Acute mountain sickness, arterial oxygen saturation and heart rate among Tibetan students who reascend to Lhasa after 7 years at low altitude: a prospective cohort study.

Objectives: The aim of the present study was to estimate the incidence of acute mountain sickness (AMS) and address the changes in arterial oxygen saturation (SaO) and heart rate (HR) in native Tibetans who reascend to the high-altitude city of Lhasa (3658 m) after a 7-year stay at low altitude.

Methods: We followed two cohorts of students aged 17-21 years (859 Native Tibetan and 801 Han Chinese), travelling from lowland China until 3 days after their arrival in highland city of Lhasa. Questionnaire information of the symptoms of AMS using the Lake Louise Scoring System, resting SaO and HR were assessed both before leaving the lowland and after arriving in Lhasa. Linear regression was performed to compare changes in SaO and HR levels from low to high altitude in Tibetan and Han Chinese.

Results: New cases of AMS occurred in only 1.2% (95% CI 0.4% to 2.0%) of the Tibetan students who came to Lhasa by train compared with 32.7% (95% CI 28.0% to 37.3%) and 42.9% (95% CI 38.0% to 47.7%) of the Han Chinese students who came to Lhasa by train and by air, respectively. Tibetan students had less changes in SaO (-2.95 percentage points, 95% CI -3.24% to -2.65%) and HR (10.89 beats per minute (bpm), 95% CI 9.62 to 12.16 bpm) from low to high altitude compared with Han Chinese students, although measurements did not differ between the two groups when measured at low altitude.

Conclusions: Healthy Tibetans are mostly protected against AMS and primarily maintain their good adaptation to high altitude, even after a long period of stay at low altitude.