Nocturnal hypoxemia, ambulatory blood pressure and chronic mountains sickness in the highest city in the world

In response to chronic hypobaric hypoxia, residents at altitude develop physiological adaptations. Despite these adaptations, chronic mountain sickness (CMS) can be observed in 5-33% of individuals residing at high altitude. CMS frequently triggers cardiorespiratory diseases such as pulmonary hypertension and right or left heart failure. Ambient hypoxia further amplifies sleep-related disorders so that sleep disturbance is an important feature of CMS. Our aim was to characterize nocturnal hypoxemia and the associated sleep and ambulatory (A) blood pressure (BP) changes in highlanders. <b>Methods:</b> Cardiorespiratory sleep and 24h ABP monitoring studies were performed in highlanders living in Puno (3800m) and La Rinconada (5100m), Peru. Subjects were divided in groups according to CMS severity scale. <b>Results:</b> 77 males were evaluated (age 43 [34-49] yr, BMI 25 [23-27] kg/m2). Subjects with CMS showed higher 24 h and daytime systolic and diastolic BP than those with no CMS. Highlanders with CMS were characterized by a lower nocturnal oxygen saturation (SpO2) mean, nocturnal SpO2 nadir and a higher oxygen desaturation index than those with no CMS. No difference was found in terms of apnea-hypopnea index. Altitude (β -4.3, p=0.02) and CMS class (β -0.5, p=0.01) were significant predictors of a lower nocturnal SpO2. <b>Conclusions:</b> At altitude lower mean nocturnal SpO2 and frequent desaturations might be implicated in CMS pathogenesis. Moreover, CMS subjects showed higher ABP, which might contribute to their reported worse cardiovascular prognosis as compared with no-CMS highlanders. Further pathophysiological and therapeutic intervention studies are needed for a better management of CMS.