Source: http://www.google.ca/patents/US20030191503
Timestamp: 2017-11-22 05:43:30
Document Index: 620703430

Matched Legal Cases: ['art.\n6', 'art.\n19', 'art.\n20', 'art.\n26', 'art.\n29', 'art.\n39', 'art.\n40', 'art.\n52', 'art.\n53', 'art.\n56', 'art.\n75', 'art.\n76', 'art.\n111', 'art.\n112', 'art\n114', 'art 106', 'art 106']

Patent US20030191503 - Cardiac rhythm management system for edema - Google Patents
A cardiac rhythm management system detects edema. In response to an episode of detected edema, it initiates or adjusts a cardiac resynchronization therapy and/or a cardiac contractility modulation (CCM) therapy....http://www.google.ca/patents/US20030191503?utm_source=gb-gplus-sharePatent US20030191503 - Cardiac rhythm management system for edema
Publication number US20030191503 A1
Also published as US7177681, US7191000, US9265950, US20030028221, US20080215108
Publication number 10411795, 411795, US 2003/0191503 A1, US 2003/191503 A1, US 20030191503 A1, US 20030191503A1, US 2003191503 A1, US 2003191503A1, US-A1-20030191503, US-A1-2003191503, US2003/0191503A1, US2003/191503A1, US20030191503 A1, US20030191503A1, US2003191503 A1, US2003191503A1
Patent Citations (99), Referenced by (75), Classifications (8), Legal Events (3)
US 20030191503 A1
comparing the baseline thoracic impedance at the first time with the baseline thoracic impedance at the second time; and
if the baseline thoracic impedance at the first time is less than the baseline thoracic impedance at the second time by a magnitude that exceeds a predetermined threshold value, then declaring a first condition to exist.
2. The method of claim 1, further comprising initiating or adjusting a cardiac rhythm management therapy in response to the first condition.
3. The method of claim 2, in which the initiating or adjusting comprises initiating or adjusting a cardiac resynchronization therapy that coordinates a spatial nature of a depolarization associated with a heart contraction in at least one heart chamber.
4. The method of claim 2, in which the initiating or adjusting comprises initiating or adjusting a cardiac contractility modulation therapy that comprises delivering electrical energy to a portion of a heart during a refractory time period of the portion of the heart.
6. The method of claim 5, further comprising initiating or adjusting a cardiac rhythm management therapy in response to the second condition.
7. The method of claim 6, in which the initiating or adjusting comprises initiating or adjusting a cardiac resynchronization therapy that coordinates a spatial nature of a depolarization associated with a heart contraction in at least one heart chamber.
8. The method of claim 6, in which the initiating or adjusting comprises initiating or adjusting a cardiac contractility modulation therapy that comprises delivering electrical energy to a portion of a heart during a refractory time period of the portion of the heart.
a comparator, comprising a first input coupled to the output of the delay circuit, and comprising a second input coupled to the output of the averager/lowpass filter, and comprising an output providing an edema indicator using a comparison of signals at the first and second inputs of the comparator; an electrical energy delivery circuit to deliver electrical energy to the subject; and
10. The system of claim 9, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject's thorax.
11. The system of claim 9, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.
12. The system of claim 11, in which the cutoff frequency is approximately equal to 0.1 Hz.
13. The system of claim 9, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject's breathing.
14. The system of claim 13, in which the edema detection circuit is configured to provide the edema indicator as determined from both a breathing rate of a subject and a thoracic impedance indication of fluid buildup in the subject's thorax.
15. The system of claim 9, in which the controller comprises a stored interelectrode delay, and in which the controller, in response to the detected edema indicator, is adapted to adjust a value of the interelectrode delay.
16. The system of claim 15, in which the interelectrode delay comprises at least one of an atrioventricular delay, an interventricular delay, and an intraventricular delay.
17. The system of claim 9, in which the controller, in response to the detected edema indicator, is configured to select at least one particular electrode, from a plurality of electrodes differently located in association with a heart of the subject, for subsequent delivery of a contraction-evoking stimulation.
18. The system of claim 17, in which the controller, in response to the detected edema indicator, is configured to select the particular electrode from a plurality of same-chamber electrodes differently located in association with a single chamber of the subject's heart.
19. The system of claim 17, in which the controller, in response to the detected edema indicator, is configured to select the particular electrode from a plurality of electrodes, at least two of which are located in association with different chambers of the subject's heart.
