High-altitude medicine

Improved oxygen saturation and acclimatization with bacteriotherapy at high altitude

High altitude imposes physiological stress on the human body due to reduced oxygen availability, and options to improve acclimatization are limited. Seventeen participants underwent a randomized, doubled-blinded, placebo-controlled study to test the effects of a multi-strain probiotic on acclimatization to high altitude (3,800 m). The primary outcome was oxygen saturation (SpO2) during both daytime and nighttime. Secondary measurements included acute mountain sickness (AMS) score, sleep measurements, ventilation, resting heart rate, blood pressure, heart rate variability, and fasting glucose levels. The probiotic group exhibited a higher daytime and nighttime SpO2 compared to the placebo group at high altitude. The probiotic group also exhibited a lower AMS score and enhanced acclimatization relative to the placebo group at high altitude, evidenced by higher SpO2 and lower AMS scores in treatment versus placebo groups. These results suggest bacteriotherapy as a novel, non-invasive intervention for high-altitude acclimatization.

Characteristics of Climbers with High Altitude Pulmonary Edema on Mount Aconcagua

INTRODUCTION—

Mount Aconcagua (6961 m) in Argentina is the highest peak in the Americas, and more than 3000 climbers attempt to summit annually. High altitude pulmonary edema (HAPE) is a leading cause of mortality and evacuation on Aconcagua.

OBJECTIVE—

This study sought to describe the characteristics of climbers who developed HAPE on Aconcagua to aid in future prevention efforts.

METHODS—

Climbers diagnosed with HAPE in January 2024 were surveyed regarding demographics, preparation, acclimatization, and illness. Healthy climbers on Aconcagua also were surveyed for the same period, providing a control population.

RESULTS—

Seventeen climbers were diagnosed with HAPE. These climbers were similar to climbers without HAPE in age, sex, origin, home elevation, hypoxic tent use, staged ascent, recent virus exposure, fitness metrics, and ascent-rate plans. Climbers with HAPE spent fewer nights at the 4300-m base camp (3.6 vs 5.0 nights). Prior to developing HAPE, 71% of patients reported unresolved acute mountain sickness symptoms. HAPE onset median elevation was 5500 m, with a median of 8.0 days over 3000 m and a median lowest SpO2 of 60% at diagnosis. There was a nonsignificant trend between acetazolamide use and increased HAPE. All surveyed HAPE patients descended, required helicopter evacuation, and survived.

CONCLUSION—

This study examined climbers who developed HAPE on Mount Aconcagua, yielding implications for high altitude illness prevention efforts and further study. HAPE cases were associated with insufficient nights at the 4300-m base camp and unresolved acute mountain sickness symptoms. The relationship between acetazolamide and HAPE warrants further study on Aconcagua.

High altitude is associated with pTau deposition, neuroinflammation, and myelin loss

Mammals are able to adapt to high altitude (HA) if appropriate acclimation occurs. However, specific occupations (professional climbers, pilots, astronauts and other) can be exposed to HA without acclimation and be at a higher risk of brain consequences. In particular, US Air Force U2-pilots have been shown to develop white matter hyperintensities (WMH) on MRI. Whether WMH are due to hypoxia or hypobaria effects is not understood. We compared swine brains exposed to 5000 feet (1524 m) above sea level (SL) with 21% fraction inspired O₂ (FiO₂) (Control group [C]; n = 5) vs. 30,000 feet (9144 m) above SL with 100% FiO₂ group (hypobaric group [HYPOBAR]; n = 6). We performed neuropathologic assessments, molecular analyses, immunohistochemistry (IHC), Western Blotting (WB), and stereology analyses to detect differences between HYPOBAR vs. Controls. Increased neuronal insoluble hyperphosphorylated-Tau (pTau) accumulation was observed across different brain regions, at histological level, in the HYPOBAR vs. Controls. Stereology-based cell counting demonstrated a significant difference (p < 0.01) in pTau positive neurons between HYPOBAR and C in the Hippocampus. Higher levels of soluble pTau in the Hippocampus of HYPOBAR vs. Controls were also detected by WB analyses. Additionally, WB demonstrated an increase of IBA-1 in the Cerebellum and a decrease of myelin basic protein (MBP) in the Hippocampus and Cerebellum of HYPOBAR vs. Controls. These findings illustrate, for the first time, changes occurring in large mammalian brains after exposure to nonhypoxic-hypobaria and open new pathophysiological views on the interaction among hypobaria, pTau accumulation, neuroinflammation, and myelination in large mammals exposed to HA.

