an embodiment of a
uni-directional stimulation electrode 2700 having a distal end
2700a and a proximal end 2700b. Electrode 2700 may include a
substantially cylindrical nerve cuff 2701 in accordance with the
principles of the present disclosure. As illustrated, nerve cuff
2701 may include an outer surface 2701a and an inner surface 2701b.
Electrode 2700 may further include a plurality of electrode
contacts 2702-2704. Electrode contacts 2702-2704 may be used as any
suitable electrode contact known to those of ordinary skill in the
art. For example, electrode contact 2702 may be used as an anode,
electrode contact 2703 may be used as a cathode, and electrode
contact 2704 may be used as a second anode. Electrode contacts
2702-2704 may also include any suitable shape and/or configuration
known in the art. For example, electrode contacts 2702-2704 may
include a substantially semi-circular configuration.
Electrode contacts 2702-2704 may be disposed on nerve cuff 2701 in
any suitable configuration to achieve the desired effect. For
example, electrode contacts 2702-2704 may be disposed on inner
surface 2701b. As depicted in FIG. 27H, cathode electrode contact
2703 may be disposed approximately equidistant from distal end
2700a and proximal end 2700b, and anode electrode contacts 2702 may
be differentially spaced around cathode electrode contact 2703, so
as to control the direction of stimulation of electrode 2700. For
example, anode electrode contact 2702 may be spaced from cathode
electrode contact 2703 by any suitable distance .chi., while second
anode electrode contact 2704 may be spaced from cathode electrode
contact 2703 by a distance that is approximately two or three times
greater than distance .chi.. In this exemplary configuration, the
direction of stimulation may be in the direction of arrow 2705.
In use, electrode 2700 may be implanted upon a nerve in accordance
with the principles of this disclosure. Electrode 2700 may be
oriented on the nerve it is implanted on in any suitable manner,
such as, for example, according to the direction of intended
stimulation. Thus, in circumstances where it may be desired to
stimulate efferent (motor) fibers of a nerve, such as, for example,
the superior laryngeal nerve SLN, while avoiding stimulation to
afferent (sensory) fibers of the nerve, the electrode 2700 may be
oriented on the nerve in a manner such that anode electrode contact
2702 is located distally of cathode electrode contact 2703, with
distal and proximal designations based on the relative location of
the electrode contact on the nerve. Alternatively, in circumstances
where it may be desired to stimulate afferent fibers of a nerve
while avoiding stimulation of efferent fibers of the nerve, the
electrode 2700 may be oriented on the nerve in a manner such that
anode electrode contact 2702 is located proximally of cathode
electrode contact 2703.
With reference now to FIG. 27I, there is depicted an embodiment of
a stimulation electrode 2750 for, among other things, selectively
stimulating differing diameter fibers of a nerve, such as, for
example, the hypoglossal nerve or superior laryngeal nerve.
Electrode 2750 may include a body 2751, and may include any
suitable configuration in accordance with the principles of the
present disclosure. Additionally, electrode 2750 may include an
array 2752 of suitable electrode contacts known to those skilled in
the art. Although the depicted embodiment of electrode 2750
includes five electrode contacts 2753a-2753e, array 2752 may
include a greater or lesser number of electrode contacts. Electrode
contacts 2753a-2753e may be disposed on body 2751 in any suitable
configuration to produce the desired effect. For example, as
depicted in FIG. 27I, electrode contacts 2753a-2753e may be
disposed serially, with approximately a one (1) millimeter spacing
in between each electrode contact 2753a-2753e. Electrode contacts
2753a-2753e may be configured to function as either anode electrode
contacts or cathode electrode contacts, as desired.
Electrode contacts 2753 may be connected to an implanted
neurostimulator (INS), such as, for example, INS 50, in accordance
with the present disclosure. The INS may be programmed to select
any of electrode contacts 2753a-2753e for nerve stimulation. For
example, in circumstances where it may be desired to stimulate the
smaller diameter fibers of a nerve, it is contemplated that all
electrode contacts 2753a-2753e may be selected for nerve
stimulation, since closely spaced electrode contacts typically
affect smaller diameter fibers (e.g., afferent or sensory fibers).
In these circumstances, electrode contacts 2753a, 2753c, and 2753e
may function as anode electrode contacts and electrode contacts
2753b and 2753d may function as cathode electrode contacts. In
circumstances where it may be desired to stimulate the larger
diameter fibers of a nerve, it is contemplated that only electrode
contacts 2753a, 2753c, and 2753e may be selected for nerve
stimulation, since loosely spaced electrode contacts typically
affect larger diameter fibers (e.g., efferent or motor fibers). In
these circumstances, electrode contacts 2753a and 2753e may
function as anode electrode contacts, and 2753c may function as a
cathode electrode contact.
Alternatively, electrode 2750 may be utilized to reduce muscle
fatigue when implanted on single function nerves, such as, for
example, the hypoglossal nerve. In such circumstances, muscle
fatigue may be reduced by alternatively switching between using
loosely spaced electrode contacts 2753a, 2753c, and 2753e, to
stimulate large diameter fibers, and closely spaced electrode
contacts 2753a-2753e, to stimulate small diameter fibers.
Turning to FIGS. 27J-27K, in accordance with the present
disclosure, there is depicted another embodiment of a nerve cuff
electrode 2760 for facilitating reduction in muscle fatigue. Nerve
cuff electrode 2760 may include a body 2761 having a plurality of
electrode contacts 2762, 2763, and 2764. Electrode contacts
2762-2764 may include any suitable electrode contacts in accordance
with the present disclosure. Although the depicted embodiment of
nerve cuff electrode 2760 includes three electrode contacts
2762-2764, nerve cuff electrode 2760 may include a greater or
lesser number of electrode contacts. Furthermore, electrode
contacts may be disposed on body 2761 in any suitable configuration
to achieve the desired effect, such as, for example, serially, as
depicted. In the depicted embodiment, electrode contacts 2762 and
2764 may function as anode electrode contacts, while electrode
contact 2763 may function as a cathode electrode contact. Electrode
contact 2763 may include two distinct, substantially triangularly
shaped portions 2763a and 2763b. However, portions 2763a and 2763b
may include any suitable shape. In addition, portions 2763a and
2763b may be configured to be of differing conductive properties,
so that, for the same stimulation pulse (e.g., a slow rising, small
amplitude pulse having a relatively long duration of approximately
0.2 to 0.35 milliseconds) applied to each of the portions 2763a and
2763b, the resultant charge densities at the surface of each of the
portions 2763a and 2763b may be different. For example, portions
2763a and 2763b may be made of electrically differing materials.
For discussion purposes only, it is assumed that portion 2763a is
configured to deliver a charge density lower than that of portion
2763b. However, portion 2763a may be configured to deliver a charge
density that is higher than the charge density of portion
2763b.
Since the small diameter fibers of a nerve are typically stimulated
by low charge densities and large diameter fibers of the nerve are
typically stimulated by high charge densities, portions 2763a and
2763b may be sequentially utilized to alternate between stimulating
the small and large diameter fibers of a nerve. In other words, in
use, a stimulation pulse may be first delivered to portion 2763a to
stimulate the small diameter fibers of a nerve. A subsequent
stimulation pulse may be then delivered to portion 2763b to
stimulate the large diameter fibers of a nerve. It is contemplated
that alternating between stimulating the small and large diameter
fibers of a nerve may facilitate reducing muscle fatigue while also
ensuring sufficient muscle mass is stimulated to maintain the
necessary contraction and force generation to successfully treat
OSA.
Turning now to FIG. 27L, there is illustrated yet another
embodiment of a nerve cuff electrode 2780 for facilitating
reduction in muscle fatigue. For the purposes of this disclosure,
nerve cuff electrode 2780 may be substantially similar to nerve
cuff electrode 2760. Nerve cuff electrode 2780, however, may differ
from nerve cuff electrode 2760 in at least one significant way. For
example, rather than having two substantially triangular portions,
cathode electrode contact 2783 may comprise two substantially
different portions 2783a and 2783b. Portions 2783a and 2783b may be
spaced apart from one another and may include differing surface
areas. For example, as illustrated, portion 2783a may include a
smaller surface area than portion 2783b. Furthermore, portions
2783a and 2783b may include any suitable shape known in the art.
Although portions 2783a and 2783b in the illustrated embodiment
together define a substantially triangular shaped electrode contact
2783, portions 2783a and 2783b together may or may not define any
suitable shape known in the art.
Each of portions 2783a and 2783b may be configured to be
substantially similar in conductance despite their differing
surface areas. For example, portion 2783a may be made of a first
material having a relatively lower conductance, while portion 2783b
may be made of a second material having a relatively higher
conductance. Thus, when subjected to the same stimulation pulse
(e.g., a slow rising, small amplitude pulse having a relatively
long duration of approximately 0.2 to 0.35 milliseconds), portion
2783a may have a higher charge density than portion 2783b because
of its relatively smaller surface area than portion 2783b.
Similarly, when subjected to the same stimulation pulse, portion
2783b may have a lower charge density than portion 2783a because of
its relatively larger surface area than portion 2783a. Accordingly,
because of the differing charge densities, portion 2783a may be
adapted to stimulate large diameter fibers of a nerve, and portion
2783b may be adapted to stimulate small diameter fibers of the
nerve.
In use, a stimulation pulse may be first delivered to portion 2783a
to stimulate the large diameter fibers of a nerve. A subsequent
stimulation pulse may be then delivered to portion 2783b to
stimulate the small diameter fibers of the nerve. It is
contemplated that alternating between stimulating the small and
large diameter fibers of a nerve may facilitate muscle fatigue
while also ensuring that sufficient muscle mass is stimulated to
maintain the necessary contraction and force generation to
successfully treat OSA.
In certain embodiments, such as when nerve cuff electrodes 2760 and
2780 are implanted on a multi-function nerve (e.g., the superior
laryngeal nerve SLN), it is contemplated that portions 2763a/2763b
and portions 2783a/2783b may be utilized to selectively stimulate
either the afferent or efferent fibers of the nerve.
With reference now to FIGS. 27M-27Q, there is depicted yet another
embodiment of a nerve cuff electrode 2790 for minimizing muscle
fatigue. Nerve cuff electrode 2790 may include a cuff body 2791 for
mounting about a nerve 2792 in accordance with the present
disclosure. Cuff body 2791 may include a plurality of electrode
contacts 2793-2796 also in accordance with the present disclosure.
Although the depicted embodiment of nerve cuff electrode 2790
includes four electrode contacts 2793-2796, nerve cuff electrode
2790 may include a greater or lesser number of electrode
contacts.
Nerve cuff electrode 2790 may be configured to selectively
stimulate both small diameter fibers contained in fascicle 2777a
and large diameter fibers contained in fascicle 2777b of nerve
2792. For example, as shown in FIG. 27P, by applying an exemplary
slow rising, long pulse width waveform to electrode contacts 2796
and 2793, nerve cuff electrode 2790 may stimulate the small
diameter fibers contained in fascicle 2777a of nerve 2792.
Similarly, as shown in FIG. 27Q, by applying an exemplary fast
rising, short pulse width waveform to electrode contacts 2794 and
2795, nerve cuff electrode 2790 may stimulate the large diameter
fibers contained in fascicle 2777b of nerve 2792. Fascicles 2777a
and 2777b may be stimulated simultaneously or separately. In
embodiments, where it is desirable to stimulate fibers contained in
fascicles 2777a and 2777b, the pulse generator (e.g., INS 50) may
be provided with dual output ports.
Description of Respiration Sensing Lead Anchoring Alternatives
With reference to the following figures, various additional or
alternative anchoring features for the respiration sensing lead 70
are schematically illustrated. Anchoring the respiration sensing
lead 70 reduces motion artifact in the respiration signal and
stabilizes the bio-impedance vector relative to the anatomy.
In each of the embodiments, by way of example, not limitation, the
respiration sensing lead 70 includes a lead body 70 with a proximal
connector and a plurality of distal respiration sensors 74
comprising ring electrodes for sensing bio-impedance. The lead body
72 of the respiration sensing lead 70 may include a jacket cover
containing a plurality of conductors 78, one for each ring
electrode 74 requiring independent control. Generally, the
impedance electrodes 74 may comprise current emitting electrodes
and voltage sensing electrodes for detecting respiration by changes
in bio-impedance.
With reference to FIGS. 28-33, various fixation devices and methods
are shown to acutely and/or chronically stabilize the respiratory
sensing lead 70. With specific reference to FIG. 28, the INS 50 is
shown in a subcutaneous pocket and the stimulation lead 60 is shown
in a subcutaneous tunnel extending superiorly from the pocket. The
respiration sensing lead 70 is shown in a subcutaneous tunnel
superficial to muscle fascia around the rib cage. A suture tab or
ring 270 may be formed with or otherwise connected to the distal
end of the lead body 72. Near the distal end of the lead 70, a
small surgical incision may be formed to provide access to the
suture tab 270 and the muscle fascia under the lead 70. The suture
tab 270 allows the distal end of the lead 70 to be secured to the
underlying muscle fascia by suture or staple 272, for example,
which may be dissolvable or permanent. Both dissolvable and
permanent sutures/staples provide for acute stability and fixation
until the lead body 72 is encapsulated. Permanent sutures/staples
provide for chronic stability and fixation beyond what tissue
encapsulation otherwise provides.
With reference to FIGS. 29A-29C, a fabric tab 280 may be used in
place of or in addition to suture tab 270. As seen in FIG. 29A, the
fabric tab 280 may be placed over a distal portion of the lead body
72, such as between two distal electrodes 74. A small surgical
incision may be formed proximate the distal end of the lead 70 and
the fabric tab 280 may be placed over the over the lead body 72 and
secured to the underlying muscle fascia by suture or staple 282,
for example, which may be dissolvable or permanent, to provide
acute and/or chronic stability and fixation. With reference to
FIGS. 29B and 29C (cross-sectional view taken along line A-A), the
fabric tab 280 may comprise a fabric layer (e.g., polyester) 284 to
promote chronic tissue in-growth to the muscle fascia and a smooth
flexible outer layer (silicone or polyurethane) 286 for acute
connection by suture or staple 282.
With reference to FIG. 30, lead 70 includes a split ring 290 that
may be formed with or otherwise connected to the distal end of the
lead body 72. The split ring 290 allows the distal end of the lead
70 to be secured to the underlying muscle fascia by suture or
staple 292, for example, which may be dissolvable or permanent. The
ring 290 may be formed of compliant material (e.g., silicone or
polyurethane) and may include a slit 294 (normally closed) that
allows the lead 70 to be explanted by pulling the lead 70 and
allowing the suture 292 to slip through the slit 294, or if used
without a suture, to allow the ring to deform and slide through the
tissue encapsulation. To further facilitate explantation, a
dissolvable fabric tab 282 may be used to acutely stabilize the
lead 70 but allow chronic removal.
With reference to FIGS. 31A-31C, deployable anchor tines 300 may be
used to facilitate fixation of the lead 70. As seen in FIG. 31A,
the self-expanding tines 300 may be molded integrally with the lead
body 72 or connected thereto by over-molding, for example. The
tines 300 may comprise relatively resilient soft material such as
silicone or polyurethane. The resilient tines 300 allow the lead 70
to be delivered via a tubular sheath or trocar 304 tunneled to the
target sensing site, wherein the tines 300 assume a first collapsed
delivery configuration and a second expanded deployed
configuration. As seen in FIGS. 31B and 31B, the tubular sheath or
trocar 304 may be initially tunneled to the target site using an
obtruator 306 with a blunt dissection tip 308. After the distal end
of the tubular sheath 304 has been tunneled into position by blunt
dissection using the obtruator 306, the obtruator 306 may be
removed proximally from the sheath 304 and the lead 70 with
collapsible tines 300 may be inserted therein. As seen in FIG. 31C,
when the distal end of the lead 70 is in the desired position, the
sheath 304 may be proximally retracted to deploy the tines 300 to
engage the muscle fascia and adjacent subcutaneous tissue, thus
anchoring the lead 70 in place.
