High-altitude illness

Pathogenesis of high altitude pulmonary edema: does alveolar epithelial lining fluid vascular endothelial growth factor exacerbate capillary leak?

Vascular endothelial growth factor (VEGF) is a potent mediator of capillary leak if it gains access to its receptors on the capillary endothelium. We have observed that there are high levels of VEGF compartmentalized in the alveolar epithelial lining fluid of normal humans at levels 500-fold greater than plasma. The potential for high altitude to result in compromise of alveolar epithelial tight junctions and experimental animal studies in which pulmonary edema is induced when VEGF is overexpressed in the alveolar epithelium, suggest a mechanism. We hypothesize that when the epithelial barrier is compromised at high altitude the normally high level of VEGF in the alveolar epithelial fluid has access to the pulmonary endothelium, where it acutely alters permeability, markedly exacerbating the high permeability pulmonary edema that characterizes high altitude pulmonary edema. If correct, this paradigm opens the possibility of testing available anti-VEGF therapies to treat this potentially fatal disorder.

Sildenafil for the treatment of altitude-induced hypoxaemia

Exposure to high altitude causes alveolar hypoxia and induces pulmonary hypertension (PH) with consequent limitation of exercise capacity. To assess the impact of sildenafil on haemodynamic and clinical parameters, and on aerobic performance, 12 young healthy unacclimatised subjects were studied (6 received sildenafil 40 mg t.i.d. and 6 received placebo) at sea level and high altitude. Systolic pulmonary artery pressure increased at high altitude, but normalised with sildenafil. The altitude-induced decrease in maximal O2 consumption was significantly smaller with sildenafil than with placebo. Enhancing pulmonary circulation with sildenafil safely protects against the high altitude-induced PH and improves gas exchange.

Greater free plasma VEGF and lower soluble VEGF receptor-1 in acute mountain sickness

Vascular endothelial growth factor (VEGF) is a hypoxia-induced protein that produces vascular permeability, and limited evidence suggests a possible role for VEGF in the pathophysiology of acute mountain sickness (AMS) and/or high-altitude cerebral edema (HACE). Previous studies demonstrated that plasma VEGF alone does not correlate with AMS; however, soluble VEGF receptor (sFlt-1), not accounted for in previous studies, can bind VEGF in the circulation, reducing VEGF activity. In the present study, we hypothesized that free VEGF is greater and sFlt-1 less in subjects with AMS compared with well individuals at high altitude. Subjects were exposed to 4,300 m for 19–20 h (baseline 1,600 m). The incidence of AMS was determined by using a modified Lake Louise symptom score and the Environmental Symptoms Questionnaire for cerebral effects. Plasma was collected at low altitude and after 24 h at high altitude, or at time of illness, and then analyzed by ELISA for VEGF and for soluble VEGF receptor, sFlt-1. AMS subjects had lower sFlt-1 at both low and high altitude compared with well subjects and a significant rise in free plasma VEGF on ascent to altitude compared with well subjects. We conclude that increased free plasma VEGF on ascent to altitude is associated with AMS and may play a role in pathophysiology of AMS.

Psychobiology of altered states of consciousness

The article reviews the current knowledge regarding altered states of consciousness (ASC) (a) occurring spontaneously, (b) evoked by physical and physiological stimulation, (c) induced by psychological means, and (d) caused by diseases. The emphasis is laid on psychological and neurobiological approaches. The phenomenological analysis of the multiple ASC resulted in 4 dimensions by which they can be characterized: activation, awareness span, self-awareness, and sensory dynamics. The neurophysiological approach revealed that the different states of consciousness are mainly brought about by a compromised brain structure, transient changes in brain dynamics (disconnectivity), and neurochemical and metabolic processes. Besides these severe alterations, environmental stimuli, mental practices, and techniques of self-control can also temporarily alter brain functioning and conscious experience.

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.

Pretravel health advice among international travelers visiting Cuzco, Peru

BACKGROUND

Cuzco, a Peruvian city of historical interest located 3,326 m above sea level, is a frequent destination for tourists. We conducted a descriptive study to assess the extent and sources of pretravel health advice received by international travelers before their arrival to Cuzco.

METHODS

Data were collected as part of a health survey among travelers. Between August and November 2002, travelers between 15 and 65 years old were invited to fill out a questionnaire in the departing area of Cuzco's international airport.

RESULTS

A total of 5,988 travelers participated. The mean age was 35.4 years (SD 11.4 yr); 50.6% were female and 50.8% were single. Tourism was the reason for traveling in 90.2% of the participants, and 89.3% of them were traveling with companions. Pretravel health information was received by 93.6%. The median number of information sources was two, with books (41.5%), travel medicine clinics (38.8%), the Internet (23.3%), and general practitioners (22.7%) as the main sources. Most frequently received recommendations were about safe food and water consumption (85%), use of insect repellents (66.0%), sunburn protection (64.4%), and condom use (22%). Only 16.5% took medication to prevent altitude sickness, and 14.2% took medication to prevent traveler's diarrhea. Variables independently associated with receiving pretravel health information from a health care professional were female gender, country of residence other than the United States, length of stay in Cuzco > 7 days, length of stay in other Peruvian cities > 7 days, tourism as the main reason for visiting Cuzco, traveling with companions, and consulting of more than one source of information.

CONCLUSIONS

Most travelers arriving to Cuzco had received pretravel health information, and the majority obtained it from more than one source. Recommendations addressed for specific health risks, such as altitude sickness prophylaxis, were received by few travelers.

On the medical edge: preparation of expatriates, refugee and disaster relief workers, and Peace Corps volunteers

Travelers to extreme environments and those who spend long periods of time in settings with limited health care resources need to have more detailed pretravel screening and education than the routine short-term traveler. Expatriates, relief workers, and Peace Corps volunteers need to receive careful pretravel medical, dental, and psychologic screening before deployment. Knowledge of special risks associated with the environment in which they will be stationed is necessary to provide effective education about ways to reduce or eliminate the risk of illness and death. The travel medicine practitioner should also provide detailed, region-specific recommendations regarding emergency care while traveling in remote regions. Information on foreign medical facilities and practitioners should be gathered in advance and regularly updated. Many fee-for-service directories of overseas medical centers are often out of date and do not include emergency contact information. Once deployed, systems should be in place to ensure the traveler's continued personal safety and maintenance of good health. Although these systems are generally beyond the scope of work of travel medicine providers, it is important for the long-term traveler to be aware of the need to be prepared to deal with unexpected medical events. In the event of an overseas emergency, the travel medicine specialist may be called on to facilitate ground or air medical evacuation to the most appropriate medical center, to communicate treatment priorities and pertinent medical details to foreign medical providers, and to facilitate international air evacuation or repatriation if necessary. In each of these cases, the experience for the patient and the travel health professional is dramatically improved by adhering to risk-reduction measures, such as pretravel screening, pretravel health and safety education, and preparing for emergencies in advance.

