U.S. patent application number 12/787206 was filed with the patent office on 2011-05-12 for system for stimulating a hypoglossal nerve for controlling the position of a patient's tongue.
This patent application is currently assigned to IMTHERA MEDICAL, INC.. Invention is credited to Stanley R. CRAIG, Monir M. ELIAS, Marcelo G. LIMA, Paul M. MEADOWS, Faisal N. ZAIDI.
Application Number | 20110112601 12/787206 |
Document ID | / |
Family ID | 43974756 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110112601 |
Kind Code |
A1 |
MEADOWS; Paul M. ; et
al. |
May 12, 2011 |
SYSTEM FOR STIMULATING A HYPOGLOSSAL NERVE FOR CONTROLLING THE
POSITION OF A PATIENT'S TONGUE
Abstract
A system for controlling a position of a patient's tongue
includes attaching at least one electrode to the patient's
Hypoglossal nerve and applying an electric signal through the
electrode to at least one targeted motor efferent located within
the Hypoglossal nerve to stimulate at least one muscle of the
tongue. The system may also include the use of more than one
contact to target more than one motor efferent and stimulating more
than one muscle. The stimulation load to maintain the position of
the tongue may be shared by each muscle. The position of the
patient's tongue may be controlled in order to prevent obstructive
sleep apnea.
Inventors: |
MEADOWS; Paul M.; (Glendale,
CA) ; LIMA; Marcelo G.; (San Diego, CA) ;
CRAIG; Stanley R.; (Westport, MA) ; ZAIDI; Faisal
N.; (San Diego, CA) ; ELIAS; Monir M.; (San
Diego, CA) |
Assignee: |
IMTHERA MEDICAL, INC.
San Diego
CA
|
Family ID: |
43974756 |
Appl. No.: |
12/787206 |
Filed: |
May 25, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61259893 |
Nov 10, 2009 |
|
|
|
Current U.S.
Class: |
607/42 ;
607/48 |
Current CPC
Class: |
A61N 1/025 20130101;
A61N 1/0551 20130101; A61N 1/37223 20130101; A61N 1/36146 20130101;
A61N 1/3611 20130101; Y02A 90/26 20180101; G06F 19/00 20130101;
A61B 5/4818 20130101; A61N 1/3787 20130101; A61N 1/36128 20130101;
A61N 1/3605 20130101; A61N 1/37247 20130101; A61N 1/37264 20130101;
G16H 40/63 20180101; Y02A 90/10 20180101; A61N 1/0556 20130101;
A61N 1/3601 20130101 |
Class at
Publication: |
607/42 ;
607/48 |
International
Class: |
A61N 1/36 20060101
A61N001/36 |
Claims
1. A system used for controlling a position of a patient's tongue,
the system comprising: an electrode configured to apply one of at
least one electric signal to one of at least one targeted motor
efferent located within a Hypoglossal nerve to stimulate at least
one muscle of the tongue.
2. The system of claim 1, further comprising an implantable pulse
generator (IPG) coupled to the electrode.
3. The system of claim 2, further comprising a remote control and
charger coupled to the IPG.
4. The system of claim 3, wherein the remote control powers the
IPG.
5. The system of claim 3, where the remote control re-charges the
IPG.
6. The system of claim 3, further comprising a docking station
configured to charge the remote control and charger.
7. The system of claim 3, wherein the remote control and charger
are configured to couple with a computer to program the IPG.
8. The system of claim 2, wherein the electrode includes a
plurality of contacts.
9. The system of claim 8, wherein the IPG is programmable to assign
the contacts to one of a plurality of functional groups.
10. The system of claim 9, wherein the IPG is programmable to
sequence or interleave the functional groups.
11. The system of claim 9, wherein each functional group maintains
an open airway in the patient and a first functional group includes
at least one or more different muscles than a second functional
group.
12. The system of claim 2, wherein the IPG is covered by a hermetic
enclosure.
13. The system of claim 2, further comprising a sensor configured
to measures the temperature of the IPG.
14. The system of claim 1, wherein the electrode includes a
plurality of contacts.
15. The system of claim 14, wherein electrode includes six
contacts.
16. The system of claim 14, wherein the contacts are each driven by
their own independent current source.
17. The system of claim 1, further comprising a primary boot
loader.
18. The system of claim 17, further comprising a secondary boot
loader.
19. The system of claim 1, further comprising a Medical Implant
Communication Service (MICS) telemetry transceiver.
20. The system of claim 1, further comprising an inductive link
telemetry transceiver.
21. The system of claim 1, wherein the electrode includes a cuff
housing configured to wrap around a portion of the Hypoglossal
nerve.
22. The system of claim 1, wherein the electric signal is applied
to the Hypoglossal nerve via an open loop system.
23. The system of claim 1, wherein the electrode is driven by
multiple current sources.
24. The system of claim 1, further comprising event logging
memory.
25. The system of claim 1, further comprising a multiplexer
configured to measure impedance of at least one of an electrode
contact and patient tissue.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/259,893 filed Nov. 10, 2009 entitled
"System For Stimulating A Hypoglossal Nerve For Controlling The
Position Of A Patient's Tongue", which is hereby incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to a system for
stimulating a Hypoglossal nerve for controlling the position of a
patient's tongue. In one embodiment, the Hypoglossal nerve is
stimulated to prevent obstructive sleep apnea.
[0003] Sleep apnea is a sleep disorder characterized by pauses in
breathing during sleep. Those affected by sleep apnea stop
breathing during sleep numerous times during the night. There are
two types of sleep apnea, generally described in medical literature
as central and obstructive sleep apnea. Central sleep apnea is a
failure of the nervous system to produce proper signals for
excitation of the muscles involved with respiration. Obstructive
sleep apnea (OSA) is caused by episodes of physical obstruction of
the upper airway channel (UAW) during sleep. The physical
obstruction is often caused by changes in the position of the
tongue 110 during sleep that results in the closure of the soft
tissues at the rear of the throat or pharynx (See FIGS. 1, 2A and
2B).
[0004] OSA is characterized by the complete obstruction of the
airway causing breathing to cease completely (Apnea) or partially
(Hypopnea). The human airway (at the level of the thorax) is lined
by soft tissue, any collapse of its walls results in the closure of
the airway which leads to insufficient oxygen intake, thereby
interrupting one's sleep (episodes or micro-arousals).
[0005] During sleep, the tongue muscles relax. In this relaxed
state, the tongue may lack sufficient muscle tone to prevent the
tongue from changing its normal tonic shape and position. When the
base of the tongue and soft tissue of the upper airway collapse,
the upper airway channel is blocked, causing an apnea event (FIG.
2B). Blockage of the upper airway prevents air from flowing into
the lungs, creating a decrease in blood oxygen level, which in turn
increases blood pressure and heart dilation. This causes a
reflexive forced opening of the upper airway channel until normal
patency is regained, followed by normal respiration until the next
apneaic event. These reflexive forced openings briefly arouse the
patient from sleep.
[0006] OSA is a potentially life-threatening disease that often
goes undiagnosed in most patients affected by sleep apnea. The
severity of sleep apnea is determined by dividing the number of
episodes of apneas and hypopneas lasting ten seconds or more by the
number of hours of sleep. The resulting number is called the
Apnea-Hypopnea Index, or AHI. The higher the index the more serious
the condition. An index between 5 and 10 is low, between 10 and 15
is mild to moderate, over 15 is moderately severe, and anything
over 30 indicates severe sleep apnea.
[0007] Current treatment options range from drug intervention,
non-invasive approaches, to more invasive surgical procedures. In
many of these instances, patient acceptance and therapy compliance
is well below desired levels, rendering the current solutions
ineffective as a long-term solution.
[0008] Current treatment options for OSA have not been consistently
effective for all patients. A standard method for treating OSA is
Continuous Positive Airway Pressure (CPAP) treatment, which
requires the patient to wear a mask through which air is blown into
the nostrils and mouth to keep the airway open. Patient compliance
is poor due to discomfort and side effects such as sneezing, nasal
discharge, dryness, skin irritation, claustrophobia, and panic
attacks. A surgical procedure where rigid inserts are implanted in
the soft palate to provide structural support is a more invasive
treatment for mild to moderate cases of OSA. Alternate treatments
are even more invasive and drastic, including
uvulopalatopharyngoplasty and tracheostomy. However, surgical or
mechanical methods tend to be invasive or uncomfortable, are not
always effective, and many are not tolerated by the patient.
[0009] Nerve stimulation to control the position of the tongue is a
promising alternative to these forms of treatment. For example,
pharyngeal dilation via Hypoglossal nerve (XII) (FIG. 3)
stimulation has been shown to be an effective treatment method for
OSA. The nerves are stimulated using an implanted electrode to move
the tongue and open the airway during sleep. In particular, the
medial XII nerve branch (i.e., in. Genioglossus), has demonstrated
significant reductions in UAW airflow resistance (i.e., increased
pharyngeal caliber). While electrical stimulation of nerves has
been experimentally shown to remove or ameliorate certain
conditions (e.g., obstructions in the UAW), current implementation
methods typically require accurate detection of a condition (e.g.,
a muscular obstruction of the airway or chest wall expansion),
selective stimulation of a muscle or nerve, and a coupling of the
detection and stimulation. These systems rely on detection of
breathing and/or detection of apnea events as pre-conditions to
control and deliver electrical stimulation in order to cause only
useful tongue motions and to periodically rest the tongue muscles
and avoid fatigue. In one system, for example, a voltage controlled
waveform source is multiplexed to two cuff electrode contacts. A
bio-signal amplifier connected to the contacts controls stimulus
based on breathing patterns. In another system, a microstimulator
uses an implanted single-contact constant current stimulator
synchronized to breathing to maintain an open airway. A third
system uses an implantable pulse generator (IPG) with a single cuff
electrode attached to the distal portion of the Hypoglossal nerve,
with stimulation timed to breathing. This last system uses a lead
attached to the chest wall to sense breathing motions by looking at
"bio-impedance" of the chest wall. Still another system monitors
vagus nerve electroneurograms to detect an apnea event and
stimulate the Hypoglossal nerve in response.
[0010] What is needed is a system and method of electrical
stimulation of the Hypoglossal nerve for controlling tongue
position that is not tied to the detection of breathing and/or an
apnea event.
BRIEF SUMMARY OF THE INVENTION
[0011] A system for stimulating a Hypoglossal nerve for controlling
the position of a patient's tongue according to some embodiments of
the present invention includes an electrode configured to apply one
of at least one electric signal to one of at least one targeted
motor efferent located within a Hypoglossal nerve to stimulate at
least one muscle of the tongue.
[0012] In a further embodiment, the system further includes an
implantable pulse generator (IPG) coupled to the electrode. In a
further embodiment the system includes a remote control and charger
coupled to the IPG. In one embodiment the remote control powers the
IPG. In a further embodiment, the remote control re-charges the
IPG. In a further embodiment, the system includes a docking station
configured to charge the remote control and charger. In one
embodiment, the remote control and charger are configured to couple
with a computer to program the IPG. In a further embodiment, the
system includes a sensor configured to measure the temperature of
the IPG. In one embodiment, the electrode includes a plurality of
contacts. In one embodiment, the IPG is programmable to assign the
contacts to one of a plurality of functional groups. In one
embodiment, the IPG is programmable to sequence or interleave the
functional groups. In one embodiment, each functional group
maintains an open airway in the patient and a first functional
group includes at least one or more different muscles than a second
functional group. In one embodiment, the electrode includes six
contacts. In one embodiment, the contacts are each driven by their
own independent current source.
[0013] In a further embodiment, the system includes a Medical
Implant Communication Service (MICS) telemetry transceiver. In a
further embodiment, the system includes an inductive link telemetry
transceiver. In a further embodiment, the system includes a primary
boot loader. In a further embodiment, the system includes a
secondary boot loader. In one embodiment, the electrode includes a
cuff housing configured to wrap around a portion of the Hypoglossal
nerve. In one embodiment, the electric signal is applied to the
Hypoglossal nerve via an open loop system. In one embodiment, the
electrode is driven by multiple current sources. In a further
embodiment, the system includes event logging memory. In a further
embodiment, the system includes a multiplexer configured to measure
impedance of at least one of the electrode contacts and patient
tissue. In one embodiment, the IPG is covered by a hermetic
enclosure.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0014] The foregoing summary, as well as the following detailed
description of exemplary embodiments of a system for stimulating a
Hypoglossal nerve for controlling a position of a patient's tongue,
will be better understood when read in conjunction with the
appended drawings. It should be understood, however, that the
invention is not limited to the precise arrangements and
instrumentalities shown.
