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The Incidence of Acute Mountain Sickness Among Passengers Traveling Across the Tibetan Plateau by Train

      To the Editor:
      The number of tourists visiting high altitude areas has increased in recent years, and they face the threat of acute mountain sickness (AMS). The reported prevalence of AMS varies between 15% and 80% depending on the speed of ascent, absolute altitude reached, and individual susceptibility.
      • Schommer K.
      • Bärtsch P.
      Basic medical advice for travelers to high altitudes.
      • Mairer K.
      • Wille M.
      • Burtscher M.
      The prevalence of and risk factors for acute mountain sickness in the Eastern and Western Alps.
      • Jackson S.J.
      • Varley J.
      • Sellers C.
      • et al.
      Incidence and predictors of acute mountain sickness among trekkers on Mount Kilimanjaro.
      We had a chance to evaluate the incidence of AMS among passengers who were first exposed to high altitude by taking the Tibetan railway train. A summary is presented here.
      High altitude areas are defined as areas at an altitude ≥2500 m above the mean sea level. Volunteer passengers aged 18 to 70 years old traveling by trains at high altitude (Tibetan Plateau) and low altitude (Urumqi railway) were selected consecutively. The inclusion criteria were passengers who were capable of finishing the questionnaires independently by themselves, who were low altitude dwellers, and who had not been to the high altitude area within 1 year. The exclusion criteria were permanent natives of high altitudes and passengers with preexisting symptoms of organ dysfunction due to severe respiratory, cardiovascular, renal, and cerebral diseases. The subjects’ demographic information and AMS symptoms were collected by questionnaires. Physical parameters, including respiratory rate, blood pressure, peripheral capillary oxygen saturation (Spo2), heart rate, and heart function (New York Heart Association functional class), were recorded for the scheduled altitude and time. The 4 selected stations at high altitude were Lanzhou (altitude 1600 m to 1800 m), Xining (2500 m to 3100 m), Naqu (4347 m to 5072 m), and Lhasa (4141 m to 3671 m), where the trains had running times of 12 hours, 20.5 hours, 38.5 hours, and 42.5 hours, respectively. Three railway stations in the control group were Yinchuan (1100 m to 1104 m), before Wuwei (1451 m to 1529 m), and before Urumqi (954 m to 987 m), where the trains ran 16 hours, 20.5 hours, and 38.5 hours, respectively. The diagnosis of AMS was according to the Lake Louise Score (LLS) and was based on presence of headache, at least one other symptom, and a total score of 3 or more on the self-report questionnaires.
      • Roach R.C.
      • Bärtsch P.
      • Oelz O.
      • Hackett P.H.
      The Lake Louise acute mountain sickness scoring system.
      In all, 148 passengers (75 men and 73 women) on the high altitude train and 60 passengers (46 male and 14 female) on the low altitude train completed questionnaires (mean age high altitude train 44.18 ± 11.94 years vs mean age low altitude train 44.8 ± 12.9 years, P = .45). The majority of the participants were of Han ethnicity (91.2% in the high altitude group vs 88.3% in the low altitude group, P = .52). No passengers used tadalafil, sildenafil, acetazolamide, or corticosteroids.
      The air pressure at the 4 designated high altitude stations was 84.0 kPa, 69.0 kPa, 56.2 kPa, and 60.1 kPa, respectively. After Xining station (the second station), most of the journey was above 2500 m, and passengers were provided with oxygen by a diffusion system in the train cabins. The fraction of inspired oxygen at the 4 stations for the high altitude group was 21.0%, 26.5%, 22.1%, and 24.3%, respectively. The fraction of inspired oxygen was stable at 20.9% for the low altitude group.
      The incidence of AMS among passengers traveling by train on the Tibetan Plateau was 20.2% (25 passengers) at the altitude of 5072 m. Six passengers (4.1%) had severe AMS (LLS ≥7 with an associated headache),
      • Roach R.C.
      • Bärtsch P.
      • Oelz O.
      • Hackett P.H.
      The Lake Louise acute mountain sickness scoring system.
      and the highest LLS was 9; none of the passengers had cerebral edema or pulmonary edema. Only 1 person (1.7%) in the control group had symptoms of AMS (LLS 3); the symptoms were stable and were not related to traveling time and altitude. In the study by Wu TY et al,
      • Wu T.Y.
      • Ding S.Q.
      • Zhang S.L.
      • et al.
      Altitude illness in Qinghai–Tibet railroad passengers.
      in which Chinese passengers went from 2808 m to 4768 m by train, the incidence of AMS was 31% for nonacclimatized Han. The incidence and severity of AMS was much lower in our study, probably because of the diffusion oxygen supply system in the train cabins. The benefits of oxygen supplementation at high altitude are well known but this is the first study to evaluate the effect of oxygen supplementation in the train cabin. However, the optimal concentration still needs to be further investigated.
      The most common symptom of AMS was headache (44.2%), and all the symptoms increased as the altitude increased. Headache, dizziness, and gastrointestinal symptoms seemed more correlated with AMS. Fatigue or weakness and difficulty sleeping were also common among the low altitude travel group. Passengers on the high altitude journey had just noticeable dyspnea going from station 3 to station 4; the mean Borg scale was 0.3 and 0.2, respectively. Compared with the control group, passengers had higher blood pressure at high altitude, and their mean heart rate increased dramatically, more than 10 beats/min, from 3671 m to 5072 m. The decreasing Spo2 was consistent with the increasing altitude; the lowest Spo2 was 87.5%. Spearman correlation analysis showed passengers with higher body mass index seemed more vulnerable to AMS, and women had more complaints of AMS symptoms.
      The study limitations are that the train trip lasted 44 hours for the high altitude group, the subjects had a sleeping cabin, and the changes in sleeping conditions might have influenced the incidence of AMS. The passengers might also have had some underestimation of symptoms because of group dynamics. Moreover, the majority of the participants were of Han ethnicity, and the incidence of AMS might differ for different ethnic groups.

      Acknowledgements

      This study was supported by Health Scientific Research special grants from Ministry of Health of the People’s Republic of China: “Early warning, early diagnosis, Standardized treatment and Results application promotion in patients of acute mountain sickness.” Project Numbers 201002012.

      References

        • Schommer K.
        • Bärtsch P.
        Basic medical advice for travelers to high altitudes.
        Dtsch Arztebl Int. 2011; 108: 839-847
        • Mairer K.
        • Wille M.
        • Burtscher M.
        The prevalence of and risk factors for acute mountain sickness in the Eastern and Western Alps.
        High Alt Med Biol. 2010; 11: 343-348
        • Jackson S.J.
        • Varley J.
        • Sellers C.
        • et al.
        Incidence and predictors of acute mountain sickness among trekkers on Mount Kilimanjaro.
        High Alt Med Biol. 2010; 11: 217-222
        • Roach R.C.
        • Bärtsch P.
        • Oelz O.
        • Hackett P.H.
        The Lake Louise acute mountain sickness scoring system.
        in: Hypoxia and Molecular Medicine. Queen City Printers, Burlington, VT1993: 272-274
        • Wu T.Y.
        • Ding S.Q.
        • Zhang S.L.
        • et al.
        Altitude illness in Qinghai–Tibet railroad passengers.
        High Alt Med Biol. 2010; 11: 189-198