Barometric pressure change and heart rate response during sleeping at ~ 3000 m altitude

We investigated effects of change in barometric pressure (P _B) with climate change on heart rate (HR) during sleep at 3000 m altitude. Nineteen healthy adults (15 males and four females; mean age 32 years) participated in this study. We measured P _B (barometry) and HR (electrocardiography) every minute during their overnight stay in a mountain lodge at ~ 3000 m. We also measured resting arterial oxygen saturation (SpO₂) and evaluated symptoms of acute mountain sickness (AMS) by using the Lake Louise Questionnaire at 2305 and 3000 m, respectively. P _B gradually decreased during the night at the speed of approximately - 0.5 hPa/h. We found that HR during sleep decreased linearly as P _B decreased in all subjects, with significance (r = 0.492-0.893; all, P < 0.001). Moreover, cross correlation analysis revealed that HR started to decrease after ~ 15 min following the decrease in P _B, on average. SpO₂ was 93.8 ± 1.7% at 2305 m before climbing, then decreased significantly to 90.2 ± 2.2% at the lodge before going to bed, and further decreased to 87.5 ± 2.7% after waking (all, P < 0.05). Four of the 19 subjects showed a symptom of AMS after waking (21%). Further, the decrease in HR in response to a given decrease in P _B (ΔHR/ΔP_B) was negatively related with a decrease in SpO₂ from before going to bed to after waking at 3000 m (r = - 0.579, P = 0.009) and with total AMS scores after waking (r = 0.489, P = 0.033).