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Acute Mountain Sickness in Iranian Trekkers Around Mount Damavand (5671 m) in Iran
Wilderness and Environmental Medicine, 14, 214 219 (2003)
ORIGINAL RESEARCH
Acute Mountain Sickness in Iranian Trekkers Around Mount Damavand (5671 m) in Iran Vahid Ziaee, MD; Masud Yunesian, MD; Zahra Ahmadinejad, MD; Farzin Halabchi, MD; Ramin Kordi, MD; Reza Alizadeh, MD; Hamid Reza Afsharjoo, MD From the Departments of Pediatrics (Dr Ziaee), Epidemiology (Dr Yunesian), and Infectious Diseases (Dr Ahmadinejad), and the Sport Medicine Research Center (Drs Ziaee, Halabchi, Kordi, and Yunesian), Tehran University of Medical Sciences, Tehran, Iran (Drs Alizadeh and Afsharjoo).
Background.—Many trekkers up Mount Damavand run the risk of developing acute mountain sickness (AMS); however, not much is documented concerning the incidence of AMS and its related factors within this population. Objective.—We designed this study to determine the incidence and risk factors for AMS in trekkers around Mount Damavand in Iran. Methods.—Symptoms of AMS and the contributing factors were assessed in the course of 6 weeks in summer 2000. Standard Lake Louise questionnaires were administered to 459 subjects, all of whom were trekkers. The questionnaires were filled out in 3 steps, first at 2900 m and then during both ascent and descent at 4200 m. Results.—The overall incidence of AMS was 60.8%. The incidence was higher in residents who lived at an altitude less than 600 m, amateur trekkers, those with a previous history of AMS, those with a history of AMS at ascent to Damavand, and those with night ascents (6 PM to midnight). Incidence was weakly dependent on rate of ascent (from 2900 m up to 4200 m in less than 4 hours) and sleep at 4200 m. No significant association was found between AMS and sex, age, body mass index, height, weight, smoking, weight of knapsacks, or the spent time in the shelter (at 4200 m). Conclusions.—We conclude that the incidence of AMS is high in Iranian trekkers ascending Mount Damavand. Some of the contributing factors are preventable, so we suggest considering an educational program for trekkers to high altitudes in Iran. Key words: acute mountain sickness, altitude illness, trekker, Damavand
Introduction Ascending to high altitudes can be troublesome for some trekkers, especially inexperienced and unfit people who ascend for recreation. Among the many risks, acute mountain sickness (AMS) is one of the most serious. Acute mountain sickness is a self-limiting syndrome with nonspecific symptoms, which occurs in unacclimatized people who ascend to altitudes greater than 2500 m. This acute syndrome is caused by low barometric pressure, subsequent decrease in partial oxygen pressure, and, finally, decreased oxygen saturation level. The exact pathology is uncertain. Headache is the main symptom, which may be accompanied by other maniCorresponding author: Vahid Ziaee, MD, Tehran University of Medical Sciences, Enghlab St, Tehran, I. R. Iran, PO Box 141555-6559 (e-mail: [email protected]).
festations, such as gastrointestinal symptoms (eg, nausea, vomiting, and anorexia), fatigue, lassitude, dizziness, lightheadedness, and sleep disorders.1,2 Several studies have been undertaken in different countries and during ascents to different peaks to determine the predisposing factors, etiology, and pathophysiology of the disease. Some evaluated predisposing factors include lack of water balance3; low age and lack of good physical fitness4; residence at low altitudes, history of previous mountain sickness4; low oxygen saturation levels5; sleeping at altitudes greater than 2500 m6; high lipid, high salt, or low carbohydrate diet7; rapid ascent rate1,2; low hypoxic ventilatory response8; and, finally, susceptibility and physiologic conditioning.1 Incidence of AMS has been reported in different studies as follows: at altitudes lower than 4000 m and higher than 4459 m in the Swiss Alps, 22% and 38%, respec-
Acute Mountain Sickness in Damavand
215
tively9; 22% in ascent from 1850 m to 2750 m1; 25% at 4890 m in the Rocky Mountains4; 26% in the Southern Alps of New Zealand6; 40% in an ascent from sea level to 5949 m in India10; 42% at 3000 m1; and 68% at altitudes greater than 4300 m in the Himalayas.11 Little has been documented concerning the incidence of AMS and its related factors among trekkers up Mount Damavand (5671 m). We devised this study to determine the incidence of mountain sickness during ascents to Damavand peak among Iranian trekkers. Subjects and Methods This cohort study was performed on 4 consecutive weekends (July 27 and 28, August 3 and 4, August 10 and 11, and August 17 and 18) in the summer of 2000. The study was approved by the epidemiologist consultants from the research office of the medical faculty of Tehran University of Medical Sciences (Tehran, Iran). In this period, all men and women who ascended Mount Damavand along the southern path (where most ascents take place) were included in the study. Subjects included both recreational and professional trekkers. After explaining the study design and objectives, we obtained verbal consent for participation. Assuming the highest available incidence of 38%9 (determined in a study at altitudes higher than 4500 m in the Alps) and considering d ⫽ 5% (the maximum difference in incidence of AMS that could be tolerated), sample size was calculated to be 362. For logistic considerations, assessment of cooperation of responders, and feasibility of the study design, we performed a preliminary pilot study on 126 subjects, 2 weeks before at the same location. Questionnaires were completed for each participant in 3 steps, at altitudes of 2900 m and 4200 m of the pass (Figure). The first questionnaire was filled out at an altitude of 2900 m (this is the starting point of the climb and trekkers arrive here by bus) and included personal information (sex, age, home altitude, etc), previous trekking skills and experiences, and medical history (eg, preexisting diseases, drug history, previous history of AMS, smoking, and family history of AMS). In addition, weight and height were measured, and body mass index (BMI) was calculated. Trekkers were divided into 3 groups based on the number of ascents they had made to altitudes above 4000 m in the last 6 months: experienced (ⱖ6 ascents), semiexperienced (1–5 ascents), and inexperienced (no ascents). The weight of each trekker’s knapsack (as a measure of physical activity) was evaluated in our study, and subjects were divided into 2 groups according to knapsack weight (⬎10 kg and ⬍10 kg).
