Tissue oxygen measurement system
First Claim
1. A non-invasive method for determining the localized tissue PO2 of a sample tissue of a patient, comprising:
- 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.
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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.
108 Citations
24 Claims
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1. A non-invasive method for determining the localized tissue PO2 of a sample tissue of a patient, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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.
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4. The method of claim 3, wherein the algorithm is a partial least-squares fitting algorithm.
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5. The method of claim 3, wherein the relationship between the optical spectra and the tissue PO2 measurements is linear.
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6. The method of claim 3, wherein the relationship between optical spectra and the tissue PO2 measurements is non-linear.
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7. The method of claim 3, further comprising collecting a tissue value over an extended range of at least one parameter selected from the group consisting of temperature and pH, prior to processing the optical spectra and PO2 measurements.
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8. The method of claim 3, wherein the plurality of optical spectra are collected from the at least one representative tissue sample in vitro.
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9. The method of claim 1, further comprising determining tissue pH simultaneously from the optical reflectance spectrum.
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10. The method of claim 9, further comprising detecting a dysoxic tissue state.
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11. The method of claim 9, further comprising determining a level of ischemia of the sample tissue using both the calculated pH and localized tissue PO2 data.
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12. The method of claim 9, further comprising 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.
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13. The method of claim 1, wherein the sample tissue comprises muscle or organ.
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14. The method of claim 1, wherein the sample tissue is disposed underneath a covering tissue of the patient.
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15. The method of claim 14, wherein irradiating comprises 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;
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collecting comprises collecting radiation from the sample tissue which passes through the covering tissue to form the optical reflectance spectrum.
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16. The method of claim 14, wherein the covering tissue is skin.
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17. The method of claim 1, wherein the optical radiation has a wavelength between about 400 nm and 2500 nm.
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18. The method of claim 1, wherein the optical radiation is near infrared radiation.
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19. The method of claim 18, wherein the infrared radiation has a wavelength between about 450 nm and 1100 nm.
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20. The method of claim 1, wherein the localized tissue PO2 is in a PO2 range of about 0.0 to about 150 mmHg.
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21. The method of claim 1, wherein the sample tissue is accessed with an endoscope.
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22. A device for determining the PO2 of an in vivo tissue sample, comprising:
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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. - View Dependent Claims (23, 24)
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Specification