Generalized pulse oximetry method for persons of all skin pigmentations

Abstract

The present invention is an in vivo non-invasive method and apparatus for the measurement of the arterial blood oxygen saturation status of a patient, the method is a generalized improvement on conventional pulse oximetry to correct for its skin pigmentation bias and significant errors in oxygen saturation assessment in the presence of methemoglobin. The method requires an additional red light sensor with an infrared long pass filter to conventional pulse oximetry, and utilizes red and infrared light and sensors to non-invasively measure the peripheral pulse optical plethysmograph waveforms (PPG) at three light wavelengths, red, long pass red and infrared, positioned over a finger, or ear or other extremity, and from the pulse oximetric ratio of ratios transforms the PPG measurements by a processing device that determines the subject's arterial blood oxygen saturation directly, without the need for an empirical correction as is required in conventional pulse oximetry. The method determines the red transmitted light waveform and thus quantifies the wavelength shift from the incident red light due to the subject's skin pigmentation, and from in vivo hemoglobin extinction coefficients, determines the relative concentrations of oxygenated and deoxygenated hemoglobin and methemoglobin in the subject's arterial blood.