Absolute calibrated tissue oxygen saturation and total hemoglobin volume fraction

• US 8,346,332 B2
• Filed: 06/10/2010
• Issued: 01/01/2013
• Est. Priority Date: 06/10/2009
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Kuhn, Jonathan L., Anderson, David A., Cinbis, Can, O'Brien, Richard J., Cho, Yong K., Mullen, Thomas J., Scheiner, Avram, Katra, Rodolphe P.
• Primary Examiner(s): BLACKMAN, ROCHELLE ANN J
• Application Number:
  US12/797,811
• Publication Number:
  US 20100317941A1
• Time in Patent Office: 936 Days
• Field of Search: 600/323, 600/324, 600/322, 600/320, 600/328, 600/331, 600/334
• US Class Current: 600/323
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61N 1/36557 controlled by chemical substances in blood
• CPC Class Codes: A61N 1/37258 Alerting the patient

Abstract

A medical device for monitoring a patient condition includes a first combination of a light source and a light detector to emit light into a volume of tissue, detect light scattered by the volume of tissue, and provide a first output signal corresponding to an intensity of the detected light. A control module is coupled to the light source to control the light source to emit light at least four spaced-apart light wavelengths, and a monitoring module is coupled to the light detector to receive the output signal, compute a measure of tissue oxygenation in response to the light detector output signal, and detect tissue hypoxia using the measure of tissue oxygenation.

Claims

1. A method for monitoring a patient condition in a medical device having an optical sensor, the method comprising:

controlling the optical sensor to emit light comprising at least four spaced-apart light wavelengths;

detecting light scattered by a volume of tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to an intensity of the scattered light, the scattered light comprising light scattered by arterial and venous blood volumes present in the volume of tissue;

computing a measure of tissue oxygenation correlated to the partial pressure of oxygen in the tissue from the detected light; and

detecting tissue hypoxia in response to the computed measure of tissue oxygenation.

2. The method of claim 1, wherein computing the measure of tissue oxygenation comprises:

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

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

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

3. The method of claim 1, further comprising computing a measure of total hemoglobin volume fraction in response to the measure of tissue oxygen saturation.

4. The method of claim 1, further comprising:

emitting light into a volume of arterial blood;

detecting light scattered by the volume of arterial blood;

computing a measure of arterial oxygen saturation from the detected light scattered by the volume of arterial blood; and

detecting tissue hypoxia in response to the measure of arterial oxygen saturation.

5. The method of claim 1, further comprising adjusting a therapy in response to the measure of tissue oxygenation.

6. The method of claim 1, further comprising adjusting a heart failure therapy in response to detecting the tissue hypoxia.

7. The method of claim 1, further comprising detecting an episode of disordered breathing in response to the detected tissue hypoxia.

8. The method of claim 7, further comprising controlling a therapy delivery in response to the detecting episode of disordered breathing.

9. The method of claim 8, wherein controlling a therapy delivery comprises adjusting a continuous positive airway pressure.

10. The method of claim 1, further comprising delivering a therapy to the patient and adjusting the therapy in response to the tissue oxygenation measurement.

11. The method of claim 1, further comprising:

computing an absolute tissue oxygen saturation in response to the detected light;

computing a total tissue hemoglobin volume fraction in response to the detected light and the computed absolute tissue oxygen saturation;

the tissue oxygenation measurement comprising both the absolute tissue oxygen saturation and the total tissue hemoglobin volume fraction.

12. The method of claim 11, further comprising:

computing a tissue uniformity index in response to the tissue oxygen saturation and the total tissue hemoglobin volume fraction measurements; and

selecting a sensor position in response to the tissue uniformity index.

13. A medical device system, comprising:

a first combination of a light source and a light detector to emit light into a volume of tissue, detect light scattered by the volume of tissue, the scattered light comprising light scattered by arterial and venous blood volumes present in the volume of tissue, and generate a first output signal corresponding to an intensity of the detected light;

a control module coupled to the light source to control the light source to emit light comprising at least four spaced-apart light wavelengths; and

a monitoring module coupled to the light detector to receive the output signal, compute a measure of tissue oxygenation correlated to the partial pressure of oxygen in the tissue in response to the light detector output signal, and detect tissue hypoxia using the measure of tissue oxygenation.

14. The system of claim 13, wherein computing the measure of tissue oxygen saturation comprises:

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

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

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

15. The system of claim 13, wherein the monitoring module computes a measure of total hemoglobin volume fraction in response to the measure of tissue oxygen saturation.

16. The system of claim 13, further comprising a second combination of a light source and light detector to detect light scattered by a volume of arterial blood and to generate a second output signal corresponding to an intensity of the detected light scattered by the volume of arterial blood, wherein the monitoring module is coupled to the light detector of the second combination, computes a measure of arterial oxygen saturation in response to the second output signal, and detects tissue hypoxia in response to the measure of arterial oxygen saturation.

17. The system of claim 13, further comprising:

a therapy delivery module; and

a therapy delivery controller coupled to the monitoring module and the therapy delivery module, the therapy delivery controller adjusting a therapy in response to the measure of tissue oxygenation.

18. The system of claim 13, further comprising an elongated electrical lead, wherein the first combination of the light source and the light detector are positioned along the lead.

19. The system of claim 13, further comprising:

a therapy delivery module; and

a controller coupled to the monitoring module and the therapy delivery module to adjust a therapy in response to detecting a kidney hypoxia.

20. The system of claim 13, wherein the monitoring module is configured to detect an episode of disordered breathing in response to the detected tissue hypoxia.

21. The system of claim 20, further comprising:

a therapy delivery module; and

a controller coupled to the therapy delivery module and the controller to control therapy delivery in response to the detected episode of disordered breathing.

22. The system of claim 21, wherein the therapy delivery module comprises a continuous positive airway pressure (CPAP) machine, and wherein controlling the therapy delivery comprises adjusting the CPAP machine.

23. A computer readable medium having computer executable instructions for performing a method for monitoring a patient condition in a medical device having an optical sensor, the method comprising:

controlling an optical sensor to emit light comprising at least four spaced-apart light wavelengths;

detecting light scattered by a volume of tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to an intensity of the scattered light, the scattered light comprising light scattered by arterial and venous blood volumes present in the volume of tissue;

computing a measure of tissue oxygenation correlated to the partial pressure of oxygen in the tissue from the detected light; and

detecting tissue hypoxia in response to the computed measure of tissue oxygenation.