SYSTEM AND METHOD FOR MONITORING CARDIOPULMONARY FLUID TRANSFER RATES USING AN IMPLANTABLE MEDICAL DEVICE

• US 20100249756A1
• Filed: 03/25/2009
• Published: 09/30/2010
• Est. Priority Date: 03/25/2009
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Koh, Steve
• Granted Patent: US 8,282,562 B2
• Time in Patent Office: Days
• US Class Current: 604/890.100
• 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 5/418 lymph vessels, ducts or nodes
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• 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 1/3962 in combination with another heart therapy
• CPC Class Codes: A61N 1/39622 Pacing therapy

Abstract

Techniques are provided for use by a pacemaker or other implantable medical device for detecting and tracking trends in cardiopulmonary fluid transfer rates—such as heart-to-lung fluid perfusion rates and lung-to-lymphatic system fluid excretion rates—and for detecting heart failure, dyspnea or other cardiopulmonary conditions. In one example, the device periodically measures transthoracic admittance values. A first exponential time-constant (k1) is determined using curve-fitting from admittance values obtained while the patient is in a sleep posture. Time-constant k1 is representative of the fluid perfusion rate. A second exponential time-constant (k2) is determined based on admittance values obtained while the patient is standing/walking/sitting. The second exponential time-constant (k2) is representative of the fluid excretion rate from the lungs. The device then detects trends, if any, in the time-constants (or in “DC” baseline values) to detect or predict medical conditions such as an imminent heart failure exacerbation.

Claims

1. A method for use with an implantable medical device for implant within a patient, the method comprising:

determining a cardiopulmonary fluid transfer rate within the patient, wherein the cardiopulmonary fluid transfer rate includes at least one of a fluid transfer rate from heart-to-lung and a fluid transfer rate from lung-to-lymphatic system; and

controlling at least one device function in response to the cardiopulmonary fluid transfer rate.

2. The method of claim 1 wherein determining the cardiopulmonary fluid transfer rate within the patient includes determining a fluid perfusion transfer rate representative of transfer of fluids from the heart-to-lung within the patient.

12. The method of claim 1 wherein determining the cardiopulmonary fluid transfer rate within the patient includes determining a lymphatic fluid excretion rate representative of transfer of fluids from lung-to-lymphatic system.

13. The method of claim 12 wherein determining the lymphatic fluid excretion rate includes:

measuring values representative of electrical admittance through at least a portion of the lungs;

identifying a second set of values measured while patient is not in a sleep posture;

determining a second exponential time-constant (k2) based on the second set of values; and

equating the second exponential time-constant (k2) with the rate of fluids from lung-to-lymphatic system within the patient.

14. The method of claim 13 further including detecting trends, if any, in the lymphatic fluid excretion rate.

15. The method of claim 14 wherein detecting trends, if any, in the lymphatic fluid excretion rate includes:

determining a plurality of said second time-constants (k2) over a period of at least two days; and

detecting trends in the second time-constants (k2).

16. The method of claim 14 wherein detecting trends, if any, in the second fluid transfer rate includes detecting a general decrease over time in the second time-constant (k2).

17. The method of claim 16 wherein controlling at least one device function includes performing one or more in response to a general decrease in the time-constant (k2):

generating a warning indicative of the onset of dyspnea;

controlling delivery of therapy; and

controlling recording of diagnostics.

18. The method of claim 1 wherein determining the cardiopulmonary fluid transfer rate within the patient includes determining both a rate of transfer from the heart-to-lung and a rate of transfer from lung-to-lymphatic system.

19. The method of claim 18 wherein determining the cardiopulmonary fluid transfer rates includes:

measuring a set of values representative of electrical admittance through at least a portion of the lungs during at least one twenty-four hour period;

determining a first exponential time-constant (k1) based on values detected while the patient is in a sleep posture;

determining a second exponential time-constant (k2) based on values detected while the patient is not in a sleep posture;

equating the first exponential time-constant (k1) with the rate of transfer of fluids from the heart-to-lung; and

equating the second exponential time-constant (k2) with the rate of transfer of fluids from the lung-to-lymphatic system.

20. The method of claim 19 wherein determining the first and second exponential time-constants (k1, k2) includes fitting a curve of the form:

Adm(u,t)=DC+A*(1−

u)*(1−

exp(−

k1*t))+A*u*exp(−

k2*t)

to the values measured throughout the twenty-four hour period, wherein “

DC”

represents a minimum detected admittance during the period, “

A”

represents a maximum detected admittance during the period minus DC, and u=0 for admittance data collected while the patient is in a sleep posture for a sufficient amount of time for admittance to increase significantly and u=1 for admittance data collected during a subsequent time interval while the patient is not in a sleep posture for a sufficient amount of time for admittance to decrease significantly.

