U.S. patent application number 15/471481 was filed with the patent office on 2017-07-13 for algorithm adaptation to an external impact on the data.
The applicant listed for this patent is Cardiac Pacemakers, Inc.. Invention is credited to Qi An, Viktoria A. Averina, Pramodsingh Hirasingh Thakur, Yi Zhang.
Application Number | 20170196518 15/471481 |
Document ID | / |
Family ID | 50185057 |
Filed Date | 2017-07-13 |
United States Patent
Application |
20170196518 |
Kind Code |
A1 |
Averina; Viktoria A. ; et
al. |
July 13, 2017 |
ALGORITHM ADAPTATION TO AN EXTERNAL IMPACT ON THE DATA
Abstract
Devices and methods for detecting a physiological target event
such as events indicative of HF decompensation status are
described. An ambulatory medical device is configured to determine
the presence and timing of a confounding event, segment a sensed
physiological signal into at least two data segments, adjust the
physiological signal by removing or lessening the impact of the
confounding event on the physiological signal. The adjusted data
can be presented to the user, and the ambulatory medical device can
detect the target events using the adjusted physiologic signal. In
some embodiments, the ambulatory medical device can be configured
to detect an event indicative of HF decompensation using a
physiological signal and the information of the detected
confounding event.
Inventors: |
Averina; Viktoria A.;
(Shoreview, MN) ; Thakur; Pramodsingh Hirasingh;
(Woodbury, MN) ; Zhang; Yi; (Plymouth, MN)
; An; Qi; (Blaine, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cardiac Pacemakers, Inc. |
St. Paul |
MN |
US |
|
|
Family ID: |
50185057 |
Appl. No.: |
15/471481 |
Filed: |
March 28, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14178078 |
Feb 11, 2014 |
9643012 |
|
|
15471481 |
|
|
|
|
61765920 |
Feb 18, 2013 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/7221 20130101;
A61B 2560/0276 20130101; A61B 5/0452 20130101; A61B 5/7278
20130101; A61B 5/02055 20130101; A61N 1/3627 20130101; A61B 5/4839
20130101; A61B 5/686 20130101 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61N 1/362 20060101 A61N001/362; A61B 5/0205 20060101
A61B005/0205 |
Claims
1. An ambulatory medical device, comprising: a signal receiver
circuit, configured to receive a physiologic signal, for detecting
a physiologic target event or condition of a patient; a confounding
event detector circuit, including a confounding event-bearing (CEB)
signal receiver circuit configured to receive at least one CEB
signal, the confounding event detector configured to determine
presence of a confounding event, different from the target event or
condition, from the at least one CEB signal; a signal processing
circuit, configured to segment the physiologic signal into at least
first and second segments, and adjust at least one of the first or
second segments, wherein adjusting at least one of the first or
second segments is capable of being independent of adjusting the
other of the first and second segments; and a target event or
condition detector circuit, configured to detect the target event
or condition from the at least one of the first or second adjusted
segments of the physiologic signal.
2. The device of claim 1, wherein the signal receiver circuit is
configured to be coupled to at least one of a signal memory or a
signal sensing circuit, and wherein the signal sensing circuit,
coupled to electrodes associated with the ambulatory medical
device, is configured to sense the physiologic signal.
3. The device of claim 1, wherein the confounding event detector
circuit is configured to detect, from the at least one CEB signal,
an event indicative of at least one of a change of integrity of the
device, a change of configuration of the device, a change of
interaction between the device and the patient, a change of patient
environment, a change of the patient condition, a replacement of
the device, and a medical event.
4. The device of claim 1, wherein the CEB signal receiver circuit
is configured to be coupled to electrodes associated with the
patient and receive at least one CEB physiologic signal, and
wherein the confounding event detector is configured to determine
the presence of the confounding event using whether the at least
one CEB physiologic signal meets at least one physiologically
relevant criterion.
5. The device of claim 1, wherein the CEB signal receiver circuit
is configured to receive at least one clinical report, and wherein
the confounding event detector is configured to determine the
presence of the confounding event using whether the at least one
clinical report indicates the confounding event.
6. The device of claim 1, wherein the CEB signal receiver circuit
is configured to receive two or more CEB signals selected from a
plurality of CEB physiologic signals and a plurality of clinical
reports, and wherein the confounding event detector circuit is
configured to perform detection of the confounding event using the
two or more CEB signals, and determine the presence of the
confounding event using a comparison of the detections from the two
or more CEB signals.
7. The device of claim 1, wherein the signal processing circuit is
configured to: segment the physiologic signal into at least the
first and second segments using a characteristic parameter of the
detected confounding event, the characteristic parameter including
a start time, a stop time, a duration, and a type of the detected
confounding event; and adjust the at least one of the first and
second segments using a comparison between a first metric
determined from the first segment and a second metric determined
from the second segment.
8. The device of claim 1, wherein the signal processing circuit is
configured to determine a mode of adjustment using at least one of
the type of the detected confounding event, a type of the
physiologic signal, and a sensing configuration of the
physiological signal, and wherein the mode of adjustment includes a
transient adjustment and a permanent adjustment.
9. A method, comprising: receiving a physiologic signal, sensed
from a patient, for detecting a physiologic target event or
condition of the patient; detecting a confounding event, different
from the target event or condition, from at least one confounding
event-bearing (CEB) signal; using the detected confounding event,
segmenting the physiologic signal into at least first and second
segments; adjusting at least one of the first or second segments,
wherein adjusting at least one of the first or second segments is
capable of being independent of adjusting the other of the first
and second segments; and applying a target event or condition
detection algorithm to the adjusted at least one of the first or
second segments of the physiologic signal, to detect the target
event or condition of the patient.
10. The method of claim 9, wherein the confounding event includes
an event indicative of at least one of a change of integrity of an
ambulatory medical device associated with the patient, a change of
configuration of the ambulatory medical device, a change of
interaction between the ambulatory medical device and the patient,
a change of patient environment, a change of the patient condition,
a replacement of the ambulatory medical device, and a medical
event.
11. The method of claim 9, wherein detecting the confounding event
includes: receiving at least one CEB physiologic signal from
electrodes associated with the patient; and determining presence of
the confounding event using whether the at least one CEB
physiologic signal meets at least one physiologically relevant
criterion, including a change in intensity, a rate of change in
intensity, and a duration of sustained shift in intensity of the
CEB physiologic signal.
12. The method of claim 9, wherein detecting the confounding event
includes: computing a similarity measure between the at least one
CEB signal and at least one confounding event template signal; and
determining presence of the confounding event using whether the
similarity measure meets at least one specified criterion.
13. The method of claim 9, wherein detecting the confounding event
includes: receiving at least one clinical report; and determining
presence of the confounding event using whether the at least one
clinical report indicates the presence of the confounding
event.
14. The method of claim 9, wherein detecting the confounding event
includes: performing detection of the confounding event using each
of two or more CEB signals, the two or more CEB signals selected
from a plurality of CEB physiologic signals and a plurality of
clinical reports; and determining presence of the confounding event
using a comparison of the detections from the two or more CEB
signals.
15. The method of claim 9, wherein detecting the confounding event
includes: generating a composite signal using the two or more CEB
signals; and determining presence of the confounding event using
whether the composite signal meets at least one physiologically
relevant criterion, including a change in intensity, a rate of
change in intensity, and a duration of sustained shift in intensity
of the composite signal.
16. The method of claim 9, wherein segmenting the physiologic
signal includes segmenting the physiologic signal into at least the
first and second segments using a characteristic parameter of the
detected confounding event, the characteristic parameter including
a start time, a stop time, a duration, and a type of the detected
confounding event.
17. The method of claim 16, wherein the first segment is taken from
the physiologic signal before the start time of the confounding
event, and the second segment is taken from the sensed physiologic
signal after the stop time of the detected confounding event.
18. The method of claim 9, wherein adjusting the physiologic signal
includes adjusting the at least one of the first and second
segments using a comparison between a first metric determined from
the first segment and a second metric determined from the second
segment.
19. The method of claim 9, wherein adjusting the physiologic signal
includes a mode of adjustment using at least one of the type of the
detected confounding event, a type of the physiologic signal, and a
sensing configuration of the physiological signal, and wherein the
mode of adjustment includes a transient adjustment and a permanent
adjustment.
20. A method, comprising: receiving an impedance signal, sensed
from a patient, for detecting a target event indicative of HF
decompensation status of the patient; detecting a confounding
event, different from the target event, from at least one
confounding event-bearing (CEB) physiologic signal, wherein
detecting the confounding event includes determining presence of
the confounding event using whether a rate of change of the
intensity of the CEB physiologic signal is within a specified range
of physiologically relevant rate of change of the CEB physiologic
signal; segmenting the impedance signal into at least first and
second segments, the first segment taken before the start time of
the detected confounding event, and the second segment taken after
the stop time of the detected confounding event; adjusting the
impedance signal by subtracting from at least one of the first and
second segments a difference between an average intensity of the
first segment and an average intensity of the second segment; and
applying a HF decompensation detection algorithm to the adjusted
impedance signal to detect the target event indicative of HF
decompensation status.
Description
CLAIM OF PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/178,078, filed Feb. 11, 2014, which claims
the benefit of U.S. Provisional Patent Application No. 61/765,920,
filed Feb. 18, 2013, the contents of all of which are herein
incorporated by reference in their entireties.
TECHNICAL FIELD
[0002] This document relates generally to medical devices, and more
particularly, to systems, devices and methods for detecting a
physiologic event or monitoring a physiologic condition of a
patient.
BACKGROUND
[0003] Congestive heart failure (CHF) is a major health problem and
affects over five million people in the United States alone. CHF
patients typically have enlarged heart with weakened cardiac
muscles, resulting in poor cardiac output of blood. Elevated
pulmonary vascular pressures can cause fluid accumulation in the
lungs over time. In many CHF patients, fluid accumulation precedes
episodes of heart failure (HF) decompensation.