[0015] In the drawings:
[0016] FIG. 1 is an illustration of the human airway;
[0017] FIG. 2A is an illustration of an open human airway;
[0018] FIG. 2B is an illustration of a closed human airway during
an apnea event;
[0019] FIG. 3 is an illustration of the human tongue;
[0020] FIG. 4A is an illustration of a cross-section of a human
Hypoglossal nerve;
[0021] FIG. 4B is an illustration of a cross-section of a human
Lingual nerve;
[0022] FIG. 4C is an illustration of a cross-section of a rat
Hypoglossal nerve;
[0023] FIG. 5 is an exemplary set of fatigue curves of human
quadriceps muscle showing maximum voluntary contraction, 50 Hz
electrical stimulation and twitch responses;
[0024] FIG. 6 is an exemplary illustration of an electrode attached
to a patient's Hypoglossal nerve;
[0025] FIG. 7 is a perspective view of the electrode;
[0026] FIG. 8 is a perspective view of the electrode showing the
plurality of contacts;
[0027] FIG. 9 is a graphical representation of an exemplary
stimulation strategy;
[0028] FIG. 10A is a graphical representation of an exemplary duty
cycle stimulation strategy;
[0029] FIG. 10B is a graphical representation of an exemplary
interleaved stimulation strategy;
[0030] FIG. 10C is a graphical representation of an exemplary
synchronous stimulation strategy;
[0031] FIG. 10D is a graphical representation of an exemplary
asynchronous or random stimulation strategy;
[0032] FIG. 11 is an exemplary strength-duration curve;
[0033] FIG. 12 is a block diagram of the IPG;
[0034] FIG. 13 is a partially exploded perspective view of the IPG
with its header and inline connector attachment to the enclosure
and feedthroughs;
[0035] FIG. 14 is a perspective view of the battery support for the
IPG;
[0036] FIG. 15 is a partial perspective view of the IPG electronics
assembly being inserted into its titanium enclosure;
[0037] FIG. 16 is an exploded perspective view of the IPG and the
silicone header components, the connector components which attach
to the feedthroughs, the guides for the connectors, the inductive
charging coil, the antenna coil, the magnet and the inline
connector assembly with strain relief;
[0038] FIG. 17 is a schematic diagram of the IPG Power
Sections;
[0039] FIG. 18 is a schematic diagram of the IPG Microcontroller
Section and Log Memory;
[0040] FIG. 19 is a schematic diagram of the IPG Pulse Generation
and Analog Signal Sampling Circuits;
[0041] FIG. 20 is a schematic diagram of the IPG Medical Implant
Communications Service (MICS) Telemetry Section;
[0042] FIG. 21 is a schematic diagram of the IPG board to board
connections and Manufacturing Test Adapter;
[0043] FIG. 22 is a diagram of the Remote Control and Charger (RCC)
Front Panel Keyboard and LEDs;
[0044] FIG. 23 is a block diagram of the RCC;
[0045] FIG. 24 is a schematic diagram of the RCC Docking Station
and Universal Serial Bus (USB) Interface Sections;
[0046] FIG. 25 is a schematic diagram o the RCC Power Sections;
[0047] FIG. 26 is a schematic diagram of the RCC Microcontroller
Section;
[0048] FIG. 27 is a schematic diagram of the RCC MICS Telemetry
Section;
[0049] FIG. 28 is a schematic diagram of the RCC Keyboard and LED
Sections;
[0050] FIG. 29 is a block diagram of the Charger Coil (CC);
[0051] FIG. 30 is a depiction of the aura Clinical Manager (aCM)
Patient Manager Screen;
[0052] FIG. 31 is a depiction of the aCM Titration Screen;
[0053] FIG. 32 is a depiction of the aCM RCC Functions Screen;
[0054] FIG. 33 is a depiction of the aCM Manual Parameter Control
Screen;
[0055] FIG. 34 is a depiction of the aCM RCC USB Comm Screen;
[0056] FIG. 35 is a block diagram of the Implantation Use
Model;
[0057] FIG. 36 is a block diagram of the Titration Phase Use
Model;
[0058] FIG. 37 is a block diagram of the Patient Use Model;
[0059] FIG. 38 is a flow diagram for the On/Off Key of the RCC
[0060] FIG. 39 is a flow diagram for the Charge Key of the RCC;
[0061] FIG. 40 is a flow diagram for the Test Key of the RCC;
[0062] FIG. 41 is a flow diagram for the Pause Key of the RCC;
[0063] FIG. 42 is a flow diagram for the IPG Pause Process;
[0064] FIG. 43 is a flow diagram for the IPG Charge Process;
[0065] FIG. 44 is a flow diagram for the Sleep Process;
[0066] FIG. 45 is a flow diagram for the Frequency Tick
Process;
[0067] FIG. 46 is a flow diagram for the Next Group Delay Tick
Process;
[0068] FIG. 47 is a flow diagram for the Sleep Duration Tick
Process;
[0069] FIG. 48 is a flow diagram for the Group On Time Tick
Process;
[0070] FIG. 49 is a flow diagram for the Impedance Measurement
Process;
[0071] FIG. 50 is a flow diagram for the secondary Boot Loader
Process;
[0072] FIG. 51 is a flow diagram for the IPG Main Application
Process;
[0073] FIG. 52 is an exemplary representation of a stimulation
strategy with two active groups;
[0074] FIG. 53 is an exemplary representation of alternative
embodiments of the system elements;
[0075] FIG. 54 depicts an alternative embodiment of a Remote
Control;
[0076] FIG. 55 depicts keyfob telemetry relays;
[0077] FIG. 56 depicts an alternative embodiment of a Charger and
Charger Coil;
[0078] FIG. 57 depicts an alternative use model for the
Clinician;
[0079] FIG. 58 depicts an another alternative use model for the
Clinician;
[0080] FIG. 59 depicts a use model for the patient;
[0081] FIG. 60 depicts another use model for the patient;
[0082] FIG. 61 depicts a use model for the patient when charging
the IPG; and
[0083] FIG. 62 depicts another use model for the patient when
charging the IPG.
DETAILED DESCRIPTION OF THE INVENTION
[0084] Similar to the embodiments described in U.S. patent
application Ser. No. 12/572,758, which is hereby incorporated by
reference in its entirety, the system described herein operates in
an open-loop continuous fashion to stimulate the hypoglossal nerve
(HGN) of a patient suffering from OSA. Referring to FIG. 3, the
Hypoglossal Nerve (HGN) 322 is primarily a motor nerve and
activates the various extrinsic and intrinsic muscles of the
tongue. The tongue 110 has been described as a hydrostat, a muscle
that is constrained within a relatively fixed volume, without the
benefit of generating forces between two bony surfaces. Much like
the trunk of an elephant, the tongue is able to change its shape by
the contraction of its various muscle elements to protrude and
retrude the tongue, curl, flatten, move up or down within the
oral-pharyngeal cavity to assist with breathing, speech,
mastication and swallowing.
[0085] The tongue muscle is different from other muscles in the
body in that it has been demonstrated to have unique fatigue
resistant properties. The tongue can be artificially activated by
electrical stimulation for long periods of time without the typical
position or force degradation that is accompanied with skeletal
muscle when it is electrically stimulated. Like the heart,
gastro-intestinal, and a few other specialized muscles within the
human body, the tongue muscles have properties that make them
particularly attractive for nearly constant activation, and thus
the HGN 322 is amenable to the methods described here to maintain
muscle tone and hence position and shape during sleep that are
normally present during wakeful hours for the patient but are
absent during the deepest levels of sleep.
[0086] As is known in the art, excitation of a nerve fiber can
occur along a strength duration iso-threshold curve, a nerve fiber
will be excited as long as the amplitude is above the curve or the
phase duration is to the right of the curve. An exemplary strength
curve is shown in FIG. 11. At either end of the curve the shape of
the curve is asymptotic; at a limiting phase duration no amount of
stimulation current elicits a response, and at the other no phase
duration is long enough to elicit a response either. The invention
described herein may refer to the use of stimulus amplitude for
means of modulating the recruitment of nerve fibers, but it shall
be understood that many methods, including phase duration and
stimulus amplitude, can be utilized to the same ends of activating
nerve fibers with electrical stimulation.
[0087] Nerve fibers are preferentially activated, or recruited, in
the order of their proximity to the electrode contact and by their
fiber diameter. As a general rule, the closer a fiber is to the
cathodic contact, the more likely it will be activated (the general
form of a stimulating system is to place the cathodic contact in
close proximity to the target nerve axons; other forms of
stimulation exist and shall be obvious to those skilled in the
art). The larger the diameter of a fiber, the more likely it will
be activated. The distance and size distribution in a nerve bundle
does not change appreciably over time. Hence, the recruitment
properties--which fibers will be activated with a particular
amplitude pulse--do not change either. If the applied stimulus is
maintained at a sufficiently high enough frequency, the recruited
muscle fibers activated by the stimulated nerve fibers eventually
fatigue. Muscle force and/or position then changes towards the
relaxed, inactivated condition. The stimulation of skeletal muscle
for postural control or limb motion is often performed at
frequencies that would normally be expected to cause fatigue in
those muscles along with the loss of desired function if the
stimulation were maintained continuously. Stimulation may be
modulated by changing the stimulus amplitude, as described above,
or by changing the phase duration of the pulse. Great care and
tremendous effort are expended in avoidance of fatigue in skeletal
muscle applications for fear of loss of desired functional effect,
for example, for patients suffering from spinal cord injury or
other neurological dysfunction.
[0088] Peripheral nerves such as the HGN 322 are organized often by
grouping fibers that go to each of the branches at the distal end
of the nerve into fascicles, or tubules within the main nerve
bundle. Cross sections views of such peripheral nerves clearly show
this organization as separate regions of nerve fibers. Stimulation
electrodes placed closed to these bundles or fascicles
preferentially activate the fibers going to the down-stream muscle
groups. FIGS. 4A, 4B and 4C demonstrate the organization structure
of the Human Hypoglossal nerve 322 (FIG. 4A) and the Human Lingual
Nerve (FIG. 4B), as well as the Rat Hypoglossal Nerve (FIG. 4C).
The Hypoglossal nerves in both Human and Rat are afascicular,
lacking the clear organizational structure present in most
peripheral nerves, and which is present in the Human Lingual Nerve,
as described in U.S. patent application Ser. No. 12/572,758, hereby
incorporated by reference in its entirety. Nonetheless, it is
organized and electrodes placed around the circumference can be
used to target specific nerve fibers and hence muscle groups to
affect only desirable muscle functions, movements, and motions.
[0089] Fatigue may be minimized or prevented by using a stimulation
duty cycle--that is, stimulating for a certain amount of time
before significant fatigue sets in, then stopping to let the muscle
rest and regain its ability to contract. For obstructive sleep
apnea this is less than optimal because without an applied stimulus
during the off period of the electrical stimulation duty cycle the
tongue would not be driven to maintain a desired position, and
could fall back against the rear of the throat and allow an apnea
event to occur. This is one of the reasons that many OSA
stimulation systems rely on sensors to detect when to apply
stimulation and when to leave it off. The method of using duty
cycle to rhythmically apply stimulation has been proposed, also, to
do away with the need to sense breathing events, in the hopes that
by introducing rhythmic stimulation to the Hypoglossal nerve that
somehow the breathing events would synchronize automatically to the
stimulation timing. This has not been proven and studies, which
used microstimulators in sheep, demonstrated that manual timing of
stimulation to the events of breathing was required to achieve a
useful outcome in single point stimulation of the Hypoglossal
nerve.
[0090] Another method of minimizing or preventing muscle fatigue is
to use one or more independent current sources to activate multiple
portions of the desired muscle groups. In certain exemplary
embodiments, one or more independent current sources drive one or
more contacts (764a, 764b, 764c and 764d for example shown in FIGS.
7 and 8) that interface with the Hypoglossal nerve 322. These
contacts are optionally contained in a single cuff electrode 764 as
shown in FIGS. 7 and 8. Each contact can be activated separately or
in combination with other contacts as discussed further below.
[0091] In certain embodiments, each contact is assigned to one or
more functional or muscle groups. Functional groups may in turn be
used to select regions of fibers within the nerve bundle that
result in a desired tongue movement. The effort of moving the
tongue to the desired position is thus shifted from one functional
group to another functional group so that no single functional
group is required to work all of the time. Thus, the effort of
moving the tongue is shared among multiple stimulated nerve fibers
and their associated muscles, preventing or reducing fatigue
because none of the groups are activated long enough to cause
significant fatigue, and during their off, or non-stimulated, state
they are allowed to recover from the stimulation. In certain
exemplary embodiments, each group is active until just before
significant fatigue sets in. One or more additional groups are then
activated to take its place, allowing the former muscle group
fibers to rest. In one embodiment, the stimulation is spread over
more than one contact wherein the duty cycle of each contact is
overlapped (FIG. 9).
[0092] A more detailed depiction of this transfer of muscle work
load from one group to the next is depicted in FIG. 52. The course
of events that occurs from the time that the patient starts a sleep
session through the first group stimulation cycle and the beginning
of the next is shown. After the initiation of a sleep session, a
delay occurs allowing the patient to fall asleep. After the delay,
the first group begins to stimulate, using its threshold amplitude,
slowly ramping up for the duration of the ramp, until at the
conclusion of the ramp and the beginning of the plateau phase the
stimulation current amplitude has reached its target level. This
ramp may help to prevent the patient from being aroused from sleep
by the sudden start of stimulation at the target level. At the time
that the ramp up began, the delay to the next group start was
started as well, to allow the coordination from one group to
another. After the plateau duration is complete for the first
group, the stimulation begins to ramp back down to threshold for
the ramp down duration. At the conclusion of the ramp down
duration, the group is deactivated and the second group should
already have begun its stimulation cycle. At the conclusion of the
next group delay, the next group begins its stimulation cycle and
the group after that begins its delay. All the while that
stimulation is being ramped in the first and even perhaps in the
second groups, frequency is being ramped down from a starting
frequency to a target frequency after which the frequency remains
at the target level until the end of the sleep therapy. This allows
the smooth transition from one stimulation group to the next, and
by ramping frequency downwards to the target frequency provides
additional opportunity to prevent arousal and promote the comfort
of the stimulation sensation to the patient.
[0093] In one embodiment, the stimulation pulses may be generally
random or pseudo random so long as the overall contractions per
unit of time is limited (see FIG. 10D).
[0094] Another method of reducing or eliminating fatigue is to
lower the stimulation frequency. The faster a nerve is stimulated,
the faster it fatigues. Each pulse produces a contraction, with
each contraction requiring a certain amount of work. The more
contractions there are, the more the muscle works, and the more
likely the muscle will become fatigued. Reducing the stimulation
frequency to a rate just fast enough to achieve the desired
response minimizes the rate at which muscle contractions occur.
This minimizes the amount of work done by the muscle, delaying or
minimizing muscle fatigue. In one embodiment, the stimulation is
spread over more than one contact wherein each contact delivers a
generally equal fraction of stimulation frequency that is out of
phase with the other contacts (FIG. 10B). This method reduces the
stimulation rate for each of the independent groups but results in
a functional stimulation rate that is essentially the sum of the
rates that are active. As shown in FIGS. 10A and 10B, the same
effective force or position is maintained, but in FIG. 10A fatigue
is prevented by duty cycle method and in FIG. 10B it is prevented
by three groups running at one third the frequency of any one group
in FIG. 10A resulting in the same muscle force or position and the
same prevention of fatigue. Stimulation frequencies that have been
used for activating skeletal muscle have often required the use of
a frequency that results in tetanus, a smooth fusion of pulses fast
enough to maintain a near continuous level of force or position.
