Statistical models of acute mountain sickness

Acute mountain sickness (AMS) is caused by exposure to altitudes exceeding 2500 m and often resolves by acclimatization without further ascent. Statistical models of AMS score and the probability of an AMS diagnosis were developed to allow the combination of dissimilar exposures for simultaneous analysis. The study population was 302 trekkers from a previous investigation who provided self-reported symptoms upon arrival at 3840 m during hikes through altitudes of 1500 to 6200 m. AMS score (Hackett scale) was estimated by linear regression and the probability of an AMS diagnosis (Lake Louise criteria) by logistic regression. AMS score or probability was significantly associated with exposure day and altitude. Increased altitude over the prior 3 days resulted in higher estimated AMS score or probability and decreased altitude in lower score or probability. The odds ratio (OR) of AMS was 3.6 if not on acetazolamide. Females appeared slightly more susceptible than males (1.5 OR). The approach offers the advantages of (1) improved statistical power by combining exposures, (2) insight into the dose-response relationship of altitude exposure and AMS risk, (3) quantitative tests for the significance of factors that might affect AMS susceptibility, and (4) practical tools to track individual climbers and plan operational ascents.     

Survey of acute mountain sickness on Mauna Kea

Although thousands of people ascend 4205 m to visit the summit of Mauna Kea each year, there has been no information on the rate of altitude illness triggered by such visits. Two surveys were used: one for tourists driving up to the summit and the other for summit astronomy workers staying at lodging facilities at intermediate altitude. The surveys included the standardized Lake Louise Self-report Acute Mountain Sickness (AMS) Questionnaire that, when scored, gave the Lake Louise Symptoms Score (LLSS). Thirty percent of surveyed day visitors and 69% of surveyed professional astronomy staff had AMS, defined as a LLSS score of 3 or greater, with headache. Nine participants reported "disorientation/confusion" or greater consciousness changes. A majority of astronomy professionals reported fatigue, disturbed sleep, reduced activity, and mental status changes. Few took any AMS medications. The incidence of AMS in visitors to Mauna Kea's summit warrants increased education and increased availability of supplemental oxygen at the summit. The absence of reported serious altitude illness in the community is probably due to the rapid descent available on Mauna Kea, with prompt reversibility of adverse effects.     

Efficacy of low-dose acetazolamide (125 mg BID) for the prophylaxis of acute mountain sickness: a prospective,double-blind,randomized, placebo-controlled trial

The objective of this study was to determine the efficacy of low-dose acetazolamide (125 mg twice daily) for the prevention of acute mountain sickness (AMS). The design was a prospective, double-blind, randomized, placebo-controlled trial in the Mt. Everest region of Nepal between Pheriche (4243 m), the study enrollment site, and Lobuje (4937 m), the study endpoint. The participants were 197 healthy male and female trekkers of diverse background, and they were evaluated with the Lake Louise Acute Mountain Sickness Scoring System and pulse oximetry. The main outcome measures were incidence and severity of AMS as judged by the Lake Louise Questionnaire score at Lobuje. Of the 197 participants enrolled, 155 returned their data sheets at Lobuje. In the treatment group there was a statistically significant reduction in incidence of AMS (placebo group, 24.7%, 20 out of 81 subjects; acetazolamide group, 12.2%, 9 out of 74 subjects). Prophylaxis with acetazolamide conferred a 50.6% relative risk reduction, and the number needed to treat in order to prevent one instance of AMS was 8. Of those with AMS, 30% in the placebo group (6 of 20) versus 0% in the acetazolamide group (0 of 9) experienced a more severe degree of AMS as defined by a Lake Louise Questionnaire score of 5 or greater (p = 0.14). Secondary outcome measures associated with statistically significant findings favoring the treatment group included decrease in headache and a greater increase in final oxygen saturation at Lobuje. We concluded that acetazolamide 125 mg twice daily was effective in decreasing the incidence of AMS in this Himalayan trekking population.     