SUMMARY
[0004] Frequent monitoring of CHF patients and timely detection of
intrathoracic fluid accumulation or other events indicative of HF
decompensation status can help prevent worsening of HF in CHF
patients, hence reducing cost associated with HF
hospitalization.
[0005] Ambulatory medical devices can be used for monitoring HF
patient and detecting HF decompensation events. Examples of such
ambulatory medical devices can include implantable medical devices
(IMD), subcutaneous medical devices, wearable medical devices or
other external medical devices. The ambulatory or implantable
medical devices can be configured to sense electrical activity and
mechanical function of the heart, and to optionally deliver therapy
such as electrical stimulation pulses to a target area, such as to
restore or improve the cardiac function.
[0006] Some of these devices can include one or more diagnostic
features, such as using a physiological signal to detect a
physiologic event or monitoring a physiologic condition. The
physiological signal may be affected by confounding events which
can be different than a target physiological event or condition of
interest. The confounding event may be physiological or
non-physiological in nature. For example, in monitoring an HF
patient or in detecting a HF decompensation event such as in an IMD
using a physiological signal, events such as lead revision, change
of pacing configuration, or a replacement of the device either at
the same location or at a different location may leave a signature
on the physiological signal, thereby being erroneously interpreted
by the user or erroneously detected by the IMD as a target HF
decompensation event. One type of erroneous detection is false
positive detection, where a confounding event is mis-detected as a
target HF decompensation event. A false positive detection may
cause unnecessary intervention and additional healthcare cost.
Another type of erroneous detection is false negative detection,
where a true target HF decompensation event is mis-detected as a
non-target event. A false negative detection may delay or miss a
necessary intervention or therapy. Therefore, the present inventors
have recognized that there remains a considerable need of devices
and methods that can detect target physiological events with
reduced false negative and false positive detections, particularly
in the presence of confounding events.
[0007] Various embodiments described herein can help improve the
process of detecting physiological events of interest or monitoring
a patient's condition. For example, an ambulatory medical device
(such as an implantable medical device or a wearable medical
device) can detect a target physiologic event such as using
confounding event information. A signal receiver circuit can be
configured to receive a physiologic signal. A confounding event
detector circuit can be configured to receive a confounding event
bearing (CEB) signal and determine the presence of a confounding
event from the CEB signal. A signal processing circuit can be
configured to adjust the physiological signal using the detected
confounding event. A physiologic target event or condition detector
circuit can be configured to detect a target event from the
adjusted physiologic signal.
[0008] A method can include detecting a target physiologic event in
a patient having an ambulatory medical device. The method can
include receiving a physiologic signal, detecting a confounding
event from one or more CEB signal, segmenting the physiological
signal into at least two data segments using the characteristics of
the detected confounding event, adjusting one or more data segment
to remove or lessen the impact of the confounding event on the
physiological signal, and detecting a physiologic target event by
applying a target event detection algorithm to the adjusted
physiological signal.
[0009] A method for detecting an event indicative of HF
decompensation status can include sensing an impedance signal from
a patient, detecting a confounding event using whether a rate of
change of the impedance signal intensity is within a specified
physiologic range, segmenting the impedance signal into two data
segments using a characteristic parameter of the detected
confounding event, the characteristic parameter including a start
time of the detected confounding event, adjusting the impedance
signal by subtracting from one segment a difference between the
average intensities between the two segments, or applying a HF
decompensation detection algorithm to the adjusted impedance signal
to detect the target event indicative of HF decompensation
status.
[0010] This Summary is an overview of some of the teachings of the
present application and not intended to be an exclusive or
exhaustive treatment of the present subject matter. Further details
about the present subject matter are found in the detailed
description and appended claims. Other aspects of the invention
will be apparent to persons skilled in the art upon reading and
understanding the following detailed description and viewing the
drawings that form a part thereof, each of which are not to be
taken in a limiting sense. The scope of the present invention is
defined by the appended claims and their legal equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Various embodiments are illustrated by way of example in the
figures of the accompanying drawings. Such embodiments are
demonstrative and not intended to be exhaustive or exclusive
embodiments of the present subject matter.
[0012] FIG. 1 illustrates an example of cardiac rhythm management
(CRM) system and portions of the environment in which the CRM
system operates.
[0013] FIG. 2 illustrates an example of a physiologic target event
detector.
[0014] FIG. 3 illustrates an example of a confounding event
detection and analysis circuit.
[0015] FIG. 4 illustrates an example of a signal processing
circuit.
[0016] FIG. 5 illustrates an example of a physiologic target event
detection circuit.
[0017] FIG. 6 illustrates an example of a method for detecting a
physiologic target event adapted to characteristics of a
confounding event.
[0018] FIGS. 7A-D illustrate examples of impacts of confounding
events on confounding event bearing (CEB) physiological
signals.
[0019] FIG. 8 illustrates an example of a confounding event's
impact on CEB signals.
[0020] FIG. 9 illustrates an example of a method for detecting and
characterizing a confounding event such as using physiologically
relevant data range.
[0021] FIG. 10 illustrates an example of a method for detecting and
characterizing a confounding event such as using template
matching.
[0022] FIG. 11 illustrates an example of a method for detecting and
characterizing a confounding event such as using two CEB
signals.
[0023] FIG. 12 illustrates an example of a method for detecting a
physiologic target event in adaptation to a detected confounding
event.
[0024] FIGS. 13A-B illustrate examples of pre-transition signal
adjustment using the information of the detected confounding
event.
[0025] FIGS. 14A-B illustrate examples of post-transition signal
adjustment using the information of the detected confounding
event.
[0026] FIG. 15 illustrates an example of a method for detecting an
HF decompensation event.
DETAILED DESCRIPTION
[0027] Disclosed herein are systems, devices and methods for
detecting physiologic target events using the information of one or
more confounding events. The physiologic target events can include
early precursors of an HF decompensation episode. That is, these
events can occur well before the systematic manifestation of
worsening of HF. Therefore, by detecting the precursor events, the
present document can provide a method and device to predict the
impending HF decompensation episode in the presence of one or more
confounding events. The methods and devices described herein can
also be applicable to predicting the progression or worsening of a
disease or a patient's health condition, to stratifying a patient's
risk of developing a disease or a condition, or to monitoring a
patient's health status or response to a medical intervention and
to providing feedback to the healthcare professionals engaged in
patient management.
[0028] FIG. 1 illustrates an example of a Cardiac Rhythm Management
(CRM) system 100 and portions of an environment in which the CRM
system 100 can operate. The CRM system 100 can include an
ambulatory medical device, such as an implantable medical device
(IMD) 110 that can be electrically coupled to a heart 105 such as
through one or more leads 108A-C, and an external system 120 that
can communicate with the IMD 110 such as via a communication link
103. The IMD 110 may include an implantable cardiac device such as
a pacemaker, an implantable cardioveter-defibrillator (ICD), or a
cardiac resynchronization therapy defibrillator (CRT-D). The IMD
110 can include one or more monitoring or therapeutic devices such
as a subcutaneously implanted device, a wearable external device, a
neural stimulator, a drug delivery device, a biological therapy
device, or one or more other ambulatory medical devices. The IMD
110 may be coupled to, or may be substituted by a monitoring
medical device such as a bedside or other external monitor.
[0029] As illustrated in FIG. 1, the IMD 110 can include a
hermetically sealed can 112 that can house an electronic circuit
that can sense a physiological signal in the heart 105 and can
deliver one or more therapeutic electrical pulses to a target
region, such as in the heart, such as through one or more leads
108A-C. The CRM system 100 can include only one lead such as 108B,
or can include two leads such as 108A and 108B.
[0030] The lead 108A can include a proximal end that can be
configured to be connected to IMD 110 and a distal end that can be
configured to be placed at a target location such as in the right
atrium (RA) 131 of the heart 105. The lead 108A can have a first
pacing-sensing electrode 141 that can be located at or near its
distal end, and a second pacing-sensing electrode 142 that can be
located at or near the electrode 141. The electrodes 141 and 142
can be electrically connected to the IMD 110 such as via separate
conductors in the lead 108A, such as to allow for sensing of the
right atrial activity and optional delivery of atrial pacing
pulses. The lead 108B can be a defibrillation lead that can include
a proximal end that can be connected to IMD 110 and a distal end
that can be placed at a target location such as in the right
ventricle (RV) 132 of heart 105. The lead 108B can have a first
pacing-sensing electrode 152 that can be located at distal end, a
second pacing-sensing electrode 153 that can be located near the
electrode 152, a first defibrillation coil electrode 154 that can
be located near the electrode 153, and a second defibrillation coil
electrode 155 that can be located at a distance from the distal end
such as for superior vena cava (SVC) placement. The electrodes 152
through 155 can be electrically connected to the IMD 110 such as
via separate conductors in the lead 108B. The electrodes 152 and
153 can allow for sensing of a ventricular electrogram and can
optionally allow delivery of one or more ventricular pacing pulses,
and electrodes 154 and 155 can allow for delivery of one or more
ventricular cardioversion/defibrillation pulses. In an example, the
lead 108B can include only three electrodes 152, 154 and 155. The
electrodes 152 and 154 can be used for sensing or delivery of one
or more ventricular pacing pulses, and the electrodes 154 and 155
can be used for delivery of one or more ventricular cardioversion
or defibrillation pulses. The lead 108C can include a proximal end
that can be connected to the IMD 110 and a distal end that can be
configured to be placed at a target location such as in a left
ventricle (LV) 134 of the heart 105. The lead 108C may be implanted
through the coronary sinus 133 and may be placed in a coronary vein
over the LV such as to allow for delivery of one or more pacing
pulses to the LV. The lead 108C can include an electrode 161 that
can be located at a distal end of the lead 108C and another
electrode 162 that can be located near the electrode 161. The
electrodes 161 and 162 can be electrically connected to the IMD 110
such as via separate conductors in the lead 108C such as to allow
for sensing of the LV electrogram and optionally allow delivery of
one or more resynchronization pacing pulses from the LV.