20. The system of claim 9, in which the controller, in response to the detected edema indicator, is configured to initiate or adjust a bi-ventricular pacing therapy to be delivered by the electrical energy circuit.
22. The method of claim 21, further comprising initiating or adjusting a cardiac rhythm management therapy in response to the thoracic fluid accumulation condition.
23. The method of claim 22, in which the initiating or adjusting comprises initiating or adjusting a cardiac resynchronization therapy that coordinates a spatial nature of a depolarization associated with a heart contraction in at least one heart chamber.
24. The method of claim 22, in which the initiating or adjusting comprises initiating or adjusting a cardiac contractility modulation therapy that comprises delivering electrical energy to a portion of a heart during a refractory time period of the portion of the heart.
26. The method of claim 25, further comprising initiating or adjusting a cardiac rhythm management therapy in response to the second condition.
27. The method of claim 26, in which the initiating or adjusting comprises initiating or adjusting a cardiac resynchronization therapy that coordinates a spatial nature of a depolarization associated with a heart contraction in at least one heart chamber.
28. The method of claim 26, in which the initiating or adjusting comprises initiating or adjusting a cardiac contractility modulation therapy that comprises delivering electrical energy to a portion of a heart during a refractory time period of the portion of the heart.
29. A cardiac rhythm management system comprising:
a comparator, comprising a first input coupled to the output of the averager/lowpass filter circuit, and comprising a second input coupled to the input of the averager/lowpass filter, and comprising an output providing an edema
indicator using a comparison of signals at the first and second inputs of the comparator;
30. The system of claim 29, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject's thorax.
31. The system of claim 29, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.
32. The system of claim 31, in which the cutoff frequency is approximately equal to 0.1 Hz.
33. The system of claim 29, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject's breathing.
34. The system of claim 33, in which the edema detection circuit is configured to provide the edema indicator as determined from both a breathing rate of a subject and a thoracic impedance indication of fluid buildup in the subject's thorax.
35. The system of claim 29, in which the controller comprises a stored interelectrode delay, and in which the controller, in response to the detected edema indicator, is adapted to adjust a value of the interelectrode delay.
36. The system of claim 35, in which the interelectrode delay comprises at least one of an atrioventricular delay, an interventricular delay, and an intraventricular delay.
37. The system of claim 29, in which the controller, in response to the detected edema indicator, is configured to select at least one particular electrode, from a plurality of electrodes differently located in association with a heart of the subject, for subsequent delivery of a contraction-evoking stimulation.
38. The system of claim 37, in which the controller, in response to the detected edema indicator, is configured to select the particular electrode from a plurality of same-chamber electrodes differently located in association with a single chamber of the subject's heart.
39. The system of claim 37, in which the controller, in response to the detected edema indicator, is configured to select the particular electrode from a plurality of electrodes, at least two of which are located in association with different chambers of the subject's heart.
40. The system of claim 29, in which the controller, in response to the detected edema indicator, is configured to initiate or adjust a bi-ventricular pacing therapy to be delivered by the electrical energy circuit.
initiating or adjusting, in response to the sensing, a cardiac resynchronization therapy that coordinates a spatial nature of a depolarization associated with a heart contraction in at least one heart chamber.
42. The method of claim 41, in which the sensing comprises detecting a change in a baseline thoracic impedance associated with fluid buildup in a portion of a thorax of the subject.
43. The method of claim 42, in which the sensing comprises detecting a decrease in the baseline thoracic impedance associated with fluid buildup in the portion of the thorax of the subject.
44. The method of claim 43, in which the baseline portion of the thoracic impedance is less than or equal to a cutoff frequency value that is between 0.01 Hz and 0.5 Hz inclusive.
45. The method of claim 44, in which the cutoff frequency value is approximately 0.1 Hz.
46. The method of claim 42, in which the sensing also comprises detecting an increase in a rate of breathing of the subject.
47. The method of claim 46, in which the detecting the increase in the breathing rate comprises sensing the breathing of the subject from a portion of the thoracic impedance that is approximately between 0.05 Hz and 2.0 Hz inclusive.
48. The method of claim 41, in which the initiating or adjusting the cardiac resynchronization therapy comprises selecting an interelectrode delay value, for subsequent delivery of contraction-evoking stimulations occurring during a single cardiac cycle.
49. The method of claim 41, in which the initiating or adjusting the cardiac resynchronization therapy comprises selecting at least one particular electrode, from a plurality of electrodes differently located in association with a heart of the subject, for subsequent delivery of a contraction-evoking stimulation.
