Transient hypobaric hypoxia improves spatial orientation in young rats

To achieve a better understanding of learning and declarative memory under mild transient stress, we investigated the effect of brief hypobaric hypoxia on spatial orientation in rats. Young male Wistar rats aged 30 days were exposed for 60 min to hypobaric hypoxia, simulating an altitude of 7,000 m (23,000 ft) either shortly prior to attempting or after mastering an allothetic navigation task in the Morris water maze with a submerged platform. The post-hypoxic group performed significantly better in the navigation task than the control animals (the mean difference in escape latencies was 11 seconds; P=0.0033, two-way ANOVA with repeated measures, group x session). The experimental group also achieved a remarkably higher search efficiency (calculated as a percentage of successful trials per session), especially during the first four days following hypoxic stress (P=0.0018). During the subsequent training, the post-hypoxic group performed better than the control animals, whilst the efficiency levels of both groups progressively converged. Spatial memory retention and recall of well-trained rats were not affected by the transient hypobaric hypoxia. These results indicate that brief hypobaric hypoxia enhances rats' spatial orientation. Our findings are consistent with several studies, which also suggested that mild transient stress improves learning.

Mini review of high altitude health problems in Ladakh

Ladakh is a sparsely populated area of Indian Himalaya lying at 3-4500 m altitude mainly consisting of arid desert. This paper will discuss high altitude health problems in Ladakh under the following headings. 1. Acute altitude illness: acute mountain sickness (AMS), high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). 2. Effects of prolonged and permanent exposure to high altitude: (subacute and chronic mountain sickness). 3. Environmental dust and domestic fire pollution resulting in non-occupational pneumoconiosis and high prevalence of respiratory morbidity.

Cardiovascular responses to orthostatic stress in healthy altitude dwellers, and altitude residents with chronic mountain sickness

High altitude (HA) dwellers have an exceptionally high tolerance to orthostatic stress, and this may partly be related to their high packed cell and blood volumes. However, it is not known whether their orthostatic tolerance would be changed after relief of the altitude-related hypoxia. Furthermore, orthostatic tolerance is known also to be influenced by the efficiency of the control of peripheral vascular resistance and by the effectiveness of cerebral autoregulation and these have not been reported in HA dwellers. In this study we examined plasma volume, orthostatic tolerance and peripheral vascular and cerebrovascular responses to orthostatic stress in HA dwellers, including some with chronic mountain sickness (CMS) in whom packed cell and blood volumes are particularly large. Eleven HA control subjects and 11 CMS patients underwent orthostatic stress testing, comprising head-up tilting with lower body suction, at their resident altitude (4338 m) and at sea level. Blood pressure (Portapres), heart rate (ECG), brachial and middle cerebral artery blood velocities (Doppler) were recorded during the test. Plasma volumes were found to be similar in both groups and at both locations. Packed cell and blood volumes were higher in CMS patients than controls. All subjects had very good orthostatic tolerances at both locations, compared to previously published data in lowland dwellers. In CMS patients responses of forearm vascular resistance to the orthostatic stress, at sea level, were smaller than controls (P < 0.05). Cerebral blood velocity was less in CMS than in controls (P < 0.01) and, at sea level, it decreased more than the controls in response to head-up tilting (P < 0.02). Cerebral autoregulation, assessed from the relationship between cerebral pressure and velocity, was also impaired in CMS patients compared to HA controls, when examined at sea level (P < 0.02). These results have shown that the good orthostatic tolerance seen in high altitude dwellers at altitude is also seen at sea level. There was no difference in orthostatic tolerance between CMS patients, with their exceptionally large blood volumes, and the HA controls. This may be because peripheral vascular and cerebrovascular responses (at least at sea level) are impaired in the CMS patients relative to HA controls. Thus, the advantage of the large blood volume may be offset by the smaller vascular responses.

