History Of Acute Mountain Sickness Research Articles

Prevalence and knowledge about acute mountain sickness in the Western Alps.

To assess the prevalence of acute mountain sickness (AMS) in 1370 mountaineers at four different altitudes in the Western Alps. We also examined the influence of potential risk factors and the knowledge about AMS on its prevalence. In this observational cross-sectional study AMS was assessed on the day of ascent by the Lake Louise score (LLS, cut-off ≥3, version 2018) and the AMS-Cerebral (AMS-C) score of the environmental symptom questionnaire (cut-off ≥0,70). The latter was also obtained in the next morning. Knowledge regarding AMS and high-altitude cerebral edema (HACE) and the potential risk factors for AMS were evaluated by questionnaires. On the day of ascent, the prevalence of AMS assessed by the LLS and AMS-C score was 5.8 and 3.9% at 2850 m, 2.1 and 3.1% at 3050 m, 14.8 and 10.1% at 3650 m, and 21.9 and 15% at 4559 m, respectively. The AMS prevalence increased overnight from 10.1 to 14.5% and from 15 to 25.2% at 3650 m and 4559 m, respectively, and was unchanged at 2850 m and 3050 m. A history of AMS, higher altitude, lower degree of pre-acclimatization, and younger age were identified as risk factors for developing AMS. Slow ascent was weakly associated with AMS prevalence, and sex and knowledge about AMS and HACE were indistinct. AMS is common at altitudes ≥ 3650 m and better knowledge about AMS and HACE was not associated with less AMS in mountaineers with on average little knowledge.

UNNOTICED ETIOLOGY IN ORTHOPEDIC COMPLAINTS: CHRONIC MOUNTAIN SICKNESS

Objective: Chronic mountain sickness (CMS) is a clinical syndrome with symptoms of polycythemia that may interfere with other nonspecific diseases. The current study aimed to investigate the symptoms of patients living at high altitudes, who initially presented complaints that seemed to be common orthopedic problems, and to examine their relationship with chronic mountain sickness. Material and Methods: The prospectively collected data of 104 patients were retrospectively evaluated for serum hemoglobin (Hb) and hematocrit (Hct) levels, oxygen saturation (sO2), Qinghai CMS questionnaire score, alcohol and tobacco use, “any history of acute mountain sickness, body mass index (BMI), blood pressure, heart rate, and duration of high-altitude living. Patients grouped according to the Qinghai score as healthy, mild, moderate or severe CMS. The groups were investigated in terms of parameters and demographic characteristics. Results: Of the 104 patients, 33 (31.7%) had a mild CMS score ≥6 (28 patients, 6–10, 5 patients, 11–14 points); remaining patients had no CMS. The frequency of excessive erythrocytosis was 4.5% in men and 3.3% in women. There was a significant difference in Hb, Hct and sO2 levels between the healthy and mild CMS groups (p<0.001). CMS score had a positive correlation with Hct (rho 0,381 p<0.001) and negative correlation between sO2 levels (rho -0.432 p<0.001). Conclusions: CMS can be observed at lower altitudes than described in literature. In individuals living in high altitudes, some of the CMS symptoms may be confused with real orthopedic symptoms and orthopedists working in these areas should increase their awareness on this issue. In order to make an appropriate approach, other symptoms related to CMS should be questioned in patients living at high altitudes.

UNNOTICED ETIOLOGY IN ORTHOPEDIC COMPLAINTS: CHRONIC MOUNTAIN SICKNESS

Objective: Chronic mountain sickness (CMS) is a clinical syndrome with symptoms of polycythemia that may interfere with other nonspecific diseases. The current study aimed to investigate the symptoms of patients living at high altitudes, who initially presented complaints that seemed to be common orthopedic problems, and to examine their relationship with chronic mountain sickness. Material and Methods: The prospectively collected data of 104 patients were retrospectively evaluated for serum hemoglobin (Hb) and hematocrit (Hct) levels, oxygen saturation (sO2), Qinghai CMS questionnaire score, alcohol and tobacco use, “any history of acute mountain sickness, body mass index (BMI), blood pressure, heart rate, and duration of high-altitude living. Patients grouped according to the Qinghai score as healthy, mild, moderate or severe CMS. The groups were investigated in terms of parameters and demographic characteristics. Results: Of the 104 patients, 33 (31.7%) had a mild CMS score ≥6 (28 patients, 6–10, 5 patients, 11–14 points); remaining patients had no CMS. The frequency of excessive erythrocytosis was 4.5% in men and 3.3% in women. There was a significant difference in Hb, Hct and sO2 levels between the healthy and mild CMS groups (p<0.001). CMS score had a positive correlation with Hct (rho 0,381 p<0.001) and negative correlation between sO2 levels (rho -0.432 p<0.001). Conclusions: CMS can be observed at lower altitudes than described in literature. In individuals living in high altitudes, some of the CMS symptoms may be confused with real orthopedic symptoms and orthopedists working in these areas should increase their awareness on this issue. In order to make an appropriate approach, other symptoms related to CMS should be questioned in patients living at high altitudes.

