Sensitivity and specificity of pulmonary edema detection when using transthoracic impedance

• US 20060293609A1
• Filed: 05/11/2005
• Published: 12/28/2006
• Est. Priority Date: 05/11/2005
• 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., Hatlestad, John
• Granted Patent: US 9,089,275 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61M 2230/40 Respiratory characteristics
• CPC Class Codes: A61M 2230/65 Impedance, e.g. conductivity, capacity
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/37282 characterised by communication with experts in remote locations using a network

Abstract

This patent document discusses, among other things, systems, devices, and methods for enhancing detection of pulmonary edema using, in addition to thoracic impedance, one or a combination of: physiologic information about a subject, at least one statistical parameter, a user-programmable detection level, at least one parameter associated with a previous pulmonary edema event, and patient symptom information about the subject. In one example, a (base) thoracic impedance threshold is modified to an adjusted thoracic impedance threshold. The adjusted thoracic impedance threshold provides an increased sensitivity of pulmonary edema detection as compared to the base thoracic impedance threshold. In another example, an alert is provided to a subject, a caregiver, or other user based on a pulmonary edema indication determined by the present systems, devices, and methods. In a further example, a therapy (provided to the subject) is adjusted or initiated in response to the pulmonary edema indication.

Claims

1. A system comprising:

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

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

a statistical analysis module adapted to compute at least one statistical parameter regarding a variability of the thoracic impedance signal,

wherein the processor is adapted to determine a pulmonary edema indication using the at least one statistical parameter and the thoracic impedance signal.

2. The system as recited in claim 1, wherein the at least one statistical parameter is selected from a statistical group consisting essentially of:

a standard deviation and a variance.

3. The system as recited in claim 1, wherein the processor determines the pulmonary edema indication when the thoracic impedance signal is less than a thoracic impedance threshold, and

wherein the processor includes a threshold adjustment module adapted to adjust the thoracic impedance threshold using the at least one statistical parameter.

4. The system as recited in claim 1, further comprising a frequency selective filter circuit coupled to the thoracic impedance measurement circuit,

wherein the frequency selective filter circuit is adapted to extract from the thoracic impedance signal a near-DC thoracic impedance signal by attenuating frequency components having a value greater than about 0.05 Hz, and

wherein the processor is adapted to determine the pulmonary edema indication using, at least in part, the near-DC thoracic impedance signal.

5. The system as recited in claim 1, further comprising:

a posture sensor adapted to sense a posture signal; and

a posture compensation module, coupled with the posture sensor,

wherein the posture compensation module is adapted to compute a posture-compensated thoracic impedance signal from the thoracic impedance signal using the posture signal, and

wherein the processor is adapted to determine the pulmonary edema indication using, at least in part, the posture-compensated thoracic impedance signal.

6. The system as recited in claim 1, further comprising:

a blood impedance measurement circuit, adapted to sense a blood impedance from the subject; and

a blood impedance correction module, coupled with the blood impedance measurement circuit,

wherein the blood impedance correction module is adapted to extract from the thoracic impedance signal a blood resistivity-influenced component using the blood impedance signal, and

wherein the processor is adapted to determine the pulmonary edema indication using, at least in part, a blood resistivity-compensated thoracic impedance signal.

7. The system as recited in claim 1, further comprising a memory storage device adapted to store a history of the thoracic impedance signal and the at least one statistical parameter.

8. The system as recited in claim 1, further comprising a therapy control module coupled to the processor,

wherein the therapy control module is adapted to adjust or initiate one or more therapy based, at least in part, on the pulmonary edema indication, and

wherein the one or more therapy is selected from a therapy group consisting essentially of:

cardiac rhythm management therapy, dietary therapy, and breathing assistance therapy.

9. The system as recited in claim 1, further comprising a parameter collection device coupled with the processor,

wherein the parameter collection device is adapted to sense or receive physiologic information about the subject, the physiologic information selected from a physiologic information group consisting essentially of:

at least one heart sound, at least one lung sound, a respiratory pattern, a weight, a neurohormone level, a creatinine level, and a heart wall motion, and

wherein the processor is adapted to determine the pulmonary edema indication using, at least in part, the physiologic information.

10. A method comprising:

implantably sensing a thoracic impedance signal from the thorax of a subject;

computing at least one statistical parameter regarding a variability of the thoracic impedance signal; and

determining a pulmonary edema indication using the at least one statistical parameter and the thoracic impedance signal.

11. The method as recited in claim 10, wherein the at least one statistical parameter is selected from a group consisting essentially of:

a standard deviation and a variance.

12. The method as recited in claim 10, further comprising one or more of:

filtering the thoracic impedance signal to obtain a near-DC thoracic impedance signal, compensating the thoracic impedance signal to attenuate or remove a posture-influenced component of the thoracic impedance signal, and compensating the thoracic impedance signal to attenuate or remove a blood resistivity-influenced component of the thoracic impedance signal,

wherein determining the pulmonary edema indication includes comparing one or a combination of;

the near-DC thoracic impedance signal, a posture-compensated thoracic impedance signal, and a blood resistivity-compensated thoracic impedance signal, to a thoracic impedance threshold.

13. The method as recited in claim 12, further comprising:

computing a change in the thoracic impedance threshold using the at least one statistical parameter;

adjusting the thoracic impedance threshold using the computed change; and

determining the pulmonary edema indication using an adjusted thoracic impedance threshold.

