Enhancements to the detection of pulmonary edema when using transthoracic impedance

• US 20060258952A1
• Filed: 05/11/2005
• Published: 11/16/2006
• 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 7,907,997 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/4878 Evaluating oedema

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 parameter collection device, 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

a processor, coupled with the thoracic impedance measurement circuit to accept the thoracic impedance signal, and coupled with the parameter collection device to accept the physiologic information,

wherein the processor is adapted to determine a pulmonary edema indication using the thoracic impedance signal and the physiologic information.

2. 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, at least in part, the physiologic information.

3. The system as recited in claim 1, 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 adapted to receive the physiologic information.

4. 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 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 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 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.

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

a posture sensor adapted to sense a posture signal; and

a posture compensation module, adapted to compute a posture-compensated thoracic impedance signal from the 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.

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 physiologic information.

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 a therapy based, at least in part, on the pulmonary edema indication, and

wherein the therapy includes at least one of:

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

9. A method comprising:

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

sensing or receiving 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

determining a pulmonary edema indication using the thoracic impedance signal and the physiologic information,

wherein determining the pulmonary edema indication includes comparing the thoracic impedance signal to a thoracic impedance threshold.

10. The method as recited in claim 9, 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 the thoracic impedance threshold.

11. The method as recited in claim 9, further comprising:

computing a change in the thoracic impedance threshold using the physiologic information;

adjusting the thoracic impedance threshold using the computed change; and

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

12. The method as recited in claim 9, further comprising alerting a user in response to the pulmonary edema indication.

13. The method as recited in claim 9, further comprising providing a therapy to the subject in response to the pulmonary edema indication,

wherein the therapy includes one or a combination of:

cardiac rhythm management therapy, dietary therapy, and sleep disordered breathing therapy.

14. A system comprising:

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

a parameter collection device, adapted to sense or receive patient symptom information about the subject, the patient symptom information selected from a patient symptom group consisting essentially of;

a shortness of breath, a difficulty breathing, at least one wheeze, at least one cough, a feeling of anxiety, a feeling of restlessness, an excessive level of perspiration, an indication of pallor, a nasal flare, a decreased level of awareness, and an increased heart rate;

a processor, coupled with the thoracic impedance measurement circuit to accept the thoracic impedance signal, and coupled with the parameter collection device to accept the patient symptom information,

wherein the processor is adapted to determine a pulmonary edema indication using the thoracic impedance signal and the patient symptom information.

15. The system as recited in claim 14, 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, at least in part, the patient symptom information.

16. The system as recited in claim 14, 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.

17. The system as recited in claim 14, 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.

18. The system as recited in claim 14, 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 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.

19. The system as recited in claim 14, further comprising:

a posture sensor coupled to the processor, the posture sensor adapted to sense a posture signal; and

a posture compensation module, adapted to compute a posture-compensated thoracic impedance signal from the 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.

20. The system as recited in claim 14, further comprising a memory storage device adapted to store a history of the thoracic impedance signal and the patient symptom information.

21. The system as recited in claim 14, further comprising a therapy control module coupled to the processor,

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

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

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

22. A method comprising:

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

sensing or receiving at least one patient symptom about the subject, the patient symptom selected from a group consisting essentially of;

a shortness of breath, a difficulty breathing, at least one wheeze, at least one cough, a feeling of anxiety, a feeling of restlessness, an excessive level of perspiration, an indication of pallor, a nasal flare, a decreased level of awareness, and an increased heart rate; and

determining a pulmonary edema indication using the at least one patient symptom,

wherein determining the pulmonary edema indication includes comparing the thoracic impedance signal to a thoracic impedance threshold.

23. The method as recited in claim 22, 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 the thoracic impedance threshold.

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

computing a change in the thoracic impedance threshold using the at least one patient symptom;

adjusting the thoracic impedance threshold using the computed change; and

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

25. The method as recited in claim 22, further comprising alerting a user in response to the pulmonary edema indication.

26. The method as recited in claim 22, further comprising providing a therapy to the subject in response to the pulmonary edema indication,

wherein the therapy includes one or a combination of:

cardiac rhythm management therapy, dietary therapy, and sleep disordered breathing therapy.