[Changes to sleep patterns in young migrants at high altitude]

Objective: To explore the relationship between the level of acclimatization and the changes to sleep architecture in migrants at high altitude. Methods: Nocturnal sleep recordings of 50 subjects aged between 18 and 25 years [mean age (20.9±2.0) years] were analyzed. Those young volunteers were divided into 3 700 m-3 m group(n=10, migrated to an altitude of 3 700 metres for 3 months), 3 700 m-1 y group(n=10, for 1 year) , 5 380 m-3 m group(n=8), 5 380 m-1 y group(n=9), and compared with a control group(n=13, at 1 400 m altitude). Results: When the migrants stayed at 5 380 m for 3 months or 1 year, the wake time increased significantly during sleep[(81.81±59.80)min vs(47.19±24.98) min, P=0.026; (77.94±25.64)min vs(47.19±24.98)min, P=0.040]. Concerning the percentage of total sleep time(TST) in each stage, participants in the 5 380 m-3 m group had a shift in sleep stage distribution with near absence of slow wave sleep(SWS) and a significant increase of N1 , but N2 and rapid eye movement(REM) did not differ. Interestingly, there were entirely concordant changes among the other 3 groups of results, decreased N2 and increased REM. Conclusions: The migrants' abilities to acclimatize themselves to plateau were varied according to the arrived altitude and the length of stay. The sleep of short- time migrants was characterized by increased N1 and decreased SWS, whereas that of well acclimatized migrants was characterized by less N2 and more REM. The efficient recovery in SWS may be an objective reference in high altitude acclimatization.