Purpose: 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