Ventricular repolarization in apparently healthy young men under short-term normobaric isocapnic and hypercapnic hypoxic exposure

BACKGROUND: The effects of hypoxic exposure on the human cardiorespiratory system have been extensively studied. Combined hypoxic and hypercapnic exposure has been shown to reduce the severity of adverse outcomes associated with oxygen deficiency across all functional systems, while also improving subjective tolerance to acute hypoxia. AIM: To assess cardiac electrical activity during the ventricular repolarization phase under exogenous normobaric hypoxic exposure with different inspired carbon dioxide levels in apparently healthy, untrained individuals. METHODS: A prospective, single-center, experimental study was conducted. The study included apparently healthy, untrained young men. Exclusion criteria: chronic pulmonary or cardiovascular diseases and recent acute respiratory viral infections. Participants were randomly assigned to one of two groups based on the type of exposure: exogenous isocapnic hypoxia (Group 1) or exogenous hypercapnic hypoxia (Group 2). Isocapnic and hypercapnic hypoxia were simulated by breathing through a facial mask for 15 minutes. The cardiac electric field was used to assess the amplitude and temporal characteristics of positive and negative extrema during the ventricular repolarization phase based on lead II electrocardiogram findings. The duration of QT, J–Tpeak, and Tpeak–Tend intervals with Bazett's correction was measured. RESULTS: Isocapnic hypoxia was found to cause more pronounced changes in SpO2 and heart rate compared to hypercapnic hypoxia. At comparable SpO2 levels, analysis of the temporal characteristics of ventricular repolarization demonstrated that the hypercapnic component of the hypoxic gas mixture reduced changes in the duration of nearly all examined electrocardiogram intervals. CONCLUSION: The study of ventricular repolarization under hypoxic exposure with various CO2 levels found that isocapnic hypoxia had a more pronounced stress effect on cardiac electrical activity than hypercapnic hypoxia in apparently healthy young men.