Mild hyperbaric hyperoxia improves aerobic capacity and suppresses cardiopulmonary stress during the maximal cycle-ergometer test

Kazufumi Hisamoto, Naoki Okubo, Mako Fujita, Hideki Fukushima, Yoshinori Okizuka, Takashi Yamanaka, Tomoyuki Matsui, Toru Morihara, Tatsuya Hojo, Yoshiyuki Fukuoka, Kenji Takahashi

Published: May 23, 2025
https://doi.org/10.1371/journal.pone.0323885

Abstract

Aerobic exercise is more recommended than anaerobic exercise for individuals with cardiopulmonary dysfunction to avoid cardiopulmonary stress. However, their oxygen-carrying capacity is already reduced, making it difficult to exercise enough. Therefore, we aimed to investigate whether mild hyperbaric hyperoxia enhances aerobic capacity and decreases cardiopulmonary stress during exercise with a particular focus on the ventilatory threshold (VT). Nineteen healthy men (age 34.9 ± 10.8 years) performed ramp-loading tests on a cycle-ergometer under the three oxygen conditions: hypobaric hypoxia (HYPO; 0.7 ATA, 14.7% O₂), normobaric normoxia (NOR; 1.0 ATA, 21% O₂), and mild hyperbaric hyperoxia (HYPER; 1.3 ATA, 35% O₂). Cardiopulmonary data were recorded using a gas exchange analyzer. VT was assessed based on minute ventilation (V_E) using the V-slope method and the work rate on VT (W_VT) was determined. Although the maximal values of V_E did not differ among the oxygen conditions, W_VT in the HYPER condition was significantly higher compared to others (HYPO; 125 ± 21, NOR; 148 ± 24, HYPER; 168 ± 32 [W], each p < 0.01). Systolic blood pressure and double product on VT in the HYPER condition were significantly reduced compared to others (HYPO; 172 ± 21, 23096 ± 4354, NOR; 173 ± 15, 23377 ± 3109, HYPER; 155 ± 18, 21255 ± 3340 [mmHg, beats·min^-1·mmHg], each p < 0.05). Although further clinical research targeting other populations is needed to apply mild hyperbaric hyperoxia in clinical practice, due to its positive effects on W_VT and cardiopulmonary stress, the HYPER oxygen condition may potentially be used to enhance aerobic capacity and make individuals with cardiopulmonary dysfunction exercise safely.