U.S. patent application number 17/371612 was filed with the patent office on 2021-10-28 for external pacing device with discomfort management.
The applicant listed for this patent is ZOLL MEDICAL CORPORATION. Invention is credited to Rachel H. Carlson, Gregory R. Frank, Gary A. Freeman, Thomas E. Kaib, Jason T. Whiting.
Application Number | 20210330973 17/371612 |
Document ID | / |
Family ID | 1000005708452 |
Filed Date | 2021-10-28 |
United States Patent
Application |
20210330973 |
Kind Code |
A1 |
Whiting; Jason T. ; et
al. |
October 28, 2021 |
EXTERNAL PACING DEVICE WITH DISCOMFORT MANAGEMENT
Abstract
A method of controlling discomfort of a patient during external
pacing by an external medical device includes detecting a cardiac
condition of the patient; receiving, via a user interface,
discomfort information descriptive of the discomfort experienced by
the patient; determining from the discomfort information whether
the patient is conscious or unconscious; responsive to determining
from the discomfort information that the patient is unconscious,
executing, via at least one therapy electrode disposed on the
patient, at least one pacing routine, the at least one pacing
routine being associated with the cardiac condition; and responsive
to determining from the discomfort information that the patient is
conscious, adjusting at least one characteristic of the at least
one pacing routine.
Inventors: |
Whiting; Jason T.;
(Gibsonia, PA) ; Kaib; Thomas E.; (Irwin, PA)
; Carlson; Rachel H.; (Falls Creek, PA) ; Frank;
Gregory R.; (Mt. Lebanon, PA) ; Freeman; Gary A.;
(Waltham, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZOLL MEDICAL CORPORATION |
Chelmsford |
MA |
US |
|
|
Family ID: |
1000005708452 |
Appl. No.: |
17/371612 |
Filed: |
July 9, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16407844 |
May 9, 2019 |
11097107 |
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17371612 |
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15196801 |
Jun 29, 2016 |
10328266 |
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16407844 |
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15079294 |
Mar 24, 2016 |
9675804 |
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15196801 |
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14610600 |
Jan 30, 2015 |
9320904 |
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15079294 |
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13907523 |
May 31, 2013 |
8983597 |
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14610600 |
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61653889 |
May 31, 2012 |
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62185940 |
Jun 29, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/361 20210101;
A61N 1/36014 20130101; A61N 1/3925 20130101; A61N 1/3625 20130101;
A61B 2562/17 20170801; A61N 1/3621 20130101; A61B 5/6831 20130101;
A61N 1/0484 20130101; A61N 1/0456 20130101; A61B 5/282 20210101;
A61N 1/046 20130101 |
International
Class: |
A61N 1/362 20060101
A61N001/362; A61B 5/00 20060101 A61B005/00; A61N 1/39 20060101
A61N001/39; A61N 1/04 20060101 A61N001/04; A61N 1/36 20060101
A61N001/36; A61B 5/361 20210101 A61B005/361; A61B 5/282 20210101
A61B005/282 |
Claims
1. A method of controlling discomfort of a patient during external
pacing by an external medical device, the method comprising:
detecting a cardiac condition of the patient; receiving, via a user
interface, discomfort information descriptive of the discomfort
experienced by the patient; determining from the discomfort
information whether the patient is conscious or unconscious;
responsive to determining from the discomfort information that the
patient is unconscious, executing, via at least one therapy
electrode disposed on the patient, at least one pacing routine, the
at least one pacing routine being associated with the cardiac
condition; and responsive to determining from the discomfort
information that the patient is conscious, adjusting at least one
characteristic of the at least one pacing routine.
2. The method of claim 1, further comprising adjusting the at least
one characteristic of the at least one pacing routine to an upper
bound of a range of values responsive to determining from the
discomfort information that the patient is unconscious.
3. The method of claim 1, wherein adjusting the at least one
characteristic of the at least one pacing routine includes
adjusting at least one of an amplitude of pacing pulses, a width of
the pacing pulses, a rate of the pacing pulses, a waveform of the
pacing pulses, a period of the pacing pulses, a duty cycle of the
pacing pulses, or a ramp time constant of the pacing pulses.
4. The method of claim 1, wherein receiving the discomfort
information descriptive of the discomfort experienced by the
patient comprises detecting an amount of pressure exerted by the
patient on an element of the user interface.
5. The method of claim 4, wherein receiving the discomfort
information descriptive of the discomfort experienced by the
patient comprises determining a duration of time the element of the
user interface remains actuated.
6. The method of claim 4, wherein detecting the amount of pressure
exerted by the patient on the element of the user interface
comprises detecting the amount of pressure exerted by the patient
on a strain gauge, a force sensor, a piezoelectric transducer, or a
rotating spring-loaded dial.
7. The method of claim 1, wherein the user interface further
comprises a force sensor, the method further comprising detecting,
by the force sensor, a force applied by the user squeezing at least
one surface of the force sensor.
8. The method of claim 1, wherein adjusting at least one
characteristic of the at least one pacing routine comprises
optimizing the at least one characteristic along a scale comprising
at least one of a linear scale, a logarithmic scale, or an
exponential scale.
9. The method of claim 8, wherein adjusting at least one
characteristic of the at least one pacing routine comprises
optimizing the at least one characteristic at least in part by
executing a regression analysis using historical values of the at
least one characteristic
10. The method of claim 1, wherein the cardiac condition comprises
at least one of bradycardia and asystole.
11. The method of claim 1, wherein executing the at least one
pacing routine comprises executing at least one of fixed rate
pacing, fixed energy pacing, adjustable rate pacing, and capture
management pacing.
12. The method of claim 1, further comprising executing a baseline
process during an initial fitting of the external medical device to
the patient.
13. The method of claim 12, wherein executing the baseline process
comprises determining a range of values for a discomfort parameter
corresponding to the at least one pacing routine.
14. The method of claim 12, wherein executing the baseline process
further comprises setting the at least one characteristic of the at
least one pacing routine to an appropriate level based on a
physiological condition of the patient.
15. A non-transitory computer readable medium storing sequences of
instructions executable by at least one processor, the sequences of
instructions instructing the at least one processor to control
discomfort of a patient during external pacing by an external
medical device, the sequences of instructions including
instructions to: detect a cardiac condition of the patient;
receive, via a user interface, discomfort information descriptive
of the discomfort experienced by the patient; determine from the
discomfort information whether the patient is conscious or
unconscious; responsive to determining from the discomfort
information that the patient is unconscious, execute, via at least
one therapy electrode disposed on the patient, at least one pacing
routine, the at least one pacing routine being associated with the
cardiac condition; and responsive to determining from the
discomfort information that the patient is conscious, adjust at
least one characteristic of the at least one pacing routine.
16. The non-transitory computer readable medium of claim 15,
wherein the sequences of instructions further include instructions
to adjust the at least one characteristic of the at least one
pacing routine to an upper bound of a range of values responsive to
determining from the discomfort information that the patient is
unconscious.
17. The non-transitory computer readable medium of claim 15,
wherein the sequences of instructions further include instructions
to adjust the at least one characteristic of the at least one
pacing routine includes adjusting at least one of an amplitude of
pacing pulses, a width of the pacing pulses, a rate of the pacing
pulses, a waveform of the pacing pulses, a period of the pacing
pulses, a duty cycle of the pacing pulses, or a ramp time constant
of the pacing pulses.
18. The non-transitory computer readable medium of claim 15,
wherein the instructions to receive the discomfort information
descriptive of the discomfort experienced by the patient comprise
instructions to detect an amount of pressure exerted by the patient
on an element of the user interface.
19. The non-transitory computer readable medium of claim 15,
wherein the instructions to adjust the at least one characteristic
of the at least one pacing routine comprise instructions to
optimize the at least one characteristic along a scale comprising
at least one of a linear scale, a logarithmic scale, or an
exponential scale.
20. The non-transitory computer readable medium of claim 19,
wherein the instructions to adjust the at least one characteristic
of the at least one pacing routine comprise instructions to
optimize the at least one characteristic at least in part by
executing a regression analysis using historical values of the at
least one characteristic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a Continuation of U.S. patent
application Ser. No. 16/407,844, titled "EXTERNAL PACING DEVICE
WITH DISCOMFORT MANAGEMENT," filed on May 9, 2019, which is a
Continuation of U.S. patent application Ser. No. 15/196,801, titled
"EXTERNAL PACING DEVICE WITH DISCOMFORT MANAGEMENT," filed on Jun.
29, 2016, now U.S. Pat. No. 10,328,266, which is a
Continuation-in-Part of U.S. patent application Ser. No.
15/079,294, titled "MEDICAL MONITORING AND TREATMENT DEVICE WITH
EXTERNAL PACING," filed on Mar. 24, 2016, now U.S. Pat. No.
9,675,804, which is a Continuation of U.S. patent application Ser.
No. 14/610,600, titled "MEDICAL MONITORING AND TREATMENT DEVICE
WITH EXTERNAL PACING," filed on Jan. 30, 2015, now U.S. Pat. No.
8,983,597, which is a Continuation of U.S. patent application Ser.
No. 13/907,523, titled "MEDICAL MONITORING AND TREATMENT DEVICE
WITH EXTERNAL PACING," filed on May 31, 2013, now U.S. Pat. No.
8,983,597, which claims priority under 35 U.S.C. .sctn. 119(e) to
U.S. Provisional Application Ser. No. 61/653,889, titled
"NONINVASIVE AMBULATORY MONITORING AND TREATMENT DEVICE WITH
EXTERNAL PACING," filed on May 31, 2012, each of which is hereby
incorporated herein by reference in its entirety. U.S. patent
application Ser. No. 15/196,801 also claims the benefit of U.S.
Provisional Patent Application Ser. No. 62/185,940, titled
"EXTERNAL PACING DEVICE WITH DISCOMFORT MANAGEMENT," filed on Jun.
29, 2015, which is hereby incorporated by reference in its
entirety.
BACKGROUND
Technical Field
[0002] The present disclosure is directed to noninvasive ambulatory
medical devices, and more particularly, to a non-invasive medical
monitoring and treatment device that is capable of externally
pacing the heart of a patient wearing the device.
Discussion
[0003] Cardiac arrest and other cardiac health ailments are a major
cause of death worldwide. Various resuscitation efforts aim to
maintain the body's circulatory and respiratory systems during
cardiac arrest in an attempt to save the life of the victim. The
sooner these resuscitation efforts begin, the better the victim's
chances of survival.
[0004] To protect against cardiac arrest and other cardiac health
ailments, some at-risk patients may use a wearable defibrillator,
such as the LifeVest.RTM. wearable cardioverter defibrillator
available from ZOLL.RTM. Medical Corporation of Chelmsford, Mass.
To remain protected, the patient wears the device continuously or
nearly continuously while going about their normal daily
activities, while awake, and while asleep.
SUMMARY
[0005] Some aspects and embodiments of the present disclosure
relate to controlling patient discomfort during administration of
external pacing to the heart. For example, the systems and
techniques described herein can be used in various medical
monitoring and/or treatment devices. In some examples, the medical
devices can be external or non-invasive, e.g., in contrast to
internal or invasive devices, such as implantable medical devices.
In some examples, a medical device as described herein can be
bodily-attached, e.g., at least a portion of the device (other than
its electrodes in the case of a defibrillator, cardioverter or
pacer) is removably attached to the body of a patient, such as by
mechanical coupling (for example, by a wrist strap, cervical
collar, bicep ring), adhesion (for example, by an adhesive gel
intermediary), suction, magnetism, fabric or other flexible
material (for example, by straps or integration into a garment) or
other body mounting features not limited by the aforementioned
examples. In some examples, such coupling elements can hold the
device in a substantially fixed position with respect to the body
of the patient. In some examples, a medical device as described
herein can be ambulatory, e.g., the device is capable of and
designed for moving with the patient as the patient goes about his
or her daily routine.
[0006] One example of a medical monitoring and treatment device
suited for use with the systems and techniques described herein is
the LifeVest.RTM. Wearable Cardioverter Defibrillator available
from ZOLL.RTM. Medical Corporation of Chelmsford, Mass. A medical
monitoring and treatment device can provide lifesaving
defibrillation treatment to a patient suffering a treatable form of
cardiac arrhythmia such as ventricular fibrillation (VF) or
ventricular tachycardia (VT). Applicants have appreciated that such
a medical monitoring and treatment device can be configured to
perform a variety of different types of cardiac pacing to treat a
wide variety of different cardiac arrhythmias, such as bradycardia,
tachycardia, an irregular cardiac rhythm, and asystole (including
asystole after a therapeutic shock). Applicants have further
appreciated that, in other embodiments, a medical monitoring and
treatment device can be configured to perform pacing to treat
pulseless electrical activity. In accordance with an aspect of the
present disclosure, the medical monitoring and treatment device can
be configured to pace the heart of the patient at a fixed energy
level (e.g., fixed current, fixed voltage, etc.) and pulse rate, to
pace the heart of the patient on demand with a fixed energy level
and an adjustable rate responsive to the detected intrinsic
activity level of the patient's heart, or to pace the heart of the
patient using capture management with an adjustable energy level
and adjustable rate responsive to the detected intrinsic rate of
the patient's heart and the detected response of the patient's
heart to pacing, including both on a beat-by-beat basis and as
analyzed over other various time intervals.
[0007] In some examples, the pacing parameters described above may
be adjusted to lessen any discomfort experienced by the patient
during pacing. In various examples, the patient can self-manage the
administration of the pacing routine based on his or her own
tolerance of the discomfort. In these examples, the medical
monitoring and treatment device may begin pacing a patient using
either default pacing parameters or baseline pacing parameters
tailored to discomfort tolerances of the patient. The baseline
pacing parameters may be configured by executing the medical
monitoring and treatment device in a baseline mode during an
initial fit of the device to the patient or by executing (or
re-executing) the medical monitoring and treatment device in a
baseline mode during subsequent operation of the device. It is
appreciated that the pacing parameters may control, for example,
the administration of pacing pulses, various characteristics of the
pacing pulses, the administration of TENS pulses, and/or various
characteristics of the TENS pulses.
[0008] In one aspect of the present invention, an external medical
device is provided comprising at least one therapy electrode
configured to be disposed on a patient, and a treatment manager,
coupled to the at least one therapy electrode, configured to
execute a baseline process to determine at least one of a range of
values for a discomfort parameter corresponding to at least one
pacing routine and a patient discomfort threshold value
corresponding to the at least one pacing routine, detect a cardiac
condition of the patient, execute the at least one pacing routine,
the at least one pacing routine being associated with the cardiac
condition, monitor the discomfort parameter associated with the
patient during execution of the at least one pacing routine,
determine whether the discomfort parameter transgresses the at
least one of the range of values and the patient discomfort
threshold value, and adjust at least one characteristic of the at
least one pacing routine in response to determining that the
discomfort parameter transgresses the at least one of the range of
values and the patient discomfort threshold value. In one
embodiment, the device further comprises a user interface for
receiving discomfort information regarding the patient in
connection with the at least one pacing routine. In one embodiment,
the discomfort parameter is based on at least one of the discomfort
information received from a user via the user interface and
information automatically detected by at least one sensor distinct
from the user interface. In another embodiment, the user interface
comprises at least one of a touch screen, a button, a microphone
for receiving audible commands, a strain gauge, a force sensor, a
piezoelectric transducer, and a rotating spring-loaded dial.
[0009] In an alternative embodiment, the treatment manager is
configured to receive the discomfort information descriptive of the
discomfort parameter with reference to an amount of pressure
exerted by the user on an element of the user interface. In one
embodiment, the treatment manager is configured to determine a
present value of the discomfort parameter during execution of the
at least one pacing routine based on at least one of an amount of
pressure detected by the user interface and a duration of time the
element of the user interface remains actuated. In one embodiment,
the element of the user interface is at least one of a quartz
sensor, a ceramic force sensor, and a piezoelectric transducer. In
another embodiment, the user interface comprises a force sensor
configured to detect a force applied by the user squeezing at least
one surface of the force sensor. In yet another embodiment, the at
least one sensor includes at least one of a motion sensor, an audio
sensor, a physiological sensor, an electrode, an accelerometer, and
a blood pressure sensor.
[0010] In one embodiment, the treatment manager is configured to
receive the discomfort information regarding the patient responsive
to selection of an element of the user interface. In one
embodiment, the user interface displays a discomfort scale and the
element includes a selectable point on the discomfort scale. In one
embodiment, the discomfort scale is at least one of numeric and
image-based. In one embodiment, the user interface includes a touch
screen configured to display a plurality of selectable points on
the discomfort scale. In another embodiment, the selection includes
at least one of a touch and an utterance. In an alternative
embodiment, the utterance includes at least one predefined
word.
[0011] In another embodiment, the treatment manager is further
configured to detect, via a touch detector, a touch having a
duration, and determine whether the discomfort parameter
transgresses the patient discomfort threshold value based on the
duration. In one embodiment, the treatment manager is further
configured to adjust at least one characteristic of the at least
one pacing routine in response to determining that a value of the
discomfort parameter is equal to or transgresses the patient
discomfort threshold value. In one embodiment, the at least one
characteristic of the at least one pacing routine includes at least
one of an amplitude of pacing pulses, a width of the pacing pulses,
a rate of the pacing pulses, a waveform of the pacing pulses, a
period of the pacing pulses, a duty cycle of the pacing pulses, and
a ramp time constant of the pacing pulses. In another embodiment,
the cardiac condition comprises at least one of bradycardia,
tachycardia, asystole, pulseless electrical activity, and erratic
heart rate.
[0012] In one embodiment, the at least one pacing routine comprises
at least one of fixed rate pacing, fixed energy pacing, adjustable
rate pacing, and capture management pacing. In one embodiment, the
discomfort parameter is indicative of a level of discomfort
experienced by the patient during the at least one pacing routine.
In one embodiment, the treatment manager is configured to execute
the baseline process during an initial fitting of the external
medical device to the patient. In another embodiment, the treatment
manager is further configured to optimize at least one
characteristic of the at least one pacing routine in response to
the determination that the discomfort parameter transgresses the at
least one of the range of values and the patient discomfort
value.
[0013] In an alternative embodiment, the treatment manager is
configured to optimize the at least one characteristic along a
scale selected from at least one of a linear scale, a logarithmic
scale, and an exponential scale. In one embodiment, the treatment
manager is configured to optimize the at least one characteristic
at least in part by executing a regression analysis using
historical values of the at least one characteristic. In one
embodiment, the treatment manager is further configured to adjust
the patient discomfort threshold value based on the patient's state
of consciousness. In another embodiment, the device further
comprises a transcutaneous electrical nerve stimulation unit
configured to provide background stimulation to the patient during
execution of the at least one pacing routine.
[0014] In one embodiment, executing the baseline process further
comprises setting at least one characteristic of the at least one
pacing routine to an appropriate level based on a physiological
condition of the patient. In one embodiment, the appropriate level
is determined based on typical impedance values for an adult or
child. In another embodiment, executing the baseline process
further comprises setting at least one characteristic of the at
least one pacing routine with reference to pacing parameter
baselines associated with multiple patients.
[0015] In another aspect of the present invention, a method of
controlling patient discomfort during pacing by an external medical
device is provided comprising determining, during a baseline
process, at least one of a range of values for a discomfort
parameter corresponding to at least one pacing routine of the
external medical device and a patient discomfort threshold value
corresponding to the at least one pacing routine, detecting a
cardiac condition of the patient, the cardiac condition being
associated with the at least one pacing routine, executing the at
least one pacing routine, monitoring the discomfort parameter of
the patient during execution of the at least one pacing routine,
and adjusting, responsive to the discomfort parameter transgressing
at least one of the range of values and the patient discomfort
threshold value, at least one characteristic of the at least one
pacing routine. In one embodiment, the method further comprises
receiving, via a user interface, discomfort information regarding
the patient in connection with the at least one pacing routine. In
one embodiment, the discomfort parameter is based on at least one
of the discomfort information received from a user via the user
interface and information automatically detected by at least one
sensor distinct from the user interface. In another embodiment, the
method further comprises receiving the discomfort information from
a user selection of an element of the user interface.
[0016] In one embodiment, the user interface comprises a touch
sensor, the method further comprising detecting, via the touch
sensor, a touch having a duration, and determining whether the
discomfort parameter is equal to or transgresses the patient
discomfort threshold value with reference to the duration. In
another embodiment, executing the baseline process further
comprises setting at least one characteristic of the at least one
pacing routine to an appropriate level based on at least one of a
physiological condition of the patient, typical impedance values
for an adult or child, and pacing parameter baselines associated
with multiple patients.