[0031] The IMD 110 can include an electronic circuit that can sense
a physiological signal. The physiological signal can include an
electrogram or a signal representing mechanical function of the
heart 105. The hermetically sealed can 112 may function as an
electrode such as for sensing or pulse delivery. For example, an
electrode from one or more of the leads 108A-C may be used together
with the can 112 such as for unipolar sensing of an electrogram or
for delivering one or more pacing pulses. A defibrillation
electrode from the lead 108B may be used together with the can 112
such as for delivering one or more cardioversion/defibrillation
pulses. In an example, the IMD 110 can sense impedance such as
between electrodes located on one or more of the leads 108A-C or
the can 112. The IMD 110 can be configured to inject current
between a pair of electrodes, sense the resultant voltage between
the same or different pair of electrodes, and determine impedance
using Ohm's Law. The impedance can be sensed in a bipolar
configuration in which the same pair of electrodes can be used for
injecting current and sensing voltage, a tripolar configuration in
which the pair of electrodes for current injection and the pair of
electrodes for voltage sensing can share a common electrode, or
tetrapolar configuration in which the electrodes used for current
injection can be distinct from the electrodes used for voltage
sensing. In an example, the IMD 110 can be configured to inject
current between an electrode on the RV lead 108B and the can
housing 112, and to sense the resultant voltage between the same
electrodes or between a different electrode on the RV lead 108B and
the can housing 112. A physiologic signal can be sensed from one or
more physiological sensors that can be integrated within the IMD
110. The IMD 110 can also be configured to sense a physiological
signal from one or more external physiologic sensors or one or more
external electrodes that can be coupled to the IMD 110. Examples of
the physiological signal can include one or more of intrathoracic
impedance, intracardiac impedance, arterial pressure, pulmonary
artery pressure, RV pressure, LV coronary pressure, coronary blood
temperature, blood oxygen saturation, one or more heart sounds,
physical activity or exertion level, posture, respiration, body
weight, or body temperature.
[0032] The arrangement and functions of these leads and electrodes
are described above by way of example and not by way of limitation.
Depending on the need of the patient and the capability of the
implantable device, other arrangements and uses of these leads and
electrodes are.
[0033] As illustrated, the CRM system 100 can include a physiologic
target event detector 113. The physiologic target event detector
113 can include a confounding event detector that can detect and
characterize a confounding event in a physiological signal, a
signal processing unit that processes the physiological signal, and
a target event detector to detect the target event from the
processed physiological signal. The confounding event detector can
detect the physiologic state using a first signal acquired from the
electrodes on the leads 108A-C, and the target event detector can
detect the target event using a second signal acquired from the
electrodes on one or more of the leads 108A-C. The first signal
used by the confounding event detector and the second signal used
for target event detection can be obtained from the same
physiological signal. Examples of physiologic target event detector
113 are discussed below, such as with reference to FIGS. 2-5.
[0034] The external system 120 can allow for programming of the IMD
110 and can receives information about one or more signals acquired
by IMD 110, such as can be received via a communication link 103.
The external system 120 can include a local external IMD
programmer. The external system 120 can include a remote patient
management system that can monitor patient status or adjust one or
more therapies such as from a remote location.
[0035] The communication link 103 can include one or more of an
inductive telemetry link, a radio-frequency telemetry link, or a
telecommunication link, such as an internet connection. The
communication link 103 can provide for data transmission between
the IMD 110 and the external system 120. The transmitted data can
include, for example, real-time physiological data acquired by the
IMD 110, physiological data acquired by and stored in the IMD 110,
therapy history data or data indicating IMD operational status
stored in the IMD 110, one or more programming instructions to the
IMD 110 such as to configure the IMD 110 to perform one or more
actions that can include physiological data acquisition such as
using programmably specifiable sensing electrodes and
configuration, device self-diagnostic test, or delivery of one or
more therapies.
[0036] The physiologic target event detector 113 may be implemented
at the external system 120, which can be configured to perform
target event detection such as using data extracted from the IMD
110 or data stored in a memory within the external system 120.
Portions of the physiologic target event detector 113 may be
distributed between the IMD 110 and the external system 120.
[0037] Portions of the IMD 110 or the external system 120 can be
implemented using hardware, software, or any combination of
hardware and software. Portions of the IMD 110 or the external
system 120 may be implemented using an application-specific circuit
that can be constructed or configured to perform one or more
particular functions, or can be implemented using a general-purpose
circuit that can be programmed or otherwise configured to perform
one or more particular functions. Such a general-purpose circuit
can include a microprocessor or a portion thereof, a
microcontroller or a portion thereof, or a programmable logic
circuit, or a portion thereof. For example, a "comparator" can
include, among other things, an electronic circuit comparator that
can be constructed to perform the specific function of a comparison
between two signals or the comparator can be implemented as a
portion of a general-purpose circuit that can be driven by a code
instructing a portion of the general-purpose circuit to perform a
comparison between the two signals.
[0038] FIG. 2 illustrates an example of a target event detector
200, which can be an embodiment of physiologic target event
detector 113. The target event detector 200 can include a signal
receiver circuit 202, a confounding event detection and analysis
circuit 203, a signal processing circuit 204, a target event or
condition detector 205, a controller 206, and an instruction
receiver 207.
[0039] The signal receiver circuit 202 can receive one or more
signals indicative of a patient's physiologic state. Examples of
the physiological signal can include electrograms from electrodes
on leads 108A-C and the can 112, intrathoracic impedance,
intracardiac impedance, arterial pressure, pulmonary artery
pressure, RV pressure, LV coronary pressure, coronary blood
temperature, blood oxygen saturation, heart sounds, or respiration
signals including respiration rate or tidal volume. In an example,
the signal receiver circuit can be configured to couple to a signal
sensing circuit which senses the physiologic signal. The signal
sensing circuit can be coupled to the electrodes such as on one or
more of the leads 108A-C and IMD can 112 connected to an ambulatory
medical device. Alternatively, the signal sensing circuit can be
coupled to electrodes on one or more of implantable subcutaneous
leads, or to external physiologic sensors. In an example, the
signal receiver circuit can be coupled to a memory circuit and
receive the physiological data stored in the memory circuit.
[0040] The confounding event detection and analysis circuit 203 can
detect a confounding event from a confounding event-bearing (CEB)
signal or other sources containing information about the
confounding event, and characterize the detected confounding event.
A confounding event can be an event other than the physiologic
target event or condition but could be mis-detected or
mis-classified by a target event detector as a physiologic target
event. For example, in detecting a target event indicative of HF
decompensation, a confounding event can be non-physiologic in
nature and include, for example, device reprogramming, revision of
an ambulatory medical device or leads and other components
associated with the device, surgical interventions, posture
changes, electromagnetic interference, or other changes in the
device and environment that affect the CEB signal but are not
generally indicative of the patient's physiologic state of
interest. The CEB signal used for detecting a confounding event can
be a physiological signal different than the received signal from
the signal receiver circuit 202 used for detecting a target event.
The CEB signal can be the same signal as the received signal from
the signal receiver circuit 202.
[0041] The signal processing circuit 204 can receive input from the
signal receiver circuit 202 and the confounding event detection and
analysis circuit 203, and perform signal processing on the received
signal 202. In an example, the signal processing circuit 204 can
include circuits for segmenting the received signal and adjusting
the segmented signal.
[0042] The target event or condition detector 205 can detect a
pre-determined target event or condition such as using the
processed signal from signal processing circuit 204. A target event
can include an event or condition indicative of an onset of a
disease, worsening of a disease state, or a change of a disease
state. Examples of target event can include a worsening HF, HF
decompensation, pulmonary edema, or myocardial infarction.
[0043] The controller 206 can control the operations of functional
blocks 202 through 205 and the data flow between these functional
blocks. The controller 206 can receive external programming input
from the instruction receiver 207 to control the signal sensing,
physiological state analysis, and HF decompensation event
detection. Examples of the instructions received by instruction
receiver 206 may include: selection of electrodes used for sensing
physiological signals, selection of source of data used for
confounding event detection, selection of confounding event
detection algorithms and the associated parameter, or configuration
of the target event and condition detector 205. In an example, the
instruction receiver 207 is coupled to a user interface on the
external system 120. The external system 120 can be configured to
present programming options to the user and receive user's
programming input.
[0044] FIG. 3 illustrates an example of confounding event detection
and analysis circuit 300, which can be an embodiment of confounding
event detection and analysis circuit 203. The confounding event
detection and analysis circuit 300 can include a CEB signal
receiver circuit 310, a confounding event detector 320, and a
confounding event characterizer 330.
[0045] The CEB signal receiver circuit 310 can receive a CEB signal
from a device-based CEB signal receiver 311 or an external CEB
signal receiver 312. The device-based CEB signal receiver 311 can
receive signals from an ambulatory medical device such as the IMD
110, a physiologic monitor, or a memory where the physiologic data
are stored. In an example, the CEB signal and the physiological
signal acquired by the signal receiver circuit 202 and used for
detecting target event or condition can be obtained from the same
physiological signal. In another example, the CEB signal can be
acquired from the signal receiver circuit 202 but undergo different
signal processing than the signal for detecting target event. For
example, the CEB signal can be a respiration rate signal derived
from an impedance signal sensed by a transthoracic impedance
sensing circuit, while the physiological signal used for target
event detection can be a total impedance signal obtained from the
same transthoracic impedance sensing circuit. In another example,
the CEB signal and the physiological signal received by the signal
receiver circuit 202 can be from different ambulatory sensors or
electrodes connected to the ambulatory medical devices. For
example, the CEB signal can be a heart sound signal obtained from
an accelerometer sensor, while the physiological signal received by
the signal receiver circuit 202 can be from an impedance sensing
circuit.
