Case studies in physiology: Nocturnal cardiorespiratory adaptive differences between an Italian trekker and a Nepali guide.

The cardiopulmonary system is a physiological cornerstone in the adaptive response to hypobaric hypoxia. Portable devices make it feasible nowadays to precisely assess the response to high altitude (HA) expeditions. In this study, we investigated breathing and arterial blood pressure responses during a Himalayan trek from 665 m to 4,780 m altitude in a white European (Italian) sojourner and a native Nepali (Tamang) guide, both healthy males. Resting diurnal and nocturnal data were acquired by means of ambulatory blood pressure monitoring (ABPM) and sleep apnea monitoring. We found an increase in the mean diurnal arterial blood pressure. Nocturnal blood pressure dipping was confirmed at all altitudes. Oxygen saturation decreased at altitude, with its additional nocturnal fall. Sleep apneic episodes, present in the Italian only, increased with altitude. We conclude that the nocturnal, more than diurnal, cardiorespiratory function is affected by HA hypoxia. Further studies should address the role of ethnicity, medications, and sociodemographic factors in the cardiorespiratory responses to hypobaric hypoxia.