Tetanus is not required, per se, in the artificial activation of
the tongue--the patient is asleep, and the cosmetic appearance of
the tongue while it is activated is not nearly as important as the
maintenance of airway patency. Experimental evidence has shown that
stimulating at frequencies below 5 pulses per second have been
adequate to maintain airway patency in patients with severe
OSA.
[0095] Continuous or near continuous stimulation of a muscle is
discouraged in the art because of fatigue problems. However, in
view of the teaching herein, the tongue 110 is a fatigue resistant
muscle. Testing in both rats and humans has confirmed this finding.
In limited animal studies, it was demonstrated that rat tongue
muscle could be stimulated at very high frequencies for extended
periods without observable changes in tongue position. In one
study, rather than stimulating at 15 pulses per second (pps), a
frequency adequate to move the tongue sufficiently to clear the
rear of the throat, stimulation was applied at supra-threshold
levels at a frequency of 100 pps. The resulting tongue response was
maintained for more than one hour before any significant change in
tongue position could be detected. If the stimulation frequency
were dropped to 15 pps, it is likely that stimulation may be
applied more than five times longer before tongue position change
would be expected to occur. In human trials, embodiments disclosed
herein successfully stimulated patients with a fixed set of
electrode contacts for many hours before the anti-apnea effect was
seen to diminish. In one embodiment, using lower frequencies and
multiple contacts on a human tongue increases the duration that
stimulation could be applied before anti-apnea effects
diminish.
[0096] Thus, with the tongue and associated rear throat tissues
consistently driven in such a manner as to clear the airway there
is no need to detect apneas because they simply will not be allowed
to occur. Rather than timing stimulation to breathing, or
monitoring for an apnea event prior to initiating treatment, the
exemplary embodiments stimulate the Hypoglossal nerve in a
predetermined manner via an open loop system to activate targeted
muscles in the tongue to maintain airway patency. With airway
resistance decreased and/or the tongue prevented from falling back
against the rear of the throat, and/or pharyngeal compliance
reduced, there is no need to monitor for apneas, because they are
prevented from occurring, nor monitor for ventilation timing
because the stimulation is not timed or synchronized to breathing
at all, it is maintained continuously during the entire sleeping
period.
[0097] The activation of a protrusor that moves the tongue forward
and away from the oral-pharyngeal junction, or the activation of a
retrusor that acts to decrease the compliance of the pharyngeal
wall are both desirable in preventing the occlusion of the airway.
Co-activation of agonistic and antagonistic muscles has been shown
in the literature to increase stiffness and to maintain position of
a joint or body segment, likewise, co-activation of protrusors and
retrusors of the tongue should have the effect of maintaining
position and stiffness of the tongue and pharanygeal walls to a
desirable effect. The activation of intrinsic muscles that change
the shape of the tongue may also lead to desirable motions even
though the actions of these muscles may not be clearly defined in
terms of protrusor or retrusor. It shall be understood that the
activation of any tongue muscle that achieves beneficial motions or
actions of the tongue musculature is a potential target of the
selective targeted methods of electrical stimulation as described
by the methods of this patent and it shall not be the single object
of the described method to only activate protrusors per se.
[0098] Since the tongue is a fatigue-resistant muscle, it can be
stimulated, using the techniques described herein, for long
durations without loss of force or movement. By stimulating the
Hypoglossal nerve, tongue activation resembling normal daytime
tongue muscle tone is restored to key muscles during sleep. The
tongue does not fall into the throat, keeping the airway open and
allowing the patient to breathe normally during sleep. Continuous
or near-continuous stimulation maintains the tongue in a desired
position, shaping the airway, without the necessity of a
complicated closed loop stimulation strategy with the associated
dependence upon sensors and their interpretation. While the tongue
musculature is fatigue resistant, it is still susceptible to
fatigue in general. Therefore methods employed herein are still
directed at maintaining therapeutic effect by utilization of
multiple groups to maintain desired function and other methods such
as frequency control to minimize the work load of any single muscle
group.
[0099] Neurostimulation is often performed on peripheral motor
nerves. Peripheral motor nerves emanate from the ventral horns of
the spinal cord and travel in bundles to various muscle groups. A
single motor nerve bundle may contain many sub-groups of neurons.
Some neuron sub-groups are organized into separate sub-bundles
called fascicles, which are easily viewed in histological cross
section, and often connect to groups of muscle fibers within the
same muscle. With these sub-groups, stimulation of the sub-group
typically results in activation of a group of muscles working
together to achieve a desired effect.
[0100] Other peripheral nerves, such as the Hypoglossal nerve, have
sub-bundles that are not organized into fascicles. Instead, these
sub-bundles run in somewhat controlled but less well defined
regions of the nerve, and are not easily recognizable in a
cross-sectional view. These sub-groups often go to multiple muscle
groups in different locations. An example of such a nerve is the
Hypoglossal nerve, which has multiple sub-groups connecting to
different portions of the tongue. A more detailed description of
the nerve structure for the human tongue is disclosed in U.S.
Patent Application No. 61/136,102, filed Oct. 9, 2008, hereby
incorporated by reference in its entirety.
[0101] Not every muscle of the human tongue is involved in the
opening of the airway. Some stimulated muscles act to block the
airway. In the embodiments described, the only nerves targeted by
the targeted selective electrical stimulation method described
herein are nerves that stimulate muscles that activate the tongue
resulting in the optimal opening of the airway and suppression of
unwanted tongue movements. In contrast, whole nerve stimulation
activates the entire nerve contents and nerve bundles containing
nerve fibers to both desirable and non-desirable groups of
contracting muscles are simultaneously activated. This not only
leads to suboptimal levels of opening, but may also produce
undesirable tongue motions. A surgical way to avoid this problem
with less than optimal stimulation methods is to place stimulating
electrodes on distal branches of the nerve that only innervate the
desired muscle groups, a task that is difficult and potentially
hazardous to the nerve.
[0102] In these cases, activation of the entire bundle from an
artificial electrical stimulus results in activation of all of the
muscles activated by the sub-groups within the stimulated nerve
group. In the present invention, to target only the desired
specific groups of fibers within a nerve bundle, exemplary
embodiments use multiple nerve electrode contacts and multiple
independent controlled current sources to activate only the desired
sub-groups. This minimizes or eliminates the likelihood of
delivering stimulation to muscles not providing the desired tongue
position.
[0103] The Hypoglossal nerve in the region just below the
sub-mandibular gland (proximal to the Styloglossus/Hyoglossus
branches and distal to the ansa cervicalis branch) is
non-fascicular, that is, the various nerve groups that separate
distally are not isolated in the bundle as fascicles, but are
present en masse with all of the fibers of the Hypoglossal nerve.
As described in the rat dye studies discussed in U.S. patent
application Ser. No. 12/572,758, and in studies on human cadavers,
there appears, however, to be an organization to the bundle, with
fibers mostly innervating the Genioglossus muscle residing in the
medial region of the bundle. Studies conducted in rats, an animal
model identified thus far that replicates the non-fascicular nature
of the human Hypoglossal nerve, revealed an organization of the
whole nerve, suggesting that targeted activation of a
sub-population of neurons in the Hypoglossal nerve would be
possible. Stimulation studies in rats and humans with multipolar
electrodes and multiple independent current sources verified this
with the result that multiple distinct motions and positions of the
tongue could be achieved using targeted stimulation methods and
devices. Placement of electrode contacts about the perimeter of the
Hypoglossal nerve at this region has achieved targeted selective
activation of the tongue muscles. The resulting airway changes
elicited by stimulation depend upon which electrode contacts are
activated.
[0104] In one exemplary system, an electrode 764 is implanted
around the Hypoglossal nerve at or near an approximately 1 cm
length of 2.5 to 4.5 mm diameter nerve bundles. This is typically
at the rear of and below the mandible, just underneath the
sub-mandibular gland, proximal to the Styloglossus/Hyoglossus
branches and distal to the ansa cervicalis branch. At this point,
the major branches to the various tongue muscles are distal to the
electrode site.
[0105] Targeted Selective Stimulation of Hypoglossal Nerve
Efferents
[0106] In one embodiment, the present invention is directed to the
targeted selective stimulation of Hypoglossal nerve efferents in
animals. In one embodiment, the present invention is directed to
the targeted selective stimulation of Hypoglossal nerve efferents
in mammals. In one embodiment, the present invention is directed to
the targeted selective stimulation of Hypoglossal nerve efferents
in rats. In one embodiment, the present invention is directed to
the targeted selective stimulation of Hypoglossal nerve efferents
in humans.
[0107] In one embodiment, the present invention is directed to the
targeted selective stimulation of Hypoglossal nerve efferents via
electric signals emitted from at least one programmable electrode
contact. In one embodiment, the targeted selective stimulation of
Hypoglossal nerve efferents occurs via multiple electrode contacts.
In one embodiment, the targeted selective stimulation of
Hypoglossal nerve efferents is driven by multiple current sources.
In one embodiment, the multiple electrode contacts are each driven
by their own independent current source.
[0108] In one embodiment, the multiple electrode contacts each
activate a beneficial muscle group and alternate in their operation
such that the beneficial function is maintained by at least one
group at all times. In one embodiment, the multiple electrode
contacts each activate a beneficial muscle group and interleave
their operation such that the patency of the airway is maintained.
In one embodiment, the multiple electrode contacts each activate a
beneficial muscle, and alternate in their operation such that the
patency of the airway is maintained. In one embodiment, the
multiple electrode contacts each activate one of a beneficial
muscle, and interleave their operation such that the patency of the
airway is maintained.
[0109] In one embodiment, the method includes activating the
ipsilateral Geniohyoid muscle. In one embodiment, the method
includes activating rostral or caudal or both compartments of the
ipsilateral Geniohyoid muscle. In one embodiment, the method
includes activating at least one compartment or both compartments
of ipsilateral or with the rostral compartment of the contralateral
Geniohyoid muscles increasing the dilation (of the pharyngeal
airway) and the patency of the airway channel.
[0110] In one embodiment, the modulating electric signals have a
frequency sufficient for a smooth tetanic contraction. In one
embodiment, the modulating electric signals have a stimulation
frequency of about 10 to about 40 pps. In one embodiment, the
modulating electric signals are of an intensity from about 10 to
about 3000 microamps (.mu.A). In one embodiment, the modulating
electric signals have a stimulation pulse width of about 10 to
about 1000 microseconds (.mu.s).
[0111] In one embodiment, the targeted selective stimulation of
Hypoglossal nerve efferents activates at least one lingual muscle.
In one embodiment, the targeted selective stimulation of
Hypoglossal nerve efferents activates at least one upper airway
channel dilator muscle. In one embodiment, at least one protrusor
muscle is activated. In one embodiment, at least one protrusor
muscle and at least one retrusor muscle are alternately activated.
In one embodiment, at least one protrusor muscle and at least one
retrusor muscle are co-activated. In one embodiment, the at least
one protrusor muscle 400 activated is the genioglossus muscle. In
one embodiment, at least one beneficial muscle group is activated.
In one embodiment, at least two beneficial muscle groups are
activated.
[0112] Method of Treating a Neurological Disorder Including
Obstructive Sleep Apnea
[0113] In one embodiment, the present invention is directed to a
method of treating, controlling, or preventing a neurological
disorder by attaching at least one programmable electrode to a
patient's Hypoglossal nerve proper 322; and selectively applying
electric signals to motor efferents located within the Hypoglossal
nerve proper 322 through the programmable electrode 764 to
selectively stimulate at least one muscle. In one embodiment, the
electric signals are modulating. In one embodiment, the method of
treating, controlling, or preventing a neurological disorder
consists essentially of the recruitment of retrusor motor
efferents. In one embodiment, the method comprises the recruitment
of protrusor motor efferents. In one embodiment, the method
comprises the recruitment of a ratio of retrusor to protrusor motor
efferents such as the ratios described above to treat a
neurological disorder.
[0114] In one embodiment, the neurological disorder suitable for
treatment, control, or prevention by the present invention is
selected from the group consisting of, but not limited to oral
myofunctional disorders, atrophies, weakness, tremors,
fasciculations, and myositis. In one embodiment, the neurological
disorder is obstructive sleep apnea. Other potential applications
of this method, in addition to treatment of obstructive sleep
apnea, include, for example, supplemental nerve stimulation to keep
the airway open for treatment of snoring, hypopnea, or countering
motor activation of the tongue during a seizure. Other health
problems related to the patency of a patient's airway may also be
treated using methods provided by the present invention.
[0115] In one embodiment, the present invention provides a method
of treating, controlling, or preventing obstructive sleep apnea
including the steps of attaching at least one programmable
electrode to a patient's Hypoglossal nerve proper 322; and
selectively applying electric signals to motor efferents located
within the patient's Hypoglossal nerve proper 322 through the
programmable electrode 764 to selectively stimulate at least one
muscle. In one embodiment, at least one programmable electrode 764
provides a continuous, low level electrical stimulation to specific
motor efferents to maintain the stiffness of the upper airway
channel throughout the respiratory cycle. In one embodiment, at
least one programmable electrode provides intermittent electrical
stimulation to specific motor efferents at controlled,
predetermined intervals sufficiently close to achieve a constantly
opened airway.
[0116] In one embodiment, the method of treating, controlling, or
preventing obstructive sleep apnea includes selectively activating
one or more muscles in the upper airway channel to effectively
reduce the severity of obstructive sleep apnea and improve airway
patency. In one embodiment, the method includes targeted selective
stimulation of motor efferents that activate the geniohyoid muscle,
causing anterosuperior movement of the hyoid bone to increase the
patency of the upper airway channel. In one embodiment, the method
includes targeted selective stimulation of functionally opposite
muscles that also effectively stiffen the upper airway channel to
reduce the risk of collapse.