[0046] In some examples, the CEB signal can include non-physiologic
data that are indicative of device condition and function, such as
frequent lead impedance measurement that provides information about
device integrity. A confounding event can leave a signature not
only in a physiological signal, but also in non-physiological
signals such as signals representing device condition and function.
For example, a confounding event of electromagnetic interference
(EMI) may cause morphological changes in intracardiac electrograms
as well as in lead impedance signals used for monitoring device
condition and functionality. In an example, the CEB signal receiver
circuit 310 can automatically select one or more physiological or
non-physiological CEB signals using the information of the type of
confounding event it sets to detect.
[0047] The external CEB signal receiver 312 can receive signal from
sources external to ambulatory medical devices or monitors. In an
example, the external CEB signals can include a clinical report, a
medical record, a lab test report, or a case report form. In
another example, the external CEB signals can include signals from
another ambulatory medical device. The clinical report may have
textual or graphical information about the confounding event. In
another example, the external CEB signal receiver 312 can receive
environmental sensor signals, such as environmental temperature,
humidity, atmospheric pressure, or other measurements of the
patient's environment.
[0048] The confounding event detector 320 can receive the input
from the CEB signal receiver circuit 310 and detects a confounding
event from one or more of CEB physiological signals, CEB signals
representing device functionality, CEB clinical reports, or CEB
environmental data. The confounding event detector 320 can include
a plurality of detectors to account for various types of
confounding events. Specifically, the confounding event detector
320 can include one or more of a device integrity detector 321, a
device configuration detector 322, a device-patient interaction
detector 323, a patient condition and medical event detector 324,
or a patient environment detector 325. Examples of method used by
the confounding event detector are discussed below, such as with
reference to FIGS. 9-11.
[0049] The device integrity detector 321 can detect an event
indicative of the integrity of an ambulatory medical device and
associated electrodes, leads, and sensors. Examples of the
confounding events indicative of the device integrity can include a
change of mechanical or electrical property of components within
the ambulatory medical device, leads, or sensors and a change of
mechanical or electrical coupling among the ambulatory medical
device, the leads, or the sensors, such as dislodgement or loose
connection.
[0050] The device configuration detector 322 can detect the change
of configuration of the ambulatory device. Examples of the
confounding events associated with the device configuration change
can include a change of device programming that affects device
operation (e.g., sensing and therapy delivery) including changes in
one or more of pacing mode, pacing vector, pacing pulse parameters,
pacing control parameters, electrogram sensing vector, or
mechanical or physiological signals sensing vector.
[0051] The device-patient interaction detector 323 can detect a
change of the interaction between the patient and one or more of
the ambulatory medical device, the leads, or the sensors associated
with the device. Examples of the confounding events associated with
the device-patient interaction can include lead revision or
replacement, lead dislodgement, device pocket revision, pocket
infection, new device placement, or a replacement of a device.
[0052] The patient condition and medical event detector 324 can
detect an event or condition associated with the patient's health
condition or medical status other than the physiologic target
event. For example, in the context of detecting a target event
indicative of HF decompensation, confounding events associated with
the patient condition and medical event can include onset of
myocardial infarction, cardiac arrest, pulmonary diseases, a change
of patient's medication, a change of the patient's activity level,
a change of posture, a surgical intervention, or a change of
patient's psychological state.
[0053] The patient environment detector 325 can detect a change in
patient environment, including a change in temperature, humidity,
atmospheric pressure, time and seasonal change, or indication of
patient's exposure to electromagnetic interferences.
[0054] The confounding event characterizer 330 can compute
characteristic parameters of the detected confounding events. In an
example, the characteristic parameters can include a start time, a
stop time, a duration, a type, or other contextual information
about the detected confounding event.
[0055] FIG. 4 illustrates an example of a signal processing circuit
400, which can be an embodiment of signal processing circuit 204.
The signal processing circuit 400 can include a signal segmentation
circuit 401 and a signal adjustment circuit 402. The signal
processing circuit 400 can receive the physiological signal from
the signal receiver circuit 202 and the confounding event
characteristics from the confounding event detection and analysis
circuit 203, and adjust the physiological signal such as using the
confounding event characteristics.
[0056] The signal segmentation circuit 401 can segment the
physiological signal into at least two segments such as using the
characteristics of the confounding event. In an example, the start
time of the confounding event creates a transition in the
physiological signal, and the two segments of the physiological
signals are identified as a pre-transition segment (i.e., data
before the start time of the confounding event) and a
post-transition segment (i.e., data after the start time of the
confounding event).
[0057] The signal adjustment circuit 402 can adjust the physiologic
signal to remove or lessen the impact of the confounding event on
the physiological signal. The adjustment can be performed on the
pre-transition signal, the post-transition signal, or both. The
adjustment of a first segment of the signal (e.g., the
post-transition signal) can be made relative to signal
characteristics of a second segment of the signal (e.g., the
pre-transition signal). In an example, the adjustment of a segment
of the signal can be made without reference to other segment(s) of
the signal. The signal adjustment circuit 402 can be configured to
be capable of adjusting one segment independently of the adjustment
of other segment(s). Examples of signal segmentation and adjustment
such as using the information of the detected confounding event are
discussed below, such as with reference to FIGS. 12-14.
[0058] FIG. 5 illustrates an example of target event detection
circuit 500, which can be an embodiment of target event detection
circuit 205. The target event detection circuit 500 can include a
target event detector 501, a target event report generator 502, and
a confounding event and signal adjustment report generator 503. The
target event detection circuit 500 can receive the adjusted
physiological signal from the signal processing circuit 204 and
detects the target event from the adjusted physiologic signal.
[0059] The target event detector 501 can detect the target event
from the adjusted physiological signal. In an example, the target
event can be an event indicative of HF decompensation status, and
the target event detector 501 can be configured to compute an HF
decompensation index such as using the adjusted physiological data
and determine whether an event indicative of HF decompensation is
detected such as by comparing the HF decompensation index to a
threshold value. Examples of target HF decompensation event
detection using the confounding event information are discussed
below, such as with reference to FIGS. 12 and 15.
[0060] The target event report generator 502 can generate a report
to inform the user the detected target event. Examples of the
report can include a textual or graphical message, a sound, an
image, or a combination thereof. In an example, the target event
report generator 502 can be coupled to the external device 120 and
the report can be presented to the user via the external device
120.
[0061] The confounding event and signal adjustment report generator
503 cam generate a report and present to the user information
including detected confounding event, the adjustment of the
physiological signal, or both. In an example, the confounding event
and signal adjustment report generator 503 can be coupled to the
external device 120, and the report can be presented to the user
via the external device 120. In another example, the presentation
of the report and the user input can be performed interactively on
the external device 120. For example, the external device 120 can
be configured to receive input from the user, and the confounding
event, and the signal adjustment report generator 503 can be
configured to receive the user input from the external device 120.
The user input can include confirmation, storage, or other
programming instructions to operate on the detected confounding
events or the adjusted physiological signal.
[0062] FIG. 6 illustrates an example of a method 600 for detecting
a target event from a physiological signal. The method 600 can be
implemented and operate in an ambulatory medical device or in a
remote patient management system. In an example, the method 600 can
be performed by physiologic target event detection circuit 113
implemented in IMD 110, or the external device 120 which can be in
communication with the IMD 110.
[0063] At 601, a physiological signal can be received. The
physiological signal may represent electrical or mechanical
activities in the body. Examples of the physiological signal
include: heart rate, heart rate variation, conduction times,
arrhythmias, intrathoracic impedance, intracardiac impedance,
arterial pressure, pulmonary artery pressure, RV pressure, LV
coronary pressure, heart sounds, respiration signals including
respiration rate or tidal volume; coronary blood temperature, blood
oxygen saturation, electrolyte concentrations, or other measures
descriptive of the patient's physiology. The physiological signal
can be received from a signal sensing circuit coupled to the
electrodes on one or more of the leads such as 108A-C, or external
sensors associated with an ambulatory medical device. The
physiologic signal can also be received from a signal memory where
the physiological data are stored.
[0064] At 602, a confounding event can be detected from a CEB
signal. One type of confounding event can be associated with the
patient's health condition or medical status other than the
physiologic target event, such as events indicative of myocardial
infarction, an event of cardiac arrest, a change of patient's
medication, a change of activity level, a change of posture, a
surgical intervention, or a change in psychological state. Another
type of confounding event can be related to changes in device
configuration, device integrity, device-patient interactions, or
patient's environment. Examples of confounding events associated
with the device integrity can include a change of mechanical or
electrical property of components within the ambulatory medical
device, the lead, or sensors; a change of mechanical or electrical
coupling among the ambulatory medical device, the lead, or sensors,
including a dislodgement and a loose connection. Examples of
confounding events associated with the device configuration change
can also include a change of device programming that affects the
mode of operation, such as changes in pacing mode, pacing vector,
pacing parameters and pacing control parameters, electrical signal
sensing vector, or mechanical or physiological signals sensing
vector. Examples of confounding events associated with the
device-patient interaction can include an implantable lead
revision, a device pocket revision, a new device implant, or a
replacement of a device either at the same or at a different
location. Examples of confounding events associated with the
patient environment can include a change in temperature, humidity,
atmospheric pressure, time and seasonal change, or indication of
patient's exposure to electromagnetic interferences.
[0065] The CEB signals can include signals from ambulatory devices,
monitors, or sensors. Examples of device data can include the
patient's physiologic signals, or signals indicative of the device
condition and function. In an example, the CEB signal and the
physiological signal acquired by signal receiver circuit 202 used
for target event detection can be obtained from the same
physiological signal. In another example, the CEB signal can be
acquired from the same signal receiver circuit 202 but undergo
different filtering or other signal processing than the signal used
for target event detection. In another example, the CEB signal and
the physiologic signal obtained from the signal receiver circuit
202 can be obtained from different ambulatory sensors or electrodes
coupled to the ambulatory medical devices.
