Method and apparatus to provide diagnostic index and therapy regulated by subject's autonomic nervous system

• US 20060094967A1
• Filed: 10/29/2004
• Published: 05/04/2006
• Est. Priority Date: 10/29/2004
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Bennett, Tommy D., Taepke, Robert T. II, Duffin, Edwin G., Kjellstrom, Barbro
• Granted Patent: US 8,244,355 B2
• Time in Patent Office: Days
• US Class Current: 600/508
• 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 5/4035 Evaluating the autonomic nervous system
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/36535 controlled by body position or posture
• CPC Class Codes: A61N 1/36578 controlled by mechanical motion of the heart wall, e.g. measured by an accelerometer or microphone
• CPC Class Codes: A61N 1/36585 controlled by two or more physical parameters
• CPC Class Codes: A61N 1/36592 controlled by the heart rate variability
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

A system and method are provided for determining an index of autonomic nervous system (ANS) or sympathetic nervous system (SNS) activity for use in patient monitoring or therapy delivery control. An ANS or SNS index is calculated as a function of multiple monitored physiological variables that strongly correlate to changes in autonomic or sympathetic tone. These ANS-influenced variables are derived from selected hemodynamic and/or electrical signals and may include variables relating to any of: the maximum rate of pressure rise (dP/dt_max), the maximum rate of pressure decline (dP/dt_min), pulse pressure (PP), pre-ejection time interval (PEI) and/or systolic time interval (STI), heart rate (HR), heart rate variability (HRV), and baro-reflex gain. Changes in the ANS or SNS index may be used to automatically adjust a device delivered therapy.

Claims

22. A system for monitoring ANS activity, comprising:

a sensor that generates a signal influenced by ANS activity;

a processor that derives multiple variables influenced by ANS activity from the sensor signal, and

means for computing an index of ANS activity from the derived variables.

1. A method for monitoring ANS activity, comprising:

obtaining at least one physiological signal influenced by ANS activity;

deriving from the physiological signal a number of variables influenced by ANS activity; and

computing an ANS index as a function of the derived variables.

2. A method according to claim 1, wherein the at least one physiological signal is a mechanical signal relating to heart function.

4. A method according to claim 2, further including obtaining an electrical signal of heart function.

5. A method according to claim 1, wherein the at least one physiological signal is a pressure signal and derived variables relate to any of heart rate, dP/dt, pulse pressure, pre-ejection time interval, systolic time interval, heart rate variability, and baro-reflex gain.

6. A method according to claim 5, wherein the baro-reflex gain variable is derived from a measured change in heart rate occurring over a cyclic pressure change known to contribute to the baroreceptor reflex.

7. A method according to claim 6, wherein the cyclic pressure change is the cyclic pressure change in blood pressure caused by respiration.

8. A method according to claim 1, wherein an index of ANS activity is computed as a function of the derived variables each assigned a weighting coefficient wherein the weighting coefficient may be any real value.

9. A method according to claim 8, wherein the function of the derived variables is a linear function.

10. A method according to claim 8, wherein the function of the derived variables is a non-linear function.

11. A method according to claim 1, further including a comparative analysis of the computed index of ANS function.

12. A method according to claim 11, further including generating a notification of a change in the ANS index based on the comparative analysis.

13. A method according to claim 11, further including adjustment of a therapy based on the comparative analysis.

14. A method according to claim 13, where the therapy comprises one of:

an electrical stimulation therapy, an adjustment in arrhythmia prevention pacing therapy, an adjustment in an arrhythmia detection technique, an adjustment in arrhythmia therapy.

15. A method according to claim 13, wherein the therapy comprises one of:

a medical therapy and an adjustment of beta-blocker dosage.

16. A method according to claim 1, further comprising:

monitoring a physiological signal used as a trigger signal;

detecting conditions for triggering ANS monitoring based on the monitored trigger signal wherein when such conditions are detected, obtaining the at least one physiological signal influenced by ANS activity is initiated.

17. A method according to claim 16, wherein the trigger signal relates to any of:

time of day, patient activity, patient posture, heart rate, heart rate variability, blood pressure, heart wall motion, baro-reflex gain, pre-ejection time interval, systolic interval, and electrical activity of the heart.

18. A method according to claim 1, further comprising:

determining a patient condition based on any of;

a physiological signal and time of day; and

stratifying the computed index of ANS function according to the patient condition.

19. A method according to claim 18, wherein the patient condition may relate to one of the following:

a patient activity, a patient posture, a heart rate, a heart rate variability, a blood pressure metric, a heart wall motion, a baro-reflex gain, a pre-ejection time interval, a systolic interval, an electrical activity of the heart.