[0117] In one embodiment, the method of treating, controlling, or
preventing obstructive sleep apnea consists essentially of the
recruitment of protrusor motor efferents. In one embodiment, the
method includes activating at least one protrusor muscle. In one
embodiment, the method includes targeted selective stimulation of
protrusor motor efferents located within the Hypoglossal nerve
proper 322 that activate the genioglossus muscle, causing
protrusion of the tongue to increase the patency of the upper
airway channel.
[0118] Elements of the System
[0119] In one embodiment, the OSA system is comprised of implanted
and external elements which together act to provide continuous open
loop targeted selective stimulation of the HGN 322. The implanted
elements (i.e. the elements implanted into the patient) may include
an Implantable Pulse Generator 1370 (IPG) (see FIGS. 13-16) and a
cuff electrode 764 (see FIG. 7). The external elements may include
a Remote Control and Charger 2272 (RCC) (see FIG. 22), a Charger
Coil 5374 (CC) and cable 5374a, a Docking Station 5378 (DS) and a
power supply for the patient, and a notebook computer 5376 and the
aura Clinical Manager (aCM) clinician's software programming
system. The IPG 1370 may be responsible for generating the pulses
that activate the desired neurons within the HGN 322, and is
implanted in the anterior chest region of the patient. The cuff
electrode 764 may attach to the IPG 1370 via an inline connector,
and runs from the chest location of the IPG 1370 to the
sub-mandibular region where it is wrapped around the HGN 322. The
IPG 1370 may contain a plurality, such as six, independent current
sources, each capacitively coupled via feedthroughs in its
enclosure to the inline connector. The inline connector may have
six torroidal spring contacts which mate with ring contacts of the
cuff electrode 764 proximal connector. Each ring contact of the
cuff electrode 764 may be connected by a wire in the cuff electrode
764 assembly to a contact within the self-sizing cuff. Each contact
may be shaped to match the curvature of the nerve bundle of the HGN
322, and the six contacts are located within the cuff so that six
sectors of the nerve circumference are in intimate contact with the
cuff contacts. The IPG 1370 may be directed by the RCC 2272 to
start and stop a sleep therapy treatment session, to provide
information on the status of the IPG 1370 and the cuff electrode
764, and is used in conjunction with the CC to replenish the energy
within the IPG 1370 battery. The aCM may be used by a clinical
engineer or clinician to program the OSA system for use in
providing therapy to the patient.
[0120] Implanted Pulse Generator (IPG)
[0121] The Implantable Pulse Generator 1370 (IPG) for the OSA
system is shown in FIG. 13. The IPG 1370 may be housed in a
titanium enclosure, containing the secondary Lithium-Ion battery,
the printed circuit board (PCB) assemblies, radio-opaque marker,
and support structures. The IPG 1370 may be covered by a hermetic
enclosure. The titanium material may be consistent with metals
traditionally used to house Active Implanted Medical Devices
(AIMD). The top of the titanium case may be sealed with a titanium
plate through which two feedthrough assemblies are attached. One
feedthrough assembly may contain four feedthrough pins, two of
which may be used for an inductive charging coil located outside
the hermetic enclosure and inside the header assembly, and two of
which may be used for the Medical Implant Communications Service
(MICS) telemetry coil similarly located. The second feedthrough
assembly may contain six feedthrough pins, which may be connected
to output pulse circuitry of the IPG 1370 and which connect
eventually to the six contacts contained within the cuff electrode
764 that attaches to the HGN 322. An embodiment of the IPG assembly
1370 is shown in FIG. 13 showing the silicone header and inline
connector separated from the IPG 1370 housing. FIG. 14 depicts the
plastic battery support that protects the Lithium Ion battery
inside the IPG 1370 enclosure. FIG. 15 depicts the completed IPG
internal assembly with circuit boards fastened to the titanium
header plate, the battery support and feedthrough assemblies being
lowered into the titanium enclosure and completed by laser welding
the enclosure to the titanium header plate. FIG. 16 shows an
exploded view of the header elements, including the inductive link
charging coil, the MICS telemetry coil, the magnet, the silicone
inner and outer header elements, the crimp contacts which mate with
the feedthrough pins, the Polyetheretherketone (PEEK) guides, and
the inline connector assembly and strain relief. An alternative to
this structure would utilize an epoxy header with the elements of
the inline connector contained within the volume of the epoxy
header, eliminating the PEEK components, crimp contacts and
allowing the proximal connector of the electrode lead to be
inserted directly into the IPG epoxy header.
[0122] The IPG 1370 elements shown in the block diagram in FIG. 12
may consist of a 16 bit microcontroller, a MICS telemetry
transceiver, a six channel custom Application Specific Integrated
Circuit (ASIC) current source, a serial electrically erasable
programmable read only memory (SEEPROM), inductive power receiving
and modulating and demodulating circuitry, battery charging
circuitry, power supplies and analog signal acquisition support
circuitry. The microcontroller may have a large number of
resources, including a 16 bit reduced instruction set core (RISC),
92 KBytes of Flash memory, 8 KBytes of RAM, a three channel DMA, a
12 bit analog to digital converter (A/D) and digital to analog
converter (D/A), 16 bit timers with 10 capture and compare
registers, four universal serial communication interfaces (UCSI)
supporting enhanced universal asynchronous receiver/transmitter
(UART), an Inter-Integrated Circuit (I.sup.2C) and Synchronous
Peripheral Interface (SPI) and a primary bootstrap loader with
Joint Test Action Group (JTAG) interface to allow program
development and memory programming.
[0123] The flash memory may be used to contain manufacturing data
such as calibration information, patient specific data, and other
constants which need to be kept in a permanent location, as well as
a secondary boot loader and application code. In one embodiment,
the secondary boot loader is required to allow transfer of code and
data to the flash memory after the IPG 1370 is welded closed (JTAG
programming may no longer be possible). The secondary boot loader
may be stored in a location which is reserved for its use and, as
viewed by the microcontroller, is actually the main application as
it is activated upon power on reset (POR) (the reset vector points
to the boot loader). The secondary boot loader may initialize the
system and wait for a finite period of time before either
responding to manufacturing software loader commands or if no
commands are received jumps to the main system application. This
architecture allows changes to be made in the flash memory of the
device once the JTAG interface is no longer accessible (such as
field upgrades to IPG 1370 device firmware). Should changes be
necessary to the secondary boot loader program, highly specialized
program images may be written that when executed can write a new
image to the region occupied by the previous secondary boot
loader.
[0124] The schematic diagrams for the IPG 1370 are shown in FIGS.
17 through 21. Beginning with FIG. 17 is the lithium battery, the
charge coil circuit, battery monitor circuit, the battery
disconnect circuit, the lithium ion battery charging circuit, the
Vcc regulator circuit, the 5V/10V/20V supply enable and voltage
regulator circuits. A resettable fuse may protect the battery from
over discharge and the battery monitor circuit may protect the
battery from under-voltage conditions. At 3.1V, IC2 monitor circuit
may generate an open-collector low level which drives the analog
switch IC1 to disconnect the battery from the system VBatt signal.
The signal S Batt may be driven from an I/O port on the
microcontroller to enable battery disconnection under program
control to allow the IPG 1370 to be placed into a low power shelf
mode for long term storage without battery depletion. Upon
disconnection of the battery, re-connection may be enabled upon
application of a charge field to the charge coil. The charge field
may be bridge rectified and zener limited and supplies power to
voltage regulator IC5, which in turn drives battery charger IC6 to
replenish power to the battery and to supply system power. Battery
power and charge power may be isolated from each other by diodes D1
and D2. Upon application of charge power and re-connection of the
battery the microcontroller goes through its POR sequence and
starts executing its primary and secondary boot loaders, described
below.
[0125] FIG. 18 depicts an embodiment of the microcontroller and log
memory circuits, as well as the manufacturing JTAG communications
connections. The microcontroller may contain all system memory with
the exception of event log memory which is interfaced to the
microcontroller using an I.sup.2C interface. This non-volatile
memory may be organized as a ring buffer to keep only the latest
events that occur during system operation. Optionally, log memory
may be contained as well within the Flash memory space of the
microcontroller.
[0126] FIG. 19 depicts an embodiment of the six channel current
ASIC used for pulse generation and the series output capacitors
used to prevent DC current leakage. A manufacturing test load is
shown, which may be removed from the PCB after testing is
completed. An analog multiplexer is shown which may allow voltage
samples to be taken to measure electrode/tissue impedances and
compliance voltage levels. The six channel current ASIC is
comprised of six identical current sources organized with shift
register interface to the microcontroller, data latches for
amplitude settings, and on-chip current mirror references and
control circuitry. Each shift register may be driven individually
or may be daisy-chained for drive from a single data line. Clock
lines, selects, address lines and enable lines all coordinate the
transfer of data into the current source logic. The current sources
are referenced to the 10V supply and supply biphasic current using
the ground and 20V supplies for source and sink current generation.
The current sources may use quasi-logarithmic methods with eight
bit data plus sign bit to control the level of current supplied.
The logarithmic scale may be approximated by eight linear segments
with their own current step and offset, resulting in very fine
current steps at low amplitudes and progressing to coarser steps as
the current reaches its maximum levels.
[0127] FIG. 20 depicts an embodiment of the MICS telemetry
circuitry and loop antenna located in the silicone header of the
IPG 1370. The MICS telemetry circuit uses the 400 MHz band to
transfer data to and from the IPG 1370 using secure data packets
with RF identification, device identification, command parsing and
sixteen bit cyclic redundancy check (CRC16) codes to detect errors
in the data transfer process. FIG. 21 depicts the connectors that
may allow the two PCB assemblies of the IPG 1370 electronics to be
attached together along with a test board that allows the boards to
be connected in a flat setting suitable for testing.
[0128] Remote Control and Charger (RCC)
[0129] The Remote Control and Charger 2272 (RCC) is a handheld
device which may be used by the patient to operate and wirelessly
charge their IPG 1370, and by the physician and clinical engineer
to program the IPG 1370. To serve these two roles, the RCC 2272 may
operate in two modes. In the primary mode, the RCC 2272 may respond
to key presses on its membrane switch panel, perform the functions
requested, and display the results on its front panel LEDs. In the
secondary mode, the RCC 2272 may act in pass-through fashion,
receiving commands from the aura Clinical Manager (aCM) software
via a Universal Serial Bus (USB) connection to a personal computer
(PC), and transferring those commands to the IPG 1370 through its
MICS telemetry interface. Responses and data from the IPG 1370 may
be received by the RCC 2272 and passed back to the aCM. In similar
fashion, the RCC 2272 may be used in the manufacturing process when
connection through the JTAG interface is not available. The front
panel of the RCC 2272 with its keyboard and LED user interface is
depicted in FIG. 22.
[0130] In one embodiment, the RCC 2272 is housed in a plastic
enclosure, containing either a set of secondary nickel metal
hydride (NiMH) AA batteries or alkaline AA batteries, a printed
circuit board (PCB) assembly, a membrane switch panel and LED
displays. The battery compartment may be accessible by the patient
to replace the rechargeable batteries should they wear out, or use
alkaline AA batteries when traveling. Located just above the
battery compartment are metal contacts that provide connection to
the internal charging circuitry of the RCC 2272. When the RCC 2272
is placed upon the docking station 5378, these metal contacts may
align with spring loaded metal contacts in the docking station 5378
which provide power to the RCC 2272 to recharge the RCC 2272 when
it is not in use by the patient.
[0131] The RCC 2272 may have two connectors: one is a mini-USB
connector used to connect to the aCM PC, and also allows charging
of the internal battery. The second connector is a four pin
circular connector which connects the RCC 2272 to the Charger Coil
(CC). The CC may receive power and control signals from the RCC
2272 and allows a secondary inductive link channel to transfer and
receive information with the IPG 1370 should the MICS telemetry
link be non-functional. The second four pin connector may also be
used during sleep laboratory tests to provide an indicator to the
clinician which stimulation group is active. A special cable may be
provided that interfaces to the various brands of PSG
equipment.
[0132] The RCC elements are shown in the block diagram FIG. 23 and
may consist of a 16 bit microcontroller, a MICS telemetry
transceiver, inductive power interface circuitry, battery charging
circuitry, power supplies and analog signal acquisition support
circuitry. The microcontroller may have a large number of
resources, including a 16 bit reduced instruction set core (RISC),
92 KBytes of Flash memory, 8 KBytes of RAM, a three channel DMA, a
12 bit A/D and D/A, 16 bit timers with 10 capture and compare
registers, four UCSI ports supporting enhanced UART, an I.sup.2C
and SPI protocols and a primary bootstrap loader with JTAG
interface to allow program development and memory programming.
[0133] The flash memory may be used to contain manufacturing data
such as calibration information, patient specific data, and other
constants which need to be kept in a permanent location, as well as
the application code. Unlike the IPG 1370, the RCC 2272 can always
be upgraded to new firmware through the USB interface or the JTAG
interface. Exemplary schematic diagrams of the RCC 2272 are shown
in FIGS. 24 through 28. The flash memory of the RCC 2272 may also
be used to log events in a similar manner to the IPG 1370.
[0134] FIG. 24 depicts the connection to the Docking Station 5378
and to the USB connection. The docking station 5378 may transfer 5V
from a USB wall mount charger to metal contacts on the underside of
the RCC 2272 chassis. This 5V signal may be fused and zener
protected before being brought to internal circuit elements of the
RCC 2272. The USB connector may be additionally capable of
supplying 5V power, as well as providing the communication link to
the aCM through circuit IC1, a USB transceiver. The Docking Station
may have its own internal power supply and the USB connector may be
replaced by a power cord connection to household power.
[0135] FIG. 25 depicts the connection to an internal three AA cell
battery pack, typically comprised of NiMH cells, or alkaline cells.