With reference to FIGS. 32A and 32B, an alternative deployable
fixation embodiment is shown schematically. In this embodiment,
self-expanding tines 310 are held in a collapsed configuration by
retention wire 312 disposed in the lumen of the lead body 72 as
shown in FIG. 32A. Each of the tines 310 includes a hole 314
through which the retention wire 312 passes to hold the tines 310
in a first collapsed delivery configuration as shown In FIG. 32A,
and proximal withdrawal of the retention wire 314 releases the
resilient tines 310 to a second expanded deployed configuration as
shown in FIG. 32B. The lead 70 may be tunneled to the desired
target site with the tines 310 in the collapsed configuration. Once
in position, the wire 312 may be pulled proximally to release the
tines 310 and secure the lead 70 to the underlying muscle fascia
and adjacent subcutaneous tissue to establish fixation thereof.
With reference to FIGS. 33A and 33B, another alternative deployable
fixation embodiment is shown schematically. In this embodiment,
self-expanding structures such as one or more resilient protrusions
320 and/or a resilient mesh 325 may be incorporated (either alone
or in combination) into the distal end of the lead 70. By way of
example, not limitation, resilient protrusions 320 may comprise
silicone or polyurethane loops and resilient mesh 325 may comprise
a polyester fabric connected to or formed integrally with the lead
body 72. Both the resilient protrusions 320 and the resilient mesh
325 may be delivered in a collapsed delivery configuration inside
tubular sheath 304 as shown in FIG. 33A, and deployed at the
desired target site by proximal retraction of the sheath 304 to
release the self-expanding structures 320/325 to an expanded
deployed configuration as shown in FIG. 33B. Both the resilient
protrusions 320 and the resilient mesh 325 engage the underlying
muscle fascia through tissue encapsulation and adjacent
subcutaneous tissues to provide fixation of the lead 70
thereto.
Other fixation embodiments may be used as well. For example, the
fixation element may engage the muscle fascia and adjacent
subcutaneous tissues or may be embedded therein. To this end, the
electrodes may alternatively comprise intramuscular electrodes such
as barbs or helical screws.
Description of Respiration Sensing Electrode Alternatives
A description of the various alternatives in number, spacing,
anatomical location and function of the impedance electrodes
follows. Generally, in each of the following embodiments, the
respiration sensing lead includes a lead body and a plurality of
respiration sensors comprising ring electrodes for sensing
bio-impedance. The lead body may include a plurality of insulated
conductors disposed therein, with one conductor provided for each
ring electrode requiring independent connection and/or control. The
impedance electrodes may comprise current emitting electrodes and
voltage sensing electrodes for detecting respiration by changes in
bio-impedance.
With reference to FIG. 34, the distal portion of a respiration
sensing lead 70 is shown by way of example, not limitation. The
respiration sensing lead 70 includes a lead body 72 with a proximal
connector and a plurality of distal impedance electrodes 74. In
this example, the lead body 72 and electrodes 74 are cylindrical
with a diameter of 0.050 inches. The distal current-carrying
electrode 74A may be 5 mm long and may be separated from the
voltage-sensing electrode 74B by 15 mm. The distal voltage sensing
electrode may be 5 mm long and may be separated from the proximal
combination current-carrying voltage-sensing electrode 74C by 100
mm. The proximal electrode 74C may be 10 mm long. The proximal
portion of the lead 70 is not shown, but would be connected to the
INS (not shown) as described previously. The lead body incorporates
a plurality of insulated electrical conductors (not shown), each of
which correspond to an electrode 74A-74C. The electrodes and
conductors may be made of an alloy of platinum-iridium. The lead
body 72 may comprise a tubular extrusion of polyurethane, silicone,
or a co-extrusion of polyurethane over silicone. The conductors may
be formed of multi-filar wire coiled to provide extensibility for
comfort and durability under high-cycle fatigue.
With reference to FIGS. 35A-35E, the position of the electrodes 74
may be characterized in terms of bio-impedance or bio-Z vectors.
The bio-Z vector may be defined by the locations of the
voltage-sensing electrodes (labeled V.sub.1 & V.sub.2). The
voltage-sensing electrodes may be located on either side of the
current-carrying electrodes (labeled I.sub.1 & 1.sub.2). For
example, it is possible to locate either one or both of the
voltage-sensing electrodes between the current-carrying electrodes
as shown in FIG. 35A (4-wire configuration
(I.sub.1-V.sub.1-V.sub.2-I.sub.2)), and it is possible to locate
either one or both of the current-carrying electrodes between the
voltage-sensing electrodes as shown in FIG. 35B (inverted 4-wire
configuration (V.sub.1-I.sub.1-I.sub.2-V.sub.2)). While at least
two separate electrodes (I.sub.1 & I.sub.2) are required to
carry current and at least two separate electrodes (V.sub.1 &
V.sub.2) are required to measure voltage, it is possible to combine
the current carrying and voltage sensing functions in a common
electrode. Examples of combining voltage sensing and current
carrying electrodes are shown in FIGS. 35C-35E. FIG. 35C (2-wire
configuration (I.sub.1V.sub.1--I.sub.2V.sub.2)) shows combination
electrode I.sub.1V.sub.1 and I.sub.2V.sub.2 where each of these
electrodes is used to carry current and sense voltage. FIGS. 35D
(3-wire configuration (I.sub.1-V.sub.1-I.sub.2V.sub.2)) and 35E
(inverted 3-wire configuration (V.sub.1-I.sub.1-I.sub.2V.sub.2))
show combination electrode I.sub.2V.sub.2 which is used to carry
current and sense voltage.
With reference to FIG. 36, insulative material such as strips 73
may cover one side of one or more electrodes 74A-74D to provide
directional current-carrying and/or voltage-sensing. The insulative
strips may comprise a polymeric coating (e.g., adhesive) and may be
arranged to face outward (toward the dermis) such that the exposed
conductive side of each electrode 74 faces inward (toward the
muscle fascia and thoracic cavity). Other examples of directional
electrodes would be substantially two-dimensional electrodes such
as discs or paddles which are conductive on only one side. Another
example of a directional electrode would be a substantially
cylindrical electrode which is held in a particular orientation by
sutures or sutured wings. Another example of a directional
electrode would be an electrode on the face or header of the
implanted pulse generator. It would likely be desirable for the
pulse generator to have a non-conductive surface surrounding the
location of the electrode.
In addition to the cylindrical electrodes shown, other electrode
configurations are possible as well. For example, the electrodes
may be bi-directional with one planar electrode surface separated
from another planar electrode surface by insulative material.
Alternatively or in combination, circular hoop electrodes may be
placed concentrically on a planar insulative surface. To mitigate
edge effects, each electrode may comprise a center primary
electrode with two secondary side electrodes separated by resistive
elements and arranged in series. An alternative is to have each
primary current-carrying electrode connected by a resistive element
to a single secondary side electrode. The conductive housing of the
INS 50 may serve as an current-carrying electrode or
voltage-sensing electrode. Alternatively or in addition, an
electrode may be mounted to the housing of the INS 50.
Because bio-impedance has both a real and imaginary component, it
is possible to measure the bio-Z phase as well as magnitude. It may
be preferable to extract both magnitude and phase information from
the bio-Z measurement because the movement of the
lung-diaphragm-liver interface causes a significant change in the
phase angle of the measured impedance. This may be valuable because
motion artifacts of other tissue have less impact on the bio-Z
phase angle than they do on the bio-Z magnitude. This means the
bio-Z phase angle is a relatively robust measure of diaphragm
movement even during motion artifacts.
An example of a bio-Z signal source is a modulated constant-current
pulse train. The modulation may be such that it does not interfere
with the stimulation signal. For example, if the stimulation signal
is 30 Hz, the bio-Z signal source signal may be modulated at 30 Hz
or a sub-multiple of 30 Hz such that bio-Z and stimulation do not
occur simultaneously. The pulses in the pulse train may have a
pulse width between 1 uS to 1 mS, such as 100 uS. The pulses may be
separated by a period of time roughly equal to the pulse width
(i.e., on-time of the pulses). The number of pulses in a train may
be determined by a trade-off between signal-to-noise and power
consumption. For example, no more than 10 pulses may be necessary
in any given pulse train. The magnitude of current delivered during
the pulse on-time may be between 10 uA and 500 uA, such as 50
uA.
Other wave forms of bio-Z source signal may be used, including,
without limitation, pulse, pulse train, bi-phasic pulse, bi-phasic
pulse train, sinusoidal, sinusoidal w/ramping, square wave, and
square w/ramping. The bio-Z source signal may be constant current
or non-constant current, such as a voltage source, for example. If
a non-constant current source is used, the delivered current may be
monitored to calculate the impedance value. The current-carrying
electrodes may have a single current source, a split-current source
(one current source split between two or more current-carrying
electrodes), or a current mirror source (one current source that
maintains set current levels to two or more current-carrying
electrodes). Different characteristics of the sensed signal may be
measured including, without limitation, magnitude, phase shift of
sensed voltage relative to the current source signal, and
multi-frequency magnitude and/or phase shift of the sensed signal.
Multi-frequency information may be obtained by applying multiple
signal sources at different frequencies or a single signal source
which contains two or more frequency components. One example of a
single multi-frequency source signal is a square wave current
pulse. The resultant voltage waveform would contain the same
frequency components as the square wave current pulse which would
allow extraction of Bio-Z data for more than a single
frequency.
With reference to FIG. 37, the bio-Z vector may be oriented with
regard to the anatomy in a number of different ways. For example,
using the electrode arrangement illustrated in FIG. 34 and the
anatomical illustration in FIG. 37, the bio-Z vector may be
arranged such that the proximal combination electrode is located
just to the right of and above the xiphoid below the pectoral
muscle between the 5.sup.th and 6.sup.th ribs and the distal
current-carrying electrode is located mid-lateral between the
7.sup.th and 8.sup.th ribs, with the distal voltage-sensing
electrode positioned between the 6.sup.th and 7.sup.th ribs 10 mm
proximal of the distal current-carrying electrode. This arrangement
places the electrodes along the interface between the right lung,
diaphragm and liver on the right side of the thoracic cavity. The
lung-diaphragm-liver interface moves relative to the bio-Z vector
with every respiratory cycle. Because the lung has relatively high
impedance when inflated and the liver has relatively low impedance
due to the conductivity of blood therein, this bio-Z vector
arrangement across the lung-diaphragm-liver interface provides for
a strong respiratory signal that is indicative of changes between
inspiration and expiration. In addition, because the heart is
situated more on the left side, positioning the bio-Z vector on the
right side reduces cardiac artifact. The net result is a bio-Z
vector that provides an excellent signal-to-noise ratio.
A variety of different bio-Z vector orientations relative to the
anatomy may be employed. Generally, bio-Z vectors for monitoring
respiration may be located on the thorax. However, bio-Z electrodes
located in the head and neck may also be used to define respiratory
bio-Z vectors. By way of example, not limitation, the bio-Z vector
may be arranged transthoracically (e.g., bilaterally across the
thorax), anteriorly on the thorax (e.g., bilaterally across the
thoracic mid-line), across the lung-diaphragm-liver interface,
perpendicular to intercostal muscles, between adjacent ribs, etc. A
single bio-Z vector may be used, or multiple independent vectors
may be used, potentially necessitating multiple sensing leads. One
or more bio-Z sub-vectors within a given bio-Z vector may be used
as well.
With reference to FIGS. 37A-37C, thoracic locations defining
examples of bio-Z vectors are shown schematically. FIG. 37A is a
frontal view of the thorax, FIG. 37B is a right-side view of the
thorax, and FIG. 37C is a left-side view of the thorax; In each of
FIGS. 37A-37C, the outline of the lungs and upper profile of the
diaphragm are shown. As mentioned previously, a bio-Z vector may be
defined by the locations of the voltage-sensing electrodes. Thus,
FIGS. 37A-37C show locations for voltage sensing electrodes which
would define the bio-Z vector.
There are several short bio-Z vectors which provide excellent
signals correlated to diaphragmatic movement. In general, these
vectors have at least one end at or near the lower edge of the
ribcage. The short diaphragmatic bio-Z vectors have been
successfully used in canines in vector lengths ranging from
approximately less than 1/2 inch to a few inches in length. FIG.
37A shows a variety of locations which are representative of the
locations which define such vectors. Locations shown just below the
ribcage on the person's right side are designated as A, B, C, and
D. Locations shown just below the ribcage on the person's left side
are E, F, G, and H. Locations shown just above the lower edge of
the ribcage on the person's right side are I, J, K, and L.
Locations shown just above the lower edge of the ribcage on the
person's left side are M, N, P, and Q. The locations just above the
lower edge of the ribcage would fall within a few inches of the
lower edge. Short diaphragmatic monitoring vectors would be
comprised of location pairs which are relatively closely spaced.
For example, vectors D-E, D-C, D-L, and D-K all provide good
diaphragmatic signal. The possible vectors fall into three groups.
Exemplary vectors which measure primarily diaphragmatic muscle
contraction are A-B, B-C, C-D, D-E, E-F, F-G, and G-H. Exemplary
vectors which measure a combination of diaphragmatic muscle
contraction combined with movement of the lung into the pleural
pocket as the diaphragm contracts are I-J, P-R, A-I, A-J, B-I, B-J,
G-P, H-R, H-P, and G-R. Exemplary vectors which measure
diaphragmatic muscle contraction combined with movement of the
diaphragm away from the thoracic wall as that portion of the lung
expands are J-K, K-L, M-N, and N-P. It is known that the signal
from any given location may be affected by body position and free
vs. obstructed respiration. The respiratory signal from short
vectors at or near the lower edge of the ribcage may be more robust
(e.g., may be not be substantially affected) to body position and
obstructed respiration. A further means of obtaining a signal which
may be also more robust to body position would be to measure the
respiratory impedance from complimentary vectors and sum the
resulting bio-Z measurements. Complimentary vectors would be
mirror-images or nearly mirror images of one another. Examples of
vectors and their mirror images may be C-D and E-F, B-C and G-F,
C-K and F-N.
By way of example, not limitation, the following bio-Z vectors may
be effective for monitoring respiration and/or for measuring
artifacts for subsequent removal of the artifact from the
respiration signal. Vector C-G is across the upper left and upper
right lobes of the lungs, and provides a good signal of ribcage
expansion with moderate cardiac artifact. Vector D-F is a
short-path version of C-G that provides a good respiratory
signature largely correlated with ribcage expansion, with less
cardiac artifact than C-G, but may be sensitive to movement of arms
due to location on pectoral muscles. Vector C-D is a short-path
ipsilateral vector of the upper right lung that may be sensitive to
arm movement but has less cardiac artifact. Vector B-H is a
transverse vector of the thoracic cavity that captures the bulk of
the lungs and diaphragm movement. Vector B-H, however, may be
relatively less susceptible to changes in body position, and may
still provide a generally good signal when the patient changes
positions. In certain circumstances, the signal produced by vector
B-H may have a less than desired signal to noise ratio. However, it
is contemplated that generally available methods of signal
processing in accordance with the present disclosure may be
utilized the improve signal to noise ratio of the signal produced
by Vector B-H. Vector A-E is an ipsilateral vector across the
lung-diaphragm-liver interface. Because the liver is higher in
conductivity and has a different impedance phase angle than the
lung, vector A-E1 yields a good signal on both bio-Z magnitude and
phase with limited cardiac artifact. Vector B-K is an ipsilateral
vector across the lung-diaphragm-liver interface that is
substantially between a common set of ribs with a current path that
is mostly perpendicular to the intercostal muscles. Because
resistivity of muscle is much higher perpendicular to the muscle
direction than parallel, vector B-K reduces current-shunting
through the muscle which otherwise detracts from the signal of the
lung-diaphragm-liver interface. Vector A-K is an ipsilateral vector
across the lung-diaphragm-liver interface similar to vector A-E1
but is more sensitive to movement of the lung-diaphragm-liver
interface than to changes in resistivity of the
lung-diaphragm-liver interface due to inspired air volume and is
thus a good indicator of diaphragm movement. Vector B-E1 is a
vector across the middle and lower right lung and is good for
detecting diaphragm movement with little cardiac artifact. Vector
C-E1 is a vector across the upper and middle right lung and is also
good for detecting diaphragm movement with little cardiac artifact.
