Detection of pleural effusion using transthoracic impedance

• US 20060264776A1
• Filed: 05/18/2005
• Published: 11/23/2006
• Est. Priority Date: 05/18/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Stahmann, Jeffrey E., Hartley, Jesse W., Fogoros, Richard, Hatlestad, John
• Granted Patent: US 7,340,296 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/36535 controlled by body position or posture

Abstract

This patent document discusses systems, devices, and methods for increasing a sensitivity or specificity of thoracic fluid detection in a subject and differentiating between pleural effusion and pulmonary edema. In one example, a thoracic impedance measurement circuit senses a thoracic impedance signal. In another example, a processor receives the thoracic impedance signal and determines whether such thoracic impedance signal is “significant.” A significant thoracic impedance signal indicates the presence of thoracic fluid and may be recognized by comparing the thoracic impedance signal (or variation thereof) to a thoracic impedance threshold. When a significant thoracic impedance signal is recognized, the processor is adapted to detect one or both of: a pleural effusion indication and a pulmonary edema indication using one or a combination of: physiologic information, patient symptom information, and posture information. In another example, the thoracic impedance threshold is adjusted using such physiologic, patient symptom, or posture information.

Claims

1. A system for the detection of thoracic fluid in a subject, the system comprising:

an implantable thoracic impedance measurement circuit, adapted to sense a thoracic impedance signal from the subject; and

a processor, coupled with the thoracic impedance measurement circuit to receive the thoracic impedance signal,

wherein the processor is adapted to recognize a significant thoracic impedance signal, and

wherein the processor is adapted to detect a pleural effusion indication upon recognition of the significant thoracic impedance signal.

2. The system as recited in claim 1, wherein the processor is further adapted to detect a pulmonary edema indication upon recognition of the significant thoracic impedance signal.

3. The system as recited in claim 2, wherein the processor is adapted to differentiate the pleural effusion indication from the pulmonary edema indication.

4. The system as recited in claim 1, further comprising at least one physiologic information device coupled to the processor,

wherein the at least one physiologic information device is adapted to sense or collect physiologic information about the subject, and

wherein the processor is adapted to detect the pleural effusion indication using, at least in part, the physiologic information.

5. The system as recited in claim 4, wherein the at least one physiologic information device includes an implantable sensor.

6. The system as recited in claim 4, wherein the physiologic information about the subject includes at least one respiratory sound.

7. The system as recited in claim 4, further comprising a memory storage device adapted to store a history of the thoracic impedance signal and a history of the physiologic information.

8. The system as recited in claim 1, further comprising at least one patient symptom device coupled to the processor,

wherein the at least one patient symptom device is adapted to sense or collect patient symptom information about the subject, and

wherein the processor is adapted to detect the pleural effusion indication using, at least in part, the patient symptom information.

9. The system as recited in claim 8, wherein the at least one patient symptom device includes an implantable sensor.

10. The system as recited in claim 8, wherein the patient symptom information includes one or both of:

a pleuritic chest pain and at least one hiccup.

11. The system as recited in claim 8, further comprising a memory storage device adapted to store a history of the thoracic impedance signal and a history of the patient symptom information.

12. The system as recited in claim 1, further comprising a posture sensor coupled to the processor, the posture sensor adapted to sense a posture signal;

and

a memory storage device adapted to store a history of the thoracic impedance signal and a history of the posture signal,

wherein the processor is adapted to detect the pleural effusion indication using, at least in part, the posture signal.

13. The system as recited in claim 1, further comprising a posture compensation module adapted to determine a posture-compensated thoracic impedance signal using a posture signal and the thoracic impedance signal,

wherein the processor is adapted to recognize the significant thoracic impedance signal using the posture-compensated thoracic impedance signal.

14. The system as recited in claim 1, further comprising a blood impedance measurement circuit adapted to extract from the thoracic impedance signal a blood resistivity-influenced component,

wherein the processor is adapted to recognize the significant thoracic impedance signal using a blood resistivity-compensated thoracic impedance signal.

15. The system as recited in claim 1, further comprising a frequency selective filter circuit adapted to extract from the thoracic impedance signal a near-DC thoracic impedance signal,

wherein the processor is adapted to recognize the significant thoracic impedance signal using the near-DC thoracic impedance signal.

