Exposure to a mild hyperbaric oxygen environment elevates blood pressure

[Purpose] This study aimed to investigate the changes in blood pressure due to mild hyperbaric oxygen at 1.3 atmospheres absolute with approximately 30% oxygen. [Participants and Methods] Ten healthy adults participated in two trials: the control (1 atmosphere absolute with 20.9% oxygen) and the mild hyperbaric oxygen (1.3 atmospheres absolute with approximately 30% oxygen) trials. All participants were exposed to either the control or mild hyperbaric oxygen conditions in a chamber for 45 min on each experiment day. [Results] A lower heart rate and higher peripheral oxygen saturation were observed after exposure in the mild hyperbaric oxygen trial than those in the control trial. After exposure, the change in ratios from the premeasurement of systolic and diastolic blood pressure in the mild hyperbaric oxygen trial was more than that in the control trial, despite no change in the absolute blood pressure values between the two groups during the exposure. [Conclusion] This is the first study to reveal that mild hyperbaric oxygen exposure might be a control method for chronic hypotension. In addition, these results suggest that people with hypertension might require some attention when using mild hyperbaric oxygen.