| Summary: | Qian Li,1,* Zhenxiang Guo,1,* Fuzheng Liu,2 Ye Liu,3 Dapeng Bao,4 Junhong Zhou5 1Sports Coaching College, Beijing Sport University, Beijing, People’s Republic of China; 2School of Medical Humanities, Capital Medical University, Beijing, People’s Republic of China; 3National Team Performance Training Center, National Sports Training Center, General Administration of Sport of China, Beijing, People’s Republic of China; 4China Institute of Sport and Health Science, Beijing Sport University, Beijing, People’s Republic of China; 5Hebrew SeniorLife Hinda and Arthur Marcus Institute for Aging Research, Harvard Medical School, Boston, MA, 02131, USA*These authors contributed equally to this workCorrespondence: Dapeng BaoChina Institute of Sport and Health Science, Beijing Sport University, No. 48 Xinxi Road, Haidian District, Beijing, 100084, People’s Republic of ChinaEmail baodp@bsu.edu.cnPurpose: The purpose exposure to hypoxia in high altitudes severely impairs the sleep quality and the related cardiovascular regulation, including the blood pressure (BP) regulation. BP regulation depends upon the continuous interaction of components over multiple temporal scales. As such, the dynamics of BP fluctuation are complex, and BP complexity has been linked to several pathological events. However, the effects of the exposure to hypoxia on BP complexity during sleep remain unknown.Methods: Twenty-five younger men naïve to high-altitude sleep (apnea severity as assessed by hypoxia apnea index (AHI): normal=8; moderate=9; severe=8) completed one nocturnal sleep under each of the three altitudes: 0 (ie, baseline), 2000, and 4000 m. The sleep characteristics and oxygen saturation (ie, SpO2) were assessed using polysomnography (PSG). The beat-to-beat BP fluctuation was recorded using a finger-blood-pressure sensor. Multiscale entropy (MSE) was used to characterize the complexity of systolic (SBP) and diastolic (DBP) BP fluctuations, and lower MSE reflected lower complexity.Results: Compared to 0-m condition, SBP (p=0.0003) and DBP (F=12.1, p=0.0002) complexity, SpO2 (p< 0.0001) and REM ratio (p< 0.0090) were decreased, AHI was increased (p=0.0004) in 2000-m and even more in 4000-m conditions. In addition, lower BP complexity was associated with greater AHI (r=− 0.66∼ 0.52, p=0.0010), lower SpO2 (r=0.48∼ 0.51, p=0.0100∼ 0.0200) and lower REM ratio (r=0.48∼ 0.52, p=0.0200). Participants with greater percent reduction in BP complexity between altitudes had greater percent reduction in REM ratio and SpO2 (r=0.38∼ 0.45, p=0.0090∼ 0.0200), after adjustment for age, BMI, baseline apnea and altitude.Conclusion: These results suggested that the characterization of BP complexity may provide novel insights into the underlying mechanisms through which the exposure to hypoxia affects cardiovascular health during sleep, as well as sleep quality. This BP complexity may serve as a novel marker to help the management of cardiovascular health and sleep quality in high-altitude living.Keywords: high altitude, beat-to-beat blood pressure, multiscale entropy, sleep quality
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