[0017] In an alternative aspect of the present invention, a
bodily-attached ambulatory medical device is provided comprising at
least one therapy electrode configured to be disposed on a patient,
and a treatment manager, coupled to the at least one therapy
electrode, configured to execute a baseline process to determine at
least one of a range of values for a discomfort parameter
corresponding to at least one pacing routine and a patient
discomfort threshold value corresponding to the at least one pacing
routine, detect a cardiac condition of the patient, and execute the
at least one pacing routine, the at least one pacing routine being
associated with the cardiac condition and having at least one
characteristic configured for the patient's tolerance for
discomfort based on the at least one of the range of values for the
discomfort parameter and the patient discomfort threshold
value.
[0018] Still other aspects, embodiments, and advantages of these
exemplary aspects and embodiments are discussed in detail below.
Moreover, it is to be understood that both the foregoing
information and the following detailed description are merely
illustrative examples of various aspects and embodiments of the
present disclosure, and are intended to provide an overview or
framework for understanding the nature and character of the claimed
aspects and embodiments. Any embodiment or example disclosed herein
may be combined with any other embodiment or example in any manner
consistent with at least one of the aspects disclosed herein, and
references to "an embodiment," "an example," "some embodiments,"
"some examples," "an alternate embodiment," "an alternate example,"
"various embodiments," "various examples," "one embodiment," "one
example," "at least one embodiment," "at least one example," "this
and other embodiments," "this and other examples," or the like are
not necessarily mutually exclusive and are intended to indicate
that a particular feature, structure, or characteristic described
in connection with the embodiment may be included in at least one
embodiment. The appearance of such terms herein is not necessarily
all referring to the same embodiment.
[0019] Furthermore, in the event of inconsistent usages of terms
between this document and documents incorporated herein by
reference, the term usage in the incorporated references is
supplementary to that of this document; for irreconcilable
inconsistencies, the term usage in this document controls. In
addition, the accompanying drawings are included to provide
illustration and a further understanding of the various aspects and
examples, and are incorporated in and constitute a part of this
specification. The drawings, together with the remainder of the
specification, serve to explain principles and operations of the
described and claimed aspects and examples.
BRIEF DESCRIPTION OF DRAWINGS
[0020] The accompanying drawings are not intended to be drawn to
scale. In the drawings, components that are identical or nearly
identical may be represented by a like numeral. For purposes of
clarity, not every component is labeled in every drawing. In the
drawings:
[0021] FIG. 1 is an illustration of one example of a wearable
medical device;
[0022] FIGS. 2A-2B are illustrations of one example of a medical
device controller for an ambulatory medical device;
[0023] FIG. 3 is a functional schematic of one example of a medical
device controller;
[0024] FIG. 4 is a flow diagram of one example baseline generation
process;
[0025] FIG. 5 is a flow diagram of one example pacing management
process;
[0026] FIG. 6 is a flow diagram of one example managed pacing
routine;
[0027] FIG. 7 is a flow diagram of one example managed pacing
routine;
[0028] FIG. 8 is a flow diagram of one example managed pacing
routine;
[0029] FIG. 9 is a graph illustrating various aspects of demand
pacing which can be adjusted in connection with on demand pacing or
capture management pacing;
[0030] FIG. 10 is a graph illustrating a pacing waveform that may
be provided by the medical monitoring and treatment device;
[0031] FIG. 11 is a graph illustrating another pacing waveform that
may be provided by the medical monitoring and treatment device;
[0032] FIG. 12 is a graph illustrating another pacing waveform that
may be provided by the medical monitoring and treatment device;
[0033] FIG. 13 is a graph illustrating another pacing waveform that
may be provided by the medical monitoring and treatment device;
[0034] FIG. 14 is a graph illustrating another pacing waveform that
may be provided by the medical monitoring and treatment device;
[0035] FIG. 15 is a graph illustrating a number of different pacing
waveforms that may be provided by the medical monitoring and
treatment device, including a 40 ms constant current pulse;
[0036] FIG. 16 is a flow diagram of one example managed pacing
routine; and
[0037] FIG. 17 is a flow diagram of one example baseline generation
process.
DETAILED DESCRIPTION
[0038] Medical monitoring and treatment devices in accord with
various examples disclosed herein are configured to monitor and
control discomfort experienced by a patient while administering
therapy to the patient. For instance, in at least one example, a
medical device is configured to provide pacing therapy to a patient
and to control parameters of a pacing routine to decrease the level
of discomfort experienced by the patient. In some examples, the
medical device is configured to allow the patient to self-manage
execution of the pacing routine (e.g., dynamically control one or
more parameters of the pacing routine) based on his or her own
tolerance of the discomfort in real time or near real time.
[0039] In some examples, the medical device is configured to
receive input descriptive of a level of discomfort being
experienced by the patient, calculate a value quantifying of the
level of discomfort being experienced by the patient, determine
whether the value is equal to or transgresses a discomfort
threshold value, and, if so, adjust a parameter of the pacing
routine to decrease the level of discomfort.
[0040] Medical devices disclosed herein may be invasive or
non-invasive. For example, medical devices disclosed herein may be
monitoring devices (e.g., configured to monitor a cardiac signal of
a patient) with or without an associated treatment component. For
example, a non-invasive medical device suited for use with the
systems and techniques as disclosed herein can include an automated
external defibrillator (AED). Such AEDs are capable of monitoring
cardiac rhythms, determining when a defibrillating shock is needed,
and administering the shock either automatically or under the
control of a trained rescuer (e.g., an EMT or other medically
trained personnel). The AED may also be configured to provide
cardiopulmonary resuscitation (CPR) counseling. Such AEDs are
available from ZOLL.RTM. Medical Corporation of Chelmsford,
Mass.
[0041] The devices as described herein may be capable of
continuously, substantially continuously, long-term and/or extended
use or wear by, or attachment or connection to a patient.
[0042] For example, devices as described herein may be capable of
being used or worn by, or attached or connected to a patient,
without substantial interruption for a predetermined period of
time. In some examples, such devices may be capable of being used
or worn by, or attached or connected to a patient for example, up
to hours or beyond (e.g., weeks, months, or even years).
[0043] In some implementations, such devices may be removed for a
period of time before use, wear, attachment, or connection to the
patient is resumed, e.g., to change batteries, to change the
garment, and/or to take a shower, without departing from the scope
of the examples described herein.
[0044] The devices as described herein may be capable of
continuously, substantially continuously, long-term and/or extended
monitoring of a patient.
[0045] For example, devices as described herein may be capable of
providing cardiac monitoring without substantial interruption for a
predetermined period of time. In some examples, such devices may be
capable of continuously or substantially continuously monitoring a
patient for cardiac-related information (e.g., ECG information,
including arrhythmia information, heart sounds, etc.) and/or
non-cardiac information (e.g., blood oxygen, the patient's
temperature, glucose levels, and/or lung sounds), for example, up
to hours or beyond (e.g., weeks, months, or even years).
[0046] In some implementations, such devices may be powered down
for a period of time before monitoring is resumed, e.g., to change
batteries, to change the garment, and/or to take a shower, without
departing from the scope of the examples described herein.
[0047] In some instances, the devices may carry out its monitoring
in periodic or aperiodic time intervals or times. For example, the
monitoring during intervals or times can be triggered by a user
action or another event. For example, one or more durations between
the periodic or aperiodic intervals or times can be
user-configurable.
[0048] In various implementations, the devices may be operated on
battery power for a duration of the device's use after which the
batteries may be replaced and/or recharged.
[0049] The examples of the methods and apparatuses discussed herein
are not limited in application to the details of construction and
the arrangement of components set forth in the following
description or illustrated in the accompanying drawings. The
methods and apparatuses are capable of implementation in other
examples and of being practiced or of being carried out in various
ways. Examples of specific implementations are provided herein for
illustrative purposes only and are not intended to be limiting. In
particular, acts, elements and features discussed in connection
with any one or more examples are not intended to be excluded from
a similar role in any other examples.
[0050] In implementations where example numerical values are
provided (e.g., as a predetermined numerical value), it should be
understood that such values can be set through one or more
user-configurable parameters. For example, the example numerical
value can be provided as a default value, and a technician or a
caregiver (such as a nurse or physician) can modify the values in
accordance with the principles described herein through a user
interface.
[0051] Also, the phraseology and terminology used herein is for the
purpose of description and should not be regarded as limiting. Any
references to examples or elements or acts of the systems and
methods herein referred to in the singular may also embrace
examples including a plurality of these elements, and any
references in plural to any example or element or act herein may
also embrace examples including only a single element. References
in the singular or plural form are not intended to limit the
presently disclosed systems or methods, their components, acts, or
elements. The use herein of "including," "comprising," "having,"
"containing," "involving," and variations thereof is meant to
encompass the items listed thereafter and equivalents thereof as
well as additional items. References to "or" may be construed as
inclusive so that any terms described using "or" may indicate any
of a single, more than one, and all of the described terms.
Example Wearable Medical Device
[0052] In one example, the medical monitoring and treatment device
is a wearable medical device that includes a garment (e.g., a vest
or belt) that is worn by the patient. The wearable medical device
monitors the patient's electrocardiogram (ECG) with sensing
electrodes, detects life-threatening arrhythmias, and delivers
pacing pulses or a cardioverting or defibrillating shock through
therapy pads if treatment is necessary. In examples, the wearable
medical device is configured to monitor the patient and the
patient's environment to quantify a level of discomfort being
experienced by the patient and optimize the effectiveness of a
pacing routine while preventing the level of discomfort of the
patient from exceeding a threshold.
[0053] FIG. 1 illustrates an example wearable medical device for
use with the systems and techniques described herein. As shown, the
wearable medical device 100 includes a harness 110 having a pair of
shoulder straps and a belt that is worn about the torso of a
patient. The harness 110 is typically made from a material, such as
cotton, nylon, spandex, or Antron.RTM. that is breathable, and
unlikely to cause skin irritation, even when worn for prolonged
periods of time. The wearable medical device 100 includes a
plurality of ECG sensing electrodes 112 that are attached to the
harness 110 at various positions about the patient's body and
electrically coupled (wirelessly or by a wired connection) to a
sensor interface of the medical device controller 120 via a
connection pod 130. The plurality of ECG sensing electrodes 112,
which may be dry-sensing capacitance electrodes, are coupled to the
medical device controller 120 to monitor the cardiac function of
the patient and generally include a front-back (FB) pair of ECG
sensing electrodes and a side-side (SS) pair of ECG sensing
electrodes. Additional ECG sensing electrodes may be provided, and
the plurality of ECG sensing electrodes 112 may be disposed at
varying locations about the patient's body. The plurality of ECG
sensing electrodes 112 may incorporate any electrode system,
including conventional stick-on adhesive electrodes, dry-sensing
capacitive ECG electrodes, radio transparent electrodes, segmented
electrodes, or one or more long term wear electrodes that are
configured to be continuously or substantially continuously worn by
a patient for extended periods (e.g., 3 or more days). One example
of such a long term wear electrode is described in U.S. Patent
Application Publication No. US2013/0325096 (hereinafter the "'096
publication"), titled "LONG TERM WEAR MULTIFUNCTION BIOMEDICAL
ELECTRODE," published Dec. 5, 2013, which is hereby incorporated
herein by reference in its entirety.
[0054] The wearable medical device disclosed herein may incorporate
sundry materials arranged in a variety of configurations to
maintain a proper fit with the patient's body. For example, some
embodiments include a garment as described in U.S. Patent
Application Publication No. US2012/0283794, titled "PATIENT-WORN
ENERGY DELIVERY APPARATUS AND TECHNIQUES FOR SIZING SAME,"
published Nov. 8, 2012, which is hereby incorporated herein by
reference in its entirety. In one example, the garment includes one
or more strain gauges configured to generate signals when pressed
upon by the patient or when the patient twists away from a source
of discomfort. In this example, the amount of deformation indicated
by the signals is quantified by the wearable medical device for use
in managing the discomforted experience by the patient. Thus
embodiments are not limited to the configuration and materials
described above with reference to FIG. 1.
[0055] The wearable medical device 100 also includes a plurality of
therapy electrodes 114a and 114b that are electrically coupled to
the medical device controller 120 via the connection pod 130 and
which are configured to deliver one or more therapeutic pacing
pulses or defibrillating shocks to the body of the patient, if it
is determined that such treatment is warranted. As shown, the
therapy electrodes 114 include a first therapy electrode 114a that
is disposed on the front of the patient's torso and a second
therapy electrode 114b that is disposed on the back of the
patient's torso. The second therapy electrode 114b includes a pair
of therapy electrodes that are electrically coupled together and
act as the second therapy electrode 114b. The use of two therapy
electrodes 114a, 114b permits a pacing pulse or other therapeutic
shock having any of a variety of waveforms to be delivered to the
body of the patient. The plurality of therapy electrodes 114 may
incorporate any electrode system, including conventional stick-on
adhesive electrodes, segmented electrodes, integrated electrodes
(e.g., including electrode patches or assemblies integrating both
sensing and therapy electrodes), or one or more long term wear
electrodes that are configured to be continuously or substantially
continuously worn by a patient for extended periods (e.g., 3 or
more days). Example electrodes are described in '096 publication,
which is hereby incorporated herein by reference in its
entirety.
[0056] One of these waveforms is a biphasic waveform in which a
first of the two therapy electrodes can deliver a first phase of
the biphasic pulse or shock with the other therapy electrode acting
as a return, and the other therapy electrode can deliver the second
phase of the biphasic pulse or shock with the first therapy
electrode acting as the return. Other waveforms may be generated by
this arrangement and several are described further below.
[0057] In some examples, the wearable medical device includes one
or more reservoirs of conductive gel. In these examples, the
wearable medical device is configured to, prior to delivering the
pulses or shock, deploy the conductive gel from the reservoir to
reduce an impedance encountered by the therapy electrodes during
the delivery of the pacing pulses or a defibrillating shock.
[0058] The connection pod 130 electrically couples the plurality of
ECG sensing electrodes 112 and the plurality of therapy electrodes
114 to the medical device controller 120, and may include
electronic circuitry. For example, in one implementation the
connection pod 130 includes signal acquisition circuitry, such as a
plurality of differential amplifiers to receive ECG signals from
different electrodes of the plurality of ECG sensing electrodes 112
and to provide a differential ECG signal to the medical device
controller 120 based on the difference there between. The
connection pod 130 may also include other electronic circuitry,
such as a motion sensor or accelerometer through which patient
activity may be monitored.
[0059] In some embodiments, both the first therapy electrode 114a
and the second therapy electrode 114b are disposed on the front of
the patient's torso. For example, the first therapy electrode 114a
may be located external to the apex of the heart and the second
therapy electrode 114b may be located along the parasternal line.
Thus embodiments are not limited to a particular arrangement of
therapy electrodes.
[0060] In some embodiments, the plurality of ECG sensing electrodes
112 are positioned and paired such that artifacts generated from
electrical activity are decreased. In other embodiments, the
electronic circuitry included in the medical device controller 120
may equalize artifacts measured at electrodes by changing a gain or
impedance. Other techniques of decreasing or preventing artifacts
within measured electrical activity that may be used in conjunction
with the embodiments disclosed herein are explained in U.S. Pat.
No. 8,185,199, titled "MONITORING PHYSIOLOGICAL SIGNALS DURING
EXTERNAL ELECTRICAL STIMULATION," issued May 22, 2012, which is
hereby incorporated herein by reference in its entirety.
[0061] Although not shown, the wearable medical device 100 may
include additional sensors, other than the ECG sensing electrodes
112, capable of monitoring the physiological condition or activity
of the patient. For example, sensors capable of measuring blood
pressure, muscular contraction, perspiration, heart rate, heart
sounds, thoracic impedance, pulse oxygen level, respiration rate,
and the activity level of the patient may also be provided.
[0062] As shown in FIG. 1, the wearable medical device 100 may
include a user interface pod 140 that is electrically coupled to,
integrated in, and/or integrated with, the user interface of the
medical device controller 120. The user interface pod 140 can be
attached to the patient's clothing or to the harness 110, for
example, via a clip (not shown) that is attached to a portion of
the interface pod 140. Alternatively, the user interface pod 140
may simply be held in a person's hand. For example, such a user
interface pod 140 can be a smartwatch or a smartphone. In some
examples, the user interface pod 140 may communicate wirelessly
with the user interface of the medical device controller 120, for
example, using a Bluetooth.RTM., Wireless USB, ZigBee, Wireless
Ethernet, GSM, or other type of communication interface.
[0063] The user interface pod 140 includes a number of buttons by
which the patient, or a bystander can communicate with the medical
device controller 120, and a speaker by which the medical device
controller 120 may communicate with the patient or the bystander.
For example, where the medical device controller 120 determines
that the patient is experiencing cardiac arrhythmia, the medical
device controller 120 may issue an audible alarm via a speaker on
the medical device controller 120 or the user interface pod 140
alerting the patient and any bystanders to the patient's medical
condition. Examples of notifications issued by the medical device
controller 120 are described in U.S. Patent Application Publication
No. US2012/0293323, titled "SYSTEM AND METHOD FOR ADAPTING ALARMS
IN A WEARABLE MEDICAL DEVICE," published Nov. 22, 2012, which is
hereby incorporated herein by reference in its entirety.
[0064] In some examples, the medical device controller 120 may
instruct the patient to press and hold one or more buttons on the
user interface of the medical device controller 120 or on the user
interface pod 140 to indicate that the patient is conscious,
thereby signaling the medical device controller 120 to withhold the
delivery of one or more therapeutic pacing pulses or defibrillating
shocks. If the patient does not respond, the device may determine
that the patient is unconscious, and proceed with the treatment
sequence, culminating in delivery of defibrillating shocks or one
or more pacing pulses with parameters set to maximum values to the
body of the patient.
[0065] In some examples, as described in detail below, the medical
device controller 120 may (depending on a type of user interface
element, e.g., one or more buttons on a user interface) instruct
the patient to press and hold the one or more buttons on the user
interface with a force proportional to the intensity of discomfort
being experienced by the patient during execution of a pacing
routine, thereby signaling the medical device controller 120 to
adjust parameters of the pacing routine to decrease the intensity
of the discomfort. If the patient does not respond, the device may
determine that the patient is unconscious, and proceed with the
treatment sequence, culminating in the delivery of one or more
pacing pulses to the body of the patient. For example, the medical
device may administer a pacing routine with values for the pacing
parameters as an upper bound of a range of values (e.g., to
maximize efficacy) as described below. As the patient recovers
consciousness, the patient may (depending on a type of user
interface element), in real time or near real time, increase the
force exerted on the one or more buttons, thereby signaling the
medical device to adjust the parameters of the pacing routine. The
medical device may, in response to receiving the signal, decrease
the intensity of the discomfort by, for example, decreasing the
values of the pacing parameters (which may result in a
corresponding decrease in efficacy). If the patient were to once
again lose consciousness or feel faint, e.g., as a result of
bradycardia, the patient may not be able to continue to exert a
same level of force on the one or more buttons. Correspondingly,
the medical device can dynamically adjust the values of the pacing
parameters to increase the efficacy of the pacing routine.
[0066] In some situations where the patient fails to provide
voluntary feedback regarding his/her level of discomfort, a
threshold value can be set for a discomfort parameter as outlined
below. When the sensed level of discomfort is equal to or
transgresses the threshold, the medical device can adjust the
values of the pacing parameters to lower the intensity of the
pacing routine. In some examples, the medical device can check for
capture before, after, or substantially simultaneous with adjusting
the values of the pacing parameters as described in further detail
below.
[0067] In some implementations, one or more response buttons and/or
user interface elements for managing discomfort during a pacing
routine may be different from one or more response buttons for
establishing user responsiveness prior to delivering a
defibrillating shock.
[0068] In another example, the functionality of the user interface
pod 140 is integrated into the housing of the medical device
controller 120. FIGS. 2A-2B illustrate such an example of the
medical device controller 120. The medical device controller 120
includes two response buttons 210 on opposing sides of a housing
206 of the medical device controller 120. As shown in FIGS. 2A-2B,
the response buttons 210 are recessed to reduce the likelihood of
accidental activation (e.g., a patient falling on the response
button). The medical device controller 120 also includes, in this
example, a display screen 220 and a speaker 204 to enable the
communication of audible and visual stimuli to the patient. It is
appreciated that the response buttons 210 do not have to be placed
on opposing sides of the housing as illustrated in FIGS. 2A-2B. The
response buttons 210, for example, may be located adjacent to each
other in the housing the ambulatory medical device controller. The
adjacent placement of the response buttons may make it easier for
individuals with smaller hands or less dexterity to engage the
response buttons. The medical device controller 120 may further
include a connector 202 to removably connect sensing electrodes
(e.g., ECG sensing electrodes 112) and/or therapy electrodes (e.g.,
therapy electrodes 114a and 114b) to the medical device controller
120.
