Cardiac rhythm management system for edema

• US 7,177,681 B2
• Filed: 04/11/2003
• Issued: 02/13/2007
• Est. Priority Date: 07/31/2001
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Spinelli, Julio C., Zhu, Qingsheng
• Primary Examiner(s): Getzow; Scott M.
• Application Number:
  US10/411,795
• Publication Number:
  US 20030191503A1
• Time in Patent Office: 1,404 Days
• Field of Search: 607 5- 25, 600/547
• US Class Current: 607/9
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3684 for stimulating the heart at multiple sites of the ventricle or the atrium
• CPC Class Codes: A61N 1/36842 Multi-site stimulation in the same chamber
• CPC Class Codes: A61N 1/36843 Bi-ventricular stimulation

Abstract

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.

Claims

1. A method comprising:

detecting a thoracic impedance of a subject;

lowpass filtering the thoracic impedance using a cutoff frequency that is approximately between 0.1 Hz and 0.5 Hz to obtain a resulting baseline thoracic impedance;

obtaining the baseline thoracic impedance at first and second times, the second time delayed from the first time;

comparing the baseline thoracic impedance at the first time with the baseline thoracic impedance at the second time;

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; and

initiating or adjusting, in response to the first condition, a cardiac resynchronization therapy that coordinates a spatial nature of a depolarization associated with a heart contraction in at least one heart chamber, the cardiac resynchronization therapy comprising at least one of an interventricular delay and an intraventricular delay.

2. The method of claim 1, 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.

3. The method of claim 1, further comprising:

detecting a breathing rate of the subject; and

if the breathing rate exceeds a predetermined threshold value and the first condition was declared to exist, then declaring a second condition to exist.

4. The method of claim 3, further comprising initiating or adjusting a cardiac rhythm management therapy in response to the second condition.

5. The method of claim 4, 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.

6. The method of claim 4, 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.

7. A cardiac rhythm management system comprising:

an edema detection circuit to sense a condition correlative to edema in a subject, the edema detection circuit comprising a thoracic impedance detection circuit that comprises;

an averager/lowpass filter, comprising an input to receive a thoracic impedance signal and an output to provide a baseline portion of the thoracic impedance signal;

a delay circuit, comprising an input coupled to the output of the averager/lowpass filter, and comprising an output to provide a delayed baseline portion of the thoracic impedance signal; and

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

a controller circuit, coupled to the edema detection circuit to receive the 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, and in which the controller is configured to initiate or adjust, in response to the edema indicator, a cardiac rhythm management therapy.

8. The system of claim 7, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject'"'"'s thorax.

9. The system of claim 7, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.

10. The system of claim 9, in which the cutoff frequency is approximately equal to 0.1 Hz.

11. The system of claim 7, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject'"'"'s breathing.

12. The system of claim 11, 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.

13. The system of claim 7, 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.

14. The system of claim 13, in which the interelectrode delay comprises at least one of an atrioventricular delay, an interventricular delay, and an intraventricular delay.

15. The system of claim 7, 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.

16. The system of claim 15, 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.

17. The system of claim 15, 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.

18. The system of claim 7, 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.

19. A method comprising:

detecting a thoracic impedance of a subject;

lowpass filtering the thoracic impedance to obtain a resulting lowpass filtered thoracic impedance;

comparing the lowpass filtered thoracic impedance to the thoracic impedance before such lowpass filtering;

if the thoracic impedance before such lowpass filtering is less than the lowpass filtered thoracic impedance by a magnitude that exceeds a predetermined threshold value, then declaring a thoracic fluid accumulation condition to exist.

20. The method of claim 19, further comprising initiating or adjusting a cardiac rhythm management therapy in response to the thoracic fluid accumulation condition.

21. The method of claim 20, 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.

22. The method of claim 20, 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.

23. The method of claim 19, further comprising:

detecting a breathing rate of the subject;

if the breathing rate exceeds a predetermined threshold value and the first condition was declared to exist, then declaring a second condition to exist.

24. The method of claim 23, further comprising initiating or adjusting a cardiac rhythm management therapy in response to the second condition.

