The lung at high altitude: bronchoalveolar lavage in acute mountain sickness and pulmonary edema

Clinical perspective of hypoxia-mediated pulmonary hypertension

Pulmonary hypertension is a condition associated with a variety of pulmonary disorders whose common denominator is alveolar hypoxia. Such disorders include chronic obstructive pulmonary disease, pulmonary fibrosis, sleep-disordered breathing, and exposure to high altitude. Acute hypoxia is characterized by vasoconstriction of small pulmonary arteries, a phenomenon called hypoxic pulmonary vasoconstriction. With prolonged hypoxia, thickening of the smooth vascular layer of the small pulmonary arteries occurs, a phenomenon described as pulmonary vascular remodeling. Although the core mechanisms of both vasoconstriction and remodeling are thought to reside in the smooth muscle cell layer, the endothelium modulates these two processes. The purpose of this review is briefly to (a) discuss the mechanisms of hypoxic pulmonary hypertension as it pertains to certain disease states, and (b) examine the pathways that have potential therapeutic applications for this condition.

High altitude pulmonary edema: a pressure-induced leak

High altitude pulmonary edema (HAPE) is a non-cardiogenic pulmonary edema that can occur in healthy individuals who ascend rapidly to altitudes above 3000-4000m. Excessive pulmonary artery pressure (PAP) is crucial for the development of HAPE, since lowering pulmonary artery pressure by nifedipine or tadalafil (phosphodiesterase-5-inhibitor) will in most cases prevent HAPE. Recent studies using microspheres in swine and magnetic resonance imaging in humans strongly support the concept and primacy of nonuniform hypoxic arteriolar vasoconstriction to explain how hypoxic pulmonary vasoconstriction occurring predominantly at the arteriolar level can cause leakage. Evidence is accumulating that the excessive PAP response in HAPE-susceptible individuals is due to a reduced NO bioavailability. HAPE-susceptible individuals show an endothelial dysfunction in the systemic circulation in hypoxia. Lower levels of exhaled NO in hypoxia before and during HAPE suggest that this abnormality also occurs in the lungs and polymorphisms of the eNOS gene are associated with susceptibility to HAPE in the Indian and Japanese population.

Time course of hypoxia-induced lung injury in rats

We investigated the effects of normobaric hypoxia on rat lungs and hypothesized that the hypoxic exposure would induce lung injury with pulmonary edema and inflammation ensued by development of fibrosis. Rats were exposed to 10% O(2) in nitrogen over 6-168h. We analyzed cardiovascular function and pulmonary changes, lung histology and mRNA expression of extracellular matrix (ECM) molecules in the lung. Significant hemodynamic changes occurred after 168h of hypoxic exposure. Moderate pulmonary edema appeared after 8h and peaked after 16h of hypoxia. It was accompanied by inflammation, fibrosis and vascular hypertrophy. mRNA expression of transforming growth factor-beta2 and -beta3 was up-regulated in lung tissue after 8h of hypoxia. After 8-16h, mRNA expression of collagen types I and III and of other ECM molecules was significantly elevated and increased further with longer exposure to hypoxia. The time course of hypoxia-induced pulmonary injury resembled that previously observed after continuous norepinephrine infusion in rats.

High-altitude physiology and pathophysiology: implications and relevance for intensive care medicine

Cellular hypoxia is a fundamental mechanism of injury in the critically ill. The study of human responses to hypoxia occurring as a consequence of hypobaria defines the fields of high-altitude medicine and physiology. A new paradigm suggests that the physiological and pathophysiological responses to extreme environmental challenges (for example, hypobaric hypoxia, hyper-baria, microgravity, cold, heat) may be similar to responses seen in critical illness. The present review explores the idea that human responses to the hypoxia of high altitude may be used as a means of exploring elements of the pathophysiology of critical illness.

