Enhanced cardiac vagal activity and mood after low-dose hypoxic gas inhalation in healthy young adults

Developing strategies to enhance cardiac vagal activity (CVA) is essential for improving mood and managing stress. Although hypoxia inhalation may boost CVA, the optimal acute hypoxic conditions remain unclear. Therefore, we aimed to achieve a comprehensive understanding of the hypoxic conditions required to improve CVA and mood following hypoxia. Twenty-one healthy adults participated in both normobaric hypoxic (NH; FIO₂: 13.5 %) and normoxic (NN; FIO₂: 20.9 %) conditions. We monitored heart rate variability (HRV), percutaneous oxygen saturation (SpO₂), and mood across pre-, hypoxia, and post-sessions and assessed psychophysiological stress using the Baevsky Stress Index (SI). Under hypoxia, SpO₂ decreased to 88.1 %, accompanied by reductions in vagally-mediated HRV, followed by supercompensation post-hypoxia. Additionally, mood declined during hypoxia but rapidly rebounded, correlating with CVA and SI fluctuations. These results indicate that acute low-dose hypoxic gas inhalation at FIO₂: 13.5 % enhances CVA and mood post-hypoxia, offering a practical method for building resilience.