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

Abstract

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 (SaO₂) 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 SaO₂ and HR were assessed both before leaving the lowland and after arriving in Lhasa. Linear regression was performed to compare changes in SaO₂ 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 SaO₂ (-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.

Keywords: acute mountain sickness; heart rate; oxygen saturation; re-ascend; tibetan.

Figure 1

Mean of oxygen saturation (%) with 95% CI in acute mountain sickness (AMS) and non-AMS subjects on the third day after arrival in Lhasa by different ethnicity.

Figure 2

Mean of heart rate (beats per minute (bpm)) with 95% CI in acute mountain sickness (AMS) and non-AMS subjects on the third day after arrival in Lhasa by different ethnicity.