Altitude profile over Mount Damavand. The open circles indicate village and camping places. The trekking distance is approximately 20 km.
The second and third parts of the questionnaires were completed at 4200 m, during ascent and descent, respectively. This part of the questionnaire included information about time schedule, duration of sleeping at this altitude, and weight of the knapsack. Moreover, AMS symptoms were investigated for each participant during both ascent and descent as laid out in the Lake Louise Scoring System,12 that is, headache along with 1 or more of the following symptoms: gastrointestinal disorders (anorexia, nausea, or vomiting), insomnia, dizziness, and lassitude or fatigue.9 Physical findings, including changes in mental status, ataxia, and peripheral edema, were also included in the questionnaire. Personal information and clinical manifestations were analyzed for all subjects, but ascent-related parameters (eg, ascent and descent rate) were analyzed only for those who had achieved the peak. For a few participants, precise data were not available for specific parameters, such as age, altitude at which they lived, or previous history of mountain sickness. These subjects were subsequently excluded from the analysis regarding the missing parameters. The Software Statistical Package for the Social Sciences (SPSS version 10) was used for statistical analysis. The relation between the following variables and AMS was assessed by 2 analysis: sex, home altitude, previous trekking and previous history of AMS, family history, smoking habits, and ascent characteristics. The relation between age and BMI was analyzed with a t test. Odds ratios (ORs) and the Mantel Haenszel adjusted odds ratio (MHOR) were computed whenever indicated. P ⱕ .05 was considered significant.
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Table 1. The prevalence of AMS in different age groups of trekkers to Damavand during study period Age group (y)
No. (%) of trekkers
ⱕ19 20–29 30–39 40–49 ⱖ50 Undetermined Total
36 183 123 76 23 18 459
(8) (40) (27) (16.5) (5) (4) (100)
No. (%) of trekkers with AMS 23 111 80 48 13 4 279
(63.9) (60.7) (60.2) (63.2) (65.5) (0.8) (60.8)
Results The overall incidence of AMS in the study population was 60.8%. We included 459 different subjects during the 4 weekends of the study. Of these, 333 hikers reached the peak (5671 m), while the other 126 did not. The peak altitudes for those failing to attain the peak ranged from 4200 to 5500 m. SEX, AGE, AND PAST MEDICAL HISTORY Participants included 148 females (32.2%) and 311 males (67.8%). Acute mountain sickness occurred in 58.1% of females, compared to 63.1% of males (P ⫽ .418). To assess the effect of age on development of AMS, the participants were divided into 5 groups based on their age (range, 13 to 71 years; Table 1). We detected no significant association between age and incidence of AMS (P ⫽ .972). HOME ALTITUDE All subjects were divided into 3 groups based on altitudes at which they lived. The first group consisted of 54 subjects who lived at an altitude below 600 m. The second group consisted of 308 subjects who lived at 600 m to 1600 m, and the third group included 95 subjects who lived above 1600 m. Acute mountain sickness occurred in 41 subjects (75.9%) from the first group, 186 subjects (60.4%) from the second, and 50 (52.6%) from the third (2 ⫽ 7.845, df ⫽ 2, P ⫽ .020). PREVIOUS TREKKING SKILLS There was a significant association between prior ascent experience and the development of AMS. Acute mountain sickness developed in 41.3% (19/41) of experienced trekkers, 57.8% (129/223) of semiexperienced, and in
68.9% (131/190) of inexperienced (2 ⫽ 13.441, df ⫽ 2, P ⫽ .001). PREVIOUS HISTORY OF AMS Incidence of AMS was also related to previous history of mountain sickness. Of 85 subjects who had previously experienced AMS, 71.8% developed it again, compared with 57.4% of 364 subjects without such a prior history (OR ⫽ 1.885, 2 ⫽ 5.917, P ⫽ .015). This correlation was preserved after omitting the confounding factor of level of accent experience (MHOR ⫽ 2.02, P ⫽ .007). In addition, we observed that subjects who had previously experienced AMS on ascent to the peak of Damavand were more likely to develop AMS (68.1% vs 45.6%; 2 ⫽ 8.765, df ⫽ 1, P ⫽ .003). ASCENT CHARACTERISTICS The relation between ascent characteristics (ie, ascent rate, time of beginning ascent, duration of stay at each shelter, duration of sleeping at 4200 m, and speed of descent from the peak) and incidence of AMS is represented in Table 2. The rate of ascent was evaluated in 2 different parts: in the first phase of ascent (from 2900 m to 4200 m) and in the second phase (from 4200 m to 5671 m). High ascent rate in the first phase (⬍4 hours) increased the incidence of AMS compared with low ascent rate (⬎4 hours). This correlation was weakly statistically positive (2 ⫽ 3.57, df ⫽ 1, P ⫽ .059). A fast ascent rate, going from 4200 m to 5671 m in less than 6 hours, actually resulted in a slightly decreased incidence of AMS (58.1%) compared to an ascent time of more than 6 hours (67.1%), although this difference was not statistically significant. The time of beginning of ascent and its effect on AMS was another factor evaluated in this study. The incidence was highest in the group who ascended between 6 PM and midnight, as all subjects in this group developed AMS without exception. The lowest incidence was observed among those who began to ascend between 7 AM and noon (2 ⫽ 17.414, df ⫽ 3, P ⫽ .001). The effect of descent rate was also evaluated in our study. Acute mountain sickness was less frequently observed in subjects with rapid descent rate (5671 m to 4200 m in ⬍6 hours), compared with slower descent rates (⬎6 hours), but this difference was not statistically significant (2 ⫽ 2.563, df ⫽ 1, P ⫽ .109). Finally, sleeping at an altitude of 4200 m for more than 3 hours was positively associated with AMS, although this association was not strong (2 ⫽ 3.600, df ⫽ 1, P ⫽ .058).