Physiological aspects of high-altitude pulmonary edema

High-altitude pulmonary edema (HAPE) develops in rapidly ascending nonacclimatized healthy individuals at altitudes above 3,000 m. An excessive rise in pulmonary artery pressure (PAP) preceding edema formation is the crucial pathophysiological factor because drugs that lower PAP prevent HAPE. Measurements of nitric oxide (NO) in exhaled air, of nitrites and nitrates in bronchoalveolar lavage (BAL) fluid, and forearm NO-dependent endothelial function all point to a reduced NO availability in hypoxia as a major cause of the excessive hypoxic PAP rise in HAPE-susceptible individuals. Studies using right heart catheterization or BAL in incipient HAPE have demonstrated that edema is caused by an increased microvascular hydrostatic pressure in the presence of normal left atrial pressure, resulting in leakage of large-molecular-weight proteins and erythrocytes across the alveolarcapillary barrier in the absence of any evidence of inflammation. These studies confirm in humans that high capillary pressure induces a high-permeability-type lung edema in the absence of inflammation, a concept first introduced under the term “stress failure.” Recent studies using microspheres in swine and magnetic resonance imaging in humans strongly support the concept and primacy of nonuniform hypoxic arteriolar vasoconstriction to explain how hypoxic pulmonary vasoconstriction occurring predominantly at the arteriolar level can cause leakage. This compelling but as yet unproven mechanism predicts that edema occurs in areas of high blood flow due to lesser vasoconstriction. The combination of high flow at higher pressure results in pressures, which exceed the structural and dynamic capacity of the alveolar capillary barrier to maintain normal alveolar fluid balance.

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.

Prevention of infection in adult travelers after solid organ transplantation

Increasing numbers of solid organ transplant recipients are traveling to the developing world. Many of these individuals either do not seek or do not receive optimal medical care prior to travel. This review considers risks of international travel to adult solid organ transplant recipients and the use of vaccines and prophylactic agents in this population.

Direct ANP inhibition of hypoxia-induced inflammatory pathways in pulmonary microvascular and macrovascular endothelial monolayers

Atrial natriuretic peptide (ANP) has been shown to reduce hypoxia-induced pulmonary vascular leak in vivo, but no explanation of a mechanism has been offered other than its vasodilatory and natriuretic actions. Recently, data have shown that ANP can protect endothelial barrier functions in TNF-alpha-stimulated human umbilical vein endothelial cells. Therefore, we hypothesized that ANP actions would inhibit pulmonary vascular leak by inhibition of TNF-alpha secretion and F-actin formation. Bovine pulmonary microvascular (MVEC) and macrovascular endothelial cell (LEC) monolayers were stimulated with hypoxia, TNF-alpha, or bacterial endotoxin (LPS) in the presence or absence of ANP, and albumin flux, NF-kappa B activation, TNF-alpha secretion, p38 mitogen-activated protein kinase (MAPK), and F-actin (stress fiber) formation were assessed. In Transwell cultures, ANP reduced hypoxia-induced permeability in MVEC and TNF-alpha-induced permeability in MVEC and LEC. ANP inhibited hypoxia and LPS increased NF-kappa B activation and TNF-alpha synthesis in MVEC and LEC. Hypoxia decreased activation of p38 MAPK in MVEC but increased activation of p38 MAPK and stress fiber formation in LEC; TNF-alpha had the opposite effect. ANP inhibited an activation of p38 MAPK in MVEC or LEC. These data indicate that in endothelial cell monolayers, hypoxia activates a signal cascade analogous to that initiated by inflammatory agents, and ANP has a direct cytoprotective effect on the pulmonary endothelium other than its vasodilatory and natriuretic properties. Furthermore, our data show that MVEC and LEC respond differently to hypoxia, TNF-alpha-stimulation, and ANP treatment.

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 is associated with sleep desaturation at high altitude

OBJECTIVE

This study was intended to demonstrate a biologically important association between acute mountain sickness (AMS) and sleep disordered breathing.

METHODOLOGY

A total of 14 subjects (eight males, six females aged 36 +/- 10 years) were studied at six different altitudes from sea level to 5050 m over 12 days on a trekking route in the Nepal Himalaya. AMS was quantified by Lake Louise (LL) score. At each altitude, sleep was studied by 13 channel polysomnography (PSG). Resting arterial blood gases (ABG) and exercise SaO2 were measured. Ventilatory responses (VR) were measured at sea level. Individual data were analysed for association at several altitudes and mean data were analysed for association over all altitudes.

RESULTS

ABG showed partial acclimatization. For the mean data, there were strong positive correlations between LL score and altitude, and periodic breathing, as expected. Strong negative correlations existed between LL score and PaO2, PaCO2, sleep SaO2 and exercise SaO2, but there was no correlation with sea level VR. There were equally tight correlations between LLs/PaO2 and LL score/sleep SaO2. The individual data showed no significant correlations with LL score at any altitude, probably reflecting the non-steady state nature of the experiment. In addition, mean SaO2 during sleep was similar to minimum exercise SaO2 at each altitude and minimum sleep SaO2 was lower, suggesting that the hypoxic insult during sleep was equivalent to or greater than walking at high altitude.

CONCLUSIONS

It is concluded that desaturation during sleep has a biologically important association with AMS, and it is speculated that under similar conditions (trekking) it is an important cause of AMS.

Changes in the pattern of health disorders diagnosed among two cohorts of French travelers to Nepal, 17 years apart

BACKGROUND

Few on-site studies involving local doctors have been published.

METHODS

We conducted a prospective on-site study of health problems occurring among French tourists to Nepal between 1 January 2001 and 31 December 2001, and compared the results with those of an identical study performed in 1984.