The NiMH cells can be recharged, the alkaline cells can be
replaced. The battery may be protected from over discharge by a
resettable fuse. In one embodiment, power from the previous diagram
is used to power the NiMH charger circuit, IC2. From either the
power from the previous circuit or the battery a Vcc 3.3V
regulator, IC3, may provide system power for the microcontroller
and other logic. In one embodiment, power may also be supplied to
IC4 which generate the 6V or 8V supply for operating the charging
coil, which supplies power to the IPG 1370 for charging its
internal lithium ion battery.
[0136] FIG. 26 depicts an embodiment of the microcontroller and
JTAG programming interface. Unlike the IPG 1370 which may lose its
JTAG interface after programming and test in manufacturing, the RCC
2272 retains this connector in the finished assembly. FIG. 27
depicts the MICS telemetry transceiver circuit and the connection
to an SMA type RF antenna which is housed inside the plastic
enclosure of the RCC 2272. FIG. 28 depicts an exemplary user
interface--a membrane switch panel, and the multi-color LEDS for
the front panel. The LEDs may be driven by an I.sup.2C interface
port expander, IC7. In one embodiment, light from the LEDs is
transferred from their position on the PCB to windows in the
membrane switch panel through clear light pipes. A piezo buzzer may
be driven from this same interface for provision of audible tones
for the user. Exemplary membrane switch panel artwork is depicted
in FIG. 22. Alternatively the RCC may provide an LCD display
instead of or in addition to the LEDs.
[0137] Charger Coil (CC)
[0138] The Charger Coil 5374a (CC) may be a small device attached
by a flexible cable to the RCC 2272 when it is necessary to charge
the IPG 1370. An exemplary block diagram for the CC is shown in
FIG. 29. In one embodiment, the CC assembly is comprised of a PCB
housing the electronics necessary for its operation, the option of
an embedded coil structure or a mounted inductive coil, and a
magnet which aids in the alignment and retention of the CC to the
IPG 1370. The IPG 1370 may contain a similar magnet in its
inductive loop coil located in the header of the IPG 1370. Much
like a cochlear implant, this simple alignment and fixation method
may assure that the best possible energy transfer between the CC
and the IPG 1370 occurs with as little impact upon the patient as
possible.
[0139] Docking Station (DS)
[0140] The Docking Station 5378 (DS) may provide a convenient place
on the patient's night stand to place and charge the RCC 2272 when
it is not in use. Having convenient alignment and holding features,
the patient can place the RCC 2272 into the DS 5378 in a single
simple motion. The RCC 2272 may be easily removed as well for use
when the patient wishes to operate the IPG 1370. In one embodiment,
the DS 5378 has contacts on its top surface which mate with
matching metal contacts in the RCC 2272. The DS 5378 may have a
mini-USB connector for attachment to a wall-mounted USB charger.
The charger can be unplugged from the DS 5378 and travel with the
RCC 2272 to allow the RCC 2272 to be charged when the patient is
traveling. The DS 5378 may have its own integrated power supply
that uses a standard wall plug to acquire power.
[0141] aura Clinical Manager (aCM)
[0142] The aura Clinical Manager (aCM) is a software application
running on a personal computer. In one embodiment, the aCM is used
by the clinical engineer or clinician to program an IPG 1370 and an
RCC 2272 for a particular patient, and to fit and optimize a
stimulation therapy for the patient. The aCM can run on a standard
PC.
[0143] Memory, or alternatively one or more storage devices (e.g.,
one or more nonvolatile storage devices) within memory, includes a
computer readable storage medium. In some embodiments, memory or
the computer readable storage medium of memory stores programs,
modules and data structures, or a subset thereof for a processor to
control the RCC 2272, IPG 1370 and other system components
described herein.
[0144] The aCM functionality may be divided along its use model
applications, selected by a series of tab selections along the left
edge of the screen. A local database on the computer may be
maintained and synchronized automatically whenever an internet
connection is provided to the computer. Database synchronization to
the host database may ensure backup of all patient data and
tracking of patient use of the implanted systems.
[0145] Patient Manager Screen
[0146] In one embodiment, the first screen is the Patient Manager
screen, and is shown in FIG. 30. It is with this screen that a
patient is first entered in the patient database and data collected
pertaining to the patient's particular case of OSA. Existing
patients may be located in the database by selecting the "Find
Patient" and the system is able to find patient records that
resemble the entry made by the user. Once a record is displayed, it
can be selected. Reports may be generated for a patient on this
screen as well and may be formatted for HTML for viewing as a file
in a browser, such as Internet Explorer or Safari.
[0147] OSA system components may be issued to the patient and their
issue date and serial numbers, as well as other pertinent
information may be entered in the patient database as well. When
elements of the system are replaced due to wear-out, loss, or
failure, etc., the new elements may be entered into the database in
a similar manner. Once all of the information for the patient is
entered, the user may select any of the other screens.
[0148] Implant/Surgery Screen
[0149] The Implant/Surgery Screen may be the primary screen used by
the clinical engineer or clinician to test the OSA system during
the surgical implantation of the IPG 1370 and electrode. It is used
in the operating room (OR) to test the system elements, to verify
electrode impedances are in an acceptable range, and that the HGN
322 response to stimulation and threshold levels are
acceptable.
[0150] Titration Screen
[0151] The Titration Screen, an exemplary embodiment being depicted
in FIG. 31 may be the primary screen used by the clinical engineer
or clinician to fit the OSA system to the patient. Following
surgery, approximately a week or more later, the Titration Screen
of the aCM may be used for the main programming session for the
patient. It is at this session where all of the stimulation
parameters may be determined in preparation for a sleep study to
verify the operation of the system in providing therapy for the OSA
condition.
[0152] In one embodiment, the Titration Screen is divided into six
sections. The largest section may be dedicated to Amplitude control
where Threshold, Target and Maximum current amplitudes are
determined for each of the six contacts of the system. Convenient
Quick Set buttons may be provided to allow the amount of current at
which amplitude changes with each increment or decrement of the up
and down arrows, marking of Threshold, Target, and Max levels, and
the setting of all enabled contacts to their Threshold or Target
levels. In one embodiment, just to the right of this area are six
slider controls with enable boxes to allow each contact to be
tested individually or in concert with other contacts. When the
Threshold is observed, selecting the Set Threshold button will
transfer the value of the current for that contact to the Threshold
box below the slider and a colored bar marker will be placed on the
slider window at the current level. When the Target level is
observed, selecting the Set Target button will transfer the value
of the current for that contact to the Target box below the slider
and another colored bar marker will be placed on the slider window
at the current level. When the Maximum level is observed, selecting
the Set Max button will transfer the value of the current for that
contact to the Maximum box below the slider and yet another colored
bar marker will be placed on the slider window at the current
level. Threshold may be tested at 1 Hz while Target and Maximum may
be selected at 15 Hz (or any other desired frequency that is
greater than 1 Hz). Below each slider bar for each contact is an
effect indicator, selected by a pull-down box, where the effect of
the stimulation applied to the electrode is indicated (protrusor,
retrusor, no effect, etc.).
[0153] The section directly below the contact slider controls may
be the Contact Impedances section, and provides a quick way to
request and receive contact impedance with respect to the case
indifferent electrode of the IPG 1370. To the right, at the top, is
the Status window. In the Status window the aCM to RCC USB
communication status may be shown, the RCC 2272 to IPG 1370 MICS
telemetry communication status may be shown, and the RCC 2272 and
IPG 1370 Battery levels may be shown. In one embodiment, directly
below this is the Frequency window in which the stimulation
frequency may be set by increment or decrement, or quickly set to 1
or 15 Hz (same as pulses per second, or pps), with the resultant
frequency shown below the up down buttons. In one embodiment,
directly below the Frequency window is the Saving and Restoring
window. This window may be used to save and recall program settings
and patient data in a time and date stamped entry into the local
patient database file. Multiple data records can be stored for a
patient on the same day, and provision is made to annotate the
records with a short field for quickly locating a record, along
with a more detailed record that allows clinician descriptions of
the actions taken to be captured. In one embodiment, the last
window is the Stimulation Control window, and is used to start and
stop stimulation.
[0154] PSG Screen
[0155] The PSG screen may be used during sleep laboratory studies
to optimally allow easy manipulation of stimulation parameters by
5% variances and to allow monitoring of the IPG 1370 status during
the test. Because the IPG 1370 operates independently, it is not
easily discerned which stimulation group is active at a particular
time. It is beneficial to identify which stimulation group is
active to correlate this information with the data visible during
the PSG test to verify that stimulation levels for that group are
adequate or in need of adjustment. Normally the IPG 1370 only
responds to commands received from a validated sender. In the PSG
setting, the IPG 1370 may be enabled to transmit messages
indicating when groups change, when channels ramp up or down, when
groups delay and when they are in plateau phases. This information
is sent to the RCC 2272 which can, using its four pin connector,
generate signals that can be monitored by the PSG system to allow
indication of IPG 1370 activity to be recorded with all of the
other PSG measurements. In addition, the aCM can use its USB
connection to the RCC 2272 to periodically inquire what the status
of the IPG 1370 is and display that information on a location
within the PSG screen.
[0156] Manual Parameter Control Screen
[0157] The Manual Parameter Control Screen, an exemplary embodiment
being depicted in FIG. 32 may be used to set parameters that are
typically not changed from their default values, but which might be
changed under certain conditions. In one embodiment, the screen is
divided into two main sections--one in which stimulation parameters
and logs may be viewed, and another section with status and data
transfer operations are conducted. The top left sections may be
used for setting and viewing Global IPG Parameters, such as Startup
Delay (or Sleep Session Delay), Pause Delay, etc., while the
section just to the right is the Group Parameters section. Groups
can consist of as few as one electrode contact, or as many as six.
Groups default to one contact each, with the first group containing
contact one., the second group containing contact two, and so on.
In situations where multiple contacts belong to a group the
percentages of contribution for each group are entered into their
respective locations. This controls the distribution of current and
thus sets the field of neural activation between two or more
contacts of the cuff electrode 764. Below the Global IPG Parameters
window may be the Electrode window, and if a contact is enabled,
its current settings may be displayed as will be the effect it
causes. Manual entries into the fields of this section are allowed,
but changes to amplitude will be corrected to the nearest actual
amplitude possible. This may be required because the output of the
current sources in the IPG 1370 is logarithmic, not linear, so
manual selection of amplitude is not as easy as it would seem. The
increment and decrement function of the Titration screen
automatically takes this non-linearity of the current sources into
effect and uses the calibration data of the IPG 1370 to display
actual currents.
[0158] The main section to the right may contain a Status Window
again, and two sections that control communication between the RCC
2272 and IPG 1370 and File Operations. In the Communication
section, stimulation parameters may be read from or sent to the IPG
1370. In the File Operations section, stimulation parameters may be
read from or written to records in the database. IPG 1370 event
logs may be retrieved from the IPG 1370 and saved to files as well.
In one embodiment, the bottom portion of the Manual Parameter
Control screen allows the viewing of the various logs that are
collected by the IPG 1370, including electrode impedances, battery
charging operations, battery use profiles, and IPG events, both
expected and unexpected (but anticipated) events.
[0159] RCC Functions Screen
[0160] The RCC Functions Screen, an exemplary embodiment being
depicted in FIG. 33 may allow the aCM to fully simulate the
operation of the RCC 2272 while the RCC 2272 is connected to the
aCM and is in pass-through mode. Indicators for the LEDs and
regions on the screen that can be clicked like the buttons of the
RCC 2272 switches allow full operation of the system as if the aCM
were not connected. This may be useful when the aCM user is located
at a distance from the RCC 2272 (such as might occur in the OR,
sleep laboratory, or other remote location).
[0161] RCC USB Comm Screen
[0162] The RCC USB Comm Screen, an exemplary embodiment being
depicted in FIG. 34 may be a special screen that is typically only
enabled for use by an engineer. The RCC USB Comm Screen may allow
complete observation of communications between aCM and RCC 2272 and
between the RCC 2272 and an IPG 1370. In one embodiment, manual
formulation of telemetry commands is supported, as well as
computation of CRC codes to be included in command packets. Port
operations on the aCM are also visible and controllable in this
screen. This may be particularly useful when certain PC platforms
and versions of Windows are used with USB devices and connect and
disconnect of USB cables causes re-assignment of ports to occur,
sometimes without obvious rhyme or reason to the user.
[0163] Operation of System
[0164] In one embodiment, operation of the system includes five
phases of operation: Manufacturing, Implantation, Titration, PSG,
Follow-up, and Patient use phases. During the Manufacturing phase,
the IPG 1370 and RCC 2272 may be programmed, tested, calibrated,
and stocked for shipment and implantation. The JTAG interface of
the PCB assemblies of the IPG 1370 (before singulation and
encapsulation into its hermetic enclosure) and RCC 2272 may allow
full programming and test to occur. Post singulation and
encapsulation of the IPG PCB assemblies may require use of the
secondary boot loader described previously to change program
contents of the IPG 1370. In one embodiment, following programming
and testing of an IPG 1370, it may be placed into a low power
consumption mode in which the battery is disconnected from the
circuit and only very low current consumption occurs due to the
single active component remaining connected to the IPG battery, a
battery monitoring circuit. This may allow an IPG 1370 to be fully
charged, then disconnected from its battery and stored for a long
period of time with little loss of battery energy. In the
programming environment a computer with a JTAG interface may be
connected to the various assemblies and code may be programmed into
the devices. In the sealed IPG 1370, the programming system may
utilize a stock RCC 2272 to transfer commands over the MICS
telemetry band to the IPG 1370.
[0165] The Implantation phase, an example being depicted in FIG.
35, occurs when the patient is surgically implanted with the
electrode and IPG 1370. In this environment, the IPG 1370 and
electrode may be contained in sterile packaging ready for use
within the sterile field of the operating room. Prior to surgery,
an RCC 2272 may be placed on the operating table next to the
patient, and a long USB mini-B cable may be connected to the RCC
2272 and crosses the border of the sterile field and may be passed
to the clinical engineer and aCM. During the implantation the IPG
1370 and electrode may be briefly tested for impedance and
threshold stimulation levels for all of the six contacts of the
cuff electrode 764.