Neuropsychological Functioning Associated with High-Altitude Exposure

This article focuses on neuropsychological functioning at moderate, high, and extreme altitude. This article summarizes the available literature on respiratory, circulatory, and brain determinants on adaptation to hypoxia that are hypothesized to be responsible for neuropsychological impairment due to altitude. Effects on sleep are also described. At central level, periventricular focal damages (leuko-araiosis) and cortical atrophy have been observed. Frontal lobe and middle temporal lobe alterations are also presumed. A review is provided regarding the effects on psychomotor performance, perception, learning, memory, language, cognitive flexibility, and metamemory. Increase of reaction time and latency of P300 are observed. Reduced thresholds of tact, smell, pain, and taste, together with somesthetic illusions and visual hallucinations have been reported. Impairment in codification and short-term memory are especially noticeable above 6,000 m. Alterations in accuracy and motor speed are identified at lower altitudes. Deficits in verbal fluency, language production, cognitive fluency, and metamemory are also detected. The moderating effects of personality variables over the above-mentioned processes are discussed. Finally, methodological flaws found in the literature are detailed and some applied proposals are suggested.

High-Altitude Pulmonary Edema in Children With Underlying Cardiopulmonary Disorders and Pulmonary Hypertension Living at Altitude

BACKGROUND

Pulmonary hypertension has not been described as a predisposing risk factor for high-altitude pulmonary edema (HAPE) in children. Previous studies have shown an association of HAPE with abnormally increased pulmonary vasoreactivity to hypoxia but generally normal pulmonary artery pressure (PAP) after recovery.

OBJECTIVE

To describe HAPE of relatively rapid onset and its management in a series of children residing at moderate to high altitudes, all of whom had underlying pulmonary hypertension.

METHODS AND RESULTS

From 1997 to 2003, 30 children came to our center with high-altitude illness. Of these, 10 children (aged 4-18 years; male-female ratio, 8:2) living at moderate to high altitudes (1610-3050 m) underwent cardiac catheterization after recovery from HAPE, and all were found to have chronic pulmonary hypertension (mean PAP, 38 +/- 9 mm Hg; pulmonary vascular resistance, 8.6 +/- 2.8 U x m2). Increases in PAP and pulmonary vascular resistance to hypoxia (16% oxygen) suggest that these children have a reactive pulmonary pressor response and hence are susceptible to HAPE. Six of the 10 patients had predisposing cardiopulmonary abnormalities, and 5 of these 6 patients did not receive a diagnosis prior to the onset of HAPE. Long-term treatment with calcium channel blockers, bosentan, sildenafil citrate, and/or oxygen lowered PAP, improved symptoms, and prevented the recurrence of HAPE.

CONCLUSION

Children living at altitude who develop HAPE should undergo screening for diagnosis of underlying cardiopulmonary abnormalities including pulmonary hypertension.

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.

Renin angiotensin aldosterone system and ACE I/D gene polymorphism in high-altitude pulmonary edema

INTRODUCTION

People who visit high altitude are exposed to a stressful environment, and many of them suffer from altitude-induced conditions, including high altitude pulmonary edema (HAPE). We investigated the renin angiotensin aldosterone system (RAAS) and the possible association of angiotensin converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism in the development of HAPE in Indian men.

METHODS

Subjects were all low-altitude natives: 19 men who developed HAPE within 1-3 d of arrival at 3000 to 3800 m (patients); and 20 age-matched men who did not develop HAPE during a period of a month or more at > or = 3500 m (controls). We recorded the arterial oxygen saturation (Sao2), heart rate (HR), and blood pressure (BP) of both groups and measured their levels of plasma renin activity (PRA), ACE, aldosterone, and serum electrolytes. Polymerase chain reaction was used to investigate a 287 base pair alu repeat sequence I/D polymorphism in the ACE gene.

RESULTS

Compared with controls, patients showed a significantly lower Sao2 and a higher HR. They also had significantly higher plasma PRA, aldosterone, ACE, and serum sodium (Na+) and potassium (K+). No significant difference was observed in ACE I/D allele frequencies.

DISCUSSION

The results suggested that RAAS is involved in the development of HAPE in low-altitude natives, but there is no association of ACE I/D gene polymorphism with HAPE.

Unraveling the mechanism of high altitude pulmonary edema

During the last decade, major advances in the understanding of the mechanism of high altitude pulmonary edema (HAPE) have supplemented the landmark work done in the previous 30 years. A brief review of the earlier studies will be described, which will then be followed by a more complete treatise on the subsequent research, which has elucidated the role of accentuated pulmonary hypertension in the development of HAPE. Vasoactive mediators, such as nitric oxide (NO) and endothelin-1, have played a major role in this understanding and have led to preventive and therapeutic interventions. Additionally, the role of the alveolar epithelium and the Na-K ATPase pump in alveolar fluid clearance has also more recently been understood. Direction for future work will be given as well.