Noninvasive Brain Physiology Monitoring for Extreme Environments: A Critical Review

Our ability to monitor the brain physiology is advancing; however, most of the technology is bulky, expensive, and designed for traditional clinical settings. With long-duration space exploration, there is a need for developing medical technologies that are reliable, low energy, portable, and semiautonomous. Our aim was to review the state of the art for noninvasive technologies capable of monitoring brain physiology in diverse settings. A literature review of PubMed and the Texas Medical Center library sites was performed using prespecified search criteria to identify portable technologies for monitoring physiological aspects of the brain physiology. Most brain-monitoring technologies require a moderate to high degree of operator skill. Some are low energy, but many require a constant external power supply. Most of the technologies lack the accuracy seen in gold standard measures, due to the need for calibration, but may be useful for screening or monitoring relative changes in a parameter. Most of the technologies use ultrasound or electromagnetic radiation as energy sources. There is an important need for further development of portable technologies that can be operated in a variety of extreme environments to monitor brain health.

The impact of physical fitness and body mass index in children on the development of acute mountain sickness: A prospective observational study

Background

Acute mountain sickness (AMS) is commonly found among people traveling above 2500 m. We investigated whether the occurrence of AMS is related to differences in individual physical fitness and BMI in subjects 11–13 years of age.

Methods

This study was conducted at Xue Mountain, Taiwan (elevation of 3886 m) between June 13, 2011 and June 17, 2011. Subjects were asked to ascend from Taipei City (25 m) to the summit (3886 m) over 3 days and 2 nights. Gender, age, weight, height, and fitness index (determined using a 3-minute step test) were recorded at sea level before ascent. The Lake Louise AMS score was used to record symptoms and diagnose AMS.

Results

A total of 179 subjects (mean age: 11.8 years; 102 males, 77 females) were included in the analysis. A total of 44.7% of subjects were diagnosed with AMS. Male gender (p = 0.004) and elevated body mass index (BMI) (p < 0.001) were each associated with the development of AMS. However the physical fitness index was comparable in subjects with and without AMS (67.8 ± 10.1 vs. 68.0 ± 9.3, p = 0.9).

Conclusions

This study shows that both BMI and male gender were associated with the development of AMS in 11–13 year old children. Physical fitness was not associated with the occurrence of AMS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-015-0373-0) contains supplementary material, which is available to authorized users.

Common High Altitudes Illnesses a Primer for Healthcare Provider

Exposure to high altitude imposes significant strain on cardiopulmonary system and the brain. As a consequence, sojourners to high altitude frequently experience sleep disturbances, often reporting restless and sleepless nights.

At altitudes above 3,000 meters (9,800 ft) almost all healthy subjects develop periodic breathing especially during NREM sleep.

Sleep architecture gradually improves with increased NREM and REM sleep despite persistence of periodic breathing.

The primary reason for periodic breathing at high altitude is a hypoxic-induced increase in chemoreceptor sensitivity to changes in PaCO₂ – both above and below eupnea, leading to periods of apnea and hyperpnea.

Acetazolamide improves sleep by reducing the periodic breathing through development of metabolic acidosis and induced hyperventilation decreasing the plant gain and widening the PCO₂ reserve. This widening of the PCO₂ reserve impedes development of central apneas during sleep. Benzodiazepines and GABA receptor antagonist such as zolpidem improve sleep without affecting breathing pattern or cognitive functions.

Rate of ascent and acute mountain sickness at high altitude

OBJECTIVE

To examine the effect of ascent rate on the induction of acute mountain sickness (AMS) in young adults during a climb to Jiaming Lake (3350 m) in Taiwan.

DESIGN

Prospective, nonrandomized.

SETTING

Climb from 2370 to 3350 m.

PARTICIPANTS

Young adults (aged 18 to 26 years) (N = 91) chose to participate in either the fast ascent (3 days; n = 43) or slow ascent (4 days; n = 48) group (1 and 2).

