U.S. patent application number 12/349413 was filed with the patent office on 2009-05-07 for system and method for evaluating cardiac performance relative to performance of an intrathoracic pressure maneuver.
Invention is credited to John D. Hatlestad, Donald L. Hopper, Veerichetty Kadhiresan, Jeffrey E. Stahmann.
Application Number | 20090118627 12/349413 |
Document ID | / |
Family ID | 36654175 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090118627 |
Kind Code |
A1 |
Stahmann; Jeffrey E. ; et
al. |
May 7, 2009 |
SYSTEM AND METHOD FOR EVALUATING CARDIAC PERFORMANCE RELATIVE TO
PERFORMANCE OF AN INTRATHORACIC PRESSURE MANEUVER
Abstract
A system and method for evaluating cardiac performance relative
to performance of an intrathoracic pressure maneuver is described.
Blood pressure is indirectly sensed by directly collecting
intracardiac impedance measures through an implantable medical
device. Cardiac functional changes to the blood pressure are
evaluated in response to performance of an intrathoracic pressure
maneuver.
Inventors: |
Stahmann; Jeffrey E.;
(Ramsey, MN) ; Hopper; Donald L.; (Maple Grove,
MN) ; Kadhiresan; Veerichetty; (Centerville, MN)
; Hatlestad; John D.; (Maplewood, MN) |
Correspondence
Address: |
PAULY, DEVRIES SMITH & DEFFNER, L.L.C.
PLAZA VII- SUITE 3000, 45 SOUTH SEVENTH STREET
MINNEAPOLIS
MN
55402-1630
US
|
Family ID: |
36654175 |
Appl. No.: |
12/349413 |
Filed: |
January 6, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10782642 |
Feb 19, 2004 |
7488290 |
|
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12349413 |
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Current U.S.
Class: |
600/486 |
Current CPC
Class: |
A61B 7/00 20130101; A61B
5/021 20130101 |
Class at
Publication: |
600/486 |
International
Class: |
A61B 5/0215 20060101
A61B005/0215 |
Claims
1. A system for evaluating cardiac performance relative to
performance of an intrathoracic pressure maneuver, comprising: an
implantable medical device to indirectly sense blood pressure by
directly collecting intracardiac impedance measures; and an
analysis component to evaluate cardiac functional changes to the
blood pressure in response to performance of an intrathoracic
pressure maneuver.
2. A system according to claim 1, wherein the blood pressure
comprises at least one of arterial pressure, cardiac chamber
pressure, systolic pressure, and diastolic pressure.
3. A system according to claim 2, wherein the cardiac chamber
pressure comprises left ventricular end diastolic pressure.
4. A system according to claim 1, wherein the implantable medical
device comprises at least one of a bradycardia, tachycardia, heart
failure, therapy delivery, and monitoring device.
5. A system according to claim 1, further comprising: at least one
lead to couple to the implantable medical device and to sense at
least one of the intracardiac impedance measures across the
thoracic cavity and the intracardiac impedance measures across the
heart.
6. A system according to claim 1, wherein the intrathoracic
pressure maneuver comprises at least one of a Valsalva and Muller
maneuver.
7. A system according to claim 1, further comprising: an evaluation
subcomponent to evaluate at least one of overdamping and
underdamping cardiac impedance response relative to normative
levels.
8. A system according to claim 7, further comprising: a
notification subcomponent to generate a notification responsive to
the at least one of overdamping and underdamping cardiac impedance
response.
9. A system according to claim 1, wherein thoracic pressure is
monitored during the intrathoracic pressure maneuver.
10. A system according to claim 9, further comprising: an external
pressure monitor to define a confined volume configured to receive
a forced exhalation and to measure the thoracic pressure relative
to the confined volume.
11. A system according to claim 9, further comprising: a thoracic
pressure sensor to internally measure thoracic pressure.
12. A method for evaluating cardiac performance relative to
performance of an intrathoracic pressure maneuver, comprising:
indirectly sensing blood pressure by directly collecting
intracardiac impedance measures through an implantable medical
device; and evaluating cardiac functional changes to the blood
pressure in response to performance of an intrathoracic pressure
maneuver.
13. A method according to claim 12, wherein the blood pressure
comprises at least one of arterial pressure, cardiac chamber
pressure, systolic pressure, and diastolic pressure.
14. A method according to claim 13, wherein the cardiac chamber
pressure comprises left ventricular end diastolic pressure.
15. A method according to claim 12, wherein the implantable medical
device comprises at least one of a bradycardia, tachycardia, heart
failure, therapy delivery, and monitoring device.
16. A method according to claim 12, further comprising: sensing at
least one of the intracardiac impedance measures across the
thoracic cavity and the intracardiac impedance measures across the
heart.
17. A method according to claim 12, wherein the intrathoracic
pressure maneuver comprises at least one of a Valsalva and Muller
maneuver.
18. A method according to claim 12, further comprising: evaluating
at least one of overdamping and underdamping cardiac impedance
response relative to normative levels.
19. A method according to claim 18, further comprising: generating
a notification responsive to the at least one of overdamping and
underdamping cardiac impedance response.
20. A method according to claim 12, further comprising: monitoring
thoracic pressure during the intrathoracic pressure maneuver.
21. A method according to claim 20, further comprising: defining a
confined volume configured to receive a forced exhalation; and
measuring the thoracic pressure relative to the confined
volume.
22. A method according to claim 20, further comprising: internally
measuring thoracic pressure.
23. An apparatus for evaluating cardiac performance relative to
performance of an intrathoracic pressure maneuver, comprising:
means for indirectly sensing blood pressure by directly collecting
intracardiac impedance measures through an implantable medical
device; and means for evaluating cardiac functional changes to the
blood pressure in response to performance of an intrathoracic
pressure maneuver.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This patent application is a divisional of the U.S. patent
application Ser. No. 10/782,642, filed Feb. 19, 2004, pending, the
disclosure of which is incorporated by reference, and the priority
filing date of which is claimed.
FIELD
[0002] The present invention relates in general to cardiac
performance assessment and, in particular, to a system and method
for evaluating cardiac performance relative to performance of an
intrathoracic pressure maneuver.
BACKGROUND
[0003] Heart disease refers to several classes of cardio and
cardiovascular disorders and co-morbidities relating to the heart
and blood vessels. Generally, heart disease is treatable through
medication, lifestyle modification and surgical intervention, which
involves repairing damaged organs and tissue. Surgical intervention
can also involve implanting active monitoring or therapy delivery
devices, such as pacemakers and defibrillators, and passive
intervention means.
[0004] Heart disease can lead to heart failure, a potentially fatal
condition in which the heart is unable to supply blood sufficient
to meet the metabolic demands of a body. In a clinical setting,
cardiac performance, including potential heart failure, can be
detected by measuring changes in arterial blood pressure
immediately before, during and immediately after the performance of
intrathoracic pressure maneuvers, known as dynamic auscultation,
which includes the Valsalva and Muller maneuvers, such as described
in Braunwald, "Heart Disease--A Textbook of Cardiovascular
Medicine," pp. 46-52 (5.sup.th ed. 1997), the disclosure of which
is incorporated by reference.
[0005] In particular, potential heart failure can be effectively
and safely detected by evaluating the profile of arterial blood
pressure and other cardiac dimensional measures relative to
performance of the Valsalva maneuver, which involves forced
expiration against a closed glottis for about 10-30 seconds. In a
healthy person with no prior history of cardiovascular disease or a
patient suffering from a diseased but not failed heart, left
ventricular ejection fraction (LVEF) and left ventricular end
diastolic pressure (LVEDP) change dramatically coincidental to
performance of the Valsalva maneuver, whereas LVEF and LVEDP change
only slightly in a heart failure patient, as discussed in Hamilton
et al., Arterial, Cerebrospinal and Venous Pressure in Man During
Cough and Strain, 144 Am. J. of Phys., pp. 42, 42-50 (1944) and
Zema et al., Left Ventricular Dysfunction-Bedside Valsalva
Maneuver, Br. Heart J., pp. 44:560-569 (1980), the disclosures of
which are incorporated by reference.
[0006] Circulatory effects and arterial blood pressure profile
undergo four well-documented phases during performance of the
Valsalva maneuver. During Phase I (initial strain), systemic
arterial pressure increases approximately equal to the increase in
intrathoracic pressure. During Phase II (strain duration and
cessation of breathing), pulse pressure narrows and systemic
systolic pressure decreases. During Phase III (strain
discontinuation and resumption of normal breathing), systolic
pressure drops rapidly. During Phase IV (recovery), diastolic and
systolic pressures overshoot and return to pre-maneuver levels. The
four phases form a characteristic signature and periodic analysis
of arterial blood pressure profile or blood pressure, specifically
LVEF and LVEDP, throughout each phase can be indicative of the
patient's heart failure status.
[0007] Regularly obtaining and evaluating LVEF and LVEDP for
cardiac performance assessment, however, can be difficult. Direct
measurements can be obtained through catheterization and
electrodes. LVEF and LVEDP can be measured directly through a
catheter distally placed into the left ventricle, but the procedure
is invasive and creates unfavorable risks. Pulmonary artery wedge
pressure (PAWP), measured through right heart catheterization, can
be used as a surrogate measure for LVEDP, but the procedure is also
invasive and risky. Moreover, catheterization is impractical in a
non-clinical setting. Finally, chronically implanted cardiac
pressure electrodes, while less risky, are generally inaccurate and
unreliable. Consequently, indirect measurements approximating LVEF
and LVEDP are preferable.
[0008] For example, intracardiac impedance is readily measured
through cardiac impedance plethysmography and can be used as an
indirect measure of LVEF and LVEDP. Changes in intracardiac
impedance correlate to cardiac dimensional changes, such as
described in McKay et al., Instantaneous Measurement of Left and
Right Ventricular Stroke Volume and Pressure-Volume relationships
with an Impedance Catheter, Circ. 69, No, 4, pp. 703-710 (1984),
the disclosure of which is incorporated by reference. As a result,
by measuring intracardiac impedance, a profile of LVEDP and LVEF
response during performance of the Valsalva maneuver can be
obtained indirectly without resorting to invasive direct
measurement techniques. Known plethysmography techniques for
indirectly measuring intracardiac impedance, however, adapt poorly
to effective long-term monitoring.
[0009] U.S. Pat. No. 4,548,211 to Marks discloses the use of
external admittance impedance plethysmography to measure pulsatile
volume and net inflow in a limb or body segment. External
electrodes are placed on the skin and a voltage is applied and
sensed for use in determining absolute physiologic values of
peak-to-peak pulsatile volume and peat net inflow. While
instrumental in non-invasively measuring peripheral blood flow
dynamics, the Marks device fails to measure or monitor cardiac
dimensional changes through intracardiac impedance.
[0010] U.S. Pat. No. 5,788,643 to Feldman discloses a process for
monitoring patients with chronic congestive heart failure (CHF) by
applying a high frequency current between electrodes placed on the
limbs of a patient. Current, voltage and phase angle are measured
to calculate resistance, reactance, impedance, total body water and
extracellular water, which are compared to a baseline for
identifying conditions relating to CHF. The Feldman process is
limited to operating on external peripheral electrodes and fails to
measure or monitor cardiac dimensional changes through intracardiac
impedance.