RESULTS

Of the 21,457 French tourists who visited Nepal in 2001, 276 (1.3%) consulted the French Embassy doctor in Kathmandu with health complaints. The main reasons for seeking medical advice were diarrhea (26.8%), high-altitude illness (15.6%), lower respiratory tract infections (11.6%), dermatoses (8.7%), and fever (8.7%). Fifteen patients (5.4%) required hospitalization, five required medical evacuation (1.8%), and 14 (5%) were rescued by helicopter in the Himalayas. One patient died of cardiovascular disease. Relative to the 1984 cohort, significantly more patients consulted for high-altitude illness (p<.001), lower respiratory tract infections (p=.001), physical trauma (p=.01), and psychiatric disorders (p<.001), and significantly fewer patients consulted for dermatoses (p=.04), sexually transmitted diseases (p=.001), and upper respiratory tract infections (p=.005).

CONCLUSION

These results, obtained 17 years apart, illustrate the changes in the pattern of health disorders causing travelers in Nepal to consult a doctor.

Sildenafil inhibits altitude-induced hypoxemia and pulmonary hypertension

Exposure to high altitude induces pulmonary hypertension that may lead to life-threatening conditions. In a randomized, double-blind, placebo-controlled study, the effects of oral sildenafil on altitude-induced pulmonary hypertension and gas exchange in normal subjects were examined. Twelve subjects (sildenafil [SIL] n = 6; placebo [PLA] n = 6) were exposed for 6 days at 4,350 m. Treatment (3 x 40 mg/day) was started 6 to 8 hours after arrival from sea level to high altitude and maintained for 6 days. Systolic pulmonary artery pressure (echocardiography) increased at high altitude before treatment (+29% versus sea level, p < 0.01), then normalized in SIL (-6% versus sea level, NS) and remained elevated in PLA (+21% versus sea level, p < 0.05). Pulmonary acceleration time decreased by 27% in PLA versus 6% in SIL (p < 0.01). Cardiac output and systemic blood pressures increased at high altitude then decreased similarly in both groups. Pa(O(2)) was higher and alveolar-arterial difference in O(2) lower in SIL than in PLA at rest and exercise (p < 0.05). The altitude-induced decrease in maximal O(2) consumption was smaller in SIL than in PLA (p < 0.05). Sildenafil protects against the development of altitude-induced pulmonary hypertension and improves gas exchange, limiting the altitude-induced hypoxemia and decrease in exercise performance.

Acute mountain sickness: controversies and advances

This review discusses the impact of recent publications on pathophysiologic concepts and on practical aspects of acute mountain sickness (AMS). Magnetic resonance imaging studies do not provide evidence of total brain volume increase nor edema within the first 6 to 10 h of exposure to hypoxia despite symptoms of AMS. After 16 to 32 h at about 4500 m, brain volume increases by 0.8% to 2.7%, but morphological changes do not clearly correlate with symptoms of AMS, and lumbar cerebrospinal fluid pressure was unchanged from normoxic values in individuals with AMS. These data do not support the prevailing hypothesis that AMS is caused by cerebral edema and increased intracranial pressure. Direct measurement of increased oxygen radicals in hypoxia and a first study reducing AMS when lowering oxygen radicals by antioxidants suggest that oxidative stress is involved in the pathophysiology of AMS. Placebo-controlled trials demonstrate that theophylline significantly attenuates periodic breathing without improving arterial oxygen saturation during sleep. Its effects on AMS are marginal and clearly inferior to acetazolamide. A most recent large trial with Ginkgo biloba clearly showed that this drug does not prevent AMS in a low-risk setting in which acetazolamide in a low dose of 2 x 125 mg was effective. Therefore, acetazolamide remains the drug of choice for prevention and the recommended dose remains 2 x 250 mg daily until a lower dose has been tested in a high-risk setting and larger clinical trials with antioxidants have been performed.

Severity and pattern of injury in survivors of alpine fall accidents

Few data are available on the medical aspects of fall accidents in mountainous terrain. Therefore, we report the severity and pattern of injury in 97 survivors of a major fall in Alpine terrain. Twenty-eight of 97 victims (29%) had severe or critical multisystem trauma, with an injury severity score >/=14, the incidence increasing to 23 out of 28 (82%) in individuals with falls exceeding 50 m. Fractures of the extremities and the sacropelvic region (n = 55) were the most common injuries. Seventeen of 21 spine fractures (81%) occurred in the thoracolumbar region. Rib fractures were found in 17 victims, in eight of them (47%) with an accompanying pneumothorax. Critical head trauma with a Glasgow Come Scale below 9 was rather uncommon (n = 6); abdominal visceral injuries were rare (n = 2). The pattern of injury observed in our study suggests a feet- or side-first body position at impact in the majority of individuals surviving Alpine fall accidents. Furthermore, it indicates a direct impact, rather than deceleration type mechanism of injury. Because of the high incidence of severe multisystem trauma, major fall in Alpine terrain should be used as triage criterion for the dispatch of an advanced trauma life support unit and direct transfer of the victim to a trauma center. Considering the high incidence of fractures, measures for adequate immobilization and analgesia will generally be necessary before the difficult evacuation from the site of the accident can be started.

Mechanisms of beta-receptor stimulation-induced improvement of acute lung injury and pulmonary edema

Acute lung injury (ALI) and the acute respiratory distress syndrome are complex syndromes because both inflammatory and coagulation cascades cause lung injury. Transport of salt and water, repair and remodeling of the lung, apoptosis, and necrosis are additional important mechanisms of injury. Alveolar edema is cleared by active transport of salt and water from the alveoli into the lung interstitium by complex cellular mechanisms. Beta-2 agonists act on the cellular mechanisms of pulmonary edema clearance as well as other pathways relevant to repair in ALI. Numerous studies suggest that the beneficial effects of beta-2 agonists in ALI include at least enhanced fluid clearance from the alveolar space, anti-inflammatory actions, and bronchodilation. The purposes of the present review are to consider the effects of beta agonists on three mechanisms of improvement of lung injury: edema clearance, anti-inflammatory effects, and bronchodilation. This update reviews specifically the evidence on the effects of beta-2 agonists in human ALI and in models of ALI. The available evidence suggests that beta-2 agonists may be efficacious therapy in ALI. Further randomized controlled trials of beta agonists in pulmonary edema and in acute lung injury are necessary.

High-altitude illness

Travel to a high altitude requires that the human body acclimatize to hypobaric hypoxia. Failure to acclimatize results in three common but preventable maladies known collectively as high-altitude illness: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). Capillary leakage in the brain (AMS/HACE) or lungs (HAPE) accounts for these syndromes. The morbidity and mortality associated with high-altitude illness are significant and unfortunate, given they are preventable. Practitioners working in or advising those traveling to a high altitude must be familiar with the early recognition of symptoms, prompt and appropriate therapy, and proper preventative measures for high-altitude illness.