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Table 2. The association between accute mountain sickness (AMS) and ascent characteristics in trekkers to Damavand during study period Ascent characteristics
Prevalence of AMS (%)
Weight of knapsacks ⬍10 kg (n ⫽ 204) ⬎10 kg (n ⫽ 254)
60.3 61
Rate of ascent from 2900 to 4200 m ⬍4 hours (n ⫽ 303) 57.8 ⬎4 hours (n ⫽ 154) 66.9
P value
Not significant
.059
Time spent at 4200 m ⬍15 hours (n ⫽ 154) ⬎15 hours (n ⫽ 207)
62.1 58.9
Not significant
Sleeping at 4200 m altitude ⬍3 hours (n ⫽ 268) ⬎3 hours (n ⫽ 174)
65.3 56.3
.058
Rate of ascent from 4200 to 5671 m ⬍6 hours (n ⫽ 214) 58.1 ⬎6 hours (n ⫽ 152) 67.1
Not significant
Rate of descent from 5671 to 4200 m ⬍6 hours (n ⫽ 188) 58.5 ⬎6 hours (n ⫽ 174) 66.7
Not significant
Time of beginning ascent 1 AM–6 AM (n ⫽ 298) 7 AM–noon (n ⫽ 38) 1 PM–5 PM (n ⫽ 14) 6 PM–midnight (n ⫽ 12)
64.8 39.5 50 100
.001
No association with AMS was noted for the following variables: height of trekkers, weight of trekkers, BMI, smoking habit, positive family history, concomitant organic diseases (27.5% had concomitant organic diseases), knapsack weight (54% of trekkers carried knapsacks weighing ⬎10 kg), and oral contraceptive use. Examination of medication use by subjects yielded subgroups too small for statistical analysis. Overall, 2.6% of participants used vitamins, 2.6% used antiemetics, 1.6% used analgesics, and 1.5% used acetazolamide. Discussion In this study, the overall incidence of AMS was 60.8%, which is one of the highest percentages compared to previous studies. Two prior studies found incidence rates of 68% and 63%.11,13 Other surveys done on trekkers and climbers in the Alps or Rocky Mountains at altitudes of 4800 m or less found an incidence of less than 40%.
The high incidence in our study can likely be explained by an insufficient awareness on the part of trekkers concerning the medical risks of high-altitude exposure and erroneous traditional beliefs of trekkers (eg, ascending in the evening or at night). Mount Damavand is a dormant volcano that releases a substantial amount of malodorous sulfur compounds, such as sulfur dioxide. Sheppard et al14 demonstrated that during increased physical activity (eg, participation in sports), considerable amounts of sulfur dioxide reach the lower respiratory tract. Studies of the toxic effects of sulfur dioxide in humans have demonstrated airway obstruction and bronchial hyperactivity.15 Exposure to sulfur compounds induces headache and respiratory symptoms.16,17 This exposure may explain the high incidence of AMS in our study. RISK FACTORS Two previous studies in the Himalayas and Nepal found the incidence of AMS to be higher in females.11,13 In our study, however, sex did not have any significant impact. Likewise, previous studies found AMS to be less frequent in subjects older than 50 years,4,18,19 while we found no significant difference in different age groups. This discrepancy may be due to the small number of subjects in our study older than 50 years. Acute mountain sickness was also not significantly associated with BMI in our study, whereas other studies have found a significantly high incidence of AMS among trekkers with higher BMIs.13,20 Our study confirmed findings of prior studies4 that there is an increased risk of AMS in trekkers who live at altitudes lower than 900 m. We found that experienced trekkers had a significantly decreased incidence of AMS, and this finding may be related to better physical conditioning or an advantage related to increased climbing knowledge. While Milledge et al8 concluded that physical fitness had no preventive effect on AMS, our findings show a significant decrease in the incidence among subjects with proper physical conditioning. Previous history of AMS significantly increased the risk of recurrence. This finding has been confirmed in other studies as well4 and may be due to individual physiologic and genetic characteristics that predispose people to the development of AMS.21,22 Moreover, it has been shown that subjects with a previous history of AMS on this particular mountain were more likely to develop AMS compared with subjects without such a history. This tendency may be greatly influenced by the unique exposure to the sulfur environment on Mount Damavand.
