System to diagnose and manage orthostatic intolerance

1. An ambulatory medical device system to monitor orthostatic intolerance of a subject, the system comprising:

a posture sensing circuit configured to detect a change in posture of a subject;

a cardiac signal sensing circuit configured to generate a sensed cardiac signal, wherein the sensed cardiac signal includes heart rate information of the subject;

a heart sound sensing circuit configured to generate a sensed heart sound signal indicative of mechanical cardiac activity of the subject, the sensed heart sound signal comprising S2 heart sound information;

a storage buffer; and

a control circuit operatively coupled to the posture sensing circuit and the storage buffer and configured, in response to a detected change in posture of the subject, to:

initiate storage of a portion of the heart rate information and a portion of the S2 heart sound information;

determine, using the S2 heart sound information, a first indication that:

amplitude of the S2 heart sound is less than a specified S2 amplitude threshold, that a change in amplitude of the S2 heart sound is greater than a specified S2 heart sound amplitude change threshold;

the heart rate exceeds a heart rate change threshold without a change in amplitude of the S2 heart sound that exceeds an S2 amplitude change threshold; or

the time over with which a detected change in an S2 heart sound parameter occurs following a detected posture transition satisfies a specified threshold time; and

generate an indication of orthostatic intolerance in response to the determined first indication and the detected change in posture of the subject.

2. The system of claim 1 , wherein the control circuit is configured to determine, using the stored heart rate and S2 heart sound information, one of that blood pressure of the subject is less than a specified blood pressure threshold, that a change in blood pressure of the subject is greater than a specified blood pressure change threshold, or that the heart rate exceeds a heart rate change threshold without a change in blood pressure that exceeds a blood pressure change threshold; and

wherein the control circuit configured to generate the indication of orthostatic intolerance includes in response to the detection.

3. The system of claim 1 , wherein the heart sound sensing circuit includes an implantable blood pressure sensing circuit.

4. The system of claim 1 , wherein the heart sound sensing circuit is configured to generate a physiologic signal in which an arterial pulsatile waveform is detectable at a body location remote from the subject's heart wherein the control circuit is configured to store, as the information related to blood pressure, a pulsatile transmit time (PTT) determined using a fiducial detected in the sensed cardiac signal and a detected arterial pulsatile waveform.

5. The system of claim 1 , wherein the control circuit is configured to initiate the storage of the heart rate information and the S2 heart sound information in response to detecting the subject changing from a supine posture to an upright posture.

6. The system of claim 1 , including a communication circuit operatively coupled to the control circuit and configured to communicate wireless signals with a second separate device, and wherein the control circuit is configured to enable the storing of the heart rate information and the S2 heart sound information in response to a signal received via the communication circuit.

7. The system of claim 1 , including a communication circuit operatively coupled to the control circuit,

wherein the control circuit is configured to initiate communicating the heart rate information and the S2 heart sound information to a second medical device in response to the detected change in posture, and

wherein the system further includes the second medical device and the second medical device includes a processor circuit configured to detect that the subject satisfies an orthostatic intolerance symptomatic threshold according to the heart rate information and the S2 heart sound information, and generate an alert in response to the detecting.

8. The system of claim 7 , wherein the second device includes a port configured to receive patient symptom information, and wherein the processor circuit configured to trend the heart rate information, the S2 heart sound information, and the posture information and adjust one or more orthostatic intolerance symptomatic thresholds using the patient symptom information and the trended heart rate information and the information related to blood pressure.

9. The system of claim 7 , wherein the processor circuit is configured to determine one of that blood pressure of the subject is less than a specified blood pressure threshold, that a change in blood pressure of the subject is greater than a specified blood pressure change threshold, or that the heart rate exceeds a heart rate change threshold without a change in blood pressure that exceeds a blood pressure change threshold, and generate an indication of orthostatic intolerance in response to the detection.

10. A method of controlling operation of an ambulatory medical device to detect orthostatic intolerance, the method comprising:

sensing a posture signal, wherein the posture signal includes posture information of a subject;

sensing a cardiac signal, wherein the sensed cardiac signal includes heart rate information of the subject;

sensing a heart sound signal indicative of mechanical cardiac activity of the subject, the heart sound signal comprising S2 heart sound information;

detecting a change in posture of the subject using the sensed posture signal;

initiating collection of the heart rate information and the S2 heart sound information;

determining, using the S2 heart sound information, a first indication that:

amplitude of the S2 heart sound is greater than a specified S2 heart sound amplitude change threshold, that a change in amplitude of the S2 heart sound is greater than a specified S2 heart sound amplitude change threshold;

that the heart rate of the subject exceeds a heart rate change threshold and a change in amplitude of the S2 heart sound energy is less than an S2 amplitude change threshold; or

that the time over with which a detected change in an S2 heart sound parameter occurs following a detected posture transition satisfies a specified threshold time; and

generating an indication of orthostatic intolerance in response to the determined first indication and the detected posture change.

