Optical device

• US 7,236,813 B2
• Filed: 11/22/2004
• Issued: 06/26/2007
• Est. Priority Date: 08/13/1998
• Status: Expired due to Fees

• Current Assignee: Whitland Research Ltd. (Edwards Lifesciences Corporation)
• Original Assignee: Edwards Lifesciences Corporation
• Inventors: Parker, Dawood
• Primary Examiner(s): Winkaur; Eric
• Assistant Examiner(s): BERHANU, ETSUB D
• Application Number:
  US10/994,682
• Publication Number:
  US 20050101850A1
• Time in Patent Office: 946 Days
• Field of Search: 600/322, 600/323, 600/331, 600/338, 600/336
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/1491 Heated applicators

Abstract

A method for monitoring blood oxygen saturation (SO₂) includes the steps of calculating an estimate of SO₂ in the blood and correcting the estimate by a scaling factor. A preferred embodiment of the method includes the steps of transmitting light containing a plurality of wavelengths into the blood; measuring a remitted spectrum over the plurality of wavelengths; calculating a measured blood absorption spectrum from the remitted spectrum; estimating local rates of change in the measured blood absorption spectrum at a plurality of the wavelengths; and calculating the estimate of SO₂ as a function of absolute values of the local rates of change of the measured blood absorption spectrum.

Claims

1. A method for SO₂ monitoring, comprising the steps of:

calculating an estimate of SO₂ in blood to be monitored;

correcting said estimate of SO₂ in blood by a scaling factor;

transmitting light containing a plurality of wavelengths into the blood;

measuring a remitted spectrum over the plurality of wavelengths;

calculating a measured blood absorption spectrum from the remitted spectrum;

estimating local rates of change in the measured blood absorption spectrum at a plurality of the wavelengths, including at least one isobestic wavelength; and

,

calculating the estimate of SO₂ as a function of absolute values of the local rates of change of the measured blood absorption spectrum.

2. The method for SO₂ monitoring according to claim 1, wherein before said step of calculating the estimate of SO_2, further comprising the steps of:

removing effects of light scattering from the measured blood absorption spectrum;

calculating an area under the measured blood absorption spectrum after said step of removing effects of light scattering; and

,

normalizing the measured blood absorption spectrum by the area under the measured blood absorption spectrum determined during said step of calculating.

3. The method for SO₂ monitoring according to claim 1, further comprising the step of applying a Kubelka Monk transformation to the measured blood absorption spectrum.

4. The method for SO₂ monitoring according to claim 1, wherein the step of calculating the estimate of SO₂ comprises the steps of:

computing a hemoglobin index value as a function of absolute values of the local rates of change of the measured blood absorption spectrum between a plurality of pairs of isobestic points, whereby the hemoglobin index value is independent of blood oxygenation;

computing an oxygenation parameter as a function of absolute values of the local rates of change of the measured blood absorption spectrum between a plurality of isobestic points and at least one non-isobestic point, whereby the oxygenation parameter is dependent on blood oxygenation;

normalizing the oxygenation parameter by the hemoglobin index value; and

,

estimating SO₂ as a measure of the level of the normalized oxygenation parameter relative to a predetermined fully deoxygenated reference value and a fully oxygenated reference value.