218 While there is some evidence that smoking may increase the risk of AMS by decreasing peak expiratory flow,21,23 this increment was not statistically significant in our study or in Kayser’s13 study. A high level of physical activity has been suggested as a risk factor for the occurrence and severity of AMS.1,22,24 In the present study, however, we detected no significant relationship between our measure of physical activity (ie, weight of knapsack) and the incidence of AMS. It may be that such a difference in weight of knapsacks in 2 groups does not significantly affect the amount of physical exertion on a trek or perhaps a confounding factor, such as level of experience or physical conditioning, may have been present (ie, experienced subjects or subjects with better physical condition carried heavier knapsacks). Ascent rate has been described as an important risk factor in previous studies.1,2,24,25 In our study, faster ascent rates during the first phase of the climb (2900–4200 m) had a borderline positive association with incidence, while a faster ascent rate at higher altitudes (4200–5671 m) actually seemed to slightly but insignificantly decrease the risk. These results may have been due to adaptation occurring in subjects during early hours of ascent or while staying at the second shelter (4200 m). Studies such as that performed by Baumgartner et al26 have shown a higher incidence of AMS within 6 to 12 hours after the start of the ascent, which may support this view.1 Further studies should be undertaken to confirm the hypothesis that staying at high altitudes and subsequent adaptation of subjects to the environmental condition can decrease the incidence and severity of AMS. In addition, unlike previous studies,1,6,27 we found that sleeping at high altitudes for more than 3 hours had a positive borderline association with occurrence of acute mountain sickness. These results may have been confounded by level of physical fitness or other factors, such as sleep disturbance (a sign of AMS). The time that trekkers chose to begin their ascent varied; however, we did not evaluate the reasons for this difference. No previous studies have evaluated the effect of the time of beginning the ascent on occurrence of AMS. The uniform occurrence of AMS in those who began their ascent between 6 PM and midnight may be due to lower physical fitness secondary to diurnal activity or other reasons; further study with a proper design is required to clarify this finding. Likewise, descent rate has not been evaluated in other studies. Rapid descent to lower altitudes has been suggested as a therapeutic approach to patients with AMS.1 The lower rate of AMS among our subjects with more rapid descent rates reinforces this paradigm.
Ziaee et al Conclusion The incidence of AMS among trekkers on Mount Damavand is high. We suggest designing a research study to evaluate the special characteristics of Mount Damavand that might explain this higher than expected incidence. Owing to the prevalence of incorrect attitudes and practices among Iranian trekkers, there also needs to be an educational program directed at these travelers concerning the preventable risk factors that affect the incidence of AMS. Acknowledgments We thank M. Nazarian Afghan (the coach of the national trekking team) for his kind and helpful assistance to the trekkers during the climb, T. Ahmadinejad for his computer assistance, and M. Ahmadinejad, PhD, for editing the manuscript. References 1. Hackett PH, Roach RC. Current concepts: high-altitude illness. N Engl J Med. 2001;345:107–114. 2. Schneider M, Bernasch D, Weymann J, Holle R, Bartsch P. Acute mountain sickness: influence of susceptibility, preexposure, and ascent rate. Med Sci Sports Exerc. 2002; 34:1886–1891. 3. Westerterp KR, Robach P, Wouters L, Richalet JP. Water balance and acute mountain sickness before and after arrival at high altitude of 4,350 m. J Appl Physiol. 1996;80: 1968–1972. 4. Honigman B, Theis MK, Koziol-McLain J, et al. Acute mountain sickness in a general tourist population at moderate altitudes. Ann Intern Med. 1993;118:587–592. 5. Kayser B, Jean D, Herry JP, Bartsch P. Pressurization and acute mountain sickness. Aviat Space Environ Med. 1993; 64:928–931. 6. Murdoch DR, Curry C. Acute mountain sickness in the Southern Alps of New Zealand. N Z Med J. 1998;111: 168–169. 7. Porcelli MJ, Gugelchuk GM. A trek to the top: a review of acute mountain sickness. J Am Osteopath Assoc. 1995; 95:718–720. 8. Milledge JS, Beeley JM, Broome J, Luff N, Pelling M, Smith D. Acute mountain sickness susceptibility, fitness and hypoxic ventilatory response. Eur Respir J. 1991;4: 1000–1003. 9. Maggiorini M, Muller A, Hofstetter D, Bartsch P, Oelz O. Assessment of acute mountain sickness by different score protocols in the Swiss Alps. Aviat Space Environ Med. 1998;69:1186–1192. 10. Mistry G, Chandrashekhar Y, Sen U, Anand IS. Study of acute mountain sickness during ‘‘rapid ascent’’ trekking to extreme altitude. J Assoc Physicians India. 1993;41:500– 502.