[0166] The Titration phase, an example being depicted in FIG. 36
may be the main programming phase for the system. In this phase,
all contacts may be tested to determine their threshold, target and
maximum stimulation levels, what the actions of each of the
electrode contacts elicits, testing of contact pairs or tripoles,
etc., if warranted, and assignment of groups that may be used
during the Patient Use phase. The Follow-up phase may be
essentially just like the Titration phase, except that changes may
be made to pre-existing stimulation parameters so that improvements
in stimulation effect may be obtained or corrections due to contact
or wire failures or other causes can be mitigated. The Patient Use
phase, an example being depicted in FIG. 37 may be the main use of
the system and encompasses the stimulation therapy and maintenance
of the OSA system. The detailed operations of the OSA system are
described in further detail below.
[0167] On/Off Button Pressed
[0168] The On/Off button on the RCC 2272 may be used to start or
stop a sleep therapy session. The procedure associated with the
On/Off key operation is represented in FIG. 38. In one embodiment,
the patient removes the RCC 2272 from the docking station 5378 and
presses the On/Off key. The RCC 2272, which may have been in a low
power consumption mode, awakens and begins to search for its
assigned IPG 1370. The RCC 2272 may send telemetry requests through
its MICS telemetry channel for a fixed period of time. If at the
end of this time window it has not found its IPG 1370, it may
generate beeps, indicate a failure to link to its IPG 1370 and end
the sleep therapy session.
[0169] If the RCC 2272 is able to link to the IPG 1370, it may then
send a request for the IPG 1370 to send its status information,
including state of charge for the IPG battery, electrode impedance
information, as well as error flags and other information that is
relevant prior to starting a sleep therapy session. The RCC 2272
may set LEDs indicating the status of the IPG 1370. If there is
sufficient charge in the battery to start a sleep session, and if
all of the electrodes programmed to operate are within operational
boundaries then the IPG 1370 may be instructed to start a sleep
therapy session. The IPG 1370 may send the RCC 2272 a data packet
with the duration of the sleep session, which the RCC 2272 may use
to control the indicator LED on its front panel showing the status
of the IPG 1370. The RCC 2272 may then go to sleep in a low power
mode until the next time that the patient presses a key. The IPG
1370 may go about the process of sleep therapy, described
below.
[0170] Charge Button Pressed
[0171] The Charge Key may initiate the process of charging the IPG
1370, an example being depicted in FIG. 39. In this process, the
patient may connect a charger coil (CC) to the RCC 2272 and places
the CC over the IPG 1370 to transfer energy from the RCC 2272 to
the IPG 1370. The RCC 2272 may be able to detect when the CC is
attached because of a loop-back connection within the connector or
by monitoring current consumption. In one embodiment, the CC is
held in place over the IPG 1370 because both devices could contain
magnets which could help to hold and align the CC optimally over
the IPG 1370. The RCC 2272 may be able to determine how well the
coil is aligned over the IPG 1370 by monitoring the current
consumption in the CC. By this same method of monitoring current
and by changing the current in the CC a secondary telemetry channel
may be available in case of problems with the primary MICS
telemetry channel.
[0172] An exemplary sequence of events in the Charge process may be
as follows. The patient presses the Charge button and the RCC 2272
may come out of its low power mode. If the charge process is
already in place, the intent of the patient may be deduced to be to
end the charge process. The RCC 2272 may stop the charge process
and disable the CC and establish a MICS communication link with the
IPG 1370. It then may then send an end of charge command to the IPG
1370, turn off the Charge LED, and request the IPG 1370 status. It
may then display the IPG battery status, and assess the impedance
data. If the impedances are acceptable (within an acceptable range
for current controlled pulses to be generated), the charge process
may end. If the impedances are not within an acceptable range, then
the On/Off LED may be set to red, the RCC 2272 may generate beeps
and the charge process may end. If the charge process was not
already set, the RCC 2272 may set the Charge LED to green and start
the IPG Charge process, described below.
[0173] Test Button Pressed
[0174] The Test button may initiate a process to demonstrate to the
patient a brief stimulation session that is representative of the
stimulation that will be applied during the sleep session. Since
the stimulation during the sleep session may not actually begin to
deliver stimulation pulses while the patient is awake, it may
sometimes be desirable for the patient to verify that the
stimulation system actually will work as expected, or to verify
that the stimulation parameters will be comfortable during the
sleep therapy. The test process may be identical to a sleep therapy
session except for the duration of the stimulation periods, the on
and off times, and the ramp times for all of the groups. In one
embodiment, stimulation starts immediately upon initiation of the
test process and ends after all of the groups have gone through
their ramp up, plateau, and ramp down phases, or when the test
button is pressed again to stop the test process immediately. The
sequence of events in the Test process is shown in FIG. 40. After
the Test key is pressed, the RCC 2272 may come out of low power
mode and seeks the IPG 1370. If the RCC 2272 cannot find the IPG
1370, the RCC 2272 may generate beeps, set its LEDs and the test
session quits. If the IPG 1370 is found, the RCC 2272 may request
the IPG 1370 status. The RCC 2272 may then set the IPG 1370 battery
status LEDs appropriately. If the Battery is sufficiently charged,
the RCC 2272 may then continue, otherwise the test process could
quit. If the impedance is within acceptable limits for the active
groups then the test command may be sent to the IPG 1370, if not,
the RCC 2272 may generate beeps, set the Test LED to red and the
test session may end.
[0175] Pause Button Pressed
[0176] The Pause button may stop a stimulation session for a brief
period to allow the patient to wake up and go to the bathroom, etc.
An exemplary pause process is outlined in FIG. 41. The key may only
valid during a sleep therapy session and may be ignored if the IPG
1370 is not in this mode. An exemplary RCC 2272 pause process may
be as follows: the patient presses the Pause key. If the IPG 1370
is not in a sleep session, the RCC 2272 beeps, turns off LEDs and
returns to low power mode. If the IPG 1370 is in a sleep session
the RCC 2272 attempts to link to the IPG 1370 and requests the
status of the IPG 1370. If the IPG 1370 is not already paused, the
RCC 2272 sends a pause command to the IPG 1370, sets the Pause LED
green, and returns to low power mode. If the IPG 1370 was already
in pause mode, the RCC 2272 may look at the IPG battery. If the
battery is low, the RCC 2272 may end the sleep session and set the
IPG LED to red and return to low power mode. If the battery is full
the RCC 2272 may set the IPG LED to green, otherwise the RCC 2272
may set the battery LED to amber. The RCC 2272 may then check the
impedance. If the impedance is not OK the RCC 2272 may set the
On/Off LED to red, generate beeps, and return to low power mode. If
the impedance is OK, then the RCC 2272 may turn the Pause LED off.
The RCC 2272 may then check to see if the sleep duration is over.
If so, it may set the On/Off LED to off and end the sleep session.
If the sleep session is not over the RCC 2272 may send a command to
the IPG 1370 to finish the pause and the RCC 2272 may go back to
low power mode.
[0177] IPG Pause Process
[0178] The IPG 1370 Pause Process may occur upon command from the
RCC 2272, and an example is depicted in FIG. 42. An exemplary IPG
Pause process may proceed as follows: If the IPG 1370 is not in a
sleep session the IPG 1370 may return and go back into low power
mode. If the IPG 1370 is not in the pause mode the IPG 1370 may
enter the pause mode, suspend stimulation and return to its low
power mode. If the IPG 1370 is in the pause mode the IPG 1370 may
start to return to stimulation mode, if several conditions are met.
First the IPG 1370 may check to see if the battery is low, and if
is the battery is low, the IPG 1370 may send status information to
the RCC 2272 and end the sleep session. If the battery is not low,
the IPG 1370 may check impedances. If the impedances are not within
an acceptable range, then the IPG 1370 may send status information
to the RCC 2272 and end the sleep session. If the impedances are
within an acceptable range, then the IPG 1370 may load the UnPause
delay (similar to the sleep session delay, but typically less time
because most patients will fall back to sleep faster than at the
beginning of the sleep session), wait for the delay to be complete,
and then the IPG 1370 may start setting up the first group for
stimulation. This may involve setting up the startup frequency
delay, the startup frequency duration, the group one ramp up
duration, the group one on time, the next group delay time, the
amplitude threshold, setting the frequency ramp to active, setting
the ramp to active, setting the plateau phase to inactive, setting
the ramp down to inactive, and enabling stimulation. The IPG 1370
then may then return to the low power sleep state.
[0179] IPG Charge Process
[0180] The IPG Charge Process may be initiated by the RCC 2272, as
described above, and an example is depicted in FIG. 43. In one
embodiment, the IPG 1370 and the CC are coupled, the RCC 2272 is
close enough for MICS telemetry, the RCC 2272 is completely charged
and able to transfer power to the IPG 1370, and all other relevant
systems are functional. The RCC 2272 and IPG 1370 may share in the
responsibility of checking that the CC is attached to the RCC 2272
and that the CC is aligned properly over the IPG 1370. With
everything in place, the RCC 2272 may then enable the CC. The RCC
2272 may then choose a charge duration based upon the state of
charge of the IPG battery. If the battery voltage is less than a
certain level the RCC 2272 may set the charge duration to 30
minutes. If the battery voltage is less than a slightly higher
level the RCC 2272 may set the charge duration to 20 minutes.
Otherwise the RCC 2272 may set the charge duration to 10 minutes.
The RCC 2272 may then wait for the charge duration to be over,
after which the RCC 2272 may disable the CC and request the status
from the IPG 1370 and set its LEDs accordingly. If the battery is
full, the RCC 2272 may generate beeps, set Charge LED green for 10
seconds and end the charge process. If not, the RCC 2272 may check
the temperature of the IPG 1370. The temperature of the IPG 1370
would be checked to see if a potentially dangerous or detrimental
condition exists because of the charging process and the effect
that can have on the chemistry of the rechargeable battery. If the
temperature of the IPG 1370 is acceptable the RCC 2272 may then go
back to choose the charge duration and continue the charge process.
If the temperature is not acceptable, the RCC 2272 may generate
beeps, set the Charge LED to red for 10 seconds, and end the charge
process. At the end of a fixed duration the RCC 2272 may terminate
the charge session regardless of the state of charge of the IPG
battery.
[0181] Sleep Session Process
[0182] An exemplary sleep Session process is depicted in FIG. 44.
The IPG 1370 may load the sleep duration counter, load the startup
delay and then wait for the startup delay to be completed. The IPG
1370 may then prepare the first stimulation group. The startup
frequency may then be loaded, the startup frequency duration may be
loaded, the first group ramp duration may be loaded, the group on
time may be loaded, the next group delay may be loaded, the
amplitude threshold(s) may be loaded, the frequency ramp may be set
to active, the ramp up may set to active, the plateau phase may be
set to inactive, the ramp down may be set to inactive, and the IPG
1370 may return to the low power sleep state.
[0183] Frequency Tick Process
[0184] The Frequency Tick Process may be the main event
coordinating the delivery of stimulation pulses. Since the
frequency tick interrupt process represents the frequency that
pulses occur during stimulation, the timer interrupt associated
with this event may be therefore the event which triggers the
delivery of a set of pulses for all of the active contacts and the
advancement from one phase to another for a group, or the
transition between groups. Typically, it is expected that when a
group is at its plateau or target level it will be the only group
active, but during the ramp up and ramp down times there may be two
or more groups active, depending upon the intent of the programming
process.
[0185] The Frequency Tick Process is depicted in FIG. 45. The IPG
1370 first checks to see if the frequency ramp is active. If yes,
the IPG 1370 may make any necessary changes in the timer value used
to generate the frequency tick interrupt, thereby adjusting the
frequency and then may decrement the frequency ramp duration. The
IPG 1370 then checks to see if the frequency ramp duration is zero.
If the frequency ramp duration is zero, the IPG 1370 may set the
frequency ramp to inactive. The IPG 1370 may then begin to service
the current active group. The IPG 1370 first checks to see if ramp
up is active. If ramp up is active, the IPG 1370 may make any
necessary adjustments to the group amplitude level. The IPG 1370
then may decrement the ramp duration and then checks to see if the
ramp up duration is zero. If the ramp up duration is zero, the IPG
1370 may de-activate the ramp up phase and may activate the plateau
phase. Next the IPG 1370 checks to see if the plateau phase is
active. If the plateau phase is active, the IPG 1370 may set the
amplitude at the target level, decrement the plateau duration, and
check to see if the plateau duration is over. If the plateau
duration is over, the IPG 1370 may deactivate the plateau phase and
activate the ramp down phase. Next the IPG 1370 may check to see if
the ramp down is active. If the ramp down is active the IPG 1370
may adjust the amplitude as needed, decrement the ramp down
duration and check to see if the duration is zero. If the ramp down
duration is zero, the IPG 1370 may inactivate the ramp down phase
and deactivate the group.
[0186] Next the IPG 1370 may check to see if the battery is charged
sufficiently. If the battery is not sufficiently charged, the IPG
1370 may end the sleep session and return to low power mode. Next
the IPG 1370 may check the impedances. If the impedances are not
within acceptable limits the IPG 1370 may end the sleep session and
return to low power mode. Next the IPG 1370 may generate the pulses
for the active group. Next the IPG 1370 may look to see if another
group is active, and if so begins to service that group as
indicated above. If not, the IPG 1370 may return to low power
mode.
[0187] Next Group Tick Process
[0188] The Next Group Tick Process, depicted in FIG. 46 is
responsible for activating the next group in the stimulation
process. When the timer interrupt associated with the Next Group
Delay Tick occurs, the IPG 1370 may decrement the next group delay
counter, and check to see if the delay counter is zero. If the
delay counter is zero, the IPG 1370 may activate the next group,
load the ramp up duration, load the group on time, load the next
group delay, and load the amplitude threshold and then return to
low power mode. If the counter is not zero the IPG 1370 may simply
return to the low power mode.