ASSESSMENT OF RISK FACTORS

Two criteria were used to define AMS. A Lake Louise score ≥3 and Lake Louise criteria [in the setting of a recent gain in altitude, the presence of headache and at least 1 of gastrointestinal discomfort (anorexia, nausea, or vomiting), fatigue or weakness, dizziness or lightheadedness, or difficulty sleeping].

MAIN OUTCOME MEASURES

Heart rate, blood oxygen saturation (SaO2), and symptoms of AMS were monitored each morning and evening.

RESULTS

Baseline characteristics were similar between groups, except for significant differences in history of alcohol consumption (P = 0.009) and climbing experience above 3000 m (P < 0.001). The incidence of AMS was not associated with the rate of ascent. Acute mountain sickness was most prevalent in group 1 on day 2 in the evening and in group 2 on day 3 in the evening. In both groups, AMS correlated with the initial reduction in SaO2. Body mass index (BMI) >24 kg/m was identified as a significant risk factor for AMS.

CONCLUSIONS

The development of AMS was closely associated with an initial reduction in SaO2. A BMI >24 kg/m also contributed to the occurrence of AMS.

CLINICAL RELEVANCE

These findings indicate that factors other than ascent rate should be considered when trying to ameliorate the risk of AMS.

An ecological study of cancer mortality rates in high altitude counties of the United States

To test the hypothesis that sustained, increased hemoglobin levels as measured by residence in high altitudes lead to an increase of malignant cancer deaths, we performed an assessment of U.S. cancer mortality rates for people residing in high altitude counties compared with those in counties with altitudes close to sea level. This included a graphical analysis of mortality rates for all cancers, female breast cancer, respiratory system cancer (RSC) and non-Hodgkin lymphoma (NHL), computation of standardized mortality ratios (SMRs) and Poisson regression modeling. Overall, our ecological evaluation showed statistically significantly reduced SMRs and rate ratios (RRs) for high altitude residents compared to sea level residents. For the causes of death categories examined, we found no evidence that persons residing in high altitude counties are at an elevated risk of cancer mortality compared with persons living close to sea level. Our results corroborate previous altitude studies of cancer mortality.

Change in oxygen saturation does not predict acute mountain sickness on Jade Mountain

OBJECTIVE

The purpose of this trial was to establish whether changes in resting oxygen saturation (Spo(2)) during ascent of Jade Mountain is useful in predicting acute mountain sickness (AMS). AMS-risk factors were also assessed.

METHODS

A prospective trial was conducted on Jade Mountain, Taiwan from October 18 to October 27, 2008. Resting oxygen saturation (Spo(2)) and heart rate (HR) were measured in subjects at the trail entrance (2610 m), on arrival at Paiyun Lodge (3402 m) on day 1, and at Paiyun Lodge after reaching the summit (3952 m) the next day (day 2). AMS was diagnosed with Lake Louise criteria (AMS score ≥4). A total of 787 subjects were eligible for analysis; 286 (32.2%) met the criteria for AMS.

RESULTS

Subjects who developed AMS had significantly lower Spo(2) than those who did not at the trail entrance (93.1% ± 2.1% vs 93.5% ± 2.3%; P = .023), on arrival at Paiyun Lodge on day 1 (86.2% ± 4.7% vs 87.6% ± 4.3%; P < .001), and on the return back to the Paiyun Lodge after a summit attempt on day 2 (85.5% ± 3.5% vs 89.6% ± 3.2%; P < .001), respectively. Trekkers with AMS were significantly younger (40.0 vs 43.2 years; P < .001), and had less high altitude (>3000 m) travel in the previous 3 months (29.9% vs 37.1%; P = .004).

CONCLUSIONS

Subjects with AMS had a lower Spo(2) than those without AMS; however, the differences between the 2 groups were not clinically significant. The results of this study do not support the use of pulse oximetry in predicting AMS on Jade Mountain.