Acute Mountain Sickness in Damavand 11. Basnyat B, Subedi D, Sleggs J, et al. Disoriented and ataxic pilgrims: an epidemiological study of acute mountain sickness and high-altitude cerebral edema at a sacred lake at 4300 m in the Nepal Himalayas. Wilderness Environ Med. 2000;11:89–93. 12. Roach RC, Bartsch P, Hackett PH, Oelz O. Lake Louise AMS Scoring Committee: the Lake Louise Acute Mountain Sickness Scoring System. In: Sutton JR, Houston CS, Coates G, eds. Hypoxia and Mountain Medicine. Burlington, Vt: Queen City Printers; 1993:272–274. 13. Kayser B. Acute mountain sickness in western tourists around the Thorong pass (5400 m) in Nepal. J Wilderness Med. 1991;2:110–117. 14. Sheppard D, Saisho A, Nadel JA, Boushey HA. Exercise increases sulfur dioxide-induced bronchoconstriction in asthmatic subjects. Am Rev Respir Dis. 1981;123:486– 491. 15. Knorst M, Kienast K, Muller QJ, Ferlinz R. Effect of sulfur dioxide on cytokine production of human alveolar macrophages in vitro. Arch Environ Health. 1996;51:150– 156. 16. Jaakkola JJ, Vilkka V, Marttila O, Jappinen P, Haahtela T. The South Karelia Air Pollution Study: the effect of malodorous sulfur compounds from pulp mills on respiratory and other symptoms. Am Rev Resp Dis. 1990;142(6 pt 1): 1344–1350. 17. Kangas J, Jappinen P, Savolainen H. Exposure to hydrogen sulfide, mercaptans and sulfur dioxide in pulp industry. Am Ind Hyg Assoc J. 1984;45:787–790. 18. Hackett PH, Rennie D. The incidence, importance, and
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prophylaxis of acute mountain sickness. Lancet. 1976;2: 1149–1155. Roach RC, Houston CS, Honigman B, et al. How well do older persons tolerate moderate altitude? West J Med. 1995;162:32–36. Hirata K, Masuyama S, Satio A. Obesity as risk factor for acute mountain sickness. Lancet. 1989;2:1040–1041. Adeoshun IO, Abid Ali M. Acute effect of cigarette smoking on peak expiratory flow rate and ventilation in resting Nigerian subjects. Afr J Med Med Sci. 1989;18:9–12. Roach RC, Maes D, Sandoval D, et al. Exercise exacerbates acute mountain sickness at simulated high altitude. J Appl Physiol. 2000;88:581–585. Backhouse CI. Peak expiratory flow in youths with varying cigarette smoking habits. Br Med J. 1975;1:360–362. Broome JR, Stoneham MD, Beeley JM, Milledge JS, Hughes AS. High altitude headache: treatment with ibuprofen. Aviat Space Environ Med. 1994;65:19–20. Bartsch P, Maggiorini M, Schobersberger W, et al. Enhanced exercise-induced rise of aldosterone and vasopressin preceding mountain sickness. J Appl Physiol. 1991;71: 136–143. Baumgartner RW, Spyridopoulos I, Bartsch P, Maggiorini M, Oelz O. Acute mountain sickness is not related to cerebral blood flow: a decompression chamber study. J Appl Physiol. 1999;86:1578–1582. Eichenberger U, Weiss E, Riemann D, et al. Nocturnal periodic breathing and the development of acute high altitude illness. Am J Respir Crit Care Med. 1996;154(6 pt 1):1748–1754.
ORIGINAL RESEARCH
Acute Mountain Sickness in Iranian Trekkers Around Mount Damavand (5671 m) in Iran Vahid Ziaee, MD; Masud Yunesian, MD; Zahra Ahmadinejad, MD; Farzin Halabchi, MD; Ramin Kordi, MD; Reza Alizadeh, MD; Hamid Reza Afsharjoo, MD From the Departments of Pediatrics (Dr Ziaee), Epidemiology (Dr Yunesian), and Infectious Diseases (Dr Ahmadinejad), and the Sport Medicine Research Center (Drs Ziaee, Halabchi, Kordi, and Yunesian), Tehran University of Medical Sciences, Tehran, Iran (Drs Alizadeh and Afsharjoo).
Background.—Many trekkers up Mount Damavand run the risk of developing acute mountain sickness (AMS); however, not much is documented concerning the incidence of AMS and its related factors within this population. Objective.—We designed this study to determine the incidence and risk factors for AMS in trekkers around Mount Damavand in Iran. Methods.—Symptoms of AMS and the contributing factors were assessed in the course of 6 weeks in summer 2000. Standard Lake Louise questionnaires were administered to 459 subjects, all of whom were trekkers. The questionnaires were filled out in 3 steps, first at 2900 m and then during both ascent and descent at 4200 m. Results.—The overall incidence of AMS was 60.8%. The incidence was higher in residents who lived at an altitude less than 600 m, amateur trekkers, those with a previous history of AMS, those with a history of AMS at ascent to Damavand, and those with night ascents (6 PM to midnight). Incidence was weakly dependent on rate of ascent (from 2900 m up to 4200 m in less than 4 hours) and sleep at 4200 m. No significant association was found between AMS and sex, age, body mass index, height, weight, smoking, weight of knapsacks, or the spent time in the shelter (at 4200 m). Conclusions.—We conclude that the incidence of AMS is high in Iranian trekkers ascending Mount Damavand. Some of the contributing factors are preventable, so we suggest considering an educational program for trekkers to high altitudes in Iran. Key words: acute mountain sickness, altitude illness, trekker, Damavand
Introduction Ascending to high altitudes can be troublesome for some trekkers, especially inexperienced and unfit people who ascend for recreation. Among the many risks, acute mountain sickness (AMS) is one of the most serious. Acute mountain sickness is a self-limiting syndrome with nonspecific symptoms, which occurs in unacclimatized people who ascend to altitudes greater than 2500 m. This acute syndrome is caused by low barometric pressure, subsequent decrease in partial oxygen pressure, and, finally, decreased oxygen saturation level. The exact pathology is uncertain. Headache is the main symptom, which may be accompanied by other maniCorresponding author: Vahid Ziaee, MD, Tehran University of Medical Sciences, Enghlab St, Tehran, I. R. Iran, PO Box 141555-6559 (e-mail: [email protected]).