High Altitude Cerebral Edema

This review focuses on the epidemiology, clinical description, pathophysiology, treatment, and prevention of high altitude cerebral edema (HACE). HACE is an uncommon and sometimes fatal complication of traveling too high, too fast to high altitudes. HACE is distinguished by disturbances of consciousness that may progress to deep coma, psychiatric changes of varying degree, confusion, and ataxia of gait. It is most often a complication of acute mountain sickness or high altitude pulmonary edema. The current leading theory of its pathophysiology is that HACE is a vasogenic edema; that is, a disruption of the blood-brain barrier, and we review possible mechanisms to explain this. Treatment and prevention of HACE are similar to those for the other altitude illnesses, but with greater emphasis on descent and steroids. We conclude the review with several case histories to illustrate key clinical features of the disorder.

An Unusual Case of an Airplane Headache

A 28-year-old man developed severe headache associated with changes in altitude during ascent and descent while flying in an airplane. Jabbing pain over the forehead and between the eyes began within minutes of ascent. It resolved once a cruising altitude was reached, but then returned at the start of descent.

Effects of five consecutive nocturnal hypoxic exposures on the cerebrovascular responses to acute hypoxia and hypercapnia in humans

The effects of discontinuous hypoxia on cerebrovascular regulation in humans are unknown. We hypothesized that five nocturnal hypoxic exposures (8 h/day) at a simulated altitude of 4,300 m (inspired O2 fraction = ∼13.8%) would elicit cerebrovascular responses that are similar to those that have been reported during chronic altitude exposures. Twelve male subjects (26.6 ± 4.1 yr, mean ± SD) volunteered for this study. The technique of end-tidal forcing was used to examine cerebral blood flow (CBF) and regional cerebral O2 saturation (SrO2) responses to acute variations in O2 and CO2 twice before, immediately after, and 5 days after the overnight hypoxic exposures. Transcranial Doppler ultrasound was used to assess CBF, and near-infrared spectroscopy was used to assess SrO2. Throughout the nocturnal hypoxic exposures, end-tidal Pco2 decreased ( P < 0.001) whereas arterial O2 saturation increased ( P < 0.001) compared with overnight normoxic control measurements. Symptoms associated with altitude illness were significantly greater than control values on the first night ( P < 0.001) and second night ( P < 0.01) of nocturnal hypoxia. Immediately after the nocturnal hypoxic intervention, the sensitivity of CBF to acute variations in O2 and CO2 increased 116% ( P < 0.01) and 33% ( P < 0.05), respectively, compared with control values. SrO2 was highly correlated with arterial O2 saturation ( R2 = 0.94 ± 0.04). These results show that discontinuous hypoxia elicits increases in the sensitivity of CBF to acute variations in O2 and CO2, which are similar to those observed during chronic hypoxia.

Randomised, double blind, placebo controlled comparison of ginkgo biloba and acetazolamide for prevention of acute mountain sickness among Himalayan trekkers: the prevention of high altitude illness trial (PHAIT)

OBJECTIVE

To evaluate the efficacy of ginkgo biloba, acetazolamide, and their combination as prophylaxis against acute mountain sickness.

DESIGN

Prospective, double blind, randomised, placebo controlled trial.

SETTING

Approach to Mount Everest base camp in the Nepal Himalayas at 4280 m or 4358 m and study end point at 4928 m during October and November 2002.

PARTICIPANTS

614 healthy western trekkers (487 completed the trial) assigned to receive ginkgo, acetazolamide, combined acetazolamide and ginkgo, or placebo, initially taking at least three or four doses before continued ascent.

MAIN OUTCOME MEASURES

Incidence measured by Lake Louise acute mountain sickness score > or = 3 with headache and one other symptom. Secondary outcome measures included blood oxygen content, severity of syndrome (Lake Louise scores > or = 5), incidence of headache, and severity of headache.

RESULTS

Ginkgo was not significantly different from placebo for any outcome; however participants in the acetazolamide group showed significant levels of protection. The incidence of acute mountain sickness was 34% for placebo, 12% for acetazolamide (odds ratio 3.76, 95% confidence interval 1.91 to 7.39, number needed to treat 4), 35% for ginkgo (0.95, 0.56 to 1.62), and 14% for combined ginkgo and acetazolamide (3.04, 1.62 to 5.69). The proportion of patients with increased severity of acute mountain sickness was 18% for placebo, 3% for acetazoalmide (6.46, 2.15 to 19.40, number needed to treat 7), 18% for ginkgo (1, 0.52 to 1.90), and 7% for combined ginkgo and acetazolamide (2.95, 1.30 to 6.70).

CONCLUSIONS

When compared with placebo, ginkgo is not effective at preventing acute mountain sickness. Acetazolamide 250 mg twice daily afforded robust protection against symptoms of acute mountain sickness.

Pathophysiological significance of peroxidative stress, neuronal damage, and membrane permeability in acute mountain sickness

Free radical-mediated changes in vascular permeability and subsequent inflammatory response may be a contributory pathogenetic cofactor responsible for the development of neurological sequelae associated with acute mountain sickness (AMS). To investigate this, 49 subjects were examined at sea level and serially after rapid ascent to 4,559 m. Although the venous concentration of total creatine phosphokinase activity was measured in all subjects, a complementary examination of lipid peroxidation (F2-isoprostanes), inflammatory (TNF-α, IL-1β, IL-2, IL-6, IL-8, C-reactive protein), and cerebrovascular tissue damage (neuron-specific enolase) biomarkers was confined to a subcohort of 24 subjects. A selective increase ( P < 0.05) in total creatine phosphokinase was observed in subjects diagnosed with AMS at high altitude ( n = 25) compared with apparently healthy controls ( n = 24). However, despite a marked increase in IL-6 and C-reactive protein attributable primarily to subjects developing high-altitude pulmonary edema, subcohort analyses demonstrated no selective differences in F2-isoprostanes, neuron-specific enolase, or remaining proinflammatory cytokines due to AMS ( n = 14). The present findings are the first to demonstrate that free radical-mediated neuronal damage of sufficient degree to be detected in the peripheral circulation does not occur and is, therefore, unlikely to be an important, initiating event that is critical for the development of AMS. The pathophysiological significance of increased sarcolemmal membrane permeability and inflammatory response, either as a cause or epiphenomenon of AMS and/or high-altitude pulmonary edema, remains to be elucidated.

