Pulse oximeter and sensor optimized for low saturation

• US 6,662,033 B2
• Filed: 06/14/2001
• Issued: 12/09/2003
• Est. Priority Date: 04/01/1994
• Status: Expired due to Fees

• Current Assignee: Nellcor Incorporated (Medtronic Plc)
• Original Assignee: Nellcor Incorporated (Medtronic Plc)
• Inventors: Mannheimer, Paul D., Nierlich, Steve L., Ruskewicz, Stephen J., Casciani, James R.
• Primary Examiner(s): Winakur, Eric F.
• Assistant Examiner(s): Kremer, Matthew J
• Application Number:
  US09/882,371
• Publication Number:
  US 20020082489A1
• Time in Patent Office: 908 Days
• Field of Search: 600/322-323, 600/338, 600/309-310, 600/313
• US Class Current: 600/338
• CPC Class Codes: A61B 2562/0242 for varying or adjusting the optical path length in the tissue
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1464 specially adapted for foetal tissue
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts

Abstract

A pulse oximeter sensor with a light source optimized for low oxygen saturation ranges and for maximizing the immunity to perturbation induced artifact. Preferably, a red and an infrared light source are used, with the red light source having a mean wavelength between 700-790 nm. The infrared light source can have a mean wavelength as in prior art devices used on patients with high saturation. The sensor of the present invention is further optimized by arranging the spacing between the light emitter and light detectors to minimize the sensitivity to perturbation induced artifact. The present invention optimizes the chosen wavelengths to achieve a closer matching of the absorption and scattering coefficient products for the red and IR light sources. This optimization gives robust readings in the presence of perturbation artifacts including force variations, tissue variations and variations in the oxygen saturation itself.

Claims

1. A method for measuring blood oxygen saturation in a fetus, comprising the steps of:

providing a sensor and a pulse oximeter;

selecting a far red and infrared light source and a light detector;

detecting light at said detector including an infrared wavelength spectrum useful for measuring oxygen saturation in a patient with high saturation, the detected light including a far red wavelength spectrum which has a mean wavelength between 700 and 790 nanometers;

placing said light sources in a single encapsulated package and mounting said package on said sensor;

placing said sensor on said fetus;

measuring an intensity of light from said light source at said light detector after scattering through a portion of said fetus; and

determining said blood oxygen saturation using said intensity and said pulse oximeter.

2. The method of claim 1 further comprising the steps of:

selecting a second red light source;

selecting a wavelength spectrum of said second red light source to have a mean wavelength less than 700 nanometers; and

selectively activating either or both said first mentioned or second red light source.

3. A fetal pulse oximeter sensor comprising:

a housing;

at least one light source mounted in said housing;

at least one detector mounted in said housing;

means for detecting light subsequent to being scattered by fetal tissue, the light including an infrared light spectrum, said infrared spectrum having a range useful for measuring oxygen saturation in a patient with high saturation, the detected light also including a red light spectrum, said red light spectrum having a mean wavelength between 700 and 790 nanometers;

said detector being mounted in said housing spaced from said light sources and positioned to detect light from said light sources; and

in which the combination of the light source and detector limit light signals received at the detector from the light source to no more than three spectra.

4. The sensor of claim 3 wherein said light source comprises at least one LED.

5. The sensor of claim 3 wherein said light source comprises red and infrared light sources spaced from said detector by at least 10 mm.

6. The sensor of claim 3 wherein said light source comprises red and infrared light sources spaced from said detector by at least 14 mm.

7. The sensor of claim 3 wherein said means for providing comprises a light source which emits a limited spectrum.

8. The sensor of claim 3 wherein said means for providing comprises a filter between said light source and said detector for passing a limited spectrum of light.

9. The sensor of claim 3 wherein said means for providing comprises a wavelength sensitive detector which detects a limited spectrum of light.

10. The sensor of claim 3 further comprising:

means for providing a red light spectrum having a mean wavelength less than 700 nanometers.

11. The sensor of claim 10 wherein

said means for providing a red light spectrum having a mean wavelength between 700 and 790 nanometers is a first light emitting diode;

and

said means for providing a red light spectrum having a mean wavelength less than 700 nanometers is a second light emitting diode.

12. A fetal pulse oximeter comprising:

an input connector for receiving at least first and second signals from a sensor obtained by scattering light through tissue of a fetus, the light having at least red and infrared spectrums and being limited to more than three spectra;

a memory storing coefficients suitable for said infrared spectrum having a range useful for measuring oxygen saturation in a patient with high saturation and said red light spectrum having a mean wavelength between 700 and 790 nanometers; and

a processor, coupled to said memory and said input connector, for calculating the oxygen saturation of said fetus using said coefficients.

13. The pulse oximeter of claim 12 wherein said memory further comprises:

coefficients for a red light spectrum having a mean wavelength less than 700 nanometers.

14. A fetal pulse oximeter sensor which comprises a housing with at least one light source and at least one light detector mounted in the housing in such a way that the detector is spaced from the light source and can detect light from the light source after scattering by fetal tissue, in which the combination of the light source and the light detector limit light signals received at the detector from the light source to no more than three spectra, a first spectrum including 735 nanometers at an intensity of at least 50% of the intensity of any other wavelengths in said first spectrum.

15. The sensor of claim 14, wherein a second spectrum has a mean wavelength of from 805 to 940 nm used, in conjunction with said first spectrum, for measuring oxygen saturation in a patient, said sensor being connectable to a pulse oximeter for using said first and second spectra to calculate arterial oxygen saturation.

16. A sensor as claimed in claim 14 in which a third spectrum has a mean wavelength near 660 nm.

17. The sensor of claim 14 wherein said sensor is a reflectance sensor.

18. The sensor of claim 14 wherein said sensor is a transmission sensor.

19. The sensor of claim 14 wherein said light source and said light detector are spaced apart by at least 10 cm.

20. The sensor of claim 14 wherein said light source and said light detector are spaced apart by at least 14 cm.

21. The sensor of claim 14 wherein only a single said light detector is provided in said sensor.