25. The method of claim 24, 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.

26. The method of claim 24, 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.

27. A cardiac rhythm management system comprising:

an edema detection circuit to sense a condition correlative to edema in a subject, the edema detection circuit comprising a thoracic impedance detection circuit that comprises;

an averager/lowpass filter, comprising an input to receive a thoracic impedance signal and an output to provide a baseline portion of the thoracic impedance signal; and

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;

an electrical energy delivery circuit to deliver electrical energy to the subject; and

a controller circuit, coupled to the edema detection circuit to receive the 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, and in which the controller is configured to initiate or adjust, in response to the edema indicator, a cardiac rhythm management therapy.

28. The system of claim 27, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject'"'"'s thorax.

29. The system of claim 27, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.

30. The system of claim 29, in which the cutoff frequency is approximately equal to 0.1 Hz.

31. The system of claim 27, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject'"'"'s breathing.

32. The system of claim 31, 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.

33. The system of claim 27, 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.

34. The system of claim 33, in which the interelectrode delay comprises at least one of an atrioventricular delay, an interventricular delay, and an intraventricular delay.

35. The system of claim 27, 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.

36. The system of claim 35, 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.

37. The system of claim 35, 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.

38. The system of claim 27, 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.

39. A method comprising:

sensing, in a subject, a condition correlative to edema; and

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, the cardiac resynchronization therapy comprising at least one of an interventricular delay and an intraventricular delay.

40. The method of claim 39, 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.

41. The method of claim 40, 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.

42. The method of claim 41, 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.

43. The method of claim 42, in which the cutoff frequency value is approximately 0.1 Hz.

44. The method of claim 40, in which the sensing also comprises detecting an increase in a rate of breathing of the subject.

45. The method of claim 44, 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.

46. The method of claim 39, 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.

47. A method comprising:

sensing, in a subject, a condition correlative to edema; and

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, 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.

48. The method of claim 47, 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.

49. The method of claim 47, 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.

50. The method of claim 47, 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.

51. A method comprising:

sensing, in a subject, a condition correlative to edema; and

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, in which the initiating or adjusting the cardiac resynchronization therapy comprises initiating or adjusting biventricular pacing.

52. The method of claim 51, in which the initiating or adjusting the cardiac resynchronization therapy comprises initiating biventricular pacing.

53. A method comprising:

sensing, in a subject, a condition correlative to edema; and

initiating or adjusting, in response to the sensing, a cardiac resynchronization therapy that comprises at least one of an interventricular delay and an intraventricular delay.

54. The method of claim 53, 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.

55. The method of claim 54, 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.

56. The method of claim 55, 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.

57. The method of claim 56, in which the cutoff frequency value is approximately 0.1 Hz.

58. The method of claim 54, in which the sensing also comprises detecting an increase in a rate of breathing of the subject.

59. The method of claim 58, 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.

60. The method of claim 53, in which the initiating or adjusting further comprises providing a non-contraction-evoking stimulus to a location of a heart of the subject during a refractory period of the heart location.

61. The method of claim 60, in which the refractory period follows a paced or sensed contraction of the heart location.

62. A method comprising:

sensing, in a subject, a condition correlative to edema; and

selecting, in response to the sensing, a cardiac rhythm management therapy from a prioritized list of therapies.

63. The method of claim 62, 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.

64. The method of claim 63, 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.

65. The method of claim 64, 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.

66. The method of claim 65, in which the cutoff frequency value is approximately 0.1 Hz.

67. The method of claim 63, in which the sensing also comprises detecting an increase in a rate of breathing of the subject.

68. The method of claim 67, 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.

69. The method of claim 62, comprising initiating/adjusting a cardiac resynchronization therapy, selecting an interelectrode delay value, for subsequent delivery of contraction-evoking stimulations occurring during a single cardiac cycle.

70. The method of claim 62, comprising initiating/adjusting a cardiac resynchronization therapy, including 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.

71. The method of claim 70, 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.

72. The method of claim 70, 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.

73. The method of claim 70, 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.

74. The method of claim 62, comprising initiating/adjusting a cardiac contractility modulation therapy, including providing a non-contraction-evoking stimulus to a location of a heart of the subject during a refractory period of the heart location.

75. The method of claim 74, in which the refractory period follows a paced or sensed contraction of the heart location.

76. The method of claim 62, in which the selecting comprises adjusting an AV delay before initiating a biventricular pacing.

77. The method of claim 62, in which the selecting comprises adjusting an AV delay before adjusting an interventricular delay.

78. The method of claim 62, in which the selecting comprises adjusting an AV delay before selecting at least one particular electrode from among multiple same-chamber electrodes.

79. The method of claim 62, in which the selecting comprises adjusting an AV delay before adjusting one or more interelectrode delays.