Vector D-E1 is a vector across the upper right lung with little
cardiac artifact. Vector A-D is an ipsilateral across a substantial
portion of the right lung and diaphragm with little cardiac
artifact, but may be susceptible to motion artifact due to arm
movement. Vector E1-E2 is a vector across the heart and provides a
good cardiac signal that may be used for removing cardiac artifact
from a respiratory signal. Vector E2-J is a vector across the
lung-diaphragm-stomach interface that provides a good measure of
diaphragm movement using bio-Z phase vs. magnitude because the
stomach has almost no capacitive component and generally low
conductivity. Vector L-M is a trans-diaphragm vector that is
generally across the lung-diaphragm-liver interface with little
cardiac artifact. Vector L-M may be relatively less susceptible to
body position and movement and may yield a good signal even if the
patient is laying on the side of the sensing lead. In embodiments
where the signal produced by vector L-M has a less than desired
signal to noise ratio, it is contemplated that generally available
methods of signal processing may be utilized to improve the signal
to noise ratio of the signal produced by vector L-M.
Electrodes placed at any of the above-noted locations may include,
but are not limited to, combination electrodes, such as, for
example, electrodes capable of both providing a current charge and
sensing a voltage.
With reference to FIGS. 37A and 38D, an exemplary vector selection
method 3800 for detecting and utilizing a signal from the vector
that produces the most desirable signal of all vectors is dicussed.
The disclosed vector selection method 3800 may be performed
continuously, periodically, singularly, and/or may be repeated as
desired. For example, method 3800 may be performed once in a 24
hour period. In addition, one or more steps associated with method
3800 may be selectively omitted and/or the steps associated with
method 3800 may be performed in any order. The steps associated
with method 3800 are described in a particular sequence for
exemplary purposes only.
With specific reference to FIG. 38D, method 3800 may include a
plurality of steps 3801-3803 for detecting and utilizing the signal
with the best characteristics of all signals produced by a
plurality of vectors. Specifically, method 3800 may include
sampling short distance vectors first to determine if any of these
vectors are producing a desirable signal, step 3801. Method 3800
may also include sampling intermediate distance vectors if the
short distance vectors are not producing a desirable signal, step
3802. Method 3800 may further include sampling long distance
vectors if the intermediate distance vectors are not producing a
desirable signal, step 3803.
Turning to FIG. 37A, there is depicted an exemplary embodiment of a
neurostimulator in accordance with the principles of the present
disclosure. The exemplary neurostimulator may include an implanted
INS 50 and implanted electrode contacts AA-DD. While the depicted
embodiment includes electrode contacts AA-DD disposed between a
patient's 5.sup.th and lowest ribs, electrode contacts AA-DD may be
disposed at any suitable location. Furthermore, electrode contacts
AA-DD may include, but are not limited to, the combination
electrodes discussed above. In the depicted embodiment, exemplary
short distance vectors may include the vectors between, for
example, adjacent electrode contacts AA, BB, CC, and DD; exemplary
intermediate distance vectors may include the vectors AA-CC, AA-DD,
and BB-DD, and exemplary long distance vectors may include the
vectors between the INS 50 and each of electrode contacts
AA-DD.
With reference to FIG. 37A and FIG. 38A, step 3801 may include, for
example, sampling short distance vectors AA-BB, BB-CC, and CC-DD
first to determine whether any of these vectors may be producing a
sufficient signal in accordance with the principles of this
disclosure, since these vectors generally produce signals with
desirable signal to noise ratios. Next, step 3802 of method 3800
may include sampling the intermediate distance vectors AA-CC,
AA-DD, and BB-DD if the short distance vectors are producing a less
than desirable signal. Lastly, step 3803 of method 3800 may include
sampling the long distance vectors INS-AA, INS-BB, INS-CC, and
INS-DD if the intermediate distance vectors are producing a less
than desirable signal.
In some embodiments, it is contemplated that several short,
intermediate, and long distance vectors may be continually sampled,
even if a desirable signal is being received from a short distance
vector, in order to identify secondary vector signals that may be
utilized if the currently utilized vector signal fails for any
reason. However, fully processing the data from signals generated
by all of the vectors may require complex sensing circuitry and
processing of detection algorithms that may utilize undesirable
amounts of battery power. Therefore, it may be desirable to only
monitor selected characteristics of the secondary vector signals.
With specific reference to FIG. 38B, there is depicted an
embodiment of a method 3850 for utilizing multiple sensing channels
to optimize respiratory sensing with minimal additional hardware
and power consumption. It uses a single sensing circuit which is
time multiplexed (interleaved) to sample each of the vectors.
Since, as noted above, fully processing the data from all vector
signals may require higher computational power, method 3850 may be
used to identify the best vector signal for respiration detection,
while simultaneously monitoring the remaining vectors signals for
only relevant fiducial points. These fiducial points may include,
but are not limited to, significant "landmarks" within a signal,
such as, for example, peak amplitude and time, point of highest
slew rate, and zero crossing. The detected fiducial points for the
secondary vector signals may be then stored in a circular buffer
memory 3854 for analysis if the primary signal fails for any
reason, thereby, allowing immediate switching to an alternate
vector signal and eliminating the need for a long signal
acquisition period after a need to switch vector signals has been
determined.
In particular, method 3850 may include feeding the signals from all
available vectors into a plurality of channel selection switches
3851. The signals may be then analyzed for relevant fiducials by
the respiratory impedance sensing circuit 3853. Once relevant
fiducials have been discriminated, it may be possible to identify
the best vector signal for respiration signal analysis. The
fiducials of the remaining vectors may be then stored in circular
buffer memory 3854 (as noted above) to facilitate switching to a
secondary vector signal if the primary signal is no longer suitable
for respiration detection.
The periodic monitoring (or interleaving) of secondary vector
signals may facilitate faster switching to those vector signals
when necessary. In particular, it is contemplated that when a
decision to switch to a secondary vector signal is made (i.e., when
the primary signals degrades to a point where it is no loner
desirable for detecting respiration), the saved data (e.g.,
relevant fiducials) may be used to "seed" a signal analysis
algorithm with recently collected data, so as to promote faster
vector switching by eliminating the need to wait for collection of
sufficient data for the secondary vector signal. In other words,
because select information of a secondary signal is available
before the signal is actually used for respiration detection,
analysis of the secondary signal for, among other things,
respiration detection may begin slightly faster than it would have
if no data was available.
Furthermore, in certain embodiments, additional impedance sensors
may be used as backup sensors to the sensor generating the primary
vector signal. In these embodiments, data from the secondary
sensors may be also analyzed to identify and save relevant
fiducials in the memory. This stored information may be used to
provide supplemental or alternate information to facilitate
identifying appropriate respiratory timing, when switching vector
signals becomes necessary as a result of primary signal
degradation.
The respiratory bio-Z signal is partly due to the resistivity
change which occurs when air infuses lung tissue, partly due to the
relative movement of electrodes as the rib cage expands, and partly
due to the displacement of other body fluids, tissue and organs as
the lungs move along with the ribcage and diaphragm. As described
above, each vector measures certain of these changes to different
extents. It may be desirable, therefore, to combine vectors which
have complementary information or even redundant information to
improve the respiratory information of the bio-Z signal. To this
end, multiple vectors may be used. For example, one vector may be
used to sense changes in the lung-diaphragm-liver interface and a
second vector may be used to detect changes (e.g., expansion,
contraction) of the lung(s). Examples of the former include A-K,
B-K, A-E1, B-E1, and A-B. Examples of the later include D-F, B-D,
C-G, D-E1, and C-E1. Note that some vector combinations which share
a common vector endpoint such as A-E1, D-E1 and B-E1, B-D may use a
common electrode which would simplify the respiratory sensing lead
or leads.
An advantage of using the lung-diaphragm-liver interface vector is
that it provides a robust signal indicative of the movement of the
diaphragm throughout the respiratory cycle. The liver is almost two
times more electrically conductive than lung tissue so a relatively
large bio-Z signal can be obtained by monitoring the movement of
the lung-diaphragm-liver interface. Because the liver functions to
filter all the blood in the body, the liver is nearly completely
infused with blood. This helps to dampen out the cardiac artifact
associated with the pulsatile flow of the circulatory system.
Another advantage of this location is that vectors can be selected
which avoid significant current path through the heart or major
arteries which will help reduce cardiac artifact.
It is worth noting that diaphragm movement is not necessarily
synchronous with inspiration or expiration. Diaphragm movement
typically causes and therefore precedes inspiration and expiration.
Respiratory mechanics do allow for paradoxical motion of the
ribcage and diaphragm, so diaphragm movement is not necessarily
coincident with inspiration. During REM sleep, the diaphragm is the
dominant respiratory driver and paradoxical motion of the ribs and
diaphragm can be problematic, especially if movement of the ribcage
is being relied upon as an inspiratory indicator. Monitoring the
diaphragm for pre-inspiratory movement becomes especially valuable
under these circumstances. Bio-Z monitoring of the diaphragm can be
used as a more sophisticated indicator of impending inspiration
rather than the antiquated approach of desperately trying to
identify and respond to inspiration in pseudo-real time based on
sensors which are responding to characteristics of inspiration.
For purposes of monitoring respiration, it is desirable to minimize
shunting of the electrical current through tissues which are not of
interest. Shunting may result in at least two problems: reduced
signal from the lungs; and increased chance of artifacts from the
shunted current path. Skeletal muscle has non-isotropic
conductivity. The muscle's transverse resistivity (1600 ohm-cm) is
more than 5 times its longitudinal resistivity (300 ohm-cm). In
order to minimize the adverse effect of shunting current, it is
desirable to select bio-Z sensing vectors which are perpendicular
to muscle structure if possible. One such example is to locate two
or more electrodes of a bio-Z sensing array substantially aligned
with the ribs because the intercostal muscles are substantially
perpendicular to the ribs.
Description of Respiration Signal Processing
With reference to FIG. 39, the neurostimulation system described
herein may operate in a closed-loop process 400 wherein stimulation
of the targeted nerve may be delivered as a function of a sensed
feedback parameter (e.g., respiration). For example, stimulation of
the hypoglossal nerve may be triggered to occur during the
inspiratory phase of respiration. Alternatively, the
neurostimulation system described herein may operate in an
open-loop process wherein stimulation is delivered as a function of
preset conditions (e.g., historical average of sleeping respiratory
rate).
With continued reference to FIG. 39, the closed-loop process 400
may involve a number of generalized steps to condition the sensed
feedback parameter (e.g., bio-Z) into a useable trigger signal for
stimulation. For example, the closed-loop process 400 may include
the initial step of sensing respiration 350 using bio-Z, for
example, and optionally sensing other parameters 360 indicative of
respiration or other physiologic process. The sensed signal
indicative of respiration (or other parameter) may be signal
processed 370 to derive a usable signal and desired fiducials. A
trigger algorithm 380, which will be discussed in greater detail
below, may then be applied to the processed signal to control
delivery of the stimulation signal 390.
As noted above, the present disclosure contemplates conditioning
sensed bio-impedance into a useable trigger signal for stimulation.
However, one exemplary limitation to using sensed bio-impedance may
be the body's nominal impedance. In practice, a sensed
bio-impedance signal may be obtained by applying a suitable, known
current through one portion of a tissue of interest and measuring
the voltage potential across the same tissue. This measurement
technique is illustrated in FIG. 38C and may be referred to herein
as the "direct measurement" technique. The applied current and
measured voltage potentials may be used to calculate the impedance
of the tissue. It is this measured impedance that may constitute
the sensed bio-impedance signal. However, sense bio-impedance
signals of the present disclosure have been found to typically
include two components, a relatively large nominal body impedance
component and a relatively small respiratory impedance component.
Thus, since the body's impedance constitutes a large portion of the
sensed signal, it may be difficult to detect that relatively small
impedance changes associated with respiration on top of a body's
nominal impedance. Therefore, in accordance with the principles of
the present disclosure, it may be desirable to "filter" the sensed
impedance signal in a manner so as to remove most or all of the
body's nominal impedance, in order to improve resolution of the
respiratory signal. In some embodiments, this may be achieved with
the aid of a conventional Wheatstone bridge at or near the
front-end of an impedance measuring circuit. In particular, the
Wheatstone bridge may facilitate precise measurements of the
relatively small impedance changes associated with respiration by
removing most, if not all, of the body's nominal impedance.
Turning now to FIG. 39A, there is depicted an exemplary Wheatstone
bridge 3900. The Wheatstone bridge 3900 may include an electrical
current source 3901. Wheatstone bridge 3900 may also include a
first resistor R.sub.1 having an impedance Z.sub.1 connected in
series to a second resistor R.sub.2 having an impedance Z.sub.2.
Resistors R.sub.1 and R.sub.2 may be connected in parallel to
resistor R.sub.3 having an impedance Z.sub.3, which may be
connected serially to the patient's body having an impedance
Z.sub.body. As discussed below, impedances Z.sub.2 and Z.sub.3 may
be substantially similar to each other. Wheatstone bridge 3900 may
further include any suitable voltage measuring device, such as, for
example, those used in conjunction the direct measurement technique
described above.
In use, the impedance Z.sub.1 of exemplary bridge 3900 may be
closely matched to the expected impedance of a patient's body
Z.sub.body, the impedance Z.sub.2 matched to impedance Z.sub.3, and
the voltage potential across voltage measuring device 3902 may be
measured. It is contemplated that if impedances Z.sub.1-Z.sub.3 are
closely matched to Z.sub.body, the measured voltage potential
across voltage measuring device 3902 will be predominantly due to
respiratory impedance changes and the voltage signal due to the
body's nominal impedance will be largely removed. Further, it is
contemplated that the voltage changes measured at 3902 due to
respiratory impedance changes will have an amplitude that is
approximately 1/2 of the amplitude of the voltage changes, measured
with the above-noted direct-measurement technique, assuming the
same currently flow through the body. The removal of the voltage
signal due to the body's nominal impedance while retaining 1/2 of
the voltage signal amplitude due to changes in respiratory
impedance, may facilitate detecting the small impedance changes
associated with respiration by improving the resolution of those
changes.
In other embodiments, the body's nominal impedance may be removed
or reduced from a sensed signal by, for example, introducing a
nominal offset removal module 3921 into an impedance measuring
circuit 3920 of the present disclosure, as depicted in FIG. 39B. An
exemplary impedance-measuring circuit may generally include feeding
a sensed respiratory signal into a demodulator. The signal exiting
the demodulator may be then fed into an integrator, and the
integrated signal exiting the integrator may then be digitized for
analysis. It is therefore contemplated that introducing nominal
offset removal module 3921 to act upon the upon the signal exiting
the demodulator may achieve the desired effect of removing or
reducing the body's nominal impedance from a sensed impedance
signal.
Turning now to FIG. 39C, module 3921 may include a switch S, a
resistor R, a capacitor C, and a non-inverting amplifier A. The
switch S, resistor R, and capacitor C create a sample and hold
reference voltage to the difference amplifier A. The amplifier
subtracts this reference voltage from the input signal. The result
is to remove or reduce the nominal body impedance component of the
signal leaving mainly the respiratory component of the measured
impedance. The Resistor-Capacitor (R-C) combination is selected
such that it will track with changes in nominal impedance levels
but does not significantly distort the respiratory signal.
Respiratory signal frequency components of interest are typically
between 0.05 Hz and 3 Hz. There are several options for how the
Nominal Offset Removal may be operated. An implanted bio -impedance
circuit would typically use a modulated excitation signal for
measuring impedance. In that case, the switch, S may be open when
there is no signal present and may be closed whenever a signal is
present. For example, if a Demodulator Signal is present for 1 ms
every 100 ms, switch S would be closed during all or a part of the
time that Signal In is present. Switch S may also be operated such
that it does not close on every instance when Demodulator Signal is
present. The switch S, may be closed on every 10.sup.th or
100.sup.th instance when Demodulator Signal is present. A third
possibility is to close switch S only when Signal Out causes the
Integrator to reach an unacceptable threshold. The integrator
reaching an unacceptable threshold may be indicative that the
reference voltage provided by the R-C combination is no longer
providing a sufficiently good estimate of the nominal signal
component and so needs to be updated with new information.