14. The method as recited in claim 12, further comprising:

sensing or receiving physiologic information about the subject;

computing a change in the thoracic impedance threshold using one or both of;

the physiologic information and the at least one statistical parameter;

adjusting the thoracic impedance threshold using the computed change; and

determining the pulmonary edema indication using an adjusted thoracic impedance threshold,

wherein the physiologic information is selected from a physiologic information group consisting essentially of;

at least one heart sound, at least one lung sound, a respiratory pattern, a weight, a neurohormone level, a creatinine level, and a heart wall motion.

15. The method as recited in claim 10, further comprising providing one or more therapy to the subject in response to the pulmonary edema indication,

wherein the one or more therapy is selected from a therapy group consisting essentially of:

cardiac rhythm management therapy, dietary therapy, and breathing assistance therapy.

16. A system comprising:

a memory storage device, adapted to store at least one previous parameter associated with a previous pulmonary edema episode, the at least one previous parameter selected from a previous parameter group consisting essentially of;

a previous thoracic impedance, a previous physiologic parameter, a previous environmental parameter, a previous compliance parameter, and a previous patient symptom parameter;

a parameter collection device, adapted to sense or receive at least one present parameter about a subject, the at least one present parameter selected from a present parameter group consisting essentially of;

a present physiologic parameter, a present environmental parameter, a present compliance parameter, and a present patient symptom parameter;

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

a processor, coupled with the memory storage device to accept the at least one previous parameter, coupled with the parameter collection device to accept the at least one present parameter, and coupled with the thoracic impedance measurement circuit to accept the present thoracic impedance signal,

wherein the processor is adapted to determine a pulmonary edema indication using one or a combination of;

the at least one previous parameter, the at least one present parameter, and the present thoracic impedance signal.

17. The system as recited in claim 16, wherein the processor determines pulmonary edema when the present thoracic impedance signal is less than 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, the at least one previous parameter and the at least one present parameter.

18. The system as recited in claim 16, wherein the parameter collection device includes one or more of:

an implantable sensor, an external sensor, an Internet connection, and an external user interface,

wherein the Internet connection is communicatively coupled to an electronic medical database, and

wherein the external user interface includes a user input device.

19. The system as recited in claim 16, further comprising a frequency selective filter circuit adapted to extract from the present thoracic impedance signal a near-DC thoracic impedance signal by attenuating frequency components having a value greater than about 0.05 Hz, and

wherein the processor is adapted to determine the pulmonary edema indication using, at least in part, the near-DC thoracic impedance signal.

20. The system as recited in claim 16, further comprising:

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

a blood impedance correction module coupled with the blood impedance measurement circuit,

wherein the blood impedance correction module is adapted to extract from the present thoracic impedance signal a blood resistivity-influenced component using the blood impedance signal, and

wherein the processor is adapted to determine the pulmonary edema indication using, at least in part, a blood resistivity-compensated thoracic impedance signal.

21. The system as recited in claim 16, further comprising:

a posture sensor adapted to sense a posture signal; and

a posture compensation module coupled with the posture sensor, adapted to compute a posture-compensated thoracic impedance signal from the present thoracic impedance signal using the posture signal,

wherein the processor is adapted to determine the pulmonary edema indication using, at least in part, the posture-compensated thoracic impedance signal.

22. The system as recited in claim 16, further comprising means for storing a history of the at least one present parameter and the thoracic impedance signal.

23. The system as recited in claim 16, further comprising a therapy control module coupled to the processor,

wherein the therapy control module is adapted to adjust or initiate one or more therapy based, at least in part, on the pulmonary edema indication, and

wherein the one or more therapy is selected from a therapy group consisting essentially of:

cardiac rhythm management therapy, dietary therapy, and breathing assistance therapy.

24. A method comprising:

implantably sensing a present thoracic impedance signal from the thorax of a subject;

storing at least one parameter associated with a previous pulmonary edema episode, the at least one previous parameter selected from a previous parameter group consisting essentially of one or more of;

a previous thoracic impedance, a previous physiologic parameter, a previous environmental parameter, a previous compliance parameter, and a previous patient symptom parameter;

sensing or receiving at least one present parameter about the subject, the at least one present parameter selected from a present parameter group consisting essentially of one or more of;

a present physiologic parameter, a present environmental parameter, a present compliance parameter, and a present patient symptom parameter; and

determining a pulmonary edema indication using one or a combination of;

the at least one previous parameter, the at least one present parameter, and the present thoracic impedance signal.

25. The method as recited in claim 24, further comprising one or more of:

filtering the present thoracic impedance signal to obtain a near-DC thoracic impedance signal, compensating the present thoracic impedance signal to attenuate or remove a posture-influenced component of the present thoracic impedance signal, and compensating the present thoracic impedance signal to attenuate or remove a blood resistivity-influenced component of the present thoracic impedance signal,

wherein determining the pulmonary edema indication includes comparing one or a combination of;

the near-DC thoracic impedance signal, a posture-compensated thoracic impedance signal, and a blood resistivity-compensated thoracic impedance signal, to a thoracic impedance threshold.

26. The method as recited in claim 24, further comprising:

computing a change in a thoracic impedance threshold using the at least one previous parameter and the at least one present parameter;

adjusting the thoracic impedance threshold using the computed change; and

determining the pulmonary edema indication using an adjusted thoracic impedance threshold.

27. The method as recited in claim 24, further comprising alerting a user in response to the pulmonary edema indication.

28. The method as recited in claim 24, further comprising providing one or more therapy to the subject in response to the pulmonary edema indication,

wherein the one or more therapy is selected from a therapy group consisting essentially of:

cardiac rhythm management therapy, dietary therapy, and breathing assistance therapy.