21. The method of claim 20 further including detecting trends, if any, in the second fluid transfer rate by:

determining a plurality of said first and second time-constants (k1, k2) over at least two days; and

detecting trends in either one or both of the time-constants (k1, k2) over the period of days.

22. The method of claim 21 wherein detecting trends, if any, in the second fluid transfer rate includes detecting a general decrease in a combination of the first and second time-constants.

23. The method of claim 21 wherein controlling at least one device function includes generating a warning indicative of heart failure exacerbation in response to a general decrease in the combination of the first and second time-constants.

24. The method of claim 20 further including detecting trends, if any, in the DC value.

25. The method of claim 24 wherein an increase in the DC value is deemed to be indicative of an increase in pulmonary congestion.

26. The method of claim 1 wherein the steps are all performed by the implantable medical device.

27. The method of claim 1 wherein the step of determining a cardiopulmonary fluid transfer rate within the patient is performed by an external system based on data transmitted from the implantable medical device.

3. The method of claim 3 wherein determining the fluid perfusion transfer rate includes:

measuring values representative of electrical admittance through at least a portion of the lungs;

identifying a first set of values measured while the patient is in a sleep posture;

determining a first exponential time-constant (k1) based on the first set of values; and

equating the first exponential time-constant (k1) with the rate of transfer of fluids from heart-to-lung within the patient.

4. The method of claim 3 wherein measuring the values representative of electrical admittance through the lungs includes measuring one or more of admittance, impedance, conductance and resistance along a sensing vector from a left ventricular lead to a housing to the device through at least a portion of the lungs.

5. The method of claim 4 wherein measuring the values representative of electrical admittance is performed using one or more of a left ventricular ring (LVr)-to-device housing vector, a right ventricular ring (RVr)-to-device housing vector and a right atrial tip (RAt)-to-device housing vector.

6. The method of claim 3 further including detecting trends, if any, in the fluid perfusion transfer rate.

7. The method of claim 6 wherein detecting trends, if any, in the fluid perfusion transfer rate includes:

determining a plurality of said first time-constants (k1) over a period of at least two days; and

detecting trends in the first time-constants (k1).

8. The method of claim 7 wherein detecting trends, if any, in the fluid perfusion transfer rate includes detecting a general decrease in the first time-constant (k1).

9. The method of claim 8 wherein controlling at least one device function includes performing one or more in response to a general decrease in the time-constant (k1):

generating a warning indicative of the onset of heart failure;

controlling delivery of therapy; and

controlling recording of diagnostics.

10. The method of claim 3 further including detecting a baseline (DC) value from the electrical admittance values and detecting trends, if any, in the baseline value.

11. The method of claim 10 wherein an increase in the baseline value is deemed to indicative of an increase in pulmonary congestion.

28. A system for use with an implantable medical device for implant within a patient, the system comprising:

a cardiopulmonary fluid transfer rate determination system operative to determine at least one of a fluid transfer rate from heart-to-lung and a fluid transfer rate from lung-to-lymphatic system; and

a cardiopulmonary fluid transfer rate-based controller operative to control at least one device function based on a cardiopulmonary fluid transfer rate.

29. The system of claim 28 wherein the cardiopulmonary fluid transfer rate determination system includes:

a fluid perfusion transfer rate determination system operative to determine a fluid transfer rate from heart-to-lung.

30. The system of claim 28 wherein the cardiopulmonary fluid transfer rate determination system includes:

a lymphatic fluid excretion rate determination system operative to determine a fluid transfer rate from lung-to-lymphatic system.

31. The system of claim 28 further including:

a fluid transfer trend-based heart failure exacerbation detector operative to detect a heart failure exacerbation based on the cardiopulmonary fluid transfer rate.

32. The system of claim 28 further including:

a fluid transfer rate-based controller operative to control one or more of fluid transfer rate-based warnings, fluid transfer rate-based therapies, and the generation of fluid transfer rate-based diagnostics.

33. The system of claim 32 wherein the fluid transfer rate-based controller is operative to control delivery of drug therapy via a drug dispensation device.

34. A system for use with an implantable medical device for implant within a patient, the system comprising:

means for determining fluid transfer rates within the patient representative of at least one form of cardiopulmonary fluid transfer; and

means for detecting an indication of heart failure within the patient based on the cardiopulmonary fluid transfer rate.