METHOD AND APPARATUS FOR POST-SHOCK EVALUATION USING TISSUE OXYGENATION MEASUREMENTS

• US 20110066204A1
• Filed: 07/29/2010
• Published: 03/17/2011
• Est. Priority Date: 09/11/2009
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Kuhn, Jonathan L., Havel, William J., Cinbis, Can, Anderson, David A.
• Granted Patent: US 8,630,708 B2
• Time in Patent Office: Days
• US Class Current: 607/17
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/6846 specially adapted to be brought in contact with an internal body part, i.e. invasive
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence
• CPC Class Codes: A61N 1/36557 controlled by chemical substances in blood
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

A method and device for delivering therapy that includes an electrode to sense cardiac signals and to deliver a therapy, a therapy delivery module coupled to the electrode to deliver a therapy via the electrode in response to the sensed cardiac signals, a sensor emitting light and detecting emitted light scattered by a tissue volume adjacent the sensor to generate a corresponding detected light intensity output signal, a control module coupled to the sensor to control light emission of the sensor in response to delivering the therapy; and a controller coupled to the therapy delivery module and the sensor, the controller configured to determine a tissue oxygenation measurement in response to the output signal, and determine whether the delivered therapy was successful in restoring cardiac hemodynamic function in response to the tissue oxygenation measurement.

Claims

1. A method of delivering therapy in a medical device, comprising:

sensing cardiac signals in a patient;

detecting an arrhythmia in response to the signals;

delivering an arrhythmia therapy in response to the arrhythmia detection;

controlling light emission of a sensor in response to delivering the arrhythmia therapy;

detecting emitted light scattered by a tissue volume adjacent the sensor to generate a corresponding detected light intensity output signal;

determining a tissue oxygenation measurement in response to the output signal; and

determining whether the arrhythmia therapy was successful in restoring cardiac hemodynamic function in response to the tissue oxygenation measurement.

2. The method of claim 1, wherein computing a tissue oxygenation measurement comprises:

computing a second derivative of a light attenuation spectrum measured by the sensor; and

computing a measurement of the total hemoglobin volume fraction in response to the second derivative, wherein determining whether the arrhythmia therapy was successful further comprises detecting an increasing trend in the total hemoglobin volume fraction.

3. The method of claim 1, wherein computing a tissue oxygenation measurement comprises:

computing a second derivative of a light attenuation spectrum measured by the sensor; and

computing a measure of tissue oxygen saturation in response to the computed second derivative.

4. The method of claim 3, wherein computing a tissue oxygenation measurement further comprises:

computing a measurement of the total hemoglobin volume fraction from the second derivative and the computed tissue oxygen saturation, and

computing a tissue oxygenation index in response to the measurements of tissue oxygen saturation and total hemoglobin volume fraction.

5. The method of claim 3, wherein computing the measure of tissue oxygen saturation comprises:

computing an attenuation for each of at least four wavelengths of detected light;

computing a second derivative of light attenuation with respect to wavelength for at least two wavelengths intermediate the at least four wavelengths; and

computing a scaled second derivative of one of the intermediate wavelengths.

6. The method of claim 1, further comprising setting a blanking interval beginning at a time of the arrhythmia therapy delivery, the measure of tissue oxygenation not being determined during the blanking interval.

7. The method of claim 6, further comprising:

receiving a signal corresponding to motion of the patient; and

determining an end point of the blanking interval in response to the signal corresponding to motion of the patient.

8. The method of claim 1, further comprising low pass filtering the measure of tissue oxygenation.

9. The method of claim 8, further comprising:

receiving a signal corresponding to motion of the patient; and

setting a pass band for the low pass filtering in response to the signal corresponding to motion of the patient.