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.

Primary vasculitis at high altitude

We describe a 34-year-old mountaineer who presented with gut infarction from necrotizing vasculitis, probably due to Churg-Strauss syndrome. Subsequently, relapses occurred whenever he climbed to 4000 meters. We hypothesize that the effects of vasculitis were compounded by the physiological changes at high altitude. We suggest that patients with systemic vasculitis should be cautious about climbing and trekking at high altitude.

The genetic basis of high-altitude pulmonary oedema

High-altitude pulmonary oedema (HAPE) is a potentially fatal condition affecting fit and previously well individuals at altitudes in excess of 3000 m. This article discusses the mechanisms of HAPE, considers the contribution of hypoxic pulmonary vasoconstriction and alterations in sodium transport to the pathological process. It discusses the various biochemical mediators such as nitric oxide (NO), endothelin-1 (ET-1), and the renin-angiotensin-aldosterone system (RAS) that may be involved and considers possible oxygen-sensing mechanisms involved in hypoxic adaptation such as hypoxia-inducible factor-1 (HIF-1). Those who have had HAPE once run an unpredictable but significant risk of recurrence; therefore, there may be a constitutional or genetic component in its aetiology. This paper considers the possible involvement of genes that may be involved in physiological adaptation to hypoxia (e.g., angiotensin-1 [AT(1)]-converting enzyme [ACE], tyrosine hydroxylase, serotonin transporter [5-HTT], and endothelial NO synthase [eNOS] genes). As yet, no formal association has been identified between an identified genetic polymorphism and HAPE, but genetic variation provides a possible mechanism to explain interindividual variation in response to hypoxia and enhanced or reduced performance at altitude.

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.

Sleep at High Altitude

New arrivals to altitude commonly experience poor-quality sleep. These complaints are associated with increased fragmentation of sleep by frequent brief arousals, which are in turn linked to periodic breathing. Changes in sleep architecture include a shift toward lighter sleep stages, with marked decrements in slow-wave sleep and with variable decreases in rapid eye movement (REM) sleep. Respiratory periodicity at altitude reflects alternating respiratory stimulation by hypoxia and subsequent inhibition by hyperventilation-induced hypocapnia. Increased hypoxic ventilatory responsiveness and loss of regularization of breathing during sleep contribute to the occurrence of periodicity. Interventions that improve sleep quality at high altitude include acetazolamide and benzodiazepines.

A Tibetan with Chronic Mountain Sickness Followed by High Altitude Pulmonary Edema on Reentry

Chronic mountain sickness (CMS) and high altitude pulmonary edema (HAPE) each occur rarely in Tibetans, and they have previously not been reported in the same person. Here we describe a 37-year-old native Tibetan man with CMS at 4300 m, who developed HAPE after his return home from a 12-day visit to sea level. Possible common pathogenetic factors included a poor ventilatory response to hypoxia, accentuated hypoxemia, pulmonary hypertension, and increased blood volume. In addition, strenuous exercise and high levels (to approximately 1000 ng/L) of plasma atrial natriuretic peptide may have contributed to HAPE.

Neurological Conditions at Altitude That Fall Outside the Usual Definition of Altitude Sickness

Altitude sickness in its commonly recognized forms consists of acute mountain sickness and the two life-threatening forms, high altitude cerebral and pulmonary edema. Less well known are other conditions, chiefly neurological, that may arise completely outside the usual definition of altitude sickness. These, often focal, neurological conditions are important to recognize so that they do not become categorized as altitude sickness because, besides oxygen and descent, treatment may be vastly different. Transient ischemic attacks, cerebral venous thrombosis, seizures, syncope, double vision, and scotomas are some of the well-documented neurological disturbances at high altitude discussed here in order to enhance their recognition and treatment.