Hypoxia-induced pulmonary vascular remodeling: cellular and molecular mechanisms

Chronic hypoxic exposure induces changes in the structure of pulmonary arteries, as well as in the biochemical and functional phenotypes of each of the vascular cell types, from the hilum of the lung to the most peripheral vessels in the alveolar wall. The magnitude and the specific profile of the changes depend on the species, sex, and the developmental stage at which the exposure to hypoxia occurred. Further, hypoxia-induced changes are site specific, such that the remodeling process in the large vessels differs from that in the smallest vessels. The cellular and molecular mechanisms vary and depend on the cellular composition of vessels at particular sites along the longitudinal axis of the pulmonary vasculature, as well as on local environmental factors. Each of the resident vascular cell types (ie, endothelial, smooth muscle, adventitial fibroblast) undergo site- and time-dependent alterations in proliferation, matrix protein production, expression of growth factors, cytokines, and receptors, and each resident cell type plays a specific role in the overall remodeling response. In addition, hypoxic exposure induces an inflammatory response within the vessel wall, and the recruited circulating progenitor cells contribute significantly to the structural remodeling and persistent vasoconstriction of the pulmonary circulation. The possibility exists that the lung or lung vessels also contain resident progenitor cells that participate in the remodeling process. Thus the hypoxia-induced remodeling of the pulmonary circulation is a highly complex process where numerous interactive events must be taken into account as we search for newer, more effective therapeutic interventions. This review provides perspectives on each of the aforementioned areas.

Altitude medicine and physiology including heat and cold: A review

With increasing numbers of people travelling to high altitude destinations for recreation or work, there is a need for practitioners of Travel Medicine to be familiar with altitude illnesses and the physiology of altitude. In mountainous areas travellers may also be exposed to problems of heat and cold. This article reviews these topics and gives practical advice on the management of the clinical problems involved, together with a discussion of underlying mechanisms, as far as they are understood at present.

Effects of altitude and exercise on pulmonary capillary integrity: evidence for subclinical high-altitude pulmonary edema

Strenuous exercise may be a significant contributing factor for development of high-altitude pulmonary edema, particularly at low or moderate altitudes. Thus we investigated the effects of heavy cycle ergometer exercise (90% maximal effort) under hypoxic conditions in which the combined effects of a marked increase in pulmonary blood flow and nonuniform hypoxic pulmonary vasoconstriction could add significantly to augment the mechanical stress on the pulmonary microcirculation. We postulated that intense exercise at altitude would result in an augmented permeability edema. We recruited eight endurance athletes and examined their bronchoalveolar lavage fluid (BALF) for red blood cells (RBCs), protein, inflammatory cells, and soluble mediators at 2 and 26 h after intense exercise under normoxic and hypoxic conditions. After heavy exercise, under all conditions, the athletes developed a permeability edema with high BALF RBC and protein concentrations in the absence of inflammation. We found that exercise at altitude (3,810 m) caused significantly greater leakage of RBCs [9.2 (SD 3.1) × 104 cells/ml] into the alveolar space than that seen with normoxic exercise [5.4 (SD 1.2) × 104 cells/ml]. At altitude, the 26-h postexercise BALF revealed significantly higher RBC and protein concentrations, suggesting an ongoing capillary leak. Interestingly, the BALF profiles following exercise at altitude are similar to that of early high-altitude pulmonary edema. These findings suggest that pulmonary capillary disruption occurs with intense exercise in healthy humans and that hypoxia augments the mechanical stresses on the pulmonary microcirculation.

