Patent ID: 8423106

Claim:
A physiological monitor for determining blood oxygen saturation of a patient, the physiological monitor comprising: a pulse oximetry sensor, wherein the pulse oximetry sensor comprises: three or more light emitting diodes, wherein each light emitting diode is operative to emit light of a different wavelength; and a detector adapted to receive light from the three or more light emitting diodes after being attenuated by tissue of a medical patient, wherein the detector provides an output signal based at least in part upon the received light; and a processor configured to: compute a ratio based at least in part on three or more plethysmographic signals obtained from the output signal, the ratio configured to have reduced tolerance at lower blood oxygen saturation levels compared to a two wavelength blood oxygen saturation system, wherein the ratio comprises a quotient of a first weighted sum of the output signals corresponding to each of the light emitting diodes multiplied by a first set of vector coefficients and a second weighted sum of the output signals corresponding to each of the light emitting diodes multiplied by a second set of vector coefficients, the first and second sets of vector coefficients determined based upon calibration data or fitting of experimental data; and determine blood oxygen saturation based at least in part upon a blood oxygen saturation curve using said ratio, wherein said blood oxygen saturation curve is substantiall linear over a range of blood oxygen saturation values from about 70% to about 100%.