[0011] U.S. Pat. Nos. 6,120,442 and 6,238,349 both to Hickey
disclose an apparatus and method for non-invasively determining
cardiac performance parameters, including systolic time intervals,
contractility indices, pulse amplitude ratios while performing the
Valsalva maneuver, cardiac output indices, and pulse wave velocity
indices. A catheter is inserted into the esophagus and a balloon is
pressurized at a distal end, positioned adjacent to the aortic arch
to sense aortic pressure. The affects of aortic pressure on the
balloon are utilized to determine the cardiac performance
parameters. The Hickey devices, while capable of assessing cardiac
performance, must be performed in a clinical setting and fails to
measure or monitor cardiac dimensional changes through intracardiac
impedance.
[0012] U.S. Pat. Nos. 3,776,221 and 5,291,895 both to McIntyre
disclose a pressure-sensing device for providing a signal
representative of systemic arterial blood pressure before and after
performance of the Valsalva maneuver. Specifically, an electrode
placed on the skin generates a blood pressure signal and measures
changes in amplitude before and after the Valsalva maneuver is
performed. The McIntyre devices are limited to operating with
external skin electrodes and fail to measure or monitor cardiac
dimensional changes through intracardiac impedance.
[0013] Therefore, there is a need for an approach to assessing
cardiac performance by indirectly measuring arterial blood pressure
profile through intracardiac impedance relative to performance of
intrathoracic pressure maneuvers, such as the Valsalva maneuver.
Preferably, such an approach would analyze an intrathoracic
pressure maneuver signature in a non-clinical setting on a regular
basis for use in automated heart disease patient management.
SUMMARY
[0014] A system and method for generating a cardiac performance
assessment based on intracardiac impedance is described.
Intracardiac impedance measures are collected during the induced
performance of an intrathoracic pressure maneuver, such as the
Valsalva maneuver, using an implantable cardiac device. The start
of the intrathoracic pressure maneuver is either expressly marked
by the patient or implicitly derived by the implantable cardiac
device or by an intrathoracic pressure sensing device. The
collected intracardiac impedance measures are periodically
evaluated for determining arterial blood pressure profile. The
intracardiac impedance measures are correlated to arterial blood
pressure and assigned to the respective phases of the Valsalva
maneuver, if applicable. A arterial blood pressure profile trend
determined for each of the phases is evaluated and the overall set
of trends is compared to the signature characteristic of the
intrathoracic pressure maneuver under consideration. A cardiac
performance assessment is generated based on the closeness of match
to the characteristic signature and a notification is generated if
the cardiac performance assessment varies beyond a set of
predefined thresholds.
[0015] An embodiment provides a system and method for evaluating
cardiac performance relative to performance of an intrathoracic
pressure maneuver. Blood pressure is indirectly sensed by directly
collecting intracardiac impedance measures through an implantable
medical device. Cardiac functional changes to the blood pressure
are evaluated in response to performance of an intrathoracic
pressure maneuver.
[0016] A further embodiment provides a system and method for
assessing cardiac performance through transcardiac impedance
monitoring. Intracardiac impedance measures are directly collected
through an implantable medical device. The intracardiac impedance
measures are correlated to cardiac dimensional measures relative to
performance of an intrathoracic pressure maneuver. The cardiac
dimensional measures are grouped into at least one measures set
corresponding to a temporal phase of the intrathoracic pressure
maneuver. The at least one cardiac dimensional measures set is
evaluated against a cardiac dimensional trend for the corresponding
intrathoracic pressure maneuver temporal phase to represent cardiac
performance.
[0017] Still other embodiments of the present invention will become
readily apparent to those skilled in the art from the following
detailed description, wherein are described embodiments of the
invention by way of illustrating the best mode contemplated for
carrying out the invention. As will be realized, the invention is
capable of other and different embodiments and its several details
are capable of modifications in various obvious respects, all
without departing from the spirit and the scope of the present
invention. Accordingly, the drawings and detailed description are
to be regarded as illustrative in nature and not as
restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram showing an implantable medical
device monitoring transcardiac impedance, in accordance with a
further embodiment of the present invention.
[0019] FIG. 2 is a schematic diagram showing an external medical
device assisting in monitoring transcardiac impedance, in
accordance with a further embodiment of the present invention.
[0020] FIGS. 3A-C are graphical representations showing, by way of
example, averaged arterial blood pressure profiles relative to
performance of the Valsalva maneuver in a healthy person, a patient
suffering from heart disease and a patient suffering from heart
failure.
[0021] FIG. 4 is a graphical representations showing, by way of
example, cardiac dimension profiles during diastole and systole,
respectively, relative to performance of the Valsalva maneuver in a
healthy person, a patient suffering from heart disease hut not
significant heart failure and a patient suffering from significant
heart failure.
[0022] FIG. 5 is a graphical representations showing, by way of
example, stroke volume index profile and left ventricular pressure
profile relative to performance of the Valsalva maneuver in a
healthy person.
[0023] FIG. 6 is a functional block diagram showing a system for
assessing cardiac performance through transcardiac impedance
monitoring, in accordance with a further embodiment of the present
invention.
[0024] FIG. 7 is a graphical representation showing, by way of
example, trend analysis of arterial blood pressure profile.
[0025] FIG. 8 is a graphical representations showing, by way of
example, trend analysis of cardiac stroke volume profile.
[0026] FIG. 9 is a flow chart showing a method for assessing
cardiac performance through transcardiac impedance monitoring, in
accordance with a further embodiment of the present invention.
[0027] FIG. 10 is a flow chart showing a routine for collecting
physiological measures for use in the method of FIG. 9.
[0028] FIG. 11 is a flow chart showing a routine for assessing
cardiac performance for use in the method of FIG. 9.
[0029] FIG. 12 is a flow chart showing a routine for evaluating
cardiac stroke volume profile relative to, by way of example, the
Valsalva maneuver, for use in the routine of FIG. 11.