Older Age as a Predictive Risk Factor for Acute Mountain Sickness

BackgroundOlder populations are increasing and comprise a substantial portion of high-altitude travelers. Aging physiology may influence susceptibility to acute mountain sickness, though prior research remains inconclusive. The goal of this study was to investigate the relationship between increasing age and acute mountain sickness. MethodsThis study was a pooled analysis of 5 prospective randomized controlled trials conducted at White Mountain, California from 2010, 2016-2019 with identical 4-hour rapid ascent from 1242 m to overnight sojourn at 3810 m. Acute mountain sickness was defined by the 2018 Lake Louise Questionnaire criteria. ResultsThere were 491 participants analyzed, 234 (48%) diagnosed with acute mountain sickness and 71 (14%) with moderate acute mountain sickness. Mean age was 37 years (±13). There was no significant correlation between Lake Louise Questionnaire severity and age (r = −0.02; 95% confidence interval [CI], −0.11-0.07, P = .7), 40-year-old dichotomy (t = −0.6; 95% CI, −0.53-0.28, P = .6), or decade of life (P = .4). Logistic regression found no increased odds of acute mountain sickness for increasing age by decade of life (odds ratio [OR] 1.0; 95% CI, 0.97-1.0) or 40-year-old dichotomy (OR 1.4; 95% CI, 0.97-2.1). A history of acute mountain sickness increased odds of acute mountain sickness (OR 3.2; 95% CI, 1.5-7.7). ConclusionsOlder age was not associated with incidence nor severity of acute mountain sickness. A history of altitude illness increased odds of acute mountain sickness and should be used for pre-ascent risk stratification.

Efficacy of acetazolamide for the prophylaxis of acute mountain sickness: A systematic review, meta-analysis, and trial sequential analysis of randomized clinical trials.

BACKGROUND:Acute mountain sickness (AMS) is a benign and self-limiting syndrome, but can progress to life-threatening conditions if leave untreated. This study aimed to assess the efficacy of acetazolamide for the prophylaxis of AMS, and disclose factors that affect the treatment effect of acetazolamide.METHODS:Randomized controlled trials comparing the use of acetazolamide versus placebo for the prevention of AMS were included. The incidence of AMS was our primary endpoint. Meta-regression analysis was conducted to explore factors that associated with acetazolamide efficacy. Trial sequential analyses were conducted to estimate the statistical power of the available data.RESULTS:A total of 22 trials were included. Acetazolamide at 125, 250, and 375 mg/bid significantly reduced incidence of AMS compared to placebo. TAS indicated that the current evidence was adequate confirming the efficacy of acetazolamide at 125, 250, and 375 mg/bid in lowering incidence of AMS. There was no evidence of an association between efficacy and dose of acetazolamide, timing at start of acetazolamide treatment, mode of ascent, AMS assessment score, timing of AMS assessment, baseline altitude, and endpoint altitude.CONCLUSION:Acetazolamide is effective prophylaxis for the prevention of AMS at 125, 250, and 375 mg/bid. Future investigation should focus on personal characteristics, disclosing the correlation between acetazolamide efficacy and body mass, height, degree of prior acclimatization, individual inborn susceptibility, and history of AMS.

Incidence and Determinants of Acute Mountain Sickness in Mount Kinabalu, Malaysia.

Yang, Su Lan, Nor At'fina Ibrahim, Grazele Jenarun, and Houng Bang Liew. Incidence and determinants of acute mountain sickness in Mount Kinabalu, Malaysia. High Alt Med Biol. 21:265–272, 2020.Background: Acute mountain sickness (AMS) is the most common type of high-altitude sickness. The incidence of AMS varies by mountain location, trail characteristics, and study design. The lack of local epidemiology data has driven us to investigate the incidence and severity of AMS and its associated factors at Mount Kinabalu, Malaysia.Methods: A cohort study was conducted to collect data from climbers after days 1 (3272 m) and 2 (4095 m) of ascent. A self-administered questionnaire was used to explore climbers' demographic and climb characteristics, history of AMS, alcohol exposure, and AMS prevention measures. The Lake Louis score 2018 was used to assess the presence and severity of AMS (cutoff ≥3). Univariate and multivariable logistic regressions were performed to determine the factors associated with the development of AMS on day 2.Results: Data from 345 climbers were analyzed. The incidence of AMS was 23.9% (95% confidence interval [CI] 19.5%–28.7%) and 21.7% (95% CI 17.5%–26.3%) on days 1 and 2, respectively. The majority were mild cases. Experiencing AMS on day 1 (odds ratio [OR] = 12.88; 95% CI 6.71–24.75), alcohol consumption (OR = 3.73; 95% CI 1.66–8.39), receiving guide advice on day 1 (OR = 0.49; 95% CI 0.26–0.93), and age (OR = 0.96; 95% CI 0.93–0.99) were significant determinants of AMS at Mount Kinabalu. Gender, history of AMS, past exposure to high altitude, ascending time, water intake, acetazolamide use, physical fitness, pulse rate, and peripheral capillary oxygen saturation (SpO2) were not associated with AMS at Mount Kinabalu.Conclusion: Future analysis with age strata is required to ascertain the association of age with AMS. Our research has signposted a strong call for collaborative efforts to improve the provision of hiking advice and discourage alcohol sales to mitigate the risk of AMS among Mount Kinabalu climbers.

The usefulness of prophylactic use of acetazolamide in subjects with acute mountain sickness.

The mechanisms of acetazolamide (ACZ) in the prophylaxis of acute mountain sickness (AMS) remain unclear. This study evaluated the changes in physiological variables of sleep and heart rate variability (HRV) in subjects with earlier history of AMS who underwent prophylactic treatment of ACZ. Nonacclimatized healthy subjects were transported using a bus from 555 m to 3150 m within 3 hours. Polysomnography (PSG) was performed 3 days before ascent (T0), for two consecutive nights at 3150 m (T1 and T2), and 2 days after descent (T3). HRV was measured before sleep and after awakening from T0 to T3. AMS was diagnosed using a self-reported Lake Louise score questionnaire. Subjects found confirmed to have AMS were enrolled in this study. The physiological variables and HRV were compared in AMS subjects without (control group) and with prophylactic ACZ (prophylactic ACZ group). Thirteen AMS subjects were enrolled. The PSG results were analyzed in eight and HRV were analyzed in nine of the 13 subjects. The prophylactic use of ACZ in the subjects with a history of AMS significantly improved sleep efficiency (p = 0.012) and awakening percentages (p = 0.017) at T1, significantly higher levels of arterial oxygen saturation (SaO2) and lower values of partial pressure end-tidal carbon dioxide tension (PETCO2) at four time points. Furthermore, they had a higher rapid eye movement sleep percentage (p = 0.05) at T2. Prophylactic ACZ treatment significantly increased the normalized unit of high frequency at T1 after awakening (p = 0.028). Significantly higher quality of sleep, higher SaO2 during sleep, and lower PETCO2 at high altitude were found in the subjects with a history of AMS using prophylactic ACZ before rapid ascent. ACZ may accelerate the acclimatization process for rapid ascents to high altitudes by increasing parasympathetic tone based on HRV analyses.

Characteristics of Headache and Relationship to Acute Mountain Sickness at 4559 Meters

The goals of this study were to characterize headache at high altitude in relation to the severity of acute mountain sickness (AMS), to investigate whether a history of migraine or nonmigrainous headache at low altitude is a risk factor for AMS and to estimate its effect size in relation to established major risk factors. We performed a secondary, extended analysis of data obtained from 1320 mountaineers staying overnight at the Capanna Margherita (4559 m). Headache at low and high altitude was classified according to the criteria of the International Headache Society. About 45% of the mountaineers suffered from headache in the evening of the arrival day at 4559 m. In those with headache, tension type headache decreased from 62% to 29% and 13% with no AMS (AMS-C <0.70), moderate AMS, and more severe AMS (AMS-C ≥1.5), while headache fulfilling the criteria of migraine increased correspondingly from 14% to 34% and 69%. A history of migraine or any type of headache at low altitude is a minor predictor of AMS that does not significantly contribute to AMS risk in a multivariate analysis including the major risk factors such as history of AMS, rate of ascent, and degree of preacclimatization in this population of alpine mountaineers. The association between more severe AMS and migrainous headache may be due to common nonspecific symptoms but a common underlying pathophysiology of AMS and migraine cannot be excluded. Despite this association a history of migraine or other headache at low altitude is not a major risk factor for AMS.

Impact of Study Design on Reported Incidences of Acute Mountain Sickness: A Systematic Review.

Published incidences of acute mountain sickness (AMS) vary widely. Reasons for this variation, and predictive factors of AMS, are not well understood. We aimed to identify predictive factors that are associated with the occurrence of AMS, and to test the hypothesis that study design is an independent predictive factor of AMS incidence. We did a systematic search (Medline, bibliographies) for relevant articles in English or French, up to April 28, 2013. Studies of any design reporting on AMS incidence in humans without prophylaxis were selected. Data on incidence and potential predictive factors were extracted by two reviewers and crosschecked by four reviewers. Associations between predictive factors and AMS incidence were sought through bivariate and multivariate analyses for different study designs separately. Association between AMS incidence and study design was assessed using multiple linear regression. We extracted data from 53,603 subjects from 34 randomized controlled trials, 44 cohort studies, and 33 cross-sectional studies. In randomized trials, the median of AMS incidences without prophylaxis was 60% (range, 16%-100%); mode of ascent and population were significantly associated with AMS incidence. In cohort studies, the median of AMS incidences was 51% (0%-100%); geographical location was significantly associated with AMS incidence. In cross-sectional studies, the median of AMS incidences was 32% (0%-68%); mode of ascent and maximum altitude were significantly associated with AMS incidence. In a multivariate analysis, study design (p=0.012), mode of ascent (p=0.003), maximum altitude (p<0.001), population (p=0.002), and geographical location (p<0.001) were significantly associated with AMS incidence. Age, sex, speed of ascent, duration of exposure, or history of AMS were inconsistently reported and therefore not further analyzed. Reported incidences and identifiable predictive factors of AMS depend on study design.

Diagnosis and prediction of the occurrence of acute mountain sickness measuring oxygen saturation--independent of absolute altitude?

Commercialization of trekking tourism enables untrained persons to participate in trekking tours. Because hypoxia is one of the main purported triggers for acute mountain sickness (AMS), pulse oximetry, which measures arterial oxygen saturation (SPO2), is discussed to be a possible and useful tool for the diagnosis of AMS. The purpose of this study was to evaluate possible associations between SPO2 values and the occurrence of AMS. In 204 trekkers, SPO2 values (pulse oximetry) were measured and the Lake Louise Self-assessment Score (LLS) was administered over the first 7 days of their trekking tours. During treks at altitudes of 2500-5500 m in Nepal, India, Africa, and South America, 100 participants suffered from mild AMS, 3 participants suffered from severe AMS, and 9 participants reported both mild and severe AMS. The lowest mean SPO2 was 85.5 (95 % confidence interval (CI), 83.9-86.1 %) on day 5. SPO2 and LLS exhibited a weak to moderate negative correlation for all days of the study (ρ ranging from -0.142 to -0.370). Calculation of time-shifted associations of 24 and 48 h resulted in the disappearance of most associations. Susceptibility to headaches (odds ratio (OR) 2.9-7.2) and a history of AMS (OR 2.2-3.1) were determined to be potential risk factors for the development of AMS. Since there is no strong altitude-independent association between AMS and SPO2 during the first week of high-altitude adaptation, the implementation of pulse oximetry during trekking in order to detect and predict AMS remains questionable.

Acute mountain sickness in athletes with neurological impairments

Acute mountain sickness (AMS) is a symptom complex noticed commonly among high altitude travelers. The occurrence of AMS depends on multiple factors that have been studied extensively. However, AMS in individuals with neurological impairments has not been considered in detail. A total of 168 subjects, including active controls, inactive controls, and those with spinal cord injury (SCI), multiple sclerosis, and traumatic brain injury (TBI), were studied at the National Veterans Winter Sports Clinic in Snowmass, Colorado, from 2007 to 2009 for the occurrence of AMS. Lake Louise Score was used to quantify symptoms. A higher than anticipated occurrence of AMS (42.85%) among the study population was noted, with significantly higher Lake Louis Scores among athletes with neurological impairments. Disability group, prior history of AMS, and prior occurrence of headache at high altitude could be used as predictors for the development of AMS symptoms. More research is warranted specifically targeting the interaction between factors affecting AMS and the pathophysiology of neurological impairments like SCI and TBI to further our understanding about prophylactic medications and treatments for AMS, especially because many military personnel with neurological impairments continue on Active Duty.