Turning now to FIG. 39D, there is depicted an alternative
embodiment of nominal offset removal module. A further improvement
on the Nominal Offset Removal module is shown in FIG. 39D. If it is
desired to measure two or more different impedance signals it will
be necessary to have a different nominal offset reference voltage
provided to amplifier A for each signal. It is also desirable to
keep the component count as low as possible. In the diagram below,
S0 and S1 may be closed and S2 may be open to provide an offset
reference for a first signal with the appropriate combination of
R-C1. S0 and S2 may be closed and S1 may be open to provide an
offset reference for a second signal with the appropriate
combination of R-C2. This strategy allows rapid sequential
measurement of two or more impedance signals.
With reference to FIG. 40, the signal processing step 370 may
include general signal amplification and noise filtering 372. The
step of amplification and filtering 372 may include band pass
filtering to remove DC offset, for example. The respiratory
waveform may then be processed to remove specific noise artifacts
374 such as cardiac noise, motion noise, etc. A clean respiratory
waveform may then be extracted 376 along with other waveforms
indicative of specific events such as obstructive sleep apnea
(OSA), central sleep apnea (CSA), hypopnea, sleep stage, etc.
Specific fiducial points may then be extracted and identified
(e.g., type, time, and value).
The step of removing specific noise artifacts 374 may be performed
in a number of different ways. However, before signal processing
374, both cardiac and motion noise artifact may be mitigated. For
example, both cardiac and motion noise artifact may be mitigated
prior to signal processing 374 by selection of bio-Z vectors that
are less susceptible to noise (motion and/or cardiac) as described
previously. In addition, motion artifact may be mitigated before
signal processing 374 by minimizing movement of the sensing lead
and electrodes relative to the body using anchoring techniques
described elsewhere herein. Furthermore, motion artifact may be
mitigated prior to signal processing 374 by minimizing relative
movement between the current-carrying electrodes and the
voltage-sensing electrodes, such as by using combined
current-carrying and voltage-sensing electrodes.
After cardiac and motion artifact has been mitigated using the
pre-signal processing techniques described above, both cardiac and
motion artifact may be removed by signal processing 374.
For example, the signal processing step 374 may involve the use of
a low pass filter (e.g., less than 1 Hz) to remove cardiac
frequency noise components which typically occur at 0.5 to 2.0 Hz,
whereas resting respiration frequency typically occurs below 1.0
Hz.
Alternatively, the signal processing step 374 may involve the use
of a band pass or high pass filter (e.g., greater than 1 Hz) to
obtain a cardiac sync signal to enable removal of the cardiac noise
from the bio-Z signal in real time using an adaptive filter, for
example. Adaptive filters enable removal of noise from a signal in
real time, and an example of an adaptive filter is illustrated in
FIG. 41. To remove cardiac artifact from the bio-Z signal which
contains both cardiac noise n(k) and respiratory information s(k),
a signal n'(k) that represents cardiac noise is input to the
adaptive filter and the adaptive filter adjusts its coefficients to
reduce the value of the difference between y(k) and d(k), removing
the noise and resulting in a clean signal in e(k). Notice that in
this application, the error signal actually converges to the input
data signal, rather than converging to zero.
Another signal processing technique to remove cardiac noise is to
combine signals from two or more bio-Z vectors wherein respiration
is the predominate signal with some cardiac noise. This may also be
used to reduce motion artifact and other asynchronous noise. Each
of the two or more signals from different bio-Z vectors may be
weighted prior to combining them into a resultant signal Vw(i). If
it is assumed that (a) the respiratory bio-impedance is the largest
component in each measured vector, (b) the non-respiratory signal
components in one vector are substantially independent of the
non-respiratory components in the other vector, and (c) the ratio
of the non-respiratory component to the respiratory components in
one vector is substantially equal to the same ratio in the other
vector, then a simple weighting scheme may be used wherein each
signal is divided by it's historic peak-to-peak magnitude and the
results are added. For example, if M.sub.A=historical average
peak-to-peak magnitude of signal from vector A, M.sub.B=historical
average peak-to-peak magnitude of signal from vector B,
V.sub.A(i)=data point (i) from vector A, V.sub.B(i)=data point (i)
from vector B, then the resultant signal V.sub.W(i) (i.e., weighted
average of A & B for data point (i)) may be expressed as
V.sub.W(i)=V.sub.A(i)/M.sub.A+V.sub.B(i)/M.sub.B.
Yet another signal processing technique for removing cardiac noise
is to subtract a first signal that is predominantly respiration
from a second signal that is predominantly cardiac. For example,
the first signal may be from a predominantly respiratory bio-Z
vector (e.g., vector B-H) with some cardiac noise, and the second
signal may be from a predominantly cardiac bio-Z vector (e.g.,
vector E1-E2) with some respiration signal. Each of the two signals
from the different bio-Z vectors may be weighted prior to
subtracting them. The appropriate weighting may be determined, for
example, by calculating the power density spectra in the range of
2-4 Hz for a range of weighted differences across at least several
respiratory cycles A minimum will occur in the power density
spectra for the weighted averages which are sufficiently
optimal.
Motion artifact may be removed by signal processing 374 as well.
Motion artifact may be identified and rejected using signal
processing techniques such as monitoring voltage magnitude, testing
the correlation of magnitude and phase, and/or testing correlation
at two or more frequencies. Motion artifacts may cause a large
change in measured bio-impedance. A typical feature of motion
artifacts is that the voltage swings are much larger than
respiration. Another feature is that the voltage changes are highly
erratic. Using these characteristics, which will be described in
more detail below, motion artifact may be removed from the
respiration signal.
The step of extracting waveforms indicative of respiration and
other events 374 may be better explained with reference to FIGS.
42-46 which schematically illustrate various representative
unfiltered bio-Z signals. FIG. 42 schematically illustrates a bio-Z
signal 420 with representative signatures indicative normal
respiration (i.e., event free) during an awake period 422 and a
sleeping period 424. FIG. 43 schematically illustrates a bio-Z
signal 430 with representative signatures indicative of normal
respiration during sleeping periods 424 interrupted by a period of
motion 432 (i.e., motion artifact). FIG. 44 schematically
illustrates a bio-Z signal 440 with representative signatures
indicative of normal respiration during a sleeping period 424
followed by periods of hypopnea (HYP) 442 and recovery 444. FIG. 45
schematically illustrates a bio-Z signal 450 with representative
signatures indicative of normal respiration during a sleeping
period 424 followed by periods of obstructive sleep apnea (OSA) 452
and recovery 454 (which typically includes an initial gasp 456).
FIG. 46 schematically illustrates a bio-Z signal 460 with
representative signatures indicative of normal respiration during a
sleeping period 424 followed by periods of central sleep apnea
(CSA) 462 (which typically includes a cessation in breathing 468)
and recovery 464.
The step of extracting 374 waveform data indicative of an awake
period 422 vs. a sleep period 424 from a bio-Z signal 420 may be
explained in more detail with reference to FIG. 42. In addition,
the step of filtering 372 waveform data indicative of motion 432
from a bio-Z signal 430 may be explained in more detail with
reference to FIG. 43. One way to determine if a person is awake or
moving is to monitor the coefficient of variation (CV) of
sequential peak-to-peak (PP) magnitudes over a given period of
time. CV is calculated by taking the standard deviation (or a
similar measure of variation) of the difference between sequential
PP magnitudes and dividing it by the average (or a similar
statistic) of the PP magnitudes. N is the number of respiratory
cycles which occur in the selected period of time.
The CV may be calculated as follows:
.function. ##EQU00001## .times. ##EQU00001.2## .function..times.
##EQU00001.3## .times. ##EQU00001.4## ##EQU00001.5## .times.
##EQU00001.6##
Generally, if the CV is greater than 0.20 over a one minute period
then person is awake. Also generally, if the CV is less than 0.20
over a one-minute period then person is asleep. These events may be
flagged for the step of fiducial extraction 378 wherein data (e.g.,
event duration, CV, PP range, PPmin, PPmax, etc.) may be time
stamped and stored with an event identifier. If CV is greater than
1.00 over a 20 second period then body movement is affecting the
bio-Z signal. By way of example, not limitation, if body movement
is detected, then (a) stimulation may be delivered in an open loop
fashion (e.g., based on historical respiratory data); (b)
stimulation may be delivered constantly the same or lower level; or
(c) stimulation may be turned off during the period of movement.
The selected stimulation response to detected movement may be
preset by the physician programmer or by the patient control
device. Other stimulation responses may be employed as will be
described hereinafter.
In each of FIGS. 44-46, maximum and minimum peak-to-peak magnitudes
(PPmax and PPmin) may be compared to distinguish hypopnea (HYP),
obstructive sleep apnea (OSA), and central sleep apnea (CSA)
events. Generally, PP values may be compared within a window
defined by the event (HYP, OSA, CSA) and the recovery period
thereafter. Also generally, the window in which PP values are taken
excludes transitional events (e.g., gasp 456, 466). As a general
alternative, peak-to-peak phases may be used instead of
peak-to-peak magnitude. The hypopnea and apnea events may be
flagged for the step of fiducial extraction 378 wherein data (e.g.,
event duration, CV, PP range, PPmin, PPmax, etc.) may be time
stamped and stored with an event identifier.
A typical indication of hypopnea (HYP) and apnea (OSA, CSA) events
is a recurrent event followed by a recovery. The period (T) of each
event (where PP oscillates between PPmax and PPmin and back to
PPmax) may be about 15 to 120 seconds, depending on the individual.
The largest PP values observed during hypopneas and apneas are
usually between 2 and 5 times larger than those observed during
regular breathing 424 during sleep. The ratio of the PPmax to PPmin
during recurrent hypopnea and apnea events is about 2 or more.
During the event and recovery periods (excluding transitional
events), PP values of adjacent respiratory cycles do not typically
change abruptly and it is rare for the change in PP amplitude to be
more than 50% of PPmax. One exception to this observation is that
some people gasp 456, 466 (i.e., transitional event) as they
recover from a CSA or OSA event.
The ratio of successive PP magnitudes during normal (non-event)
sleep 424 is mostly random. The ratio of successive PP magnitudes
during apnea and hypopnea events will tend to be a non-random
sequence due to the oscillatory pattern of the PP values. Recurrent
apneas and hypopneas may be diagnosed by applying a statistical
test to the sequence of successive PP ratios.
The step of extracting 374 waveform data indicative of an hypopnea
event 442 from a bio-Z signal 440 may be explained in more detail
with reference to FIG. 44. The ratio of PPmax to PPmin during
recurrent hypopneas is typically between 2 and 5. This is in
contrast to CSA's which have very small PPmin due to the complete
cessation of breathing. This results in CSA's having PPmax to PPmin
ratios larger than 5. Accordingly, hypopnea events may be detected,
identified and flagged for the step of fiducial extraction 378
wherein data (e.g., event duration, CV, PP range, PPmin, PPmax,
etc.) may be time stamped and stored with an event identifier.
The step of extracting 374 waveform data indicative of an OSA event
452 from a bio-Z signal 450 may be explained in more detail with
reference to FIG. 45. The sharp change 456 in the bio-Z respiratory
magnitude due to OSA is typically in the range of 1 to 4 times the
magnitude of the peak-to-peak respiratory cycle magnitude. The
sharp change 456 typically takes less than 5 seconds to occur. OSA
tends to occur in a recurring sequence where the period (T) between
sequential events is between 15 and 120 seconds. A one-minute
period is commonly observed. According to these characteristics,
OSA events may be detected, identified and flagged for the step of
fiducial extraction 378 wherein data (e.g., event duration, CV, PP
range, PPmin, PPmax, etc.) may be time stamped and stored with an
event identifier.
The step of extracting 374 waveform data indicative of a CSA event
462 from a bio-Z signal 460 may be explained in more detail with
reference to FIG. 46. The behavior of the Bio-Z signal throughout
recurrent CSA events differ from other hypopnea and OSA in three
ways. First, during CSA there is complete cessation of respiratory
activity which results in a flat Bio-Z signal. This means the ratio
of PPmax to PPmin is typically greater than 5 during recurrent CSA
events. The duration of the estimated respiratory cycle may also be
used to distinguish between CSA from OSA and hypopnea. The lack of
respiratory activity during CSA results in an inflated estimate for
the respiratory cycle period. The PP typically does not vary by
more than 50% for successive cycles. The respiratory cycle duration
during a CSA event is more than twice as long as the duration of
the respiratory cycles preceding the CSA event. Second, during CSA
the Bio-Z magnitude will drift outside the PP magnitude range
observed during respiration. It has been observed that with the
onset of central sleep apnea (CSA) the magnitude and phase of the
Bio-Z signal settle to a steady-state value outside the
peak-to-peak range observed during the normal respiratory cycle
during sleep. Third, upon arousal from CSA a person will typically
gasp. This gasp results in a large PP. The PP of the first
respiratory cycle following the CSA event and the PP observed
during the CSA (which is essentially noise) will exceed 50% of
PPmax.
With continued reference to FIG. 46, the flat portions 468 of the
data traces are periods of respiratory cessation. Upon arousal the
subject gasps 466 and the raw bio-Z signal resumes cyclic
oscillation above the static impedance level observed during CSA.
According to these characteristics, CSA events may be detected,
identified and flagged for the step of fiducial extraction 378
wherein data (e.g., event duration, CV, PP range, PPmin, PPmax,
etc.) may be time stamped and stored with an event identifier.
The step of extracting 374 waveform data indicative of sleep stage
(e.g., rapid eye movement (REM) sleep vs. no-rapid eye movement
(NREM) sleep) may be performed by comparing the phase difference
between a first vector and a second vector wherein the first bio-Z
vector is along the lung-diaphragm-liver interface (e.g., vector
A-K or vector B-K) and the second bio-Z vector is about the
lung(s). Examples of the first bio-Z vector include A-K, B-K, A-E1,
B-E1, and A-B. Examples of the second bio-Z vector include D-F,
B-D, C-G, D-E1, and C-E1. Note that some vector combinations which
share a common vector endpoint such as A-E1, D-E1 and B-E1, B-D may
use a common electrode and to simplify the respiratory sensing lead
or leads. Typically, during NREM sleep, the two vectors are
substantially in phase. During REM sleep, the diaphragm is the
primary respiratory driver and a common consequence is paradoxical
motion of the ribcage and diaphragm (i.e., the two vectors are
substantially out of phase). This characteristic would allow for an
effective monitor of a person's ability to reach REM sleep.
Accordingly, REM and NREM sleep stages may be detected, identified,
and flagged for the step of fiducial extraction 378 wherein
characteristic data (e.g., event duration, phase, etc.) may be time
stamped and stored with an event identifier.
An alternative method of detecting an OSA event is to make use of a
split current electrode arrangement as shown in FIG. 47 which shows
the positions of three electrodes on the subject. Electrode A may
be above the zyphoid, electrode B may be just above the belly
button, and electrode C may be on the back a couple of inches below
electrode A. Electrodes A and B are connected to a common constant
current source through resistors R1 and R2. The voltage measured
across the current source is a measure of the bio-impedance during
normal respiration. The voltage across R1 is an indicator of the
paradoxical motion associated with apnea. An unbalanced current
split between R1 and R2 resulting in large bio-Z voltage swings is
indicative of OSA. During normal respiration or even very deep
breaths there is almost no effect on the apnea detection channel.
Accordingly, OSA events may be detected, identified, and flagged
for the step of fiducial extraction 378 wherein characteristic data
(e.g., event duration, voltage swing magnitude, etc.) may be time
stamped and stored with an event identifier.
Generally, the extracted 378 waveform and event data may be used
for therapy tracking, for stimulus titration, and/or for closed
loop therapy control. For example, data indicative of apneas and
hypopneas (or other events) may be stored by the INS 50 and/or
telemetered to the patient controlled 40. The data may be
subsequently transmitted or downloaded to the physician programmer
30. The data may be used to determine therapeutic efficacy (e.g.,
apnea hypopnea index, amount of REM sleep, etc.) and/or to titrate
stimulus parameters using the physician programmer 30. The data may
also be used to control stimulus in a closed loop fashion by, for
example, increasing stimulus intensity during periods of increased
apnea and hypopnea occurrence or decreasing stimulus intensity
during periods of decreased apnea and hypopnea occurrence (which
may be observed if a muscle conditioning effect is seen with
chronic use). Further, the data may be used to turn stimulus on
(e.g., when apnea or hypopnea events start occurring or when motion
artifact is absent) or to turn stimulus off (e.g., when no apnea or
hypopnea events are occurring over a present time period or when
motion artifact is predominant).