Increased Oxidative Stress Following Acute and Chronic High Altitude Exposure

The generation of reactive oxygen species is typically associated with hyperoxia and ischemia reperfusion. Recent evidence has suggested that increased oxidative stress may occur with hypoxia. We hypothesized that oxidative stress would be increased in subjects exposed to high altitude hypoxia. We studied 28 control subjects living in Lima, Peru (sea level), at baseline and following 48 h exposure to high altitude (4300 m). To assess the effects of chronic altitude exposure, we studied 25 adult males resident in Cerro de Pasco, Peru (altitude 4300 m). We also studied 27 subjects living in Cerro de Pasco who develop excessive erythrocytosis (hematocrit > 65%) and chronic mountain sickness. Acute high altitude exposure led to increased urinary F(2)-isoprostane, 8-iso PGF(2 alpha) (1.31 +/- 0.8 microg/g creatinine versus 2.15 +/- 1.1, p = 0.001) and plasma total glutathione (1.29 +/- 0.10 micromol versus 1.37 +/- 0.09, p = 0.002), with a trend to increased plasma thiobarbituric acid reactive substance (TBARS) (59.7 +/- 36 pmol/mg protein versus 63.8 +/- 27, p = NS). High altitude residents had significantly elevated levels of urinary 8-iso PGF(2 alpha) (1.3 +/- 0.8 microg/g creatinine versus 4.1 +/- 3.4, p = 0.007), plasma TBARS (59.7 +/- 36 pmol/mg protein versus 85 +/- 28, p = 0.008), and plasma total glutathione (1.29 +/- 0.10 micromol versus 1.55 +/- 0.19, p < 0.0001) compared to sea level. High altitude residents with excessive erythrocytosis had higher levels of oxidative stress compared to high altitude residents with normal hematological adaptation. In conclusion, oxidative stress is increased following both acute exposure to high altitude without exercise and with chronic residence at high altitude.

Transient High Altitude Neurological Dysfunction: An Origin in the Temporoparietal Cortex

This case report describes three separate episodes of isolated ataxia, hallucinations of being accompanied by another person, and bilateral dressing apraxia occurring in a single individual without prior warning signs. These symptoms are attributable to disruption of vestibular processing in the temporoparietal cortex or associated limbic structures. Neurological dysfunction at high altitude is usually ascribed to high altitude cerebral edema or acute mountain sickness. However, transient neurological symptoms occur abruptly at more extreme altitudes, often following vigorous exertion, without overt altitude-induced prodromes. These symptoms may be caused by intense neuronal discharge or neuronal synchronization as a feature of epileptic discharges or cortical spreading depression. Transient high altitude neurological dysfunction should be recognized as a separate complication of extreme altitude, distinct from high altitude cerebral edema.

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.

A pig model of high altitude pulmonary edema

High altitude pulmonary edema (HAPE) affects unacclimatized individuals ascending rapidly to high altitude. The pathogenesis of HAPE is not fully elucidated, and many investigative techniques that could provide valuable information are not suitable for use in humans; thus, an animal model is desirable. Rabbits, sheep, dogs, and ferrets have been shown not to consistently develop HAPE, and studies in rats are limited by the animal's small size and inconsistent response. Pigs develop a marked pulmonary vasoconstrictive response to hypoxia, and preliminary studies of HAPE in pigs have been promising. To determine the suitability of pigs as an animal model of HAPE, we exposed six subadult (20 to 25 kg) pigs to normobaric hypoxia (10% oxygen) for 48 hr. One week before, and immediately after exposure to hypoxia, under anesthesia, arterial blood gases were obtained and bronchoalveolar lavage (BAL) and chest x-ray were performed. Hypoxia increased alveolar-arterial pressure difference for oxygen from 22 +/- 9 to 38 +/- 5 torr, p < 0.01) and red cell (from 12.3 +/- 5.9 to 27.4 +/- 5.3 cells x 10(5)/mL(-1), p < 0.001) and white cell (from 1.59 +/- 0.90 to 7.88 +/- 3.36 cells x 10(5)/mL(-1), p < 0.05) concentrations in BAL in all animals. Total BAL protein concentration increased by 64% and fractional albumin by 38% (both p < 0.05) posthypoxia. One animal had evidence of pulmonary edema on X ray. Some pigs develop findings consistent with early HAPE when exposed to normobaric hypoxia. Increasing the duration of hypoxic exposure or exercising the animals in hypoxia may better model the disease process observed in humans with clinically significant HAPE.