Adventures in high-altitude physiology

I have probably had more fun doing high-altitude physiology than most people. Some 45 years ago I applied to be a member of Sir Edmund Hillary's Silver Hut expedition and was accepted in spite of having no previous climbing experience. On this project a group of physiologists wintered at an altitude of 5800 m just south of Everest and carried out an extensive research program. Subsequently measurements were extended up to an altitude of 7440 m on Makalu. In fact the altitude of these field measurements of VO(2max) has never been exceeded. This led to a long interest in high-altitude medicine and physiology which culminated in the 1981 American Medical Research Expedition to Everest during which 5 people reached the summit and the first physiological measurements on the summit were made. Among the extraordinary findings were an extremely low alveolar PCO2 of 7-8 mmHg, an arterial pH (from the measured PCO2 and blood base excess) of over 7.7, and a VO(2max) of just over one liter/min. More recently a major interest has been the pathogenesis of high altitude pulmonary edema which we believe is caused by damage to pulmonary capillaries when the pressure inside some of them increases as a result of uneven hypoxic pulmonary vasoconstriction ("stress failure"). Another interest is improving the conditions of people who need to work at high altitude by oxygen enrichment of room air. This enhances well-being and productivity, and is now being used or planned for several high-altitude telescopes up to altitudes of 5600 m. Other recent high-altitude projects include establishing an international archive on high-altitude medicine and physiology at UCSD, several books in the area including the historical study High Life, and editing the journal High Altitude Medicine & Biology.

Responses and limitations of the respiratory system to exercise

During maximal exercise, the gas exchange function of the lung is challenged because of the major cardiopulmonary changes that must occur to meet the increased metabolic demands imposed by exercise. In healthy untrained young adults, the respiratory system is able to meet these demands imposed on it during maximal exercise by implementing several key mechanisms. Nonetheless, there are several exceptional cases in which the lung is unable to accommodate the demands of exercise because of vascular or airway limitations.

Exercise training prevents the inflammatory response to hypoxia in cremaster venules

Systemic hypoxia produces microvascular inflammation in several tissues, including skeletal muscle. Exercise training (ET) has been shown to reduce the inflammatory component of several diseases. Alternatively, ET could influence hypoxia-induced inflammation by improving tissue oxygenation or increasing mechanical antiadhesive forces at the leukocyte-endothelial interface. The effect of 5 wk of treadmill ET on hypoxia-induced microvascular inflammation was studied in the cremaster microcirculation of rats using intravital microscopy. In untrained rats, hypoxia (arterial Po2 = 32.3 ± 2.1 Torr) increased leukocyte-endothelial adherence from 2.3 ± 0.4 to 10.2 ± 0.3 leukocytes per 100 μm of venule ( P < 0.05) and was accompanied by extravasation of FITC-labeled albumin after 4 h of hypoxia (extra-/intravascular fluorescence intensity ratio = 0.50 ± 0.07). These responses were attenuated in ET (leukocyte adherence was 1.5 ± 0.4 during normoxia and 1.8 ± 0.7 leukocytes per 100 μm venule after 10 min of hypoxia; extra-/intravascular fluorescence intensity ratio = 0.11 ± 0.02; P < 0.05 vs. untrained) despite similar reductions of arterial (32.4 ± 1.8 Torr) and microvascular Po2 (measured with an oxyphor-quenching method) in both groups. Shear rate decreased during hypoxia to similar extents in ET and untrained rats. In addition, circulating blood leukocyte count was similar in ET and untrained rats. The effects of ET on hypoxia-induced leukocyte-endothelial adherence remained up to 4 wk after discontinuing training. Thus ET attenuated hypoxia-induced inflammation despite similar effects of hypoxia on tissue Po2, venular shear rate, and circulating leukocyte count.

Hypoxia, leukocytes, and the pulmonary circulation

Data are rapidly accumulating in support of the idea that circulating monocytes and/or mononuclear fibrocytes are recruited to the pulmonary circulation of chronically hypoxic animals and that these cells play an important role in the pulmonary hypertensive process. Hypoxic induction of monocyte chemoattractant protein-1, stromal cell-derived factor-1, vascular endothelial growth factor-A, endothelin-1, and tumor growth factor-beta(1) in pulmonary vessel wall cells, either directly or indirectly via signals from hypoxic lung epithelial cells, may be a critical first step in the recruitment of circulating leukocytes to the pulmonary circulation. In addition, hypoxic stress appears to induce release of increased numbers of monocytic progenitor cells from the bone marrow, and these cells may have upregulated expression of receptors for the chemokines produced by the lung circulation, which thus facilitates their specific recruitment to the pulmonary site. Once present, macrophages/fibrocytes may exert paracrine effects on resident pulmonary vessel wall cells stimulating proliferation, phenotypic modulation, and migration of resident fibroblasts and smooth muscle cells. They may also contribute directly to the remodeling process through increased production of collagen and/or differentiation into myofibroblasts. In addition, they could play a critical role in initiating and/or supporting neovascularization of the pulmonary artery vasa vasorum. The expanded vasa network may then act as a conduit for further delivery of circulating mononuclear cells to the pulmonary arterial wall, creating a feedforward loop of pathological remodeling. Future studies will need to determine the mechanisms that selectively induce leukocyte/fibrocyte recruitment to the lung circulation under hypoxic conditions, their direct role in the remodeling process via production of extracellular matrix and/or differentiation into myofibroblasts, their impact on the phenotype of resident smooth muscle cells and adventitial fibroblasts, and their role in the neovascularization observed in hypoxic pulmonary hypertension.