Description of Stimulus Trigger Algorithms
As mentioned previously with reference to FIG. 39, the
neurostimulation system described herein may operate in a
closed-loop process wherein the step of delivering stimulation 390
to the targeted nerve may be a function of a sensed feedback
parameter (e.g., respiration). For example, stimulation of the
hypoglossal nerve may be triggered to occur during the inspiratory
phase of respiration. In a health human subject, the hypoglossal
nerve is triggered about 300 mS before inspiration. Accordingly, a
predictive algorithm may be used to predict the inspiratory phase
and deliver stimulation accordingly. FIG. 48 schematically
illustrates a system 480 including devices, data and processes for
implementing a self-adjusting predictive trigger algorithm.
The system components 482 involved in implementing the algorithm
may include the physician programmer (or patient controller), INS
and associated device memory, and the respiratory sensor(s). The
sensors and device memory are the sources of real-time data and
historical fiducial data which the current algorithm uses to
generate a stimulation trigger signal. The data 484 utilized in
implementing the algorithm may include patient specific data
derived from a sleep study (i.e., PSG data), data from titrating
the system post implantation, and historic and real-time
respiratory data including respiratory and event fiducials. The
processes 486 utilized in implementing the algorithm may include
providing a default algorithm pre-programmed in the INS, patient
controller or physician programmer, modifying the default
algorithm, and deriving a current algorithm used to generate a
trigger signal 488.
More specifically, the processes 486 utilized in implementing a
predictive trigger algorithm may involve several sub-steps. First,
a default algorithm may be provided to predict onset of inspiration
from fiducial data. Selecting an appropriate default algorithm may
depend on identifying the simplest and most robust fiducial data
subsets which allow effective prediction of onset. It also may
depend on a reliable means of modifying the algorithm for optimal
performance. Second, modification of the default algorithm may
require a reference datum. The reference datum may be the estimated
onset for past respiratory cycles. It is therefore useful to
precisely estimate inspiratory onset for previous respiratory
cycles from historical fiducial data. This estimation of
inspiratory onset for previous respiratory cycles may be specific
to person, sensor location, sleep stage, sleep position, or a
variety of other factors. Third, the current algorithm may be
derived from real-time and historical data to yield a stimulation
trigger signal 488.
As alluded to above, a trigger algorithm, such as, for example,
trigger algorithm 4700 depicted in FIG. 47A, may be applied to a
detected respiratory signal to begin and/or control delivery of the
stimulation signal. As illustrated, trigger algorithm 4700 may
include a plurality of sub-routines 4701-4703 for performing
various analyses on a sensed respiratory signal. These sub-routines
may include, but are not limited to, performing peak detection
4701, error checking 4702, and prediction 4703, on a detected
respiratory signal.
With reference now to FIG. 47D, there is depicted an exemplary
sensed respiratory signal 4750. Respiratory signal 4750 may be
displayed as a substantially sinusoidal waveform having a component
that varies with time. As shown in FIG. 47D, respiratory signal
4750 may include a plurality of peaks, such as, for example, the
peak located at v.sub.4t.sub.4, and a plurality of valleys, such
as, for example, the valley located v.sub.4.sup.-t.sub.4.sup.-.
Therefore, as will be discussed in greater detail below, peak
detection sub-routine 4701 may be applied to sensed respiratory
signal 4750 to detect the peaks of signal 4750. Error checking
sub-routine 4702 may be applied to signal 4750 to, among other
things, ensure signal 4750 is an accurate representation of a
patient's respiration and free from undesirable artifacts caused
by, for example, a patient's movement or cardiac activity.
Prediction sub-routine 4703 may then be applied to signal 4750 to
predict when future peaks will occur in accordance with the sensed
signal 4750.
With reference to FIG. 47B, peak detection 4701 may include a
plurality of steps 4701a-g. Step 4701a may include first detecting
the peaks, such as, for example, the peak located at
v.sub.4t.sub.4, of signal 4750. The detected peaks may be an
indication of when onset of expiration occurs during the monitored
respiratory cycles. Next, step 4701b may include acquiring and/or
considering a new voltage V.sub.k, where V.sub.k may be the most
recently acquired data point time T.sub.k under consideration,
where a number of recently acquired data points may be under
consideration. Step 4701c may determine whether the data points
under consideration meet the criteria to indicate that a minimum
(min) peak has been detected. One example of such a criteria to
indicate a minimum peak has been detected is if the oldest data
point under consideration, V.sub.k+m is less than more recent data
points under consideration, (V.sub.k+m-1 . . . V.sub.k), which can
be expressed mathematically as V.sub.k+m.ltoreq.min (V.sub.k+m-1 .
. . V.sub.k). Another example of such a criteria to indicate a
minimum peak has been detected is if the most recent data point
under consideration, V.sub.k, is greater than all other
less-recently acquired data points under consideration, (V.sub.k+m
. . . V.sub.k+1), which can be expressed mathematically as
V.sub.k.gtoreq.max (V.sub.k+m-1 . . . V.sub.k+1). If the criteria
for detecting a minimum peak is not met, step 4701b may be repeated
to acquire and/or consider a new voltage V.sub.k. If the criteria
has been met, step 4701d may declare a minimum peak reference.
Next, step 4701e may again acquire and/or consider a new voltage
V.sub.k. Subsequently, step 4701f may determine whether the data
points under consideration meet the criteria to indicate a maximum
peak has been detected. One example of such a criteria to indicate
a maximum peak has been detected is if the oldest data point under
consideration, V.sub.k+m, is greater than more recent data points
under consideration (V.sub.k+m-1 . . . V.sub.k), which can be
expressed mathematically as V.sub.k+m.gtoreq.max (V.sub.k+m-1 . . .
V.sub.k). Another example of such a criteria to indicate a maximum
peak has been detected is if the most recent data point under
consideration, V.sub.k, is less than all other less-recently
acquired data points under consideration, (V.sub.k+m . . .
V.sub.k+)), which can be expressed mathematically as
V.sub.k.ltoreq.max (V.sub.k+m . . . V.sub.k+1). If the criteria for
detecting a maximum peak is not met, step 4701e may be repeated to
acquire and/or consider a new voltage V.sub.k. If the criteria has
been met, step 4701g may declare a maximum peak, and trigger
algorithm 4700 may proceed to error-checking sub-routine 4702. The
declared peak will depend on the criteria used for peak detection.
For example, if the criteria for detecting a peak was based on
comparing V.sub.k to less recently acquired data points, (V.sub.k+m
. . . V.sub.k+1), then the peak magnitude and time would be
declared to be V.sub.k+m/2, t.sub.k+m/2. As another example, if the
criteria for detecting a peak was based on comparing the oldest
considered data point, V.sub.k+m, to more recently acquired data
points (V.sub.k+m . . . V.sub.k), then the peak magnitude and time
would be declared to be V.sub.k+m, t.sub.k+m.
With reference now to FIG. 47C, error-checking sub-routine 4702 may
include a plurality of steps 4702a-e to determine whether a sensed
respiratory signal may be adequate for respiration detection. For
example, step 4702a, peak correction, may include receiving
information relating to the peaks detected in step 4701 and
corrections, as necessary. Next, steps 4702b-e may include
analyzing the sensed respiratory signal to determine whether the
signal includes "noise" caused by a patient's movement (4702b),
whether the signal is sub-threshold (e.g., has a relatively low
amplitude) (4702c), whether the signal is sufficiently stable
(4702d), and whether the inversion detection is possible with the
sensed signal (4702e). If the sensed signal passes all of
error-checking steps 4702b-e, trigger algorithm 4700 may proceed to
prediction sub-routine 4703. However, if the sensed signal fails
any of steps 4702b-e, the trigger algorithm may terminate and the
pulse generator (e.g., INS 50) may either cease stimulation,
continue stimulation with continuous pulses of predetermined
duration, and/or continue to stimulate at the same or a fraction
(e.g., one quarter) of the stimulation rate for the most recently
measured respiratory cycle, as discussed in greater detail
below.
As described above, a peak is declared for a given set of data
points under consideration when a peak detection criteria is met.
The declared peak itself may be used in further algorithm
calculations or a more precise estimate of peak time and voltage
may be calculated. The more precise estimates of peak time and
voltage are referred to as the peak correction. With regard to step
4702a, peak correction may be calculated as follows:
.DELTA.V.sub.pk,i=V.sub.pk,i-V.sub.pk,i-1 for -n.ltoreq.i.ltoreq.n
V.sub.pk,0 is defined to be the declared peak for which a
correction is being calculated. The difference in voltage between
successive data points is calculated for a given number of data
points, n, to either side of the declared peak.
.DELTA..times..times..times..times..times..times..times..times..DELTA..ti-
mes..times..times..times. ##EQU00002## The peak in signal ideally
occurs when the rate of change of the signal is zero. Taking
successive differences in measured voltage is an approximation to
the rate of change of the signal. Linear regression is used on a
range of successive differences to estimate the point in time when
the rate of change is zero. Due to the fact that the data points
are collected at equal increments of time, calculating the
statistics .DELTA.V.sub.pk,0th, .DELTA.V.sub.pk,1st and DEN allows
a simple calculation based on linear regression to estimate the
point in time at which the rate of change of the signal is
zero.
.DELTA..times..times..times..times..times..DELTA..times..times..times..ti-
mes..times..times..ltoreq..ltoreq. ##EQU00003##
.times..times..ltoreq..ltoreq. ##EQU00003.2##
.DELTA..times..times..times..times..times..times..function..DELTA..times.-
.times..times..times..times. ##EQU00003.3## Additionally, an
estimated peak time after correction may be determined as follows:
t'.sub.pk.0=t.sub.pk,0+Correction
With regards to step 4702e, a peak curvature estimate for inversion
detection can be obtained from one of the statistics,
.DELTA.V.sub.pk,1st, calculated for peak correction. Maximum peaks
are sharper than minimum peaks and so typically have higher values
of .DELTA.V.sub.pk,1st. One means of determining if a signal is
inverted would be to compare the values of .DELTA.V.sub.pk,1st for
a series of maximum peaks to a series of minimum peaks.
With renewed reference to FIG. 47A, prediction sub-routine 4703 may
include predicting the time between sequentially identified peaks
with either a parametric option or a non-parametric option. The
parametric option makes a prediction of the duration of the next
respiratory period based on the average duration of recent
respiratory cycles and the rate of change of the duration of recent
respiratory cycles. The parametric option also takes advantage of
the fact that data points are collected at equal increments of time
which simplifies the linear regression calculation. The parametric
option may be defined as follows:
.DELTA.t.sub.i=t.sub.i-t.sub.i-1
Zeroth order estimate of next peak.
.DELTA.t.sub.0,0th=1/h.SIGMA.(.DELTA.t.sub.i), for
1.ltoreq.i.ltoreq.n
where n is the number of past respiration cycles used
First Order Estimate
.DELTA..times..times..times..DELTA..times..times..times..times..ltoreq..l-
toreq. ##EQU00004## .times..times..times..times..ltoreq..ltoreq.
##EQU00004.2##
Predicted Interval Length for Current Respiration Cycle
.DELTA..times..times..DELTA..times..times..times..times..times..times.
##EQU00005##
Next Predicted Offset at
t.sub.0,pred=t.sub.1+.DELTA.t.sub.0,pred
Begin therapy delivery at:
t.sub.therapy=t.sub.1+(1-DC)*.DELTA.t.sub.0,pred, where DC may be
the allowable duty cycle for therapy delivery.
The non-parametric option is very similar to the parametric option
in that it also estimates the duration of the next respiratory
period based on the nominal duration of recent respiratory cycles
and the rate of change of the duration of recent respiratory
periods. The method is explained in more detail in "Nonparametric
Statistic Method" by Hollander and Wolfe in sections related to the
Theil statistic and the Hodges-Lehman, there disclose of which is
incorporated herein by reference. The non-parametric prediction
method may be defined as follows:
.DELTA.t.sub.i=t.sub.i-t.sub.i-1
Zeroth Order Estimate
.DELTA.t.sub.0,oth=1/2median{.DELTA.t.sub.i+.DELTA.t.sub.j,i+
.sub.0.ltoreq.j.ltoreq.1, . . . , n}
Where .sub.0 is optimally 0, 1, 2 or 3
First Order Estimate
.DELTA..times..times..DELTA..times..times..times..ltoreq.
<.ltoreq..times. ##EQU00006## .times..times.
.times..times..times..times..times..times..times. ##EQU00006.2##
.DELTA..times..times..times..times..ltoreq..ltoreq. <.ltoreq.
##EQU00006.3##
Predicted Interval Length for Current Respiration cycle
.DELTA..times..times..DELTA..times..times..times..DELTA..times.
##EQU00007##
Next Predicted Offset t.sub.0,pred=t.sub.1+.DELTA.t.sub.0,pred
Begin Therapy Delivery at
t.sub.therapy=t.sub.1+(1-DC)*.DELTA.t.sub.0,pred, where DC may be
the allowable duty cycle for therapy delivery.
Stimulation may then commence at the calculated t.sub.therapy.
With reference to FIG. 48, a self adjusting predictive algorithm
may be implemented in the following manner.
The Programmer block illustrates means by which PSG-derived data
may be uploaded into the device.
The Sensors and Device Memory block includes the sources of
real-time data and historical fiducial variables which the current
algorithm uses to generate a stimulation trigger signal.
The Patient PSG Titration Data block includes conventional
polysomnographic (PSG) data obtained in a sleep study. A
self-adjusting predictive algorithm utilizes a reference datum to
which the algorithm can be adjusted. Onset may be defined as onset
of inspiration as measured by airflow or pressure sensor used in a
sleep study, for example. Estimated Onset may be defined as an
estimate of Onset calculated solely from information available from
the device sensors and memory. To enable the predictive algorithm
to be self-adjusting, either Onset or Estimated Onset data is used.
During actual use, the implanted device will typically not have
access to Onset as that would require output from an airflow
sensor. The device then may rely on an estimate of Onset or
Estimated Onset. The calibration of Estimated Onset to Onset may be
based on PSG data collected during a sleep study. The calibration
may be unique to a person and/or sleep stage and/or sleep position
and/or respiratory pattern.
The Historical Fiducial Variables block represents the Historical
Fiducial Variables (or data) which have been extracted from the
bio-Z waveform and stored in the device memory. This block assumes
that the raw sensor data has been processed and is either clean or
has been flagged for cardiac, movement, apnea or other artifacts.
Note that fiducial data includes fiducials, mathematical
combinations of fiducials or a function of one or more fiducials
such as a fuzzy logic decision matrix.
The Real-Time Data and Historical Fiducial Variables block
incorporates all the information content of the Historical Fiducial
Variables block and also includes real-time bio-Z data.
The Default Algorithm block represents one or more preset trigger
algorithms pre-programmed into the INS or physician programmer. The
default algorithm used at a specific point in time while delivering
therapy may be selected from a library of pre-set algorithms. The
selection of the algorithm can be made automatically by the INS
based on: patient sleep position (position sensor), heart rate
(detectable through the impedance measuring system) or respiration
rate. Clinical evidence supports that the algorithm used to predict
the onset of inspiration may be dependant on sleep position, sleep
state or other detectable conditions of the patient.
The Modify Algorithm block represents the process of modifying the
Default Algorithm based on historical data to yield the Current
Algorithm. Once the calibration of Estimated Onset to Onset is
resident in the device memory it can be used to calculate Estimated
Onset for past respiratory cycles from Fiducial Variables. The
variable used to represent the Estimated Onset will be TEST or
TEST(i) where the "i" indicates the cycle number. Note that
Estimated Onset is calculated for past respiratory cycles. This
means that sensor fiducial variables which either proceed or follow
each Onset event may be used to calculate the Estimated Onset.