[0069] Another example wearable medical device includes an
ambulatory external defibrillator described in FIG. 1 of U.S. Pat.
No. 8,904,214, titled "SYSTEM AND METHOD FOR CONSERVING POWER IN A
MEDICAL DEVICE," issued Dec. 2, 2014 (hereinafter the "'214
patent"), which is hereby incorporated herein by reference in its
entirety. In at least one example, the ambulatory defibrillator 100
illustrated in FIG. 1 of the '214 patent may employ the medical
device controller 120, as disclosed in the present application, as
a substitute for the medical device controller 200 described in the
'214 patent. In such an example, the ECG Electrodes and Therapy
Pads illustrated in FIG. 1 of the '214 patent may be logically and
physically coupled to the medical device controller 120. While some
of the examples disclosed herein are directed to wearable medical
devices, the systems and methods disclosed herein may be readily
applied to other medical devices including, for example, an
Automated External Defibrillator (AED).
[0070] In some implementations, the medical device as described
herein can be a hospital-based wearable defibrillator and/or pacing
device. For example, such a hospital-based device can include a
defibrillator and/or pacing device configured for continuous or
substantially continuous use, wear, connection, attachment, or
monitoring to/of a patient in a hospital environment. The
hospital-based device can include a plurality of therapy and
sensing electrodes that are attached to the patient's skin. In some
examples, the electrodes are disposable adhesive electrodes. In
some implementations, the electrodes are affixed to an electrode
assembly (a patch), which can then be adhesively attached to the
patient's skin. The electrodes can be attached to the patient's
skin at particular locations as prescribed by a trained
professional.
[0071] In operation, the hospital-based device can include a
monitor configured to operate in a manner that is different from
that of the monitor of wearable defibrillator described above with
respect to FIG. 1. For example, an interface, prompts, and
communication performed by the hospital-based device can be
configured for and/or directed to a user other than the patient,
e.g., a caregiver such as a nurse or a patient service
representative. For example, a caregiver can program the device
and/or set the device up for use by the patient. The interface,
prompts, and communication can be directed to the patient in
scenarios such as when a response is required to let the device
know whether or not the patient is conscious, which can be used in
deciding when to shock the patient, and when a patient is given an
alert to call the caregiver.
Example Medical Device Controller
[0072] FIG. 3 illustrates a medical device controller 300 that is
configured to monitor the cardiac activity of a patient and/or
provide pacing or other therapy to the patient as needed. The
medical device controller 300 may, for example, be configured for
use in a wearable medical device (e.g., medical device controller
120). The medical device controller 300 has a variety of potential
applications and is well suited to devices that notify external
entities of one or more events of interest (e.g., cardiac events).
Examples of medical devices to which the medical device controller
300 is well suited include critical care medical devices, such as a
wearable ambulatory external defibrillator, an AED, pacing devices,
or a mechanical chest compression device, such as the
Autopulse.RTM. system from ZOLL.RTM. Medical Corporation of
Chelmsford, Mass.
[0073] As shown in FIG. 3, the medical device controller 300
includes a processor 318, a sensor interface 312, a treatment
manager 314, a therapy delivery interface 302, data storage 304, a
communication network interface 306, a user interface 308, and a
battery 310. The data storage 304 includes patient data 316 and
discomfort scale data 332. The treatment manager 314 includes a
cardiac monitor 320, a discomfort monitor 322, one or more pacing
routines 324, and a transcutaneous electrical nerve stimulation
(TENS) routine 334. Both the sensor interface 312 and the network
interface 306 are illustrated using dashed lines to indicate they
are optional components in at least some examples. The sensor
interface 312, as illustrated, is coupled to electrodes including a
front-back (FB) electrode pair 326 and a side-side (SS) electrode
pair 328.
[0074] The therapy delivery interface 302, as illustrated, can be
coupled to one or more therapy electrodes, e.g., therapy electrode
pair 330. The therapy delivery interface 302 may be optionally
coupled to one or more TENS electrodes (e.g., TENS electrodes 336)
and/or one or more pacing electrodes (e.g., pacing electrodes 338).
For example, TENS electrodes 336 may include a TENS electrode pair,
and pacing electrodes 338 may include a pacing electrode pair. It
is appreciated that the electrode configuration and/or the number
of electrodes may be changed to best suit the particular
application. For example, the therapy delivery interface 302 may be
coupled to the therapy electrode pair 330 and provide any
combination of defibrillation pulses, pacing pulses, and TENS
pulses to the patient via the therapy electrode pair 330. In some
implementations, the therapy delivery interface 302 may be coupled
to separate pacing electrodes 338 for providing pacing pulses in
addition to the therapy electrode pair 330 for providing
defibrillation pulses. Accordingly, the TENS pulses may be provided
to the patient via either the pacing electrodes 338 and/or the
therapy electrode pair 330 under control of a treatment protocol as
described herein. As such, the therapy delivery interface 302 may
be coupled to any combination of the therapy electrode pair 330,
the TENS electrodes 336, and pacing electrodes 338 to provide
treatment to the patient.
[0075] In some examples, the therapy delivery interface 302 is
coupled to at least the therapy electrode pair 330 and the pacing
electrodes 338. Employing the therapy electrode pair 330 to provide
defibrillation pulses and separate pacing electrodes 338 to provide
pacing pulses may be advantageous, for example, where different
electrode configurations enable different gels to be deployed for
pacing and defibrillation. For example, the therapy electrode pair
330 may be configured to deploy a gel with a low impedance and the
pacing electrodes 338 may be configured to deploy a gel with a
higher impedance. In these examples, the therapy delivery interface
302 may delivery defibrillation pulses via the therapy electrode
pair 330 and deliver pacing and/or TENS pulses via the pacing
electrodes 338 and/or another electrode pair (e.g., TENS electrodes
336).
[0076] For example, the therapy electrodes (or, in some
implementations, pacing electrodes) may deploy a high impedance gel
(e.g., 500 ohms) to decrease external skin pain during pacing
routines as described herein. For example, the therapy electrodes
may also be configured to dispense a low impedance gel (e.g., 1
ohm) should defibrillation be required before or after pacing.
[0077] In some examples, the battery 310 is a rechargeable battery
that provides electrical power to other components within the
medical device. The particular capacity and type of battery (e.g.,
lithium ion, nickel-cadmium, or nickel-metal hydride) employed may
vary based on the desired runtime between charges of the medical
device and the power consumption of the components. For example,
the battery 310 may be selected to provide a minimum runtime
between charges of 44 hours. In this example, a suitable battery
may include a 3 cell 4200 mAh lithium ion battery pack. It is
appreciated that various mechanisms may be employed to removably
secure the battery 310 to the medical device controller 300
including, for example, a latching mechanism.
[0078] According to the example illustrated in FIG. 3, the
processor 318 is coupled to the sensor interface 312, the therapy
delivery interface 302, the data storage 304, the network interface
306, and the user interface 308. The processor 318 performs a
series of instructions that result in manipulated data which are
stored in and retrieved from the data storage 304. According to a
variety of examples, the processor 318 is a commercially available
processor such as a processor manufactured by Texas Instruments,
Intel, AMD, Sun, IBM, Motorola, Freescale, and ARM Holdings.
However, the processor 318 may be any type of processor,
multiprocessor or controller, whether commercially available or
specially manufactured. For instance, according to one example, the
processor 318 may include a power conserving processor arrangement
such as described in the'214 patent. In another example, the
processor 318 is an Intel.RTM. PXA270.
[0079] In addition, in some examples, the processor 318 may be
configured to execute a conventional operating system. The
operating system may provide platform services to application
software, such as some examples of the treatment manager 314 which
are discussed further below. These platform services may include
inter-process and network communication, file system management and
standard database manipulation. One or more of many operating
systems may be used, and examples are not limited to any particular
operating system or operating system characteristic. For instance,
operating systems can include a Windows based operating system,
OSX, or other operating systems. For instance, in some examples,
the processor 318 may be configured to execute a real time
operating system (RTOS), such as RTLinux, or a non-real time
operating system, such as BSD or GNU/Linux.
[0080] In some examples, the treatment manager 314 is configured to
monitor the cardiac activity of the patient, identify cardiac
events experienced by the patient, treat identified cardiac events,
and manage discomfort experienced by patients during treatment. In
these examples, the cardiac monitor 320 is configured to process
data descriptive of cardiac function to identify cardiac events.
The one or more pacing routines 324 are configured to apply one or
more pacing pulses via the therapy electrode pair 330 to the
patient to treat arrhythmias, such as bradycardia. For example, the
wearable medical device can be configured to treat a patient
experiencing bradycardia when the patient's heart rate is about 40
beats per minute or less.
[0081] In some examples, prior to and during the execution of one
or more pacing routines, the discomfort monitor 322 can request
that the user interface 308 instruct the patient to press and hold
one or more buttons on the user interface with a force proportional
to the intensity of discomfort being experienced by the patient
during execution of the one or more pacing routines. In this
manner, the discomfort monitor 322 can adjust the parameters of the
pacing routine to increase or decrease the intensity of the one or
more pacing routines based on the patient's comfort level and/or
efficacy of the routines. For example, if the patient does not
respond, the discomfort monitor 322 may determine that the patient
is unconscious, and proceed with the treatment sequence,
culminating in the delivery of one or more pacing pulses to the
body of the patient. For example, the medical device may administer
a pacing routine with values for the pacing parameters as an upper
bound of a range of values (e.g., to maximize efficacy) as
described below. As the patient recovers consciousness, the patient
may (depending on a type of user interface element), in real time
or near real time, increase the force exerted on the one or more
buttons of the user interface 308, thereby signaling the medical
device to adjust the parameters of the pacing routine. The
discomfort monitor 322 may, in response to receiving the signal,
decrease the intensity of the discomfort by, for example,
decreasing the values of the pacing parameters (with a
corresponding decrease in efficacy).
[0082] In some implementations, the discomfort monitor 322 is
configured to receive input descriptive of patient discomfort,
quantify a level of discomfort being experienced by the patient,
compare the quantified level of discomfort to a discomfort
threshold value, and adjust parameters of the active pacing routine
to decrease the level of discomfort being experienced by the
patient. One of the parameter adjustments that may be executed by
the discomfort monitor 322 is execution of the TENS routine 334.
The TENS routine 334 is configured to apply one or more TENS pulses
to a patient via, for example, one or more TENS electrodes 336. It
is appreciated that the TENS pulses may be applied by other
electrodes including, for example, the therapy electrode pair 330
and/or one or more pacing electrodes 338. These TENS pulses may
serve to distract the patient so that the level of discomfort
experienced by the patient is lessened. In some examples, the TENS
pulses are applied in intervals between pacing pulses. Additional
description regarding the use of TENS pulses in conjunction with
external pacing is provided in U.S. Pat. No. 5,205,284, titled
"METHOD AND APPARATUS FOR TRANSCUTANEOUS ELECTRICAL CARDIAC PACING
WITH BACKGROUND STIMULATION" and issued on Apr. 27, 1993, which is
hereby incorporated herein by reference in its entirety.
[0083] Processes executed by the treatment manager 314 and its
constituent components (i.e., the cardiac monitor 320, the pacing
routines 324, the discomfort monitor 332, and the TENS routine 334)
are described in greater detail below with reference to FIGS. 4-15.
The treatment manager 314 and its constituent components may be
implemented using hardware or a combination of hardware and
software. For instance, in one example, the treatment manager 314
and its constituent components are implemented as software
components that are stored within the data storage 304 and executed
by the processor 318. In this example, the instructions included in
the treatment manager 314 and its constituent components program
the processor 318 to execute the processes described herein. In
other examples, the treatment manager 314 and its constituent
components may be application-specific integrated circuits (ASICs)
that are coupled to the processor 318. Thus, examples of the
treatment manager 314 and its constituent components are not
limited to particular hardware or software implementations.
[0084] In some examples, the components disclosed herein, such as
the treatment manager 314 and its constituent components, may read
parameters that affect the functions performed by the components.
These parameters may be physically stored in any form of suitable
memory including volatile memory, such as RAM, or nonvolatile
memory, such as a flash memory or magnetic hard drive. In addition,
the parameters may be logically stored in a propriety data
structure, such as a database or file defined by a user mode
application, or in a commonly shared data structure, such as an
application registry that is defined by an operating system. In
addition, some examples provide for both system and user
interfaces, as may be implemented using the user interface 308,
that allow external entities to modify the parameters and thereby
configure the behavior of the components.
[0085] The data storage 304 includes a computer readable and
writeable nonvolatile data storage medium configured to store
non-transitory instructions and data. In addition, the data storage
304 includes processor memory that stores data during operation of
the processor 318. In some examples, the processor memory includes
a relatively high performance, volatile, random access memory such
as dynamic random access memory (DRAM), static memory (SRAM) or
synchronous DRAM. However, the processor memory may include any
device for storing data, such as a non-volatile memory, with
sufficient throughput and storage capacity to support the functions
described herein. According to several examples, the processor 318
causes data to be read from the nonvolatile data storage medium
into the processor memory prior to processing the data. In these
examples, the processor 318 copies the data from the processor
memory to the non-volatile storage medium after processing is
complete. A variety of components may manage data movement between
the non-volatile storage medium and the processor memory and
examples are not limited to particular data management components.
Further, examples are not limited to a particular memory, memory
system or data storage system.
[0086] The instructions stored on the data storage 304 may include
executable programs or other code that can be executed by the
processor 318. The instructions may be persistently stored as
encoded signals, and the instructions may cause the processor 318
to perform the functions described herein. The data storage 304
also may include information that is recorded, on or in, the
medium, and this information may be processed by the processor 318
during execution of instructions. The medium may, for example, be
optical disk, magnetic disk or flash memory, among others, and may
be permanently affixed to, or removable from, the medical device
controller 300.
[0087] In some examples, the patient data 316 includes pacing
parameter baselines associated with one or more patients, one or
more pacing routines, or a combination of one or more patient
parameter baselines and one or more pacing routines. The pacing
parameter baselines may be stored as, for example, a series of
tuples that include a parameter name that identifies a pacing
parameter and a parameter value that specifies a baseline value of
the identified pacing parameter to be used when a pacing routine is
initiated for a patient. In some examples, each of the series of
tuples may further include a patient name that identifies the
patient and a pacing routine name that identifies a particular
pacing routine to which the identified pacing parameter applies.
The discomfort scale data 332 includes information representing one
or more discomfort scales that may be used to quantify a level of
discomfort being experienced by a patient. For example, the
discomfort scale data 332 may include data representative of the
Wong-Baker FACES.RTM. Pain Rating Scale.
[0088] As illustrated in FIG. 3, the treatment manager 314, the
patient data 316, and the discomfort scale data 332 are separate
components. However, in other examples, the treatment manager 314,
the patient data 316, and the discomfort scale data 332 may be
combined into a single component or re-organized so that a portion
of the patient data 316 or the discomfort scale data 332 is
included in the treatment manager 314. Such variations in these and
the other components illustrated in FIG. 3 are intended to be
within the scope of the examples disclosed herein.
[0089] The patient data 316 and the discomfort scale data 332 may
be stored in any logical construction capable of storing
information on a computer readable medium including, among other
structures, flat files, indexed files, hierarchical databases,
relational databases, or object oriented databases. These data
structures may be specifically configured to conserve storage space
or increase data exchange performance. In addition, various
examples organize the patient data 316 and the discomfort scale
data 332 into particularized and, in some cases, unique structures
to perform the functions disclosed herein. In these examples, the
data structures are sized and arranged to store values for
particular types of data, such as integers, floating point numbers,
character strings, arrays, linked lists, and the like.
[0090] As shown in FIG. 3, the medical device controller 300
includes several system interface components 302, 306, and 312.
Each of these system interface components is configured to
exchange, i.e. send or receive, data with one or more specialized
devices that may be located within the housing of the medical
device controller 300 or elsewhere. The components used by the
interfaces 302, 306, and 312 may include hardware components,
software components or a combination of both hardware and software
components. Within each interface, these components physically and
logically couple the medical device controller 300 to the
specialized devices. This physical and logical coupling enables the
medical device controller 300 to communicate with and, in some
instances, power or control the operation of the specialized
devices. These specialized devices may include physiological
sensors, therapy delivery devices, and computer networking
devices.
[0091] For instance, in some examples, the therapy delivery
interface 302 includes waveform-shaping circuitry that receives
pulse stream output and modifies signal characteristics of the
pulse stream, e.g., pulse shape, polarity, and amplitude, to
generate pacing pulses having configurable signal parameters. In
these examples, the therapy delivery interface 302 delivers the
pacing pulses to the therapy electrodes 330, which together
externally deliver the pacing pulses to the patient for
transcutaneous pacing of the patient's heart. Examples of the
waveforms that may be delivered via the therapy delivery interface
302 are illustrated in FIGS. 10-15.
[0092] According to various examples, the hardware and software
components of the interfaces 302, 306, and 312 implement a variety
of coupling and communication techniques. In some examples, the
interfaces 302, 306, and 312 use leads, cables or other wired
connectors as conduits to exchange data between the medical device
controller 300 and specialized devices. In other examples, the
interfaces 302, 306, and 312 communicate with specialized devices
using wireless technologies such as radio frequency or infrared
technology. The software components included in the interfaces 302,
306, and 312 enable the processor 318 to communicate with
specialized devices. These software components may include elements
such as objects, executable code, and populated data structures.
Together, these software components provide software interfaces
through which the processor 318 can exchange information with
specialized devices. Moreover, in at least some examples where one
or more specialized devices communicate using analog signals, the
interfaces 302, 306, and 312 further include components configured
to convert analog information into digital information, and vice
versa, to enable the processor 318 to communicate with specialized
devices.
[0093] As discussed above, the system interface components 302,
306, and 312 shown in the example of FIG. 3 support different types
of specialized devices. For instance, the components of the sensor
interface 312 couple the processor 318 to one or more physiological
sensors such as a body temperature sensors, respiration monitors,
perspiration sensors, muscular contraction sensors, and
electrocardiogram (ECG) sensing electrodes, one or more
environmental sensors such as atmospheric thermometers, airflow
sensors, video sensors, audio sensors, accelerometers, GPS
locators, and hygrometers, or one or more motion detection sensors
such as altimeters, accelerometers, and gyroscopes. In these
examples, the sensors may include sensors with varying sampling
rates, including wireless sensors. The sensor interface 312, as
illustrated, is coupled to four ECG sensing electrodes that form a
front-back (FB) electrode pair 326 and a side-side (SS) electrode
pair 328. The sensor interface may include various circuitry to
amplify the ECG signal detected by the electrodes, condition the
received ECG signal, and/or digitize the ECG signals as described
in U.S. Pat. No. 8,600,486, titled "METHOD OF DETECTING SIGNAL
CLIPPING IN A WEARABLE AMBULATORY MEDICAL DEVICE" and issued on
Dec. 3, 2013, which is hereby incorporated herein by reference in
its entirety. It is appreciated that the particular number of ECG
sensing electrodes coupled to the sensor interface 312 and/or the
pairing of the ECG sensing electrodes may vary based on the
specific implementation.
[0094] In some examples, the components of the therapy delivery
interface 302 couple one or more therapy delivery devices, such as
capacitors, defibrillator electrodes, pacing electrodes or
mechanical chest compression devices, to the processor 318. It is
appreciated that the functionality of the therapy delivery
interface 302 may be incorporated into the sensor interface 312 to
form a single interface coupled to the processor 318. Additional
description regarding certain features, such as the
waveform-shaping circuitry described above, that may be included in
various examples is provided in U.S. Pat. No. 5,431,688, titled
"METHOD AND APPARATUS FOR TRANSCUTANEOUS CARDIAC PACING" and issued
on Jul. 11, 1995, which is hereby incorporated herein by reference
in its entirety. In some examples, the components of the network
interface 306 couple the processor 318 to a computer network via a
networking device, such as a bridge, router or hub. According to a
variety of examples, the network interface 306 supports a variety
of standards and protocols, examples of which include USB (via, for
example, a dongle to a computer), TCP/IP, Ethernet, Wireless
Ethernet, Bluetooth, ZigBee, M-Bus, CAN-bus, IP, IPV6, UDP, DTN,
HTTP, HTTPS, FTP, SNMP, CDMA, NMEA and GSM. It is appreciated that
the network interface 306 of medical device controller 300 may
enable communication between other medical device controllers
within a certain range.
