RELATIONSHIP BETWEEN SLEEP BREATHING PATTERNS AND BLOOD PRESSURE CHANGES DURING ACUTE HIGH ALTITUDE EXPOSURE. DATA FROM HIGHCARE STUDIES

Abstract

Objective: Acute exposure to high/moderate altitude (HMA) induces increase in ambulatory blood pressure (BP), which may be particularly pronounced during the night, leading to reduced nocturnal BP dipping. Occurrence of central sleep apneas (CSA) is also typical for HMA exposure. Aim of this study was to investigate the relationship between variables characterizing respiration during sleep with nocturnal BP in subjects acutely exposed to HMA. Design and method: Aggregate data from several studies performed in the framework of HIGHCARE projects were analysed (HIGHCARE-Himalaya – 5400 m, Alps - 4559 m, Sestriere 2035 m, all in healthy volunteers; Andes – 3260 m, hypertensive subjects). HMA exposure duration ranged between 1 and 15 days. Data of subjects with at least 1 ambulatory BP monitoring at sea level (SL) and HMA (validated oscillometric device) and at least 1 cardio-respiratory sleep study (CSS) were analysed. Study variables included: mean nocturnal systolic(S) and diastolic (D)BP; size of nocturnal BP fall (%), apnea-hypopnea index (AHI), central apnea index (cAI), mean and minimum nocturnal oxygen saturation (SpO2mean and SpO2 min). Mixed linear models adjusting for age, sex, BMI, study, treatment were used to assess the relationship between variables of interest. Results: After excluding participants with incomplete data, 178 subjects were included (52.8% male, age 45.6 ± 11.7, BMI 25.3 ± 4.3). During HMA exposure we observed an increase in nocturnal SBP/DBP by 10.8 ± 12.9 mmHg, a reduction in nocturnal SBP/DBP fall by 2.5 ± 7.9%. Median SpO2mean was 82.6%, SpO2 min 70%, AHI 22.5, cAI 1.1. 82% of participants had AHI > 5. After adjusting for covariates no association was found between changes in nocturnal BP/dipping and AHI or cAI. We observed a direct relationship between SpO2mean and the change in nocturnal SBP fall (β=0.21 [0.04–0.39], p = 0.017). In categorical analysis participants who at HMA became nondippers (SBP fall < 10%) had lower SpO2mean than those who maintained nocturnal dipping (77.9 vs. 84.2%, adjusted p = 0.044). Conclusions: Attenuation of physiological nocturnal BP fall at HMA is associated with the degree of nocturnal hypoxemia but not with the severity of sleep breathing disorders induced by HMA exposure. These results may be relevant in conditions associated with nocturnal hypoxia and/or CSA.