A method and apparatus for non-invasively determining the blood
oxygen saturation level within a subject's tissue is provided that utilizes a near
infrared spectrophotometric (NIRS) sensor capable of transmitting a
light signal into the tissue of a subject and sensing the
light signal once it has passed through the tissue via
transmittance or reflectance. The method includes the steps of: (1) transmitting a
light signal into the subject's tissue, wherein the
transmitted light signal includes a first
wavelength, a second
wavelength, and a third
wavelength; (2) sensing a first intensity and a second intensity of the light
signal, along the first, second, and third wavelengths after the light
signal travels through the subject at a first and second predetermined distance; (3) determining an attenuation of the light signal for each of the first, second, and third wavelengths using the sensed first intensity and sensed second intensity of the first, second, and third wavelengths; (4) determining a difference in attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength; and (5) determining the blood
oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength.