A network physiology approach to oxygen saturation variability during normobaric hypoxia

Area of Science:

• Cardiovascular Physiology
• Respiratory Physiology
• Network Physiology

Background:

• Peripheral capillary oxygen saturation (SpO2) shows complex fluctuations during hypoxia.
• The physiological meaning of SpO2 variability is not fully understood.
• Network physiology offers a framework to study integrated physiological control.

Purpose of the Study:

• To test if SpO2 fluctuations contain information about integrated cardio-respiratory control in healthy individuals.
• To investigate the information flow between SpO2 and other cardio-respiratory signals during hypoxia using transfer entropy.
• To explore the potential of SpO2 entropy analysis for non-invasive assessment of respiratory control.

Main Methods:

• Twelve healthy males were exposed to varying levels of normobaric hypoxia (inspired oxygen fraction from 0.12 to 0.2093).
• Transfer entropy was used to analyze information flow between SpO2, respiratory frequency, tidal volume, minute ventilation, heart rate, and end-tidal pressures.
• SpO2 time series entropy significantly increased during hypoxia.

Main Results:

• Hypoxia led to a significant increase in SpO2 time series entropy.
• Transfer entropy analysis revealed a bidirectional information flow between SpO2 and other cardio-respiratory variables, especially at lower oxygen levels (FiO2 0.145 and 0.12).
• SpO2 emerged as a central hub in the cardio-respiratory network during hypoxic exposure.

Conclusions:

• SpO2 fluctuations during graded hypoxia carry significant information about cardio-respiratory control.
• The findings support the use of SpO2 entropy analysis for non-invasive assessment of the respiratory control system's functional connectivity.
• This approach has potential applications in various healthcare settings for evaluating respiratory control in health and disease.