Altitude mountain sickness among tourist populations: a review and pathophysiology supporting management with hyperbaric oxygen

In the mountain climbing community, conventional prevention of altitude mountain sickness (AMS) relies primarily on a formal acclimatization period. AMS symptoms during mountaineering climbs are managed with medication, oxygen and minor recompression (1524-2438 m altitude) using a portable chamber, such as the Gamow Bag. This is not always an acceptable therapy alternative in a predominantly elderly tourist population. The primary problem with reduced pressure at high altitude is hypoxaemia, which causes increased sympathetic activity, induces pulmonary venous constriction, while increasing pulmonary blood flow and regional perfusion. Rapid assents to altitude contribute to an increased incidence of decompression sickness (DCS). The treatment of choice for DCS is hyperbaric oxygenation, thus, treatment of high-altitude induced hypoxaemia using hyperbaric oxygenation (HBO(2)) is logical. Life Support Technologies group and the Center for Investigation of Altitude Medicine (CIMA, in Cusco, Peru) propose a comprehensive and multidisciplinary approach to AMS management. This approach encompasses traditional and advanced medical interventions including the use of a clinical HBO(2) chamber capable of recompression to three times greater than sea level pressure (3 atmosphere absolute (ATA)). The system uses a series of AMS hyperbaric treatment profiles that LST has previously developed to the US military and NASA, and that take greater advantage of vasoconstrictive effects of oxygen under true hyperbaric conditions of 1.25 ATA. These profiles virtually eliminate AMS rebound after the initial treatment often seen in conventional AMS treatment, where the patient is either treated at altitude, or does not recompress back to sea level or greater pressure (1.25 ATA), but returns directly to the same altitude where AMS symptoms first manifested.

Reverse association between high-altitude headache and nasal congestion

No evidence is available to show that nasal congestion is a manifestation of exposing an individual to high altitude and hypoxia. Since both nasal congestion and high-altitude headache are vasogenic, we explored whether there is a coincidence between these two symptoms. A prospective observational study was carried out on a cohort of 118 adults (>18 years old) in a mountain clinic at 3450 m. After 24 h of ascent, an interview was held to ask if each individual experienced acute mountain sickness symptoms (headache, etc.) and nasal congestion. Sixty-six (55.9%) individuals mentioned headache within 24 h after ascent and nasal congestion was reported by 34 (28.8%) individuals. There was a reverse association between headache and nasal congestion (P < 0.001). In conclusion, there is a reverse association between altitude headache and nasal congestion, probably as result of contradictory autoregulation effects or exaggerated sympathetic activity.

High altitude cerebral and pulmonary edema

Altitude illness, which comprises of acute mountain sickness (AMS) and its life threatening complications, high altitude cerebral edema (HACE) and high altitude pulmonary edema (HAPE) is now a well recognized disease process. AMS and HACE are generally thought to be a continuum. Some historical facts about the illness, its new intriguing pathophysiological processes, and clinical picture are discussed here. Although the review deals with both HACE and HAPE, HAPE is covered in greater detail due to the recent important findings related to its pathophysiology and prevention mechanisms. Relevant clinical correlation, the differential diagnosis of altitude sickness for a more sophisticated approach to the disease phenomenon, the possibility of dehydration being a risk factor for altitude sickness, the hypothetical role of angiogenesis in cerebral edema, and the emphasis on some vulnerable groups at high altitude are some of the other newer material discussed in this review. A clear-cut treatment and basic prevention guidelines are included in two panels, and finally the limited literature on the role of genetic factors on susceptibility to altitude sickness is briefly discussed.

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.

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-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.

Neurological disorders and travel

Travel is associated with a number of neurological disorders that can be divided into two categories: (1) Neurological infections including encephalitides, neurotuberculosis, neurobrucellosis, cysticercosis and trichinosis. Some of these disorders can be prevented by vaccinations, such as Japanese B encephalitis and rabies, some by the use of insect repellents and some by avoiding raw milk products and undercooked meat. (2) Non-infective neurological disorders, such as acute mountain sickness and high altitude cerebral oedema, problems occurring during air travel such as syncope, seizures, strokes, nerve compression, barotrauma and vertigo, motion sickness and foodborne neurotoxic disorders such as ciguatera, shellfish poisoning and intoxication by cassava. This group of diseases and disorders could be prevented if the traveller knows about them, applies simple physiological rules, takes some specific medications and knows how to avoid intoxications in certain geographical areas. Meningococcal meningitis, malaria and jet lag syndrome are extensively discussed in other articles of this issue. The discussion in this paper will be limited to the other disorders.