The Current Algorithm block represents the process of using the
Modified Default Algorithm to predict the next inspiratory onset
(Predicted Onset). The Predicted Onset for the next respiratory
cycle may be calculated from real-time data and historical fiducial
variables. The calculation may be based on the Modified Default
Algorithm. Modification of the Modified Default Algorithm to derive
the Current Algorithm may be dependent on the calibration of
Estimated Onset to Onset which was input from the physician
programmer and may be based on comparison of real-time bio-Z data
to data collected during a PSG titration study. The Current
Algorithm may use historic and/or real-time sensor fiducial
variables to predict the next onset of inspiration. This predicted
onset of inspiration may be referred to as Predicted Onset. The
variable used to represent Predicted Onset may be TPRED or TPRED(i)
where the "i" indicates the respiratory cycle.
The Stimulation Trigger Signal block represents the Current
Algorithm generating a trigger signal which the device uses to
trigger stimulation to the hypoglossal nerve.
FIG. 49 is a table of some (not all) examples of waveform fiducials
which can be extracted from each respiratory cycle waveform. For
each fiducial there is a magnitude value and a time of occurrence.
Each waveform has a set of fiducials associated with it. As a
result, fiducials may be stored in the device memory for any
reasonable number of past respiratory cycles. The values from past
respiratory cycles which are stored in device memory are referred
to as Historical Fiducial Variables.
The graphs illustrated in FIG. 50 are examples of fiducials marked
on bio-Z waveforms. The first of the three graphs illustrate the
bio-impedance signal after it has been filtered and cleared of
cardiac and motion artifacts. The first graph will be referred to
as the primary signal. The second graph is the first derivative of
the primary signal and the third graph is the second derivative of
the primary signal. Each graph also displays a square wave signal
which is derived from airflow pressure. The square wave is low
during inspiration. The falling edge of the square wave is onset of
inspiration.
Due to the fact that it may be difficult to identify onset of
inspiration in real-time from respiratory bio-impedance, a goal is
to construct an algorithm which can reliably predict onset of
inspiration "T" for the next respiratory cycle from information
available from the current and/or previous cycles. A reliable,
distinct and known reference point occurring prior to onset of
inspiration, "T", is "A", the peak of the primary signal in the
current cycle. As can be seen in FIG. 50, the upper peak of the
bio-Z waveform "A" approximately corresponds to the onset of
expiration "O." A dependent variable t.sub.T-PK is created to
represent the period of time between the positive peak of the
primary signal for the current cycle, t.Vmax(n), indicated by "An"
on the graph, and onset of inspiration for the next cycle,
t.onset(n+1), indicated by "T" on the graph. The variable
t.sub.T-PK may be defined as: t.sub.T-PK=t.onset(n+1)-t.Vmax(n)
Note that t.Vmax could be replaced by any other suitable fiducial
in defining a dependent variable for predicting onset.
A general model for a predictive algorithm may be of the following
form:
t.sub.T-PK=f(fiducials extracted from current and/or previous
cycles)
A less general model would be to use a function which is a linear
combination of Fiducial Variables and Real-Time Data.
The following fiducials may be both highly statistically
significant and practically significant in estimating T:
t.Vmax(n)=the time where positive peak occurs for the current
cycle;
t.dV.in(n)=the time of most positive 1.sup.st derivative during
inspiration for the current cycle; and
t.Vmax(n-1)=the time of positive peak for the previous cycle.
This model can be further simplified by combining the variables as
follows: .DELTA.t.pk(n)=t.Vmax(n)-t.Vmax(n-1)
.DELTA.t.in(n)=t.Vmax(n)-t.dV.in(n)
Either .DELTA.t.pk(n) or .DELTA.t.in(n) is a good predictor of
Onset.
The following example uses .DELTA.t.pk(n). The time from a positive
peak until the next inspiration onset can be estimated by:
T.sub.pred=t.Vmax(n)+k0+k1*.DELTA.t.pk(n)
The coefficients k0 and k1 would be constantly modified by
optimizing the following equation for recent historical respiratory
cycles against T.sub.est:
T.sub.est=t.Vmax(n)+k0+k1*.DELTA.t.pk(n)
Thus, the predictive trigger time T.sub.pred may be determined by
adding t.sub.T-PK to the time of the most recent peak (PK) of the
bio-Z signal, where: t.sub.T-PK=k0+k1*.DELTA.t.pk(n)
The predictive equation we are proposing is based on the fact that
the very most recent cycle times should be negatively weighted.
Regression analysis supports this approach and indicates a negative
weighting is appropriate for accurate prediction of onset. Thus,
predicting onset is more effective if the most recent historical
cycle time is incorporated into an algorithm with a negative
coefficient.
As noted above, stimulation may be delivered for only a portion of
the respiratory cycle, such as, for example, during inspiration.
Additionally, it may be desirable to begin stimulation
approximately 300 milliseconds before the onset of inspiration to
more closely mimic normal activation of upper airway dilator
muscles. However, predicting and/or measuring inspiration, in
particular, the onset of inspiration, may be relatively
challenging. Thus, since the onset of expiration may be relatively
easy to measure and/or predict (as discussed in greater detail
below) when an adequate measure of respiration is available, it is
contemplated that stimulation may be triggered as a function of
expiration onset.
Turning now to FIG. 50A, there is depicted an exemplary respiratory
waveform 5500 for two complete respiratory cycles A and B. In
analyzing exemplary waveform 5500, it may be determined that peaks
M of the waveform 5500 may indicate onset of the expiratory phases
of respiration cycles A and B. Furthermore, it may be discovered
that peaks M occur at regular intervals of approximately 3-4
seconds. Thus, it may be relatively easy to predict the occurrence
of subsequent peaks M, and consequently, the onset of expiration
for future respiratory cycles.
Therefore, in order to deliver a stimulus to a patient in
accordance with the principles of the present disclosure, the start
of stimulation may be calculated by first predicting the time
intervals between the start of expiration for subsequently
occurring respiratory cycles. Next, in order to capture the entire
inspiratory phase, including the brief pre-inspiratory phase of
approximately 300 milliseconds, stimulation may be started at the
time N that is prior to the next onset of expiration by
approximately 30% to 50% of the time between subsequently occurring
expiratory phases. Stimulating less than 30% or more than 50% prior
to the next expiratory phase may result in an inadequate
stimulation period and muscle fatigue, respectively.
In some embodiments, however, it is contemplated that an adequate
measure of respiration may not be available, such as, for example,
when a relied upon signal has failed. In these embodiments, it is
contemplated that the implanted neurostimulator system may be
configured to respond in one or more of the following three ways.
First, the implanted neurostimulator may completely cease
stimulation until an adequate signal is acquired. Second, the
neurostimulator may deliver continuous simulation pulses of
predetermined durations (e.g., up to 60 seconds) until an adequate
signal is acquired; or if an adequate signal is not acquired in
this time, the stimulation will be turned off. Third, the
neurostimulator may continue to stimulate at the same or a fraction
(e.g., one quarter) of the stimulation rate for the most recently
measured respiratory cycle. That is to say, the neurostimulator may
deliver stimulation pulses of relatively long durations at a
frequency that is less than the frequency of stimulation utilized
with an adequate measure of respiration. Alternatively, the
neurostimulator may deliver stimulation pulses of relatively short
durations at a frequency that is greater than the frequency used
with an adequate measure of respiration.
Description of an Exemplary Stimulation Pulse
Turning now to FIG. 50B, there is depicted an exemplary stimulation
pulse waveform 5000 that may be emitted from an INS in accordance
with the principles of the present disclosure. Typically, exemplary
stimulation pulse waveform 5000 may include a square wave pulse
train having one or more square wave pulses 5001 of approximately 1
to 3 volts in amplitude, a duration of approximately 100 ms, and a
frequency of approximately 30 Hz, assuming a 1000 ohm impedance at
the electrodes and a constant current or voltage.
In some embodiments, exemplary stimulation pulse waveform 5000 may
include a bi-phasic charge balanced waveform square pulses 5001 and
5002, as depicted in FIG. 50B. Square pulse 5002 may be included in
waveform 5000 to, among other things, promote efficient stimulation
and/or mitigate electrode corrosion. However, square pulse 5002 may
be excluded from waveform 5000 as desired. Furthermore, although
the depicted exemplary waveform 5000 includes square pulse 5002
that exactly balances the stimulation wave pulse 5001, in certain
circumstances, square pulse 5002 may not exactly balance the
stimulation wave pulse 5001, and may not be a square pulse.
In some embodiments, exemplary stimulation pulse waveform 5000 may
include the delivery of a low amplitude (e.g., below the
stimulation threshold), long duration, pre-stimulation pulse 5004.
The pre-stimulation pulse 5004 may include any suitable low
amplitude, long duration pulse, and may be provided approximately
0.5 ms before the delivery of a first stimulation pulse 5001.
Pre-stimulation pulse 5004 may facilitate selectively stimulating
certain fibers of a nerve, such as, for example, the hypoglossal
nerve or the superior laryngeal nerve. In particular, when
stimulating the hypoglossal nerve, the presence of a
pre-stimulation pulse, such as, for example, pulse 5004, before a
stimulation pulse (e.g., the bi-phasic stimulation pulse 5001
depicted in FIG. 50B) may serve to saturate the large diameter
fibers of the nerve so as to allow the stimulation pulse 5001 to
only affect (e.g., stimulate) the smaller diameter fibers of the
nerve. In circumstances where a nerve (e.g., the hypoglossal nerve)
may be stimulated for extended periods of time, a pre-stimulation
pulse 5004 may be selectively introduced to waveform 5000, so as to
permit selective switching between stimulating the large and small
diameter fibers of the nerve, in order to reduce muscle fatigue.
Similarly, in situations where OSA may be treated by stimulating
the superior laryngeal nerve to open the upper airway through a
reflex mechanism, the presence of pre-stimulation pulse 5004 may
serve to saturate the larger diameter efferent fibers so as to
allow the stimulation pulse 5001 to only affect the smaller
diameter afferent fibers of the nerve.
Description of External (Partially Implanted) System
With reference to FIGS. 51A and 51B, an example of an external
neurostimulator system inductively coupled to an internal/implanted
receiver is shown schematically. The system includes
internal/implanted components comprising a receiver coil 910, a
stimulator lead 60 (including lead body 62, proximal connector and
distal nerve electrode 64). Any of the stimulation lead designs and
external sensor designs described in more detail herein may be
employed in this generically illustrated system, with modifications
to position, orientation, arrangement, integration, etc. made as
dictated by the particular embodiment employed. The system also
includes external components comprising a transmit coil 912
(inductively linked to receiver coil 910 when in use), an external
neurostimulator or external pulse generator 920 (ENS or EPG), and
one or more external respiratory sensors 916/918.
As illustrated, the receiver coil 910 is implanted in a
subcutaneous pocket in the pectoral region and the stimulation lead
body 62 is tunneled subcutaneously along the platysma in the neck
region. The nerve electrode 64 is attached to the hypoglossal nerve
in the submandibular region.
The transmitter coil 912 may be held in close proximity to the
receiver coil 910 by any suitable means such as an adhesive patch,
a belt or strap, or an article of clothing (e.g., shirt, vest,
brazier, etc.) donned by the patient. For purposes of illustration,
the transmitter coil 912 is shown carried by a t-shirt 915, which
also serves to carry the ENS 920 and respiratory sensor(s) 916,
918. The ENS 920 may be positioned adjacent the waist or abdomen
away from the ribs to avoid discomfort while sleeping. The
respiratory sensor(s) 916, 918 may be positioned as a function of
the parameter being measured, and in this embodiment, the sensors
are positioned to measure abdominal and thoracic/chest expansion
which are indicative of respiratory effort, a surrogate measure for
respiration. The external components may be interconnected by
cables 914 carried by the shirt or by wireless means. The shirt may
incorporate recloseable pockets for the external components and the
components may be disconnected from the cables such that the
reusable components may be removed from the garment which may be
disposed or washed.
The transmitting coil antenna 912 and the receiving coil antenna
910 may comprise air core wire coils with matched wind diameters,
number of wire turns and wire gauge. The wire coils may be disposed
in a disc-shaped hermetic enclosure comprising a material that does
not attenuate the inductive link, such as a polymeric or ceramic
material. The transmitting coil 912 and the receiving coil 910 may
be arranged in a co-axial and parallel fashion for coupling
efficiency, but are shown side-by-side for sake of illustration
only.
Because power is supplied to the internal components via an
inductive link, the internal components may be chronically
implanted without the need for replacement of an implanted battery,
which would otherwise require re-operation. Examples of inductively
powered implantable stimulators are described in U.S. Pat. No.
6,609,031 to Law et al., U.S. Pat. No. 4,612,934 to Borkan, and
U.S. Pat. No. 3,893,463 to Williams, the entire disclosures of
which are incorporated herein by reference.
With reference to FIGS. 51C-51G, alternative embodiments of an
external neurostimulator system inductively coupled to an
internal/implanted receiver are schematically shown. These
embodiments are similar to the external embodiment described above,
with a few exceptions. In these embodiments, the receiver coil 910
is implanted in a positioned proximate the implanted stimulation
lead body 62 and nerve electrode 64. The receiver coil 910 may be
positioned in a subcutaneous pocket on the platysma muscle under
the mandible, with the lead body 62 tunneling a short distance to
the nerve electrode 64 attached to the hypoglossal nerve. Also in
these embodiments, the respiratory sensor(s) 916/918 may be
integrated into the ENS 920 and attached to a conventional
respiratory belt 922 to measure respiratory effort about the
abdomen and/or chest. An external cable 914 connects the ENS 920 to
the transmitter coil 912.
In the embodiment of FIG. 51D, the transmitter coil 912 is carried
by an adhesive patch 924 that may be placed on the skin adjacent
the receiver coil 910 under the mandible. In the embodiment of FIG.
51E, the transmitter coil 912 is carried by an under-chin strap 926
worn by the patient to maintain the position of the transmitter
coil 912 adjacent the receiver coil 910 under the mandible. In the
embodiment of FIG. 51F, the receiver coil 910 may be positioned in
a subcutaneous pocket on the platysma muscle in the neck, with the
lead body 122 tunneling a slightly greater distance. The
transmitter coil 912 may be carried by a neck strap 928 worn by the
patient to maintain the position of the transmitter coil 912
adjacent the receiver coil 910 in the neck.
With reference to FIGS. 51G-51K, additional alternative embodiments
of an external neurostimulator system inductively coupled to an
internal/implanted receiver are schematically shown. These
embodiments are similar to the external embodiment described above,
with a few exceptions. As above, the receiver coil 910 may be
positioned in a subcutaneous pocket on the platysma muscle under
the mandible, with the lead body 62 tunneling a short distance to
the nerve electrode 64 attached to the hypoglossal nerve. However,
in these embodiments, the ENS 920 (not shown) may be located remote
from the patient such as on the night stand or headboard adjacent
the bed. The ENS 920 may be connected via a cable 930 to a large
transmitter coil 912 that is inductively coupled to the receiver
coil 910. The respiratory sensor 916 may comprise a conventional
respiratory belt 922 sensor to measure respiratory effort about the
abdomen and/or chest, and sensor signals may be wirelessly
transmitted to the remote ENS 920. As compared to other embodiments
described above, the transmitter coil 912 is not carried by the
patient, but rather resides in a proximate carrier such as a bed
pillow, under a mattress, on a headboard, or in a neck pillow, for
example. Because the transmitter coil 912 is not as proximate the
receiver coil as in the embodiments described above, the
transmitter coil may be driven by a high powered oscillator capable
of generating large electromagnetic fields.
As shown in FIG. 51H, the transmitter coil 912 may be disposed in a
bed pillow 934. As shown in FIG. 51I, the transmitter coil 912 may
comprise a series of overlapping coils disposed in a bed pillow 934
that are simultaneously driven or selectively driven to maximize
energy transfer efficiency as a function of changes in body
position of the patient corresponding to changes in position of the
receiver coil 910. This overlapping transmitter coil arrangement
may also be applied to other embodiments such as those described
previously wherein the transmitter coil is carried by an article
donned by the patient. In FIG. 51J, two or more transmitter coils
912 are carried by orthogonal plates 936 arranged as shown to
create orthogonal electromagnetic fields, thereby increasing energy
transfer efficiency to compensate for movement of the patient
corresponding to changes in position of the receiver coil 910. FIG.