Tolerance of liver transplant patients to strenuous physical activity in high-altitude

Physical functioning is improved after liver transplantation but studies comparing liver transplant recipients with normal healthy people are lacking. How liver (and other organ) transplant recipients tolerate strenuous physical activities is unknown. There are no data on the tolerance of transplant patients at high altitude. Six liver transplant subjects were selected to participate in a trek up Mount Kilimanjaro 5895 m, Tanzania. Physical performance and susceptibility to acute mountain sickness were prospectively compared with fifteen control subjects with similar profiles and matched for age and body mass index. The Borg-scale (a rating of perceived exertion) and cardiopulmonary parameters at rest were prospectively compared with six control subjects also matched for gender and VO2max. Immunosuppression in transplant subjects was based on tacrolimus. No difference was seen in physical performance, Borg-scales and acute mountain sickness scores between transplant and control subjects. Eight-three percent of transplant subjects and 84.6% of control subjects reached the summit (p=0.7). Oxygen saturation decreased whereas arterial blood pressure and heart rate increased with altitude in both groups. The only difference was the development of arterial hypertension in transplant subjects at 3950 m (p=0.036). Selected and well-prepared liver transplant recipients can perform strenuous physical activities and tolerate exposure to high altitude similar to normal healthy people.

Irreversible Subcortical Dementia Following High Altitude Illness

In this report, we present the cases of two 63-year-old women who developed high altitude cerebral edema complicated by the occurrence of permanent neuropsychiatric sequelae. They shared a similar clinical course, in that both developed disturbance of consciousness shortly after their arrival at Cuzco, Peru (3500 m), and both developed persistent neuropsychiatric symptoms after resolution of the acute illness. Interestingly, in case 2 there was a 1-month lucid interval between remission of high altitude illness and occurrence of the irreversible neuropsychiatric sequelae. Brain computerized tomography in case 1 and brain magnetic resonance imaging in case 2 disclosed lesions in the globus pallidus bilaterally, suggesting that the neuropsychiatric symptoms in these patients were manifestations of subcortical dementia. The development of high altitude illness was considered to be attributable to mild restrictive lung impairment in case 1 and to a deficient ventilatory response to hypoxia in case 2. It must therefore be borne in mind that irreversible subcortical dementia may be associated with high altitude cerebral edema.

Flunarizine in prevention of headache, ataxia, and memory deficits during decompression to 4559 m

Our purpose was to study the preventive effect of the calcium channel blocker flunarizine on headache, postural ataxia, and memory deficits occurring during decompression to high altitude in a randomized, placebo-controlled, double-blind study. After 7-day pretreatment with the study drugs, 20 healthy men were investigated at 490 m and 0.5, 2, 4, and 6 h later at a simulated altitude of 4559 m. Headache severity was evaluated on a 4-point scale. Sway path and anteroposterior and lateral sway were recorded with open and closed eyes by static posturography. Short- and long-term memory was studied by testing the recall of verbal and figural material immediately and 2 h after presentation, respectively. Blood pressure (BP) and arterial oxygen saturation (Sa(O2)) were also assessed. Headache scores showed a trend to be lower in the flunarizine group that was significant after 4 and 6 h. Headache scores expressed as difference from baseline values showed a nonsignificant trend to be lower at 4 and 6 h in subjects treated with flunarizine. Postural stance, memory, BP, and Sa(O2) were similar in both treatment groups. Although the low number of investigated subjects may have prevented the detection of a significant therapeutic effect of flunarizine, the present data do not show that flunarizine is effective for prevention of headache, postural ataxia, and neurocognitive deficits occurring at simulated high altitude.

Symptoms of infection and acute mountain sickness; associated metabolic sequelae and problems in differential diagnosis

Infections and acute mountain sickness (AMS) are common at high altitude, yet their precise etiologies remain elusive and the potential for differential diagnosis is considerable. The present study was therefore designed to compare clinical nonspecific symptoms associated with these pathologies and basic changes in free radical and amino-acid metabolism. Nineteen males were examined at rest and after maximal exercise at sea level before (SL(1)/SL(2)) and following a 20 +/- 5 day ascent to Kanchenjunga base camp located at 5100 m (HA). Four subjects with symptoms consistent with an ongoing respiratory and recent gastrointestinal infection were also diagnosed with clinical AMS on the evening of day 1 at HA. These and six other subjects recovering from symptoms consistent with a respiratory infection presented with a greater increase (HA minus SL(1)) in AMS scores and resting venous concentration of lipid hydroperoxides (LH) and in total creatine phosphokinase and ratio of free tryptophan/branched chain amino acids, and greater decrease in glutamine (Gln) compared to healthy controls (n = 9, p < 0.05). The decrease in Gln was consistently related to the altitude/exercise-induced increase in LH (r = -0.69/r = -0.45; p < 0.05) and altitude-induced increase in myoglobin (r = -0.73, p < 0.05). These findings highlight the potential for the misdiagnosis of altitude illness due to the similarity of nonspecific constitutional symptoms associated with infection and AMS. Both conditions were characterized by parallel changes in peripheral biomarkers related to free-radical, skeletal muscle damage and amino acid metabolism. While clearly not establishing cause and effect, free radical-mediated changes in peripheral amino acid metabolism known to influence immune and cerebral serotoninergic function may enhance susceptibility to and/or delay recovery from altitude illness.

Whole-body hypoxic preconditioning protects mice against acute hypoxia by improving lung function

Survival in severe hypoxia such as occurs in high altitude requires previous acclimatization, which is acquired over a period of days to weeks. It was unknown whether intrinsic mechanisms existed that could be rapidly induced and could exert immediate protection on unacclimatized individuals against acute hypoxia. We found that mice pretreated with whole-body hypoxic preconditioning (WHPC, 6 cycles of 10-min hypoxia-10-min normoxia) survived significantly longer than control animals when exposed to lethal hypoxia (5% O2, survival time of 33.2 ± 6.1 min vs. controls at 13.8 ± 1.2 min, n = 10, P < 0.005). This protective mechanism became operative shortly after WHPC and remained effective for at least 8 h. Accordingly, mice subjected to WHPC demonstrated improved gas exchange when exposed to sublethal hypoxia (7% O2, arterial blood Po2 of 49.9 ± 4.2 vs. controls at 39.7 ± 3.6 Torr, n = 6, P < 0.05), reduced formation of pulmonary edema (increase in lung water of 0.491 ± 0.111 vs. controls at 0.894 ± 0.113 mg/mg dry tissue, n = 10, P < 0.02), and decreased pulmonary vascular permeability (lung lavage albumin of 7.63 ± 0.63 vs. controls at 18.24 ± 3.39 mg/dl, n = 6–10, P < 0.025). In addition, the severity of cerebral edema caused by exposure to sublethal hypoxia was also reduced after WHPC (increase in brain water of 0.254 ± 0.052 vs. controls at 0.491 ± 0.034 mg/mg dry tissue, n = 10, P < 0.01). Thus WHPC protects unacclimatized mice against acute and otherwise lethal hypoxia, and this protection involves preservation of vital organ functions.