Acute mountain sickness and ascent rates in trekkers above 2500 m in the Nepali Himalaya

INTRODUCTION: The aim of this study was to ascertain the incidence of acute mountain sickness (AMS) at different altitudes in the Solu-Khumbu. This was a pilot to examine the feasibility of investigating demographic, behavioral, and physiological factors related to the etiology of AMS and to assess the region's suitability for a future study. METHODS: A convenience sample of 150 recreational trekkers staying in teahouses was interviewed at altitudes above 2500 m. Two interviews were performed, firstly in the evening and then the subsequent morning. Trekker's age, gender, ascent profile, and use of acetazolamide were noted. A Lake Louise score was calculated to determine the presence of AMS. RESULTS: The incidence of AMS was 0% at 2500-3000 m, 10% between 3000-4000 m, 15% between 4000-4500 m, 51% between 4500-5000 m, and 34% over 5000 m. There was no significant association between age or gender and the altitude studied or incidence of AMS. Subjects with AMS ascended significantly further in the preceding 72 h than subjects without AMS, with a mean altitude gained of 846 m vs. 722 m. DISCUSSION: We concur with the literature that incidence of AMS increases with altitude. We found an abrupt increase in incidence over 4500 m. This appears to be a new finding. A future study examining factors predisposing to AMS would be most effectively performed above 4500 m. No association was found between age or gender and AMS. Mean vertical ascent gained in the previous 72 h was significantly higher among the trekkers with AMS but remained within recommended guidelines.     

Incidence and predictors of acute mountain sickness among trekkers on Mount Kilimanjaro

We investigated the incidence of AMS amongst a general population of trekkers on Mount Kilimanjaro, using the Lake Louise consensus scoring system (LLS). Additionally we examined the effect of prophylactic acetazolamide and different ascent profiles. Climbers on 3 different ascent itineraries were recruited. At 2743 m we recruited 177 participants (mean age 31, range [18-71]) who completed LLS together with an epidemiological questionnaire. At 4730 m participants (n=189, male=108, female=68, mean age 33, range [1871]) completed LLS, 136 of whom had been followed up from 2730 m. At 2743 m, 3% (5/177) of climbers were AMS positive, and 47% (89/189) of climbers from all itineraries were AMS positive at 4730 m. Of climbers attempting the Marangu itineraries, 33% (45/136) were taking acetazolamide. This group had a similar rate of AMS and no statistical difference in severity of LLS when compared with those not taking prophylactic drugs. We also did not demonstrate a difference between the incidence of AMS in climbers who did or did not take a rest day at 3700 m. However, there was a significant reduction in the incidence of AMS amongst pre-acclimatized subjects. Consistent with previous work, we found that the rate of AMS on Mount Kilimanjaro is high. Furthermore, at these fast ascent rates, there was no evidence of a protective effect of acetazolamide or a single rest day. There is a need to increase public awareness of the risks of altitude sickness and we advocate a pragmatic "golden rules" approach (http://www.altitude.org/altitude_sickness.php).     

Prediction of acute mountain sickness by monitoring arterial oxygen saturation during ascent

Acute mountain sickness (AMS) is a common problem while ascending at high altitude. AMS may progress rapidly to fatal results if the acclimatization process fails or symptoms are neglected and the ascent continues. Extensively reduced arterial oxygen saturation at rest (R-Spo?) has been proposed as an indicator of inadequate acclimatization and impending AMS. We hypothesized that climbers less likely to develop AMS on further ascent would have higher Spo? immediately after exercise (Ex-Spo?) at high altitudes than their counterparts and that these postexercise measurements would provide additional value for resting measurements to plan safe ascent. The study was conducted during eight expeditions with 83 ascents. We measured R-Spo? and Ex-Spo? after moderate daily exercise [50?m walking, target heart rate (HR) 150?bpm] at altitudes of 2400 to 5300?m during ascent. The Lake Louise Questionnaire was used in the diagnosis of AMS. Ex-Spo? was lower at all altitudes among those climbers suffering from AMS during the expeditions than among those climbers who did not get AMS at any altitude during the expeditions. Reduced R-Spo? and Ex-Spo? measured at altitudes of 3500 and 4300?m seem to predict impending AMS at altitudes of 4300?m (p?相似文献   

Everest or bust: a cross sectional, epidemiological study of acute mountain sickness at 4243 meters in the Himalayas.

BACKGROUND: Thousand of tourists trek in the Himalayas every season and risk acute mountain sickness (AMS). Prior studies have shown that the rate of ascent is one of the primary risk factors for the development of AMS but the role of body hydration, age, gender, alcohol and medication usage, body weight, and altitude of residence continues to be in question. This study estimates the incidence of AMS at 4234 m at Pheriche in the Everest region, explores a number of risk factors predisposing trekkers to a diagnosis of AMS and attempts to quantify the relationship between the Lake Louise AMS diagnostic criteria and oxygen saturation. METHODS: Demographic data and information about risk factors felt to place trekkers at increased risk of AMS was collected from 550 trekkers for 1 mo in the fall of 1996 at 4234 m in the Everest region. RESULTS: Diagnosis of AMS was made in 29.8% (159 trekkers) of the study population. Low water intake (odds ratio 1.57; 95% confidence interval,1.02-2.40), the presence of respiratory symptoms (odds ratio 2.21; 95% confidence interval, 1.43-3.40), and an oxygen saturation below 85% at 4243 m (odds ratio 2.35; 95% confidence interval, 1.55-3.56) were identified as independent risk factors for AMS diagnosis in this sample. In addition, AMS risk decreased 18.7% (95% confidence interval, 3.8-31.2%) for each additional night spent between Lukla (2804 m) and the study site at 4243 m. CONCLUSION: Increased reported fluid intake decreased the risk of AMS in this cross sectional prospective study. Further studies need to be done to confirm this finding before recommendations can be made. In addition the rise in the risk of AMS as the rate of ascent increased along this popular Everest trek was quantified for the first time. Finally, AMS was also associated with respiratory symptoms and with a lower oxygen saturation.     

Intravenous iron supplementation may protect against acute mountain sickness: a randomized, double-blinded, placebo-controlled trial

Acute mountain sickness (AMS) is a common and disabling condition that occurs in healthy individuals ascending to high altitude. Based on the ability of iron to influence cellular oxygen sensing pathways, we hypothesized that iron supplementation would protect against AMS. To examine this hypothesis, 24 healthy sea-level residents were randomized to receive either intravenous iron(III)-hydroxide sucrose (200?mg) or saline placebo, before ascending rapidly to Cerro de Pasco, Peru (4340?m). The Lake Louise scoring system was used to assess incidence and severity of AMS at sea level and on the first full day at altitude. No significant difference in absolute AMS score was detected between the two groups either at baseline or at high altitude. However, the mean increase in AMS score was 65% smaller in the iron group than in the saline group (p<0.05), and the change in AMS score correlated negatively with the change in ferritin (R=-0.43; p<0.05). Hematocrit and arterial oxygen saturation were unaffected by iron. In conclusion, this preliminary randomized, double-blinded, placebo-controlled trial suggests that intravenous iron supplementation may protect against the symptoms of AMS in healthy volunteers.     