10. The method of claim 1, further comprising:

simulating an arrhythmia in the patient;

terminating the simulated arrhythmia;

monitoring the tissue oxygenation measurement subsequent to terminating the simulated arrhythmia; and

setting a threshold for the tissue oxygenation measurement in response to the monitoring, wherein determining if the arrhythmia therapy was successful in restoring hemodynamic function comprises;

determining a trend in the tissue oxygenation measurement; and

comparing the trend to the stored threshold.

11. A medical device for delivering a therapy, comprising:

an electrode to sense cardiac signals and to deliver a therapy;

a therapy delivery module coupled to the electrode to deliver a therapy via the electrode in response to the sensed cardiac signals;

a sensor emitting light and detecting emitted light scattered by a tissue volume adjacent the sensor to generate a corresponding detected light intensity output signal;

a control module coupled to the sensor to control light emission of the sensor in response to delivering the therapy; and

a controller coupled to the therapy delivery module and the sensor, the controller configured to determine a tissue oxygenation measurement in response to the output signal, and determine whether the delivered therapy was successful in restoring cardiac hemodynamic function in response to the tissue oxygenation measurement.

12. The device of claim 11, wherein computing a tissue oxygenation measurement comprises:

computing a second derivative of a light attenuation spectrum measured by the sensor; and

computing a measurement of the total hemoglobin volume fraction in response to the second derivative, wherein determining whether the arrhythmia therapy was successful further comprises detecting an increasing trend in the total hemoglobin volume fraction.

13. The device of claim 11, wherein computing a tissue oxygenation measurement comprises:

computing a second derivative of a light attenuation spectrum measured by the sensor; and

computing a measure of tissue oxygen saturation in response to the computed second derivative.

14. The device of claim 13, wherein computing a tissue oxygenation measurement further comprises:

computing a measurement of the total hemoglobin volume fraction from the second derivative and the computed tissue oxygen saturation, and

computing a tissue oxygenation index in response to the measurements of tissue oxygen saturation and total hemoglobin volume fraction.

15. The device of claim 13, wherein computing a measure of tissue oxygen saturation comprises:

computing an attenuation for each of at least four wavelengths of detected light;

computing a second derivative of light attenuation with respect to wavelength for at least two wavelengths intermediate the at least four wavelengths; and

computing a scaled second derivative of one of the intermediate wavelengths.

16. The device of claim 11, wherein the processor is further configured to set a blanking interval beginning at a time of the delivered therapy, the measure of tissue oxygenation not being determined during the blanking interval.

17. The device of claim 16, further comprising a motion sensor to sense motion and generate a corresponding motion signal, wherein the processor determines an end point of the blanking interval in response to the motion signal.

18. The device of claim 11, further comprising:

a filter to low pass filter the measure of tissue oxygenation; and

a motion sensor to sense motion and generate a corresponding motion signal, wherein the processor is further configured to set a pass band for the low pass filtering in response to the motion signal.

19. The device of claim 14, wherein the controller is further configured to deliver a signal via the therapy delivery module and the electrode to simulate an arrhythmia, and deliver a therapy via the therapy delivery module and the electrode to terminate the simulated arrhythmia, monitor tissue oxygenation measurements subsequent to terminating the simulated arrhythmia, and set a trend threshold for the tissue oxygenation measurement in response to the monitoring, wherein determining whether the delivered arrhythmia therapy restored cardiac hemodynamic function comprises:

determining a trend in the tissue oxygenation measurement; and

comparing the trend to the trend threshold.

20. A computer readable medium having computer executable instructions for performing a method comprising:

sensing cardiac signals in a patient;

detecting an arrhythmia in response to the signals;

delivering an arrhythmia therapy in response to the arrhythmia detection;

controlling light emission of a sensor in response to delivering the arrhythmia therapy;

detecting emitted light scattered by a tissue volume adjacent the sensor to generate a corresponding detected light intensity output signal;

determining a tissue oxygenation measurement in response to the output signal; and

determining whether the arrhythmia therapy was successful in restoring cardiac hemodynamic function in response to the tissue oxygenation measurement.