Methods and apparatus for estimation of ventricular afterload based on ventricular pressure measurements

• US 6,887,207 B2
• Filed: 02/26/2003
• Issued: 05/03/2005
• Est. Priority Date: 02/26/2003
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Hettrick, Douglas A.
• Primary Examiner(s): Hindenburg, Max F.
• Assistant Examiner(s): MALLARI, PATRICIA C
• Application Number:
  US10/376,064
• Publication Number:
  US 20040167410A1
• Time in Patent Office: 797 Days
• Field of Search: 600/481, 600/485, 600/486, 600/490, 600/508, 607/6, 607/17, 607/18, 607/23
• US Class Current: 600/485
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/36564 controlled by blood pressure

Abstract

A method and system incorporated into an IMD that detects changes in ventricular afterload using the morphology of a ventricular blood pressure wave. A peak positive pressure value P_b, peak positive and peak negative derivative pressures dP/dt_PP and dP/dt_NP, and a decreasing pressure P_c are determined. The sample times t_b, at P_b, t_a at dP/dt_PP and t_c at dP/dt_NP are determined. An index α of the relative timing of peak positive pressure P_b in the blood ejection phase is calculated from, α=(t_b−t_a)/(t_c−t_a), the severity of ventricular afterload is proportional to the value α in the range between 0 and 1. The slope of the early ejection pressure in the blood ejection phase is calculated from β=(P_c−P_b)/(t_c−t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β.

Claims

1. A method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P_b, the peak positive derivative pressure dP/dt_PP and the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

determining the sample time t_b of peak positive pressure, the sample time t_a of the peak positive derivative pressure dP/dt_PP, and the sample times t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values; and

calculating an index α

of the relative timing of peak positive pressure P_b in the blood ejection phase in accordance with the formula α

=(t_b−

t_a)/(t<sub>c−

ta</sub>), wherein the severity of ventricular afterload is proportional to the value of index α

in the range between 0 and 1.

2. The method of claim 1, further comprising:

determining the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values; and

calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

.

3. The method of claim 2, wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

4. The method of claim 2, wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

5. A method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P_b, the peak negative derivative pressure dP/dt_NP, and the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

determining the sample time t_b of peak positive pressure, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values; and

calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

.

6. The method of claim 5, wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

7. The method of claim 5, wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

8. In an implantable heart monitor adapted to be implanted in a patient'"'"'s body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

operating the pressure sensor to obtain a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P_b, the peak positive derivative pressure dP/dt_PP and the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

determining the sample time t_b of peak positive pressure, the sample time t_a of the peak positive derivative pressure dP/dt_PP, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values;

calculating an index α

of the relative timing of peak positive pressure P_b in the blood ejection phase in accordance with the formula α

=(t_b−

t_a)/(t_c−

t_a), wherein the severity of ventricular afterload is proportional to the value of index α

in the range between 0 and 1; and

storing the calculated index α

in data storage memory.

9. The method of claim 8, further comprising:

determining the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

; and

storing the calculated index β

in data storage memory.

10. The method of claim 8, wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

11. The method of claim 8, wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

12. In an implantable heart monitor adapted to be implanted in a patient'"'"'s body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P_b, the peak negative derivative pressure dP/dt_NP, and the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

determining the sample time t_b of peak positive pressure, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values; and

calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

; and

storing the calculated index β

in data storage memory.

13. The method of claim 12, wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

14. The method of claim 12, wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

15. The method of claim 12, wherein the implantable medical device adapted to be implanted in the patient'"'"'s body comprises means for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters.

16. In an implantable medical device adapted to be implanted in a patient'"'"'s body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P_b, the peak positive derivative pressure dP/dt_PP and the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

determining the sample time t_b of peak positive pressure, the sample time t_a of the peak positive derivative pressure dP/dt_PP, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values;

calculating an index α

of the relative timing of peak positive pressure P_b in the blood ejection phase in accordance with the formula α

=(t_b−

t_a)/(t_c−

t_a), wherein the severity of ventricular afterload is proportional to the value of index α

in the range between 0 and 1; and

adjusting one of a therapy delivery operating mode or parameter to minimize the value of index α

.