DETAILED DESCRIPTION
Internal Transcardiac Impedance Monitoring System
[0030] FIG. 1 is a schematic diagram 100 showing an implantable
medical device (IMD) 103 monitoring transcardiac impedance, in
accordance with a further embodiment of the present invention. The
IMD 103 is surgically implanted in the chest or abdomen of a
patient and consists generally of a housing 104 and terminal block
105. The IMD 103 is coupled to a set of leads 106a-b at the
terminal block 105. During surgery, the leads 106a-b are threaded
through a vein and placed into the heart 102 with the distal tips
of each lead 106a-b positioned in direct contact with tissue inside
the heart 102.
[0031] The housing 104 contains a battery 107, control circuitry
108, memory 109, and telemetry circuitry 110. The battery 107
provides a finite power source for the IMD components. The control
circuitry 108 samples and processes raw data signals and includes
signal filters and amplifiers, memory and a microprocessor-based
controller, as would be appreciated by one skilled in the art. The
memory 109 includes a short-term, volatile memory store in which
raw physiological signals can be stored as telemetered signals for
later retrieval and analysis. The telemetry circuitry 110 provides
an interface between the IMD 103 external devices (not shown). The
telemetry circuitry 110 enables operating parameters to be
non-invasively programmed into the memory 109 through an external
device in telemetric communication with the IMD 103. The telemetry
circuitry 110 also allows patient information collected by the IMD
103 and transiently stored in the memory 109 to be sent to the
external device for processing and analysis.
[0032] The IMD 103 is in direct electrical communication with the
heart 102 through electrodes 111a-b positioned on the distal tips
of each lead 106a-b. By way of example, the set of leads 106a-b can
include a right ventricular electrode 111a and a right atrial
electrode 111b. The right ventricular electrode 111a is preferably
placed in the right ventricular apex 112 of the heart 102 and the
right atrial electrode 111b is preferably placed in the right
atrial chamber 113 of the heart 102. The electrodes 111a-b enable
the IMD 103 to directly collect raw physiological measures,
preferably through millivolt measurements. Other configurations and
arrangements of leads and electrodes, including the use of single
and multiple leads arrays and single and multiple electrodes, can
be used, as would be recognized by one skilled in the art.
[0033] In the described embodiment, the IMD 103 can be implemented
as part of cardiac pacemakers used for managing bradycardia,
implantable cardioverter defibrillators (IMDs) used for treating
tachycardia, and other types of implantable cardiovascular monitors
and therapeutic devices used for monitoring and treating heart
failure, structural problems of the heart, such as congestive heart
failure, rhythm problems, and other heart conditions, as would be
appreciated by one skilled in the art. Examples of cardiac
pacemakers suitable for use in the described embodiment include the
Pulsar Max II, Discovery, and Discovery II pacing systems, sold by
Guidant Corporation, St. Paul, Minn. An example of an IMD suitable
for use in the described embodiment includes the Contak Renewal
cardiac resynchronization therapy defibrillator, also sold by
Guidant Corporation, St. Paul, Minn.
[0034] On a regular basis, the telemetered signals stored in the
memory 109 are retrieved. By way of example, a programmer (not
shown) can be used to retrieve the telemetered signals. However,
any form of programmer, interrogator, recorder, monitor, or
telemetered signals transceiver suitable for communicating with IMD
103 could be used, as would be appreciated by one skilled in the
art. In addition, a server, personal computer or digital data
processor could be interfaced to the IMD 103, either directly or
via a telemetered signals transceiver configured to communicate
with the implantable medical device 103.
[0035] The programmer communicates with the IMD 103 via radio
frequency signals exchanged through a wand placed over the location
of the IMD 103. Programming or interrogating instructions are sent
to the IMD 103 and the stored telemetered signals are downloaded
into the programmer. Once downloaded, the telemetered signals can
be sent via a network, such as the Internet, to a server (not
shown), which periodically receives and stores the telemetered
signals in a database, as further described below with reference to
FIG. 6.
[0036] An example of a programmer suitable for use in the present
invention is the Model 2901 Programmer Recorder Monitor,
manufactured by Guidant Corporation, Indianapolis, Ind., which
includes the capability to store retrieved telemetered signals on a
proprietary removable floppy diskette. The telemetered signals
could later be electronically transferred using a personal computer
or similar processing device, as would be appreciated by one
skilled in the art.
[0037] Other alternate telemetered signals transfer means could
also be employed. For instance, the stored telemetered signals
could be retrieved from the IMD 103 and electronically transferred
to a network using a combination of a remote external programmer
and analyzer and a remote telephonic communicator, such as
described in U.S. Pat. No. 5,113,869, the disclosure of which is
incorporated by reference. Similarly, the stored telemetered
signals could be retrieved and remotely downloaded to a server
using a world-wide patient location and data telemetry system, such
as described in U.S. Pat. No. 5,752,976, the disclosure of which is
incorporated herein by reference.
Externally-Assisted Transcardiac Impedance Monitoring System
[0038] FIG. 2 is a schematic diagram 120 showing an external
medical device 122 assisting in monitoring transcardiac impedance,
in accordance with a further embodiment of the present invention.
The external medical device 122 facilitates transcardiac impedance
monitoring by ensuring consistent intrathoracic pressure,
particularly when thoracic pressure is elevated when induced, for
instance, by performance of the Valsalva maneuver. The external
medical device 122 includes a mouthpiece 123 functionally connected
to a pressure monitor 124 via a hose 125. The pressure monitor 124
defines a confined volume into which the patient 121 blows. A
pressure regulating device 126 releases expired air. The pressure
monitor 124 provides a pressure reading representative of the
pressure in the confined volume. The pressure monitor 124 can also
provide recording functions that record the pressure levels during
performance of a transcardiac maneuver by a patient 121.