Pulse oximetry in the diagnosis of acute mountain sickness

Acute mountain sickness (AMS) is a common condition in individuals who travel to altitudes over 2000 m. While AMS is an important public health problem, no measurements can reliably support or predict the diagnosis with any degree of confidence. We therefore set out to study whether pulse oximetry data are associated with AMS. We studied 169 subjects who had recently arrived by foot at 3080 m. Subjects completed a demographic survey, which collected data on ascent profiles and AMS symptoms. Resting arterial oxygen saturation and pulse rate were then measured using finger pulse oximetry. Forty-six subjects (27%) had AMS, using the Lake Louise score. Only pulse rate was significantly associated with the presence of AMS (OR: 1.4; 95% CI, 1.1 to 1.9; p < 0.05, backwards stepwise logistical regression). A trend showed worse AMS diagnoses were associated with higher mean pulse rates (p < 0.05, ANOVA linear weighted analysis). While some previous studies have shown an association between decreased oxygen saturation and acute mountain sickness at altitude, our results did not demonstrate such an association. The utility of pulse oximetry remains limited in the diagnosis of AMS. We recommend further study to determine the possible utility of pulse rate in the diagnosis and prediction of AMS.     

关于高原病的命名、临床分型和诊断标准的建议

本文阐述了高原病的定义、命名、临床分型和诊断标准。强调指出高原病的命名和临床分型应根据临床特征并结合病因、病理生理、病理诸因素综合考虑,应力求精简,明确和实用,有利于临床诊断、治疗、预后判断和研究以及疾病统计管理,并对命名、分(?)和诊断标准作了简要讨论。     

Awareness, prevalence, medication use, and risk factors of acute mountain sickness in tourists trekking around the Annapurnas in Nepal: a 12-year follow-up

Acute altitude exposure may lead to acute mountain sickness (AMS). Increased awareness of altitude-related health hazards in trekkers may accompany a decrease in AMS prevalence. We compared awareness and AMS prevalence in trekkers in two cohorts on an altitude trek up to 5400 m and assessed risk factors for AMS by repeating an observational cohort study 12 yr after an initial study. Questionnaires in English were distributed to two cohorts of 500 trekkers in 1986 and 1998. All trekkers over a several day period were asked to participate. Average participation rate was 62% (71% in 1986 and 53% in 1998). We found an increase in AMS awareness in trekkers from 80% to 95%, a decrease in AMS prevalence from 43% to 29%, and significant slower climbing profiles. We found no relationship between AMS and smoking habits, body mass index, oral contraception intake, or training status. By contrast, age was a strong independent risk factor inversely related to AMS. Subjects over 55 yr were 2.6 times less likely to suffer from AMS than subjects under 25 yr. Self-medication, including acetazolamide and analgesics, had increased importantly from 17% to 56%, and contraception intake in women had increased from 19% to 32%. In conclusion, in 1998 as compared to 1986, trekkers were older, climbed more slowly, had better awareness of altitude illness, used more medication, and suffered less from AMS.     

Acute mountain sickness, antacids, and ventilation during rapid, active ascent of Mount Rainier

A double-blind randomized study of 45 climbers on Mt. Rainier was conducted to test the effectiveness of antacids in preventing acute mountain sickness. All 45 climbed to 3353 m, and 31 continued to the summit. Ten climbers listed acute mountain sickness as the reason for not attaining the summit. Of symptoms monitored throughout the climb, neither headache, nausea, dizziness, pounding heart, nor shortness of breath differed in severity between antacid-treated and placebo-treated groups. In both groups vital capacity decreased significantly with ascent (p less than 0.05), while peak flow (p less than 0.005) and minute ventilation (p less than 0.001) increased significantly. The 7 climbers with the most severe AMS symptom scores above 4000 m had significantly lower peak flow at sea level prior to ascent compared with the other 25 climbers who completed sea level tests (p less than 0.005). The results of this study fail to document efficacy for antacid use for the prevention of acute mountain sickness.     