High-altitude–related disorders—part ii: prevention, special populations, and chronic medical conditions

This second section of a 2-part review on high-altitude-related disorders focuses on strategies for prevention of high-altitude illness, identification of populations at increased risk for high-altitude illness, and effects of high altitude on selected chronic medical conditions. Practical aspects of advising and educating patients traveling to high altitude will be discussed, with special reference to pregnant women, infants and young children, healthy elders, and chronic medical conditions that may place persons at greater risk for high-altitude illness. The special concerns of pre-verbal children will be covered relative to the risks of high altitude for those too young to voice symptoms of illness and, thus, at-risk for potential serious consequences caused by delay in diagnosis and treatment.

High altitude sickness. Is acute cortisol deficiency involved in its pathophysiology?

High altitude illness (HAI) affects 42% of individuals climbing above 3000 m. The pathophysiology of HAI, including water retention remains unclear. Although decreased nitric oxide (NO) production is implicated in the pathophysiology, a recent study reported increased NO in breathes of high altitude inhabitants, apparently produced to combat the high altitude hypoxia. NO binds heme generally and impairs cytochrome P450 steroidogenic enzymes. A consequence of increased NO production may be decreased steroidogenesis. An acute cortisol deficiency may thus be the reason for water retention and oedema, and explains why dexamethasone is effective in treating some aspects of HAI.

Prevention and Treatment of High-altitude Illness in Travelers

High-altitude illness is the collective term for acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). These syndromes can affect unacclimatized travelers shortly after ascent to high altitude (especially higher than 2500 m). AMS is relatively common and usually is mild and self-limiting; HACE and HAPE are uncommon but life-threatening. Gradual ascent is the best strategy for preventing or minimizing high-altitude illness, although chemoprophylaxis may be useful in some situations. Acetazolamide remains the chemoprophylactic agent of choice, although other drugs, such as gingko biloba, are being investigated. Immediate descent remains the cornerstone of treatment for HACE and HAPE, although pharmacologic and hyperbaric therapies may facilitate this process.

High-altitude-related disorders—part I: pathophysiology, differential diagnosis, and treatment

As increasing numbers of people choose to sojourn or retire to the mountains, high-altitude illness is becoming a pathological phenomenon about which healthcare providers should have greater awareness. Hypoxia is the primary cause of high-altitude illness, but other stressors on the sympathetic nervous system, such as cold and exertion, also contribute to disease development and progression. Although variable across persons, symptoms of high-altitude disorders usually occur at altitudes over 7000 feet, and typically in 1 of 3 forms: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), or high-altitude pulmonary edema (HAPE). Major symptoms include nausea, poor sleep, headache, lassitude, cough, dyspnea on exertion and at rest, ataxia, and mental status changes. As a rule, illness occurring at high altitude should be attributed to the altitude until proven otherwise. Treatment is best accomplished by descent and by oxygen or pharmacologic intervention if necessary. Under no circumstances should a person with worsening symptoms of high-altitude illness delay descent. As will be discussed in part II of this article, gradual ascent and subsequent acclimatization to altitude is the most effective prevention, though acetazolamide (Diamox) may be a useful prophylactic measure in some.

Long-term Intermittent Exposure to High Ambient CO 2 Causes Respiratory Disturbances During Sleep in Submariners *

BACKGROUND

During most of the cruise, submarines are detached from their environment. Therefore, O(2) levels are relatively low (19 kPa, 144 mm Hg) and CO(2) levels are high (1 kPa, 7.6 mm Hg). There are, however, periods during ventilation of the submarine in which CO(2) levels drop and O(2) levels increase. The objective of this study was to determine whether these unique gas changes might result in sleep-disordered breathing in submariners.

METHODS AND MATERIALS

The sleep of eight healthy soldiers was assessed three times: (1) control night, in submarine docking; (2) at the beginning of the cruise (reflecting acute exposure to gas changes); and (3) at the end of the cruise (chronic exposure to gas changes). Each night was divided to three parts because of different CO(2) levels (secondary to ventilation of the submarine). Sleep and breathing were measured using the portable Watch PAT100 device (Itamar Medical, Ltd; Caesarea, Israel) to detect breathing abnormalities during sleep.

RESULTS

Sleep and breathing data were categorized according to four CO(2) conditions: acute moderate (inhaled CO(2) levels of 2.3 to 5 mm Hg during first 1 to 2 nights of the cruise); acute high (inhaled CO(2) levels of 5 to 9.2 mm Hg during the first 1 to 2 nights of the cruise); chronic moderate (inhaled CO(2) levels of 2.3 to 5 mm Hg during nights 9 to 10 of the cruise); and chronic high (inhaled CO(2) levels of 5 to 9.2 mm Hg during nights 9 to 10 of the cruise). Respiratory disturbance index (RDI) was significantly higher in the chronic moderate CO(2) condition than the chronic high condition (18.9/h vs 8/h, p < 0.005). RDI did not correlate with CO(2) levels during the first nights of the cruise (R = - 0.2, not significant), but significantly negatively correlated with it during the last nights of the cruise (R = - 0.56, p < 0.05).

CONCLUSIONS

We conclude that during an 11-day cruise, submariners adapt to high CO(2) levels, as evidenced by the significant dependence of RDI on CO(2) during the final but not initial days of the cruise. This adaptation resulted in a significant increase in RDI when CO(2) levels declined during the later nights of the cruise.

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.

