Noninvasive optical method of measuring tissue and arterial saturation: anapplication to absolute pulse oximetry of the brain

We present a frequency-domain optical method for real-time noninvasive meas urement of absolute tissue and arterial saturation. This method is based on quantitative measurement of the tissue absorption spectrum (for tissue sat uration) and of the amplitude of the arterial-pulsation-induced absorption oscillations (for arterial saturation) at eight wavelengths in the range 63 3-841 nm. We report results obtained from readings taken from the forehead of a healthy volunteer, showing baseline saturation values of 74.7 +/- 0.2% (tissue) and 96.9 +/- 0.5% (arterial). These values dropped to minimum val ues of 71.6 +/- 0.2% and 90.0 +/- 0.2%, respectively, after 1 min of reduce d inspired oxygen concentration [10% (by volume) O-2 from a baseline value of 21% O-2]. (C) 1999 Optical Society of America.