High altitude pulmonary edema

Clinical and Pathophysiological Features of High-altitude Pulmonary Edema in the Japanese Population: A Review of Studies on High-altitude Pulmonary Edema in Japan

High-altitude pulmonary edema (HAPE) is a life-threatening, noncardiogenic pulmonary edema that occurs in unacclimatized individuals rapidly ascending to high altitudes above 2,500 m above sea level. Until the entity of HAPE was first identified in a case report published in Japan in 1966, the symptoms of severe dyspnea or coma occurring in climbers of the Japan Alps were incorrectly attributed to pneumonia or congestive heart failure. The Shinshu University Hospital serves as the central facility for rescuing and treating patients with HAPE in the region. Over the past 50 years, a series of studies have been conducted at Shinshu University to gain a better understanding of the characteristics of HAPE. This review summarizes the major achievements of these studies, including their clinical features, management, and pathogenesis of HAPE, particularly in the Japanese population.

Hypobaric hypoxia modulated structural characteristics of circulating cell-free DNA in high-altitude pulmonary edema

The utility of cell-free (cf) DNA has extended as a surrogate or clinical biomarker for various diseases. However, a more profound and expanded understanding of the diverse cfDNA population and its correlation with physiological phenotypes and environmental factors is imperative for using its full potential. The high-altitude (HA; altitude > 2,500 m above sea level) environment characterized by hypobaric hypoxia offers an observational case-control design to study the differential cfDNA profile in patients with high-altitude pulmonary edema (HAPE) (number of subjects, n = 112) and healthy HA sojourners (n = 111). The present study investigated cfDNA characteristics such as concentration, fragment length size, degree of integrity, and subfractions reflecting mitochondrial-cfDNA copies in the two groups. The total cfDNA level was significantly higher in patients with HAPE, and the level increased with increasing HAPE severity (P = 0.0036). A lower degree of cfDNA integrity of 0.346 in patients with HAPE (P = 0.001) indicated the prevalence of shorter cfDNA fragments in circulation in patients compared with the healthy HA sojourners. A significant correlation of cfDNA characteristics with the peripheral oxygen saturation levels in the patient group demonstrated the translational relevance of cfDNA molecules. The correlation was further supported by multivariate logistic regression and receiver operating characteristic curve. To our knowledge, our study is the first to highlight the association of higher cfDNA concentration, a lower degree of cfDNA integrity, and increased mitochondrial-derived cfDNA population with HAPE disease severity. Further deep profiling of cfDNA fragments, which preserves cell-type specific genetic and epigenetic features, can provide dynamic physiological responses to hypoxia.NEW & NOTEWORTHY This study observed altered cell-free (cf) DNA fragment patterns in patients with high-altitude pulmonary edema and the significant correlation of these patterns with peripheral oxygen saturation levels. This suggests deep profiling of cfDNA fragments in the future may identify genetic and epigenetic mechanisms underlying physiological and pathophysiological responses to hypoxia.

Effect of Acetazolamide and Zoledronate on Simulated High Altitude-Induced Bone Loss

Exposure to hypobaric hypoxia at high altitude puts mountaineers at risk of acute mountain sickness. The carbonic anhydrase inhibitor acetazolamide is used to accelerate acclimatization, when it is not feasible to make a controlled and slow ascend. Studies in rodents have suggested that exposure to hypobaric hypoxia deteriorates bone integrity and reduces bone strength. The study investigated the effect of treatment with acetazolamide and the bisphosphonate, zoledronate, on the skeletal effects of exposure to hypobaric hypoxia. Eighty 16-week-old female RjOrl : SWISS mice were divided into five groups: 1. Baseline; 2. Normobaric; 3. Hypobaric hypoxia; 4. Hypobaric hypoxia + acetazolamide, and 5. Hypobaric hypoxia + zoledronate. Acetazolamide was administered in the drinking water (62 mg/kg/day) for four weeks, and zoledronate (100 μg/kg) was administered as a single subcutaneous injection at study start. Exposure to hypobaric hypoxia significantly increased lung wet weight and decreased femoral cortical thickness. Trabecular bone was spared from the detrimental effects of hypobaric hypoxia, although a trend towards reduced bone volume fraction was found at the L4 vertebral body. Treatment with acetazolamide did not have any negative skeletal effects, but could not mitigate the altitude-induced bone loss. Zoledronate was able to prevent the altitude-induced reduction in cortical thickness. In conclusion, simulated high altitude affected primarily cortical bone, whereas trabecular bone was spared. Only treatment with zoledronate prevented the altitude-induced cortical bone loss. The study provides preclinical support for future studies of zoledronate as a potential pharmacological countermeasure for altitude-related bone loss.

