Adaptation to Life in the High Andes: Nocturnal Oxyhemoglobin Saturation in Early Development

Abstract

Physiological adaptation to high altitude hypoxia may be impaired in Andeans with significant European ancestry. The respiratory ‘burden’ of sleep may challenge adaptation, leading to relative nocturnal hypoxia. Developmental aspects of sleep-related breathing in high-altitude native children have not previously been reported. We aimed to determine the influence of development on diurnal-nocturnal oxyhemoglobin differences in children living at high altitude. This was a cross-sectional, observational study. Seventy-five healthy Bolivian children aged 6 mo to 17 y, native to low altitude (500 m), moderate high altitude (2,500 m), and high altitude (3,700 m) were recruited. Daytime resting pulse oximetry was compared to overnight recordings using Masimo radical oximeters. Genetic ancestry was determined from DNA samples. Children had mixed European/Amerindian ancestry, with no significant differences between altitudes. Sixty-two participants had ≥ 5 h of nocturnal, artifact-free data. As predicted, diurnal mean oxyhemoglobin saturation decreased across altitudes (infants and children, both P < 0.001), with lowest diurnal values at high altitude in infants. At high altitude, there was a greater drop in nocturnal mean oxyhemoglobin saturation (infants, P < 0.001; children, P = 0.039) and an increase in variability (all P ≤ 0.001) compared to low altitude. Importantly, diurnal to nocturnal altitude differences diminished (P = 0.036), from infancy to childhood, with no further change during adolescence. Physiological adaptation to high-altitude living in native Andeans is unlikely to compensate for the significant differences we observed between diurnal and nocturnal oxyhemoglobin saturation, most marked in infancy. This vulnerability to sleep-related hypoxia in early childhood has potential lifespan implications. Future studies should characterize the sleep- related respiratory physiology underpinning our observations. This is the first study to report significant differences between diurnal and nocturnal oxyhaemoglobin in infants and children resident at high altitude. These differences are dramatic in infants, where oxyhaemoglobin saturation is also unstable, but improve in childhood. Urban Andean high altitude dwelling populations have significant European ancestry and sleep physiology may challenge an already constrained system. Whether reduction in tissue oxygen delivery is clinically significant requires further study. Intermittent nocturnal hypoxia in obstructive sleep apnoea in children living at sea-level, has long-term consequences for cognitive performance and cardiovascular health. We hypothesise that exposure to low nocturnal oxyhaemoglobin may contribute to the subtle psychomotor slowing we have demonstrated in Andean high altitude dwelling children.