Reproducibility of Acute Mountain Sickness in Children and Adults: A Prospective Study

Although a history of previous acute mountain sickness (AMS) is commonly used for providing advice and recommending its prophylaxis during subsequent exposure, the intraindividual reproducibility of AMS during repeated high-altitude exposure has never been examined in a prospective controlled study. In 27 nonacclimatized children and 29 adults, AMS was assessed during the first 48 hours after rapid ascent to 3450 m on 2 consecutive occasions 9 to 12 months apart. During the first exposure, 18 adults (62%) and 6 children (22%) suffered from AMS; during the second exposure, 14 adults (48%) and 4 children (15%) suffered from this problem (adults versus children, P ≤ .01). Most importantly, the intraindividual reproducibility of AMS was very different (P < .001) between children and adults. None of the 6 children having suffered from AMS during the first exposure suffered from AMS during the second exposure, but 4 children with no AMS during the first exposure did experience this problem during the second exposure. In contrast, 14 of the 18 adults who suffered from AMS on the first occasion also presented with this problem during the second exposure, and no new case developed in those who had not experienced AMS on the first occasion. In adults, a history of AMS is highly predictable of the disease on subsequent exposure, whereas in children it has no predictive value. A history of AMS should not prompt practitioners to advise against reexposure to high altitude or to prescribe drugs for its prophylaxis in children.

Epidemiology of Acute Mountain Sickness on Jade Mountain, Taiwan: An Annual Prospective Observational Study

Acute mountain sickness (AMS) is a pathophysiological symptom complex that occurs in high altitude areas. The AMS prevalence is reportedly 28% on Jade Mountain, the highest mountain (3952 m) in Taiwan. We conducted this study owing to the lack of annual epidemiological data on AMS in Taiwan. Between April 2007 and March 2008, 1066 questionnaires were completed by trekkers visiting Paiyun Lodge on Jade Mountain. Information in the questionnaire included demographic data, mountaineering experience, AMS history, and trekking schedule. Weather data were obtained from the Central Weather Bureau of Taiwan. The Lake Louise AMS score was used to record symptoms and diagnose AMS. The chi-square test or the Student t test was used to evaluate associations between variables and AMS. In our study, the AMS prevalence was 36%. It increased significantly at different rates at different locations on the Jade Mountain trail and varied significantly in different months. Rainy weather tended to slightly increase the incidence of AMS. A lower incidence of AMS was correlated with hig-altitude trekking experience or preexposure (p < 0.05), whereas a higher incidence of AMS was correlated with a prior history of AMS (p < 0.05). The trekkers with AMS were significantly younger, ascended faster from their residence to the entrance or to Paiyun Lodge, and ascended slower from the entrance to the Paiyun Lodge (p < 0.05), but the differences lacked clinical significance. No differences in the incidence of AMS based on blood type, gender, or obesity were observed. The most common symptom among all trekkers was headache, followed by difficulty sleeping, fatigue or weakness, gastrointestinal (GI) symptoms, and dizziness or lightheadedness. In conclusion, the AMS prevalence on Jade Mountain was 36%, varied by month, and correlated with trekking experience, preexposure, and a prior history of AMS. The overall presentation of AMS was similar to that on other major world mountains.

Mt. Whitney

The aim of this study was to determine the prevalence of summit success and acute mountain sickness (AMS) on Mt. Whitney (4419 m) and to identify variables that contribute to both. Hikers (N = 886) attempting the summit were interviewed at the trailhead upon their descent. Questionnaires included demographic and descriptive data, acclimatization and altitude history, and information specific to the ascent. The Lake Louise Self-Assessment Score was used to make a determination about the occurrence of AMS. Logistic regression techniques were used to calculate odds ratios (OR) for AMS and summit success. Forty-three percent of the sample met the criteria for AMS, and 81% reached the summit. The odds of experiencing AMS were reduced with increases in age (adjusted 10-yr OR = 0.78; P < 0.001), number of hours spent above 3000 m in the 2 wk preceding the ascent (adjusted 24-h OR = 0.71; P < 0.001), and for females (OR = 0.68; P = 0.02). Climbers who had a history of AMS (OR = 1.41; P = 0.02) and those taking analgesics (OR = 2.39; P < 0.001) were more likely to experience AMS. As climber age increased, the odds of reaching the summit decreased (adjusted 10-yr OR = 0.75; P < 0.001). However, increases in the number of hours per week spent training (adjusted 5-h OR = 1.24; P = 0.05), rate of ascent (adjusted 50 m x h(-1) OR = 1.13; P = 0.04), and previous high-altitude record (adjusted 500 m OR = 1.26; P < 0.001) were all associated with increased odds for summit success. A high percentage of trekkers reached the summit despite having symptoms of AMS.

