Adaptive calibration pulsed oximetry method and device

• US 20030109776A1
• Filed: 07/15/2002
• Published: 06/12/2003
• Est. Priority Date: 07/14/1999
• Status: Active Grant

• Current Assignee: Providence Health System - Oregon
• Original Assignee: Providence Health System - Oregon
• Inventors: Jacques, Steven L.
• Granted Patent: US 6,760,609 B2
• Time in Patent Office: Days
• US Class Current: 600/331
• 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 method for determining an arterial blood oxygen saturation level according to this invention includes measuring the light transmittance through tissue of light of a first wavelength and a second wavelength. A steady-state component of the measured light transmission is used to select an appropriate calibration curve. A pulsatile component of the measured light transmission is used to determine the arterial blood oxygen saturation level using the selected calibration curve. An oximetry system is also provided. An improved oximetry system is further provided wherein a plurality of light transmission measurements are used to determine a blood oxygen saturation level.

Claims

1. A method of calibrating an oximeter and determining an arterial blood oxygen saturation level in tissue, comprising:

using a plurality of measurements to determine properties of a light transmission passing through or reflected from a tissue; and

using the properties of the light transmission or reflection to select a calibration curve, said calibration curve representing a level of arterial blood oxygen saturation in relation to a pulsatile factor.

2. A method according to claim 1, wherein the plurality of measurements are obtained by varying a separation distance between a light source and a light detector to detect light passed through or reflected from different portions of the tissue.

3. A method according to claim 1, wherein the plurality of measurements are obtained by using two or more light sources and at least one light detector, wherein the light sources and detector are arranged so that the detector detects light passed through or reflected from different portions of the tissue.

4. A method according to claim 1, wherein the plurality of measurements are obtained by using at least one light source and two or more detectors, wherein the light source and detectors are arranged so that the two or more detectors detect light passed through or reflected from different portions of the tissue.

5. A method according to claim 1, wherein the plurality of measurements are obtained by varying a position of a light source or a light detector relative to the tissue to detect light passed through or reflected from different portions of the tissue.

6. A method according to claim 1, wherein the plurality of measurements are obtained by varying a wavelength of a light source being supplied to the tissue.

7. A method according to claim 6, wherein varying a wavelength of a light source comprises supplying light of two or more wavelengths in the visible to near-infrared wavelength range to the light source.

8. A method according to claim 1, wherein the plurality of measurements are obtained by modulating a light source being supplied to the tissue.

9. A method according to claim 8, wherein the light source is modulated at various frequencies between 50 kHz and 1 GHz, and wherein the phase and modulation of the transmitted light are measured.

10. A method according to claim 9, further comprising using the phase and modulation measurements to determine the properties of the light transmission used to select the calibration curve.

11. A method according to claim 1, wherein the plurality of measurements are obtained by digitally modulating a light source transmitted through or reflected from the tissue.

12. A method according to claim 11 wherein the light source is digitally modulated as a unique source stream of pulses of variable pulse duration.

13. A method according to claim 11, wherein the light source is digitally modulated with pulse durations of an order of magnitude approximately between 1 ns and 1 μ

s.

14. A method according to claim 11, further comprising detecting the light transmitted from the light source through or reflected from the tissue and correlating the detected light to the source stream of pulses to determine a delay time.

15. A method according to claim 1, wherein the properties of the light transmission comprise values for a plurality of variables, said variables comprising a vessel wall thickness, an average path length of photons, and optical properties of the tissue.

16. A method according to claim 1, wherein the properties are associated with the nonpulsatile component of the light transmission.

17. A method according to claim 1, further comprising normalizing a steady-state component of the light transmission or reflection to remove the effects of variation of a strength of a light source and a sensitivity of a transducer from the steady-state component.

18. An oximetry apparatus, comprising:

a plurality of light sources arranged in various locations in proximity to a tissue sample;

a plurality of detectors arranged to detect light transmitted from the plurality of light sources onto the tissue sample;

a measurement device configured to receive signals from the light detectors and provide measurements for a plurality of variables; and

a calculation device configured to use the measurements from the measurement device to calculate an oxygen saturation level.

19. An oximetry apparatus according to claim 18, wherein the plurality of light sources and corresponding ones of the plurality of light detectors are spaced at varying distances apart from each other so as to provide varying path lengths for the light transmission from the light sources to the light detectors.

20. An oximetry apparatus according to claim 18, wherein the plurality of variables comprise a vessel wall thickness, an average path length of photons, and optical properties of the tissue sample.

21. An oximetry apparatus, comprising:

a light source configured to transmit light onto a tissue sample;

a light detector arranged to detect the light transmitted from the light source onto the tissue sample;

a measurement device configured to receive signals from the light detector and obtain a plurality of measurements to determine values for a plurality of variables;

means for varying the characteristics of the light transmitted from the light source to produce the plurality of measurements; and

a calculation device configured to use the variable values to determine a blood oxygen saturation level of the tissue sample.

22. An oximetry apparatus according to claim 21, wherein means for varying the characteristics of the light transmitted from the light source to produce the plurality of measurements comprises a means for varying a wavelength of the light source.

23. An oximetry apparatus according to claim 21, wherein the means for varying the characteristics of the light transmitted from the light source to produce the plurality of measurements comprises a means for modulating the light source at various frequencies.

24. An oximetry apparatus according to claim 21, wherein the means for varying the characteristics of the light transmitted from the light source to produce the plurality of measurements comprises a digital modulator for digitally modulating the light source as a stream of pulses.

25. An oximetry apparatus according to claim 21, wherein the plurality of measurements comprises five or more separate and independent measurements.