A network physiology approach to oxygen saturation variability during normobaric hypoxia.

NEW FINDINGS: What is the central question of this study? What is the physiological interpretation of SpO2 fluctuations observed during normobaric hypoxia in healthy individuals? What is the main finding and its importance? There is a significant flow of information between SpO2 and other cardio-respiratory time series during graded hypoxia. Analysis of the pattern of SpO2 variations has potential for non-invasive assessment of the engagement of respiratory control system in health and disease.

ABSTRACT: Peripheral capillary oxygen saturation ( SpO2 ) exhibits a complex pattern of fluctuations during hypoxia. The physiological interpretation of SpO2 variability is not well understood. In this study, we tested the hypothesis that SpO2 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 ( FIO2 ): 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 ( SpO2 , 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 SpO2 time series. The transfer entropy analysis showed that, particularly at FIO2 0.145 and 0.12, the flow of information between SpO2 and other physiological variables exhibits a bidirectional relationship. While reciprocal interactions were observed between different cardio-respiratory parameters during hypoxia, SpO2 remained the main hub of this network. SpO2 fluctuations during graded hypoxia exposure carry information about cardio-respiratory control. Therefore, SpO2 entropy analysis has the potential for non-invasive assessment of the functional connectivity of respiratory control system in various healthcare settings.