Physical and Medical Characteristics of Successful and Unsuccessful Summiteers of Mount Everest in 2003

To describe physiological attributes (height, weight, sex, resting heart rate, etc.) of climbers attempting to summit Mt Everest and to investigate differences between successful and unsuccessful summiteers. One-hundred thirteen Everest climbers were surveyed by questionnaire before and after the spring 2003 climbing season. Climbers' previous high-altitude climbing experience and physical characteristics were recorded, as well as health before and during expedition, medication used, body weight before expedition and after summit attempt, and ultimate summit success or failure. The most common afflictions among climbers were cough, diarrhea, nausea, and vomiting, and the most common medications used were acetazolamide, aspirin, and antibiotics. Average postacclimatization, presummit "rest" altitude was 4571 m, and average weight carried 10.7 kg. Average body mass loss during expedition, regardless of success, was 7%. Oxygen use and existence of gastrointestinal disorders are strongly correlated with success in summiting Mt Everest. On the other hand, a history of acute mountain sickness before the attempt is correlated with failure in summiting Mt Everest. Several other factors were found to be marginally correlated with chance of success, but the power of the study was limited by a low postsummit attempt questionnaire return rate (34%).

Acute Mountain Sickness in Iranian Trekkers Around Mount Damavand (5671 m) in Iran

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. We designed this study to determine the incidence and risk factors for AMS in trekkers around Mount Damavand in Iran. 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. 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). 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.

Acute Mountain Sickness in a General Tourist Population at Moderate Altitudes

To determine the incidence of acute mountain sickness in a general population of visitors to moderate elevations, the characteristics associated with it, and its effect on physical activity. A cross-sectional study. Resort communities located at 6300 to 9700 feet elevation in the Rocky Mountains of Colorado. Convenience sample of 3158 adult travelers, 16 to 87 years old (mean age [+/- SD], 43.8 +/- 11.8 years). Twenty-five percent of the travelers to moderate elevations developed acute mountain sickness, which occurred in 65% of travelers within the first 12 hours of arrival. Fifty-six percent of those with symptoms reduced their physical activity. The odds favoring acute mountain sickness were 3.5 times as large for visitors whose permanent residence was below 3000 feet elevation as for those whose residence was above 3000 feet; 2.8 times as large for visitors with previous symptoms of acute mountain sickness; and twice as large in travelers younger than 60 years. Women, obese persons, those in poor or average physical condition, and those with underlying lung disease also had a higher occurrence of acute mountain sickness (P < 0.05). Acute mountain sickness occurs in 25% of visitors to moderate altitudes and affects activity in most symptomatic visitors. Persons who are younger, less physically fit, live at sea level, have a history of acute mountain sickness, or have underlying lung problems more often develop these symptoms.

Angiotensin converting enzyme response to hypoxia in man: its role in altitude acclimatization.

The response of serum angiotensin converting enzyme (ACE) activity to three grades of hypoxia was studied in two groups of human subjects. Hypoxic gas mixtures having oxygen concentrations of 14, 12.6 and 10.4% were breathed successively for a period of 10 min at each concentration. Venous blood was sampled at the end of each of the three periods and arterial oxygen saturation was recorded throughout the experiment. The subjects were selected as being 'good' or 'poor' acclimatizers according to their history of acute mountain sickness. There were five subjects in each group. Hypoxia resulted in a reduction in ACE activity in both groups, the reduction being linear with respect to arterial oxygen saturation. The reduction in ACE activity was greater in the good acclimatizer group as shown by a significantly greater slope of the response line of ACE activity to arterial oxygen saturation. The significance of this finding in relation to the mechanism underlying acute mountain sickness is discussed.