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

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

Physiological aspects of high-altitude pulmonary edema

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

Strenuous physical exercise inhibits granulocyte activation induced by high altitude

To test the hypothesis of whether strenuous physical exercise inhibits neutrophils that can get activated by hypobaric hypoxia, we analyzed the effects of both high altitude and strenuous exercise alone and in combination on potentially cytotoxic functions of granulocytes in healthy volunteers ( n = 12 men; average age 27.6 yr; range 24–38 yr). To this end, a field study was prospectively performed with an open-labeled within-subject design comprising three protocols. Protocol I (high altitude) involved a helicopter ascent, overnight stay at 3,196 m, and descent on the following day. Protocol II (physical exercise) involved hiking below an altitude of 2,100 m with repetitive ascents amounting to a total ascent to that of protocol III. Protocol III (combination of physical exercise and high altitude) involved climbing from 1,416 to 3,196 m, stay overnight, and descent on the following day. In protocol I, number of granulocytes did not change, but potentially cytotoxic functions of cells (CD18 expression and superoxide production) were early and significantly upregulated. In protocol II, subjects developed granulocytosis, but functions of cells were inhibited. In protocol III, granulocytosis occurred at higher values than those observed under protocol II. Potentially cytotoxic functions of cells, however, were strongly inhibited again. In conclusion, high altitude alone, even moderate in extent, can activate potentially cytotoxic functions of circulating granulocytes. Strenuous physical exercise strongly inhibits this activation, which may give protection from an otherwise inflammatory injury.

The Effects of a 5-Lipoxygenase Inhibitor on Acute Mountain Sickness and Urinary Leukotriene E 4 After Ascent to High Altitude

BACKGROUND

Elevated urine and blood leukotriene levels have been reported after ascent to high altitude in association with acute mountain sickness (AMS) and high-altitude pulmonary edema. Zileuton is an inhibitor of the enzyme 5-lipoxygenase that catalyzes conversion of arachidonic acid to leukotrienes. Study objectives and design: The objectives of this randomized, double-blind, placebo-controlled clinical trial were to determine whether zileuton (600 mg po qid) is effective prophylaxis for AMS, and to measure the effect of ascent to high altitude and zileuton on urinary leukotriene E(4) levels.

SETTING AND PARTICIPANTS

The study group consisted of volunteers from among climbers on the West Buttress of Mt. McKinley (Denali), Alaska. After baseline urine samples at sea level, subjects flew by airplane to 2,300 m, and then ascended to the 4,200-m camp in 5 to 10 days.

MEASUREMENTS AND RESULTS

Using an enzyme immunoassay, urinary leukotriene E(4) was found to decrease after ascent to high altitude in both the zileuton and placebo groups. Urinary leukotriene E(4) in the zileuton group (n = 9) decreased from 67 +/- 35 pg/mg creatinine at sea level to 33 +/- 22 pg/mg creatinine at high altitude (p = 0.003) [mean +/- SD]. Urinary leukotriene E(4) in the placebo group (n = 9) decreased from 97 +/- 82 pg/mg creatinine at sea level to 44 +/- 21 pg/mg creatinine at high altitude (p = 0.045). One subject in the zileuton group and three subjects in the placebo group met Lake Louise criteria for AMS after arriving at 4,200 m (p = 0.257).