51J also illustrates a non-contact respiratory sensor 916
arrangement as utilized for detecting sudden infant death syndrome
(SIDS). As shown in FIG. 51K, two orthogonal transmitter coils 912
are located on each side of a neck pillow 938, which is
particularly beneficial for bilateral stimulation wherein a
receiver coil 910 may be located on either side of the neck.
With reference to FIGS. 51L (front view) and 51M (rear view),
external respiratory effort sensors 916/918 are schematically shown
incorporated into a stretchable garment 945 donned by the patient.
The sensors 916/918 generally include one or more inductive
transducers and an electronics module 942. The inductive
transducers may comprise one or more shaped (e.g., zig-zag or
sinusoidal) stranded wires to accommodate stretching and may be
carried by (e.g., sewn into) the garment 945 to extend around the
patient's abdomen and chest, for example. As the patient breathes,
the patient's chest and/or abdomen expands and contracts, thus
changing the cross-sectional area of the shape (i.e., hoop) formed
by the wire resulting in changes in inductance. The electronics
module may include an oscillator (LC) circuit with the inductive
transducer (L) comprising a part of the circuit. Changes in
frequency of the oscillator correspond to changes in inductance of
the shaped wires which correlate to respiratory effort. The
electronics module may be integrated with an ENS (not shown) or
connected to an ENS via a wired or wireless link for triggering
stimulus as described previously.
The garment 945 may include features to minimize movement artifact
and accommodate various body shapes. For example, the garment 945
may be form-fitting and may be sleeveless (e.g., vest) to reduce
sensor artifacts due to arm movement. Further, the garment 945 may
be tailored to fit over the patient's hips with a bottom elastic
band which helps pull the garment down and keep the sensors 916/918
in the proper location.
Description of a Specific External (Partially Implanted)
Embodiment
With reference to FIGS. 52A-52G a specific embodiment utilizing an
external neurostimulator system inductively coupled to an
internal/implanted receiver is schematically shown. With initial
reference to FIG. 52A, the illustrated hypoglossal nerve stimulator
includes several major components, namely: an implantable
electronics unit that derives power from an external power source;
a stimulation delivery lead that is anchored to the nerve or
adjacent to the nerve and provides electrical connection between
the electronics unit and the nerve, an external (non-implanted)
power transmitting device that is inductively coupled with the
implant to convey a powering signal and control signals; a power
source for the external device that is either small and integrated
into the body-worn coil and transmitter or is wired to the
transmitter and transmit induction coil and can be powered by
primary or secondary batteries or can be line powered; and a
respiratory sensor such as those described previously.
These components may be configured to provide immediate or delayed
activation of respiration controlled stimulation. Initiation of the
stimulation regimen may be by means of activation of an input
switch. Visual confirmation can be by an LED that shows adequate
signal coupling and that the system is operating and is or will be
applying stimulation. As a means of controlling gentleness of
stimulation onset and removal, either pulse width ramping of a
constant amplitude stimulation signal can be commanded or amplitude
of a constant pulse width stimulation signal or a combination
thereof can be performed.
The electrical stimulation signal is delivered by the stimulation
lead that is connected to the implanted nerve stimulator and
attached to or in proximity of a nerve. The implanted electronics
unit receives power through a magnetically coupled inductive link.
The operating carrier frequency may be high enough to ensure that
several cycles (at least 10) of the carrier comprise the output
pulse. The operating frequency may be in a band of frequencies
approved by governmental agencies for use with medical instruments
operating at high transmitted radio frequency (RF) power (at least
100 milliwatts). For example, the operating frequency may be 1.8
MHz, but 13.56 MHz is also a good candidate since it is in the ISM
(Industrial/Scientific/Medical) band. The non-implanted (external)
transmitter device integrates respiration interface, waveform
generation logic and transmit power driver to drive an induction
coil. The power driver generates an oscillating signal that drives
the transmitter induction coil and is designed to directly drive a
coil of coil reactance that is high enough or can be resonated in
combination with a capacitor. Power can come from a high internal
voltage that is used to directly drive the transmit induction coil
or power can come from a low voltage source applied to a tap point
on the induction coil.
With reference to FIGS. 52B-52E, the waveform generation logic may
be used to modulate the carrier in such a way that narrow gaps in
the carrier correspond to narrow stimulation pulses. When
stimulator pulses are not needed, interruptions to the carrier are
stopped but the carrier is maintained to ensure that power is
immediately available within the stimulator upon demand. Presence
or absence of electrical nerve stimulation is based on respiration
or surrogates thereof. The transmitted signal may comprise a
carrier of about 1.8 MHz. To control the implanted electronics unit
to generate individual nerve stimulation pulses, the carrier signal
is interrupted. The duration of the interruption is about equal to
the duration of the output stimulation pulse. The stimulation
pulses may be about 110 microseconds in duration and are repeated
at a rate of approximately 33 per second. In addition, multiple
pulses can be transmitted to logic within the implant to control
stimulation pulse amplitude, pulse width, polarity, frequency and
structure if needed. Further, onset and removal of stimulation can
be graded to manage patient discomfort from abruptness. Grading may
comprise pulse width control, signal amplitude control or a
combination thereof.
An indicator (not shown) may be used to show when the transmitter
is properly positioned over the implant. The indicator may be a
part of the transmitter or by way of communication with the
transmitter, or a part of related patient viewable equipment.
Determination of proper position may be accomplished by monitoring
the transmitter power output loading relative to the unloaded power
level. Alternatively, the implant receive signal level transmitted
back by a transmitter within the implant may be monitored to
determine proper positioning. Or, the implant receive signal level
that is communicated back to the transmitter by momentarily
changing the loading properties presented to the transmitter, such
a shorting out the receive coil may be monitored to determine
proper positioning. Such communication may be by means of
modulation such as pulse presence, pulse width, pulse-to-pulse
interval, multi-pulse coding.
The transmitter may be powered by an internal primary power source
that is used until it is exhausted, a rechargeable power source or
a power source wired to a base unit. In the case of the wired base
unit, power can be supplied by any combination of battery or line
power.
The respiration interface may transduce sensed respiratory activity
to an on-off control signal for the transmitter. Onset of
stimulation may be approximately correlated slightly in advance of
inspiration and lasts through the end of inspiration, or onset may
be based on anticipation of the next respiration cycle from the
prior respiration cycle or cycles. The respiration sensor may
comprise any one or combination of devices capable of detecting
inspiration. The following are examples: one or more chest straps;
an impedance sensor; an electromiographical measurement of the
muscles involved with respiration; a microphone that is worn or is
in proximity to the patients' face; a flow sensor; a pressure
sensor in combination with a mask to measure flow; and a
temperature sensor to detect the difference between cool inspired
air versus warmed expired air.
The circuit illustrated in FIG. 52F may be used for the implanted
electronics unit. There are five main subsystems within the design:
a receive coil, a power rectifier, a signal rectifier, an output
switch and an output regulator. The signal from the inductive link
is received by L1 which is resonated in combination with C1 and is
delivered to both the power and signal rectifiers. Good coupling
consistent with low transmitter coil drive occurs when the transmit
coil diameter is equal to the receive coil diameter. When coil
sizes are matched, coupling degrades quickly when the coil
separation is about one coil diameter. A large transmit coil
diameter will reduce the criticality of small coil spacing and
coil-to-coil coaxial alignment for maximum signal transfer at the
cost of requiring more input drive power.
The power rectifier may comprise a voltage doubler design to take
maximum advantage of lower signal levels when the transmit to
receive coil spacing is large. The voltage doubler operates with an
input AC voltage that swing negative (below ground potential)
causes D1 to conduct and forces C2 to the maximum negative peak
potential (minus a diode drop). As the input AC voltage swings away
from maximum negative, the node of C2, D1, D2 moves from a diode
drop below ground to a diode drop above ground, forward biasing
diode D2. Further upswing of the input AC voltage causes charge
accumulated on C2 to be transferred through D2 to C3 and to "pump
up" the voltage on C3 on successive AC voltage cycles. To limit the
voltage developed across C3 so that an over-voltage condition will
not cause damage, and Zener diode, D3 shunts C3. Voltage limiting
imposed by D3 also limits the output of the signal rectifier
section. The power rectifier has a long time constant, compared to
the signal rectifier section, of about 10 milliseconds.
The signal rectifier section may be similar in topology to the
power rectifier except that time constants are much shorter--on the
order of 10 microseconds--to respond with good fidelity to
drop-outs in the transmitted signal. There is an output load of
100K (R1) that imposes a controlled discharge time constant. Output
of the signal rectifier is used to switch Q1, in the output
switching section, on and off.
The output switching section compares the potential of C3 to that
across C5 by means of the Q1, Q2 combination. When there is a gap
in the transmitted signal, the voltage across C5 falls very rapidly
in comparison with C3. When the voltage difference between C5 and
C3 is about 1.4 volts, Q1 and Q2 turn on. Q1 and Q2 in combination
form a high gain amplifier stage that provides for rapid output
switching time. R3 is intended to limit the drive current supplied
to Q2, and R2 aids in discharging the base of Q2 to improve the
turn-off time.
In the output regulator section, the available power rectifier
voltage is usually limited by Zener diode D3. When the coil
separation becomes suboptimal or too large the power rectifier
output voltage will be come variable as will the switched voltage
available at the collector of Q2. For proper nerve stimulation, it
may be necessary to regulate the (either) high or variable
available voltage to an appropriate level. An acceptable level is
about 3 volts peak. A switched voltage is applied to Zener diode D6
through emitter follower Q3 and bias resistor R5. When the switched
voltage rises to a level where D6 conducts and develops about 0.6
volts across R4 and the base-emitter junction of Q4, Q4 conducts. o
Increased conduction of Q4 is used to remove bias from Q3 through
negative feedback. Since the level of conduction of Q4 is a very
sensitive function of base to emitter voltage, Q4 provides
substantial amplification of small variations in D6 current flow
and therefore bias voltage level. The overall result is to regulate
the bias voltage applied to Zener diode D6. Output is taken from
the junction of the emitter of Q3 and D6 since that point is well
regulated by the combination of Zener diode breakdown voltage
combined with the amplification provided by Q4. In addition to good
voltage regulation a the junction of the emitter of Q3 and D6, the
output is very tolerant of load current demand since the
conductivity of Q3 will be changed by shifts in the operating point
of Q4. Due to amplification by Q3 and Q4, the circuit can drive a
range of load resistances. Tolerable load resistances above 1000
ohms and less than 200 ohms. The regulator has the advantage of
delivering only the current needed to operate the load while
consuming only moderate bias current. Further, bias current is only
drawn during delivery of the stimulation pulse which drops to zero
when no stimulation is delivered. As a comparison, a simple series
resistance biased Zener diode requires enough excess current to
deliver a stimulation pulse and still maintain adequate Zener bias.
As a further comparison, conventional integrated circuit
regulators, such as three terminal regulators are not designed to
well regulate and respond quickly to short input pulses. Experiment
shows that three-terminal regulators exhibit significant output
overshoot and ramp-up time upon application of an input pulse. This
can be addressed by applying a constant bias to a regulator circuit
or even moving the regulator before the output switching stage but
this will be at the cost of constant current drain and subsequently
reduced range.
The implanted electronics unit may be used to manage the loss of
control and power signals. With this design, more than enough
stimulation power is stored in C3 to supply multiple delivered
stimulation pulses. This design is intended to ensure that the
voltage drop is minimal on any individual pulse. One of the
consequences is that when signal is lost, the circuit treats the
condition as a commanded delivery of stimulation and will apply a
single, extended duration, energy pulse until the full stored
capacity of C3 is empty. An alternative method may be to use an
indirect control modulation to command delivery of a nerve
stimulation pulse through logic and provide for a time-out that
limits pulse duration.
To stimulate tissue, a modified output stage may be used to
mitigate electrode corrosion and establish balanced charging. The
output stage is illustrated in FIG. 52G and includes a capacitive
coupling between the ground side of the stimulator and tissue
interface in addition to a shunt from the active electrode to
circuit ground for re-zeroing the output coupling capacitor when an
output pulse is not being actively delivered.
Description of Alternative Screening Methods
Screening generally refers to selecting patients that will be
responsive to the therapy, namely neurostimulation of the upper
airway dilator nerves and/or muscles such as the hypoglossal nerve
that innervates the genioglossus. Screening may be based on a
number of different factors including level of obstruction and
critical collapse pressure (Pcrit) of the upper airway, for
example. Because stimulation of the hypoglossal nerve affects the
genioglossus (base of tongue) as well as other muscles, OSA
patients with obstruction at the level of the tongue base and OSA
patients with obstruction at the level of the palate and tongue
base (collectively patients with tongue base involvement) may be
selected. Because stimulation of the hypoglossal nerve affects
upper airway collapsibility, OSA patients with airways that have a
low critical collapse pressure (e.g., Pcrit of less than about 5 cm
water) may be selected. Pcrit may be measured using pressure
transducers in the upper airway and measuring the pressure just
prior to an apnea event (airway collapse). Alternatively, a
surrogate for Pcrit such as CPAP pressure may be used. In this
alternative, the lowest CPAP pressure at which apnea events are
mitigated may correlate to Pcrit.
The critical collapse pressure (Pcrit) may be defined as the
pressure at which the upper airway collapses and limits flow to a
maximal level. Thus, Pcrit is a measure of airway collapsibility
and depends on the stability of the walls defining the upper airway
as well as the surrounding pressure. Pcrit may be more accurately
defined as the pressure inside the upper airway at the onset of
flow limitation when the upper airway collapses. Pcrit may be
expressed as: Pcrit=Pin-Pout
where
Pin=pressure inside the upper airway at the moment of airway
collapse; and
Pout=pressure outside the upper airway (e.g., atmospheric
pressure).
Other screening methods and tools may be employed as well. For
example, screening may be accomplished through acute testing of
tongue protruder muscle contraction using percutaneous fine wire
electrodes inserted into the genioglossus muscle, delivering
stimulus and measuring one or more of several variables including
the amount of change in critical opening pressure, the amount of
change in airway caliber, the displacement of the tongue base,
and/or the retraction force of the tongue (as measured with a
displacement and/or force gauge). For example, a device similar to
a CPAP machine can be used to seal against the face (mask) and
control inlet pressure down to where the tongue and upper airway
collapse and occlude during inspiration. This measurement can be
repeated while the patient is receiving stimulation of the
geneoglossus muscle (or other muscles involved with the patency of
the upper airway). Patients may be indicated for the stimulation
therapy if the difference in critical pressure (stimulated vs.
non-stimulated) is above a threshold level.
Similarly, a flexible optical scope may be used to observe the
upper airway, having been inserted through the mask and nasal
passage. The difference in upper airway caliber between stimulation
and non-stimulation may be used as an inclusion criterion for the
therapy. The measurement may be taken with the inlet air pressure
to the patient established at a pre-determined level below
atmospheric pressure to better assess the effectiveness of the
stimulation therapy.
Another screening technique involves assessing the protrusion force
of the tongue upon anterior displacement or movement of the tongue
with and without stimulation while the patient is supine and
(possibly) sedated or asleep. A minimum increase in protrusion
force while under stimulation may be a basis for patient
selection.
For example, with reference to FIG. 53, a non-invasive oral
appliance 530 may be worn by the patient during a sleep study that
can directly measure the protrusion force of the tongue as a basis
for patient selection. The oral appliance 530 may include a
displacement probe 532 for measuring tongue movement protrusion
force by deflection (D). The oral appliance 530 may also include a
force sensor 534 for measuring the force (F) applied by protrusion
of the tongue. The sensors in the displacement probe 532 and the
force sensor 534 may be connected to measurement apparatus by wires
536.
FIG. 54 illustrates another example of a non-invasive oral
appliance 540 that may be worn by the patient during a sleep study
to directly measure the protrusion force of the tongue as a basis
for patient selection. The oral appliance 540 includes a
displacement sensor 542 for measuring tongue movement and a force
sensor for measuring tongue protrusion force. The displacement
sensor and the force sensor may be connected to measurement
apparatus by wires 546.