Patchy Vasoconstriction Versus Inflammation: A Debate in the Pathogenesis of High Altitude Pulmonary Edema

High altitude pulmonary edema (HAPE) occurs in individuals rapidly ascending at altitudes greater than 2,500 m within one week of arrival. HAPE is characterized by orthopnea, breathlessness at rest, cough, and pink frothy sputum. Several mechanisms to describe the pathophysiology of HAPE have been proposed in different kinds of literature where most of the mechanisms are reported to be activated before a drop in oxygen saturation levels. The majority of the current studies favor diffuse hypoxic pulmonary vasoconstriction (HPV) as a pathophysiological basis for HAPE. However, some of the studies described inflammation in the lungs and genetic basis as the pathophysiology of HAPE. So, there is a major disagreement regarding the exact pathophysiology of HAPE in the current literature, which raises a question as to what is the exact pathophysiology of HAPE. So, we reviewed 23 different articles which include clinical trials, review articles, randomized controlled trials (RCTs), and original research published from 2010 to 2020 to find out widely accepted pathophysiology of HAPE. In our study, we found out sympathetic stimulation, reduced nitric oxide (NO) bioavailability, increased endothelin, increased pulmonary artery systolic pressure (PASP) resulting in diffuse HPV, and reduced reabsorption of interstitial fluid to be the most important determinants for the development of HAPE. Similarly, with the evaluation of the role of inflammatory mediators like C-reactive protein (CRP) and interleukin (IL-6), we found out that inflammation in the lungs seems to modulate but not cause the process of development of HAPE. Genetic basis as evidenced by increased transcription of certain gene products seems to be another promising hypoxic change leading to HAPE. However, comprehensive studies are still needed to decipher the pathophysiology of HAPE in greater detail.

High-altitude mountain telemedicine

Introduction

An innovative teleconsultation platform has been designed, developed and validated between summer 2017 and winter 2018, in five mountain huts and in three remote outpatient clinical centres of the Italian region Valle d’Aosta of the Mont Blanc massif area.

Methods

An ad-hoc videoconference system was developed within the framework of the e-Rés@MONT (Interreg ALCOTRA) European project, to tackle general health problems and high-altitude diseases (such as acute mountain sickness, high-altitude pulmonary and cerebral oedema). The system allows for contacting physicians at the main hospital in Aosta to perform a specific diagnosis and to give specific advice and therapy to the patients in an extreme environment out-hospital setting. At an altitude between 1500–3500 m, five trained nurses performed clinical evaluations (anamnesis, blood pressure, heart rate, oxygen saturation), electrocardiographic and echography monitoring on both tourists and residents as necessary; all of the collected data were sent to the physicians in Aosta.

Results

A total of 702 teleconsultation cases were performed: 333 dismissed (47%), 356 observed (51%) and 13 immediate interventions (2%). In 30 cases the physicians decided there was no need for helicopter and ambulance rescue intervention and hospital admissions. The main physiological measures, the classified pathologies, the severe cases and the cost savings are described in this article.