CONCLUSIONS

Elevated leukotrienes are not associated with ascent to high altitude. In subjects with AMS, urinary leukotrienes were not elevated, suggesting that leukotrienes may not be a component of the pathophysiology of AMS. The low incidence of AMS and the small sample size in this study prevented determination of whether zileuton is effective prophylaxis for AMS.

Pulse oximetry in the diagnosis of acute mountain sickness

Acute mountain sickness (AMS) is a common condition in individuals who travel to altitudes over 2000 m. While AMS is an important public health problem, no measurements can reliably support or predict the diagnosis with any degree of confidence. We therefore set out to study whether pulse oximetry data are associated with AMS. We studied 169 subjects who had recently arrived by foot at 3080 m. Subjects completed a demographic survey, which collected data on ascent profiles and AMS symptoms. Resting arterial oxygen saturation and pulse rate were then measured using finger pulse oximetry. Forty-six subjects (27%) had AMS, using the Lake Louise score. Only pulse rate was significantly associated with the presence of AMS (OR: 1.4; 95% CI, 1.1 to 1.9; p < 0.05, backwards stepwise logistical regression). A trend showed worse AMS diagnoses were associated with higher mean pulse rates (p < 0.05, ANOVA linear weighted analysis). While some previous studies have shown an association between decreased oxygen saturation and acute mountain sickness at altitude, our results did not demonstrate such an association. The utility of pulse oximetry remains limited in the diagnosis of AMS. We recommend further study to determine the possible utility of pulse rate in the diagnosis and prediction of AMS.

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.

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.

Thoughts on the pulmonary blood-gas barrier

The pulmonary blood-gas barrier is an extraordinary structure because of its extreme thinness, immense strength, and enormous area. The essential components of the barrier were determined early in evolution and have been highly conserved. For example, the barriers of the African, Australian, and South American lungfish that date from as much as 400 million years ago have essentially the same structure as in the modern mammal or bird. In the evolution of vertebrates from bony fishes through amphibia, reptiles, and ultimately mammals and birds, changes in the pulmonary circulation occurred to limit the stresses in the blood-gas barrier. Only in mammals and birds is there a complete separation of the pulmonary and systemic circulations, which is essential to protect the extremely thin barrier from the necessary high-vascular pressures. To provide the blood-gas barrier with its required strength, evolution has exploited the high ultimate tensile strength of type IV collagen in basement membrane. Nevertheless, stress failure of the barrier occurs under physiological conditions in galloping Thoroughbred racehorses and also apparently in elite human athletes at maximal exercise. The human blood-gas barrier maintains its integrity during all but the most extreme physiological conditions. However, many pathological conditions cause stress failure. The structure of the blood-gas barrier is apparently continually regulated in response to wall stress, and this regulation is essential to maintain the extreme thinness but adequate strength. The mechanisms of this regulation remain to be elucidated and constitute one of the fundamental problems in lung biology.

Pulmonary edema and pleural effusion in norepinephrine-stimulated rats--hemodynamic or inflammatory effect?

Stimulation with norepinephrine (NE) leads to pulmonary edema and pleural effusion in rats. These pulmonary fluid shifts may result from pulmonary congestion due to the hemodynamic effects of NE and/or inflammation with an increase in vascular permeability. The contribution of these two factors were investigated in the present study. Female Sprague-Dawley rats received continuous i.v. NE infusion (0.1 mg/kg/h) over time intervals between 90 min and 72 h. After heart catheterization, pleural fluid (PF) and lung tissue were obtained. In some of the animals, a bronchoalveolar lavage (BAL) was performed. Pulmonary edema and inflammation were shown histologically. We determined the expression of interleukin (IL)-6 as one of the most potent acute-phase protein mediators in serum, PF and BAL supernatant fluid (BALF) using ELISA as well as in the lung tissue using Western blotting. Total protein concentration in BALF and PF served as indicators of increased capillary permeability. Pulmonary edema and pleural effusion appeared coincidentally with an increase in total peripheral resistance (TPR) after 6 h of NE infusion. PF reached a maximum between 8 and 16 h (2.2 +/- 0.3 ml, controls < 0.5 ml) and disappeared within 48 h. Activation of IL-6 in the fluids was observed after 8 h of NE stimulation. In the lung tissue it started after 12 h and reached 330% of the control value after 48 h. Pulmonary inflammation was documented histologically. It was accompanied by increased protein concentration in BALF after 24 h of NE treatment. Hemodynamic effects of NE are the main causative factors in the initial phase of the pulmonary fluid shifts. Additionally, NE leads to an activation of cytokines such as IL-6 and to inflammation and to an increase in capillary permeability. However, inflammation and increased capillary permeability occurred later than pulmonary edema and pleural effusion. Hence, we conclude that they are secondary factors which may contribute to maintain the fluid shifts over a longer period of time.