[0066] The CEB signals can also include data from sources external
to devices or sensors. Examples of signals from external sources
can include a clinical report, a medical record, a lab test report,
a case report form, a physician's input on a device programmer, or
a signal from another ambulatory medical device. The external CEB
signals can include environmental sensor signals such as
environmental temperature, humidity, atmospheric pressure, or other
measurements of the patient's environment.
[0067] Once a confounding event is detected, a number of parameters
that characterize the detected confounding event can be computed at
602. Examples of the characteristic parameters can include a start
time, a stop time, a duration, a type, or contextual information
about the detected confounding event.
[0068] At 603, the received physiological signal can be processed
to remove or lessen the impact of the confounding event on the
physiological signal. In an example, the method of signal
processing can be performed by signal processing circuit 400, where
the physiological signal can be segmented and adjusted such as
using the characteristics of the detected confounding events. At
604, the processed physiological signal can be used to detect a
target event. In an example, the method of target event detection
can be performed by the target event detection circuit 500.
Examples of the methods for physiological signal adjustment and
target event detection using the information of the confounding
event are discussed below, such as with reference to FIGS.
12-15.
[0069] FIGS. 7A-D illustrate examples of impacts of confounding
events on CEB physiological signals. The CEB signal can include a
physiological signal, a signal representing the device condition or
functionality, or a signal representing a medical event or change
in patient condition, such as a surgery. In an example, the signals
illustrated on FIGS. 7A-D can be received from the device-based CEB
signal receiver circuit 311.
[0070] A confounding event on a CEB signal may be characterized by
morphological changes on the CEB signal, including morphologies
during signal transition and during signal recovery. For example,
while slow and gradual transitions may typically be a result of an
underlying physiologic change in the patient, sharp and transient
transitions in the signal are more likely due to a non-physiologic
confounding event. The transiency of a transition can be determined
using the information of the time scale of target event of
interest. For example, the transition can be considered transient
if it is within 1-5 hours, within 1-2 days, or within 1-2
weeks.
[0071] Several patterns of transitional morphologies and recovery
morphologies have been identified. For example, signal transition
may be transient or gradual, and signal recovery may be a full
recovery (i.e., recovery to the pre-trigger signal intensity level)
or a reset recovery (i.e., recovery to a steady-state level
different than the pre-trigger signal level). FIG. 7A illustrates
an example of a confounding event with transient transition with
full recovery. This may be identified as "spike noise" on the CEB
signal, where the confounding event signature 702 lasts for a very
short period of time. Following the transition, the post-transition
signal 703 has an average intensity 713 comparable to the average
signal intensity 711 of the pre-transition signal 701. FIG. 7B
illustrates an example of a confounding event with transient
transition with reset recovery. Following a brief transition 702,
the post-transition signal 704 quickly levels off at signal
intensity level 714 which is lower than the average signal level
711 of the pre-trigger signal 701. FIG. 7C illustrates an example
of a confounding event with gradual transition with full recovery.
The confounding event first causes an abrupt change 702 in signal
intensity, followed by a slower and longer period of transition
where the signal level 721 during the transition gradually ramps up
to a steady-state signal level 715. The steady-state signal level
715 of the post-transition signal 705 is similar to the average
signal level 711 of the pre-transition signal 701. FIG. 7D
illustrates an example of a confounding event with gradual
transition with reset recovery. The confounding event first causes
an abrupt change 702 in signal intensity, followed by a slower and
longer period of transition where the signal level 722 gradually
levels off at a steady-state signal level 716. The steady-state
signal level 716 of the post-transition signal 706 is lower than
the average signal level 711 of the pre-transition signal 701.
[0072] FIG. 8 illustrates an example of a confounding event's
impact on the CEB signals sensed from various physiological
sensors. In the context of detecting a target event indicative of
HF decompensation, two confounding events were detected and later
confirmed. As illustrated in FIG. 8, dotted line 831 marks the time
of the first confounding event of a dislodgement of an RA lead from
the implantable device on the patient during a procedure of mitral
valve repair; and dotted line 332 marks the time of the second
confounding event of repositioning of the dislodged RA lead. The
two events are separated in two days.
[0073] Two sensors were used to provide CEB signals for confounding
event detection. Signal 810 is a two-hour average of a
transthoracic impedance signal (Z.sub.RA-CAN) sensed from one or
more electrodes on the RA lead 108A and the IMD can housing 112.
Signal 820 is a 20-minute average of a tidal volume (TV) signal
sensed from a respiration sensor such as using a transthoracic
impedance measured from electrodes on one or more of the
implantable leads 108A-C and the can housing 112. Cyclic
respiration signal can be obtained by passing the transthoracic
impedance signal through a filter, and from the filtered
respiration signal a breadth-by-breadth TV may be determined as the
difference between the peaks and the troughs of the respiration
signal. Also shown in FIG. 8 are daily characteristic values of the
tidal volume: daily maximum TV.sub.max 821, daily median TV.sub.med
822, and daily minimum TV.sub.min 823.
[0074] The first confounding event of RA lead dislodgment causes
the impedance signals Z.sub.RA-CAN 810 to transiently increase
above the pre-transition signal baseline and then decrease to a
steady level lower than the pre-transition signal intensity. The
impedance changes almost instantaneously upon the occurrence of the
first confounding event. With regard to the TV signal, upon the
occurrence of the first confounding event, the TV intensity and the
variability in TV intensity decrease. Comparing the daily
characteristic values, TV.sub.max 821 decreases gradually from its
pre-transition level within 1-2 day. In contrast, TV.sub.med 822
does not decrease significantly, and TV.sub.min 823 barely changes
during course of the first confounding event.
[0075] The second confounding event of RA lead repositioning does
not significantly affect the signal intensity of any TV
measurement. Z.sub.RA-CAN increases slightly in signal intensity
but instantaneously in response to the second confounding event.
The consistent low TV and low Z.sub.RA-CAN are associated with the
surgery for mitral valve repair which coincides in time with the
first confounding event.
[0076] FIG. 9A illustrates an example of a method 900 for detecting
and characterizing a confounding event such as using
physiologically relevant data range. The method 900 is an
embodiment of 602. In an example, the method 900 can be performed
by the confounding event detection and analysis circuit 203 or the
confounding event detection and analysis circuit 300.
[0077] At 901, a CEB physiological signal is received. In an
example, the CEB physiological signal can be obtained from
device-based CEB signal receiver 311, which can be coupled to
ambulatory devices and associated leads, monitors, or sensors. In
another example, the CEB physiological signal can be retrieved from
the memory in the IMD 110 or the external system 120. Examples of
CEB physiological signal can include impedance signals, respiration
signals, coronary blood temperature, blood oxygen saturation, or
heart sound signal. More than one physiological signal can be used
to determine the physiological state.
[0078] The CEB physiological signal can be processed and one or
more CEB features can be extracted at 902. The one or more CEB
signal features can be statistical measurement of signal amplitude
or other intensity quantities including change of signal amplitude
over specified time duration, duration of the change of signal
amplitude, rate of change of signal amplitude (i.e. first
derivative of the signal), shift of DC level of signal amplitude,
signal variability, change of signal intensity within a certain
frequency range, or signal morphologies.
[0079] At 903, the one or more CEB signal features can be compared
to one or more pre-determined criteria to determine the presence of
a confounding event. In an example, the criterion can include
pre-determined threshold values for the signal features, where the
threshold values can be used to determine whether the one or more
CEB signal features are physiologically relevant to the target
event. If the values of the one or more CEB signal features are
outside the range of physiological relevancy, then a confounding
event is deemed detected; and the detected confounding event is
characterized at 904. If the values of the one or more CEB signal
features are within the range of physiological relevancy, then no
confounding event is deemed detected.
[0080] The range of the physiological relevancy, or the thresholds
for CEB signal features, can be fixed values empirically determined
such as using population data or patient's historical data. For
example, a change of intrathoracic impedance of greater than 50
ohms is considered physiologically irrelevant. In another example,
a duration of an impedance change that sustains for less than
several hours to less than two days, or a rate of change in
impedance greater than 5 ohm/day or 10% of the baseline impedance
value per day is considered physiologically irrelevant. In yet
another example, shift in signal DC level that sustains more than
three days is considered physiologically irrelevant.
[0081] The range of the physiological relevancy may also be
determined using the information of the type of the confounding
event, the type of physiologic sensor, the configuration of the
sensor used for sensing the CEB physiological signal, or any
combination thereof. In an example, a searchable data structure
such as a lookup table or association map can be created and
stored. The data structure can contain a plurality of values of
thresholds or range of physiological relevancy. Each value can be
indexed by one or more of the type of physiologic state trigger
event, sensor configurations for sensing the CEB physiological
signal, or the CEB signal features. Then, at 903, an appropriate
threshold for physiological relevancy can be determined from the
pre-stored searchable threshold structures, which can then be
compared with the calculated CEB signal feature values to determine
if a confounding event is detected. The detected confounding event
can be characterized at 904 by extracting information regarding the
time and type of the confounding event. In an example, the
characteristics include the start and end time of the confounding
event.
[0082] FIG. 10 illustrates an example of a method 1000 for
detecting and characterizing a confounding event such as using
template matching. The method 1000 is an embodiment of 602. In an
example, the method 1000 is performed by the confounding event
detection and analysis circuit 203 or the confounding event
detection and analysis circuit 300.