festations, such as gastrointestinal symptoms (eg, nausea, vomiting, and anorexia), fatigue, lassitude, dizziness, lightheadedness, and sleep disorders.1,2 Several studies have been undertaken in different countries and during ascents to different peaks to determine the predisposing factors, etiology, and pathophysiology of the disease. Some evaluated predisposing factors include lack of water balance3; low age and lack of good physical fitness4; residence at low altitudes, history of previous mountain sickness4; low oxygen saturation levels5; sleeping at altitudes greater than 2500 m6; high lipid, high salt, or low carbohydrate diet7; rapid ascent rate1,2; low hypoxic ventilatory response8; and, finally, susceptibility and physiologic conditioning.1 Incidence of AMS has been reported in different studies as follows: at altitudes lower than 4000 m and higher than 4459 m in the Swiss Alps, 22% and 38%, respec-
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215
tively9; 22% in ascent from 1850 m to 2750 m1; 25% at 4890 m in the Rocky Mountains4; 26% in the Southern Alps of New Zealand6; 40% in an ascent from sea level to 5949 m in India10; 42% at 3000 m1; and 68% at altitudes greater than 4300 m in the Himalayas.11 Little has been documented concerning the incidence of AMS and its related factors among trekkers up Mount Damavand (5671 m). We devised this study to determine the incidence of mountain sickness during ascents to Damavand peak among Iranian trekkers. Subjects and Methods This cohort study was performed on 4 consecutive weekends (July 27 and 28, August 3 and 4, August 10 and 11, and August 17 and 18) in the summer of 2000. The study was approved by the epidemiologist consultants from the research office of the medical faculty of Tehran University of Medical Sciences (Tehran, Iran). In this period, all men and women who ascended Mount Damavand along the southern path (where most ascents take place) were included in the study. Subjects included both recreational and professional trekkers. After explaining the study design and objectives, we obtained verbal consent for participation. Assuming the highest available incidence of 38%9 (determined in a study at altitudes higher than 4500 m in the Alps) and considering d ⫽ 5% (the maximum difference in incidence of AMS that could be tolerated), sample size was calculated to be 362. For logistic considerations, assessment of cooperation of responders, and feasibility of the study design, we performed a preliminary pilot study on 126 subjects, 2 weeks before at the same location. Questionnaires were completed for each participant in 3 steps, at altitudes of 2900 m and 4200 m of the pass (Figure). The first questionnaire was filled out at an altitude of 2900 m (this is the starting point of the climb and trekkers arrive here by bus) and included personal information (sex, age, home altitude, etc), previous trekking skills and experiences, and medical history (eg, preexisting diseases, drug history, previous history of AMS, smoking, and family history of AMS). In addition, weight and height were measured, and body mass index (BMI) was calculated. Trekkers were divided into 3 groups based on the number of ascents they had made to altitudes above 4000 m in the last 6 months: experienced (ⱖ6 ascents), semiexperienced (1–5 ascents), and inexperienced (no ascents). The weight of each trekker’s knapsack (as a measure of physical activity) was evaluated in our study, and subjects were divided into 2 groups according to knapsack weight (⬎10 kg and ⬍10 kg).
Altitude profile over Mount Damavand. The open circles indicate village and camping places. The trekking distance is approximately 20 km.
The second and third parts of the questionnaires were completed at 4200 m, during ascent and descent, respectively. This part of the questionnaire included information about time schedule, duration of sleeping at this altitude, and weight of the knapsack. Moreover, AMS symptoms were investigated for each participant during both ascent and descent as laid out in the Lake Louise Scoring System,12 that is, headache along with 1 or more of the following symptoms: gastrointestinal disorders (anorexia, nausea, or vomiting), insomnia, dizziness, and lassitude or fatigue.9 Physical findings, including changes in mental status, ataxia, and peripheral edema, were also included in the questionnaire. Personal information and clinical manifestations were analyzed for all subjects, but ascent-related parameters (eg, ascent and descent rate) were analyzed only for those who had achieved the peak. For a few participants, precise data were not available for specific parameters, such as age, altitude at which they lived, or previous history of mountain sickness. These subjects were subsequently excluded from the analysis regarding the missing parameters. The Software Statistical Package for the Social Sciences (SPSS version 10) was used for statistical analysis. The relation between the following variables and AMS was assessed by 2 analysis: sex, home altitude, previous trekking and previous history of AMS, family history, smoking habits, and ascent characteristics. The relation between age and BMI was analyzed with a t test. Odds ratios (ORs) and the Mantel Haenszel adjusted odds ratio (MHOR) were computed whenever indicated. P ⱕ .05 was considered significant.
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Ziaee et al
Table 1. The prevalence of AMS in different age groups of trekkers to Damavand during study period Age group (y)
No. (%) of trekkers
ⱕ19 20–29 30–39 40–49 ⱖ50 Undetermined Total
36 183 123 76 23 18 459
(8) (40) (27) (16.5) (5) (4) (100)
No. (%) of trekkers with AMS 23 111 80 48 13 4 279
(63.9) (60.7) (60.2) (63.2) (65.5) (0.8) (60.8)
Results The overall incidence of AMS in the study population was 60.8%. We included 459 different subjects during the 4 weekends of the study. Of these, 333 hikers reached the peak (5671 m), while the other 126 did not. The peak altitudes for those failing to attain the peak ranged from 4200 to 5500 m. SEX, AGE, AND PAST MEDICAL HISTORY Participants included 148 females (32.2%) and 311 males (67.8%). Acute mountain sickness occurred in 58.1% of females, compared to 63.1% of males (P ⫽ .418). To assess the effect of age on development of AMS, the participants were divided into 5 groups based on their age (range, 13 to 71 years; Table 1). We detected no significant association between age and incidence of AMS (P ⫽ .972). HOME ALTITUDE All subjects were divided into 3 groups based on altitudes at which they lived. The first group consisted of 54 subjects who lived at an altitude below 600 m. The second group consisted of 308 subjects who lived at 600 m to 1600 m, and the third group included 95 subjects who lived above 1600 m. Acute mountain sickness occurred in 41 subjects (75.9%) from the first group, 186 subjects (60.4%) from the second, and 50 (52.6%) from the third (2 ⫽ 7.845, df ⫽ 2, P ⫽ .020). PREVIOUS TREKKING SKILLS There was a significant association between prior ascent experience and the development of AMS. Acute mountain sickness developed in 41.3% (19/41) of experienced trekkers, 57.8% (129/223) of semiexperienced, and in