20. A method according to claim 1, wherein the index of ANS activity comprises an SNS index.

21. A method according to claim 20, further comprising:

computing an ANS index as a function of the SNS index and one or more derived variables influenced by the ANS.

23. A system according to claim 22, wherein the sensor comprises a mechanical sensor.

24. A system according to claim 23, wherein the mechanical sensor generates a signal relating to at least one of:

a blood pressure, a heart wall motion, a blood flow, a blood volume.

25. A system according to claim 23, further including a sensor of electrical signals of heart function.

26. A system according to claim 22, wherein the sensor is deployed on an deployable lead.

30. A system according to claim 22, wherein the means for computing an index of ANS activity includes means for storing a weighting coefficient assigned to each of the derived variables wherein the weighting coefficient may be any real value.

31. A system according to claim 30, wherein the function used to compute the index of ANS activity is a linear function of the derived variables.

32. A system according to claim 30, wherein the function used to compute the index of ANS activity is a non-linear function of the derived variables.

33. A system according to claim 22, further comprising means for performing a comparative analysis of the computed index of ANS function.

34. A system according to claim 33, further including means for generating a notification of a change in the ANS index based on the comparative analysis.

35. A system according to claim 33, further comprising:

means for delivering a therapy; and

means for controlling the delivery of the therapy wherein the control means is responsive to the comparative analysis.

36. A system according to claim 35, wherein the therapy comprises at least one of:

an electrical stimulation therapy, an adjustment of arrhythmia prevention pacing;

an adjustment of arrhythmia detection techniques;

an adjustment of an arrhythmia therapy.

37. A system according to claim 35, wherein the therapy comprises one of:

a drug therapy and an adjustment of a beta-blocker dosage.

38. A system according to claim 22, further comprising:

means for monitoring a trigger signal;

means for detecting predetermined trigger signal conditions and when trigger signal conditions are detected enabling the sensor of the at least one physiological signal influenced by ANS activity

39. A system according to claim 38, wherein the means for monitoring trigger signal includes means for monitoring any of:

time of day, patient activity, patient posture, heart rate, heart rate variability, blood pressure, heart wall motion, baro-reflex gain, pre-ejection time interval, systolic interval, and electrical activity of the heart.

40. A system according to claim 22, further comprising:

means for determining a patient condition based on any of;

a physiological signal and time of day; and

means for stratifying the computed index of ANS function according to the patient condition.

41. A system according to claim 40, wherein the patient condition may relate to any of:

patient activity, patient posture, heart rate, heart rate variability, blood pressure, heart wall motion, baro-reflex gain, pre-ejection time interval, systolic interval, and electrical activity of the heart.

42. A system according to claim 22, wherein the index of ANS activity is an SNS index.

43. A system according to claim 42, wherein an ANS index is computed as a function of the SNS index and one or more derived variables influenced by the ANS.

26-1. A system according to claim 22, wherein the sensor comprises a pressure sensor.

27-2. A system according to claim 26, wherein the processor derives variables from the pressure sensor signal relating to at least one of:

a heart rate, a dP/dt metric, a pulse pressure, a pre-ejection time interval, a systolic time interval, a heart rate variability, a baro-reflex gain.

27-3. A system according to claim 27, wherein the processor for deriving variables further comprises means for processing the pressure sensor signal by any of:

means for identifying a maximum pressure;

means for identifying a minimum pressure rate;

means for identifying a maximum dP/dt;

means for identifying a minimum dP/dt;

means for determining a heart rate;

means for determining a heart rate variability;

means for determining a threshold crossing.

44. A computer readable medium bearing instructions performed under computer processor control to effect a technical effect, said medium comprising:

instructions for obtaining at least one physiological signal influenced by ANS activity;

instructions for deriving from the physiological signal a number of variables influenced by ANS activity; and

instructions for computing an ANS index as a function of the derived variables.

45. A medium according to claim 44, wherein the at least one physiological signal is a mechanical signal relating to heart function.

46. A medium according to claim 45, wherein the mechanical signal relating to heart function is a signal sensitive to changes at least one of:

a blood pressure, a heart wall motion, a blood flow, a blood volume.

47. A medium according to claim 45, further comprising instructions for obtaining an electrical signal of heart function.

48. A medium according to claim 44, wherein the at least one physiological signal comprises a pressure signal and derived variables relate to at least one of:

a heart rate, a dP/dt, a pulse pressure, a pre-ejection time interval, a systolic time interval, a heart rate variability, a baro-reflex gain.