Changes in functional and histological distributions of nitric oxide synthase caused by chronic hypoxia in rat small pulmonary arteries

1. Chronic hypoxia (CH) increases lung tissue expression of all types of nitric oxide synthase (NOS) in the rat. However, it remains unknown whether CH-induced changes in functional and histological NOS distributions are correlated in rat small pulmonary arteries. 2. We measured the effects of NOS inhibitors on the internal diameters (ID) of muscular (MPA) and elastic (EPA) pulmonary arteries (100-700 micro m ID) using an X-ray television system on anaesthetized rats. We also conducted NOS immunohistochemical localization on the same vessels. 3. Nonselective NOS inhibitors induced ID reductions in almost all MPA of CH rats (mean reduction, 36+/-3%), as compared to approximately 60% of control rat MPA (mean, 10+/-2%). The inhibitors reduced the ID of almost all EPA with similar mean values (approximately 26%) in both CH and control rats. On the other hand, inducible NOS (iNOS)-selective inhibitors caused ID reductions in approximately 60% of CH rat MPA (mean, 15+/-3%), but did so in only approximately 20% of control rat MPA (mean, 2+/-2%). This inhibition caused only a small reduction (mean, approximately 4%) in both CH and control rat EPA. A neuronal NOS-selective inhibitor had no effect. 4. The percentage of endothelial NOS (eNOS)-positive vessels was approximately 96% in both MPA and EPA from CH rats, whereas it was 51 and 91% in control MPA and EPA, respectively. The percentage for iNOS was approximately 60% in both MPA and EPA from CH rats, but was only approximately 8% in both arteries from control rats. 5. The data indicate that in CH rats, both functional and histological upregulation of eNOS extensively occurs within MPA. iNOS protein increases sporadically among parallel-arranged branches in both MPA and EPA, but its vasodilatory effect is predominantly observed in MPA. Such NOS upregulation may serve to attenuate hypoxic vasoconstriction, which occurs primarily in MPA and inhibit the progress of pulmonary hypertension.

High-altitude illness

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

Vascular endothelial growth factor in patients with high-altitude pulmonary edema

To examine the role of VEGF in the pathogenesis of high-altitude pulmonary edema (HAPE), we measured the concentrations of VEGF in venous serum and bronchoalveolar lavage fluid in patients with HAPE and in healthy volunteers. The VEGF in venous serum of the patients was normal at admission and significantly increased at recovery. Similarly, the VEGF in bronchoalveolar lavage fluid of the patients was increased at recovery compared with admission, but values at both admission and recovery were significantly lower than those of the controls. The present finding suggests that VEGF probably is destroyed in the lung of HAPE, and it appears less likely to have a critical part in the pathogenesis of HAPE but has rather an important role in the repair process for the impaired cell layer.

