Fig. 1. Visible light spectroscopy versus pulse oximetry during hypoxemia. Muscle microvascular hemoglobin oxygen saturation (StO2) in pigs and esophageal StO2in human subjects were linearly correlated with oxygen saturation measured by pulse oximetry (SpO2) during the induction of hypoxemia (animals, r 2= 0.98; humans, r 2=0.87).