16. The system as recited in claim 1, further comprising an external user interface coupled to the processor,

wherein the external user interface is adapted to receive from the processor the pleural effusion indication, and

wherein the external user interface is adapted to provide a user-detectable indication of the pleural effusion indication.

17. The system as recited in claim 1, further comprising an external user interface coupled to the processor,

wherein the external user interface includes a user input device, adapted to collect from a user one or a combination of:

physiologic information, patient symptom information, and posture information, and

wherein the external user interface is adapted to transmit the physiologic information, the patient symptom information, or the posture information to the processor.

18. The system as recited in claim 1, further comprising a therapy control module adapted to adjust or initiate a therapy using the pleural effusion indication.

19. A system for the detection of thoracic fluid in a subject, the system comprising:

a thoracic impedance measurement circuit, adapted to sense a thoracic impedance signal from the subject;

a processor, coupled with the thoracic impedance measurement circuit to receive the thoracic impedance signal; and

a differentiation module, adapted to differentiate a pleural effusion indication and a pulmonary edema indication using, at least in part, one or a combination of;

the thoracic impedance signal, physiologic information, patient symptom information, and posture information.

20. The system as recited in claim 19, wherein the processor detects one or both of:

the pleural effusion indication and the pulmonary edema indication when the thoracic impedance signal is less than, or substantially equal to, a thoracic impedance threshold, and

wherein the processor includes a threshold adjustment module adapted to adjust the thoracic impedance threshold using, at least in part, one or a combination of;

the physiologic information, the patient symptom information, and the posture information.

21. The system as recited in claim 19, further comprising a memory storage device, adapted to store a history of one or a combination of:

the thoracic impedance signal, the physiologic information, the patient symptom information, and the posture information.

22. A method for the detection of thoracic fluid in a subject, the method comprising:

sensing a thoracic impedance signal using an implantable device from a thorax of the subject;

recognizing a significant thoracic impedance signal in the subject; and

detecting a pleural effusion indication upon recognizing the significant thoracic impedance signal,

wherein recognizing the significant thoracic impedance signal includes comparing the thoracic impedance signal to a thoracic impedance threshold.

23. The method as recited in claim 22, further comprising detecting a pulmonary edema indication.

24. The method as recited in claim 22, further comprising differentiating the pleural effusion indication from a pulmonary edema indication.

25. The method as recited in claim 22, further comprising sensing or receiving physiologic information about the subject,

wherein detecting the pleural effusion indication includes using the physiologic information.

26. The method as recited in claim 25, wherein the physiologic information includes at least one respiratory sound.

27. The method as recited in claim 22, further comprising sensing or receiving patient symptom information about the subject,

wherein detecting the pleural effusion indication includes using the patient symptom information.

28. The method as recited in claim 22, further comprising sensing or receiving a posture orientation of the subject,

wherein detecting the pleural effusion indication includes using a change in the thoracic impedance signal with a change in the posture orientation.

29. The method as recited in claim 22, further comprising alerting a user in response to the pleural effusion indication.

30. The method as recited in claim 22, further comprising providing a therapy to the subject in response to the pleural effusion indication.

31. The method as recited in claim 22, further comprising filtering the thoracic impedance signal to obtain a near-DC thoracic impedance signal,

wherein recognizing the significant thoracic impedance signal includes comparing the near-DC thoracic impedance signal to the thoracic impedance threshold.

32. The method as recited in claim 22, further comprising compensating the thoracic impedance signal to extract a blood resistivity-influenced component of the thoracic impedance signal,

wherein recognizing the significant thoracic impedance signal includes comparing a blood resistivity-compensated thoracic impedance signal to the thoracic impedance threshold.

33. The method as recited in claim 22, further comprising compensating the thoracic impedance signal to attenuate or remove a posture-influenced component of the thoracic impedance signal,

wherein recognizing the significant thoracic impedance signal includes comparing a posture-compensated thoracic impedance signal to the thoracic impedance threshold.

34. The method as recited in claim 22, further comprising:

computing a change in the thoracic impedance threshold using, at least in part, one or a combination of;

physiologic information, patient symptom information, and posture information;

adjusting the thoracic impedance threshold using the computed change in the thoracic impedance threshold; and

recognizing the significant thoracic impedance signal using an adjusted thoracic impedance threshold.