The prevalence of and risk factors for acute mountain sickness in the Eastern and Western Alps

Acute mountain sickness (AMS) is the most common condition of high altitude illnesses. Its prevalence varies between 15% and 80% depending on the speed of ascent, absolute altitude reached, and individual susceptibility. Additionally, we assumed that the more experienced mountaineers of the Western Alps are less susceptible to developing AMS than recreational mountaineers of the Eastern Alps or tourist populations. Therefore, the main goals of the present study were the collection of data regarding the AMS prevalence and triggers in both the Eastern and Western Alps using identical methods. A total of 162 mountaineers, 79 in the Eastern Alps (3454?m) and 83 in the Western Alps (3817?m) were studied on the morning after their first night at high altitude. A diagnosis of AMS was based on a Lake Louise Score (LLS) ≥4, the presence of headache, and at least one additional symptom. Thirty of 79 subjects (38.0%) suffered from AMS at 3454?m in the Eastern Alps as did 29 of 83 (34.9%) at 3817?m in the Western Alps. After adjustment for altitude, the prevalence in the Western Alps constituted 24.5%, which differed significantly (p?=?0.04) from that found in the Eastern Alps. The lower mountaineering experience of mountaineers in the Eastern Alps turned out to be the only factor for explaining their higher AMS prevalence. Thus, expert advice by mountain guides or experienced colleagues could help to reduce the AMS risk in these subjects.     

High altitude headache and acute mountain sickness at moderate elevations in a military population during battalion-level training exercises

Few studies have evaluated high altitude headache (HAH) and acute mountain sickness (AMS) in military populations training at moderate (1,500-2,500 m) to high altitudes (>2,500 m). In the current study, researchers interviewed active duty personnel training at Marine Corps Mountain Warfare Training Center. Participants were asked about HAH and AMS symptoms, potential risk factors, and medications used. In a sample of 192 U.S. Navy and Marine Corps personnel, 14.6% reported AMS (Lake Louise Criteria > or = 3) and 28.6% reported HAH. Dehydration and recent arrival at altitude (defined as data collected on days 2-3) were significantly associated with AMS; decreased sleep allowance was significantly associated with HAH. Although ibuprofen/Motrin users were more likely to screen positive for AMS, among AMS-positive participants, ibuprofen/Motrin users had decreased likelihood of reporting robust AMS relative to non-ibuprofen/Motrin users (p < 0.01). These results suggest that maintenance of hydration and adequate sleep allowance may be critical performance requirements at altitude. Further, ibuprofen/Motrin may be a reasonable treatment for the symptoms of AMS and HAH, although further study is warranted.     

Ginkgo biloba for the prevention of severe acute mountain sickness (AMS) starting one day before rapid ascent

Previous studies suggest that 5 days of prophylactic ginkgo decreases the incidence of acute mountain sickness (AMS) during gradual ascent. This trial was designed to determine if ginkgo is an effective prophylactic agent if begun 1 day prior to rapid ascent. In this double-blind, randomized, placebo-controlled trial, 26 participants residing at sea level received ginkgo (60 mg TID) or placebo starting 24 h before ascending Mauna Kea, Hawaii. Subjects were transported from sea level to the summit (4205 m) over 3 hours, including 1 hour at 2835 m. The Lake Louise Self-report Questionnaire constituted the primary outcome measure at baseline, 2835 m, and after 4 h at 4205 m. AMS was defined as a Lake Louise Self-report Score (LLSR) >/= 3 with headache. Subjects who developed severe AMS were promptly transported to lower altitude for the remainder of the study. The ginkgo (n = 12) and placebo (n = 14) groups were well matched (58% vs. 50% female; median age 28 yr, range 22-53 vs. 33 yr, range 21-53; 58% vs. 57% Caucasian). Two (17%) subjects on ginkgo and nine (64%) on placebo developed severe AMS and required descent for their safety (p = 0.021); all recovered without sequelae. Median LLSR at 4205 m was significantly lower for ginkgo versus placebo (4, range 1-8 vs. 5, range 2-9, p = 0.03). Ginkgo use did not reach statistical significance for lowering incidence of AMS compared with placebo (ginkgo 7/12, 58.3% vs. placebo 13/14, 92.9%, p = 0.07). Twenty-one of 26 (81%) subjects developed AMS overall. This is the first study to demonstrate that 1 day of pretreatment with ginkgo 60 mg TID may significantly reduce the severity of AMS prior to rapid ascent from sea level to 4205 m.     