[0083] At 1001, a CEB physiological signal is received, such as by
using method 901. The features of the CEB physiological signal can
then be extracted at 1002, which may be performed such as using
method 902. Then, a stored confounding event template can be
retrieved from memory at 1003. In an example, the confounding event
template can be a morphological template computed such as using one
or more segments of the CEB signal during and around the time of
confounding event. The confounding event template can include at
least the CEB signal morphology during the transition and recovery
in response to the confounding event. The confounding event
template may be obtained directly from the CEB signal, or it may be
obtained from the CEB signal after signal processing such as signal
filtering. For example, a low pass-filtered CEB signal, or a
moving-averaged CEB signal, such as the signal levels during
transition 712 in FIGS. 7C and 7D, is used to create confounding
event template. The confounding event template may be created such
as using one or more of patient's historical data with known
confounding events, population data, or empirical knowledge of
signal morphology when a confounding event is present.
[0084] In some examples, multiple confounding event templates can
be used to detect a confounding event with unknown type. Each
template represents a particular confounding event. In an example
of detecting a confounding event using multiple templates, each
template may be indexed by the type of physiologic state trigger
event, sensor configurations for sensing the CEB physiological
signal, or other user specified conditions.
[0085] At 1004, the received CEB signal features are compared to
the confounding event template and a similarity measure is
calculated. In an example, the similarity measure can be a
correlation function. In another example, the similarity measure
can be computed such as using the area of difference between the
confounding event template and the CEB signal features with proper
scaling to compensate the discrepancy of signal ranges. If the
similarity is greater than a predetermined threshold, a confounding
event is declared detected and the confounding event is
characterized at 1005. Otherwise, no confounding event is deemed
detected and the process of detecting confounding event
continues.
[0086] The CEB signal can include data from sources external to
devices or sensors. Examples of signals from external sources
include a clinical report, a medical record, a lab test report, or
a case report form. The external CEB signals can include
environmental sensor signals such as temperature, humidity, or
atmospheric pressure. In an example, a method is provided to
directly receive the input from users the information (such as
start and end time and type) of a confounding event, or
automatically reads, parses and interprets textual or graphical
clinical reports to detect confounding event.
[0087] FIG. 11 illustrates an example of a method 1100 for
detecting a confounding event from more than one CEB signals or
sources. The method 1100 is an embodiment of 602. In an example,
the method 1100 is performed by the confounding event detection and
analysis circuit 203 or the confounding event detection and
analysis circuit 300.
[0088] A first CEB signal can be received at 1101 and features of
the CEB signal can be extracted at 1102. The first CEB signal can
be a CEB physiologic signal, CEB signals of device condition and
function, or data from external sources such as a clinical report.
In an example, the first CEB signal is a physiological signal, and
features of the CEB physiological signal are extracted such as
using method 902. In another example, the first CEB signal is a
clinical report, and features of the CEB physiological signal are
extracted such as using clinical report interpretation. At 1103, a
second CEB signal different than the first CEB signal can be
received, and features of the second CEB signal can be extracted at
1104. The second CEB signal can be a CEB physiologic signal, CEB
signals of device condition and function, or data from external
sources such as a clinical report. Features extracted at 1104 can
be performed such as using method 902 if the second CEB signal is a
physiological signal, or using clinical report interpretation if
the second CEB signal is a clinical report.
[0089] At 1005, both the first and the second CEB signals can be
used to determine the presence of a confounding event. In an
example, a cascade detection algorithm such as a decision tree can
be used at 1105. For example, the first CEB signal can be a
clinical report and the second CEB signal can be a physiological
signal. The clinical report (i.e., the first CEB signal) can be
interpreted. If the clinical report indicates the presence of a
confounding event, the extracted features from the CEB
physiological signal (i.e., the second CEB signal) can be processed
to confirm the presence of the confounding event using, for
example, the methods of physiologic relevancy criteria at 903 or
template matching at 1004.
[0090] In another example, each CEB signal can be individually
processed to detect the confounding event, and a decision fusion
method can be used to yield the detection decision at 1105. The
decision fusion can include logic operation "OR" (where a positive
detection is declared if a confounding event is detected from at
least one CEB signal), "AND" (where a positive detection is
declared only if a confounding event is detected from all the CEB
signals), majority voting or weighted voting schemes (where, for
example, a positive detection is declared if the confounding event
is detected from a significant number of CEB signals), or other
functions of the detection decisions or any combination
thereof.
[0091] A composite CEB signal can be generated using more than one
received CEB signal, or a composite feature set can be generated
such as using extracted features from the more than one CEB
signals. A composite CEB signal can be a linear or nonlinear
function of the individual CEB signal. The composite CEB signal or
the composite feature set can be compared to at least one
physiologically relevant criterion, such as that in 903, to
determine the presence of a confounding event. The detected
confounding event can then be characterized at 1106, where the
characteristics can include the start time or the end time of the
confounding event.
[0092] Various variations of the FIG. 11 have also been
contemplated. In an example, the second CEB signal can be provided
in an on-demand mode, that is, the second CEB signal may not be
received or processed until it is requested. For example, if a
confounding event is declared detected from the first CEB signal, a
request for confirmation can be generated. In response, a second
CEB signal, such as a user confirmation input, a clinical report
signal, or another CEB physiological signal, can then be received
and processed to confirm the presence of the confounding event.
[0093] FIG. 12 illustrates an example of a method 1200 for
detecting a target event in adaptation to the detected confounding
event. The method 1200 is a specific embodiment of 600. In an
example, method 1200 is performed by system 200.
[0094] At 1201, a physiological signal is received. The physiologic
signal may be received from a signal sensing circuit coupled to
electrodes or external sensors associated with an ambulatory
medical device or a physiological monitor, or from a signal memory.
At 1202, a confounding event can be detected using one or more of
the physiological signal received at 1202, a different CEB
physiological signal, or clinical report. The received
physiological signal can be segmented into at least two segments
such as using the confounding event characteristics at 1203. In an
example, the start time of the confounding event (T.sub.0) can be
used to segment the physiologic signal into a pre-transition
segment before T.sub.0 and a post-transition segment after T.sub.0.
In another example, a transition period can be identified as
between T.sub.0 and T.sub.0+.DELTA.t where .DELTA.t is transition
duration; and the pre-transition segment is defined as the segment
before T.sub.0, while the post-transition segment is defined as the
data after T.sub.0+.DELTA.t to remove the transient effect of the
onset of confounding event on the physiological signal. In an
example, the transition duration .DELTA.t can be a predetermined
value between 1-3 days. In another example, .DELTA.t can be
programmable and the range for .DELTA.t can be determined using the
information of the type of the confounding event or the sensing
configuration of the physiological signal (i.e., electrodes used
for intrathoracic impedance sensing). In another example, both the
start time T.sub.0 and end time T.sub.1 of the confounding event
can be used to segment the data. For example, the pre-transition
segment may include the physiological data before T.sub.0 and the
post-transition segment may include the physiological data after
T1. In another example, the post-transition segment can include the
physiological data after T.sub.1+.DELTA.t where .DELTA.t is
transition duration.
[0095] At 1204, the segmented physiologic signal can be adjusted to
remove or reduce the impact of the confounding event on the
physiological signal. The adjustment can be made to one or both of
the pre-transition segment and the post-transition segment. When
both segments are adjusted, the adjustment of one segment can be
made such as by using signal characteristics of the other segment.
Alternatively, the adjustment of one segment can be made without
using the signal characteristics of other segment of the signal.
The adjustment process of one segment can be independent of the
adjustment of the other segment. In some examples, more than two
segments can be made and each segment can be adjusted.
[0096] In an example, the segment to adjust can be determined by
the type of the detected confounding event. For example, if the
confounding event is a "steady" event that has sustained effects on
the physiological signal such that the signal is unlikely to
recover over time (for example, the signal as illustrated in FIG.
7B), then only the pre-transition segment is adjusted.
Post-transition segment is not to be adjusted because it represents
the new and steady patient condition. Example of the steady event
can include a change of device programming. If the confounding
event is an "acute" event that has a transient effect on the
physiological signal such that the signal is expected to recover
towards the pre-transition value over time (as illustrated in FIG.
7C), then the post-transition segment can be adjusted because it
reflects a temporary patient condition that would resolve over
time. Examples of acute event can include a surgical intervention,
a replacement of the device either at the same location or at a
different location, or a pocket revision. If the confounding event
is an acute event that causes the signal following the event to
recover towards a value different than the pre-transition value (as
illustrated in FIG. 7D), then both the pro and post-transition
segment can be adjusted because the baseline is changing.
[0097] The adjustment of the pre-transition or post-transition
segment can be made by comparing a first metric determined from the
pre-transition segment to a second metric determined from the
post-transition segment, determining an adjustment factor from the
comparison, and adjusting the selected segment(s) using the
adjustment factor. In an example, the second metric can be a
"recent" signal level computed as a central tendency measure over a
short period in the post-transition segment, and the first metric
can be a "baseline" signal level computed as the central tendency
measure over relatively longer time window into the past. Examples
of central tendency measure can include mean, median,
weighted-mean, or mode. In another example, the first metric can be
a central tendency measure over a short period .DELTA..sub.0 ending
at the beginning of the confounding event (T.sub.0), that is,
(T.sub.0-.DELTA..sub.0, T.sub.0); and the second metric can be a
central tendency measure over a short period .DELTA..sub.1
beginning at the end of the confounding event (T.sub.1), that is,
(T.sub.1, T.sub.1+.DELTA..sub.1).