Discussion

The e-Rés@MONT teleconsultation platform has been discussed in terms of treated cases, feasibility, proactivity in reducing complexities, direct and indirect advantages, and diagnostics help; moreover, general and specific pros and cons have been debated, and future steps have been exposed.

Physiological and psychological illness symptoms at high altitude and their relationship with acute mountain sickness: a prospective cohort study

BACKGROUND

The aim of this prospective observational cohort study was to investigate relationships between acute mountain sickness (AMS) and physical and mental health during a high altitude expedition.

METHODS

Forty-four participants (mean age, 34 ± 13 y; body mass index, 23.6 ± 3.5 kg·m(2) ; 57% male) completed the Dhaulagiri base camp trek in Nepal, a 19-day expedition attaining 5,372 m. Participants self-reported the following daily physical and mental health: AMS (defined by Lake Louise diagnosis and individual and total symptom scores), upper respiratory symptoms, diarrhea, and anxiety, plus physiological and behavioral factors.

RESULTS

The rate of Lake Louise-defined AMS per 100 person days was 9.2 (95% CI: 7.2-11.7). All investigated illnesses except diarrhea increased with altitude (all p < 0.001 by analysis of variance). Total AMS symptom score was associated with a lower arterial oxygen saturation, higher resting heart rate, more upper respiratory and diarrhea symptoms, greater anxiety, and lower fluid intake (all p < 0.02 by longitudinal multiple regression analyses). However, only upper respiratory symptoms, heart rate, arterial oxygen saturation, and fluid intake predicted future AMS symptoms [eg, an increase in upper respiratory symptoms by 5 units predicted an increase in the following day's AMS total symptom score by 0.72 units (0.54-0.89)].

CONCLUSIONS

Upper respiratory symptoms and anxiety increasingly contributed to symptom burden as altitude was gained. Data were consistent with increased heart rate, decreased arterial oxygen saturation, reduced fluid intake, and upper respiratory symptoms being causally associated with AMS. Upper respiratory symptoms and fluid intake are the simplest targets for intervention to reduce AMS during high altitude exposure.

Changes in Spirometric Parameters and Arterial Oxygen Saturation During a Mountain Ascent to Over 3000 Meters

OBJECTIVE

To ascertain whether climbing a mountain over 3000 meters high produces any alterations in ventilation, whether such alterations are modified by acclimatization, and whether they correlate with changes in arterial oxygen saturation (SaO2) or the development of acute mountain sickness (AMS).

SUBJECTS AND METHODS

The following parameters were measured in 8 unacclimatized mountaineers who climbed Aneto (3404 m) and spent 3 days at the summit: forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), airway response to inhaled terbutaline, SaO2, and the symptoms of AMS.

RESULTS

At the summit, mean (SD) FEV1 declined by 12.3% (5.7%) and mean FVC by 7.6% (6.7%) while the ratio of FEV1 to FVC remained normal. The means for both parameters were higher on the following day. No airway response to bronchodilator treatment was observed. The restriction disappeared entirely on descent. At the peak, SaO2 increased progressively as the climbers became acclimatized. During the ascent, FEV1 correlated with SaO2 (r=0.79). One participant who suffered from AMS had a ratio of FEV1 to FVC less than 70% and the worst SaO2 during the 3 days on the summit. Obstruction preceded the AMS symptoms, did not respond to bronchodilator treatment, and disappeared when the climber descended.

CONCLUSIONS

The mountaineers who climbed over 3000 meters presented restriction that correlated with hypoxemia. This restriction did not respond to bronchodilator treatment, improved with acclimatization, and disappeared on descent. One person with AMS presented obstruction that did not respond to terbutaline and disappeared on descent.

[Respiratory changes during ascension to 8,000 meters mountain]

BACKGROUND

Our goal was to determine whether spirometric alterations occur during expeditions to 8,000-metre peaks, and whether these are modified by acclimatization or are related to acute mountain sickness, to arterial oxygen saturation (SaO2) or to muscular deterioration due to chronic hypoxic exposure.