Exercise delays the hypoxic thermal response in rats

Exercise exacerbates acute mountain sickness. In infants and small mammals, hypoxia elicits a decrease in body temperature (Tb) [hypoxic thermal response (HTR)], which may protect against hypoxic tissue damage. We postulated that exercise would counteract the HTR and promote hypoxic tissue damage. Tb was measured by telemetry in rats (n = 28) exercising or sedentary in either normoxia or hypoxia (10% O2, 24 h) at 25 degrees C ambient temperature (Ta). After 24 h of normoxia, rats walked at 10 m/min on a treadmill (30 min exercise, 30 min rest) for 6 h followed by 18 h of rest in either hypoxia or normoxia. Exercising normoxic rats increased Tb ( degrees C) vs. baseline (39.68 +/- 0.99 vs. 38.90 +/- 0.95, mean +/- SD, P < 0.05) and vs. sedentary normoxic rats (38.0 +/- 0.09, P < 0.05). Sedentary hypoxic rats decreased Tb (36.15 +/- 0.97 vs. 38.0 +/- 0.36, P < 0.05) whereas Tb was maintained in the exercising hypoxic rats during the initial 6 h of exercise (37.61 +/- 0.55 vs. 37.72 +/- 1.25, not significant). After exercise, Tb in hypoxic rats reached a nadir similar to that in sedentary hypoxic rats (35.05 +/- 1.69 vs. 35.03 +/- 1.32, respectively). Tb reached its nadir significantly later in exercising hypoxic vs. sedentary hypoxic rats (10.51 +/- 1.61 vs. 5.36 +/- 1.83 h, respectively; P = 0.002). Significantly greater histopathological damage and water contents were observed in brain and lungs in the exercising hypoxic vs. sedentary hypoxic and normoxic rats. Thus exercise early in hypoxia delays but does not prevent the HTR. Counteracting the HTR early in hypoxia by exercise exacerbates brain and lung damage and edema in the absence of ischemia.

High-altitude illness

High-altitude illness is the collective term for acute mountain sickness (AMS), high-altitude cerebral oedema (HACE), and high-altitude pulmonary oedema (HAPE). The pathophysiology of these syndromes is not completely understood, although studies have substantially contributed to the current understanding of several areas. These areas include the role and potential mechanisms of brain swelling in AMS and HACE, mechanisms accounting for exaggerated pulmonary hypertension in HAPE, and the role of inflammation and alveolar-fluid clearance in HAPE. Only limited information is available about the genetic basis of high-altitude illness, and no clear associations between gene polymorphisms and susceptibility have been discovered. Gradual ascent will always be the best strategy for preventing high-altitude illness, although chemoprophylaxis may be useful in some situations. Despite investigation of other agents, acetazolamide remains the preferred drug for preventing AMS. The next few years are likely to see many advances in the understanding of the causes and management of high-altitude illness.

Transient minor improvement of high altitude headache by sumatriptan

High-altitude headache often fulfills the criteria of migraine. Therefore, we hypothesized that sumatriptan, a 5-HT1 receptor agonist specifically effective for treatment of migraine, would also alleviate high altitude headache. A randomized, placebo-controlled double-blind trial was performed on 29 mountaineers with at least moderate headache on the day of arrival at 4559 m. Fourteen subjects received 100 mg sumatriptan orally and 15 subjects received placebo. Before treatment there were no significant differences between groups regarding rate of ascent, duration and severity of headache, and acute mountain sickness score. All 6 female subjects were randomly assigned to placebo. Absolute values and the reduction of headache scores 1, 3, and 12 h after the administration of sumatriptan did not differ between treatment groups, but headache scores tended to be lower with sumatriptan after 1 or 3 h when compared with placebo. Considering only male mountaineers, there was a significant decrease of headache scores after 1 and 3 h. Because there was only a minor transient amelioration of high altitude headache with sumatriptan, we conclude that 5-HT1 receptors do not play a major role in the pathophysiology of high altitude headache.

Environmental insults: smoke inhalation, submersion, diving, and high altitude

In the expanding search for recreation, we spend more and more of our time in various environments. Whether the air is thin or compressed or smoke-filled or there is no air at all, emergency physicians continue to meet and treat the various pulmonary emergencies that the environment may create. The authors present the background, diagnosis, and management of a few of the more common pulmonary emergencies that the environment may produce.

Oxygen-hemoglobin affinity at sea level may predict acute illness at altitude: theory and simulation

Acute mountain sickness carries with it serious health and economic costs. In their pursuit of the mechanisms that produce acute mountain sickness, researchers have overlooked the existence of a possible screening test, a test based on individual variation in cerebral oxygen exchange at sea level. In this paper, I highlight the mathematical link between cerebral oxygen exchange at sea level - this is reflected in the magnitude of the oxygen extraction coefficient - and a change in brain blood flow at altitude; this link has been overlooked. A lower oxygen extraction coefficient at sea level can act - at altitude - to reduce the capacity of the intracranial compartment to accommodate brain swelling, exacerbate increases in cell volume, promote the stimulation of angiogenesis, and further cerebral edema, each of which may contribute to acute mountain sickness. In retrospect, it seems obvious that the initial state of cerebral oxygen exchange will impact the cerebral circulatory response to subsequent hypoxia. This deceptively simple notion offers us an opportunity to identify beforehand those people likely to develop acute mountain sickness when they travel to altitude.

Preparing the traveller

The four steps for giving travellers the foundation for healthy journeys are to assess their health, analyse their itineraries, select vaccines, and provide education about prevention and self-treatment of travel-related diseases. This process takes time. Since there is a risk of information overload, travellers should leave the clinic with some written advice for reinforcement. The order of these steps can be tailored to what best suits the travel clinic, but vaccinating early in the process allows monitoring for adverse reactions. Face-to-face discussion is vital for explaining the use and side-effects of medications. Those who provide a travel medicine service should be seeing many travellers and should seek specialist training. In 2003, the International Society of Travel Medicine introduced a certificate of knowledge examination in travel medicine. We cannot make travellers bullet-proof but it is possible to make them bullet-resistant. The pre-travel visit should minimise health risks specific to the journey, give travellers the capability to handle most minor medical problems, and allow them to identify when to seek local care during the trip or on return.

Working in permanent hypoxia for fire protection-impact on health

OBJECTIVES

A new technique to prevent fires is continuous exchange of oxygen with nitrogen which leads to an oxygen concentration of between 15% and 13% in the ambient air. This paper reviews the effect of short-term, intermittent hypoxia on health and performance of people working in such atmospheres.

METHODS

We reviewed the effect of ambient air hypoxia on human health in the literature using Medline, as well as reference lists of articles and handbooks. Articles were assessed from the perspective of working conditions in fire-protected rooms.

