Incidence and risk factors during ascent to Hoh Xil and the physiological responses before and after acclimatization: a cross-sectional study

Abstract

Background Ascending to altitudes > 2,500 meters may lead to acute mountain sickness (AMS). This study determines the incidence, symptoms and risk factors of AMS, anthropometric data before and after hypoxia acclimatization, and the effect of oxygen therapy in a cohort of travelers to Hoh Xil (4,200 meters). Method This study considered 104 healthy Chinese people, data on their demographics, height, weight, body mass index (BMI), smoking and drinking status were collected in Chengdu (500 meters). Heart rate (HR), saturation of pulse oxygen (SpO2), and AMS-related symptoms were collected in Hoh Xil (4,200 meters). Participants with headache and a score ≥ 3 was considered to have AMS. Results The incidence of AMS was 60.58%. AMS group had a lower SpO2 (84.67% vs. 90.66%, p<0.001) and higher HR (96.16 vs. 87.39 bp/min, p<0.001) than non-AMS group. Drinking seemed a risk factor for AMS. However, there was no difference in the BMI, age, height, weight, and smoking between AMS and non-AMS groups. The most common AMS symptom was headache, followed by dyspnea, insomnia, dizziness, lassitude, and anorexia. Women were prone to suffer from dizziness (p<0.001). The value of SpO2 and HR were improved both in AMS and non-AMS groups after hypoxia acclimatization (p<0.001), and the value showed greater improvement in AMS group (p<0.001). Oxygen therapy decreased the AMS-induced tachycardia (p = 0.018), which had no any effect on SpO2 and symptom alleviating time. Conclusions Lower SpO2 value and higher HR value were associated with increased risk for AMS. The anthropometric data of non-AMS group was better than AMS group before and after hypoxia acclimatization, however, AMS group showed a bigger improvement than non-AMS group. Oxygen therapy was effective in relieving AMS-induced tachycardia, but not the SpO2 value and duration of AMS.