Tissue oxygen measurement system

• US 20030088163A1
• Filed: 10/11/2002
• Published: 05/08/2003
• Est. Priority Date: 10/15/2001
• Status: Active Grant

• Current Assignee: University Of Massachusetts
• Original Assignee: University Of Massachusetts
• Inventors: Soller, Babs R.
• Granted Patent: US 6,766,188 B2
• Time in Patent Office: Days
• US Class Current: 600/322
• CPC Class Codes: A61B 5/14539 for measuring pH
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes

Abstract

A device and method in accordance with the invention for determining the oxygen partial pressure (PO₂) of a tissue by irradiating the tissue with optical radiation such that the light is emitted from the tissue, and by collecting the reflected or transmitted light from the tissue to form an optical spectrum. A spectral processor determines the PO₂ level in tissue by processing this spectrum with a previously-constructed spectral calibration model. The tissue may, for example, be disposed underneath a covering tissue, such as skin, of a patient, and the tissue illuminated and light collected through the skin. Alternatively, direct tissue illumination and collection may be effected with a hand-held or endoscopic probe. A preferred system also determines pH from the same spectrum, and the processor may determine critical conditions and issue warnings based on parameter values.

Claims

1. A non-invasive method for determining the localized tissue PO₂ of a sample tissue of a patient, comprising the steps of:

irradiating the sample tissue with optical radiation such that the radiation propagates into the tissue to illuminate the sample tissue;

collecting light radiation emitted from the sample tissue, the light radiation having been reflected or transmitted from the tissue;

forming an optical reflectance spectrum of the collected light radiation; and

processing the optical reflectance spectrum formed with a predetermined mathematical model of tissue PO₂ to determine the localized tissue PO₂ of the sample tissue, wherein the mathematical model relates optical spectra to known tissue PO₂ values in tissue.

2. The method of claim 1, wherein the predetermined mathematical model of tissue PO₂ is constructed prior to the step of processing the optical reflectance spectrum.

3. The method of claim 2, wherein the predetermined mathematical model of tissue PO₂ is constructed by the steps of:

collecting a plurality of optical spectra from at least one representative tissue sample;

collecting a plurality of direct measurements of PO₂ from the same representative tissue sample over an extended range; and

processing the optical spectra and PO₂ measurements with a mathematical multivariate calibration algorithm to determine the relationship between the optical spectra and the tissue PO₂ measurements.

4. The method of claim 3, wherein the algorithm is a partial least-squares fitting algorithm.

5. The method of claim 3, wherein the relationship between the optical spectra and the tissue PO₂ measurements is linear.

6. The method of claim 3, wherein the relationship between optical spectra and the tissue PO₂ measurements is non-linear.

7. The method of claim 3, further including the step of collecting a tissue value over an extended range of at least one parameter selected from the group consisting of temperature and pH, prior to the step of processing the optical spectra and PO₂ measurements.

8. The method of claim 3, wherein the plurality of optical spectra are collected from the at least one representative tissue sample in vitro.

9. The method of claim 1, further including the step of determining tissue pH simultaneously from the optical reflectance spectrum.

10. The method of claim 9, further including the step of detecting a dysoxic tissue state.

11. The method of claim 9, further including the step of determining a level of ischemia of the sample tissue using both the calculated pH and localized tissue PO₂ data

12. The method of claim 9, further including the step of determining the success or failure of a resuscitation by comparing the calculated pH and localized tissue PO₂ data to predetermined values for pH and tissue PO₂.

13. The method of claim 1, wherein the sample tissue comprises muscle or organ.

14. The method of claim 1, wherein the sample tissue is disposed underneath a covering tissue of the patient.

15. The method of claim 14, wherein the step of irradiating includes irradiating the sample tissue with optical radiation not substantially absorbed by the covering tissue such that the radiation propagates through the covering tissue to irradiate the sample tissue;

and

the step of collecting includes collecting radiation from the sample tissue which passes through the covering tissue to form the optical reflectance spectrum.

16. The method of claim 14, wherein the covering tissue is skin.

17. The method of claim 1, wherein the optical radiation is between about 400 nm and 2500 nm.

18. The method of claim 1, wherein the optical radiation is near infrared radiation.

19. The method of claim 18, wherein the infrared radiation is between about 450 nm and 1100 nm.

20. The method of claim 1, wherein the localized tissue PO₂ is in a PO₂ range of about 0.0 to about 150 mmHg.

21. The method of claim 1, wherein the sample tissue is accessed with an endoscope.

22. A device for determining the PO₂ of an in vivo tissue sample, comprising:

a spectrometer for irradiating the tissue sample with optical radiation spanning a range of visible and near infrared (NIR) wavelengths, and for collecting a spectrum of light returned from the tissue sample, the spectrometer forming a spectral representation thereof; and

a microprocessor operative on the spectral representation to calculate the tissue PO₂ of the sample, the microprocessor being programmed to compare the spectral representation to a predetermined mathematical model of tissue PO₂ to determine the PO₂ of the sample.

23. The device of claim 22, wherein the spectrometer includes visible wavelengths above 400 nm.

24. The device of claim 22, wherein the predetermined mathematical model of tissue PO₂ relates a spectral representation of a representative tissue to tissue PO₂.