Sickness at high altitude: a literature review

When some individuals spend just a few hours at low atmospheric pressure above 1,500 m (5,000 ft)--such as when climbing a mountain or flying in a plane at high altitude--they become ill. Altitude sickness studies originally concentrated on life-threatening illnesses which beset determined and athletic climbers at extreme altitudes. In recent years, however, research attention is moving towards milder forms of sickness reported by a significant proportion of the growing number of visitors to mountain and ski resorts at more moderate altitude. Some of this research is also relevant in understanding the problems experienced by passengers in newer planes that fly at a significantly higher equivalent cabin altitude, i.e. 2,440 m (8,000 ft), than earlier designs. Engineering solutions--such as enriched oxygen in enclosed spaces at altitude, or in the case of aircraft, lower cabin altitudes--are possible, but for an economic assessment to be realistic an engineer needs to identify the scale of the problem and to understand the factors determining susceptibility. This review concentrates on the problems of mountain sickness in the ordinary population at altitudes of around 3,000 m (10,000 ft); this is a problem of growing concern as ski resorts develop, mountain trekking increases in popularity, and as higher altitude cabin pressures are achieved in aircraft.

Neurologic complications of respiratory disease

The respiratory system and the central nervous system are interconnected in a delicate balance; disorders in this equilibrium can have devastating consequences. Respiratory dysfunction, whether acute or chronic, may cause neurologic disease, including headache, encephalopathy, and in extreme cases, coma and death. This article will discuss abnormalities in ventilation and gas exchange, their subsequent pathophysiologic effects on the nervous system, and mechanisms of treatment for these disorders.

Atrial natriuretic peptide blockade exacerbates high altitude pulmonary edema in endotoxin-primed rats

High altitude pulmonary edema (HAPE) is associated with increases in pulmonary arterial and hydrostatic pressures and an increase in pulmonary vascular permeability. There is evidence to suggest that inflammatory mediators may cause some forms of HAPE, and Salmonella enteritidis endotoxin (ETX) is known to activate neutrophils and inflammatory mediators, such as TNF-alpha and IL1-beta. Since HAPE has been produced in rats primed with ETX, we hypothesized that ANP release and action may ameliorate HAPE and that ANP blockade may exacerbate HAPE in ETX-primed rats exposed to high altitude (HA). Plasma ANP, right atrial ANP mRNA, and indexes of lung injury were measured in rats primed with endotoxin (ETX) (0.1 mg/kg BW, i.p.) and exposed to simulated HA (4267 m; P(B) = 440 mmHg) for either 12 or 24 h. Catheters were chronically inserted into the right carotid artery, pulmonary artery, and jugular vein for assessment of hemodynamic parameters in response to ETX and/or HA. In addition, some rats were injected with an antibody against ANP (alphaANP) prior to normoxic (NX) or HA exposure. Pulmonary arterial pressure increased in the alphaANP group (50 +/- 20%; p < or = 0.05) and in the HA + alphaANP (51 +/- 15%; p < or = 0.05) group at 12 h compared to NX sham rats injected with normal rabbit serum. In addition, systemic arterial pressure was significantly lower in the HA + ETX rats compared to HA + ETX + alphaANP rats (p < or = 0.001). Plasma ANP levels were significantly higher at 12 and 24 h in ETX, HA, and HA + ETX groups (p <or = 0.05) compared to NX controls. There was an inverse relationship (p <or = 0.001) between plasma ANP levels and lung wet to dry (W/D) weight when data from NX, ETX, HA, and HA + ETX groups were pooled. The HA + alphaANP rats had significantly higher lung W/D ratios (p < 0.001) compared to sham rats. These results support the hypothesis that ANP, at physiological levels, modulates the development of pulmonary edema in HA-exposed ETX-primed rats.

Infections at high altitude

Every year, thousands of outdoor trekkers worldwide visit high-altitude (>2500 m) destinations. Although high-altitude areas per se do not harbor any specific agents, it is important to know the pathogens encountered in the mountains to be better able to help the ill sojourner at high altitude. These are the same pathogens prevalent in the surrounding lowlands, but various factors such as immunomodulation, hypoxia, physiological adaptation, and harsh environmental stressors at high altitude may enhance susceptibility to these pathogens. Against this background, various gastrointestinal, respiratory, dermatological, neurological, and other infections encountered at high altitude are discussed. Because there are few published data on infections at high altitude, this review is largely anecdotal and based on personal experience.