Catecholamine-induced pulmonary edema and pleural effusion in rats--alpha- and beta-adrenergic effects

We investigated the contribution of alpha- and beta-adrenergic pathways to catecholamine-induced pulmonary edema and the role of pleural effusion in preventing alveolar edema. Female Sprague-Dawley rats received continuous intravenous infusion of norepinephrine and of separate alpha- or beta-adrenergic stimulation over 6-24 h. We performed heart catheterization in vivo and excised post mortem lung tissue for histological analysis. Interleukin (IL)-6 and total protein concentrations were determined in serum, pleural fluid (PF) and bronchoalveolar lavage fluid. alpha-Adrenergic treatment increased right ventricular systolic pressure (RVSP) and total peripheral resistance (TPR) and caused severe alveolar edema associated with IL-6 activation in serum and diffuse pulmonary inflammation. PF amounts were moderate (0.9+/-0.2 ml). beta-Adrenergic stimulation also increased RVSP but decreased TPR. Interstitial but not alveolar edema and focal inflammation without IL-6 activation developed. Large PF amounts (6.2+/-1.5 ml) occurred which were considered to prevent alveolar edema. We conclude that both alpha- and beta-adrenergic stimulation contribute to pulmonary fluid shifts in rats, but alpha-adrenergic pathways cause more acute and more severe lung injury than beta-adrenergic mechanisms.

Update: High altitude pulmonary edema

Recent high altitude studies with pulmonary artery (PA) catheterization and broncho-alveolar lavage (BAL) in early high altitude pulmonary edema(HAPE) have increased our understanding of the pathogenetic sequence in HAPE. High preceding PA and pulmonary capillary pressures lead to a non-inflammatory leak of the alveolar-capillary barrier with egress of red cells, plasma proteins and fluid into the alveolar space. The mechanisms accounting for an increased capillary pressure remain speculative. The concept that hypoxic pulmonary vasoconstriction (HPV) is uneven so that regions with less vasoconstriction are over-perfused and become edematous remains compelling but unproved. Also uncertain is the role and extent of pulmonary venoconstriction. With disruption of the normal alveolar-capillary barrier, some individuals may later develop a secondary inflammatory reaction. A high incidence of preceding or concurrent respiratory infection in children with HAPE has been used to support a causative role of inflammation in HAPE. However, alternatively even mild HPV may simply lower the threshold at which inflammation-mediated increases in alveolar capillary permeability cause significant fluid flux into the lung. Other major questions to be addressed in future research are: 1.) What is the mechanism of exaggerated hypoxic pulmonary vasoconstriction? Is there a link to primary pulmonary hypertension? Several observations suggest that susceptibility to HAPE is associated with endothelial dysfunction in pulmonary vessels. This has not yet been studied adequately. 2.) What is the nature of the leak? Is there structural damage, i. e. stress failure, or does stretch cause opening of pores? 3.) What is the pathophysiologic significance of a decreased sodium and water clearance across alveolar epithelial cells in hypoxia? 4.) What is the role of exercise? Do HAPE-susceptible individuals develop pulmonary edema when exposed to hypoxia without exercise? Answers to these questions will increase our understanding of the pathophysiology of HAPE and also better focus research on the genetic basis of susceptibility to HAPE.

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.

High-altitude pulmonary edema is initially caused by an increase in capillary pressure

BACKGROUND

High-altitude pulmonary edema (HAPE) is characterized by severe pulmonary hypertension and bronchoalveolar lavage fluid changes indicative of inflammation. It is not known, however, whether the primary event is an increase in pressure or an increase in permeability of the pulmonary capillaries.

METHODS AND RESULTS

We studied pulmonary hemodynamics, including capillary pressure determined by the occlusion method, and capillary permeability evaluated by the pulmonary transvascular escape of 67Ga-labeled transferrin, in 16 subjects with a previous HAPE and in 14 control subjects, first at low altitude (490 m) and then within the first 48 hours of ascent to a high-altitude laboratory (4559 m). The HAPE-susceptible subjects, compared with the control subjects, had an enhanced pulmonary vasoreactivity to inspiratory hypoxia at low altitude and higher mean pulmonary artery pressures (37 +/- 2 versus 26 +/- 1 mmHg, P<0.001) and pulmonary capillary pressures (19 +/- 1 versus 13 +/- 1 mmHg, P < 0.001) at high altitude. Nine of the susceptible subjects developed HAPE. All of them had a pulmonary capillary pressure >19 mm Hg (range 20 to 26 mmHg), whereas all 7 susceptible subjects without HAPE had a pulmonary capillary pressure < 19 mm Hg (range 14 to 18 mm Hg). The pulmonary transcapillary escape of radiolabeled transferrin increased slightly from low to high altitude in the HAPE-susceptible subjects but remained within the limits of normal and did not differ significantly from the control subjects.

