The Temporal Effects of Hyperbaric Oxygen Intervention on Heart Rate Variability in Young Adults

OBJECTIVE: This prospective cohort study aimed to investigate the temporal effects and additional characteristics of hyperbaric oxygen (HBO) intervention on heart rate variability (HRV) and autonomic nervous system (ANS) function in young adults. METHODS: Portable single-lead ambulatory ECG devices were used to collect HRV data. Fourteen young male participants underwent five daily 90-min HBO sessions. HRV was measured before intervention (T0), 2 h after the fifth session (T1), and 1 month later (T2). Circadian variation characteristics were further investigated by segmenting data into daytime and nighttime periods and calculating ΔHRV. RESULTS: Following five HBO sessions, the young adults showed progressive increases in HTI, TINN, and DFAα2 from T0 to T2, with TINN significantly higher at T2 than at T0 (p < 0.05). Sympathetic tone-related indices (daytime SDANN, SDNNI, and SD2) were significantly higher at T2 compared to T0 (p < 0.05), and their corresponding ΔHRV values were significantly reduced at T2 (p < 0.05). However, no significant changes were observed in vagal tone indicators (such as RMSSD, NN50, HF, SD1) or other HRV parameters. The maximal heart rate at T2 was significantly lower than at T0 (p = 0.036). CONCLUSION: Five sessions of HBO intervention significantly enhanced the overall ANS function in young adults during the daytime 1 month post-intervention, reduced heart rate and daytime sympathetic activity, and effectively narrowed circadian differences in both overall ANS and sympathetic function. No significant effects were observed on vagal tone related indices.