SUBJECTS AND METHOD

Forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), inspiratory (MIP) and expiratory (MEP) maximal static pressures, grip strength in both hands, and SaO2 at rest and exercise were measured in eight subjects during an expedition to Gasherbrum II (8,035 m).

RESULTS

Upon arrival at the base camp (5,200 m), both FVC and FEV1 decreased, with no changes in the FEV1/FVC ratio. FVC did not improve after a brief pressurisation in a portable hyperbaric chamber. A month later, FVC in the base camp returned to normal values. FVC fall correlated with both the severity of acute mountain sickness and weight loss. Resting SaO2 improved with acclimatisation and correlated with the previous hypoxic ventilatory response, both before and after acclimatisation. Acclimatisation led to a decrease in the exercise-induced SaO2 fall. Stay at a high altitude lowered body weight and grip strength, although MIP and MEP remained unchanged.

CONCLUSIONS

We observed a restrictive alteration was corrected by with acclimatisation. This phenomenon seems to be related to a subclinical high-altitude pulmonary oedema rather than to an increase in the pulmonary vascular volume. Despite the high-altitude muscular deterioration, respiratory muscle weakness was not

Role of airway receptors in altitude-induced dyspnea

PURPOSE

The purpose of this study was to examine the role of airway receptors in respiratory-related sensations after ascent to altitude.

METHODS

Ratings of respiratory-related sensations, perceived exertion and acute mountain sickness, heart rate, and peripheral oxygen saturation were recorded at rest and exercise in male and female subjects who had inhaled either aerosolized saline or saline with tetracaine after acute ascent to an altitude of 3500 m and after prolonged acclimatization of 18 d at altitudes between 4000 and 5000 m.

RESULTS

Tetracaine had no effect on respiratory-related sensations at altitude either at rest or during exercise, and male and female subjects experienced similar respiratory-related sensations. Sensations of rapid breathing were experienced at rest after acute exposure to 3500 m as compared with sea level, but not after acclimatization to 5000 m. Sensations of rapid breathing, air hunger, and heavy breathing were experienced during exercise after acute and prolonged altitude exposure as compared with sea level, with a sensation of chest tightness experienced at 3500 m and a sensation of gasping experienced at 5000 m.

CONCLUSION

These results suggest that airway afferents play no role in the respiratory-related sensations experienced by male and female subjects either during acute ascent to altitude or after prolonged acclimatization at altitude.

Hypoxia decreases exhaled nitric oxide in mountaineers susceptible to high-altitude pulmonary edema

An exaggerated hypoxic pulmonary vasoconstriction is essential for development of high-altitude pulmonary edema (HAPE). We hypothesized that susceptibility to HAPE may be related to decreased production of nitric oxide (NO), an endogenous modulator of pulmonary vascular resistance, and that a decrease in exhaled NO could be detected during hypoxic exposure. Therefore, we investigated respiratory tract NO excretion by chemiluminescence and pulmonary artery systolic pressure (Ppa,s) by echocardiography in nine HAPE-susceptible mountaineers and nine HAPE-resistant control subjects during normoxia and acute hypoxia (fraction of inspired oxygen [FI(O2)] = 0.12). The subjects performed oral breathing. Nasally excreted NO was separated from respiratory gas by suction via a nasal mask. In HAPE-susceptible subjects, NO excretion in expired gas significantly decreased (p < 0.05) during hypoxia of 2 h in comparison with normoxia (28 +/- 4 versus 21 +/- 2 nl/min, mean +/- SEM). In contrast, the NO excretion rate of control subjects remained unchanged (31 +/- 6 versus 33 +/- 6 nl/ min, NS). Nasal NO excretion did not differ significantly between groups during normoxia (HAPE-susceptible group, 183 +/- 16 nl/ min; control subjects, 297 +/- 55 nl/min, NS) and was not influenced by hypoxia. The changes in Ppa,s with hypoxia correlated with the percent changes in lower respiratory tract NO excretion (R = -0.49, p = 0.04). Our data provide the first evidence of decreased pulmonary NO production in HAPE-susceptible subjects during acute hypoxia that may contribute among other factors to their enhanced hypoxic pulmonary vascular response.