Reliability and utility of a visual analog scale for the assessment of acute mountain sickness

Acute mountain sickness (AMS) is a common condition that affects people that ascend too rapidly to high altitude. It is typically assessed with the Lake Louise AMS Self-report Score (LLSelf) that uses a categorical numeric rating scale to answer five questions addressing AMS-related symptoms, such as headache. A 100-mm visual analog scale (VAS) is commonly used to assess subjective phenomena such as pain, but this scale has never been used for the self-assessment of AMS. The purpose of this study was to compare a VAS score to the total LLSelf and to evaluate the test-retest and interrater reliability of the VAS when used as an assessment of AMS. Participants (N = 356) completed both the LLSelf and the VAS on the summit of Mt. Whitney (4419 m). There was a significant relationship (r = 0.65, p < 0.01) between the LLSelf (2.8 +/- 2.0, mean +/- SD) and the VAS (14.4 +/- 14.1 mm). Fifty-seven participants were randomly selected for reliability testing of the VAS. Both test-retest reliability (ICC = 0.996, 95% CI = 0.992 to 0.998) and interrater reliability (ICC = 1.000, 95% CI = 0.999 to 1.000) were high. The mean difference in the VAS score between tests was <1 mm, as was the difference between raters. These results demonstrate excellent reliability for the VAS as an assessment of AMS.     

Comparing questionnaires for the assessment of acute mountain sickness

Exposure to high altitude in nonacclimatized subjects may lead to acute mountain sickness (AMS). AMS is a syndrome characterized by headache accompanied by one or more other symptoms, such as light-headedness, dizziness, loss of appetite, nausea, vomiting, fatigue, lassitude, and trouble sleeping. Assessing the presence and degree of AMS can be done using self-administered questionnaires like the Lake Louise Questionnaire (LLQ) and the Environmental Symptoms Questionnaire-III (ESQ-III). We compared LLQ and ESQ-III in 266 trekkers of different nationalities trekking over a 5400-m-high pass to assess if the two questionnaires identify the same population as suffering from AMS and to see whether using English questionnaires poses problems for nonnative English-speaking persons. The use of English questionnaires by nonnative English speakers influenced the outcome for some nationalities. For criterion scores yielding similar prevalence of AMS, ESQ-III labeled 20% of cases differently (AMS or no AMS) when compared to LLQ. Correlations between similar individual questions of ESQ-III and LLQ were variable, and there was considerable scatter between ESQ-III and LLQ scores. In conclusion, English questionnaires may pose problems in some international settings, and ESQ-III and LLQ may identify different populations as suffering from AMS.     

Visual analogue scores in assessment of acute mountain sickness

Acute mountain sickness (AMS) is common on ascent to high altitude, with self assessment being the current method used to assess symptoms. The Lake Louise Self-Report Score (LLSRS) and the Environmental Symptoms Questionnaire (ESQ) are widely used and validated. A Visual Analogue Scale (VAS) may be used as a simpler alternative for AMS assessment. Our aims were to compare a VAS using lines of length 100 mm, for both individual symptoms of AMS and self-assessed overall AMS with both LLSRS and a shortened Environmental Symptoms Questionnaire (ESQc) on ascent to 4392 m. We set out to suggest a specific score as a cut off point for diagnosis of AMS when using the VAS. There were significant positive correlations (p<0.01), between VAS and both LLSRS and ESQc scores for overall AMS and a composite AMS score derived from the individual symptom scores at 4392 m. The sensitivity and specificity of the VAS were calculated as 0.67 and 0.98, respectively, when using the LLSRS as the standard test for comparison, and 0.91 and 0.96, respectively, when using the ESQc for comparison. The cut off point for diagnosis of AMS was calculated to be 22 mm or above when using a VAS for overall AMS or 15 mm or above when using the VAS composite score, when using LLSRS as the comparative test. Our results show significant correlations between the VAS and the LLSRS and ESQc, when assessing AMS at 4392 m. Our study suggests that a VAS could provide a simple alternative method of assessing AMS at high altitude.     