[0039] In a further embodiment, a thoracic pressure electrode, such
as described in U.S. Pat. No. 6,132,384, the disclosure of which is
incorporated by reference, can be combined with the IMD 103 to
provide a fully implanted solution. The use of an implanted
thoracic pressure electrode enables measurements during normal
activities of daily living that produce elevated thoracic pressure
similar to an induced performance of the Valsalva maneuver. When an
elevated thoracic pressure is detected by the implanted thoracic
pressure electrode, intracardiac impedance is recorded by the IMD
103 on a continuous basis. After the cardiac response period ends,
the recorded intracardiac impedance data can either be downloaded
to an external device (not shown) for further analysis, as further
described below with reference to FIG. 11, or can be analyzed by
the IMD 103.
Arterial Blood Pressure Profiles
[0040] FIGS. 3A-C are graphical representations showing, by way of
example, averaged arterial blood pressure profiles 130, 150, 170
relative to performance of the Valsalva maneuver in a healthy
person, a patient suffering from heart disease but not significant
heart failure and a patient suffering from significant heart
failure, respectively. The x-axis 131, 151, 171 respectively
represent time. The y-axis 132, 152, 172 respectively indicate
arterial pressure (mmHg). Averaged changes in arterial pressure are
plotted over time throughout each of the four phases 133-136,
153-156, 173-176 of the Valsalva maneuver, respectively. For
clarity, the pulsatile arterial blood pressure changes are shown as
averaged values and each of the averaged arterial blood pressure
profiles 130, 150, 170 have respectively been normalized relative
to time.
[0041] The Valsalva maneuver involves deep inspiration followed by
forced exhalation against a closed glottis for ten to twelve
seconds. The four phases of the Valsalva maneuver exhibit a
characteristic signature for normal healthy people and for patients
suffering from heart disease, but not significant heart failure.
During Phase I, initial strain, systemic blood pressure undergoes a
transient rise as straining commences. During Phase II, strain
duration and cessation of breathing, systemic venous return, blood
pressure and pulse pressure decrease perceptibly. During Phase III,
strain discontinuation and resumption of normal breathing, blood
pressure and systemic venous return exhibit abrupt, transient
decreases. During Phase IV, recovery, systemic arterial pressure
overshoots with reflex bradycardia. However, for patients suffering
from heart failure, the response signature is a muted square wave
response with a slight elevation in blood pressure during phase III
and minimal perceptible changes during Phases I, II and IV.
[0042] Cardiac performance response profile is significantly
dependent on left ventricular function, specifically LVEF and mean
LVEDP. A healthy person with no history of cardiovascular diseases
may, for example, be expected to have an LVEF and mean LVEDP of
approximately 70% and 14 mmHg, respectively. A patient suffering
from heart disease but not significant heart failure may, for
example, typically be expected to have an LVEF and mean LVEDP of
approximately 50% and 20 mmHg, respectively. A patient suffering
from heart failure may, for example, typically be expected to have
an LVEF and mean LVEDP of approximately 30% and 40 mmHg,
respectively.
[0043] Healthy Person
[0044] Referring first to FIG. 3A, the graphical representation
shows, by way of example, an averaged arterial blood pressure
profile 130 relative to performance of the Valsalva maneuver in a
healthy person with no history of cardiovascular diseases. During
Phase I 133, intrathoracic pressure increases in response to the
strain associated with the maneuver, along with a sharp rise 137 in
arterial pressure approximately equal to the intrathoracic pressure
increase. During Phase II 134, pulse pressure narrows and arterial
pressure undergoes a transient decrease 138. During Phase III 135,
systolic pressure drops rapidly 139. Finally, during Phase IV 136,
diastolic and systolic pressures return to pre-maneuver levels 141
following a large overshoot 140 in arterial pressure.
[0045] Patient Suffering from Heart Disease but not Significant
Heart Failure
[0046] Referring next to FIG. 3B, the graphical representation
shows, by way of example, an averaged arterial blood pressure
profile 150 relative to performance of the Valsalva maneuver in a
patient suffering from heart disease but not significant heart
failure. During Phase I 153, systemic arterial pressure increases
only slightly 157. During Phase II 154, systemic arterial pressure
158 increases approximately equal to the increase in intrathoracic
pressure followed by a narrowing of pulse pressure and arterial
pressure decrease 159. During Phase III 155, systolic pressure
drops rapidly 160. Finally, during Phase IV 156, diastolic and
systolic pressures return to pre-maneuver levels 161 without
overshoot.
[0047] Patient Suffering from Heart Failure
[0048] Finally, referring first to FIG. 3C, the graphical
representation shows, by way of example, an averaged arterial blood
pressure profile 170 relative to performance of the Valsalva
maneuver in a patient suffering from heart failure. During Phase I
173, almost no appreciable increase in systemic arterial pressure
occurs 177. During Phase II 174, pulse pressure and systemic
systolic pressure remain at approximately the same elevated level
178 throughout the phase. During Phase III 175, systolic pressure
decreases to approximately the same level as in Phase I 173. During
Phase IV 176, diastolic and systolic pressures return to their
pre-maneuver levels 180 almost immediately upon cessation of
strain.
Cardiac Dimension Profiles
[0049] FIG. 4 is a graphical representations showing, by way of
example, cardiac dimension profiles 182a, 182b, during diastole and
systole, respectively, relative to performance of the Valsalva
maneuver in a healthy person, a patient suffering from heart
disease but not significant heart failure and a patient suffering
from significant heart failure. The x-axis represents time. The
y-axis indicates average dimensional change (%). Averaged changes
in dimension are plotted over time throughout each of the four
phases 183a-186a, 183b-186b of the Valsalva maneuver.
[0050] Healthy Person
[0051] During Phase I 183a, 183b, cardiac dimension decreases in
response to the strain associated with the maneuver for a healthy
person with no history of cardiovascular diseases. During Phase II
184a, 184b, cardiac dimension reduces rapidly. During Phase III
185a, 185b, cardiac dimension increases rapidly. Finally, during
Phase IV 186a, 186b, cardiac dimension pressures return to
pre-maneuver levels.