High-altitude pulmonary edema: from exaggerated pulmonary hypertension to a defect in transepithelial sodium transport

High-altitude pulmonary edema (HAPE) is a form of lung edema which occurs in otherwise healthy subjects, thereby allowing the study of underlying mechanisms of pulmonary edema in the absence of confounding factors. Exaggerated pulmonary hypertension is a hallmark of HAPE and is thought to play an important part in its pathogenesis. Pulmonary vascular endothelial dysfunction and augmented hypoxia-induced sympathetic activation may be underlying mechanisms contributing to exaggerated pulmonary vasoconstriction in HAPE. Recent observations by our group suggest, however, that pulmonary hypertension itself may not be sufficient to trigger HAPE. Based on studies in rats, indicating that perinatal exposure to hypoxia predisposes to exaggerated hypoxic pulmonary vasoconstriction in adulthood, we examined effects of high-altitude exposure on pulmonary-artery pressure in a group of young adults who had suffered from transient perinatal pulmonary hypertension. We found that these young adults had exaggerated pulmonary vasoconstriction of similar magnitude to that observed in HAPE-susceptible subjects. Surprisingly, however, none of the subjects developed lung edema. These findings strongly suggest that additional mechanisms are needed to trigger pulmonary edema at high-altitude. Observations in vitro, and in vivo suggest that a defect of the alveolar transepithelial sodium transport could act as a sensitizer to pulmonary edema. The aim of this article is to review very recent experimental evidence consistent with this concept. We will discuss data gathered in mice with targeted disruption of the gene of the alpha subunit of the amiloride-sensitive epithelial sodium channel (alpha ENaC), and present preliminary data on measurements of transepithelial sodium transport in vivo in HAPE-susceptible and HAPE-resistant mountaineers.

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.

Exaggerated endothelin release in high-altitude pulmonary edema

BACKGROUND

Exaggerated pulmonary hypertension is thought to play an important part in the pathogenesis of high-altitude pulmonary edema (HAPE). Endothelin-1 is a potent pulmonary vasoconstrictor peptide that also augments microvascular permeability.

METHODS AND RESULTS

We measured endothelin-1 plasma levels and pulmonary artery pressure in 16 mountaineers prone to HAPE and in 16 mountaineers resistant to this condition at low (580 m) and high (4559 m) altitudes. At high altitude, in mountaineers prone to HAPE, mean (+/-SE) endothelin-1 plasma levels were approximately 33% higher than in HAPE-resistant mountaineers (22.2+/-1.1 versus 16.8+/-1.1 pg/mL, P<0.01). There was a direct relationship between the changes from low to high altitude in endothelin-1 plasma levels and systolic pulmonary artery pressure (r=0.82, P<0.01) and between endothelin-1 plasma levels and pulmonary artery pressure measured at high altitude (r=0.35, P=0.05).

CONCLUSIONS

These findings suggest that in HAPE-susceptible mountaineers, an augmented release of the potent pulmonary vasoconstrictor peptide endothelin-1 and/or its reduced pulmonary clearance could represent one of the mechanisms contributing to exaggerated pulmonary hypertension at high altitude.