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.

Lack of evidence for association of high altitude pulmonary edema and polymorphisms of the NO pathway

One essential factor in the development of high altitude pulmonary edema (HAPE) is elevated pulmonary artery pressure, possibly due to a lack of nitric oxide (NO) in pulmonary vessels. NOS3 gene polymorphisms (G894T, T-786C, and CA-repeats > or =38) might be linked to decreased NO synthesis and increased susceptibility to HAPE, while the C242T polymorphism of the CYBA gene [encoding for the NAD(P)H oxidase subunit p22phox] may increase NO availability and thus convey resistance to HAPE. To test this hypothesis, we genotyped 51 mountaineers susceptible and 52 mountaineers not susceptible to HAPE. Genotyping revealed similar genotype frequencies of the G894T and the T-786C NOS3 polymorphism in both groups (G894T: susceptibles, 39.2% GG, 47.1% GT, 13.7% TT; nonsusceptibles, 48.0% GG, 44.0% GT, 8.0% TT; p = 0.54. T-786C: susceptibles, 45.1% TT, 39.2% TC, 15.7% CC; nonsusceptibles, 53.8% TT, 40.4% TC, 5.8% CC; p = 0.28). Genotype frequencies of the C242T CYBA polymorphism were 43.1% CC, 47.1 % CT, and 9.8% TT in HAPE susceptibles and 38.0% CC, 52.0 % CT, and 10.0% TT (p = 0.92) in nonsusceptibles. There was also no difference between the two groups in the number of CA repeats (p = 0.57), and individuals with > or =38 CA repeats were not more likely to develop HAPE (p = 1.0). Haplotype analysis for the NOS3 polymorphisms also revealed no association with HAPE. The results of this study suggest that none of these genetic variants plays a substantial role in the pathogenesis of HAPE in Caucasians, but does not exclude epistatic effects that might still involve the genetic systems studied here.

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.

High-altitude pulmonary hypertension: a pathophysiological entity to different diseases

Pulmonary hypertension is a hallmark of high-altitude pulmonary oedema (HAPE) and of congestive right heart failure in subacute mountain sickness (SMS) and chronic mountain sickness (CMS) in the Himalayas and in the end-stage of CMS (Monge's disease) in the Andes. There are studies to suggest that transmission of excessively elevated pulmonary artery pressure and/or flow to the pulmonary capillaries leading to alveolar haemorrhage is the pathophysiological mechanism of HAPE. In the Himalayas, HAPE was successfully prevented by extending the acclimatisation period from a few days to 5 weeks, however, this did not prevent the occurrence of congestive right heart failure after several weeks of stay at 6,000 m. This leads to the concept that rapid remodelling of the small precapillary arteries prevents HAPE but not the development of right heart failure in SMS and CMS. Unresponsiveness of pulmonary hypertension to oxygen at high altitude and its complete resolution only after weeks of stay at low altitude suggest that structural rather than functional changes are its pathophysiological mechanism. Since pulmonary hypertension at high altitude is the driving force leading to high-altitude pulmonary oedema and "high-altitude right heart failure" in newcomers and residents of high altitude, the authors propose to adjust current terminology accordingly.

Obesity: associations with acute mountain sickness

BACKGROUND

Although few retrospective studies of high altitude have reported that obesity might be associated with the development of acute mountain sickness (AMS), this association has not been studied prospectively.

OBJECTIVE

To determine whether obesity is associated with the development of AMS.

DESIGN

Obese and nonobese men were compared at a simulated altitude of 3658 m (12 000 ft).

SETTING

24 hours in a hypobaric environmental chamber.

PARTICIPANTS

9 obese and 10 nonobese men.

MEASUREMENTS

Percentage body fat (by hydrostatic weighing), Lake Louise AMS score, and Sao2 level (by pulse oximetry) were measured.

RESULTS

Average AMS scores increased more rapidly with time spent at simulated high altitudes for obese men than for nonobese men (P < 0.001). The response of Sao2 with exposure differed between nonobese and obese men. After 24 hours in the altitude chamber, seven obese men (78%) and four nonobese men (40%) had AMS scores of 4 or more.

CONCLUSION

Obesity seems to be associated with the development of AMS, which may be partly related to greater nocturnal desaturation with altitude exposure.