17. The method of claim 16, further comprising:

determining the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

; and

adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β

.

18. The method of claim 16, wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

19. The method of claim 16, wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

20. In an implantable medical device adapted to be implanted in a patient'"'"'s body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P_b, the peak negative derivative pressure dP/dt_NP, and the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

determining the sample time t_b of peak positive pressure, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values; and

calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

; and

adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β

.

21. The method of claim 20, wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

22. The method of claim 20, wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

23. Apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P_b, the peak positive derivative pressure dP/dt_PP and the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for determining the sample time t_b of peak positive pressure, the sample time t_a of the peak positive derivative pressure dP/dt_PP, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values; and

means for calculating an index α

of the relative timing of peak positive pressure P_b in the blood ejection phase in accordance with the formula α

=(t_b−

t_a)/(t_c−

t_a), wherein the severity of ventricular afterload is proportional to the value of index α

in the range between 0 and 1.

24. The apparatus of claim 23, further comprising:

means for determining the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values; and

means for calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

.

25. The apparatus of claim 23, wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

26. The apparatus of claim 23, wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

27. Apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P_b, the peak negative derivative pressure dP/dt_NP, and the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for determining the sample time t_b of peak positive pressure, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values; and

means for calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

.

28. The apparatus of claim 27, wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

29. The apparatus of claim 27, wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

30. In an implantable heart monitor adapted to be implanted in a patient'"'"'s body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for operating the pressure sensor to obtain a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P_b, the peak positive derivative pressure dP/dt_PP and the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for determining the sample time t_b of peak positive pressure, the sample time t_a of the peak positive derivative pressure dP/dt_PP, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index α

of the relative timing of peak positive pressure P_b in the blood ejection phase in accordance with the formula α

=(t_b−

t_a)/(t_c−

t_a), wherein the severity of ventricular afterload is proportional to the value of index α

in the range between 0 and 1; and

means for storing the calculated index α

in data storage memory.

31. The apparatus of claim 30, further comprising:

means for determining the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c−

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportioned to the magnitude of the index β

; and

means for storing the calculated index β

in data storage memory.

32. The apparatus of claim 30, wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

33. The apparatus of claim 30, wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

34. In an implantable heart monitor adapted to be implanted in a patient'"'"'s body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P_b, the peak negative derivative pressure dP/dt_NP, and the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for determining the sample time t_b of peak positive pressure, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c −

P_b)/(t_c−

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

; and

means for storing the calculated index β

in data storage memory.

35. The apparatus of claim 34, wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

36. The apparatus of claim 34, wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

37. In an implantable medical device adapted to be implanted in a patient'"'"'s body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P_b, the peak positive derivative pressure dP/dt_PP and the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for determining the sample time t_b of peak positive pressure, the sample time t_a of the peak positive derivative pressure dP/dt_PP, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index α

of the relative timing of peak positive pressure P_b in the blood ejection phase in accordance with the formula α

=(t_b−

t_a)/(t_c −

t_a), wherein the severity of ventricular afterload is proportional to the value of index α

in the range between 0 and 1; and

means for adjusting one of a therapy delivery operating mode or parameter to minimize the value of index β

.

38. The apparatus of claim 37, further comprising:

means for determining the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c −

P_b)/(t_c −

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

; and

means for adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β

.

39. The apparatus of claim 37 wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

40. The apparatus of claim 37, wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

41. In an implantable medical device adapted to be implanted in a patient'"'"'s body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P_b, the peak negative derivative pressure dP/dt_NP, and the decreasing pressure P_c associated with the peak negative derivative pressure dP/dt_NP from the set of ventricular pressure values;

means for determining the sample time t_b of peak positive pressure, and the sample time t_c of the peak negative derivative pressure dP/dt_NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index β

of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β

=(P_c −

P_b)/(t_c −

t_b), wherein the severity of ventricular afterload is proportional to the magnitude of the index β

; and

means for adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β

.

42. The apparatus of claim 41, wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

43. The apparatus of claim 41, wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.