80. The method of claim 62, in which the selecting comprises adjusting an AV delay before initiating a cardiac contractility modulation therapy.

81. The method of claim 62, in which the selecting comprises adjusting an AV delay before adjusting one or more cardiac contractility modulation therapy parameters.

82. The method of claim 62, in which the selecting comprises initiating biventricular pacing before adjusting an interventricular delay.

83. The method of claim 62, in which the selecting comprises initiating biventricular pacing before selecting at least one particular electrode from among multiple same-chamber electrodes.

84. The method of claim 62, in which the selecting comprises initiating biventricular pacing before adjusting one or more interelectrode delays.

85. The method of claim 62, in which the selecting comprises initiating biventricular pacing before initiating cardiac contractility modulation therapy.

86. The method of claim 62, in which the selecting comprises initiating biventricular pacing before adjusting one or more cardiac contractility modulation parameters.

87. The method of claim 62, in which the selecting comprises adjusting an interventricular delay before selecting at least one particular electrode from among multiple same-chamber electrodes.

88. The method of claim 62, in which the selecting comprises adjusting an interventricular delay before adjusting one or more interelectrode delays.

89. The method of claim 62, in which the selecting comprises adjusting an interventricular delay before initiating a cardiac contractility modulation therapy.

90. The method of claim 62, in which the selecting comprises adjusting an interventricular delay before adjusting one or more cardiac contractility modulation parameters.

91. The method of claim 62, in which the selecting comprises selecting at least one particular electrode from among multiple same-chamber electrodes before adjusting one or more interelectrode delays.

92. The method of claim 62, in which the selecting comprises selecting at least one particular electrode from among multiple same-chamber electrodes before initiating cardiac contractility modulation therapy.

93. The method of claim 62, 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.

94. The method of claim 62, in which the selecting comprises adjusting one or more interelectrode delays before initiating a cardiac contractility modulation therapy.

95. The method of claim 62, in which the selecting comprises adjusting one or more interelectrode delays before adjusting one or more cardiac contractility modulation parameters.

96. The method of claim 62, 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.

97. A cardiac rhythm management system comprising:

an edema detection circuit to sense a condition correlative to edema in a subject;

an electrical energy delivery circuit to deliver electrical energy to the subject; and

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, the cardiac resynchronization therapy comprising at least one of an interventricular delay and an intraventricular delay.

98. The system of claim 97, in which the edema detection circuit comprises a thoracic impedance detection circuit.

99. The system of claim 98, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject'"'"'s thorax.

100. The system of claim 99, 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.

101. The system of claim 100, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.

102. The system of claim 101, in which the cutoff frequency is approximately equal to 0.1 Hz.

103. The system of claim 99, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject'"'"'s breathing.

104. The system of claim 97, 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.

105. The system of claim 97, 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.

106. The system of claim 105, in which the interelectrode delay comprises at least one of an atrioventricular delay, an interventricular delay, and an intraventricular delay.

107. A cardiac rhythm management system comprising:

an edema detection circuit to sense a condition correlative to edema in a subject;

an electrical energy delivery circuit to deliver electrical energy to the subject; and

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, 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.

108. The system of claim 107, 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.

109. The system of claim 107, 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.

110. A cardiac rhythm management system comprising:

an edema detection circuit to sense a condition correlative to edema in a subject;

an electrical energy delivery circuit to deliver electrical energy to the subject; and

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, 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.

111. A cardiac rhythm management system comprising:

an edema detection circuit to sense a condition correlative to edema in a subject;

an electrical energy delivery circuit to deliver electrical energy to the subject; and

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 resynchronization therapy that comprises at least one of an interventricular delay and an intraventricular delay.

112. The system of claim 111, in which the edema detection circuit comprises a thoracic impedance detection circuit.

113. The system of claim 112, in which the thoracic impedance detection circuit comprises first and second electrodes configured for association with a portion of the subject'"'"'s thorax.

114. The system of claim 113, 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.

115. The system of claim 114, in which the averager/lowpass filter comprises an effective cutoff frequency that is between 0.01 Hz and 0.5 Hz.

116. The system of claim 115, in which the cutoff frequency is approximately equal to 0.1 Hz.

117. The system of claim 113, in which the thoracic impedance circuit further comprises a filter circuit to obtain information about the subject'"'"'s breathing.

118. The system of claim 111, 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.