High altitude pulmonary oedema

Altitude, speed and mode of ascent and, above all, individual susceptibility are the most important determinants for the occurrence of high altitude pulmonary oedema (HAPE). This illness usually develops only within the first 2-5 days after acute exposure to altitudes above 2500-3000 m. An excessive rise in pulmonary artery pressure preceding oedema formation is the crucial pathophysiological factor. Recent investigations using right heart catheterisation and bronchoalveolar lavage (BAL) in incipient pulmonary oedema have shown that HAPE is a hydrostatic oedema in the presence of normal left atrial pressure with non-inflammatory high permeability leakage of the alveolocapillary barrier and mild alveolar haemorrhage. An inflammatory response may develop later in more advanced cases, as has been documented by BAL. Furthermore, decreased fluid clearance from the alveoli may contribute to such non-cardiogenic pulmonary oedema. Supplemental oxygen is the primary treatment in areas with medical facilities, while the treatment of choice in remote mountain areas is immediate descent. When this is impossible and supplemental oxygen is not available, treatment with nifedipine is recommended until descent is possible. Even susceptible individuals can avoid HAPE if they ascend slowly with an average gain of altitude not exceeding 300-350 m/day above an altitude of 2500 m.

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.

High altitude headache: efficacy of acetaminophen vs. ibuprofen in a randomized, controlled trial

Ibuprofen has been shown to be more effective than placebo in the treatment of high altitude headache (HAH), but nonsteroidal anti-inflammatory agents have been linked to increased incidence of gastrointestinal (GI) side effects and high-altitude pulmonary edema (HAPE). We postulated that acetaminophen, which does not share ibuprofen's theorized causal link to GI side effects or HAPE, could provide effective HAH therapy. We conducted a prospective, randomized, double-blind, clinical trial of ibuprofen vs. acetaminophen in the Solu Khumbu, Nepal: Mt. Everest Base Camp, Pheriche, Dingboche (4240 m to 5315 m). Seventy-four consecutive patients (ages 13 to 61 years) were randomized, were assessed with the Lake Louise Acute Mountain Sickness (AMS) criteria, and received a physical examination (which included vital signs, oxygen saturation as measured by pulse oximetry (SpO(2)), and assessment of clinical Lake Louise AMS criteria). Patients then received either 400 mg of ibuprofen (IBU) or 1000 mg of acetaminophen (ACET), and were asked to rate their cephalgia using a 10-cm visual analog scale (VAS). Thirty-nine patients received IBU, and 35 received ACET. Baseline Lake Louise AMS scores were identical in the two groups (mean = 5.9). No differences in mean VAS scores between IBU and ACET groups were noted at time 0 (presentation), 30, 60, or 120 min. No cases of HAPE or high altitude cerebral edema were noted during the study period. In this study population, acetaminophen was as effective as ibuprofen in relieving the pain of HAH.

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.

[Acute mountain sickness and high-altitude pulmonary edema. How to protect the mountain climber from the effects of the "altitude haze"]

Acute mountain sickness (AMS) usually occurs after 6-12 hours of acute exposure to altitudes above 2,500 m. If there is no further altitude gain, it normally resolves spontaneously within a day or two. However, it may, in rare cases, progress to life-threatening cerebral edema. High-altitude pulmonary edema (HAPE) is a non-cardiogenic edema that is often preceded by symptoms of AMS. The major preventive measure is slow ascent. Acetazolamide and dexamethasone are effective in preventing AMS, while nifedipine is effective only against HAPE. Immediate descent and/or the administration of oxygen is the treatment of choice for both conditions. If this is not possible, dexamethasone may be given for severe AMS and nifedipine for HAPE.

Exercise-related headache

Headache related to exercise is present in many active individuals. Prospective studies on exercise-related headache are rare. There are several subtypes of headache either exacerbated or caused exclusively by exercise or exertion. Many descriptors exist, but few clear guidelines have been established to allow the practitioner to easily differentiate and treat these subtypes. Recent research has gained insight into new types of exertional headache, as well as broadened our understanding of known types. Other reviews have recommended careful thorough screening of patients with sudden onset of headache during or shortly after exercise. This article offers a concise overview of current thinking and recent investigation, as well as areas that need continued exploration.