High altitude pulmonary edema

High altitude pulmonary edema. Med. Sci. Sports Exerc., Vol. 31, No. 1 (Suppl.), pp. S23-S27, 1999. Altitude, speed and mode of ascent, and, above all, individual susceptibility are the most important determinants for the occurrence of high altitude pulmonary edema (HAPE). This illness usually occurs only 2-5 d after acute exposure to altitudes above 2500-3000 m. Chest radiographs and CT scans show a patchy predominantly peripheral distribution of edema. Wedge pressure is normal at rest, and there is an excessive rise of pulmonary artery pressure (PAP) that precedes edema formation and appears to be a crucial pathophysiologic factor for HAPE. Additional factors such as an inflammatory response and/or a decreased fluid clearance from the lung may, however, be necessary for the development of this noncardiogenic pulmonary edema. Bronchoalveolar lavage in patients with mostly advanced HAPE shows evidence of inflammatory response with increased permeability. There are, however, no prospective data to decide whether the inflammatory response is a primary cause of HAPE or a consequence of edema formation. Supplemental oxygen is the primary treatment in areas with medical facilities whereas 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 when they ascend slowly with an average gain of altitude not exceeding 300-350 m.d-1 above an altitude of 2500 m.

Effects of inhaled nitric oxide and oxygen in high-altitude pulmonary edema

BACKGROUND

High-altitude pulmonary edema (HAPE) is characterized by pulmonary hypertension, increased pulmonary capillary permeability, and hypoxemia. Treatment is limited to descent to lower altitude and administration of oxygen.

METHODS AND RESULTS

We studied the acute effects of inhaled nitric oxide (NO), 50% oxygen, and a mixture of NO plus 50% oxygen on hemodynamics and gas exchange in 14 patients with HAPE. Each gas mixture was given in random order for 30 minutes followed by 30 minutes washout with room air. All patients had severe HAPE as judged by Lake Louise score (6.4+/-0.7), PaO2 (35+/-3. 1 mm Hg), and alveolar to arterial oxygen tension difference (AaDO2) (26+/-3 mm Hg). NO had a selective effect on the pulmonary vasculature and did not alter systemic hemodynamics. Compared with room air, pulmonary vascular resistance fell 36% with NO (P<0.001), 23% with oxygen (P<0.001 versus air, P<0.05 versus NO alone), and 54% with NO plus 50% oxygen (P<0.001 versus air, P<0.005 versus oxygen and versus NO). NO alone improved PaO2 (+14%) and AaDO2 (-31%). Compared with 50% oxygen alone, NO plus 50% oxygen had a greater effect on AaDO2 (-18%) and PaO2 (+21%).

CONCLUSIONS

Inhaled NO may have a therapeutic role in the management of HAPE. The combined use of inhaled NO and oxygen has additive effects on pulmonary hemodynamics and even greater effects on gas exchange. These findings indicate that oxygen and NO may act on separate but interactive mechanisms in the pulmonary vasculature.

Inflammatory processes may predispose children to high-altitude pulmonary edema

We investigated retrospectively whether the preexistence of inflammation-producing illnesses such as viral respiratory tract infections contributed to the development of high-attitude pulmonary edema in children. We found that the large majority of native low-attitude children, but not adults, who had this form of edema after traveling to high altitude also had evidence of a preexisting illness. We speculate that the release of inflammatory mediators associated with these illnesses may be tolerated at sea level but may predispose children to increased capillary permeability when superimposed on hypoxia and, possibly, cold and exercise.

High-altitude medicine

This article discusses prevention, recognition, and treatment of altitude illnesses, especially acute mountain sickness, high-altitude pulmonary edema, and high-altitude cerebral edema. Physicians advising travelers and trekkers who will be visiting high-altitude areas will find an organized approach to giving pretravel advice. Physicians practicing in or visiting high-altitude areas will find guidelines for diagnosis and treatment. This article also addresses the issue of patients with underlying diseases who wish to travel to high-altitude destinations.