Oral appliances 530 and 540 could be worn during a sleep study and
would measure the tongue protrusion force during (and just prior
to) an apnea event when the protruder muscle tone is presumed to be
inadequate to maintain upper airway patency. The protrusion force
measured as the apnea is resolved by the patient will increase as
the patient changes sleep state and the airway again becomes
patent. The force difference may be used as a basis for patient
selection.
Another screening technique involves the use of an oral appliance
with sub-lingual surface electrodes contacting the base of the
tongue or fine wire electrodes inserted into the genioglossus
muscle to stimulate the tongue protruder muscle(s) synchronous with
respiration during a sleep study. The oral appliance may be fitted
with a drug delivery system (e.g., drug eluting coating,
elastomeric pump, electronically controlled pump) for topical
anesthesia to relieve the discomfort of the electrodes.
For example, with reference to FIG. 55, an oral appliance 550
includes a pair of small needle intramuscular electrodes 552 that
extend into the genioglossus. The electrodes 552 are carried by
flexible wires 554 and may be coupled to an external pulse
generator (not shown) by wires 556. The electrodes 552 may be
supported by a drug (e.g., anesthetic) eluting polymeric member
558.
Alternatively, with reference to FIG. 56, an oral appliance 560
includes a cathode electrode 562 guarded by two anode electrodes
564 carried by a soft extension 565 that extends under the tongue.
The surface electrodes 562 and 564 contact the floor of the mouth
under the tongue to indirectly stimulate the genioglossus. The
electrodes 562 and 564 may be coupled to an external pulse
generator (not shown) by wires 566. The extension 565 may
incorporate holes 568 through which a drug (e.g., anesthetic) may
be eluted.
Oral appliances 550 and 560 may be used during a sleep study and
stimulation of the target tissue can be performed synchronous with
respiration and while inlet airflow pressure can be modulated. The
ability to prevent apneas/hypopneas can be directly determined.
Also the critical opening pressure with and without stimulation can
be determined. Alternatively or in addition, the intramuscular or
surface electrodes may be used to measure genioglossus EMG
activity, either with or without stimulation. On any of theses
bases, patient selection may be made.
Patient selection may also be applied to the respiratory sensors to
determine if the respiratory sensors will adequately detect
respiration for triggering stimulation. For example, in the
embodiment wherein bio-Z is used to detect respiration using an
implanted lead 70, skin surface or shallow needle electrodes may be
used prior to implantation to determine if the signal will be
adequate. This method may also be sued to determine the preferred
position of the electrodes (i.e., optimal bio-Z vector). This may
be done while the patient is sleeping (i.e., during a sleep study)
or while the patient is awake.
Description of Alternative Intra-operative Tools
Intra-operatively, it may be desirable to determine the correct
portion of the nerve to stimulate in order to activate the correct
muscle(s) and implant the nerve cuff electrode accordingly.
Determining the correct position may involve stimulating at
different locations along the length or circumference of the nerve
and observing the effect (e.g., tongue protrusion). In addition or
in the alternative, and particularly in the case of field steering
where multiple combinations of electrode contacts are possible, it
may be desirable to determine optimal electrode or filed shape
combinations.
An example of an intra-operative stimulating tool 570 is shown in
FIGS. 57A and 57B. In this embodiment, the tool 570 includes a
first shaft 571 with a distal half-cuff 573. Tool 570 further
includes a second shaft 575 with a proximal movable collar 574 and
a distal half-cuff 575. Stimulating tool 570 includes multiple
electrodes 572 on half-cuff 573 and/or half-cuff 575 that may be
arranged in an array or matrix as shown in FIG. 57C, which is a
view taken along line A-A in FIG. 57B. The half-cuffs 573 and 575
may be longitudinally separated for placement about a nerve and
subsequently closed such that the half-cuffs 573 and 575 gently
grasp the nerve. The electrodes 575 may be sequenced through a
series of electrode/field shape combinations to optimize (lower)
the critical opening pressure, airway caliber, tongue protrusion
force or other acute indicia of therapeutic efficacy.
The tool 570 may be part of an intra-operative system including:
(1) tool 570 or other tool with one or more stimulating electrodes
that are designed to be easily handled by the surgeon during
implant surgery; (2) an external pulse generator which triggers off
of a respiration signal; (3) a feedback diagnostic device that can
measure critical closing pressure intra-operatively; and (4) an
algorithm (e.g., firmware or software in the programmer) that is
design to automatically or manually sequence through a series of
electrode configurations that will identify the best placement of
electrode cuffs on the nerves and configuration of electrode
polarity and amplitude settings. Information from the
intra-operative system may greatly speed the process of identifying
where to place the electrode cuff(s) on the hypoglossal nerve and
what field steering may be optimal or necessary to provide
efficacy.
In certain circumstances, such as, when treating a child or a small
adult, it may be difficult to implant a nerve cuff electrode of the
present disclosure about a nerve in a patient's body. Accordingly,
it may be desirable to provide a tool capable of facilitating
temporary expansion of a nerve cuff electrode of the present
disclosure, so as to slip the nerve cuff electrode around a
patient's nerve. Turning now to FIGS. 58A-58B, there is depicted a
tool 5800 for temporarily expanding a nerve cuff electrode in
accordance with the principles of the present disclosure. Tool 5800
may include a substantially scissor-like configuration having a
first element 5801 and a second element 5802 pivotably secured
together by a suitable fastener, such as, for example, pivot pin
5803, acting as a fulcrum. Elements 5801 and 5802 may be
substantially similar to each other or may differ as necessary. In
the depicted embodiment, elements 5801 and 5802 may include levers
having distal effecting portions 5804, 5805 and proximal actuating
portions 5806, 5807.
Proximal actuating portions 5806, 5807 may be of any suitable
length and may be connected to respective handles (not shown),
which may be used to operate tool 5800. Alternatively, proximal
actuating portions 5806, 5807 themselves may be used to operate
tool 5800. Distal effecting portions 5804, 5805 may include any
suitable configuration to achieve the desired effect. For example,
each portion 5804, 5805 may include a substantially curved
configuration. Additionally, a distal end of each portion 5804,
5805 may be provided with a fastening mechanism, such as, for
example, hook-like projection 5804a, 5805a, for facilitating
connection of tool 5800 to a nerve cuff electrode. As shown in
FIGS. 58A-58B, hook-like projections 5804a, 5805a may be configured
to be disposed in differing parallel planes, such that projections
5804a, 5805a may be spaced (offset) horizontally from one another.
In use, distal effecting portions 5804, 5805 may be opened and
closed as proximal actuating portions 5806, 5807 may be rotated
about pivot pin 5803.
In embodiments where tool 5800 may be used to temporarily expand a
nerve cuff electrode for implantation purposes, the nerve cuff
electrode, e.g., nerve cuff electrode 5810, may be provided with
one more geometric configurations for facilitation connection with
tool 5800. In the depicted embodiment, nerve cuff electrode 5810
may be provided with extensions 5811, 5812 for facilitating
connection with tool 5800. Each extension 5811, 5812 may be
provided with openings 5811a, 5812a, respectively, for receiving
hook-like projections 5804a, 5805a, so as to operably couple nerve
cuff electrode 5811 with tool 5800.
Description of Miscellaneous Alternatives
The implanted neurostimulation system may be configured so that
stimulation of the nerve is set at a relatively low level (i.e.,
low voltage amplitude, narrow pulse width, lower frequency) so as
to maximize battery life of the INS and to minimize the chances
that the electrical stimulation will cause arousal from sleep. If
apneas/hypopneas are detected, then the electrical stimulation can
be increased progressively until the apneas/hypopneas are no longer
detected, up to a maximum pre-set stimulation level. This auto
titration may automatically be reset to the low level after the
patient is awakened and sits up (position detector) or manually
reset using the patient controller. The stimulation level may be
automatically reduced after a period of time has elapsed with no
(or few) apneas/hypopneas detected.
The stimulation level (i.e., voltage amplitude, pulse width,
frequency) may be adjusted based on changes in respiration rate.
Respiration rate or patterns of rate change may be indicative of
sleep state. A different power level based on sleep state may be
used for minimal power consumption, minimal unwanted stimulation
(sensory response), etc., while providing adequate efficacy.
The electrical field shape used to stimulate the target nerve can
be changed while the system is proving therapy based on feedback
indicating the presence (or lack) of apneas/hypopneas. The
electrical field shape for an implanted system can be changed by
adjusting the polarity, amplitude and other stimulation intensity
parameters for each of the electrodes within the nerve stimulating
cuff. An algorithm within the INS may change the currently
operating electrical field shape if the presence of
apneas/hypopneas is detected, and then wait a set period of time to
determine if the new configuration was successful in mitigating the
apneas/hypopneas before adjusting the field shape again.
Additionally, the system may be designed to keep a log of the most
successful stimulation patterns and when they were most likely to
be effective. This may allow the system to "learn" which settings
to be used during what part of the night, for example, or with
specific breathing patterns or cardiac signal patterns or
combinations thereof.
The proportion of stimulation intensity of two electrode cuffs used
to stimulate a nerve can be modulated while the system is providing
therapy based on feedback indicating the presence (or lack) of
apneas/hypopneas. For example, one nerve stimulating electrode cuff
may be place on the more proximal section of the hypoglossal nerve,
while a second is placed more distally. The proximal cuff will be
more likely to stimulate branches of the hypoglossal nerve going to
muscles in the upper airway involved with tongue or hyoid retrusion
while the more distal electrode cuff will more likely stimulate
only the muscles involved with tongue/hyoid protrusion. Research
suggests that to best maintain upper airway patency, stimulating
both protrudes and retruders (in the right proportion) may be more
effective that stimulating protruders alone. Software within the
INS may change the currently operating proportion of electrical
stimulation going to the distal electrode cuff in proportion to
that going to the proximal cuff based on the presence of
apneas/hypopneas detected. The system may then wait a set period of
time to determine if the new configuration was successful in
mitigating the apneas/hypopneas before adjusting the system again.
Additionally, the system software may be designed to keep a log of
the most successful stimulation proportion and when they were most
likely to be effective. This may allow the system to "learn" which
settings to be used during what part of the night, for example, or
with specific breathing patterns or cardiac signal patterns or
combinations thereof.
The system described above may modulate electrical stimulation
intensity proportion based on electromyogram (EMG) feedback from
the muscles in the upper airway being stimulated or others in the
area. This feedback may be used to determine the correct proportion
of stimulation between protruders and retruders. The correct ratio
of EMG activity between retruders and protruders may be determined
during a sleep study for an individual, may be determined to be a
constant for a class of patients or may be "learned" my the
implanted system by using the detection of apneas/hypopneas as
feedback.
A library of electrical stimulation parameter settings can be
programmed into the INS. These settings listed in the library may
be selected by the patient manually using the patient programmer
based on, for example: (1) direct patient perception of comfort
during stimulation; (2) a log of the most successful settings
compiled by the software in the INS (assumes apnea/hypopnea
detection capability); (3) a sleep physician's or technician's
assessment of the most effective stimulation as determined during a
sleep study; and/or (4) a list of the most effective parameters
produced for a particular class of patient or other.
The electrical stimulation parameters described above may be
adjusted based on patient position as detected by a position sensor
within the INS. The best setting for a given position may be
determined by, for example: (1) a log of the most successful
settings compiled or learned by the software in the INS (assumes
apnea/hypopnea detection capability); (2) a sleep physician's or
technician's assessment of the most effective stimulation as
determined during a sleep study; and/or (3) a list of the most
effective parameters produced for a particular class of patient or
other.
To avoid fatigue using a normal duty cycle or to extend the time
that the upper airway is opened through neurostimulation, different
parts of the genioglossus muscle and/or different muscles involved
with establishing patency of the upper airway can be alternately
stimulated. For example, using two or more nerve or muscle
electrode cuffs, the left and right side genioglossus muscles can
be alternately stimulated, cutting the effective duty cycle on each
muscle in half. In addition, different protruder muscles on the
ipsilateral side such as the geniohyoid and the genioglossus muscle
can be alternately stimulated to the same effect. This may also be
accomplished through one electrode cuff using field steering
methods that selectively stimulated the fascicles of the
hypoglossal nerve going to one group of protruders alternating with
stimulating the fascicles leading to a different protruder muscle
group. This method may also be used to alternately stimulate one
group of muscle fibers within the genioglossus muscle with the
compliment of muscle fibers in the same muscle group.
To increase the ability of the upper airway to open during a
(sensed) apnea/hypopnea through neurostimulation, different parts
of the genioglossus muscle and/or different muscles involved with
establishing patency of the upper airway can be simultaneously
stimulated. For example, using two or more nerve or muscle
electrode cuffs, the left and right side genioglossus muscles can
be simultaneously stimulated, greatly increasing the protrusion
forces. In addition, different protruder muscles on the ipsilateral
side such as the geneohyoid and the genioglossus muscle can be
simultaneously stimulated to the same effect. This may also be
accomplished through one electrode cuff using field steering
methods that selectively stimulated the fascicles of the
hypoglossal nerve going to one group of protruders simultaneously
with stimulating the fascicles leading to a different protruder
muscle group. This may be achieved with one electrode cuff using
field steering on a more proximal location on the hypoglossal nerve
or two or more electrode cuffs, one on each branch going to a
muscle involved with maintaining muscle patency.
A sensor inside the INS (or elsewhere in system implanted) may
detect body position and automatically shut off stimulation when
patient sits up or stands up. This will prevent unwanted
stimulation when patient is no longer sleeping. The device may
automatically restart the stimulation after the sensor indicates
the patient is again horizontal, with or without a delay. The
system may also be configured so that the stimulation can only be
restarted using the patient controller, with, or without a
delay.
The respiration signal using impedance and/or EMG/ENG are easily
capable of determining heart rate. The stimulation may be
interrupted or turned off when the heart rate falls outside out a
pre-determined acceptable range. This may be an effective safety
measure that will decrease the chance that hypoglossal nerve
stimulation will interfere with mitigating physiological processes
or interventional emergent medical procedures.
Respiration waveforms indicating apneas/hypopneas or of other
clinical interest may be recorded and automatically telemetered to
a bed-side receiver unit or patient programmer. Respiration
waveforms indicating frequent apneas/hypopneas, abnormal breathing
patterns, irregular heart rate/rhythm may be recorded and
automatically telemetered to a bed-side deceiver unit or patient
programmer causing an alarm to be issued (audible/visible). The INS
status such as low battery or system malfunction may also trigger
an alarm.
Electrical stimulation intensity could be ramped up for each
respiration cycle by increasing amplitude or pulse width from 0 to
a set point to prevent sudden tongue protrusion or sudden airway
opening causing the patient to wake up. During inspiration, the
system may deliver approximately 30 pulses per second for a length
of time of one to one and one half seconds, totaling between about
30 and 45 pulses per respiration cycle. Prior to delivery of these
30 to 45 pulses, amplitude of each individual therapy pulse (in an
added group of pulses) could be ramped up from 0 to a set point at
a rate of <10% of the amplitude intended for the active duty
cycle or 200 mS, whichever is less. The pulse width of each
individual therapy pulse could be ramped up from 0 to a set point
at a rate of <10% of the active duty cycle or 200 mS, whichever
is less. Each of these ramp methods would require a predictive
algorithm that would stimulate based on the previous inspiration
cycle.
Nerves innervating muscles that are involved with inspiration, such
as the hypoglossal nerve, have been shown to have greater
electrical activity during apnea or hypopnea. This signal cannot be
easily measured while simultaneously stimulating the same nerve.
One method of stimulating and sensing using the same lead is to
interleave a sensing period within the stimulation pulse bursts
during the duty cycle. In other words, the sensing period may occur
between pulses within the stimulation pulse train. This approach
may be used with electrodes/leads that directly stimulate and
alternately sense on a nerve involved with inspiration or on a
muscle involved with inspiration or a combination of the two. The
approach may allow sensing of apnea/hypopnea, as well as
therapeutic stimulation.
From the foregoing, it will be apparent to those skilled in the art
that the present invention provides, in exemplary non-limiting
embodiments, devices and methods for nerve stimulation for OSA
therapy. Further, those skilled in the art will recognize that the
present invention may be manifested in a variety of forms other
than the specific embodiments described and contemplated herein.
Accordingly, departures in form and detail may be made without
departing from the scope and spirit of the present invention as
described in the appended claims.
* * * * *