[0189] Sleep Duration Tick Process
[0190] The Sleep Duration Tick Process, depicted in FIG. 47 is
responsible for controlling the duration of the sleep therapy. The
end of therapy may or may not coincide with the ramp down of the
currently active group(s). In the process, upon the timer interrupt
assigned to the sleep duration, the duration may be decremented,
and if zero, the sleep session may be ended and the IPG 1370 may
return to a low power mode. If the duration is not zero the IPG
1370 may simply return to the low power mode. It should be recalled
that the sleep duration may be sent to the RCC 2272 by the IPG 1370
at the beginning of the sleep treatment session. The RCC 2272 may
independently count down its own copy of this value, and when this
count reaches zero the RCC 2272 may set the LEDs of the RCC 2272
accordingly. No communication between the IPG 1370 and RCC 2272 may
need to occur at the end of the therapy session.
[0191] Group On Time Tick Process
[0192] The Group On Time Tick Process is depicted in FIG. 48, and
occurs when the timer interrupt associated with the group on time
counter occurs. When this event occurs, the group on time may be
decremented, and if the counter value reaches zero, the group may
be disabled. This is a redundant process to the frequency tick in
that both processes are able to control the duration of a group,
but may be used in some instances when specific on times are
desired that are different than the sum of the ramp up, plateau,
and ramp down phases.
[0193] Impedance Measurement Process
[0194] The Impedance Measurement Process is depicted in FIG. 49.
Impedances may be regularly measured for all active contacts by
measuring the voltage across the contact with respect to a
reference, and knowing the current at which the stimulus pulse was
generated, the impedance of the contact may be calculated. When
impedances are detected on contacts that are programmed to
participate in stimulation groups that fall outside of acceptable
bounds, then stimulation from that point forward may be suspended.
Upon noticing that stimulation cannot be started, the patient may
be instructed to seek the advice of their physician, who could
re-program their IPG 1370 to use other contacts, if possible, or to
schedule revision surgery to correct the problem. An error flag
associated with the measurement process may be updated and utilized
for detection of out of bounds impedances for the stimulation
process.
[0195] The impedance measurement process may begin with the
initialization of several items. First, the total number of
channels (contacts) may be loaded, the sample count loaded, the
sample accumulator cleared, the sample rate set, and the impedance
error flag may be cleared. The sampling process may then begin. The
impedance for the first contact may be read and added to the
accumulator. This may repeat until the last sample is read. Next an
average value may be computed and stored in the impedance array for
the contacts. If the channel/contact was active, the impedance may
be checked for validity. If the impedance is outside the required
bounds the impedance error flag may be logically OR'ed with the bit
value for the channel. If that was not the last channel, the sample
count may be re-loaded, the accumulator cleared, and the process
begins for the next channel/contact. If the last contact/channel
tested was the last channel/contact, the impedance data and error
flag may be stored, the impedance data reported back to the RCC
2272, and the IPG 1370 may go into the low power mode.
[0196] Boot Loader Process
[0197] The Boot Loader Process (meaning the Secondary Boot Loader,
and do not discuss the primary boot loader of the microcontroller)
is depicted in FIG. 50, and may be the default program of the IPG
1370 processor--i.e., the Boot Loader Process is the program
associated with the reset vector of the microcontroller of the IPG
1370. This boot loader may be required because the mask
read-only-memory (ROM) boot loader of the microcontroller may only
support a JTAG or similar interface to debug or program the flash
memory of the microcontroller, and when the PCB assemblies are
welded into the IPG 1370 case there may be no alternative method to
re-program the IPG 1370 other than this secondary Boot Loader
process.
[0198] The IPG 1370 can be placed into a power off state by being
commanded to disconnect the battery from the IPG 1370 main
circuitry. Once this command is executed, the only portion of the
IPG 1370 circuitry being powered may be the battery monitor. This
mode may be used to store the IPG 1370 in shelf mode, while it is
awaiting shipment to a customer. The IPG 1370 may be taken out of
the shelf mode by application of charger inductive power. This may
supply power to the processor, which with its Power On Reset (POR)
sequence, may vector to the Boot Loader. The Boot Loader may
initialize the microcontroller and IPG 1370 resources, log an event
that the Boot Loader has done so, open the MICS telemetry channel,
load a Boot Message timeout counter, and wait for an incoming
message from the RCC 2272. If no message is received before the
timeout counter reaches zero, then the boot loader may check to see
if there is a valid application image. If not, the Boot Loader may
disconnect the battery and return to shelf mode. If a valid
application image is available, then the Boot Loader may call the
application. The use of a call instruction may allow a jump to any
space in program memory without the expectation that a return from
the application will occur.
[0199] Main Application Process
[0200] The Main Application is depicted in FIG. 51. The main
application may be called by the Boot Loader, and may be
responsible for initialization of system resources, servicing RCC
2272 telemetry commands, and monitoring system operation. The Main
Application may proceed from power up by initializing the system,
log a "begin main application" event, enable MICS wakeup interrupts
and enter a low power mode. Upon receiving MICS wakeup interrupts
the IPG 1370 may service the RCC 2272 command, load a MICS timeout
window value, and await another command. When the timeout reaches
zero, the main application may re-enable the MICS wakeup interrupt
and may then go back into low power mode. The application may spend
as much time as possible in low power mode to conserve battery
energy for the convenience of the patient. All processes may
essentially occur as needed by interrupt mechanisms. Interrupts,
and thus processes, may be prioritized and masked or enabled as
needed, to control the orderly operation of the IPG 1370. This may
be extremely important to allow concurrent operations such as
telemetry during stimulation, to allow changes in stimulation to be
commanded by the RCC 2272 and the aCM. Without this interrupt
concurrent system design there could be unacceptable latencies in
certain events, which could manifest themselves as apparent lack of
operational capability or delays to the patient or clinician.
[0201] System Programming
[0202] System programming and stimulation of the exemplary
embodiments do not have to take into account the timing of
respiration. When electrical stimulation is applied to a nerve
bundle there are essentially two factors that determine which
fibers within the bundle will be excited. The first is distance of
the fiber to the contact--the closer a fiber is to the contact, the
higher the current gradient and the more likely that the fiber will
be excited. The second is the diameter of the fiber, which
determines the voltage changes across the membrane and hence the
likelihood of reaching the threshold of generating an action
potential--the larger the diameter, the more likely that the fiber
will be excited. At a particular current amplitude of sufficient
duration, all of the fibers within a certain distance or diameter
of the stimulation will be excited. As current amplitude increases,
more fibers will be excited. Since each fiber is associated with a
muscle fiber or fibers (jointly referred to as a motor unit), as
more nerve fibers are excited, more muscle fibers are caused to
contract, causing a gradation in force production or position as
the stimulation current or phase duration is increased. The point
at which this force is first generated is referred to as the motor
threshold, and the point at which all of the fibers are all
recruited is the maximum stimulation level. The comfort of this
activity to the patient is often exceeded before this maximum level
is attained, and it is important to determine the threshold level
and the level at which the useful level of force or position is
obtained at a level that is not uncomfortable for the patient. The
point at which the optimal or best possible force or position is
obtained is the target level.
[0203] In certain exemplary embodiments, system programming entails
operatively connecting at least one electrode with a motor efferent
located within a nerve (for example, the Hypoglossal nerve). This
connection need not be a physical connection. The connection can be
any connection known to those skilled in the art where the
connection is sufficient to deliver a stimulus to the targeted
motor efferent of the targeted nerve. Once the electrode is
operatively connected with the targeted nerve, two or more
electrode contacts are activated to determine their applicable
stimulus thresholds (i.e., the threshold at which a desired
response is achieved). The level of stimulation comfortable to the
patient can also be measured. The contacts may also be assigned
into functional groups that provide tongue motions that are
beneficial in maintaining airway patency.
[0204] In certain exemplary embodiments, stimulation may be
provided to the nerve using at least two functional groups. A
functional group is defined as one or more electrode contacts (for
example contacts 764a, 764b, 764c and 764d shown in FIGS. 7 and 8)
that deliver a stimulus that results in a tongue movement that
maintains an open airway. Each functional group may have a single
contact, or may have multiple contacts. For example, a functional
group with two contacts could be used to excite a population of
nerve fibers that lie between two adjacent contacts. A non-limiting
example of how stimulation from the functional group can be
delivered is field or current steering, described in International
Patent PCT/US2008/011599, incorporated by reference in its
entirety. In another exemplary embodiment, two or more adjacent
contacts may be used to focus the stimulation field to limit the
area of excited neurons to a smaller area than what might be
achieved with a single contact using a pulse generator case as a
return contact. In another exemplary embodiment, two or more
non-adjacent contacts may be used together to generate a useful
response that is better than the response by the single contacts
alone could produce. The table below shows various exemplary
combinations of functional groups for an embodiment having six
contacts numbered 1-6. A single contact can be a member of more
than one functional group. For example, contact two could be in two
different groups--one group made up of contact 1 and 2, and another
group made up of contact 2 and 3. Exemplary contact groups are
shown below.
[0205] a. Single Contact Groups: 1,2,3,4,5,6
[0206] b. Double Contact Groups:
1&2,2&3,3&4,4&5,5&6,6&1
[0207] c. Triple Contact Groups:
1&2&3,2&3&4,3&4&5,4&5&6,5&6&1,6&1&2
[0208] d. Non-Adjacent Contact Groups: 1&3, 2&4, 3&5,
4&6, 5&1, 1&3&5, 2&4&6, 3&5&1,
4&6&1, 1&2&4, etc.
[0209] FIG. 9 illustrates an exemplary stimulation strategy. FIG.
52 provides a more detailed view as the stimulation transitions
from one active group to the next. As shown in FIG. 9, functional
groups may be used to establish load sharing, amplitude ramping,
and delayed start of stimulation to optimize the delivery of
stimulation of the targeted nerve (the Hypoglossal nerve, for
example). In the exemplary strategy of FIG. 9, stimulation is
delayed after a patient begins a sleep session, allowing the
patient to fall asleep before stimulation begins. Stimulation from
each of the functional groups takes turns ramping up, holding the
tongue in the desired position for a period of time that is
sustainable without significant fatigue, before the next group
starts and the previous group stops allowing muscle fibers
associated with the previous group to relax, and which helps to
prevent fatigue but which maintains desirable tongue position all
the time.
[0210] The remaining effort in programming the two or more
electrode contacts is to select electrode contacts and assign them
to functional groups. During stimulation, only a single functional
group will be on at a time or on at overlapping out of phase
intervals, but a group may contain more than one contact. The
effect of having more than one contact should additionally be
tested to make sure that the sensation of the two contacts or
groups on at the same time does not result in discomfort for the
patient. Ostensibly, if a single contact results in good airway
opening there is little reason to add another contact to the same
targeted efferent. If the use of two contacts provides better
opening then the pair should be tested together and assigned to the
same group.
[0211] In certain embodiments, at least two functional groups are
defined, so that the load of maintaining tongue position is shared,
prolonging the time until fatigue sets in or preventing it
altogether. Stimulation starts with the first group, which ramps up
in amplitude to a target amplitude, stays at the target level for a
pre-determined amount of time and then is replaced or overlapped by
the next group. This repeats through one or more of the functional
groups. The pattern may repeat beginning with the first functional
group, but need not begin with the same functional group each time.
In certain exemplary embodiments, the groups may be programmed to
ramp up in amplitude while the previous group is still on and at
the target level of the next group the first group would be
programmed to terminate. This would maintain a constant, continuous
level of stimulation that is shared amongst the programmed groups.
The cycle repeats until the end of the sleep session.
[0212] The load of maintaining muscle tone and position is shared
by all of the functional groups. In one embodiment, each contact is
pulsed at different or overlapping intervals (FIGS. 10A and 10B).
This prevents or minimizes fatigue by alternately resting and
stimulating targeted muscle groups and thereby preventing the
tongue from falling into a position that can cause apnea or
hypopnea. The predetermined amount of time that a group is
programmed to stay on may be determined by observing the tongue at
a chosen stimulation frequency and determining how long the
resulting contraction can be maintained before fatigue causes the
resulting position control to degrade.
[0213] In another embodiment, each contact is pulsed at a fraction
of the total target frequency (discussed below) and out of phase
with each of the other contacts (FIG. 10B). For example, if the
target frequency is 30 pps, each contact is pulsed at 10 pps with
the other contacts interleaved between each pulse rather than
pulsing each contact for an interval at 30 pps as shown in FIG. 9.
In such an embodiment, the pulses are out of phase with one another
so each contact pulses sequentially in a nearly continuous pattern
to share the stimulation load of the contacts. Spreading the load
over each of the contacts allows a much lower frequency to be used
that allows for near constant muscle stimulation without or
substantially without fatigue or diminished positioning.
[0214] Using multiple functional groups, in either a staggered or
interleaved configuration, allows the tongue to be continuously or
near-continuously stimulated, maintaining the tongue in a desired
position even though each functional group only stimulates its
neural population for a portion of a stimulation cycle. This
exemplary method maintains continuous or near-continuous
stimulation by load sharing between multiple functional groups,
with each group--activating one or more desired tongue muscle. This
method has the additional feature that group ramps would occur once
for a sleep session and that stimulation levels would be maintained
at their target levels, reducing the complexity of stimulation
control.
[0215] Stimulus Ramping
[0216] FIGS. 9 and 52 illustrate an exemplary stimulus ramp. In
certain exemplary embodiments, a stimulus ramp is used to maximize
patient comfort and/or for prevention of arousal. With a patient
who is awake, stimulation producing a noticeable, smooth
contraction is important. In treating a sleeping patient suffering
from obstructive sleep apnea, however, achieving the smallest
contraction necessary to treat the condition--without waking the
patient--is important. The contraction only needs to be sufficient
to move the tongue forward enough or make airway (the pharyngeal
wall) tense/rigid enough to prevent an apnea event from occurring,
and may not even be visible to the naked eye.
[0217] The sensation of the applied electrical pulses to the nerve,
and the accompanying involuntary movement of the tongue generates
is, at best, unnatural. In certain exemplary embodiments, the goal
is to minimize sensation to a level acceptable to the patient. In
certain exemplary embodiments, stimulus is gradually ramped up to
ease the patient up to a target stimulus level. Stimulus starts at
a threshold level, with stimulus magnitude slowly increasing to the
target level. As is known to those skilled in the art, either
stimulus magnitude or phase duration may be modulated to achieve
control between the threshold and target levels.