[0095] To ensure data transfer is secure, in some examples, the
medical device controller 300 can transmit data via the network
interface 306 using a variety of security measures including, for
example, TLS, SSL or VPN. In other examples, the network interface
306 includes both a physical interface configured for wireless
communication and a physical interface configured for wired
communication. According to various examples, the network interface
306 enables communication between the medical device controller 300
and a variety of personal electronic devices including, for
example, computer enabled glasses, wristwatches, earpieces, and
phones.
[0096] In one example, the network interface 306 is also capable of
transmitting and/or receiving information to assist in managing
discomfort while treating a patient. This may be accomplished
through one or more antennas integrated with or coupled to the
network interface 306, and consequently coupled to the processor
318. For example, the one or more antennas may receive information
representative of the pacing parameter baselines associated with
the patient. The wireless signals received by the antennas may be
analyzed by the processor 318 to generate pacing parameter
baselines for the patient. The network interface 306 may also
transmit signals descriptive of one or more generated pacing
parameter baselines to an external system. For example, the medical
device may transmit signals descriptive of the pacing parameter
baselines associated with a patient to a computer system associated
with a health care provider of the patient. The computer system
associated with the health care provider may transmit signals
descriptive of the pacing parameter baselines to one or more other
medical devices employed to provide treatment to the patient.
[0097] Thus, the various system interfaces incorporated in the
medical device controller 300 allow the device to interoperate with
a wide variety of devices in various contexts. For instance, some
examples of the medical device controller 300 are configured to
perform a process of sending critical events and data to a
centralized server via the network interface 306. An illustration
of a process in accord with these examples is disclosed in U.S.
Pat. No. 6,681,003, titled "DATA COLLECTION AND SYSTEM MANAGEMENT
FOR PATIENT-WORN MEDICAL DEVICES," and issued on Jan. 20, 2004,
which is hereby incorporated herein by reference in its
entirety.
[0098] As illustrated in FIG. 3 by dashed lines, the sensor
interface 312 is optional and may not be included in every example.
For instance, a pacing device may employ the medical device
controller 300 to deliver pacing pulses at a regular, set rhythm
and receive data descriptive of the intensity of discomfort
experienced by a patient via the user interface 308. Similarly, a
pacing device may include the medical device controller 300 to
provide alarm functionality but may not include a network interface
306 where, for example, the ambulatory defibrillator is designed to
rely on the user interface 308 to announce alarms.
[0099] The user interface 308 shown in FIG. 3 includes a
combination of hardware and software components that allow the
medical device controller 300 to communicate with an external
entity, such as a patient or other user. These components may be
configured to receive information from actions such as physical
movement, verbal intonation, or thought processes. In addition, the
components of the user interface 308 can provide information to
external entities. Examples of the components that may be employed
within the user interface 308 include keyboards, strain gauges,
pressure sensors, quartz and/or ceramic force sensors,
piezoelectric transducers, rotating switches (spring loaded or
otherwise), elastic deformable solids (e.g., a stress relief ball),
mouse devices, buttons, microphones, electrodes, touch screens,
printing devices, display screens, and speakers. In some examples,
the electrodes include an illuminating element, such as an LED. In
other examples, the printing devices include printers capable of
rendering visual or tactile (Braille) output.
[0100] In some examples, the user interface 308 may be configured
to provide information to external entities regarding a cardiac
event experienced by the patient. For example, the user interface
308 may provide an alarm indicting that the patient has experienced
an arrhythmia and is being paced. In these examples, the user
interface may also receive input from the patient regarding any
discomfort being experienced during pacing. For example, the user
interface 308 may issue an alarm requesting the patient to interact
with at least one element of the user interface 308 (e.g., push a
button) to acknowledge the alarm and adjust parameters of the
therapy (e.g., pacing pulses).
[0101] In some examples, functions of the treatment manager 314 may
be divided between a baseline mode (e.g., a "learning mode"), where
pacing parameter baselines are generated, and a management mode,
where the pacing parameter baselines are used to administer
treatment to the patient. As illustrated in FIG. 3, the treatment
manager 314 is configured to execute various processes associated
with the baseline mode and the management mode. The treatment
manager 314 may receive requests to enter either the baseline mode
or the management mode from another component (e.g., the user
interface 308). In response to receiving a request to enter the
baseline mode, the treatment manager 314 executes a baseline
process, such as the baseline process 400 described below with
reference to FIG. 4. In response to receiving a request to enter
the management mode, the treatment manager 314 executes a
management process, such as the management process 500 described
below with reference to FIG. 5. It is appreciated that the
particular architecture shown in FIG. 3 is for illustration only
and other architectures and/or modes may be employed by the
treatment manager 314.
Example Baseline Generation Process
[0102] In some examples, a treatment manager (e.g., the treatment
manager 314 described above with reference to FIG. 3) is configured
to generate baseline parameters associated with a patient, with a
pacing routine, or a combination of both. The baseline parameters
are indicative of a patient's tolerance for discomfort while being
treated by execution of one or more pacing routines. The baseline
process can yield information relating to a patient's discomfort
threshold and further establish baseline values for the pacing
parameters. In particular, the baseline process can yield a range
of values for a discomfort parameter for the patient. As noted
below, the baseline process can calculate a threshold value for the
discomfort parameter from the range of values and use this
threshold during active pacing management. In addition, the
baseline process can determine baseline values for the pacing
parameters to use as a starting point in the pacing management
process.
[0103] FIG. 4 illustrates an example baseline process 400 performed
by, for example, the treatment manager when the medical device is
executing in baseline mode. In some examples, the baseline mode of
the medical device is activated to initiate execution of the
baseline process 400. The baseline process 400 may be performed
before active patient monitoring begins via the management process
500 (described below with respect to FIG. 5). As discussed below,
in some implementations, the baseline process 400 can be repeated
periodically, e.g., once every two weeks, or when triggered by an
external event (e.g., user-triggered event) or an internal event
(e.g., automated detection of a triggering condition).
[0104] Example triggering conditions can include, without
limitation, one or more of a change in patient profile information
or data (e.g., through a manual or automated remote or local
download process), device or user initiated periodic or aperiodic
self-tests, mechanical impact detection (e.g., when the device is
subject to forces beyond a predetermined threshold), tampering of
the device, assembly and/or disassembly events involving the
device, excess temperature and/or moisture events, battery change
events, post-shock delivery (e.g., a period of time after a shock
or pacing pulse has been delivered), an arrhythmia warning or alert
event (e.g., when the patient is conscious and able to respond by
pushing the response buttons), actuation of the response buttons
(e.g., actuation of the buttons in a predetermined manner), changes
in and/or tampering of the gel deployment mechanism, detected
excessive cabling and/or device strains, error conditions thrown by
software, and software updates.
[0105] During execution of the baseline process 400, the patient's
tolerance for discomfort can be recorded and analyzed as described
below. A user interface (e.g., the user interface 308 described
above with reference to FIG. 3) can provide messages and interact
with a user (either the patient or a caregiver) to allow the
recording of the baseline pacing parameters. In some examples, the
medical device notifies the user, via the user interface, upon
completion of the baseline process 400. The patient (or caregiver)
can abort the baseline process 400 at any time.
[0106] In one example, the baseline process 400 includes acts of
fitting the medical device to a patient, delivering a pacing test
pattern, calculating a level of discomfort experienced by the
patient during delivery of the pacing test pattern, adjusting
characteristics of the pacing test pattern, recording the test
data, and optimizing pacing parameters. The baseline process 400
may also include transmitting the baseline parameters to an
external system (e.g., a computer system of a health care provider
associated with the patient) for storage, review, and analysis.
[0107] In act 402, the medical device is fitted to the patient. In
some examples, the act 402 includes adjusting physical aspects of
the medical device (e.g., a garment or belt) to fit snugly and
securely to the patient's body. The act 402 may further include
initiation of the baseline mode in the medical device via the user
interface.
[0108] In act 404, the treatment manager initiates delivery of a
test pattern to the patient that includes one or more pacing pulses
delivered through one or more therapy electrodes (e.g., the therapy
electrode pair 330 described above with reference to FIG. 3) and,
optionally, one or more TENS pulses through one or more TENS
electrodes (e.g., the TENS electrodes 336, the therapy electrode
pair 330, and/or the pacing electrodes 338 described above with
reference to FIG. 3). The pacing pulses and the TENS pulses
included in the test pattern may have varied characteristics. These
characteristics may be controlled by one or more pacing parameters
(including TENS parameters) that are set by, for example, the
treatment manager 314 discussed above with reference to FIG. 3.
Example characteristics that may vary from pulse to pulse include
pacing pulse amplitude, pacing pulse width, pacing pulse rate,
pacing pulse waveform, pacing pulse period, pacing pulse duty
cycle, pacing pulse ramp time constant, TENS pulse width, TENS
pulse rate, TENS pulse amplitude, and TENS waveform. The pacing
pulse amplitude may vary within a range of values between
approximately 15 milliamps and 140 milliamps. The pacing pulse
width may vary within a range of values between approximately 2
milliseconds and 40 milliseconds. The pacing pulse rate may vary
within a range of values between approximately 20 pacing pulses per
minute and 80 pacing pulses per minute. The pacing pulse period may
vary within a range of values between approximately 20 microseconds
and 500 microseconds. The pacing pulse duty cycle may vary within a
range of values between approximately 10 percent and 100 percent.
The pacing pulse ramp time constant may vary within a range of
values between approximately 40 microseconds and 100 microseconds.
The pacing pulse waveform may vary within a range of values
including a rectilinear waveform, a pulse train waveform, a
truncated exponential waveform, a variable waveform, and a biphasic
waveform. The TENS pulse amplitude may vary within a range of
values between approximately 0 milliamps and 200 milliamps. The
TENS pulse width may vary within a range of values between
approximately 0.001 milliseconds and 0.5 milliseconds. The TENS
pulse rate may vary within a range of values between approximately
0.5 pulse per minute and 500 pulses per minute. The TENS pulse
waveform may be selected to be any one of a rectilinear waveform, a
pulse train waveform, and a biphasic waveform.
[0109] In various examples, different TENS stimulation modes may be
used to ameliorate patient sensation and discomfort during cardiac
pacing. For example, an optimal mode of TENS stimulation may be
tested and adjusted during a baselining process of the medical
device, e.g., a fitting period of a wearable defibrillator and/or
pacing device. For example, one or more of the following TENS
stimulation modes can be used in any of the examples described
herein.
[0110] 1. Constant or Continuous Mode.
[0111] In this example mode, a medical device administering TENS
can constantly output a set pulse rate, pulse width and amplitude.
The pulse rate can determine which theory of TENS should be
administered (e.g., Gate or Endorphin theory). For example, the
Gate theory of TENS implicates a high pulse rate (e.g., 80-150 Hz).
Under the Gate theory, asymmetrical biphasic square wave pulses
administered at high frequencies are understood to block a pain
signal from an end of a nerve to the brain. For example, the
Endorphin theory is implicated at lower pulse rates (e.g., 1-10
Hz). Under the Endorphin theory, a rubbing and/or pulsing sensation
delivered through TENS can trigger a release of endorphins at the
area when the TENS is applied.
[0112] In some implementations, the pulse width and amplitude can
be set in accordance with the patient's comfort preferences (e.g.,
enough to feel the pulsing sensation, and just under the threshold
of a muscle contraction). In an example, the TENS parameters can be
set such that the patient is able to feel the stimulation while not
finding it painful.
[0113] In some examples, the Constant Mode can be used to determine
the baseline settings for the patient. Over time, the patient can
acclimate to the perceived sensation of the output. In some
implementations, in the Constant or Continuous Mode of operation,
the patient may acclimate sooner because there is no modulation or
change in the settings.
[0114] 2. Pulse Rate Modulation Mode.
[0115] In this example mode based on varying a frequency of the
pulses, the device can shift the frequency setting to, e.g., 50% of
the set value over, e.g., 5 seconds. For example, if the pulse rate
(in Hz) is set at 100 Hz, the device can be configured to shift the
frequency downwards to about 50 Hz and, in some cases, upwards to
about 150 Hz over a duration of, e.g., 5 seconds.
[0116] For example, if the pulse rate is set at 5 Hz, then the
frequency can shift from about 3-8 Hz over, e.g., 5 seconds using
the Endorphin theory. Accordingly, the patient may not acclimate to
the sensation as quickly as in the Constant Mode.
[0117] 3. Pulse Width Modulation Mode.
[0118] In this example mode, the sensations felt by the patient due
to the TENS output of the device can be varied using shifts in
pulse width. For example, the device can change the pulse width
setting while holding the pulse rate (Hz) setting constant and
determining what theory of TENS is to be used. The changing pulse
width can keep the patient from acclimating to the TENS output over
time. When the pulse width is increased (e.g., to about 50% over a
5 second cycle), the sensation typically feels stronger. As a
result of this change, each individual pulse lasts longer. In an
example, the pulse width setting can be set to be as high as
possible without generating a visible muscle contraction or
discomfort. Conversely, the pulse width setting can be decreased by
up to, e.g., 50% of an initial setting over a 5 second cycle to
ease the sensation felt by the patient.
[0119] 4. Pulse Rate & Pulse Width Modulation Mode.
[0120] In this example mode, the device can be configured such that
as the pulse rate (Hz) increases, the pulse width (uS) can be
decreased and vice versa. The pulse rate (Hz) setting can determine
whether the Gate or Endorphin Theory is to be applied. The pulse
width can be used to determine how long each pulse is delivered,
but both the pulse rate and pulse width can shift over time to
prevent acclimation.
[0121] 5. Cycled Burst Mode.
[0122] In this example mode, the pulse rate and pulse width
settings can be configured to remain constant, but the amplitude
can be dropped to be at or near zero for a first predetermined
amount of time, e.g., 2.5 seconds. After this period elapses, the
amplitude can be restored to the original amplitude setting for a
second predetermined amount of time, e.g., another 2.5 seconds.
This process can be repeated. In this manner, the device can create
a "tapping" or "rubbing" sensation. For example, the pulse rate
setting (Hz) can be in the 80-120 Hz range and be able to cause the
release of endorphins.
[0123] 6. Optimal Settings Mode.
[0124] Increase of set Pulse Width 40%, decrease of set Pulse Rate
45% and decrease of set Amplitude 10% over a 3 second period.
Values return to original settings over the next 3 seconds.
[0125] In this example mode, the device can be configured to
modulate some or all of the waveform settings as described herein
to achieve maximum patient comfort. For example, when the pulse
width shifts to higher settings (e.g., more aggressive sensation)
the amplitude (or power level of the waveform) can be configured to
drop, e.g., 10% of the original setting, to allow for an increase
in the pulse width setting to ensure patient comfort. The pulse
rate (e.g., characterized in Hz) can be used to determine whether
the Gate or Endorphin theory of TENS is to be applied. In some
examples, the frequency can be shifted e.g., up to 40%, to prevent
patient acclimation.
[0126] In implementations, the device can be configured to
intelligently shift all of the waveform settings to adjust in a
predetermined pattern for maximizing patient comfort. For example,
there can be a 90% shift in the pulse rate setting to allow for
both the Gate and Endorphin Theories to be used within the same
mode. For example, assuming that the initial pulse rate is set at
80 Hz, a 90% shift can allow for the pulse rate to swing from,
e.g., 85 Hz (Gate Theory) to about, e.g., 10 Hz (Endorphin Theory).
For example, one or more of the above modes (e.g., the Optimal
Settings Mode) may be suited for patients with pain conditions
relating to both parasympathetic and sympathetic nerve groups.
[0127] In some examples, the test pattern delivered by the initial
execution of the act 404 includes one or more pacing pulses and one
or more TENS pulses with mild characteristics that reside within
the lower portions of each range of values described above. For
instance, in at least one example, these one or more pacing pulses
have characteristics set to the lower bound (minimum) within their
respective ranges of values. In these examples, the TENS pulses are
delivered within the interval between pacing pulses and provide
background stimulation to the patient to distract the attention of
the patient away from the discomfort caused by the pacing
pulses.
[0128] In act 406, a discomfort monitor (e.g., the discomfort
monitor 322) prompts for, receives, and records patient feedback
regarding the test pattern through a user interface element as
described herein. For example, the user feedback includes
discomfort information acquired during execution of the test
pattern for subsequent processing. In some examples, the discomfort
information is recorded in data storage (e.g., the data storage 304
described above with reference to FIG. 3). This discomfort
information may be received as voluntary or involuntary input from
the user via the user interface or may be acquired from one or more
other sensors coupled to a sensor interface (e.g., the sensor
interface 312 described above with reference to FIG. 3). Examples
of discomfort information received via the user interface include
utterances (e.g., words, moans, groans, crying, or other
expressions) and actuation of a discomfort measuring and/or
indicating device (e.g., strain gauge, force sensor, push or
squeeze button, rotary dial, elastic deformable solid). For
example, the user can indicate a level of discomfort he or she
feels by actuating any of one or more user interface elements as
described herein. Examples of discomfort information received via
other sensors (e.g., motion detection sensors, strain gauges in a
garment) include movements (e.g., tensing of muscles, jerking,
shuttering, flinching, changes in respiration) and lack of
movement.
[0129] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for the input by, for example, presenting a discomfort scale
via the user interface. The discomfort scale may include numeric
values and the user interface may request that the user rate the
discomfort experienced on the numeric scale. The discomfort scale
may also include graphical representations (e.g., faces) and the
user interface may request that the user rate the discomfort
experienced on the graphical scale. In some examples, the
discomfort monitor infers the intensity of the discomfort based on
the amount of pressure detected by the user interface or the period
of time a user interface element remains actuated. For instance, in
one example, the number of seconds that the user interface element
remains actuated equates to a number of the Wong-Baker FACES.RTM.
Pain Rating Scale.
[0130] In the act 408, the discomfort monitor determines whether
the test pattern delivered in the previous iteration of the act 404
was tolerable to the patient. For example, the patient might
indicate that the last administered test pattern is the maximum
discomfort he or she is willing to tolerate by responding to a
prompt presented by the user interface requesting this information.
If the test pattern was tolerable, the treatment manager proceeds
to the act 410. In some examples, if additional data is desired and
the patient (or caregiver administering the baseline process 400)
has not aborted the baseline process 400, a same or different
(slightly higher or lower level) test pattern can be delivered to
confirm the patient's tolerance level. If the test pattern was not
tolerable, the treatment manager proceeds to the act 412. In some
examples, the discomfort monitor determines whether the test
pattern was tolerable at least in part by quantifying discomfort
information. The discomfort information quantified by the
discomfort monitor may have been acquired during execution of the
test pattern in the act 404 or may have been received as voluntary
input in response to one or more prompts provided to the user via
the user interface within the act 406 (i.e., after execution of the
test pattern in act 404 is complete). In some examples, the
discomfort monitor assigns a value to the discomfort parameter
based on the discomfort information. For instance, the discomfort
monitor may store any of the following values as the value of the
discomfort parameter: a value of a point on the discomfort scale
selected via user input, a value calculated based on an amount of
pressure exerted by the user on an element of the user interface
(e.g., a quartz or ceramic force sensor, or a piezoelectric
transducer), a value calculated based on a period of time a user
interface element is actuated, or a value calculated based on
motion of the patient or some other involuntary reaction to the
test pattern exhibited by the patient. For example, in the case of
a piezoelectric transducer, an active element (e.g., a polarized
material such as quartz (SiO2) or barium titanate (BaTiO3)) can
produce an electric field when the element changes dimensions as a
result of an imposed mechanical force. For example, a force applied
to a transducer or force sensor as described herein can be in a
range between 0-25 lbs. (110 N). In some examples, when more force
is applied, a resistance of the transducer can decrease. For
example, in the case of a Flexiforce.RTM. pressure sensor from
Tekscan.RTM., a resistance range changes from substantially open
circuit to about 50 k ohms. When the force is applied, the
resistance measured between leads of the transducer lowers until it
reaches a maximum force value (e.g., 25 lbs). In an implementation,
the force applied may be in the form of a user squeezing two
opposing surfaces of a sensor. The examples described herein are
not limiting and other kinds of force sensors can be used.
[0131] For example, in the case of a ceramic or quartz force
sensor, a piezoelectric transduction mechanism can be coupled to a
integrated circuit, e.g., a voltage or charge amplifier. The
applied force can produce a quantity of charge, e.g., Aq. The
charge accumulates in the crystal capacitance and forms a voltage
according to the law: .DELTA.V=.DELTA.q/C. For example, a low
capacitance quartz sensing element can produce a high voltage
output. In such applications, a MOSFET voltage amplifier can be
used to control the output voltage. Ceramic sensing elements can
exhibit a high charge output, and so can be coupled to a charge
amplifier.