50. The method of claim 49, in which selecting the interelectrode delay value comprises selecting at least one of an atrioventricular delay value, an interventricular delay value, and an intraventricular delay value.
51. The method of claim 49, in which the selecting the particular electrode comprises selecting the particular electrode from a plurality of same-chamber electrodes differently located in association with a single chamber of the subject's heart.
52. The method of claim 49, in which the selecting the particular electrode comprises selecting the particular electrode from a plurality of electrodes, at least two of which are located in association with different chambers of the subject's heart.
53. The method of claim 41, in which the initiating or adjusting the cardiac resynchronization therapy comprises initiating or adjusting biventricular pacing.
54. The method of claim 53, in which the initiating or adjusting the cardiac resynchronization therapy comprises initiating biventricular pacing.
initiating or adjusting, in response to the sensing, a cardiac contractility modulation therapy that comprises delivering electrical energy to a portion of a heart during a refractory time period of the portion of the heart.
56. The method of claim 55, in which the sensing comprises detecting a change in a baseline thoracic impedance associated with fluid buildup in a portion of a thorax of the subject.
57. The method of claim 56, in which the sensing comprises detecting a decrease in the baseline thoracic impedance associated with fluid buildup in the portion of the thorax of the subject.
58. The method of claim 57, in which the baseline portion of the thoracic impedance is less than or equal to a cutoff frequency value that is between 0.01 Hz and 0.5 Hz inclusive.
59. The method of claim 58, in which the cutoff frequency value is approximately 0.1 Hz.
60. The method of claim 56, in which the sensing also comprises detecting an increase in a rate of breathing of the subject.
61. The method of claim 60, in which the detecting the increase in the breathing rate comprises sensing the breathing of the subject from a portion of the thoracic impedance that is approximately between 0.05 Hz and 2.0 Hz inclusive.
62. The method of claim 55, in which the initiating/adjusting the cardiac contractility modulation therapy comprises providing a non-contraction-evoking stimulus to a location of a heart of the subject during a refractory period of the heart location.
63. The method of claim 62, in which the refractory period follows a paced or sensed contraction of the heart location.
65. The method of claim 64, in which the sensing comprises detecting a change in a baseline thoracic impedance associated with fluid buildup in a portion of a thorax of the subject.
66. The method of claim 65, in which the sensing comprises detecting a decrease in the baseline thoracic impedance associated with fluid buildup in the portion of the thorax of the subject.
67. The method of claim 66, in which the baseline portion of the thoracic impedance is less than or equal to a cutoff frequency value that is between 0.01 Hz and 0.5 Hz inclusive.
68. The method of claim 67, in which the cutoff frequency value is approximately 0.1 Hz.
69. The method of claim 65, in which the sensing also comprises detecting an increase in a rate of breathing of the subject.
70. The method of claim 69, in which the detecting the increase in the breathing rate comprises sensing the breathing of the subject from a portion of the thoracic impedance that is approximately between 0.05 Hz and 2.0 Hz inclusive.
71. The method of claim 64, in which the initiating/adjusting the cardiac resynchronization therapy comprises selecting an interelectrode delay value, for subsequent delivery of contraction-evoking stimulations occurring during a single cardiac cycle.
72. The method of claim 64, in which the initiating/adjusting the cardiac resynchronization therapy comprises selecting at least one particular electrode, from a plurality of electrodes differently located in association with a heart of the subject, for subsequent delivery of a contraction-evoking stimulation.
73. The method of claim 72, in which selecting the interelectrode delay value comprises selecting at least one of an atrioventricular delay value, an interventricular delay value, and an intraventricular delay value.
74. The method of claim 72, in which the selecting the particular electrode comprises selecting the particular electrode from a plurality of same-chamber electrodes differently located in association with a single chamber of the subject's heart.
75. The method of claim 72, in which the selecting the particular electrode comprises selecting the particular electrode from a plurality of electrodes, at least two of which are located in association with different chambers of the subject's heart.
76. The method of claim 64, in which the initiating/adjusting the cardiac contractility modulation therapy comprises providing a non-contraction-evoking stimulus to a location of a heart of the subject during a refractory period of the heart location.
77. The method of claim 76, in which the refractory period follows a paced or sensed contraction of the heart location.
78. The method of claim 64, in which the selecting comprises adjusting an AV delay before initiating a biventricular pacing.
79. The method of claim 64, in which the selecting comprises adjusting an AV delay before adjusting an interventricular delay.