Low pulmonary diffusing capacity in subjects with acute mountain sickness

This study was conducted to investigate whether the changes in the pulmonary diffusing capacity found in individuals with acute mountain sickness (AMS) reflect the early stage of high-altitude pulmonary edema (HAPE). We measured the pulmonary diffusion capacity for carbon monoxide (DCO) by the single-breath method, arterialized capillary blood gas, and spirometry in a group of 32 healthy subjects (24 men, eight women) at an altitude of 2,260 m and after ascent to 4,700 m. Twelve subjects (10 men, two women) had symptoms of AMS (AMS group) by the second day after arrival at 4,700 m, but none had clinical signs of pulmonary or cerebral edema. In the non-AMS group, almost all subjects exhibited an increase in DCO at 2,260 to 4,700 m (delta DCO, 10.7 +/- 1.25 mL/min/mm Hg), while the degree of increase in DCO in the AMS group (n = 12) was significantly lower (delta DCO, 1.26 +/- 1.74 mL/min/mm Hg) than that of the non-AMS group (p < 0.01). In four of the 12 subjects with AMS who had a high AMS score, DCO decreased from 38.4 +/- 4.5 to 33.2 +/- 5.3 mL/min/mm Hg (delta DCO, -5.84 +/- 1.1 mL/min/mm Hg). The AMS group showed significantly lower vital capacity, forced expiratory flow during the middle half of FVC, PaO2, and a greater alveolar-arterial oxygen pressure difference at 4,700 m compared with the non-AMS group. DCO showed a significant negative correlation with AMS score (r = -0.885) and a positive correlation with PaO2 (r = 0.757) at 4,700 m. These results suggest that the decreased pulmonary diffusing capacity in subjects with AMS reflects the presence of pulmonary gas exchange abnormality, which is probably due to subclinical interstitial edema of the lung.

Inhaled nitric oxide for high-altitude pulmonary edema

BACKGROUND

Pulmonary hypertension is a hallmark of high-altitude pulmonary edema and may contribute to its pathogenesis. When administered by inhalation, nitric oxide, an endothelium-derived relaxing factor, attenuates the pulmonary vasoconstriction produced by short-term hypoxia.

METHODS

We studied the effects of inhaled nitric oxide on pulmonary-artery pressure and arterial oxygenation in 18 mountaineers prone to high-altitude pulmonary edema and 18 mountaineers resistant to this condition in a high altitude laboratory (altitude, 4559 m). We also obtained lung-perfusion scans before and during nitric oxide inhalation to gain further insight into the mechanism of action of nitric oxide.

RESULTS

In the high-altitude laboratory, subjects prone to high-altitude pulmonary edema had more pronounced pulmonary hypertension and hypoxemia than subjects resistant to high-altitude pulmonary edema. Arterial oxygen saturation was inversely related to the severity of pulmonary hypertension (r=-0.50, P=0.002). In subjects prone to high-altitude pulmonary edema, the inhalation of nitric oxide (40 ppm for 15 minutes) produced a decrease in mean (+/-SD) systolic pulmonary-artery pressure that was three times larger than the decrease in subjects resistant to such edema (25.9+/-8.9 vs. 8.7+/-4.8 mm Hg, P<0.001). Inhaled nitric oxide improved arterial oxygenation in the 10 subjects who had radiographic evidence of pulmonary edema (arterial oxygen saturation increased from 67+/-10 to 73+/-12 percent, P=0.047), whereas it worsened oxygenation in subjects resistant to high-altitude pulmonary edema. The nitric oxide-induced improvement in arterial oxygenation in subjects with high-altitude pulmonary edema was accompanied by a shift in blood flow in the lung away from edematous segments and toward nonedematous segments.

CONCLUSIONS

The inhalation of nitric oxide improves arterial oxygenation in high-altitude pulmonary edema, and this beneficial effect may be related to its favorable action on the distribution of blood flow in the lungs. A defect in nitric nitric oxide synthesis may contribute to high-altitude pulmonary edema.