[0132] In the manner described above, a discomfort parameter can be
calculated to correspond to a force sensed by a force sensor. For
instance, the discomfort parameter based on the force sensor can be
scaled to be within a range of 1-10 units (e.g., the parameter can
be configured in accordance to a predefined numerical relationship
to an output voltage level of the force sensor).
[0133] In some examples, the discomfort monitor determines whether
the test pattern was tolerable by comparing the value of the
discomfort parameter to a discomfort threshold value. This
discomfort threshold value may be a configurable parameter of the
medical device that may be adjusted to each particular patient. For
instance, in one example, the discomfort threshold is set to a
value of 4 in the Wong-Baker FACES.RTM. Pain Rating Scale.
Similarly, on the force sensor scale described above, the
discomfort threshold may be set to a value of 5. It is appreciated
that the patient discomfort scale and threshold as described above
can vary depending on the patient's personal preferences and/or the
caregiver's recommendations. For example, the scale employed may be
a percentage scale (e.g., 1-100) and a threshold can be set to be
40 percent of full range. In some examples, color coded zones may
be used to indicate the discomfort scale, e.g., a red zone
corresponding to maximum intensity, a yellow zone corresponding to
minimal discomfort, and a green zone corresponding to discomfort in
the middle of the range.
[0134] In some examples, the discomfort monitor determines that the
test pattern was tolerable where the value of the discomfort
parameter maintains a predefined relationship with a discomfort
threshold value (e.g., where the value of the discomfort parameter
does not transgress the discomfort threshold value). In these
examples, the discomfort monitor determines that the test pattern
was not tolerable where the value of the discomfort parameter does
not maintain a predefined relationship with the discomfort
threshold value (e.g. where the value of the discomfort parameter
is equal to or transgresses the discomfort threshold value). It is
appreciated that, depending on the specific calculations used, a
discomfort threshold value may be transgressed by a value that is
greater than or less than the discomfort threshold value.
[0135] In act 410, the discomfort monitor adjusts the test pattern.
In some examples, the discomfort monitor adjusts the test pattern
by varying characteristics of pulses included in the test pattern.
In these examples, each characteristic of each pulse may be varied
within its respective range as described above with reference to
the act 404. In general, the discomfort monitor adjusts one or more
characteristics upward within their respective ranges to increase
the efficacy of each pulse. For instance, in at least one example,
the discomfort monitor adjusts each characteristic upward by a step
value specified by a configurable parameter of the medical device.
One effect of this approach is to shorten the overall execution
time of the baseline process 400. Another effect of this approach
is to collect fewer test data points for subsequent analysis. In
another example, the discomfort monitor adjusts only one
characteristic upward by the step value. One effect of this
approach is to more precisely measure the effect that each
characteristic has on the patient. Another effect of this approach
is to collect more test data points for subsequent analysis. In
another example, the discomfort monitor adjusts some
characteristics upward by the step value and adjusts others
downward by a step value to establish discomfort parameter samples
for a broad mix of characteristics. It is appreciated that the step
values by which each characteristic is adjusted may reside on
continuums having different scales. Examples of these scales
include linear scales, log scales, and exponential scales.
[0136] Pacing discomfort may stem from at least two sources: 1)
electrical stimulation of the cutaneous nerves; and 2) skeletal
muscle contraction, particularly the intercostal muscles.
Electrical stimulation can feel to a patient like pin-pricks on the
skin, while skeletal muscle contraction can feel like getting hit
in the chest with a hammer or a fist. In examples, a degree of
cutaneous nerve stimulation can be difficult to measure
non-invasively but may be easier to ameliorate than the skeletal
muscle contraction. The cutaneous nerve stimulation may be reduced
by, for instance, increasing the resistivity of the electrically
conductive gel that is against the skin. Thus, some examples as
described herein can include and deploy electrically conductive gel
for pacing, such that a resistivity of the gel against the skin can
be varied in accordance with patient discomfort For example, in
some implementations, the impedance as seen by the pacing
electrodes can be varied as one of the pacing routine parameters in
response to the patient's discomfort management as described
herein.
[0137] In some example implementations, the device can measure a
degree of skeletal muscle stimulation and use the measurement to
determine the discomfort parameter. For instance, in some examples,
the discomfort monitor uses the value of the measurement as the
value of the discomfort parameter. In some examples, the discomfort
monitor calculates the discomfort parameter using the value of the
measurement and other factors, such as voluntary input as described
in detail herein.
[0138] In some examples, the discomfort monitor measures the degree
of skeletal muscle contraction using a flexible strain gauge
adhered to the patient's skin. The strain gauge may be composed of,
for instance, a bi-layer, laminate construction of polyvinylidene
fluoride (PVDF), also sometimes called Kynar. The bi-layer
construction generates a voltage inversely proportional to the
radius of curvature of the strain gauge laminate sheet. Thus the
electrical voltage generated by the strain gauge deformation will
be proportional to the degree of intercostal muscle contractions.
Alternatively, the measure of the degree of intercostal muscle
contraction may be accomplished by having at least two motion
sensors such as micro-electro-mechanical systems (MEMS)
accelerometers affixed to adjacent ribs and the relative motion
measured in, e.g., the 0-500 millisecond, time period subsequent to
the electrical pulse.
[0139] The patient may also enter a perceived discomfort via the
user interface, which is configured to receive this input. In these
examples, the discomfort monitor can be configured to store the two
values: e.g., the patient-perceived discomfort on the discomfort
scale and the measured skeletal muscle contraction. This sampling
can be repeated for two or more pacing parameters to create a
series of two or more vectors composed of at least a perceived
discomfort score (PDS) and a measure of skeletal muscle contraction
(SMC). In these examples, the discomfort monitor generates a lookup
table from the multiple values of PDS/SMC vectors that were
generated using the multiple instances of pacing parameters. The
pacing parameter may be pacing current, with the PDS/SMC vector
pairs generated, for instance, at 10-100 mA in 10 mA increments. An
example of such a lookup table is shown below:
TABLE-US-00001 Current 10 20 30 40 50 60 70 80 90 100 PDS 0 2 5 6 8
9 10 10 10 10 SMC 0.35 1.2 1.7 2.3 2.7 3.2 5.6 7.7 9.2 11.3
[0140] Thus, where the wearable medical device determines that the
patient is in need of pacing, the wearable medical device initiates
pacing with the pacing current amplitude that corresponds to a low
level of perceived discomfort of that particular patient. The
correspondence of PDS and SMC levels with changes in pacing
amplitude or other parameters can vary from patient to patient. As
such, an initial baselining process can be used to calibrate the
pacing parameter values with a particular patient's perception of
discomfort.
[0141] Next, the wearable medical device checks a patient
physiological parameter, such as the ECG or pulse oximetry. In some
examples, the wearable medical device checks the physiological
parameter by analyzing information transmitted by another wearable
device, such as an iWatch (from Apple, Inc., of Cupertino Calif.),
that is in wireless communication with the wearable medical device
via the sensor interface. Through this analysis, the wearable
medical device determines whether pacing has been effective and is,
therefore, generating blood flow. If the pacing is effective, then
the wearable medical device identifies the current pacing parameter
values as being an effective level for pacing that is still
comfortable for the patient.
[0142] If, however, a pulse or other measure of pacing
effectiveness is not detected in one or more of the physiological
parameter measurements, then the wearable medical device increases
the amplitude of a pacing parameter, for example, pacing current,
to the next setting. This will likely result in a higher level of
discomfort but also a higher chance of being effective. The
wearable medical device may repeat this process until pacing
effectiveness has been achieved. More elaborate search methods may
be employed, such as a binary search, to minimize the amount of
time required to achieve effective pacing.
[0143] Alternatively, instead of a lookup table, the wearable
medical device may generate a mathematical relationship--the
"discomfort estimation function" (DEF)--between the pacing
parameters, SMC, and an estimate of discomfort. The mathematical
relationship may be interpolation of the data points in the lookup
table. The interpolation may be linear or nonlinear as well as
employ splines. The wearable medical device may generate the
mathematical relationship using one or more techniques such as
logistic regression, neural networks, or fuzzy logic.
[0144] It has been found that patient's perceptions of discomfort
shift with varying external circumstances as well as internal
mental and emotional status. In another embodiment, the wearable
medical device estimates the patient's actual discomfort level by
analyzing the SMC measurements in real time (or near real time)
while pacing is occurring.
[0145] In some examples, the user interface includes one or more
elements that receive input indicating the discomfort level being
experienced by the patient during actual pacing process execution,
rather than as a result of operating in a baseline or test mode. In
these examples, the discomfort monitor stores these discomfort
levels for a particular set of pacing parameters during actual
pacing as a secondary, calibrating set that modifies the original
discomfort levels acquired during the baseline process 400. The
wearable medical device can use these additional data points to
provide a more accurate DEF estimate. For instance, the wearable
medical device may store the data points and calculate a new DEF in
real time (or near real time). In some examples, the wearable
medical device may transmit the actual pacing discomfort levels to
a server and database that stores the results for that patient as
well as many other patients. In these examples, the server may
execute the optimization and download new pacing parameter values
to the wearable medical device at some point after the clinical
event.
[0146] In act 412, the discomfort monitor uses the test data to
determine baseline values for the pacing parameters. In an example,
the discomfort monitor can select the baseline pacing parameter
values for the patient based on a predetermined relationship (e.g.,
a formula) between the patient's range of discomfort parameters,
the threshold discomfort, and underlying pacing parameters. For
example, the baseline pacing parameter values can be the pacing
parameter values corresponding to a discomfort parameter value that
is a fraction of the patient's discomfort threshold value, e.g.,
25-75% of the patient discomfort threshold.
[0147] In some implementations, the baseline pacing parameter
values can be selected without reference to the patient's
discomfort threshold. For example, the baseline pacing parameter
values can be a set of values selected at a lower (minimum) bound
of the ranges of values for the pacing parameters. For example, the
baseline pacing parameter values can be a set of values selected at
a lower (minimum) bound of the ranges of values for a first set of
pacing parameters (e.g., pulse amplitude and pulse width), and a
values selected around a middle of the range of values for a second
set of pacing parameters (e.g., pulse rate and/or pulse duty
cycle). It is appreciated that the baseline pacing parameter values
can be selected by any process reflecting the patient's tolerance
and are not limited to the examples described above. In some cases,
where a baseline process 400 is not available, a set of values can
be selected as default values in accordance with the principles
described herein.
[0148] In some implementations, the baseline process 400 may set
values for only a subset of the parameters. For example, the
baseline process 400 may set values for only an amplitude and a
pulse width. The remaining parameters may either be assigned
default values in accordance with the principles described herein,
or the manually provided by the patient and/or caregiver, e.g., via
a user interface.
[0149] In one example, the discomfort monitor determines the
baseline values of the pacing parameters by solving an optimization
problem. In this example, the discomfort monitor maximizes the
efficacy of each pacing routine executable by the treatment manager
subject to the range constraints described with reference to the
act 404 above and subject to the value of the discomfort parameter
maintaining a predefined relationship with to the discomfort
threshold value.
[0150] For instance, according to one example, for all pacing
pulses 1 to n in a pacing routine p, let the following variables
represent the following characteristics of pacing pulses and TENS
pulses, where 1.ltoreq.i.ltoreq.n. It is appreciated that each of
the pacing and TENS pulse characteristics in Table 1 and Table 2
below may be controlled by a pacing parameter set by the medical
device controller (e.g., controlled by treatment manager 314 of
medical device controller 300).
TABLE-US-00002 TABLE 1 Variable Pacing Pulse Characteristic a.sub.i
amplitude of pulse i w.sub.i width of pulse i r.sub.i rate of pulse
i v.sub.i waveform of pulse i p.sub.i period of pulse i d.sub.i
duty cycle of pulse i c.sub.i ramp time constant of pulse i
TABLE-US-00003 TABLE 2 Variable TENS Pulse Characteristic x.sub.i
amplitude of pulse i y.sub.i width of pulse i z.sub.i rate of pulse
i q.sub.i waveform of pulse i
[0151] Given these variables, the optimization problem to maximize
the efficacy of the baseline parameters may be formulated as
follows:
max .SIGMA..sub.i=1.sup.n f(i), where f(i) is the efficacy of a
pacing pulse resulting from the combination of pacing pulse
characteristics (a.sub.i, w.sub.i, r.sub.i, v.sub.i, p.sub.i,
d.sub.i, c.sub.i); subject to:
[0152] d(i).ltoreq.t for all i, where d(i) is the discomfort
parameter resulting from the pacing pulse characteristics (a.sub.i,
w.sub.i, r.sub.i, v.sub.i, p.sub.i, d.sub.i, c.sub.i) in
combination with the TENS pulse characteristics (x.sub.i, y.sub.i,
z.sub.i, q.sub.i) and t is the value of the discomfort
threshold;
[0153] 15 milliamps .ltoreq.a.sub.i.ltoreq.200 milliamps;
[0154] 0.5 milliseconds .ltoreq.w.sub.i.ltoreq.40 milliseconds;
[0155] 20 pacing pulses per minute .ltoreq.r.sub.i.ltoreq.200
pacing pulses per minute;
[0156] 20 microseconds .ltoreq.p.sub.i.ltoreq.500 microseconds;
[0157] 10 percent .ltoreq.d.sub.i.ltoreq.100 percent;
[0158] 40 microseconds .ltoreq.c.sub.i, .ltoreq.100
microseconds;
[0159] v.sub.i .di-elect cons. {rectilinear, pulse train, truncated
exponential, variable, biphasic};
[0160] 0 milliamps .ltoreq.x.sub.i, .ltoreq.200 milliamps;
[0161] 0.001 milliseconds .ltoreq.y.sub.i, .ltoreq.0.5
milliseconds;
[0162] 0.5 pulses per minute .ltoreq.z.sub.i.ltoreq.500 pulses per
minute; and
[0163] v.sub.i .di-elect cons. {rectilinear, pulse train,
biphasic};
In some examples, the discomfort monitor approximates d(i) by
fitting a mathematical function to the test data recorded during
the act 406 (by, for example, logistic regression analysis). In
these examples, the discomfort monitor uses the fitted expression
as a constraint in the optimization problem as described above and
solves the optimization problem to generate a set of baseline
parameter values (a.sub.b, w.sub.b, r.sub.b, v.sub.b, p.sub.b,
d.sub.b, c.sub.b, x.sub.b, y.sub.b, z.sub.b) for each pacing
routine p executable by the treatment manager. The baseline process
400 ends after execution of the act 412.
[0164] Processes in accord with the baseline process 400 enable
patients to establish an individualized set of baseline values for
the pacing parameters. The processes enable execution of tolerable
external pacing routines, thereby providing patients with a measure
of control not afforded by conventional external pacing processes.
Accordingly, the patient may initially be administered a pacing
routine in accordance with the established baseline values (e.g.,
as a set of default values for the pacing parameters). The patient
may then control the pacing parameters through one or more user
interface elements as described herein. In the event the patient is
unable to provide voluntary feedback, the medical device can use
other sensor information to determine and evaluate the efficacy of
the pacing routine as described herein.
[0165] In some examples, the optimization problem described above
may be applied to test data that represents a population of
patients to determine baseline values for the "average" patient.
These "average" baseline values may be stored as default values to
be used where the baseline process 400 has not been executed or
where the baseline process 400 is not available to be performed for
a patient prior to commencement of patient monitoring.
[0166] In one example, the following baselining procedure may be
employed.
[0167] First, set pace pulse width to 75 ms, no TENS, pace pulse
ramp to minimum (e.g. 0.01 milliseconds). These settings provide
for maximum effectiveness of pace pulse.
[0168] Second, for pace pulse amplitudes from 10 mA to 150 mA in
increments of 10 mA, check to see if there is pace pulse capture
and obtain the discomfort measure from the patient for each mA
setting.
[0169] Third, for the pace current setting that is at least 20 mA
higher than the first setting at which pacing capture was detected
("test pace current setting"), adjust the pace ramp from the
minimum ramp to a ramp of 75 ms in steps of 15 ms. Assess for pace
capture at each setting and the user's assessment of the discomfort
measure. Ramp time for step 4 ("test ramp time") below is the ramp
time value for which there has been no loss of pace capture and
results in the least amount of patient discomfort.
[0170] Fourth, setting the device to the test pace current setting
and the test ramp time, decrease the pace pulse width from 75 ms
down to 5 ms in increments of 10 ms. The "test pace pulse width" is
the pace pulse width that is 20 ms larger than the minimum pulse
width where capture was still achieved.
[0171] Using the test pace current setting, test ramp time, and
test pace pulse width, determine the response of the discomfort
measure to variation in the TENS parameters.
[0172] FIG. 17 illustrates an example baseline process 1700 in
accordance with an implementation based on the above process. For
example, the baseline process 1700 begins at 1702 where the
discomfort monitor (e.g., discomfort monitor 322 of treatment
manager 314 of FIG. 3) sets the pacing pulse width to 75
milliseconds, sets the pacing pulse ramp to minimum (e.g. 0.01
milliseconds), and sets the active TENS routine to none (e.g., no
TENS pulses). In implementations, such settings can provide for
maximum effectiveness of the pacing routine.
[0173] In act 1704, the discomfort monitor increases the pacing
pulse amplitude by a predetermined amount, e.g., in increments of
10 mA. In some implementations, both or either of the initial
pacing pulse amplitude and the predetermined increment in the
pacing pulse amplitude can be governed by user-configurable
parameters. For example, a default value for the initial pacing
pulse amplitude of 10 mA can be programmed into the device (either
during the initial device configuration or prior to shipping the
device to the caregiver). Similarly, a default value for the
increment in pacing pulse amplitude of 10 mA can be programmed into
the device. In implementations, the caregiver may be able to modify
these values for his or her patient. Once the initial pacing pulse
amplitude value is set, the discomfort monitor can gradually
increase the amplitude according to the predetermined increment
values. For example, the discomfort monitor can increase the pacing
pulse amplitude by 10 mA in each iteration. In some examples, the
discomfort monitor can be configured to change the increment value
for one or more iteration. For instance, after about 10-12
iterations, the discomfort monitor may increase the amplitude by
only 5 mA for each successive iteration.
[0174] In act 1706, the wearable medical device delivers one or
more pacing pulses in accordance to the pacing routine parameters
set in acts 1702-04. For example, the device may be configured to
deliver a preconfigured number of pulses (e.g., 1-3 or more
pulses).
[0175] In act 1708, the discomfort monitor records discomfort
information in accordance with the principles described herein.
Further, the cardiac monitor records capture information, e.g.,
checks to see if there is pacing pulse capture using one or more
techniques described herein. The recorded information is associated
with the pulse amplitude and either stored locally (e.g., on a
memory disposed within the device, such as, data storage 304 of
FIG. 3) or transmitted to a remote processing site.
[0176] In act 1710, the discomfort monitor determines whether the
pacing pulse amplitude is equal to a predetermined maximum
amplitude value, e.g., 150 milliamps. If the pacing pulse amplitude
is not equal to the predetermined maximum amplitude value of 150
milliamps, the discomfort monitor returns to the act 1704. If the
pacing pulse amplitude is equal to the predetermined maximum
amplitude value of 150 milliamps, the discomfort monitor proceeds
to act 1712.
[0177] In act 1712, the discomfort monitor determines the baseline
pacing pulse amplitude by identifying the first pacing pulse
amplitude that resulted in capture and adding a certain current
value, e.g., at least 20 milliamps, to the identified pacing pulse
amplitude. Also in act 1712, the discomfort monitor sets the pacing
pulse amplitude to the determined baseline pacing pulse amplitude,
e.g., the test pace current setting referenced above.
[0178] In act 1714, the discomfort monitor increases the pacing
ramp time by a predetermined amount, e.g., 15 microseconds.
[0179] In act 1715, the wearable medical device delivers one or
more pacing pulses and in act 1717, the discomfort monitor records
discomfort information and the cardiac monitor records capture
information.
[0180] In act 1718, the discomfort monitor determines whether the
pacing ramp time is equal to a predetermined maximum ramp time
value of, e.g., 75 microseconds. If the pacing ramp time is not
equal to the predetermined maximum ramp time value of 75
microseconds, the discomfort monitor returns to the act 1714. If
the pacing ramp time is equal to predetermined maximum ramp time
value of 75 microseconds, then the discomfort monitor proceeds to
act 1720.