[0218] If stimulation were immediately applied without a ramp, the
stimulation could awaken or arouse the patient and adversely affect
their sleep, just as an apnea event would. The exemplary
embodiments of the present invention therefore employ the method of
amplitude magnitude ramps at the start of stimulation to address
this issue. The duration of this ramp is often several seconds long
so that the change is gradual and the patient is able to adjust to
the delivery of stimulation to the tissue.
[0219] In certain exemplary embodiments, an amplitude ramp of
approximately 5 to 10 seconds is selected, (i.e., where stimulus
increases to a desired level in 5 to 10 seconds). Stimulation is
started at the threshold amplitude and slowly increased to the
target amplitude until significant tongue movement is observed.
Significant movement is defined as at least one movement that
decreases airway resistance or results in increased airway air
flow, or which maintains tongue muscle tone. The movement of the
tongue and its affect on the airway can be observed with an
endoscope placed in the nasal cavity, by use of fluoroscopy, or by
observing the front of the oral cavity and the overall position of
the tongue. Other ways of observing known to those skilled in the
art can be used without departing from the scope of the invention.
This is the operational point or targeted stimulation level that
will be used if it is decided that this contact is to be included
in the programmed stimulation protocol designed to affect the
tongue during the sleeping session.
[0220] Frequency Adjustment
[0221] Another factor affecting the perceived comfort for the
patient is the frequency of a pulsatile waveform. Stimulating at a
very low frequency, such as approximately 1 to 3 pps, allows the
easy identification of an amplitude threshold as distinct twitches
or brief contractions of the muscle. These twitches or contractions
are readily discernible, and often can be felt by the patient.
Increasing the frequency to a sufficiently fast rate results in the
fusion of the twitches (referred to as tetanus) and the relaxation
between them into a smooth muscle contraction. This also quite
often results in a sensation that is more comfortable for the
patient, and is it is generally more comfortable for the patient as
the frequency increases. Above a certain frequency, however, the
sensation may again become uncomfortable, possibly associated with
the level of work associated with the increased number of muscle
contractions. This comfort level must be experimentally determined
and it can vary from patient to patient. The amplitude is then
increased to the target amplitude to sufficiently position the
tongue as described above.
[0222] Delayed Stimulation Onset
[0223] In certain embodiments, stimulation is delayed until after a
patient is asleep. By monitoring a patient in a sleep laboratory
and/or by interviewing a patient's partner, it can be determined
how much time is necessary to delay stimulation onset. In certain
embodiments, this delay is programmed into the IPG 1370. When the
patient initiates a sleep session of the device, the IPG 1370 then
waits for the programmed delay period to complete before applying
stimulation to the Hypoglossal nerve. The delay for stimulation
onset may also be associated with the point at which sleep apnea
begins to appear in the sleep cycle of the patient. If apneas do
not begin to appear until the deepest stage of sleep (rapid eye
movement or REM) then it may be advantageous to delay the onset of
stimulation well past the point at which the patient begins to
sleep and until just before the point at which apnea becomes
apparent. The stimulation may then be applied for a predetermined
period of time and/or until the IPG 1370 is deactivated. In one
embodiment, the IPG 1370 is activated and deactivated via the RCC
2272.
[0224] Delaying stimulation onset, using frequency and/or amplitude
modulation for a gradual ramp up or down to a desired stimulation
all reduce the chances of arousing the patient in the middle of
sleep, making tonic stimulation more likely to succeed. In certain
treatment methods, sleeping medication for those patients who may
be sensitive to the electrical stimulation activated movement may
increase the chances of successful treatment.
[0225] In an exemplary embodiment, a stimulation amplitude
threshold is determined by initially setting a low stimulation
frequency between 1 and 3 pps. A typical waveform such as 200 .mu.s
cathodic phase duration, 50 .mu.s interphase interval and 800 .mu.s
anodic phase duration is selected (the andodic phase amplitude
would then be one fourth the amplitude of the cathodic phase
amplitude), and then waveform amplitude is slowly increased from
approximately 0 .mu.A up to a level at which the tongue muscle can
be seen to twitch with each pulse, or when the patient begins to
feel the pulsatile sensation. This is the point at which the
electrical stimulation is just enough to excite fibers within the
nerve bundle. This setting is noted as the threshold amplitude and
stimulation is stopped.
[0226] Each contact may be further tested to see what frequency
should be used for initial stimulation. Experience and literature
evidence suggests that the higher the frequency, the more
comfortable the sensation of electrical stimulation is for the
patient. The more comfortable the stimulation, the less likely the
patient will be awakened. In these exemplary embodiments,
stimulation starts at a frequency above the target frequency, and
gradually decreases to the preferred target frequency. A preferred
frequency is a frequency comfortable to the patient that produces a
desired stimulus response. In one embodiment, one or more contacts
deliver the target frequency at different intervals (FIGS. 9 and
10A). In another embodiment, the target frequency is generally
divided by the number of contacts and is spread or interleaved over
the contacts (FIG. 10C).
[0227] Determining the starting frequency is performed by setting
the contact stimulation parameters to those determined for target
stimulation and including an amplitude ramp, typically 5 to 10
seconds. Stimulation is started and the frequency is slowly
adjusted upwards, checking with the patient for comfort. It may be
necessary to reduce amplitude with higher frequency in order to
maintain comfort but if so, then the target frequency should be
checked again at the lower amplitude to verify that it still
produces a functional movement.
[0228] Once all of the contacts have been evaluated a common higher
frequency should be selected which is the lowest of all of the
contact frequencies. The frequency is set to the lowest contact
frequency that achieves a response resulting in increased airway
airflow or decreased airway resistance. Using the lowest frequency
increases the time until fatigue occurs. This frequency is used as
the startup frequency to be used after the delay from the beginning
of the session has completed.
[0229] Exemplary Method of Use
[0230] The section below describes an exemplary method of patient
use of the system. In the method described, the patient uses a
remote control and charger 2272 (RCC) to operate and maintain the
system. In this embodiment, the combination remote control and
charger has a mini-USB connector, which charges an internal battery
in the RCC 2272. Optionally the RCC 2272 may rest in a cradle kept
on the patient's nightstand. The cradle would have spring loaded
contacts, which make connection to the RCC 2272 much like a
cordless phone to charge the RCC battery. The cradle may also use a
mini-USB connector to attach to a wall mounted power supply.
[0231] To start a sleep session the patient uses the RCC 2272 to
activate the implantable pulse generator (IPG). In certain
embodiments, the patient first activates the RCC 2272, which then
attempts to communicate to the IPG 1370. If the RCC 2272 is unable
to communicate with the IPG 1370, the RCC 2272 indicates to the
patient (by, for example, beeping three times and illuminating an
LED) that the RCC 2272 could not communicate with the IPG 1370.
This might mean that the IPG 1370 is so low in battery power that
the IPG 1370 needs to be charged, or that the RCC 2272 is not close
enough to communicate to the IPG 1370. If the IPG 1370 needs
charging then the patient would attach a charge coil and cable to
the RCC 2272, place the coil over the IPG 1370, press the charge
switch on the RCC 2272 and charge the IPG 1370 until the battery of
the IPG 1370 has enough energy to stimulate, up to two or three
hours for a completely depleted IPG 1370.
[0232] If the IPG 1370 has enough energy to communicate and is in
range of the RCC 2272, then the RCC 2272 would acquire the
stimulation status and battery level. Assuming that this is the
start of a normal sleep session the IPG 1370 would have been in the
"Stimulation Off" state. The RCC 2272 then reports the battery
status by indicating the battery LED in the green state for full,
amber for medium and red for low. If the battery level is full or
medium then the IPG 1370 would be instructed to start a sleep
session and the IPG 1370 On/Off LED would be set to green. If the
battery were low then the IPG 1370 would be instructed to stay off
and the IPG On/Off LED would be set to red. The patient could then
charge the IPG 1370 to use for one or more sleep sessions.
[0233] Once a sleep session starts, the IPG 1370 initiates a
startup delay period allowing the patient to fall asleep before
stimulation starts. At the end of this delay, stimulation starts
with the first functional group, ramping amplitude from threshold
to target amplitude and then holding for the remainder of its
On-Time duration. In interleaved or staggered mode, all groups
would start simultaneously, utilizing their individual ramp up
parameters, then maintain stimulation levels at the target levels
for the duration of the sleep period. At the beginning of
stimulation, the stimulation frequency is set to the startup
frequency determined during programming. This frequency would be
ramped downwards to the target frequency for a programmed duration
after which the target frequency is used.
Alternative Embodiments
[0234] FIGS. 53 through 62 depict alternative embodiments of the
OSA system that may be considered as alternatives to the system
elements described above. FIG. 53 depicts the various elements that
could be alternatively and/or additionally used: a small charger
that may or may not have a user interface, a keyfob 5380 that may
or may not have a user interface, and a remote control that may
take advantage of commercially available devices, such as a
hand-held computer, smart phone 5382, or similar commercially
available device, which may provide useful wireless interfaces and
user interfaces for the OSA application.
[0235] FIG. 54 depicts a pair of exemplary devices which could act
as remote controls. On the left is the Apple iPod.RTM. Touch 5382a,
and on the right is a Blackberry.RTM. Smartphone 5382b. Both
devices have excellent user interfaces, have wireless technology
support to allow communication to the various OSA system elements,
and are readily available and understandable by many of the
patients that could use the OSA system.
[0236] FIG. 55 depicts a keyfob telemetry relay that could be used
to provide a communication bridge between the remote control and
the IPG 1370. Standard wireless technologies, such as
Bluetooth.RTM. or Wi-Fi could be implemented within the keyfob
relay, along with MICS telemetry for communication to the IPG 1370.
The keyfob relay need only be within telemetry range of the IPG
1370 and the remote control, for instance, in the pocket of the
patient. Since the keyfob 5380 may only be required as a relay
device, current consumption may be quite low, and the keyfob 5380
could run off a small lithium primary coin cell battery that would
only need to be changed after rather long periods of time. Since
the keyfob 5380 may only act as a relay, the keyfob 5380 may not
need a user interface (such as a keyboard or LED display) at all,
but if desired, either or both of these could be added.
Alternatively, the remote control could allow the insertion of a
hardware relay function to provide MICS telemetry directly from the
remote control to the IPG.
[0237] FIG. 56 depicts an exemplary charger and charger coil. This
element may also have no user interface such as a keyboard or LED
displays, but they could be added if desired.
[0238] FIG. 57 illustrates a potential use model for the
alternative embodiments for use by the clinician in programming or
interrogating the OSA system. The aCM could be the same as that
described previously, and a wireless interface such as
Bluetooth.RTM. or Wi-Fi could be used to communicate with the
charger. The charger could then communicate with the IPG 1370 using
MICS telemetry, or if that were not possible for some reason, then
the charger coil (CC) could be used as a backup telemetry channel.
Alternatively, as depicted in FIG. 58, the aCM could communicate
through the keyfob relay to the IPG 1370. Using Bluetooth.RTM.,
Wi-Fi or some other industry standard wireless interface between
the aCM and the keyfob 5380, and MICS telemetry between the keyfob
relay and the IPG 1370, communication could be provided to program
or interrogate the IPG 1370 in the OSA system. Alternatively, the
aCM computer could allow the insertion of a hardware relay function
to provide MICS telemetry directly from the aCM to the IPG.
[0239] FIG. 58 illustrates the use of the iPhone.RTM. (or
SmartPhone) 5382 as the remote control to perform routine
operations in the OSA system. The remote control would communicate
with the keyfob 5380 which would relay the communication with the
IPG 1370 via MICS telemetry. FIG. 60 illustrates that the charger
and telemetry coil could take the place of the keyfob 5380 by
providing MICS telemetry or secondary inductive link telemetry
should the MICS telemetry be non-functional for some reason.
[0240] FIG. 59 illustrates the use of the simplified charger and
charger coil for charging of the IPG 1370. The charger would
normally be placed upon a cradle or docking station 5378 to
re-charge its own internal battery supply, possibly a lithium
polymer battery. A microcontroller inside of the charger could
detect when the patient removes the charger from its cradle and
begin to automatically search for the IPG 1370. Once the IPG 1370
is located and it has determined that the charger coil is placed
over the IPG 1370 it may then proceed to charge the IPG 1370 as
described previously. If the charger did not find the IPG 1370
within say five minutes of removal from the cradle or docking
station 5378, then if the charger had a membrane switch panel or
other user interface it could be independently commanded to start
or stop the charging process. Again, alternatively, and as depicted
in FIG. 62, the remote control could be used to communicate with
the charger to start and/or stop the charging process.
[0241] It shall be understood that these and many other embodiments
of the OSA system could be implemented that would provide the OSA
treatment, maintain the operation of the OSA system, and provide
information to the patient and clinician for routine use,
programming and maintenance of the OSA sleep therapy.
[0242] It will be appreciated by those skilled in the art that
changes could be made to the exemplary embodiment shown and
described above without departing from the broad inventive concept
thereof It is understood, therefore, that this invention is not
limited to the exemplary embodiment shown and described, but it is
intended to cover modifications within the spirit and scope of the
present invention as defined by the claims. For example, "an
embodiment," and the like, may be inserted at the beginning of
every sentence herein where logically possible and appropriate such
that specific features of the exemplary embodiment may or may not
be part of the claimed invention and combinations of disclosed
embodiments may be combined. Unless specifically set forth herein,
the terms "a", "an" and "the" are not limited to one element but
instead should be read as meaning "at least one".
[0243] Further, to the extent that the method does not rely on the
particular order of steps set forth herein, the particular order of
the steps should not be construed as limitation on the claims. The
claims directed to the method of the present invention should not
be limited to the performance of their steps in the order written,
and one skilled in the art can readily appreciate that the steps
may be varied and still remain within the spirit and scope of the
present invention.
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