Acute medical problems in the Himalayas outside the setting of altitude sickness

Well-recognized medical threats at high altitude (>2,500 m) include acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE). Thousands of travelers in the Himalayas are exposed annually to these often life-threatening syndromes. Their recognition and treatment has advanced considerably in recent years. In the Himalayas, we frequently see acute medical problems outside the setting of AMS and the two types of altitude edemas. Many of these other conditions are also hypoxia related and sometimes may mimic the classic high altitude illnesses of AMS, HAPE, and HACE. Although the vast majority of these medical problems are neurological, pulmonary and other organ system dysfunction also occur. These "non-high altitude sickness" disease entities in persons who sojourn to remote mountainous environments are reviewed in this paper to enhance their recognition, diagnosis, and treatment.

Trends in the workload of the two high altitude aid posts in the Nepal Himalayas

BACKGROUND

Acute mountain sickness (AMS), High altitude pulmonary edema (HAPE) and High Altitude Cerebral Edema (HACE) are well known problems in the high altitude region of the Nepal Himalayas. To assess the proportion of AMS, HAPE, and HACE from 1983 to 1995 in the Himalaya Rescue Association (HRA) aid posts' patients at the Everest (Pheriche 4,243 m) and Annapurna (Manang 3,499 m) regions, the two most popular trekking areas in the Himalayas. A retrospective study was conducted at the HRA medical aid posts in Manang (3,499 m) and Pheriche (4,243 m) in the Himalayas, where 4,655 trekkers (tourists, mostly Caucasians) and 4,792 Nepalis (mostly porters and villagers) were seen at the two high-altitude clinics from 1983 to 1995, for a variety of medical problems, including AMS.

METHODS

The number of trekking permits issued for entering the two most popular regions in the Himalayas was calculated and referenced to the proportion of trekkers with medical conditions. Well established guidelines like the Lake Louise Diagnostic Criteria were used in the assessment of AMS, HAPE and HACE. Linear regression analyses were performed on data collected from the two aid posts to determine the effect of time on each variable. For comparison between the aid posts, angular transformation (arcsine) and analysis of variance (ANOVA) were performed on all proportional (incidence) data.

RESULTS

Approximately 20% of all visitors (Nepali plus trekkers) who visited the higher Pheriche aid post were diagnosed with AMS compared to around 6% at the lower Manang aid post. There was a linear increase over time in the number of trekkers entering the Everest (r=0.904, p<.001) and the Annapurna (r=0.887, p<.001) regions. The proportion of trekker patients with any medical condition visiting the two HRA aid posts at Manang and Pheriche, expressed as a function of the total number of trekkers entering the Everest and Annapurna regions, was not significantly different between Pheriche (average 4%) and Manang (average 1%). However, the proportion of AMS, HAPE and HACE in patients (Nepali plus trekkers) to the aid posts was greater in those visiting the higher Pheriche aid post compared to the lower Manang aid post (f=56.74, n=13; p<. 001). Importantly, only the proportion of AMS (r=0.568; p<.05) and not HAPE or HACE increased over time in Pheriche, alongside an unchanged proportion of trekker patients, amongst all Pheriche aid post patients. There was no increase of AMS, HAPE or HACE in Manang.

CONCLUSIONS

HAPE and HACE are the life-threatening forms of AMS and although there is a linear increase of trekkers entering the Himalayas in Nepal, the findings revealed that HAPE and HACE have not increased over time. One possible explanation may be that awareness drives by organizations like the Himalayan Rescue Association may be effective in preventing the severe forms of AMS.

Prevention of common travel ailments

An understanding of the subjects covered in this article is significant in keeping travelers healthy and comfortable. Each section covers a range of problems and suggestions for their prevention. The areas that are reviewed are: 1) fitness to fly; 2) problems in transit; 3) altitude sickness; 4) marine and swimming hazards; 5) insect precautions; 6) pre- and posttravel care; and 7) illness abroad. An effort has been made to provide practical recommendations as in many cases there is little data and no rules, thus the travel health advisor, with the patients' input, will need to determine the best course of action for each individual and itinerary.