Pulmonary function and hypoxic ventilatory response in subjects susceptible to high-altitude pulmonary edema

To determine if spirometric changes reflect early high-altitude pulmonary edema (HAPE) formation, we measured the FVC, FEV1, and FEF25-75 serially during the short-term period following simulated altitude exposure (4,400 m) in eight male subjects, four with a history of HAPE and four control subjects who had never experienced HAPE. Three of the four HAPE-susceptible subjects developed acute mountain sickness (AMS), based on their positive Environmental Symptom Questionnaire (AMS-C) scores. Clinical signs and symptoms of mild pulmonary edema developed in two of the three subjects with AMS after 4 h of exposure, which prompted their removal from the chamber. Their spirometry showed small decreases in FVC and greater decreases in FEV1 and FEF25-75 after arrival at high altitude in the presence of rales or wheezing on clinical examination and normal chest radiographs. One of the two subjects had desaturation (59 percent) and tachycardia during mild exercise, and excessive fatigue and inability to complete the exercise protocol developed in the other at 4 h. The six other subjects had minimal changes in spirometry and did not develop signs of lung edema. Further, we measured each subject's ventilatory response to hypoxia (HVR) prior to decompression to determine whether the HVR would predict the development of altitude illness in susceptible subjects. In contrast to anticipated results, high ventilatory responses to acute hypoxia, supported by increased ventilation during exposure to high altitude, occurred in the two subjects in whom symptoms of HAPE developed. The results confirm that HAPE can occur in susceptible individuals despite the presence of a normal or high ventilatory response to hypoxia.

High altitude medicine

Altitude illness is common and may result in major disruption of travel plans. Visitors to altitude need to be aware of the various health problems they might encounter and how they may be prevented. Self-diagnosis and treatment is the norm in many remote locations. The hallmark of therapy remains descent, but with newer treatment modalities, this may be easily forgotten. People with preexisting health problems may desire to visit high altitude destinations. It is reasonable to support some strongly motivated people in undertaking such trips, providing they recognize the difficulties of coping with illness in remote locations.

Prevention of high-altitude pulmonary edema by nifedipine

BACKGROUND

Exaggerated pulmonary-artery pressure due to hypoxic vasoconstriction is considered an important pathogenetic factor in high-altitude pulmonary edema. We previously found that nifedipine lowered pulmonary-artery pressure and improved exercise performance, gas exchange, and the radiographic manifestations of disease in patients with high-altitude pulmonary edema. We therefore hypothesized that the prophylactic administration of nifedipine would prevent its recurrence.

METHODS

Twenty-one mountaineers (1 woman and 20 men) with a history of radiographically documented high-altitude pulmonary edema were randomly assigned to receive either 20 mg of a slow-release preparation of nifedipine (n = 10) or placebo (n = 11) every 8 hours while ascending rapidly (within 22 hours) from a low altitude to 4559 m and during the following three days at this altitude. Both the subjects and the investigators were blinded to the assigned treatment. The diagnosis of pulmonary edema was based on chest radiography. Pulmonary-artery pressure was measured by Doppler echocardiography and the difference between alveolar and arterial oxygen pressure was measured in simultaneously sampled arterial blood and end-expiratory air.

RESULTS

Seven of the 11 subjects who received placebo but only 1 of the 10 subjects who received nifedipine had pulmonary edema at 4559 m (P = 0.01). As compared with the subjects who received placebo, those who received nifedipine had a significantly lower mean (+/- SD) systolic pulmonary-artery pressure (41 +/- 8 vs. 53 +/- 16 mm Hg, P = 0.01), alveolar-arterial pressure gradient (6.6 +/- 3.8 vs. 11.8 +/- 4.4 mm Hg, P less than 0.001), and symptom score of acute mountain sickness (2.0 +/- 0.7 vs. 3.9 +/- 1.9, P less than 0.01) at 4559 m.

CONCLUSIONS

The prophylactic administration of nifedipine is effective in lowering pulmonary-artery pressure and preventing high-altitude pulmonary edema in susceptible subjects. These findings support the concept that high pulmonary-artery pressure has an important role in the development of high-altitude pulmonary edema.