68.9% (131/190) of inexperienced (2 ⫽ 13.441, df ⫽ 2, P ⫽ .001). PREVIOUS HISTORY OF AMS Incidence of AMS was also related to previous history of mountain sickness. Of 85 subjects who had previously experienced AMS, 71.8% developed it again, compared with 57.4% of 364 subjects without such a prior history (OR ⫽ 1.885, 2 ⫽ 5.917, P ⫽ .015). This correlation was preserved after omitting the confounding factor of level of accent experience (MHOR ⫽ 2.02, P ⫽ .007). In addition, we observed that subjects who had previously experienced AMS on ascent to the peak of Damavand were more likely to develop AMS (68.1% vs 45.6%; 2 ⫽ 8.765, df ⫽ 1, P ⫽ .003). ASCENT CHARACTERISTICS The relation between ascent characteristics (ie, ascent rate, time of beginning ascent, duration of stay at each shelter, duration of sleeping at 4200 m, and speed of descent from the peak) and incidence of AMS is represented in Table 2. The rate of ascent was evaluated in 2 different parts: in the first phase of ascent (from 2900 m to 4200 m) and in the second phase (from 4200 m to 5671 m). High ascent rate in the first phase (⬍4 hours) increased the incidence of AMS compared with low ascent rate (⬎4 hours). This correlation was weakly statistically positive (2 ⫽ 3.57, df ⫽ 1, P ⫽ .059). A fast ascent rate, going from 4200 m to 5671 m in less than 6 hours, actually resulted in a slightly decreased incidence of AMS (58.1%) compared to an ascent time of more than 6 hours (67.1%), although this difference was not statistically significant. The time of beginning of ascent and its effect on AMS was another factor evaluated in this study. The incidence was highest in the group who ascended between 6 PM and midnight, as all subjects in this group developed AMS without exception. The lowest incidence was observed among those who began to ascend between 7 AM and noon (2 ⫽ 17.414, df ⫽ 3, P ⫽ .001). The effect of descent rate was also evaluated in our study. Acute mountain sickness was less frequently observed in subjects with rapid descent rate (5671 m to 4200 m in ⬍6 hours), compared with slower descent rates (⬎6 hours), but this difference was not statistically significant (2 ⫽ 2.563, df ⫽ 1, P ⫽ .109). Finally, sleeping at an altitude of 4200 m for more than 3 hours was positively associated with AMS, although this association was not strong (2 ⫽ 3.600, df ⫽ 1, P ⫽ .058).
Acute Mountain Sickness in Damavand
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Table 2. The association between accute mountain sickness (AMS) and ascent characteristics in trekkers to Damavand during study period Ascent characteristics
Prevalence of AMS (%)
Weight of knapsacks ⬍10 kg (n ⫽ 204) ⬎10 kg (n ⫽ 254)
60.3 61
Rate of ascent from 2900 to 4200 m ⬍4 hours (n ⫽ 303) 57.8 ⬎4 hours (n ⫽ 154) 66.9
P value
Not significant
.059
Time spent at 4200 m ⬍15 hours (n ⫽ 154) ⬎15 hours (n ⫽ 207)
62.1 58.9
Not significant
Sleeping at 4200 m altitude ⬍3 hours (n ⫽ 268) ⬎3 hours (n ⫽ 174)
65.3 56.3
.058
Rate of ascent from 4200 to 5671 m ⬍6 hours (n ⫽ 214) 58.1 ⬎6 hours (n ⫽ 152) 67.1
Not significant
Rate of descent from 5671 to 4200 m ⬍6 hours (n ⫽ 188) 58.5 ⬎6 hours (n ⫽ 174) 66.7
Not significant
Time of beginning ascent 1 AM–6 AM (n ⫽ 298) 7 AM–noon (n ⫽ 38) 1 PM–5 PM (n ⫽ 14) 6 PM–midnight (n ⫽ 12)
64.8 39.5 50 100
.001
No association with AMS was noted for the following variables: height of trekkers, weight of trekkers, BMI, smoking habit, positive family history, concomitant organic diseases (27.5% had concomitant organic diseases), knapsack weight (54% of trekkers carried knapsacks weighing ⬎10 kg), and oral contraceptive use. Examination of medication use by subjects yielded subgroups too small for statistical analysis. Overall, 2.6% of participants used vitamins, 2.6% used antiemetics, 1.6% used analgesics, and 1.5% used acetazolamide. Discussion In this study, the overall incidence of AMS was 60.8%, which is one of the highest percentages compared to previous studies. Two prior studies found incidence rates of 68% and 63%.11,13 Other surveys done on trekkers and climbers in the Alps or Rocky Mountains at altitudes of 4800 m or less found an incidence of less than 40%.
The high incidence in our study can likely be explained by an insufficient awareness on the part of trekkers concerning the medical risks of high-altitude exposure and erroneous traditional beliefs of trekkers (eg, ascending in the evening or at night). Mount Damavand is a dormant volcano that releases a substantial amount of malodorous sulfur compounds, such as sulfur dioxide. Sheppard et al14 demonstrated that during increased physical activity (eg, participation in sports), considerable amounts of sulfur dioxide reach the lower respiratory tract. Studies of the toxic effects of sulfur dioxide in humans have demonstrated airway obstruction and bronchial hyperactivity.15 Exposure to sulfur compounds induces headache and respiratory symptoms.16,17 This exposure may explain the high incidence of AMS in our study. RISK FACTORS Two previous studies in the Himalayas and Nepal found the incidence of AMS to be higher in females.11,13 In our study, however, sex did not have any significant impact. Likewise, previous studies found AMS to be less frequent in subjects older than 50 years,4,18,19 while we found no significant difference in different age groups. This discrepancy may be due to the small number of subjects in our study older than 50 years. Acute mountain sickness was also not significantly associated with BMI in our study, whereas other studies have found a significantly high incidence of AMS among trekkers with higher BMIs.13,20 Our study confirmed findings of prior studies4 that there is an increased risk of AMS in trekkers who live at altitudes lower than 900 m. We found that experienced trekkers had a significantly decreased incidence of AMS, and this finding may be related to better physical conditioning or an advantage related to increased climbing knowledge. While Milledge et al8 concluded that physical fitness had no preventive effect on AMS, our findings show a significant decrease in the incidence among subjects with proper physical conditioning. Previous history of AMS significantly increased the risk of recurrence. This finding has been confirmed in other studies as well4 and may be due to individual physiologic and genetic characteristics that predispose people to the development of AMS.21,22 Moreover, it has been shown that subjects with a previous history of AMS on this particular mountain were more likely to develop AMS compared with subjects without such a history. This tendency may be greatly influenced by the unique exposure to the sulfur environment on Mount Damavand.
