Effects of Normobaric Hypoxia on Oxygen Saturation Variability

The study is the first to evaluate the effects of graded normobaric hypoxia on SpO₂ variability in healthy individuals. Twelve healthy males (mean [standard deviation] age 22 [4] years) were exposed to four simulated environments (fraction of inspired oxygen [F_IO₂]: 0.12, 0.145, 0.17, and 0.21) for 45 minutes, in a balanced crossover design. Sample entropy, a tool that quantifies the irregularity of pulse oximetry fluctuations, was used as a measure of SpO₂ variability. SpO₂ entropy increased as the F_IO₂ decreased, and there was a strong significant negative correlation between mean SpO₂ and its entropy during hypoxic exposure (r = -0.841 to -0.896, p < 0.001). In addition, SpO₂ sample entropy, but not mean SpO₂, was correlated (r = 0.630-0.760, p < 0.05) with dyspnea in F_IO₂ 0.17, 0.145, and 0.12 and importantly, SpO₂ sample entropy at F_IO₂ 0.17 was correlated with dyspnea at F_IO₂ 0.145 (r = 0.811, p < 0.01). These findings suggest that SpO₂ variability analysis may have the potential to be used in a clinical setting as a noninvasive measure to identify the negative sequelae of hypoxemia.