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Abstract

The disclosed invention is for use in extracting more accurate information from signals employed in pulse oximetry. Basically, pulse oximetry involves the illumination of arterial blood flowing in tissue with light at two wavelengths. Upon emerging from the tissue the light is received by a detector (38) that produces signals that are proportional to the intensity of the light received at each of the wavelengths. Each signal includes a slowly varying baseline component representing the attenuation .beta.(t) of light produced by bone, tissue, skin, and hair. The signals also include pulsatile components representing the attenuation .alpha.(t) produced by the changing blood volume and oxygen saturation within the finger. The signals produced by the detector (38) are converted by an analog-to-digital (A/D) converter (72) for subsequent analysis by a microcomputer (16). The microcomputer (16) extracts the following information from the signal corresponding to each wavelength. V.sub.H is determined to be the signal magnitude at a second pulse diastole. V.sub.L is, similarly, the signal magnitude at systole of the same pulse. A term .DELTA.V is identified equal in value to the difference in signal magnitudes at the adjacent systoles. Finally, values are determined for .DELTA.ts and .DELTA.tp, being the interval between an adjacent systole and diastole and the pulse period, respectively. The microcomputer (16) then determines a value for R.sub.OS in accordance with the relationship: ##EQU1## Empirically derived oxygen saturation curves are used to develop an indication of the oxygen saturation from the value of R.sub.OS computed.

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First Claim