218 While there is some evidence that smoking may increase the risk of AMS by decreasing peak expiratory flow,21,23 this increment was not statistically significant in our study or in Kayser’s13 study. A high level of physical activity has been suggested as a risk factor for the occurrence and severity of AMS.1,22,24 In the present study, however, we detected no significant relationship between our measure of physical activity (ie, weight of knapsack) and the incidence of AMS. It may be that such a difference in weight of knapsacks in 2 groups does not significantly affect the amount of physical exertion on a trek or perhaps a confounding factor, such as level of experience or physical conditioning, may have been present (ie, experienced subjects or subjects with better physical condition carried heavier knapsacks). Ascent rate has been described as an important risk factor in previous studies.1,2,24,25 In our study, faster ascent rates during the first phase of the climb (2900–4200 m) had a borderline positive association with incidence, while a faster ascent rate at higher altitudes (4200–5671 m) actually seemed to slightly but insignificantly decrease the risk. These results may have been due to adaptation occurring in subjects during early hours of ascent or while staying at the second shelter (4200 m). Studies such as that performed by Baumgartner et al26 have shown a higher incidence of AMS within 6 to 12 hours after the start of the ascent, which may support this view.1 Further studies should be undertaken to confirm the hypothesis that staying at high altitudes and subsequent adaptation of subjects to the environmental condition can decrease the incidence and severity of AMS. In addition, unlike previous studies,1,6,27 we found that sleeping at high altitudes for more than 3 hours had a positive borderline association with occurrence of acute mountain sickness. These results may have been confounded by level of physical fitness or other factors, such as sleep disturbance (a sign of AMS). The time that trekkers chose to begin their ascent varied; however, we did not evaluate the reasons for this difference. No previous studies have evaluated the effect of the time of beginning the ascent on occurrence of AMS. The uniform occurrence of AMS in those who began their ascent between 6 PM and midnight may be due to lower physical fitness secondary to diurnal activity or other reasons; further study with a proper design is required to clarify this finding. Likewise, descent rate has not been evaluated in other studies. Rapid descent to lower altitudes has been suggested as a therapeutic approach to patients with AMS.1 The lower rate of AMS among our subjects with more rapid descent rates reinforces this paradigm.
Ziaee et al Conclusion The incidence of AMS among trekkers on Mount Damavand is high. We suggest designing a research study to evaluate the special characteristics of Mount Damavand that might explain this higher than expected incidence. Owing to the prevalence of incorrect attitudes and practices among Iranian trekkers, there also needs to be an educational program directed at these travelers concerning the preventable risk factors that affect the incidence of AMS. Acknowledgments We thank M. Nazarian Afghan (the coach of the national trekking team) for his kind and helpful assistance to the trekkers during the climb, T. Ahmadinejad for his computer assistance, and M. Ahmadinejad, PhD, for editing the manuscript. References 1. Hackett PH, Roach RC. Current concepts: high-altitude illness. N Engl J Med. 2001;345:107–114. 2. Schneider M, Bernasch D, Weymann J, Holle R, Bartsch P. Acute mountain sickness: influence of susceptibility, preexposure, and ascent rate. Med Sci Sports Exerc. 2002; 34:1886–1891. 3. Westerterp KR, Robach P, Wouters L, Richalet JP. Water balance and acute mountain sickness before and after arrival at high altitude of 4,350 m. J Appl Physiol. 1996;80: 1968–1972. 4. Honigman B, Theis MK, Koziol-McLain J, et al. Acute mountain sickness in a general tourist population at moderate altitudes. Ann Intern Med. 1993;118:587–592. 5. Kayser B, Jean D, Herry JP, Bartsch P. Pressurization and acute mountain sickness. Aviat Space Environ Med. 1993; 64:928–931. 6. Murdoch DR, Curry C. Acute mountain sickness in the Southern Alps of New Zealand. N Z Med J. 1998;111: 168–169. 7. Porcelli MJ, Gugelchuk GM. A trek to the top: a review of acute mountain sickness. J Am Osteopath Assoc. 1995; 95:718–720. 8. Milledge JS, Beeley JM, Broome J, Luff N, Pelling M, Smith D. Acute mountain sickness susceptibility, fitness and hypoxic ventilatory response. Eur Respir J. 1991;4: 1000–1003. 9. Maggiorini M, Muller A, Hofstetter D, Bartsch P, Oelz O. Assessment of acute mountain sickness by different score protocols in the Swiss Alps. Aviat Space Environ Med. 1998;69:1186–1192. 10. Mistry G, Chandrashekhar Y, Sen U, Anand IS. Study of acute mountain sickness during ‘‘rapid ascent’’ trekking to extreme altitude. J Assoc Physicians India. 1993;41:500– 502.
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