11. The method of claim 10 , including determining, using collected heart rate information and collected S2 heart sound information, one of that blood pressure of the subject is less than a specified blood pressure threshold, that a change in blood pressure of the subject is greater than a specified blood pressure change threshold, or that the heart rate exceeds a specified heart rate change threshold while change in blood pressure is less than a specified blood pressure change threshold; and

generating an indication of orthostatic intolerance in response to the detection.

12. The method of claim 10 , wherein sensing the heart sound signal includes sensing a signal representative of blood pressure of the subject using an implantable blood pressure sensing circuit.

13. An ambulatory medical device system to monitor orthostatic intolerance of a subject, the system comprising:

a posture sensing circuit configured to detect a change in posture of a subject;

a cardiac signal sensing circuit configured to generate a sensed cardiac signal, wherein the sensed cardiac signal includes heart rate information of the subject;

a physiologic sensing circuit configured to generate a physiologic signal in which an arterial pulsatile waveform is detectable at a body location remote from the subject's heart, wherein the physiologic signal includes information related to blood pressure of the subject; a storage buffer; and

a control circuit operatively coupled to the posture sensing circuit and the storage buffer and configured to initiate storage of a portion of the heart rate information and a portion of the information related to blood pressure in response to a detected change in posture of the subject and to generate an indication of orthostatic intolerance using the heart rate information and the information related to blood pressure of the subject in response to the detected change in posture of the subject,

wherein the control circuit is configured to store, as the information related to blood pressure, a pulsatile transmit time (PTT) determined using a fiducial detected in the sensed cardiac signal and a detected arterial pulsatile waveform.

14. The system of claim 13 , wherein the physiologic sensing circuit includes a heart sound sensing circuit configured to generate a sensed heart sound signal indicative of mechanical cardiac activity of the subject, wherein the control circuit is configured to initiate storage of S2 heart sound information as the information related to blood pressure and storage of the heart rate information in response to the detected change in posture.

15. The system of claim 14 , wherein the control circuit is configured to determine, using the S2 heart sound information, one of that amplitude of the S2 heart sound is less than a specified S2 amplitude threshold, that a change in amplitude of the S2 heart sound is greater than a specified S2 heart sound amplitude change threshold, that the heart rate exceeds a heart rate change threshold without a change in amplitude of the S2 heart sound that exceeds an S2 amplitude change threshold, or that the time over with which a detected change in an S2 heart sound parameter occurs following a detected posture transition satisfies a specified threshold time, and wherein the control circuit is configured to generate the indication of orthostatic intolerance in response to the detection.

16. The system of claim 13 , wherein the physiologic sensing circuit includes an implantable blood pressure sensing circuit.

17. The system of claim 13 , wherein the control circuit is configured to initiate the storage of the heart rate information and the information related to blood pressure in response to detecting the subject changing from a supine posture to an upright posture.

18. The system of claim 13 , including a communication circuit operatively coupled to the control circuit and configured to communicate wireless signals with a second separate device, and wherein the control circuit is configured to enable the storing of the heart rate information and the information related to blood pressure in response to a signal received via the communication circuit.

19. The system of claim 13 , including a communication circuit operatively coupled to the control circuit,

wherein the control circuit is configured to initiate communicating the heart rate information and the information related to blood pressure to a second medical device in response to the detected change in posture, and

wherein the system further includes the second medical device and the second medical device includes a processor circuit configured to detect that the subject satisfies an orthostatic intolerance symptomatic threshold according to the heart rate information and the information related to blood pressure, and generate an alert in response to the detecting.

20. The system of claim 19 , wherein the second device includes a port configured to receive patient symptom information, and wherein the processor circuit configured to trend the heart rate information, the information related to blood pressure, and the posture information and adjust one or more orthostatic intolerance symptomatic thresholds using the patient symptom information and the trended heart rate information and the information related to blood pressure.