Case discussion: impaired renal function and tolerance to high altitude

A 58-year-old woman who plans a trek in the Himalayas at altitudes from 4500 to 5000 m is known to have the loss of about 50% of renal function based on glomerular filtration studies and renal biopsy. Possible risks and management are discussed.

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.

[A retrospective clinical study of chronic high altitude disease complicated by acute exacerbation in high altitude environment]

OBJECTIVE

To study chronic high altitude disease (CHAD) with concurrent acute high altitude disease (AHAD) in regions of high altitude.

METHODS

18,090 inpatients from Feb. 1956 to Dec. 1995 conforming to a screening standard were observed in a hospital located at altitude 3658 m. 1,028 inpatients suffering from CHAD when hospitalized were collected as a study group. 17,020 inpatients suffering from non-HAD when first hospitalized served as a control group. The morbidity rate of AHAD in these two groups in a follow-up period of 1 - 20 years was analyzed.

RESULTS

(1) AHAD morbidity rate was increasing with prolongation of observation time in the control group, but it was not so in the study group. Annual and accumulative morbidity of AHAD in the study group was obviously higher than that in the control group (P < 0.005, OR = 5.03, RR = 4.33). (2) The morbidity rates of three types of AHAD aside from high altitude pulmonary edema (HAPE) of high altitude hypertension (HAH) group and high altitude cerebral edema (HACE) of high altitude heart disease (HAHD) group was obviously higher in the study group than in the control (P < 0.05 - 0.005). AHAD morbidity rate in HAHD group and Monge's disease was 23.5% and 22.0% (OR = 7.33 - 6.71, RR = 5.86 - 5.47). (3) AHAD morbidity rate in HAHD group and Monge's disease group was obviously higher than that in the control, constituting mainly a high morbidity of mild acute high altitude disease.

CONCLUSION

The risk of AHAD increases about 5-fold in CHAD patients than in the multitude of high altitude acclimatization, being most evident in HAHD and Monge's disease.

High altitudes, anxiety, and panic attacks: is there a relationship?

People exposed to high altitudes often experience somatic symptoms triggered by hypoxia, such as breathlessness, palpitations, dizziness, headache, and insomnia. Most of the symptoms are identical to those reported in panic attacks or severe anxiety. Potential causal links between adaptation to altitude and anxiety are apparent in all three leading models of panic, namely, hyperventilation (hypoxia leads to hypocapnia), suffocation false alarms (hypoxia counteracted to some extent by hypocapnia), and cognitive misinterpretations (symptoms from hypoxia and hypocapnia interpreted as dangerous). Furthermore, exposure to high altitudes produces respiratory disturbances during sleep in normals similar to those in panic disorder at low altitudes. In spite of these connections and their clinical importance, evidence for precipitation of panic attacks or more gradual increases in anxiety during altitude exposure is meager. We suggest some improvements that could be made in the design of future studies, possible tests of some of the theoretical causal links, and possible treatment applications, such as systematic exposure of panic patients to high altitude.

Anterior ischaemic optic neuropathy at high altitude

High altitude retinopathy with various manifestations is common after exposure to high altitude. Inadequate autoregulatory response of the retinal vascular system is thought to be responsible for this. We report a case of anterior ischaemic optic neuropathy following exposure to high altitude.

Globus pallidus lesions associated with high mountain climbing

Acute mountain sickness (AMS) occurs commonly in hikers who are rapidly exposed to high altitude environments. Despite the numerous reports of AMS, few studies have reported pallidal lesions associated with altitude sickness. A previously healthy 49-yr-old Korean patient, after ascent to 4,700 m, suffered symptoms consistent with AMS. After returning home, the patient showed changes in personality characterized by abulia, indifference, and indecisiveness. T2 weighted brain magnetic resonance imaging showed high signal lesions involving bilateral globus pallidus. Our case suggests that globus pallidus injury should be included in the differential diagnosis of patients with personality or cognitive change after recovery from AMS.

[High-altitude retinopathy]

High-altitude retinopathy is a very rare ocular disease in our country, which can occur isolately or as a part of high-altitude illness. This paper presents the case of a patient with high-altitude illness and the diagnosis and treatment problems of this case.