Abstract
Voluntary Isocapnic Hyperpnea (VIH), a respiratory muscle training method, is assumed to stabilize blood CO(2) levels during increased ventilation, potentially supporting cellular homeostasis. The study aimed to empirically validate the concept and determine whether VIH effectively preserves key blood gas indices across different ambient oxygen levels in various populations. Two cross-sectional experiments (longitudinal in normoxia in highly trained athletes, n = 9 and single session in severe hypoxia of 4200 m above sea level in healthy and active participants, n = 18) were performed. Paired Bayesian t-tests and repeated measures analysis of variance were used to compare values of hydrogen ion concentration (pH), bicarbonate ion (HCO(3)(-)), partial pressure of oxygen (pO(2)), and partial pressure of carbon dioxide (pCO(2)) before and after VIH sessions. Except for pO(2) (BF(10) = 1.596 to 7.986), there were no meaningful differences in the analyzed variables before and after VIH in normoxia (BF(10) = 0.322 to 0.490). These findings remained consistent for different familiarization and training statuses of participants, as well as sessions' length and intensity. The likelihood of differences in pH, pO(2), and pCO(2) in hypoxia was supported by BF(10) values between 1.349 and 6.304. No between-sex differences were observed. Our observations highlight the physiological robustness of VIH in maintaining blood gas and pH equilibrium in normoxia, with potential implications for supporting cellular acid-base homeostasis and mitochondrial function. In severe hypoxia, VIH was associated with changes in multiple analyzed variables, suggesting the need for caution, along with increased requirements for protocol individualization and monitoring.