[0052] Patient Suffering from Heart Disease but not Significant
Heart Failure
[0053] The average cardiac dimensional change for a patient
suffering from heart disease but not significant heart failure
182ab, 182bb, is essentially the same as the changes observed for a
healthy person with no history of cardiovascular diseases.
[0054] Patient Suffering from Heart Failure
[0055] The average cardiac dimensional change for a patient
suffering from significant heart failure reflects only slight
changes during each of the four phases of a Valsalva maneuver.
Stroke Volume and Left Ventricular Pressure Profiles
[0056] FIG. 5 is a graphical representations showing, by way of
example, stroke volume index profile 188a and left ventricular
pressure profile 188b relative to performance of the Valsalva
maneuver in a healthy person. The x-axis represents time. The left
hand y-axis indicates stroke volume index (ml/M.sup.2) and the
right hand y-axis indicates LV pressure. Changes in stroke volume
index and left ventricular pressure are plotted over time
throughout each of the four phases 187a, 187b, 187c and 187d of a
Valsalva maneuver. During Phase I 187a, the stroke volume index
decreases slightly and left ventricular systolic and diastolic
pressures increase slightly. During Phase II 187b, the stroke
volume index and left ventricular and diastolic systolic pressures
decrease significantly. During Phase III 187c, the stroke volume
index begins an increase towards pre-maneuver levels, but the left
ventricular diastolic and systolic pressures remain stable.
Finally, during Phase IV 187d, the stroke volume index and left
ventricular diastolic and systolic pressures return to pre-maneuver
levels.
[0057] LVEF and LVEDP Correlations
[0058] Heart disease patient management requires carefully
monitoring and evaluation of LVEF and LVEDP. In heart failure
patients, an increase in LVEDP can lead to an acute exasperation of
heart failure and acute decompensation. Changes to LVEDP associated
with the acute exasperation of heart failure can occur in a few
days, whereas changes to LVEF occur more slowly and are associated
with long-term changes. Thus, effectively assessing cardiac
performance, particularly for heart disease and heart failure
patients, requires evaluating LVEF and LVEDP or equivalent values
that approximate LVEF and LVEDP changes, such as intracardiac
impedance.
[0059] Comparing the averaged cardiac dimension profiles 182a, 182b
described above with reference to FIG. 4, healthy people and
patients suffering from heart disease undergo significant
dimensional changes during performance of the Valsalva maneuver,
while the cardiac dimensions in patients with significant heart
failure changes only slightly. Intracardiac impedance has been
empirically correlated to changes in left ventricular pressure,
such as described in Wortel et al., Impedance Measurements in the
Human Right Ventricular Using a New Pacing System, Pacing Clinical
Electrophysiology, Vol. 14(9), pp. 1336-42 (September 1991), the
disclosure of which is incorporated by reference, and can therefore
be used as a surrogate measure of cardiac dimensional changes.
[0060] In a further embodiment, the Muller maneuver is performed
either in lieu of or in addition to the Valsalva maneuver. The
Muller maneuver involves deep inspiration while the nose is held
closed and mouth firmly sealed for ten seconds. The Muller maneuver
exaggerates inspiration effort and augments murmurs and right side
cardiac filling sounds.
System Modules
[0061] FIG. 6 is a functional block diagram showing a system 190
for assessing cardiac performance through transcardiac impedance
monitoring, in accordance with a further embodiment of the present
invention. Each component is a computer program, procedure or
process written as source code in a conventional programming
language, such as the C++ programming language, and is presented
for execution by one or more CPUs as object or byte code in a
uniprocessing, distributed or parallelized configuration, as would
be appreciated by one skilled in the art. The various
implementations of the source code and object and byte codes can be
held on a computer-readable storage medium or embodied on a
transmission medium in a carrier wave.
[0062] The system 190 consists of a server 191 coupled to a
database 197, which provides persistent secondary storage. The
server 191 consists of three modules: telemetry 192, database 193,
and analysis 194. The telemetry module 192 communicatively
interfaces to the IMD 103 through a logically-formed, non-invasive
communication channel, such as provided though induction, static
magnetic field coupling, or by related means, as would be
appreciated by one skilled in the art. The telemetry module 192
facilitates the transferal and exchange of physiological measures
195 and programming parameters 196 between the IMD 103 and the
server 191. The physiological measures 195 include raw
physiological data regularly collected by the IMD 103 and stored in
the memory 109. The programming parameters 196 include monitoring
and therapy delivery device configuration settings, which are
exchanged between the IMD 103 and the server 191. The telemetry
module 192 communicates with the telemetry circuitry 110 on the IMD
103 using standard programmer communication protocols, as would be
appreciated by one skilled in the art.
[0063] For an exemplary cardiac implantable medical device, the
physiological measures 195 and programming parameters 196
non-exclusively present patient information recorded on a per
heartbeat, binned average or derived basis and relating to atrial
electrical activity, ventricular electrical activity, minute
ventilation, patient activity score, cardiac output score, mixed
venous oxygenation score, cardiovascular pressure measures, time of
day, the number and types of interventions made, and the relative
success of any interventions, plus the status of the batteries and
programmed settings.
[0064] The database module 193 maintains information stored in the
database 197 as structured records for facilitating efficient
storage and retrieval. The database module 193 stores the
physiological measures 195 and programming parameters 196 exchanged
with the IMD 103 in the database 197. The database 197 stores the
physiological measures 195 as derived measures, which include,
non-exclusively, impedance measures 198, cardiac dimensional
measures 199, LVEF measures 200, and LVEDP measures 201. Other raw
and derived measures can be stored in the database 197, as would be
recognized by one skilled in the art. The programming parameters
196 are maintained in the database as programming values 202. In
addition, patient profile information 203 is maintained in the
database 197.
