A network physiology approach to oxygen saturation variability during normobaric hypoxia

Abstract

Abstract: Peripheral capillary oxygen saturation ((Formula presented.)) exhibits a complex pattern of fluctuations during hypoxia. The physiological interpretation of (Formula presented.) variability is not well understood. In this study, we tested the hypothesis that (Formula presented.) fluctuation carries information about integrated cardio-respiratory control in healthy individuals using a network physiology approach. We explored the use of transfer entropy in order to compute the flow of information between cardio-respiratory signals during hypoxia. Twelve healthy males (mean (SD) age 22 (4) years) were exposed to four simulated environments (fraction of inspired oxygen ((Formula presented.)): 0.12, 0.145, 0.17, and 0.2093) for 45 min, in a single blind randomized controlled design. The flow of information between different physiological parameters ((Formula presented.), respiratory frequency, tidal volume, minute ventilation, heart rate, end-tidal pressure of O2 and CO2) were analysed using transfer entropy. Normobaric hypoxia was associated with a significant increase in entropy of the (Formula presented.) time series. The transfer entropy analysis showed that, particularly at (Formula presented.) 0.145 and 0.12, the flow of information between (Formula presented.) and other physiological variables exhibits a bidirectional relationship. While reciprocal interactions were observed between different cardio-respiratory parameters during hypoxia, (Formula presented.) remained the main hub of this network. (Formula presented.) fluctuations during graded hypoxia exposure carry information about cardio-respiratory control. Therefore, (Formula presented.) entropy analysis has the potential for non-invasive assessment of the functional connectivity of respiratory control system in various healthcare settings.