80. The method of claim 64, in which the selecting comprises adjusting an AV delay before selecting at least one particular electrode from among multiple same-chamber electrodes.
81. The method of claim 64, in which the selecting comprises adjusting an AV delay before adjusting one or more interelectrode delays.
82. The method of claim 64, in which the selecting comprises adjusting an AV delay before initiating a cardiac contractility modulation therapy.
83. The method of claim 64, in which the selecting comprises adjusting an AV delay before adjusting one or more cardiac contractility modulation therapy parameters.
84. The method of claim 64, in which the selecting comprises initiating biventricular pacing before adjusting an interventricular delay.
85. The method of claim 64, in which the selecting comprises initiating biventricular pacing before selecting at least one particular electrode from among multiple same-chamber electrodes.
86. The method of claim 64, in which the selecting comprises initiating biventricular pacing before adjusting one or more interelectrode delays.
87. The method of claim 64, in which the selecting comprises initiating biventricular pacing before initiating cardiac contractility modulation therapy.
88. The method of claim 64, in which the selecting comprises initiating biventricular pacing before adjusting one or more cardiac contractility modulation parameters.
89. The method of claim 64, in which the selecting comprises adjusting an interventricular delay before selecting at least one particular electrode from among multiple same-chamber electrodes.
90. The method of claim 64, in which the selecting comprises adjusting an interventricular delay before adjusting one or more interelectrode delays.
91. The method of claim 64, in which the selecting comprises adjusting an interventricular delay before initiating a cardiac contractility modulation therapy.
92. The method of claim 64, in which the selecting comprises adjusting an interventricular delay before adjusting one or more cardiac contractility modulation parameters.
93. The method of claim 64, in which the selecting comprises selecting at least one particular electrode from among multiple same-chamber electrodes before adjusting one or more interelectrode delays.
94. The method of claim 64, in which the selecting comprises selecting at least one particular electrode from among multiple same-chamber electrodes before initiating cardiac contractility modulation therapy.
95. The method of claim 64, in which the selecting comprises selecting at least one particular electrode from among multiple same-chamber electrodes before adjusting one or more cardiac contractility modulation parameters.
96. The method of claim 64, in which the selecting comprises adjusting one or more interelectrode delays before initiating a cardiac contractility modulation therapy.
97. The method of claim 64, in which the selecting comprises adjusting one or more interelectrode delays before adjusting one or more cardiac contractility modulation parameters.
98. The method of claim 64, in which the selecting comprises using a prioritization between cardiac rhythm management therapies in which adjusting an AV delay is prioritized higher than initiating biventricular pacing, which is prioritized higher than adjusting an interventricular delay, which is prioritized higher than selecting at least one particular electrode from among multiple same-chamber electrodes, which is prioritized higher than adjusting one or more interelectrode delays, which is prioritized higher than initiating a cardiac contractility modulation therapy, which is prioritized higher than adjusting one or more cardiac contractility modulation parameters.
99. A cardiac rhythm management system comprising:
a controller circuit, coupled to the edema detection circuit to receive a detected edema indicator, and coupled to the energy delivery circuit to provide a control signal for timing delivery of the electrical energy to the subject, the controller comprising a cardiac resynchronization therapy parameter, and in which the controller is configured to initiate or adjust, in response to the detected edema indicator, a cardiac resynchronization therapy that coordinates a spatial nature of a depolarization associated with a heart contraction in at least one heart chamber.
100. The system of claim 99, in which the edema detection circuit comprises a thoracic impedance detection circuit.
101. The system of claim 100, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject's thorax.
102. The system of claim 101, in which the thoracic impedance detection circuit further comprises an averager/lowpass filter to obtain a baseline portion of the thoracic impedance signal associated with the condition correlative to edema.
103. The system of claim 102, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.
104. The system of claim 103, in which the cutoff frequency is approximately equal to 0.1 Hz.
105. The system of claim 101, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject's breathing.
106. The system of claim 99, in which the edema detection circuit provides the condition correlative to edema as determined from both a breathing rate of a subject and a thoracic impedance indication of fluid buildup in the subject's thorax.
107. The system of claim 99, in which the controller comprises a stored interelectrode delay, and in which the controller, in response to the detected edema indicator, adjusts a value of the interelectrode delay.
108. The system of claim 107, in which the interelectrode delay comprises at least one of an atrioventricular delay, an interventricular delay, and an intraventricular delay.