[0065] The analysis module 194 derives and evaluates the
physiological data maintained in the database 197. As necessary,
the physiological measures 195 retrieved from the IMD 103 are
converted and derived into the impedance measures 198, cardiac
dimensional measures 199, LVEF measures 200, and LVEDP 201, as
would be appreciated by one skilled in the art. In particular, the
impedance measures 198 are analyzed and evaluated to determine an
overall arterial blood pressure profile, which is compared to
predefined thresholds 204 for assessing cardiac performance
relative to the performance of an intrathoracic pressure maneuver,
as further described below with reference to FIG. 11. The analysis
module 194 generates a cardiac performance assessment 205, which
identifies trends indicating cardiovascular disease and, in
particular, heart failure, absence, onset, progression, regression,
and status quo. The cardiac performance assessment 205 can be
further evaluated to determine whether medical intervention is
necessary.
[0066] In a further embodiment, the functions of the server 191 are
performed by the IMD 103, which directly generates the cardiac
performance assessment 205, for retrieval by an external
device.
Arterial Blood Pressure Profile Trend Analysis
[0067] FIG. 7 is a graphical representation showing, by way of
example, trend analysis 210 of arterial blood pressure profile 213.
The x-axis 211 represents time. The y-axis 212 indicates arterial
pressure in mmHg. Averaged changes in arterial pressure are plotted
over time throughout each of the four phases 214-217 of the
Valsalva maneuver.
[0068] The arterial blood pressure profile 213 models the
characteristic signature exhibited during each phase of the
Valsalva maneuver. During Phase I 214, the arterial pressure is
evaluated for an increasing trend 218. During Phase II 215, the
arterial pressure is evaluated for a transient decreasing trend
219. During Phase III 216, the arterial pressure is evaluated for a
significantly decreasing trend 220. Finally, during Phase VI 217,
the arterial pressure is evaluated for a steeply increasing trend
221, followed by an overshooting trend 222, followed by a
decreasing trend 223 with resumption of normal arterial pressure.
In addition to the arterial pressure trends 218-223, pulsatile
volume and heart rate can also be evaluated for trends, as would be
recognized by one skilled in the art.
Cardiac Stroke Volume Profile Trend Analysis
[0069] FIG. 8 is a graphical representation showing, by way of
example, trend analysis 213 of cardiac stroke volume profile. The
x-axis represents time. The y-axis indicates stroke volume index in
ml/M.sup.2. Averaged changes in stroke volume index are plotted
over time throughout each of four phases 214, 215, 216, 217 of a
Valsalva maneuver.
Transcardiac Impedance Monitoring Method
[0070] FIG. 9 is a flow chart showing a method 225 for assessing
cardiac performance through transcardiac impedance monitoring, in
accordance with a further embodiment of the present invention. The
method 225 is described as a sequence of process operations or
steps, which can be executed, for instance, by a server 191 (shown
in FIG. 6). In a further embodiment, the method 225 can be executed
directly by the IMD 103 or related means, which generates a cardiac
performance assessment 205 for retrieval by an external device.
[0071] The method 225 preferably executes as a continuous
processing loop 226-229. During each iteration (block 226), the
physiological measures 195 are retrieved from the IMD 103 and
stored in the database 197, as further described below with
reference to FIG. 10. Cardiac performance is then assessed (block
228), as further described below with reference to FIG. 11.
Processing continues (block 229), until the method exits or
terminates.
Collecting Physiological Measures
[0072] FIG. 10 is a flow chart showing a routine 230 for collecting
physiological measures for use in the method 225 of FIG. 9. The
purpose of this routine is to regularly interface to the IMD 103,
retrieve the physiological measures 195 and programming parameters
196, and store the retrieved physiological measures 195 and
programming parameters 196 in the database 197.
[0073] The routine begins initially by interfacing to the IMD 103
(block 231), using, for instance, inductive or static magnetic
means, as would be appreciated by one skilled in the art. Raw
physiological measures 195 are retrieved from the IMD 103 (block
232). The raw physiological measures 195 are converted and derived
into impedance measures 198, cardiac dimensional measures 199, LVEF
measures 200, and LVEDP measures 201 (block 233). The physiological
measures are stored in the database 197 (block 234). If further
physiological measures 195 or programming parameters 196 require
exchange with the IMD 103 (block 235), processing continues.
Otherwise, the interface to the IMD 103 is closed (block 236), the
routine returns.
Assessing Cardiac Performance
[0074] FIG. 11 is a flow chart showing a routine 240 for assessing
cardiac performance for use in the method 225 of FIG. 9. The
purpose of this routine is to periodically assess cardiac
performance through an analysis of the cardiac stroke volume
profile trends 224 (shown in FIG. 8).
[0075] As an initial step, physiological measures, including
impedance measures 198, cardiac dimensional measures 199, LVEF
measures 200, and LVEDP measures 201, are retrieved from the
database 197 (shown in FIG. 6) (block 241). The start of the
intrathoracic pressure maneuver under consideration is determined
(block 242). In the described embodiment, the start of the
intrathoracic pressure maneuver is determined by retrieving an
explicit marker recorded by the patient 100 or by indirect means
based upon an analysis of the retrieved physiological measures, as
would be appreciated by one skilled in the art.
[0076] Next, the cardiac stroke volume profile 224 is evaluated to
form a cardiac performance assessment 205 (block 243), further
described below with reference to FIG. 12. If the cardiac
performance assessment 205 exceeds the predefined threshold 204
(block 244), a notification is generated (block 245). In the
described embodiment, the notification takes the form of generating
an alert for review and possible action by healthcare providers and
can include generating appropriate feedback to the patient 100,
such as described in commonly-assigned U.S. Pat. No. 6,203,495, the
disclosure of which is incorporated by reference.