[0181] In the act 1720, the discomfort monitor determines the
baseline ramp time by identifying the ramp time value for which
there was no loss of pacing capture and for which the patient
experiences the least amount of discomfort. Also in the act 1720,
the discomfort manager sets ramp time to the determined baseline
ramp time value, e.g., the test ramp time referenced above.
[0182] In act 1722, with the device set to the test pace current
setting and the test ramp time in accordance with the acts
described above, the discomfort manager decreases the pacing pulse
width by a predetermined amount, e.g., 10 microseconds. For
example, the initial pacing pulse width is set to be 75 ms, and is
decreased in the aforementioned steps of 10 ms to a minimum pacing
pulse width value of 5 ms. In act 1723, the wearable medical device
delivers one or more pacing pulses. In act 1724, the cardiac
monitor determines whether the pacing pulses resulted in capture.
If the pacing pulses resulted in capture, the discomfort monitor
returns to the act 1722. If the pacing pulses did not result in
capture, the discomfort monitor determines the baseline pulse width
value, e.g., the test pace pulse width, by identifying a smallest
pacing pulse width that resulted in capture and adding a
predetermined value, e.g., 20 milliseconds, to the identified
pacing pulse width.
[0183] In act 1728, with the device set to the above test pace
current setting, test ramp time, and test pace pulse width in
accordance with the acts described above, the discomfort manager
applies TENS routines with various parameters as described above,
acquires and records discomfort information for each, and
identifies the TENS routine parameters that are associated with the
least patient discomfort.
[0184] From the set of data generated from the baseline process
1700 above, a mathematical function can be derived that describes
the relationship between the pacing parameters (including, in some
implementations, the TENS parameters) and both discomfort and
pacing effectiveness, and known statistical methods such as
response surface methodology and logistic regression can be used to
find the optimal trade-off between minimizing discomfort and
maximizing pacing effectiveness. In one example, a process such as
response surface methodology (RSM) can be used to explore the
relationships between several explanatory variables and one or more
response variables in implementing a pacing effectiveness/patient
discomfort program. For example, a sequence of designed experiments
can be used to obtain an optimal response using at least a
second-degree polynomial model. For example, a first-degree
polynomial model can be used to determine which explanatory
variables may have an impact on the response variables of interest.
A more complicated design, such as a central composite design, can
be implemented to estimate a second-degree polynomial model for use
in the optimization of the parameters as described herein (e.g. to
maximize, minimize, or attain a specific target for the
parameters).
Example Pacing Management Process
[0185] As described above, various examples implement processes
through which a medical device manages discomfort experienced by a
patient during execution of a pacing routine. FIG. 5 illustrates
one such pacing management process 500. As shown, the pacing
management process 500 includes acts of receiving signals,
analyzing the received signals, determining whether the analyzed
signals represent a normal cardiac rhythm, identifying a pacing
routine to treat an arrhythmia, loading baseline pacing parameters
associated with the patient and the identified pacing routine, and
managing execution of the identified pacing routine.
[0186] In act 502, the treatment manager receives electrode signals
generated from detectable characteristics of the patient's cardiac
function via one or more electrodes (e.g., the electrode pairs 326
and 328 described above with reference to FIG. 3). In act 504, the
treatment manager analyzes the received signals using a cardiac
monitor (e.g., the cardiac monitor 320 described above with
reference to FIG. 3).
[0187] In act 506, the cardiac monitor determines whether the
patient's cardiac rhythm is normal. If so, the pacing management
process 500 returns to the act 502. Otherwise, the cardiac monitor
identifies an arrhythmia in act 508. In act 510, the treatment
manager determines whether the identified arrhythmia is treatable
by either a defibrillating shock or a pacing routine. Where the
treatment manager detects an arrhythmia that requires
defibrillation, the treatment manager may begin a defibrillation
treatment protocol potentially culminating in a defibrillating
shock. Where the treatment manager determines that the identified
arrhythmia is treatable by an identified pacing routine (e.g., from
the pacing routines 324 described above with reference to FIG. 3),
the treatment manager proceeds to act 512. The treatment manager
may determine that the identified arrhythmia is treatable by the
identified pacing routine by, for example, referring to one or more
configurable parameters stored in a data storage (e.g., the data
storage 304 described above with reference to FIG. 3) that
associates arrhythmias to pacing routines.
[0188] In the act 512, the treatment manager loads baseline pacing
parameters associated with the patient and identified pacing
routine. These baseline pacing parameters may identify a TENS
routine (e.g., from the TENS routines 334 described above with
reference to FIG. 3) to be executed in conjunction with the
identified pacing routine. As illustrated in FIG. 5 by dashed
lines, the act 512 is optional and may not be executed in some
examples where the baseline process 400 has been omitted. For
example, as indicated below, if a baseline process was not
completed, then default values can be used for the parameters of
the pacing routine.
[0189] In the act 514, the treatment manager executes the
identified pacing routine and any associated TENS routines as
described below with reference to FIGS. 6-8 and 16 and the pacing
management process 500 ends. The pacing management process 500 may
execute repeatedly during operation of the medical device to
monitor and treat the patient as needed. The following sections
describe processes that may be executed within the act 514.
Example Direct Control Pacing Process
[0190] In one example of the act 514, the treatment manager is
configured to provide the patient with direct control of a pacing
routine. FIG. 16 illustrates one example of a managed pacing
routine 1600 that is executed within the act 514. The managed
pacing routine 1600 executes a direct control pacing process that
is managed to decrease discomfort relative to conventional pacing
processes. As shown in FIG. 16, the managed pacing routine 1600
includes acts of delivering pacing pulses, calculating a discomfort
parameter, adjusting pacing parameters, and determining whether
pacing should continue.
[0191] In act 1602, the treatment manager delivers one or more
pacing pulses and monitors patient discomfort. In some examples,
the treatment manager delivers the one or more pacing pulses to the
patient according to the baseline parameters loaded in the act 512
described above with reference to FIG. 5. In examples where the act
512 has been omitted, the treatment manager delivers one or more
pacing pulses to the patient in accord with default pacing
parameters stored in the data storage. In at least one example, the
default pacing parameter values are each set at the upper bound
(maximum) of each range of values. In some examples, the default
pacing parameter values may be a set of values selected at a lower
(minimum) bound of the ranges of values. In some examples, the
default pacing parameter values may be a set of values selected at
a lower (minimum) bound of the ranges of values for a first set of
pacing parameters (e.g., pulse amplitude and pulse width), and a
values selected around a middle of the range of values for a second
set of pacing parameters (e.g., pulse rate and/or pulse duty
cycle). It is appreciated that one or more combinations of default
pacing parameter values for each pacing parameter can be selected.
In some implementations, rather than automatically using default
values, the treatment manager can prompt the user (e.g., patient
and/or caregiver) to provide initial values for the pacing
parameters via the user interface. For example, the user interface
element may provide a suggested range of values and prompt the user
to select from within the range. In some instances, the user may be
able to override the default pacing recommendations and provide his
or her own preferences for pacing parameters.
[0192] In some examples, the user may be prompted to specify an
initial discomfort threshold value, which the treatment manager can
use to determine the optimum pacing parameters, e.g., using the
optimization process described above. In an implementation, the
user can change a previously stored baseline and/or default
discomfort threshold value, or change any of the baseline and/or
default pacing parameter values.
[0193] In the act 1602, the one or more pacing pulses may be
delivered in conjunction with one or more TENS pulses executed
according to a TENS routine associated with the pacing routine
1600. In at least some examples, the TENS pulses are delivered
between pacing pulses, e.g., to distract the patient and further
reduce the discomfort experienced by the patient during the pacing
routine 1600.
[0194] In act 1604, the discomfort monitor prompts for, receives,
and records discomfort information and records any discomfort
information acquired during execution of the pacing pulses for
subsequent processing. In some examples, the discomfort information
is recorded in the data storage. This discomfort information may be
received as voluntary input from the user via the user interface.
Examples of discomfort information received via the user interface
include utterances (e.g., words, moans, groans, crying, or other
expressions) and actuation of a discomfort measuring and/or
indicating device (e.g., strain gauge, button, rotary dial, elastic
deformable solid). For example, the user can indicate a level of
discomfort he or she feels by actuating any of one or more user
interface elements as described herein.
[0195] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for the input by, for example, presenting a discomfort scale
via the user interface. The discomfort scale may include numeric
values and the user interface may request that the user rate the
discomfort experienced on the numeric scale. The discomfort scale
may also include graphical representations (e.g., faces) and the
user interface may request that the user rate the discomfort
experienced on the graphical scale. In some examples, the
discomfort monitor infers the intensity of the discomfort based on
the amount of pressure detected by the user interface or the amount
of time a user interface element remains actuated. For example, in
a manner similar to that outlined above for the baseline process,
the voluntary input may be in the form of actuation of one or more
user interface elements, such as a force sensor (e.g.,
piezoelectric, quartz, or ceramic based transducer), a push or
squeeze button, a rotary spring-loaded dial, or an elastic
deformable solid.
[0196] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for a change in input where the input has not changed state
for a time period greater than a value of a timeout configurable
parameter of the medical device. In this way, these examples
prevent involuntary input received as voluntary input from
affecting the behavior of the medical device for a time period
greater than the timeout.
[0197] Also in the act 1604, the discomfort monitor calculates a
discomfort parameter that quantifies the discomfort information.
This discomfort information quantified by the discomfort monitor
may have been voluntary input acquired during execution of the
pacing pulses in the act 1602 or may have been received as
voluntary input in response to one or more prompts provided to the
user via the user interface within the act 1604. In some examples,
the discomfort monitor assigns a value to the discomfort parameter
based on the discomfort information using one or more of the
mechanisms described herein (e.g., the mechanisms described above
with reference to the act 408 of FIG. 4). For instance, the
discomfort monitor may store any of the following values as the
value of the discomfort parameter: a value of a point on the
discomfort scale selected via user input, a value calculated based
on an amount of pressure exerted by the user on an element of the
user interface, or a value calculated based on motion of the
patient or some other voluntary action exhibited by the patient and
detected by the medical device. For example, the discomfort monitor
may cause the medical device to display the value of the discomfort
parameter to the user during administration of the pacing routine.
As noted above, a user interface may display the discomfort
information, for example, in the form of a numerical scale (e.g.,
1-10 scale, or percentage scale) or a color coded band of
zones.
[0198] In act 1606, the discomfort monitor dynamically adjusts the
pacing parameters in response to the patient's input. Accordingly,
where the patient is conscious and actively contributing discomfort
information (e.g., by providing feedback about discomfort
substantially in real time and during the administration of the
pacing routine), the discomfort monitor determines the adjusted
pacing parameters based on a predetermined relationship between the
pacing parameters and the discomfort parameter. For instance, where
discomfort parameter indicates a conscious patient experiencing a
high degree of discomfort, the discomfort monitor may adjust the
pacing parameters to deliver no pacing pulses, or only background
TENS pulses. Conversely, where the discomfort parameter indicates a
conscious patient is experiencing little or no discomfort, and
pacing is still required, the discomfort manager may adjust the
pacing parameters to deliver pacing pulses with higher efficacy
(e.g., by increasing, among other parameters, rate, width, and/or
amplitude) in accordance with the principles described herein.
[0199] In one example, the range of each pacing parameter within a
pacing routine is inversely mapped to a range including all
possible values of the discomfort parameter, with lower pacing
parameter values corresponding to higher discomfort parameters. In
this example, the discomfort manager converts the discomfort
parameters to pacing parameters using the inverse map, thereby
decreasing pacing parameters (and associated discomfort) in direct
portion to the intensity of discomfort reported by the patient.
[0200] In act 1608, the treatment manager receives (via the one or
more electrodes) and analyzes (via the cardiac monitor) electrode
signals generated from detectable characteristics of the patient's
cardiac function. During the analysis, the cardiac monitor
determines whether the patient's current cardiac condition warrants
further pacing. If so, the treatment manager returns to the act
1602 and continues execution of the pacing routine 1600. If the
cardiac monitor determines that the patient's current cardiac
condition does not warrant further pacing (e.g., determines that a
normal sinus rhythm has returned), the pacing routine 1600 ends. In
some examples, upon termination of the pacing routine 1600, the
treatment manager returns to the process 500 and continues to
monitor the patient's physiological signals, such as the patient's
ECG, temperature, pulse oxygen level, respiration, etc.
[0201] Processes in accord with the managed pacing routine 1600
enable patients to control parameters of pacing routines via
immediate feedback provided via a user interface element, thereby
enabling patients to actively manage discomfort associated with
external pacing processes.
[0202] In one example, the patient may not control the pacing
(including TENS) parameters individually, but rather controls the
degree to which the wearable medical device trades off
effectiveness of a pacing routine against discomfort. For instance,
the wearable medical device may determine, as a result of the
baseline process that the patient responds particularly well to
increases in pacing ramp time.
[0203] For example, the wearable medical device may determine that
the patient is responding well based on a parameter indicating that
there are larger changes (system gain) in patient discomfort levels
for a particular change in the pacing parameter (e.g., ramp time),
and at the same time smaller changes (system gain) in pacing
effectiveness for a particular change in the pacing parameter
(e.g., ramp time). In some examples, such a parameter can be based
on optimizing for either a difference or ratio of these two system
gains. For example, such a difference or ratio may be in the form
of a "parameter efficiency." These system gains can be estimated in
the slopes of the particular parameter on the response surface or
the coefficients of the logistic regression or other statistical
model.
[0204] In one example, the pacing parameters can be changed at the
same time in steps for each user request to decrement the pacing
discomfort. For example, the step sizes for each parameter can be
proportional to a predetermined parameter efficiency. In some
cases, the parameter with the highest parameter efficiency can be
changed first until there is some loss in pacing capture of the
patient, at which point the pacing parameter with the next highest
parameter efficiency can be changed in increments. In this manner,
the process can be repeated in a predetermined sequence for the
remaining parameters.
[0205] In some examples, the TENS parameters can be changed in a
similar fashion as described above either along with or after other
pacing pulse parameters have been set. This results in the changes
following along an optimal trajectory along the response surface,
minimizing pacing discomfort while maximizing pacing
effectiveness.
[0206] For example, the response surface may be dynamic depending
on the patient's mental or physiologic status or external
circumstances. Accordingly, in some embodiments, though the patient
may be capable of adjusting the pacing parameters to reduce
discomfort, the reduction may be temporary, as a reduction in
discomfort may introduce some increase in the level of pacing
effectiveness. In one scenario, patient-initiated reduction in
discomfort could cause a pacing routine to no longer be effective.
As such, if user input is provided by the patient that the
discomfort is perceived to be too high, then the discomfort monitor
can modify one or more of the pacing parameters to decrease the
patient discomfort. Assuming that the original settings provided
maximum pacing effectiveness, after a predetermined period of time
of e.g., about 5 seconds to 5 minutes, the device can begin to
revert all the modified pacing parameters to their original, more
effective settings. In this fashion, if the patient loses
consciousness because the pacing was ineffectiveness in generating
sufficient blood flow, then the device can automatically revert to
a life-sustaining (albeit uncomfortable) pacing parameter settings.
In some examples, the pacing parameters may be modified in such a
fashion that the pacing remains optimally effective during the
course of the parameter modifications. In some examples,
maintaining optimal effectiveness during the course of parameter
modification may take the form of having the parameter changes
follow the response surface determined during prior testing and
baselining of the patient, or of multiple patients.
[0207] In some implementations, the pacing parameter settings may
be regulated by a pressure sensitive input, such that, as long as
the patient is squeezing the pressure (or force) sensitive input
with at least some predetermined threshold level of pressure (or
force) then the device will not continue to revert to the original
settings.
[0208] In some implementations, the pressure sensing may be
continuous or substantially continuous, and the patient themselves
can autoregulate their pacing parameter settings as described
herein.
Fixed Rate and Energy Pacing
[0209] In accordance with one example of the act 514, the treatment
manager is configured to manage patient discomfort while pacing the
heart of a patient at a fixed rate and fixed energy. Fixed rate and
energy pacing may be appropriate in response to various types of
cardiac arrhythmias. Examples of these types of cardiac arrhythmias
include bradycardia, a lack of sensed cardiac activity (spontaneous
or post shock asystole), and pulseless electrical activity. In some
cases, these cardiac arrhythmias may occur before or after one or
more defibrillation shocks. For example, the treatment manager may
be configured to provide pulses at a fixed energy level, a fixed
pulse width, and a fixed frequency in response to detection of any
of the above-noted events via the ECG sensing electrodes. The
energy level of the pacing pulses may be set to a fixed value by
applying a desired current waveform for a determined duration of
time by one or more of the plurality of therapy electrodes.
[0210] FIG. 6 illustrates one example of a managed pacing routine
600 that is executed within the act 514. The managed pacing routine
600 executes a fixed rate and energy pacing process that is managed
to decrease discomfort relative to conventional pacing processes.
As shown in FIG. 6, the managed pacing routine 600 includes acts of
delivering pacing pulses, calculating a discomfort parameter,
adjusting pacing parameters, and determining whether pacing should
continue.
[0211] In act 602, the treatment manager delivers one or more
pacing pulses to the patient according to the baseline parameters
loaded in the act 512 described above with reference to FIGS. 5 and
16. In examples where the act 512 has been omitted, the treatment
manager delivers one or more pacing pulses to the patient in accord
with default pacing parameters stored in the data storage. In the
act 602, the one or more pacing pulses may delivered in conjunction
with one or more TENS pulses executed according to a TENS routine
associated with the pacing routine 600.
[0212] In act 604, the discomfort monitor prompts for, receives,
and records discomfort information and records any discomfort
information acquired during execution of the pacing pulses for
subsequent processing. In some examples, the discomfort information
is recorded in the data storage. This discomfort information may be
received as voluntary or involuntary input from the user via the
user interface or may be acquired from one or more other sensors
coupled to a sensor interface. Examples of discomfort information
received via the user interface include utterances (e.g., words,
moans, groans, crying, or other expressions) and actuation of a
discomfort measuring and/or indicating device (e.g., strain gauge,
button, rotary dial, elastic deformable solid). For example, the
user can indicate a level of discomfort he or she feels by
actuating any of one or more user interface elements as described
herein. Examples of discomfort information received via other
sensors (e.g., motion detection sensors, strain gauges in a
garment) include movements (e.g., tensing of muscles, jerking,
shuttering, flinching, changes in respiration) and lack of
movement.
[0213] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for the input by, for example, presenting a discomfort scale
via the user interface. The discomfort scale may include numeric
values and the user interface may request that the user rate the
discomfort experienced on the numeric scale. The discomfort scale
may also include graphical representations (e.g., faces) and the
user interface may request that the user rate the discomfort
experienced on the graphical scale. In some examples, the
discomfort monitor infers the intensity of the discomfort based on
the amount of pressure detected by the user interface or the amount
of time a user interface element remains actuated. For example, in
a manner similar to that outlined above for the baseline process,
the voluntary input may be in the form of actuation of one or more
user interface elements, such as a force sensor (e.g.,
piezoelectric, quartz, or ceramic based transducer), a push or
squeeze button, a rotary spring-loaded dial, or an elastic
deformable solid.
[0214] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for a change in input where the input has not changed state
for a time period greater than a value of a timeout configurable
parameter of the medical device. In this way, these examples
prevent involuntary input received as voluntary input from
affecting the behavior of the medical device for a time period
greater than the timeout.
[0215] In the act 606, the discomfort monitor determines whether
the pacing pulses delivered in the previous iteration of the act
602 were tolerable to the patient based on any of the mechanisms
described herein. If the pacing pulses were tolerable, the
treatment manager proceeds to the act 610. If the pacing pulses
were not tolerable, the treatment manager proceeds to the act 608.
In some examples, the discomfort monitor determines whether the
pacing pulses were tolerable at least in part by quantifying
discomfort information. This discomfort information quantified by
the discomfort monitor may have been acquired during execution of
the pacing pulses in the act 602 or may have been received as
voluntary input in response to one or more prompts provided to the
user via the user interface within the act 604 (i.e., after
execution of the pacing pulses in act 602 is complete). In some
examples, the discomfort monitor assigns a value to the discomfort
parameter based on the discomfort information using one or more of
the mechanisms described herein (e.g., the mechanisms described
above with reference to the act 408 of FIG. 4). For instance, the
discomfort monitor may store any of the following values as the
value of the discomfort parameter: a value of a point on the
discomfort scale selected via user input, a value calculated based
on an amount of pressure exerted by the user on an element of the
user interface, or a value calculated based on motion of the
patient or some other involuntary reaction to the pacing pulses
exhibited by the patient.