[0098] Various embodiments of adjustment factor, determined from
the first and the second metrics, have been contemplated. In an
example, the adjustment factor can be a difference between the
second metric and the first metric. The adjustment factor can then
be added to the pre-transition segment of physiological data. In
another example, the adjustment factor can be a ratio between the
second metric and the first metric. The pre-transition segment of
physiological data can then be scaled by multiplying the adjustment
factor. In another example, the adjustment factor can be
time-varying, that is, the amount of adjustment can be dependent on
the timing location of the data with reference to the start time or
end time of the confounding event. For example, to adjust the
pre-transition segment, the value of the adjustment factor can
increase with time up to the transition start-time (T.sub.0). In
another example, to adjust the post-transition data segment, the
value of the adjustment factor can decrease with time from the
transition end-time (T.sub.1). In another example, a base value of
an offset (D.sub.0) can be computed as the difference between the
second metric and the first metric. The time-varying adjustment
factor D.sub.t can be an exponential function of time in reference
to T.sub.0 or T.sub.1:
{ D t = D 0 e t - T 0 if t .ltoreq. T 0 D t = D 0 if T 0 < t
< T 1 D t = D 0 e T 1 - t if t .gtoreq. T 1 ##EQU00001##
[0099] The adjustment of the signal segment can be made on
derivatives of the physiological signal. For example, a confounding
event may cause abrupt change in signal intensity. Such change in
signal intensity may be detected as a peak or a trough in first
derivative of the physiological signal (i.e., point-to-point
difference). To remove the abrupt change, the derivative signal may
be smoothened, for example, by replacing the identified peak or
trough derivatives with the mean derivatives calculated over a
pre-transition period, so that the signature of the confounding
event on the physiological signal can be eliminated or lessened.
The smoothened derivative signal may then be reconstructed by
taking the integral from the first point of the pre-transition
period.
[0100] At 1204 a mode of adjustment can be determined. The mode of
adjustment, including a transient adjustment or a permanent
adjustment, can determine the amount of data to be adjusted in the
selected segment. In an example, the mode of adjustment can be
determined such as using one or more of a type of the detected
confounding event, a type of the physiologic signal, or a sensing
configuration of the physiological signal. For example, if the
pre-transition segment is chosen to be adjusted, then the
adjustment can be performed on the data within a data window
(T.sub.0-t.sub.H, T.sub.0) from the pre-transition segment, where
T.sub.0 is the start time of the confounding event, and the
programmable parameter t.sub.H controls how far back in the signal
history from T.sub.0 the data in the pre-transition segment should
be adjusted. As an example, t.sub.H can take a value between 1 to 8
weeks. In another example, t.sub.H can be the same as the window
size used for updating a signal baseline. For example, if the
signal baseline is calculated as the moving average of data over 2
months, then t.sub.H can also be set to 2 months. In an example, a
patient's entire historic data can be adjusted.
[0101] If the post-transition segment is chosen to be adjusted,
then the adjustment can be made within a data window after T.sub.0.
In an example, the post-transition data window for adjustment can
be chosen to be (T.sub.0, T.sub.0+t.sub.C). In another example, the
post-transition data window for adjustment can be (T.sub.1,
T.sub.1+t.sub.C). The programmable parameter t.sub.C controls how
much "forward" from the start (T.sub.0) or the end (T.sub.1) of the
confounding event the data in the post-transition segment are to be
adjusted. To ensure that the complete signal transition can be
observed and adjusted, t.sub.C can be programmed to a value greater
than the expected duration of transition. For example, t.sub.C can
be programmed to two days or longer.
[0102] In an example, t.sub.C can be a predetermined fixed value.
The adjustment can be made only when all data within the data
window become available. Then, the signal adjustment is a one-time
operation on the data within the data window. In another example,
t.sub.C is not fixed value; and the post-transition segment can be
adjusted while current signal data are being collected. This
repeated and continuous post-transition segment adjustment can
provide continuous presentation of the adjusted data for patient
monitoring and timely detection of health state change and
notification to the caregiver. In an example, the post-transition
segment adjustment method can be updated while the data from the
post-transition segment are collected and assessed. For example,
the adjustment factor, such as the scaling factor applied to the
post-transition segment, may be tuned dynamically while new
post-transition data become available. Each adjustment attempt can
use the unadjusted data and produce a new set of adjusted
post-transition values. The adjustment of the post-transition
segment can continue for as long as the adjusted data are used to
detect a health state change.
[0103] In an example, both the pre-transition and the
post-transition segments can be adjusted. Methods discussed above
pertaining to pre-transition segment adjustment or to
post-transition segment adjustment can be applied to the concurrent
pre-transition and post-transition segment adjustment. For example,
a first adjustment factor (e.g., a DC shift or a scaling factor)
can be applied to the pre-transition segment and a second
adjustment factor can be applied to the second-transition segment,
and the pre-transition segment adjustment and the post-transition
adjustment can be performed sequentially or concurrently.
[0104] At 1205, a notification of detection of confounding event
and the data adjustment can be generated and prompted for user
confirmation. The notification can include an indication that the
pre-transition or post-transition segment are to be adjusted, the
segment(s) selected for adjustment, or the mode of adjustment
(i.e., permanent or transient adjustment). In an example, the
notification and the request for confirmation (RFC) may be
generated and presented in a sequence of steps. For example, a
first notification and RFC can be presented to the user upon the
detection and characterization of a confounding event. Once a
confirmation is received, a second notification and RFC can be
presented upon the data segmentation and adjustment. The confirmed
confounding events and the adjusted physiological signal can be
stored in a memory at 1206.
[0105] The adjusted physiological signal can be at 1207 to detect a
target event. In an example, the target event is an event
indicative of HF decompensation status. A HF decompensation
detection algorithm can compute an HF decompensation index such as
using the adjusted physiologic data and determine whether an event
indicative of HF decompensation is detected such as by comparing
the decompensation index to a pre-determined threshold value.
[0106] The decompensation index can be a quantitative measure
indicating the presence or severity of a physiologic condition
precipitating an HF decompensation episode, such as excessive
intrathoracic fluid accumulation. In another example, the
decompensation index can be an accumulated deviation of the sensed
physiological signal from a reference signal over time. The
reference signal can represent the trend of the physiological
signal intensity, such as signal amplitude or a function of the
signal amplitude, or the signal's power spectral density or a
function of the power spectral density. In an example, the
reference signal can be a moving average of the physiological data
over a specified time period. In another example, the reference
signal can be a low-pass or band-pass filtered physiological data
with pre-determined filter coefficients.
[0107] The deviation can be computed as a difference between the
intensity of the sensed physiological signal and the reference
signal. In an example, the intensity of the sensed physiological
signal can include a central tendency measure of the signal
amplitude over a specified time such as 3-10 days. In another
example, the decompensation index can be accumulated only if a
certain criterion is met, such as the difference between the signal
intensity and the decompensation index being greater than a
specified threshold. Other examples of decompensation index can
include the cumulative sum in detecting persistent shifts in the
trended signal found in Brockway et al., U.S. Pat. No. 7,761,158,
entitled "Detection of Heart Failure Decompensation Based on
Cumulative Changes in Sensor Signals," filed Dec. 20, 2005, which
is incorporated herein by reference in its entirety.
[0108] At 1208, a decision can be made as to whether a target event
is detected. For example, in the context of detecting HF
decompensation, the computed decompensation index can be compared
to a specified threshold at 1208. If the decompensation index is
greater than the threshold, then a target event is detected. At
1209, a report is generated to inform the user the detected target
event. Examples of the report can include a textual or graphical
message, a sound, an image, or any combination thereof. If the
decompensation index is greater than the threshold, then no target
event is detected, and the detection continues with receiving the
physiological signal at 1201.
[0109] FIGS. 13A-B illustrate examples of pre-transition signal
adjustment using the information of the detected confounding event
such as using the adjustment method at 1204, as discussed above.
The physiological signal illustrated in FIG. 13A is the amplitude
signal of first heart sound (S1) computed from a heart sound (HS)
signal. In this example, the HS signal was collected in a span of
12 months from an accelerometer coupled to an IMD 110. The y-axis
indicates the intensity of the S1 amplitude in the unit of milli-G.
In an example, the HS sensor can be a microphone sensor; and the HS
sensor may be located within IMD 110, on a lead, or externally in a
patch. S1 amplitude can be measured as the peak or peak-to-peak
deflection on the HS signal or a root-mean-square of a segment of
the HS signal around the peak of S1. Also shown in FIG. 13A is the
average baseline S1 amplitude signal 1322. A confounding event,
later confirmed to be a device reprogramming of atrial-ventricular
pace delay, occurred in around October 2011. The confounding event
causes an abrupt increase 1312 in S1 amplitude signal occurred
within one day. The post-transition signal 1313 remains at a level
with a higher DC offset than the pre-transition signal 1311. The
"baseline" of the S1 amplitude is computed as the moving-average of
the S1 amplitude collected in consecutive 42 days. Due to the
abrupt change in S1 amplitude 1312, the moving-average S1
amplitude, which is a low-pass filtered signal of the raw S1
amplitude signal, demonstrates a slow ramp-up 1322 from the
pre-transition baseline 1321. No baseline data was obtained during
the transition; and a stable post-transition baseline 1323 was not
achieved until 42 days after the onset of the confounding
event.
[0110] FIG. 13B illustrates the same S1 amplitude signal as in FIG.
13A which is subsequently adjusted such as using the information of
the start time of the confounding event and the post-transition and
the pre-transition segments signal characteristics. In this
example, a pre-transition baseline signal (i.e., 42-day moving
average) 1321 is compared to the post-transition baseline signal
1313. An adjustment factor, computed as the difference between the
post-transition baseline value and the pre-transition baseline
value, is added to the pre-transition signal 1311. The resulting
adjusted pre-transition signal 1331 has the same signal morphology
as the unadjusted pre-transition signal 1311, but different DC
offset. As a result, the adjusted pre-transition baseline signal
1341 has a comparable DC offset level as the post-transition
baseline signal 1342, and the impact of the confounding event on
the S1 amplitude signal (i.e., the abrupt signal change 1312) is
substantially reduced.
[0111] FIGS. 14A-B illustrate examples of post-transition signal
adjustment using the information of the detected confounding event.
In this example, a template is used in data adjustment. The
template can be created for a particular confounding event using a
particular type of physiological signal. The template can represent
the expected behavior of the signal (e.g., statistical property
like the mean or DC trend, or morphological characteristics) in
response to a given confounding event.