Acute mountain sickness,dehydration, and bicarbonate clearance: preliminary field data from the Nepal Himalaya

BACKGROUND: In 1999, Basnyat et al. published preliminary data demonstrating an inverse correlation between hydration status and acute mountain sickness during an epidemiological study performed in the vicinity of Mount Everest. To expand on these findings, we have re turned to the Langtang area of the Nepal Himalaya to perform more specific studies of altitude illness related to dehydration and hypoxemia using urine studies, pulse oximetry, and physical examination. HYPOTHESIS: Dehydration will incite physiological changes aimed at the preservation of vascular volume homeostasis characterized by the production of sodium and water sparing hormones. As sodium is reabsorbed in the kidney, bicarbonate anion is also reabsorbed resulting in insufficient bicarbonate anion excretion by the kidney leading to an incomplete compensation for altitude induced hypocapnic alkalosis and the development of clinical disease. METHODS: Estimates of intravascular volume (urine specific gravity), oxygen saturation (pulse oximetry), urinary bi carbonate excretion (urine pH), and AMS (Lake Louise Score) were collected from Hindu pilgrims at 4243 m during an annual sacred festival at Lake Gosinkunda. RESULTS: Worsening altitude illness approx imated by increasing Lake Louise Score was associated with increasing urine specific gravity (p = 0.043), decreasing oxygen saturation (p = 0.020), and decreasing urine pH (p = 0.040) after rapid ascent to 4243 m. CONCLUSIONS: Worsening altitude illness, indicated by increasing Lake Louise score, was associated with increasing measures of dehydration, hypoxemia, and urine acidity.     

Association between physiological responses after exercise at low altitude and acute mountain sickness upon ascent is sex-dependent

Background:Acute mountain sickness (AMS) is the mildest form of acute altitude illnesses,and consists of nonspecific symptoms when unacclimatized persons ascend to elevation of ≥2500 m.Risk factors of AMS include:the altitude,individual susceptibility,ascending rate and degree of pre-acclimatization.In the current study,we examined whether physiological response at low altitude could predict the development of AMS.Methods:A total of 111 healthy adult healthy volunteers participated in this trial;and 99 (67 men and 32 women)completed the entire study protocol.Subjects were asked to complete a 9-min exercise program using a mechanically braked bicycle ergometer at low altitude (500m).Heart rate,blood pressure (BP) and pulse oxygen saturation (SpO2)were recorded prior to and during the last minute of exercise.The ascent from 500m to 4100m was completed in 2 days.AMS was defined as ≥3 points in a 4-item Lake Louise Score,with at least one point from headache wat 6-8 h after the ascent.Results:Among the 99 assessable subjects,47 (23 men and 24 women) developed AMS at 4100 m.In comparison to the subjects without AMS,those who developed AMS had lower proportion of men (48.9％ vs.84.6％,P＜0.001),height(168.4±5.9cm vs.171.3±6.1cm,P=0.019),weight (62.0±10.0kg vs.66.7±8.6kg,P=0.014) and proportion of smokers(23.4％ vs.51.9％,P=0.004).Multivariate regression analysis revealed the following independent risks for AMS:female sex (odds ratio (OR)=6.32,P＜0.001),SpO2 change upon exercise at low altitude (OR=0.63,P=0.002) and systolic BP change after the ascent (OR=0.96,P=0.029).Women had larger reduction in SpO2 after the ascent,higher AMS percentage and absolute AMS score.Larger reduction of SpO2 after exercise was associated with both AMS incidence(P=0.001) and AMS score (P＜0.001) in men but not in women.Conclusions:Larger SpO2 reduction after exercise at low altitude was an independent risk for AMS upon ascent.Such an association was more robust in men than in women.Trial registration:Chinese Clinical Trial Registration,ChiCTR1900025728.Registered 6 September 2019.