RESULTS

Oxygen reduced to 15% and 13% in normobaric atmospheres is equivalent to the hypobaric atmospheres found at 2,700 and 3,850-m altitudes. When acutely exposed, a healthy person responds within minutes to hours with increased ventilation, stimulation of the sympathetic system, increased heart rate, increased pulmonary-circulation resistance, reduced plasma volume, and stimulation of erythropoesis. Acute mountain sickness occurs frequently at these oxygen partial pressures, but the full syndrome is rare if continuous exposure is limited to 6 h. Mood, cognitive, and psychomotor functions may be mildly impaired in these conditions, but data are inconclusive. Persons suffering from cardiac, pulmonary, or hematological diseases should consult a specialist in order for their individual risk to be assessed, and medical screening for any of these diseases is strongly recommended prior to exposure.

CONCLUSION

Preliminary evidence suggests that working environments with low oxygen concentrations to a minimum of 13% and normal barometric pressure do not impose a health hazard, provided that precautions are observed, comprising medical examinations and limitation of exposure time. However, evidence is limited, particularly with regard to workers performing strenuous tasks or having various diseases. Therefore, close monitoring of the health problems of people working in low oxygen atmospheres is necessary.

Acetazolamide reduces exercise capacity and increases leg fatigue under hypoxic conditions

Acetazolamide (Acz) is used at altitude to prevent acute mountain sickness, but its effect on exercise capacity under hypoxic conditions is uncertain. Nine healthy men completed this double-blind, randomized, crossover study. All subjects underwent incremental exercise to exhaustion with an inspired O(2) fraction of 0.13, hypoxic ventilatory responses, and hypercapnic ventilatory responses after Acz (500 mg twice daily for 5 doses) and placebo. Maximum power of 203 +/- 38 (SD) W on Acz was less than the placebo value of 225 +/- 40 W (P < 0.01). At peak exercise, arterialized capillary pH was lower and Po(2) higher on Acz (P < 0.01). Ventilation was 118.6 +/- 20.0 l/min at the maximal power on Acz and 102.4 +/- 20.7 l/min at the same power on placebo (P < 0.02), and Borg score for leg fatigue was increased on Acz (P < 0.02), with no difference in Borg score for dyspnea. Hypercapnic ventilatory response on Acz was greater (P < 0.02), whereas hypoxic ventilatory response was unchanged. During hypoxic exercise, Acz reduced exercise capacity associated with increased perception of leg fatigue. Despite increased ventilation, dyspnea was not increased.

Ataxia in acute mountain sickness does not improve with short-term oxygen inhalation

Stability of stance declines at high altitude in subjects with and without acute mountain sickness (AMS), suggesting that postural ataxia might result from different hypoxia-related mechanisms than those causing the signs and symptoms of AMS. The aim of this study was to determine whether short-term oxygen inhalation improves stability of stance assessed by static posturography and/or the symptoms of AMS. Twenty male volunteers with cerebral AMS scores above 0.70 were investigated the first or second morning of their stay at an altitude of 4559 m. Posturographic parameters remained unchanged, whereas cerebral AMS scores decreased (p < 0.001) after inhalation of 3 L/min of oxygen for at least 10 min. We conclude that ataxia of stance assessed by posturography may result from different hypoxia-triggered mechanisms that need more time for recovery than those causing AMS.

Polymorphisms of the tyrosine hydroxylase gene in subjects susceptible to high-altitude pulmonary edema

STUDY OBJECTIVES

A blunted hypoxic ventilatory response (HVR) has been observed in some sufferers of high-altitude pulmonary edema (HAPE), and was proposed as a potential mechanism in its pathogenesis. Tyrosine hydroxylase (TH) is a rate-limiting enzyme in the carotid body responding to hypoxia to synthesize dopamine neurotransmitter to heighten ventilation. The association of constitutional susceptibility to HAPE regarding the blunted HVR aspect with polymorphisms of the TH gene was examined.

DESIGN

A cross-sectional case control study.

SETTING

Shinshu University Hospital, Matsumoto, Japan.

PARTICIPANTS

Forty-three subjects with a history of HAPE (HAPE group) and 51 healthy climbers without a history of HAPE (control group).

MEASUREMENTS

The (TCAT)n tetranucleotide microsatellite repeats within intron 1 and Met81Val variant in exon 2 of the TH gene were investigated by polymerase chain reaction following either direct sequencing or restriction fragment length polymorphism. The HVR in 21 subjects among the HAPE group was also measured.

RESULTS

No significant frequency differences could be found in terms of either of the two polymorphisms between the HAPE and control groups. Meanwhile, no relationships were observed between the HVR values of HAPE subjects and the individual alleles in both polymorphisms of the TH gene.

CONCLUSION

The genetic susceptibility of HAPE, specifically the blunted HVR in HAPE, is probably not associated with the mutations of the TH gene, implying that these two polymorphisms may not be a sufficient genetic marker for predicting a predisposition to the susceptibility to HAPE.

High-altitude pulmonary edema at moderate altitude (< 2,400 m; 7,870 feet): a series of 52 patients

STUDY OBJECTIVES

To describe a group of patients who acquired pulmonary edema at a moderate altitude of 1,400 to 2,400 m.

DESIGN

Observational, retrospective chart review (1992-2000) of a series of 52 consecutive patients admitted for high-altitude pulmonary edema (HAPE) that occurred at 1,400 to 2,400 m.

SETTING

Emergency department of a community hospital in the French Alps (altitude, 500 m).

PATIENTS

Vacationing skiers who met criteria for altitude-related pulmonary edema, and in whom other causes (infectious, cardiogenic, neurogenic, and toxic) were excluded.

MEASUREMENTS AND RESULTS

All patients presented with signs of pulmonary edema. Diagnoses of infectious, cardiogenic, neurogenic, or toxic edema were ruled out in each patient. All patients were hypoxemic and had radiographic signs of pulmonary edema. Virtually all patients (96%) had dyspnea, and most (77%) had moist rales. All patients were treated with supplemental oxygen (3 to 12 L/min), bed rest, moderate fluid restriction, and continuous positive airway pressure. All recovered fully and were discharged after 4 +/- 2 days (mean +/- SD).

CONCLUSION

This study suggests that HAPE at moderate altitudes is more frequent than usually reported. Patients are likely to be young, vacationing men, with no history of prior disease. The disease has a favorable prognosis, and requires simple treatment and a short hospital stay.

Role of Cerebral Blood Volume in Acute Mountain Sickness

This review focuses on the role of cerebral blood volume in the intracranial hemodynamics that may influence the pathophysiology of acute mountain sickness (AMS). Cerebral blood flow is elevated in acute hypoxia exposure in humans, but the response in this setting of cerebral blood volume is unknown. After discussing the background, attention is given to noninvasive measurement of cerebral blood volume, and recent preliminary data on cerebral blood volume in AMS