[0077] If the cardiac performance assessment 205 does not exceed
the threshold 204 (block 244), no notification is generated. If
further retrieved physiological measures require evaluation (block
246), processing continues. Otherwise, the routine returns.
Evaluating Arterial Blood Pressure Profile Relative to Valsalva
Maneuver
[0078] FIG. 12 is a flow chart showing a routine 250 for evaluating
cardiac stroke volume profile 224 relative to, by way of example,
the Valsalva maneuver, for use in the routine 240 of FIG. 11. The
purpose of this routine is to generate a cardiac performance
assessment 205 by forming a trend analysis of the retrieved
physiological measures based on the phases of the Valsalva
maneuver.
[0079] The trend analysis proceeds in four groups of steps (blocks
251-253, 254-256, 257-259, 260-268, respectively), which track each
of the four phases of the Valsalva maneuver. During the first
group, if the cardiac stroke volume profile 224 is in Phase I
(block 251) and an increase in arterial pressure is apparent (block
252), the increase is marked (block 253). During the second group,
if the cardiac stroke volume profile 224 is in Phase II (block 254)
and a transient decrease in arterial pressure is apparent (block
255), the transient decrease is marked (block 256). During the
third group, if the cardiac stroke volume profile 224 is in Phase
III (block 256) and a significant decrease in arterial pressure is
apparent (block 258), the significant decrease is marked (block
259). Finally, during the fourth group, if the cardiac stroke
volume profile 224 is in Phase VI (block 260), four conditions are
evaluated. If an increase in arterial pressure is apparent (block
261), the increase is marked (block 262). If the increase in
arterial pressure is followed by an overshoot (block 263), the
overshoot is marked (block 264). For the Valsalva maneuver, the
overshoot is the strongest trend indication in the characteristic
signature and indicates a healthy, non-heart failure person. If the
overshoot is followed by a decrease in arterial pressure (block
265), the decrease is marked (block 266). Finally, if a resumption
of normal arterial pressure is apparent (block 267), the resumption
is marked (block 268).
[0080] Following the evaluation of each of the groups, the
impedance measures are correlated to cardiac stroke volume to
reflect cardiac dimensional changes, as described above with
reference to FIG. 3. Next, the overall cardiac stroke volume
profile 224 is determined (block 270) to generate a cardiac
performance assessment 205. The cardiac performance assessment 205
quantifies the variants between the physiological measures
determined during each of the phases against the cardiac stroke
volume profile trends 224e-224h. Following determination of the
cardiac performance assessment 205, the routine returns.
[0081] In the described embodiment, the cardiac impedance data can
be analyzed in several ways. In one embodiment, a statistical
analysis can be performed on impedance data to determine the mean
impedance level and standard deviation over the entire response
period. The mean Z and the standard deviation S.sub.z of the
impedance data over the response period can be used as a cardiac
performance assessment 205, where:
Z _ = Zi n ##EQU00001## S z = 1 N i = 1 N ( Zi - Z _ )
##EQU00001.2##
[0082] In a further embodiment, a statistical analysis can be
performed on different phases of the response period based on the
collected impedance data to determine the cardiac performance
assessment 205. For example, the mean and standard deviation
analysis, described above, can be performed on physiological data
from Phase IV of the response period relative to the performance of
the Valsalva maneuver. The analyzed values reflect the amplitude of
impedance change during the Valsalva maneuver as the cardiac
performance assessment 205.
[0083] In a further embodiment, the impedance data can be analyzed
for trends by calculating a linear regression over the collected
data for Phase IV of the response period, such as described in
Seborg et al., "Process Dynamics and Control," pp. 165-167 (John
Wiley & Sons, 1989), the disclosure of which is incorporated by
reference. By performing a linear regression, the response pattern
during Phase IV can be fitted into a second-order system response,
which is characterized by a transfer function, such as:
G ( s ) = K ( .tau. 1 s + 1 ) ( .tau. 2 s + 1 ) ##EQU00002##
where .tau..sub.1 and .tau..sub.2 are derived empirically by linear
regression. Alternatively, a second order process transfer function
can arise upon transforming a second-order differential equation
process model that has the general form of:
G ( s ) = K .tau. 2 s 2 + 2 .zeta..tau. s + 1 ##EQU00003##
where .zeta. is the dimensionless damping factor. By equating the
two transfer functions, the value of the damping factor can be
derived as:
.zeta. = .tau. 1 + .tau. 2 2 .tau. 1 .tau. 2 ##EQU00004##
The resulting response pattern is characterized by the derived
value of the damping factor .zeta. according to the following
table:
[0084] .zeta.>1 Over damped
[0085] .zeta.=1 Critically damped
[0086] 0<.zeta.<1 Under damped
[0087] Phase IV of the Valsalva maneuver exhibits the most
noticeable difference in cardiac response for the three groups of
individuals described above with reference to FIGS. 3A-C and 4,
that is, a healthy person, a patient suffering from heart disease
and a patient suffering from heart failure. During Phase IV, the
response pattern from the healthy person group closely resembles an
under-damped second-order response, which is characterized by a
damping factor between zero and one. The response pattern from the
heart disease patient group closely resembles a critically-damped
or under-damped second-order response, which is characterized by a
damping factor that is equal to or greater than one but not
substantially higher than one. The response pattern from the heart
failure patient group shows no appreciable change, which resembles
a severely-over damped system characterized by a large damping
factor. The damping factor serves as a cardiac performance
assessment 205. Other types of statistical analyses can also be
performed, as would be recognized by one skilled in the art.
[0088] While the invention has been particularly shown and
described as referenced to the embodiments thereof, those skilled
in the art will understand that the foregoing and other changes in
form and detail may be made therein without departing from the
spirit and scope of the invention.
* * * * *