IMPLANTABLE TISSUE PERFUSION SENSING SYSTEM AND METHOD

• US 20080208020A1
• Filed: 02/28/2008
• Published: 08/28/2008
• Est. Priority Date: 02/28/2007
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Cinbis, Can, Carney, James K.
• Granted Patent: US 8,886,465 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting

Abstract

A medical device for sensing cardiac events that includes a plurality of light sources capable of emitting light at a plurality of wavelengths, and a detector to detect the emitted light. A processor determines a plurality of light measurements in response to the emitted light detected by the detector, updates, for each of the plurality of wavelengths, a first normalization coefficient and a second normalization coefficient in response to the detected emitted light, and adjusts the determined plurality of light measurements in response to the first normalization coefficient and the second normalization coefficient.

Claims

1. A medical device for sensing cardiac events, comprising:

a plurality of light sources capable of emitting light at a plurality of wavelengths;

a detector to detect the emitted light; and

a processor to determine a plurality of light measurements in response to the emitted light detected by the detector, to update, for each of the plurality of wavelengths, a first normalization coefficient and a second normalization coefficient in response to the detected emitted light, and to adjust the determined plurality of light measurements in response to the first normalization coefficient and the second normalization coefficient.

2. The device of claim 1, further comprising a timing unit to determine when to update the first normalization coefficient and the second normalization coefficient dependent on a time period since initiation of the device.

3. The device of claim 2, wherein the timing unit determines timing of a next update in response to relative changes between a current update of the first normalization coefficient and the second normalization coefficient and a previous update of the first normalization coefficient and second normalization coefficient.

4. The device of claim 1, further comprising an activity sensor to sense a physical mode of a patient, wherein the processor updates the first normalization coefficient and the second normalization coefficient in response to the sensed physical mode.

5. The device of claim 1, wherein the first normalization coefficient corresponds to peak-to-peak changes in the plurality of light measurements and the second normalization coefficient corresponds to average amplitudes of the plurality of light measurements.

6. The device of claim 5, wherein the processor determines a first baseline associated with the first normalization coefficient and a second baseline associated with the second normalization coefficient, and wherein the first normalization coefficient is updated in response to a ratio of the first baseline and an average of the peak-to-peak changes in the plurality of light measurements, and the second normalization coefficient is updated in response to a difference between a product of the previously updated first normalization coefficient and a current average amplitude and the second baseline.

7. The device of claim 6, wherein the processor adjusts a current light measurement of the plurality of light measurements in response to a difference between a product of the current updated first normalization coefficient and the current light measurement and the current updated second normalization coefficient.

8. The device of claim 4, wherein the physical mode corresponds to walking, and wherein the first normalization coefficient corresponds to vibration amplitudes associated with the plurality of light measurements and the second normalization coefficient corresponds to average pulse amplitudes associated with the plurality of light measurements.

9. The device of claim 8, wherein the processor determines a first baseline associated with the first normalization coefficient and a second baseline associated with the second normalization coefficient, and wherein the first normalization coefficient is updated in response to a ratio of the first baseline and a current vibration amplitude, and the second normalization coefficient is updated in response to a difference between a product of the previously updated first normalization coefficient and a current average amplitude and the second baseline.

10. The device of claim 9, wherein the processor adjusts a current light measurement of the plurality of light measurements in response to a difference between a product of the current updated first normalization coefficient and a current light measurement of the plurality of light measurements and the current updated second normalization coefficient.

11. A medical device for sensing cardiac events, comprising:

a plurality of light sources capable of emitting light at a plurality of wavelengths;

a detector to detect the emitted light;

a processor to determine a plurality of light measurements in response to the emitted light detected by the detector, to update, for each of the plurality of wavelengths, a first normalization coefficient and a second normalization coefficient in response to the detected emitted light, and to adjust the determined plurality of light measurements in response to the first normalization coefficient and the second normalization coefficient; and

a timing unit to determine when to update the first normalization coefficient and the second normalization coefficient, wherein the first normalization coefficient corresponds to peak-to-peak changes in the plurality of light measurements and the second normalization coefficient corresponds to average amplitudes of the plurality of light measurements, and wherein the processor determines a first baseline associated with the first normalization coefficient and a second baseline associated with the second normalization coefficient, the first normalization coefficient being updated in response to a ratio of the first baseline and an average of the peak-to-peak changes in the plurality of light measurements, and the second normalization coefficient being updated in response to a difference between a product of the previously updated first normalization coefficient and a current average amplitude and the second baseline.

12. The device of claim 11, further comprising a timing unit to determine when to update the first normalization coefficient and the second normalization coefficient dependent on a time period since initiation of the device.

13. A method of adjusting sensing in a medical device, comprising:

determining light emitted by a plurality of light sources at a plurality of wavelengths received at a detector;

determining a plurality of light measurements in response to the emitted light detected by the detector;

updating, for each of the plurality of wavelengths, a first normalization coefficient and a second normalization coefficient in response to the detected emitted light; and

adjusting the determined plurality of light measurements in response to the first normalization coefficient and the second normalization coefficient.

14. The method of claim 13, further comprising determining when to update the first normalization coefficient and the second normalization coefficient in response to a time period since initiation of the device.

15. The method of claim 13, further comprising determining timing of a next update in response to relative changes between a current update of the first normalization coefficient and the second normalization coefficient and a previous update of the first normalization coefficient and second normalization coefficient.

16. The method of claim 13, wherein the first normalization coefficient corresponds to peak-to-peak changes in the plurality of light measurements and the second normalization coefficient corresponds to average amplitudes of the plurality of light measurements.

17. The method of claim 16, further comprising:

determining a first baseline associated with the first normalization coefficient and a second baseline associated with the second normalization coefficient;

updating the first normalization coefficient in response to a ratio of the first baseline and an average of the peak-to-peak changes in the plurality of light measurements; and

updating the second normalization coefficient in response to a difference between a product of the previously updated first normalization coefficient and a current average amplitude and the second baseline.

18. The method of claim 17, further comprising adjusting a current light measurement of the plurality of light measurements in response to a difference between a product of the current updated first normalization coefficient and the current light measurement and the current updated second normalization coefficient.

19. The method of claim 13, further comprising:

sensing a physical mode of a patient; and

updating the first normalization coefficient and the second normalization coefficient in response to the sensed physical mode, wherein the physical mode corresponds to walking, and wherein the first normalization coefficient corresponds to vibration amplitudes associated with the plurality of light measurements and the second normalization coefficient corresponds to average pulse amplitudes associated with the plurality of light measurements.

20. The method of claim 19, further comprising:

determining a first baseline associated with the first normalization coefficient and a second baseline associated with the second normalization coefficient;

updating the first normalization coefficient in response to a ratio of the first baseline and a current vibration amplitude; and

updating the second normalization coefficient in response to a difference between a product of the previously updated first normalization coefficient and a current average amplitude and the second baseline.

21. The method of claim 20, further comprising adjusting a current light measurement of the plurality of light measurements in response to a difference between a product of the current updated first normalization coefficient and a current light measurement of the plurality of light measurements and the current updated second normalization coefficient.