109. The system of claim 99, in which the controller, in response to the detected edema indicator, selects at least one particular electrode, from a plurality of electrodes differently located in association with a heart of the subject, for subsequent delivery of a contraction-evoking stimulation.
110. The system of claim 109, in which the controller, in response to the detected edema indicator, selects the particular electrode from a plurality of same-chamber electrodes differently located in association with a single chamber of the subject's heart.
111. The system of claim 109, in which the controller, in response to the detected edema indicator, selects the particular electrode from a plurality of electrodes, at least two of which are located in association with different chambers of the subject's heart.
112. The system of claim 99, in which the controller, in response to the detected edema indicator, is configured to initiate or adjust a bi-ventricular pacing therapy to be delivered by the electrical energy circuit.
113. A cardiac rhythm management system comprising:
a controller circuit, coupled to the edema detection circuit to receive a detected edema indicator, and coupled to the energy delivery circuit to provide a control signal for timing delivery of the electrical energy to the subject, the controller comprising a cardiac contractility therapy mode, and in which the controller is configured to initiate or adjust, in response to the detected edema indicator, a cardiac contractility modulation therapy that comprises delivering electrical energy to a portion of a heart during a refractory time period of the portion of the heart
114. The system of claim 113, in which the edema detection circuit comprises a thoracic impedance detection circuit.
115. The system of claim 114, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject's thorax.
116. The system of claim 115, in which the thoracic impedance detection circuit further comprises an averager/lowpass filter to obtain a baseline portion of the thoracic impedance signal associated with the condition correlative to edema.
117. The system of claim 116, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.
118. The system of claim 117, in which the cutoff frequency is approximately equal to 0.1 Hz.
119. The system of claim 115, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject's breathing.
120. The system of claim 113, in which the edema detection circuit provides the condition correlative to edema as determined from both a breathing rate of a subject and a thoracic impedance indication of fluid buildup in the subject's thorax.
[0008]FIG. 1 is a block diagram example of portions of a cardiac rhythm management system and portions of an environment in which it is used.
[0009]FIG. 2 is a block diagram example of one possible edema detection circuit.
[0010]FIG. 3 is a block diagram example of portions of a possible signal processor.
[0011]FIG. 4 is a block diagram example of one possible edema detection module.
[0012]FIG. 5 is a block diagram example of an alternative edema detection module.
[0013]FIG. 6 is a block diagram example of an alternative signal processing circuit that determines whether edema is present based not only on the baseline thoracic impedance signal, but also on an additional breathing rate criterion.
[0014]FIG. 7 is a block diagram example in which a cardiac rhythm management device is associated with a heart at both an atrium (right or left) and a ventricle (right or left).
[0015]FIG. 8 is a block diagram example in which various responses to a detected edema episode are prioritized.
[0017]FIG. 1 is a block diagram example of portions of one possible cardiac rhythm management system 100 and portions of an environment in which it is used. In this example, system 100 includes, among other things, a cardiac rhythm management device 102 and leadwire (“lead”) 104. Leadwire 104 is coupled to device 102 for communicating one or more signals between device 102 and a portion of a living organism or other subject, such as heart 106. Some examples of device 102 include, among other things, bradycardia and antitachycardia pacemakers, cardioverters, defibrillators, combination pacemaker/defibrillators, cardiac resynchronization therapy devices, and drug delivery devices. Other examples of device 102 include any other implantable or external cardiac rhythm management apparatus capable of providing cardiac rhythm management therapy to heart 106. Such cardiac rhythm management therapy is not limited to managing cardiac rate. For example, cardiac rhythm management therapy also includes cardiac resynchronization therapy. Cardiac resynchronization therapy typically coordinates the spatial nature of a depolarization associated with a heart contraction in one or more heart chambers. While such cardiac resynchronization therapy may modify cardiac rate, it can also occur without any modification of the rate at which heart contractions occur. Some examples of cardiac resynchronization therapy include simultaneous or offset multichamber (e.g., biventricular) pacing and/or simultaneous or offset delivery of pacing pulses to multiple electrodes associated with a single heart chamber. Moreover, the cardiac rhythm management therapy discussed in this document also includes cardiac contractility modulation (CCM) therapy. CCM therapy includes delivering electrical energy to a portion of the heart during a refractory time period when that portion of the heart is relatively unlikely to contract in response to the received electrical energy. Therefore, CCM therapy need not adjust cardiac rate and, moreover, need not even evoke responsive heart contractions. System 100 may also include additional components such as, for example, an external or other remote interface 108 capable of communicating with device 102.