[0216] In some examples, the discomfort monitor determines whether
the pacing pulses were tolerable by comparing the value of the
discomfort parameter to a discomfort threshold value. This
discomfort threshold value may be a configurable parameter of the
medical device. In some examples, the discomfort monitor determines
that the pacing pulses were tolerable where the value of the
discomfort parameter maintains a predefined relationship with to
the discomfort threshold value (e.g., where the value of the
discomfort parameter does not transgress the discomfort threshold
value). In these examples, the discomfort monitor determines that
the pacing pulses were not tolerable where the value of the
discomfort parameter does not maintain a predefined relationship
with the discomfort threshold value (e.g. where the value of the
discomfort parameter is equal to or transgresses the discomfort
threshold value). It is appreciated that, depending on the specific
calculations used, a discomfort threshold value may be transgressed
by a value that is greater than or less than the discomfort
threshold value.
[0217] In act 608, the discomfort monitor adjusts the pacing
parameters. In some examples, the discomfort monitor determines the
adjusted pacing parameters substantially in real time based on
immediate feedback from the patient as described above with
reference to FIG. 16.
[0218] In some examples, where voluntary feedback is unavailable
(e.g., the patient is unable to provide dynamic feedback regarding
his or her level of discomfort) the discomfort monitor determines
the adjusted pacing parameters in a similar manner as outlined
above with respect to the baseline process 400 by solving an
optimization problem similar to the optimization problem described
above with reference to described above with reference to act 412
of FIG. 4. However, the optimization problem solved within the act
608 replaces these constraints:
[0219] 15 milliamps .ltoreq.a.sub.i.ltoreq.200 milliamps;
[0220] 0.5 milliseconds .ltoreq.w.sub.i.ltoreq.40 milliseconds;
and
[0221] 20 pacing pulses per minute .ltoreq.r.sub.i.ltoreq.200
pacing pulses per minute with the following constraints:
[0222] a.sub.i=a.sub.b (or the value of a configurable parameter
set for fixed energy and rate pacing);
[0223] w.sub.i=w.sub.b (or the value of a configurable parameter
set for fixed energy and rate pacing); and
[0224] r.sub.i=r.sub.b (or the value of a configurable parameter
set for fixed energy and rate pacing). In addition, the discomfort
monitor improves any approximation of the function d(i) by
incorporating the data point(s) generated in act 606.
[0225] In act 610, the treatment manager receives (via the one or
more electrodes) and analyzes (via the cardiac monitor) electrode
signals generated from detectable characteristics of the patient's
cardiac function. The cardiac monitor determines whether the
patient's current cardiac condition warrants further pacing. If so,
the treatment manager returns to the act 602 and continues
execution of the pacing routine 600. If the cardiac monitor
determines that the patient's current cardiac condition does not
warrant further pacing (e.g., determines whether a normal sinus
rhythm has returned), the pacing routine 600 ends. In some
examples, upon termination of the pacing routine 600, the treatment
manager returns to the process 500 and continues to monitor the
patient's physiological signals, such as the patient's ECG,
temperature, pulse oxygen level, respiration, etc.
[0226] During an initial fitting of a medical device that may
execute the fixed rate and energy pacing routine 600, the level of
current (pulse amplitude), the pulse width, and the frequency
(rate) of the pulses may be set to an appropriate level based on
the input of a medical professional (such as the patient's
cardiologist) and the physiological condition of the patient (e.g.,
based on the patient's normal resting heart rate, the patient's
thoracic impedance, etc.) In some examples, the level of current,
the pulse width, and the frequency of the pulses may simply be set
to an appropriate value based on typical impedance values for an
adult or child, and typical resting heart rates for an adult or
child. This initial fitting may be performed in accord with the act
402 described above with reference to FIG. 4 or otherwise.
[0227] It should be appreciated that because pacing at a fixed rate
may interfere with the patient's own intrinsic heart rate, the
treatment manager can be configured to perform such fixed rate and
energy pacing only in the event of a life-threatening bradycardia,
a lack of any detected cardiac activity following shock, or in
response to pulseless electrical activity following a shock.
[0228] Processes in accord with the managed pacing routine 600
enable patients to control parameters of pacing routines via
feedback provided to a user interface, thereby enabling patients to
actively manage discomfort associated with external pacing
processes.
Demand (Adjustable Rate) Pacing
[0229] In accordance with one example of the act 514, the treatment
manager is configured to manage patient discomfort while pacing the
heart of a patient at a variable rate and a fixed energy. Variable
rate and fixed energy pacing may be appropriate in response to
various types of cardiac arrhythmias, including a bradycardia
(i.e., an excessively slow heart rate below 40 beats per minute),
tachycardia (i.e., an excessively fast heart rate), an erratic
heart rate with no discernible regular sinus rhythm, a lack of
sensed cardiac activity (asystole), and pulseless electrical
activity. Some of these cardiac arrhythmias may occur following one
or more defibrillation shocks.
[0230] As known to those skilled in the art, pacing at a fixed rate
and energy may not be appropriate for the particular type of
cardiac arrhythmia of the patient, and even where the rate and
energy level are appropriate, pacing at a fixed rate can result in
competition between the rate at which the pacing pulses are being
applied and the intrinsic rhythm of the patient's heart. For
example, pacing at a fixed rate may result in the application of a
pacing pulse during the relative refractory period of the normal
cardiac cycle (a type of R wave on a T wave effect) that could
promote ventricular tachycardia or ventricular fibrillation. To
overcome some of the disadvantages of fixed rate and energy pacing,
the treatment manager can be configured to perform demand pacing,
wherein the rate of the pacing pulses may be varied dependent on
the physiological state of the patient and the patient's current
discomfort parameter. For example, during demand pacing, the
treatment manager can deliver a pacing pulse only when needed by
the patient. In general, when executing in demand mode, the device
searches for any intrinsic cardiac activity of the patient, and if
a heartbeat is not detected within a designated interval, a pacing
pulse is delivered and a timer is set to the designated interval.
Where the designated interval expires without any detected
intrinsic cardiac activity of the patient, another pacing pulse is
delivered and the timer reset. In some examples, where an intrinsic
heartbeat of the patient is detected within the designated
interval, the device resets the timer and continues to search for
intrinsic cardiac activity.
[0231] FIG. 9 helps to illustrate some of the aspects of demand
pacing and the manner in which demand pacing can be performed by
the treatment manager. As illustrated in FIG. 9, when executing
demand pacing, the treatment manager may have a variable pacing
interval 910 corresponding to the rate at which pacing pulses are
delivered to the patient in the absence of any intrinsic cardiac
activity as may be detected by the cardiac monitor. For example,
the rate at which pulsing paces are to be delivered to the patient
(referred to as the "base pacing rate" herein) may be set at 60
pulses per minute and therefore, the corresponding base pacing
interval 910 would be set to 1 second.
[0232] Although the base pacing rate may be set to a particular
value based on the physiological condition of the patient and input
from a medical professional, the treatment manager can include a
number of different pacing routines to respond to different cardiac
arrhythmias, such as bradycardia, tachycardia, an erratic heart
rate with no discernible regular sinus rhythm, asystole, or
pulseless electrical activity. These pacing routines may be
implemented using a variety of hardware and software components and
examples are not limited to a particular configuration of hardware
or software. For instance, the pacing routines may be implemented
using an application-specific integrated circuit (ASIC) tailored to
perform the functions described herein.
[0233] The treatment manager may also have a hysteresis rate (not
shown in FIG. 9) corresponding to the detected intrinsic heart rate
of the patient below which the device performs pacing. According to
some examples, the hysteresis rate is a configurable parameter that
is expressed as a percentage of the patient's intrinsic heart rate.
In the above example, the hysteresis rate may correspond to 50
beats per minute. In this example, if the intrinsic heart rate of
the patient fell to 50 beats per minute or below (e.g., more than
approximately 1.2 seconds between detected beats), the treatment
manager would generate and apply a pacing pulse to the patient.
[0234] During application of a pacing pulse to the body of a
patient and a short time thereafter, the treatment manager may
intentionally blank out a portion of the ECG signals being received
by the ECG monitoring and detection circuitry (e.g., the
electrodes, sensor interface, and cardiac monitor) to prevent this
circuitry, which may include amplifiers, A/D converters, etc. from
being overwhelmed (e.g., saturated) by the pacing pulse. This may
be performed in hardware, software, or a combination of both. This
period of time, referred to herein as "the blanking interval" 920
may vary (e.g., between approximately 30 milliseconds to 200
milliseconds), but is typically between approximately 40
milliseconds to 80 milliseconds in duration.
[0235] In addition to the blanking interval 920, the treatment
manager can have a variable refractory period 930 that may vary
dependent upon the base pacing rate. The refractory period 930
corresponds to a period of time in which signals sensed by the ECG
sensing electrodes are ignored, and may include the blanking
interval. The refractory period 930 allows any generated QRS
complexes or T waves induced in the patient by virtue of the pacing
pulse to be ignored, and not interpreted as intrinsic cardiac
activity of the patient. The refractory period can be configured as
is done with VVI implanted pacemakers, e.g., with a single chamber,
ventricular sensed, ventricular stimulation pacemakers known to
those skilled in the art. For example, the refractory period can be
an interval following a paced or sensed event in the chamber
containing the pacing or sensing lead, during which the inhibited
(SSI) or triggered (SST) pacemaker is not reset. In a VVI
pacemaker, a first part of the refractory period is a programmable,
absolutely refractory blanking period. For example, it prevents a
resetting of the pacemaker by a sensing of a) post-pacing
ventricular potentials, b) the end of the QRS, or c) the T wave.
For example, an occurrence of an event during the blanking period
may not be visible on the marker channels. For typical
applications, the refractory period is generally between about 150
milliseconds and 400 milliseconds.
[0236] In one example, the sensitivity of the ECG monitoring and
detection that is performed by the treatment manager may also be
varied to adjust the degree by which the ECG monitoring and
detection circuitry can detect the patient's intrinsic cardiac
activity. For example, where the amplitude of certain discernible
portions (e.g., an R-wave) of a patient's intrinsic ECG signal is
below that typically encountered, the voltage threshold over which
this discernible portion can be detected as belonging to an ECG
signal (and not attributed to noise or other factors) may be
lowered, for example from 2.5 millivolts to 1.5 millivolts, to
better detect the patient's intrinsic cardiac activity. For
instance, during an initial fitting of the medical device, the
sensitivity threshold of the device may be reduced to a minimal
value (e.g., 0.4 millivolts) and the patient's intrinsic ECG
signals may be monitored. The sensitivity threshold may then be
incrementally increased (thereby decreasing the sensitivity of the
device) and the patient's intrinsic ECG signals monitored until
these ECG signals are no longer sensed. The sensitivity threshold
may then be incrementally decreased (thereby increasing the
sensitivity of the device) until the patient's intrinsic ECG
signals are again sensed, and the sensitivity threshold of the
device may be set to approximately half this value.
[0237] As with fixed energy and rate pacing, the treatment manager
may be configured during an initial fitting per the act 402 or
otherwise to provide pulses at a fixed energy level and a fixed
pulse width in response to detection of any of the above-noted
events by the cardiac monitor. The maximum current level of the
current waveform may be set to a value between approximately 10
milliamps to 200 milliamps, the pulse width may be set to a fixed
value between approximately 20 milliseconds to 40 milliseconds, and
the base rate of the pulses may be set to a fixed value between
approximately 30 pulses per minute to approximately 200 pulses per
minute, although the actual rate of the pacing pulses can vary
based upon the intrinsic cardiac activity of the patient. In
accordance with one example, a 40 millisecond constant current
pulse is used, and the current level is set to a fixed value based
upon the input of a medical professional, such as the patient's
cardiologist and the physiological condition of the patient. The
base pacing rate and the hysteresis rate may also be set based upon
the input of the patient's cardiologist (or other medical
professional) and the physiological condition of the patient, and
the blanking interval and refractory period set to an appropriate
time interval based upon the base pacing rate and/or the hysteresis
rate.
[0238] FIG. 7 illustrates one example of a managed pacing routine
700 that is executed within the act 514. The managed pacing routine
700 executes a variable rate and fixed energy pacing process that
is managed to decrease discomfort relative to conventional pacing
processes. As shown in FIG. 7, the managed pacing routine 700
includes acts of delivering pacing pulses, calculating a discomfort
parameter, adjusting pacing parameters, and determining whether
pacing should continue.
[0239] In act 702, the treatment manager delivers one or more
pacing pulses to the patient according to the baseline parameters
loaded in the act 512 described above with reference to FIG. 5. In
examples where the act 512 has been omitted, the treatment manager
delivers one or more pacing pulses to the patient in accord with
default pacing parameters stored in the data storage. In the act
702, the one or more pacing pulses may be delivered in conjunction
with one or more TENS pulses executed according to a TENS routine
associated with the pacing routine 700.
[0240] In act 704, the discomfort monitor prompts for, receives,
and records discomfort information and records any discomfort
information acquired during execution of the pacing pulses for
subsequent processing. In some examples, the discomfort information
is recorded in the data storage. This discomfort information may be
received as voluntary or involuntary input from the user via the
user interface or may be acquired from one or more other sensors
coupled to a sensor interface. Examples of discomfort information
received via the user interface include utterances (e.g., words,
moans, groans, crying, or other expressions) and actuation of a
discomfort measuring and/or indicating device (e.g., strain gauge,
button, rotary dial, elastic deformable solid). For example, the
user can indicate a level of discomfort he or she feels by
actuating any of one or more user interface elements as described
herein. Examples of discomfort information received via other
sensors (e.g., motion detection sensors, strain gauges in a
garment) include movements (e.g., tensing of muscles, jerking,
shuttering, flinching, changes in respiration) and lack of
movement.
[0241] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for the input by, for example, presenting a discomfort scale
via the user interface. The discomfort scale may include numeric
values and the user interface may request that the user rate the
discomfort experienced on the numeric scale. The discomfort scale
may also include graphical representations (e.g., faces) and the
user interface may request that the user rate the discomfort
experienced on the graphical scale. In some examples, the
discomfort monitor infers the intensity of the discomfort based on
the amount of pressure detected by the user interface or the amount
of time a user interface element remains actuated. For example, in
a manner similar to that outlined above for the baseline process,
the voluntary input may be in the form of actuation of one or more
user interface elements, such as a force sensor (e.g.,
piezoelectric, quartz, or ceramic based transducer), a push or
squeeze button, a rotary spring-loaded dial, or an elastic
deformable solid.
[0242] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for a change in input where the input has not changed state
for a time period greater than a value of a timeout configurable
parameter of the medical device. In this way, these examples
prevent involuntary input received as voluntary input from
affecting the behavior of the medical device for a time period
greater than the timeout.
[0243] In the act 706, the discomfort monitor determines whether
the pacing pulses delivered in the previous iteration of the act
702 were tolerable to the patient. If the pacing pulses were
tolerable, the treatment manager proceeds to the act 710. If the
pacing pulses were not tolerable, the treatment manager proceeds to
the act 708. In some examples, the discomfort monitor determines
whether the pacing pulses were tolerable at least in part by
quantifying discomfort information. This discomfort information
quantified by the discomfort monitor may have been acquired during
execution of the pacing pulses in the act 702 or may have been
received as voluntary input in response to one or more prompts
provided to the user via the user interface within the act 704
(i.e., after execution of the pacing pulses in act 702 is
complete). In some examples, the discomfort monitor assigns a value
to the discomfort parameter based on the discomfort information
using one or more of the mechanisms described herein (e.g., the
mechanisms described above with reference to the act 408 of FIG.
4). For instance, the discomfort monitor may store any of the
following values as the value of the discomfort parameter: a value
of a point on the discomfort scale selected via user input, a value
calculated based on an amount of pressure exerted by the user on an
element of the user interface, or a value calculated based on
motion of the patient or some other involuntary reaction to the
pacing pulses exhibited by the patient.
[0244] In some examples, the discomfort monitor determines whether
the pacing pulses were tolerable by comparing the value of the
discomfort parameter to a discomfort threshold value. This
discomfort threshold value may be a configurable parameter of the
medical device. In some examples, the discomfort monitor determines
that the pacing pulses were tolerable where the value of the
discomfort parameter maintains a predefined relationship with to
the discomfort threshold value (e.g., where the value of the
discomfort parameter does not transgress the discomfort threshold
value). In these examples, the discomfort monitor determines that
the pacing pulses were not tolerable where the value of the
discomfort parameter does not maintain a predefined relationship
with the discomfort threshold value (e.g. where the value of the
discomfort parameter is equal to or transgresses the discomfort
threshold value). It is appreciated that, depending on the specific
calculations used, a discomfort threshold value may be transgressed
by a value that is greater than or less than the discomfort
threshold value.
[0245] In act 708, the discomfort monitor adjusts the pacing
parameters. In some examples, the discomfort monitor determines the
adjusted pacing parameters substantially in real time based on
immediate feedback from the patient as described above with
reference to FIG. 16.
[0246] In some examples, where voluntary feedback is unavailable
(e.g., the patient is unable to provide dynamic feedback regarding
his or her level of discomfort) the discomfort monitor determines
the adjusted pacing parameters in a similar manner as outlined
above with respect to the baseline process 400 by solving an
optimization problem similar to the optimization problem described
above with reference to described above with reference to act 412
of FIG. 4. However, the optimization problem solved within the act
708 replaces the these constraints:
[0247] 15 milliamps .ltoreq.a.sub.i.ltoreq.200 milliamps;
[0248] 0.5 milliseconds .ltoreq.w.sub.i.ltoreq.40 milliseconds;
and
[0249] 20 pacing pulses per minute .ltoreq.r.sub.i.ltoreq.200
pacing pulses per minute;
with the following constraints:
[0250] a.sub.i=a.sub.b (or the value of a configurable parameter
set for demand pacing);
[0251] w.sub.i=w.sub.b (or the value of a configurable parameter
set for demand pacing); and
[0252] r.sub.i.gtoreq.hysteresis rate. In addition, the discomfort
monitor improves any approximation of the function d(i) by
incorporating the data point(s) generated in act 706.
[0253] In act 710, the treatment manager receives (via the one or
more electrodes) and analyzes (via the cardiac monitor) electrode
signals generated from detectable characteristics of the patient's
cardiac function. The cardiac monitor determines whether the
patient's current cardiac condition warrants further pacing. If so,
the treatment manager returns to the act 702 and continues
execution of the pacing routine 700. If the cardiac monitor
determines that the patient's current cardiac condition does not
warrant further pacing (e.g., determines whether a normal sinus
rhythm has returned), the pacing routine 700 ends. In some
examples, upon termination of the pacing routine 700, the treatment
manager returns to the process 500 and continues to monitor the
patient's physiological signals, such as the patient's ECG,
temperature, pulse oxygen level, respiration, etc.
[0254] Processes in accord with the managed pacing routine 700
enable patients to control parameters of pacing routines via
feedback provided to a user interface, thereby enabling patients to
actively manage discomfort associated with external pacing
processes.
Demand Pacing--Bradycardia
[0255] As discussed above, where bardycardia is detected and the
intrinsic cardiac rate of the patient is below that of the
hysteresis rate, the treatment manager will pace the patient at the
pre-set base pacing rate and manage the patient's discomfort by
executing the pacing routine process 700. During this time, the
device will continue to monitor the patient's intrinsic heart rate
and will withhold pacing pulses in the event that an intrinsic
heartbeat is detected within designated interval corresponding to
the hysteresis rate. This type of on demand pacing is frequently
termed "maintenance pacing."
Demand Pacing--Tachycardia
[0256] For responding to tachycardia, the treatment manager may
additionally include another pacing rate, referred to as an
"anti-tachyarrhythmic pacing rate" herein, above which the
treatment manager will identify that the patient is suffering from
tachycardia, and will pace the patient in a manner to bring the
patient's intrinsic heart back toward the base pacing rate and
manage the patient's discomfort by executing the pacing routine
process 700. For example, the treatment manager may employ a
technique known as overdrive pacing wherein a series of pacing
pulses (e.g., between about 5 and 10 pacing pulses) are delivered
to the patient at a rate above the intrinsic rate of the patient in
an effort to gain control of the patient's heart rate. Once it is
determined that the treatment manager is in control of the
patient's heart rate, the rate of the pulses may be decremented,
for example by about 10 milliseconds, and another series of pacing
pulses delivered. This delivery of pulses and the decrease in
frequency may continue until the detected intrinsic cardiac rate of
the patient is below the anti-tachyarrhythmic pacing rate. This
type of pacing is frequently termed "overdrive pacing" or "fast
pacing."