[0112] As illustrated in FIG. 14A, a confounding event can cause an
abrupt and transient reduction in the intensity of a physiological
signal 1401. Abrupt decrease in intrathoracic impedance may be a
result of, for example, an open chest surgery that transiently
reduces the patient's tidal volume. Following the abrupt change,
the intensity of the post-transition signal 1402 gradually
recovers. The confounding event can be detected and characterized
such as using one of the methods 900, 1000, or 1100. According to
the type of the confounding event and the type of physiological
signal used for target event detection, an appropriate template can
be retrieved from the memory. In the example as illustrated in FIG.
14A, the template may represent the expected pattern of changes in
physiological signal intensity. The template can include a
pre-transition branch 1410 with a fixed amplitude extended for a
specified duration, and a post-transition branch 1412 with a linear
ramp with a pre-determined slope. The template can be matched to
the impedance signal before and after the transition event. In an
example, the match can be performed by aligning a fiducial point on
the template, such as the point of change in the signal intensity,
to the start time of the confounding event (T.sub.0) on the
physiological signal. In another example, prior to template
matching, the template can be scaled so that the amplitude of the
pre-transition branch 1410 is equivalent to the average intensity
of the physiological signal 1401. Then, by subtracting the template
from the unadjusted impedance signal, the ramp-up trend is removed
from the unadjusted post-transition signal 1402. The resulting
adjusted post-transition segment 1422 has about the same DC offset
level as the pre-transition signal 1401.
[0113] The template can include a first-order response curve with a
given step response and a time constant for post-transition signal
recovery. Examples of the recovery curve can include exponential,
power, logarithm functions, or other non-parametric numeric
descriptors of the curve. In an example, the slope of
post-transition branch of the template 1412, or similarly the step
response curve and time constant, can be variable within an
acceptable range for a given type of confounding event. For
example, the time constant of the post-transition recovery curve
for the confounding event of post chest surgery can vary between 1
and 2 months. The template, including the time constant of recovery
curve, can be adjusted automatically as the new data is
gathered.
[0114] FIG. 14B illustrates a mismatch between a template and a
physiological signal. The selected template includes a
pre-transition branch 1420 and a post-transition branch 1413. The
post-transition branch 1413 does not match the post-transition
physiological signal 1402. Specifically, the post-transition
physiological signal 1402 has a slower signal recovery rate than
the post-transition branch of the template 1413. Consequently, the
adjusted post-transition physiological signal 1423 demonstrates a
decline in signal intensity because of the steeper slope of the
post-transition branch of the template 1413. The mismatch between
the template and the physiological signal during a confounding
event can trigger an alert to the user. The alert may include the
information of mismatch, unexpected rate of post-transition
recovery in the physiological signal, or possible complications
associates with the confounding event. The alert may also be
generated during the data adjustment confirmation at 1205.
[0115] In an example, in response to a detected mismatch between
the template and the physiological signal during a confounding
event, a different template can be used to re-adjust the
post-transition signal 1402. In another example, the mismatched
template can be modified by adjusting the post-transition branch of
the template 1413, and the adjusted template can be reapplied to
the physiological signal.
[0116] FIG. 15 illustrates an example of a method 1500 for
detecting an HF decompensation event. In this example, an HF
decompensation event is detected from a physiological signal 1501
using an HF decompensation algorithm such as the method 1200. A
reference signal 1502 can be computed such as using the
physiological signal 1501. In an example, the reference signal 1502
can be a low-pass filtered or moving-averaged physiological signal
1501. A HF decompensation risk index (DI) signal 1503 can be
computed and updated such as using the comparison between the
intensity of the present physiological signal 1520 and the
reference signal 1502. The DI signal 1503 can be obtained such as
using the method 1207. The DI can be accumulated if the present
physiological signal 1520 is smaller than the reference signal 1502
beyond a range of tolerance, and the DI can be reset to a
pre-determined value if the present physiological signal 1520 is
greater than the reference signal 1502 beyond a range of tolerance,
that is,
DI ( t ) = { DI ( t - 1 ) + f ( x ( t ) , Ref ( t ) ) , if x ( t )
- Ref ( t ) .ltoreq. .delta. DI ( 0 ) , if x ( t ) - Ref ( t ) >
.delta. ##EQU00002##
where x(t) is the intensity of the physiological signal at time t,
Ref(t) the reference signal intensity at time t, DI(t) the DI at
time t, DI(0) the pre-determined value of DI, o the predetermined
tolerance for comparing x(t) and Ref(t), and f(x(t), Ref(t)) the
accumulation factor as a function of x(t) and Ref(t). In an
example, f(x(t), Ref(t)) is proportional to the difference between
Ref(t) and x(t), that is, f(x(t), Ref(t))=k*(Ref(t)-x(t)), where k
is a positive scalar.
[0117] As illustrated in FIG. 15, a confounding event occurring at
time (T.sub.0) causes an abrupt decrease 1520 in the physiological
signal 1501. The reference signal 1502 decreases slightly but is
less impacted by the confounding event than the physiological
signal 1501. The reference signal 1502 remains greater than the
physiological signal 1520 before, during, and after the confounding
event. As a result, the DI accumulates and monotonically increases.
When the DI increases above a pre-set threshold 1530, a HF
decompensation event is detected, and an alert can be issued. The
detection, however, is a false alarm detection because it is
triggered by the confounding event that causes the abrupt change
1520 in the physiological signal 1501. The DI signal remains above
the threshold for over a month and remains insensitive to most
physiological changes in signal 1520.
[0118] The false alarm may be avoided using the disclosed method,
such as that illustrated in 1200. Upon the detection of the
confounding event from the signal 1501, the confounding event can
be characterized and the start time (T.sub.0) of the confounding
event is identified. The physiological signal 1501 can be segmented
into the pre-transition and post-transition segments, and the
pre-transition segment can be adjusted using the information of the
confounding event detected from the signal 1501. In an example, a
method as illustrated in FIG. 13 can be used for pre-transition
segment adjustment. The signature of the confounding event can be
removed or greatly lessened from the adjusted signal 1511, as
illustrated in FIG. 15. The reference signal 1502 can be updated
accordingly such as using the adjusted physiological signal 1511 to
obtain an adjusted reference signal 1512. The "adjusted" DI signal
1513 can then be computed using the adjusted physiological signal
1511 and the adjusted reference signal 1512. As illustrated in FIG.
15, the adjusted DI can be accumulated until the accumulation
condition fails at 1540 when the adjusted physiological signal
intensity is greater than the adjusted reference signal over a
tolerance o, and the adjusted DI is reset to the initial value.
Because DI does not exceed the DI threshold 1530, no HF
decompensation event is detected. The adjusted DI remains sensitive
to deviations of the physiological signal from its reference.
[0119] The above detailed description includes references to the
accompanying drawings, which form a part of the detailed
description. The drawings show, by way of illustration, specific
embodiments in which the invention can be practiced. These
embodiments are also referred to herein as "examples." Such
examples can include elements in addition to those shown or
described. However, the present inventors also contemplate examples
in which only those elements shown or described are provided.
Moreover, the present inventors also contemplate examples using any
combination or permutation of those elements shown or described (or
one or more aspects thereof), either with respect to a particular
example (or one or more aspects thereof), or with respect to other
examples (or one or more aspects thereof) shown or described
herein.
[0120] In the event of inconsistent usages between this document
and any documents so incorporated by reference, the usage in this
document controls.
[0121] In this document the terms "a" or "an" are used, as is
common in patent documents, to include one or more than one,
independent of any other instances or usages of "at least one" or
"one or more." In this document, the term "or" is used to refer to
a nonexclusive or, such that "A or B" includes "A but not B," "B
but not A," and "A and B," unless otherwise indicated. In this
document, the terms "including" and "in which" are used as the
plain-English equivalents of the respective terms "comprising" and
"wherein." Also, in the following claims, the terms "including" and
"comprising" are open-ended, that is, a system, device, article,
composition, formulation, or process that includes elements in
addition to those listed after such a term in a claim are still
deemed to fall within the scope of that claim. Moreover, in the
following claims, the terms "first," "second," and "third," etc.
are used merely as labels, and are not intended to impose numerical
requirements on their objects.
[0122] Method examples described herein can be machine or
computer-implemented at least in part. Some examples can include a
computer-readable medium or machine-readable medium encoded with
instructions operable to configure an electronic device to perform
methods as described in the above examples. An implementation of
such methods can include code, such as microcode, assembly language
code, a higher-level language code, or the like. Such code can
include computer readable instructions for performing various
methods. The code may form portions of computer program products.
Further, in an example, the code can be tangibly stored on one or
more volatile, non-transitory, or non-volatile tangible
computer-readable media, such as during execution or at other
times. Examples of these tangible computer-readable media can
include, but are not limited to, hard disks, removable magnetic
disks, removable optical disks (e.g., compact disks and digital
video disks), magnetic cassettes, memory cards or sticks, random
access memories (RAMs), read only memories (ROMs), and the
like.
[0123] The above description is intended to be illustrative, and
not restrictive. For example, the above-described examples (or one
or more aspects thereof) may be used in combination with each
other. Other embodiments can be used, such as by one of ordinary
skill in the art upon reviewing the above description. The Abstract
is provided to comply with 37 C.F.R. .sctn.1.72(b), to allow the
reader to quickly ascertain the nature of the technical disclosure.
It is submitted with the understanding that it will not be used to
interpret or limit the scope or meaning of the claims. Also, in the
above Detailed Description, various features may be grouped
together to streamline the disclosure. This should not be
interpreted as intending that an unclaimed disclosed feature is
essential to any claim. Rather, inventive subject matter may lie in
less than all features of a particular disclosed embodiment. Thus,
the following claims are hereby incorporated into the Detailed
Description as examples or embodiments, with each claim standing on
its own as a separate embodiment, and it is contemplated that such
embodiments can be combined with each other in various combinations
or permutations. The scope of the invention should be determined
with reference to the appended claims, along with the full scope of
equivalents to which such claims are entitled.
* * * * *