[0020]FIG. 2 is a block diagram example of one possible edema detection circuit 112 that senses thoracic impedance to determine whether the edema condition is present. In this example, edema detection circuit includes exciter 200 and signal processor 202, both of which are coupled to electrodes associated with a portion of the subject's thorax. In this document, the term “thorax” refers to the subject's body other than the subject's head, arms, and legs. Exciter 200 provides, at node/bus 204, a test signal to the thorax, from which thoracic impedance is determined. Exciter 200 need not, and typically does not, stimulate tissue or muscle contractions in the thorax; it is referred to as an exciter because it provides a test excitation signal for determining impedance. Signal processor 202 receives from the thorax, at node/bus 206, signals responsive to the test signal provided by exciter 200. Signal processor 202 outputs, at node/bus 208, the edema indicator to controller 110.
[0023]FIG. 3 is a block diagram example of portions of a possible signal processor 202. The input signal from the thoracic electrodes, which is responsive to the test stimulus provided by exciter 200, is received by an analog signal processing circuit 300 at its preamplifier 302 circuit. A signal provided by an output of preamplifier 302 is received by a demodulator 304 circuit. Demodulator 304 demodulates the high frequency carrier signal to extract thoracic impedance information. A signal provided by an output of demodulator 304 is received by analog-to-digital (A/D) converter 306, where it is converted into a digital thoracic impedance signal. Suitable examples of preamplifier 302, demodulator 304, and A/D converter 306 are discussed in the Hartley et al. patent, which was above incorporated by reference in its entirety.
[0025]FIG. 4 is a block diagram example of one possible edema detection module 312. It includes a delay 400 that outputs a long-term value of the lowpass-filtered thoracic impedance, that is, the baseline thoracic impedance including information about fluid shifts to and away from the thorax. Comparator 402 compares the substantially instantaneous and long-term values of the baseline thoracic impedance at its respective comparator inputs. If the substantially instantaneous baseline thoracic impedance is less than the long-term value of the baseline thoracic impedance by a predetermined threshold value, then comparator 402 provides a resulting signal, at node 208, that indicates that edema is present. Otherwise, the resulting signal at node 208 indicates that edema is not present.
[0026]FIG. 5 is a block diagram example of an alternative edema detection module 312. In this example, comparator 402 compares the unfiltered thoracic impedance from the output A/D converter 306 to the lowpass-filtered thoracic impedance (i.e., the baseline thoracic impedance) from the output of lowpass filter or averager 310. If the unfiltered thoracic impedance from A/D converter 306 is less than the baseline thoracic impedance from lowpass filter or averager 310 by a predetermined threshold value, then comparator 402 provides the resulting signal, at node 208, that indicates that edema is present. Otherwise, the resulting signal at node 208 indicates that edema is not present.
[0027]FIG. 6 is a block diagram example of an alternative signal processing circuit 202 that determines whether edema is present based not only on the baseline thoracic impedance signal, but also on an additional breathing rate criterion. In the example of FIG. 6, the digitized thoracic impedance signal from A/D converter 306 is also received at an input of bandpass filter 600. Bandpass filter 600 attenuates frequencies outside the frequency range associated with the breathing component of the thoracic impedance signal (e.g., approximately between 0.05 Hz and 2.0 Hz inclusive). Bandpass filter 600 outputs a signal correlative to the subject's breathing, which is received at an input of breathing rate module 602. Breathing rate module 602 includes a fiducial point detector (e.g., zero-cross detector, level detector, peak detector, etc.) Dejection a fiducial point on the breathing signal that occurs a known number of one or more times during breathing cycle (of inhaling and exhaling). A timer measures the time interval between respective successive fiducial points, from which the breathing rate is determined. A comparator compares the breathing rate to a threshold value that is approximately between 10 breaths per minute and 40 breaths per minute, such as about 25 breaths per minute. Breathing rate module 602 outputs at node 604 a digital signal indicating whether the breathing rate threshold is being exceeded. This signal is used (e.g., by AND gate 606) to qualify the signal output from edema detection module 312. Therefore, the edema-present indicator at node 208 is asserted only if both the baseline thoracic impedance indicates a fluid accumulation in the thorax and the breathing rate exceeds the threshold value.
[0035]FIG. 8 is a block diagram example in which various responses to a detected edema episode are prioritized. In this example, controller 110 sequentially attempts the various edema-response measures in the order of priority until the edema abates or all possible responses have been exhausted.
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