Demand Pacing--Erratic Heart Rate
[0257] For responding to an erratic heart rate, the treatment
manager may perform a type of pacing that is similar to a
combination of maintenance pacing and overdrive pacing discussed
above. For example, where the treatment manager detects an erratic
heart rate with no discernible sinus rhythm, the treatment manager
may deliver a series of pacing pulses (e.g., between about 5 and 10
pacing pulses) to the patient at a particular rate, while managing
the patient's discomfort in accord with the pacing routine 700.
This rate may be one that is above a lower rate of a series of
detected intrinsic beats of the patient's heart and below an upper
rate of the detected intrinsic beats of the patient's heart. After
delivering the series of pulses, the treatment manager may monitor
the patient's heart to determine if it has synchronized to the rate
of the series of delivered pulses. Where the intrinsic rate of the
patient's heart is still erratic, the treatment manager may
increase the rate of the series of pulses and deliver another
series. This may continue until it is established that the
patient's heart assumes a more regular state. Upon determining that
the patient's heart is in a more regular state, the treatment
manager may perform maintenance pacing if it is determined that the
patient's intrinsic heart rate is too low as discussed in the
"Demand Pacing--Bradycardia" section above, or perform pacing at a
decremented rate in the manner discussed in "Demand
Pacing--Tachycardia" section above, if such is warranted.
Demand Pacing--Asystole or Pulseless Electrical Activity
[0258] For responding to asystole or a detected condition of
pulseless electrical activity, the treatment manager may perform
maintenance pacing similar to that described in the "Demand
Pacing--Bradycardia" section above and manage patient discomfort by
executing the pacing routine 700. This type of pacing would be
performed after a series of one or more defibrillating shocks that
attempt to restore a normal sinus rhythm to the heart of the
patient.
[0259] In each of the types of pacing described above, the
treatment manager may be configured to perform a particular type of
pacing only after a programmable delay after such cardiac
arrhythmias are detected, or after a programmable period of time
after one or more defibrillating shocks are delivered.
Capture Management
[0260] In one example of the act 514, the treatment manager is
configured to manage patient discomfort while pacing the heart of a
patient using capture management with an adjustable energy level
and an adjustable rate in response to various types of cardiac
arrhythmias. The various types of cardiac arrhythmias can include a
bradycardia, tachycardia, an erratic heart rate with no discernible
regular sinus rhythm, a lack of sensed cardiac activity (asystole)
following or independent of one or more defibrillation shocks, a
life-threatening bradycardia following one or more defibrillation
shocks, or pulseless electrical activity following one or more
defibrillation shocks.
[0261] As known to those skilled in the art, capture management
refers to a type of pacing in which the energy level of pacing
pulses and the rate of delivery of those pacing pulses may be
varied based upon the detected intrinsic activity level of the
patient's heart and the detected response of the patient's heart to
those pacing pulses. In cardiac pacing, the term "capture" is used
to refer to the response of a patient's heart to a pulse of energy
which results in ventricular depolarization. In cardiac pacing, it
is desirable to limit the amount of energy in each pulse to a
minimal amount required for capture; thereby decreasing the amount
of discomfort associated with external pacing.
[0262] In general, the manner in which the treatment manager
performs capture management pacing is similar to that of demand
pacing described above, in that it may adjust the rate at which
pacing pulses are delivered based upon the detected intrinsic rate
of cardiac activity of the patient and, potentially, based on the a
level of discomfort being experienced by the patient. The
sensitivity of the device to the patient's ECG may be adjusted in a
similar manner to that described above with respect to demand
pacing. Further, capture management pacing may be used to treat the
same types of cardiac arrhythmias as the demand pacing described
above, such as bradycardia, tachycardia, an erratic heart rate with
no discernible sinus rhythm, asystole, or pulseless electrical
activity.
[0263] However, in contrast to a medical device that performs
demand pacing, a medical device that is configured to perform
capture management pacing will typically have a refractory period
930 (see FIG. 9) that is significantly shorter than a device
configured to perform demand pacing. Indeed, when using capture
management pacing, there may be no refractory period 930 at all,
but only a blanking interval 920. In some examples, where there is
a refractory period 930, the refractory period 930 may be similar
in duration to the blanking interval 920. As would be appreciated
by those skilled in the art, this is because during capture
management pacing, the response of the patient's heart is monitored
to detect whether the delivered pulse of energy resulted in
capture.
[0264] During capture management pacing, the treatment manager can
initially deliver a pulse of energy at a predetermined, low energy
level and monitor the patient's response to determine if capture
resulted. Where it is determined that the delivered pulse did not
result in capture, the energy level of the next pulse may be
increased. For example, where the treatment manager resides in a
medical device that is external to the patient, the initial setting
may be configured to provide a 40 milliseconds rectilinear and
constant current pulse of energy at a current of 40 milliamps, and
increase the amount of current in increments of 2 milliamps until
capture results. The next pacing pulse may be delivered at
increased current relative to the first pacing pulse and at a
desired rate relative to the first pacing pulse in the absence of
any detected intrinsic cardiac activity of the patient or
intolerable discomfort to the patient. Where the next pacing pulse
does not result in capture, the energy may be increased until
capture is detected. The treatment manager may then continue pacing
at this energy level and at a desired rate in the absence of any
detected intrinsic cardiac activity of the patient or intolerable
discomfort to the patient. During this period of time, the
treatment manager monitors the patient's cardiac response to the
pacing pulses, and may increment the energy level further, should
it be determined over one or more subsequent pulses that capture
did not result. Similarly, during this period, the discomfort
monitor tracks the patient's discomfort parameter and may adjust
one or more pacing parameters in response to determining that the
patient's discomfort parameter has, for example, transgressed a
discomfort threshold value.
[0265] In one example, the treatment manager may apply a series of
pulses at an initial energy level and rate, and monitor the
patient's response to determine if capture resulted. Where capture
did not result, or where capture resulted in response to some of
the pulses, but not all, the treatment manager may increase the
energy of a next series of pulses until capture results for each
pulse.
[0266] In some examples, the treatment manager may be configured to
identify a minimum amount of energy that results in capture during
capture management pacing. Where it is determined that the
delivered pulse did result in capture, the energy level of the next
pulse may be decreased. For example, where the treatment manager
resides in a medical device that is external to the patient, the
initial setting may be configured to provide a 40 milliseconds
constant current pulse of energy at a current of 70 milliamps.
Where it is determined that the delivered pulse resulted in
capture, subsequent pacing pulse may be delivered at decreased in
increments of 5 milliamps (or more where the discomfort parameter
value exceeds the discomfort threshold value) and at a desired rate
relative to the first pacing pulse in the absence of any detected
intrinsic cardiac activity of the patient until capture is no
longer achieved or until the discomfort parameter of the patient
transgress the discomfort threshold value. Where the next pacing
pulse does not result in capture, the energy setting may be
increased to the last current known to produce a pulse resulting in
capture, and then delivering a pulse at the higher energy setting,
thus delivering the minimal amount of energy required for capture.
The treatment manager may then continue pacing at this energy level
and at a desired rate in the absence of any detected intrinsic
cardiac activity of the patient or intolerable discomfort to the
patient. During this period of time, a similar routine may be
re-performed at predetermined intervals to ensure that the minimum
amount of energy is being delivered for capture. In addition,
during this period of time, the treatment manager monitors the
patient's cardiac response to the pacing pulses, and may increase
the energy level should it be determined over one or more
subsequent pulses that capture did not result.
[0267] FIG. 8 illustrates one example of a managed pacing routine
800 that is executed within the act 514. The managed pacing routine
800 executes a capture management pacing process that is managed to
decrease discomfort relative to conventional pacing processes. As
shown in FIG. 8, the managed pacing routine 800 includes acts of
delivering pacing pulses, receiving and analyzing ECG signals,
determining whether capture occurred, calculating a discomfort
parameter, determining whether the discomfort caused by the pacing
routine 800 is intolerable, adjusting pacing parameters, and
determining whether pacing should continue.
[0268] In act 802, the treatment manager delivers one or more
pacing pulses to the patient according to the baseline parameters
loaded in the act 512 described above with reference to FIG. 5. In
examples where the act 512 has been omitted, the treatment manager
delivers one or more pacing pulses to the patient in accord with
default pacing parameters stored in the data storage. In at least
one example, the default pacing parameter values are each set at
the maximum of each range.
[0269] In the act 802, the one or more pacing pulses may be
delivered in conjunction with one or more TENS pulses executed
according to a TENS routine associated with the pacing routine 800.
In at least some examples, the TENS pulses are delivered between
pacing pulses to distract the patient and decrease the discomfort
of the pacing routine 800.
[0270] In act 804, the treatment manager receives (via the one or
more electrodes) and analyzes (via the cardiac monitor) electrode
signals generated from detectable characteristics of the patient's
cardiac function. In act 806, the cardiac monitor determines
whether delivery of the one or more pacing pulses resulted in
capture or improved cardiac function. The cardiac monitor may make
this determination by analyzing processed electrode data to
determine whether a normal heart beat resulted from one of the one
or more pacing pulses. The cardiac monitor may also make this
determination by analyzing processed acoustic data from an acoustic
sensor included in the medical device as disclosed in U.S. Patent
Application Publication No. US2015/0005588, titled "THERAPEUTIC
DEVICE INCLUDING ACOUSTIC SENSOR" and published Jan. 1, 2015, which
is hereby incorporated herein by reference in its entirety. For
instance, the cardiac monitor may infer capture from detection of
the S1 and S2 heart sounds proximal to delivery of the pacing
pulse.
[0271] In some examples of the act 806, the cardiac monitor does
not infer capture has occurred until the patient's heart rate is
equal to or transgresses the patient's hysteresis rate for a
predetermined period (e.g., 6 seconds or 5 heartbeats). If delivery
of the one or more pacing pulses did not result in capture, the
treatment manager proceeds to act 812.
[0272] In act 808, the discomfort monitor prompts for, receives,
and records discomfort information and records any discomfort
information acquired during execution of the pacing pulses for
subsequent processing. In some examples, the discomfort information
is recorded in the data storage. This discomfort information may be
received as voluntary or involuntary input from the user via the
user interface or may be acquired from one or more other sensors
coupled to a sensor interface. Examples of discomfort information
received via the user interface include utterances (e.g., words,
moans, groans, crying, or other expressions) and actuation of a
discomfort measuring and/or indicating device (e.g., strain gauge,
button, rotary dial, elastic deformable solid). For example, the
user can indicate a level of discomfort he or she feels by
actuating any of one or more user interface elements as described
herein. Examples of discomfort information received via other
sensors (e.g., motion detection sensors, strain gauges in a
garment) include movements (e.g., tensing of muscles, jerking,
shuttering, flinching, changes in respiration) and lack of
movement.
[0273] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for the input by, for example, presenting a discomfort scale
via the user interface. The discomfort scale may include numeric
values and the user interface may request that the user rate the
discomfort experienced on the numeric scale. The discomfort scale
may also include graphical representations (e.g., faces) and the
user interface may request that the user rate the discomfort
experienced on the graphical scale. In some examples, the
discomfort monitor infers the intensity of the discomfort based on
the amount of pressure detected by the user interface or the amount
of time a user interface element remains actuated. For example, in
a manner similar to that outlined above for the baseline process,
the voluntary input may be in the form of actuation of one or more
user interface elements, such as a force sensor (e.g.,
piezoelectric, quartz, or ceramic based transducer), a push or
squeeze button, a rotary spring-loaded dial, or an elastic
deformable solid.
[0274] In some examples where the discomfort information is
received as voluntary input, the discomfort monitor may prompt the
user for a change in input where the input has not changed state
for a time period greater than a value of a timeout configurable
parameter of the medical device. In this way, these examples
prevent involuntary input received as voluntary input from
affecting the behavior of the medical device for a time period
greater than the timeout.
[0275] In the act 810, the discomfort monitor determines whether
the pacing pulses delivered in the previous iteration of the act
802 were tolerable to the patient. If the pacing pulses were
tolerable, the treatment manager proceeds to the act 810. If the
pacing pulses were not tolerable, the treatment manager proceeds to
the act 808. In some examples, the discomfort monitor determines
whether the pacing pulses were tolerable at least in part by
quantifying discomfort information. This discomfort information
quantified by the discomfort monitor may have been acquired during
execution of the pacing pulses in the act 802 or may have been
received as voluntary input in response to one or more prompts
provided to the user via the user interface within the act 808
(i.e., after execution of the pacing pulses in act 802 is
complete). In some examples, the discomfort monitor assigns a value
to the discomfort parameter based on the discomfort information
using one or more of the mechanisms described herein (e.g., the
mechanisms described above with reference to the act 408 of FIG.
4). For instance, the discomfort monitor may store any of the
following values as the value of the discomfort parameter: a value
of a point on the discomfort scale selected via user input, a value
calculated based on an amount of pressure exerted by the user on an
element of the user interface, or a value calculated based on
motion of the patient or some other involuntary reaction to the
pacing pulses exhibited by the patient.
[0276] In some examples, the discomfort monitor determines whether
the pacing pulses were tolerable by comparing the value of the
discomfort parameter to a discomfort threshold value. This
discomfort threshold value may be a configurable parameter of the
medical device. In some examples, the discomfort monitor determines
that the pacing pulses were tolerable where the value of the
discomfort parameter maintains a predefined relationship with to
the discomfort threshold value (e.g., where the value of the
discomfort parameter does not transgress the discomfort threshold
value). In these examples, the discomfort monitor determines that
the pacing pulses were not tolerable where the value of the
discomfort parameter does not maintain a predefined relationship
with the discomfort threshold value (e.g. where the value of the
discomfort parameter is equal to or transgresses the discomfort
threshold value). It is appreciated that, depending on the specific
calculations used, a discomfort threshold value may be transgressed
by a value that is greater than or less than the discomfort
threshold value.
[0277] In act 808, the discomfort monitor adjusts the pacing
parameters. In some examples, the discomfort monitor determines the
adjusted pacing parameters substantially in real time based on
immediate feedback from the patient as described above with
reference to FIG. 16.
[0278] In some examples, where voluntary feedback is unavailable
(e.g., the patient is unable to provide dynamic feedback regarding
his or her level of discomfort) the discomfort monitor determines
the adjusted pacing parameters in a similar manner as outlined
above with respect to the baseline process 400 by solving an
optimization problem similar to the optimization problem described
above with reference to described above with reference to act 412
of FIG. 4. However, the optimization problem solved within the act
812 replaces at least one of the these constraints:
[0279] 15 milliamps .ltoreq.a.sub.i.ltoreq.200 milliamps;
[0280] 0.5 milliseconds .ltoreq.w.sub.i.ltoreq.40 milliseconds;
[0281] 20 pacing pulses per minute .ltoreq.r.sub.i.ltoreq.200
pacing pulses per minute;
[0282] 20 microseconds .ltoreq.p.sub.i.ltoreq.500 microseconds;
[0283] 10 percent .ltoreq.d.sub.i.ltoreq.100 percent; and
[0284] 40 microseconds .ltoreq.c.sub.i.ltoreq.100 microseconds;
with a corresponding one of these following constraints:
[0285] a.sub.i.gtoreq.a.sub.i-1;
[0286] w.sub.i.gtoreq.w.sub.i-1;
[0287] r.sub.i.gtoreq.r.sub.i-1;
[0288] p.sub.i.gtoreq.p.sub.i-1;
[0289] d.sub.i.gtoreq.d.sub.i-1; and
[0290] c.sub.i.gtoreq.c.sub.i-1. In addition, the discomfort
monitor improves any approximation of the function d(i) by
incorporating the data point(s) generated in act 810.
[0291] In some examples, where the patient is not actively
contributing discomfort information (e.g., the patent is
unconscious), the treatment manager adjusts the pacing parameters
to increase the efficacy of the pacing pulses as described above,
for instance, by increasing the current by 2 milliamps. In some
examples, wherein the patient is not actively contributing
discomfort information, the treatment manager determines the
adjusted pacing parameters by solving an optimization problem
similar to the optimization problem described above with reference
to described above with reference to act 412 of FIG. 4. However,
the optimization problem solved within the at 812 replaces at least
one of the these constraints:
[0292] 15 milliamps .ltoreq.a.sub.i.ltoreq.200 milliamps;
[0293] 0.5 milliseconds .ltoreq.w.sub.i.ltoreq.40 milliseconds;
[0294] 20 pacing pulses per minute .ltoreq.r.sub.i.ltoreq.200
pacing pulses per minute;
[0295] 20 microseconds .ltoreq.p.sub.i.ltoreq.500 microseconds;
[0296] 10 percent .ltoreq.d.sub.i.ltoreq.100 percent; and
[0297] 40 microseconds .ltoreq.c.sub.i.ltoreq.100 microseconds;
[0298] with a corresponding one of these following constraints:
[0299] a.sub.i.ltoreq.a.sub.i-1;
[0300] w.sub.i.ltoreq.w.sub.i-1;
[0301] r.sub.i.ltoreq.r.sub.i-1;
[0302] p.sub.i.ltoreq.p.sub.i-1;
[0303] d.sub.i.ltoreq.d.sub.i-1; and
[0304] c.sub.i.ltoreq.c.sub.i-1. In addition, the discomfort
monitor improves any approximation of the function d(i) by
incorporating the data point(s) generated in act 810.
[0305] In act 814, the treatment manager receives (via the one or
more electrodes) and analyzes (via the cardiac monitor) electrode
signals generated from detectable characteristics of the patient's
cardiac function. During the analysis, the cardiac monitor
determines whether the patient's current cardiac condition warrants
further pacing. If so, the treatment manager returns to the act 802
and continues execution of the pacing routine 800. If the cardiac
monitor determines that the patient's current cardiac condition
does not warrant further pacing (e.g., determines whether a normal
sinus rhythm has returned), the pacing routine 800 ends. In some
examples, upon termination of the pacing routine 800, the treatment
manager returns to the process 500 and continues to monitor the
patient's physiological signals, such as the patient's ECG,
temperature, pulse oxygen level, respiration, etc.
[0306] Processes in accord with the managed pacing routine 800
enable patients to control parameters of pacing routines via
feedback provided to a user interface, thereby enabling patients to
actively manage discomfort associated with external pacing
processes.
[0307] It should be appreciated that in the various examples
described above, an medical device has been described which may not
only provide life-saving defibrillation or cardioversion therapy,
but may also provide a wide variety of different pacing regimens.
Because the medical device can monitor a patient's intrinsic
cardiac activity, the patient's thoracic impedance, and other
physiological characteristics of the patient, the medical device
may be configured to recommend various settings to a medical
professional for review and approval. The various settings that may
be recommended may include a recommended base pacing rate, a
recommended hysteresis rate, a recommended anti-tachyarrhythmic
pacing rate, a recommended energy level (or initial energy level if
capture management is used), a recommended blanking interval,
and/or refractory period, and a recommended sensitivity threshold.
In the case of a pacing device such as the LifeVest.RTM.
cardioverter defibrillator, this initial recommendation may be
performed when the patient is being fitted for and trained on the
use of the medical device.
[0308] Although the ability to recommend such settings to a medical
professional for their review and approval is particularly well
suited to a LifeVest.RTM. cardioverter defibrillator, such
functionality could also be implemented in an Automated External
Defibrillator (AED) or an Advanced Life Support (ALS) type of
defibrillator, such as the M Series defibrillator, R Series ALS
defibrillator, R Series Plus defibrillator, or E Series
defibrillator manufactured by the ZOLL Medical Corporation of
Chelmsford Mass. It should be appreciated that monitoring the
patient's intrinsic cardiac activity and other physiological
characteristics and making recommendations to a trained medical
professional for their review and approval (or possible
modification) could reduce the amount of time that is spent
manually configuring such devices prior to use on the patient.
[0309] Each of the processes described herein depict one particular
sequence of acts in a particular embodiment. The acts included in
these processes may be performed by, or using, one or more computer
systems specially configured as discussed herein. Some acts are
optional and, as such, may be omitted in accord with one or more
embodiments. Additionally, the order of acts can be altered, or
other acts can be added, without departing from the scope of the
embodiments described herein.
[0310] Having thus described several aspects of at least one
example of this disclosure, it is to be appreciated various
alterations, modifications, and improvements will readily occur to
those skilled in the art. Such alterations, modifications, and
improvements are intended to be part of this disclosure, and are
intended to be within the scope of the disclosure. Accordingly, the
foregoing description and drawings are by way of example only.
* * * * *