CONCLUSIONS

HAPE is initially caused by an increase in pulmonary capillary pressure.

Inhaled nitric oxide improves survival in the rat model of high-altitude pulmonary edema

OBJECTIVES

High-altitude pulmonary edema (HAPE) afflicts certain individuals after a rapid gain in elevation. Those susceptible demonstrate an exaggerated hypoxic pulmonary vasoconstrictive response. This causes pulmonary hypertension, which may disrupt vascular integrity. This experiment was designed to test whether inhaled nitric oxide would affect development of HAPE in a rat model.

METHODS

Subjects were exposed in a hypobaric chamber to a simulated altitude of 6200 m (barometric pressure = 380 mm Hg, fraction of inspired oxygen = 0.19) for 24 hours. Control animals (n = 48) spontaneously breathed a mixture of 90% room air and 10% nitrogen, whereas the nitric oxide group (n = 48) received a similar mixture containing 83 ppm nitric oxide. Postmortem examination of lungs was performed for light microscopy, total hemoglobin, and gravimetric estimates of water content.

RESULTS

Mortality was 39.5% (n = 19) in control animals and 6.2% (n = 3) in the nitric oxide group (P < .001). Both groups significantly increased their lung weight-body weight ratio. Percentage of lung water was similar in both groups despite increases in lung weight, which is consistent with the protein-rich edema characteristic of HAPE. Light microscopic examination of survivors' lungs in both groups revealed scattered alveolar hemorrhage. No significant cellular inflammatory response was present.

CONCLUSIONS

We conclude that inhaled nitric oxide improves survival in the rat model of HAPE.

Urinary leukotriene E(4) levels are not increased prior to high-altitude pulmonary edema

STUDY OBJECTIVE

To examine whether increased urinary cysteinyl-leukotriene E(4) (LTE(4)) excretion, which has been found to be elevated in patients presenting with high-altitude pulmonary edema (HAPE), precedes edema formation.

DESIGN

Prospective studies in a total of 12 subjects with susceptibility to HAPE.

SETTING

In a chamber study, seven subjects susceptible to HAPE and five nonsusceptible control subjects were exposed for 24 h to an altitude of 450 m (control day), and exposed for 20 h to 4,000 m after slow decompression over 4 h. In a field study, prospective measurements at low and high altitude were performed in five subjects developing HAPE at 4,559 m.

PARTICIPANTS

Mountaineers with a radiographically documented history of HAPE and control subjects who did not develop HAPE with identical high-altitude exposure.

INTERVENTIONS

24-h urine collections.

MEASUREMENTS AND RESULTS

In the hypobaric chamber, none of the subjects developed HAPE. The 24-h urinary LTE(4) did not differ between HAPE susceptible and control subjects, nor between hypoxia and normoxic control day. In the field study, urinary LTE(4) was not increased in subjects with HAPE compared to values obtained prior to HAPE at high altitude and during 2 control days at low altitude.

CONCLUSIONS

These data do not provide evidence that cysteinyl-leukotriene-mediated inflammatory response is associated with HAPE susceptibility or the development of HAPE within the context of our studies.

High altitude increases circulating interleukin-6, interleukin-1 receptor antagonist and C-reactive protein

Hypoxic pulmonary vasoconstriction is associated with but may not be sufficient for the development of high-altitude pulmonary oedema (HAPO). Hypoxia is known to induce an inflammatory response in immune cells and endothelial cells. It has been speculated that hypoxia-induced inflammatory cytokines at high altitude may contribute to the development of HAPO by causing capillary leakage in the lung. We were interested if such an inflammatory response, possibly involved in a later development of HAPO, is detectable at high altitude in individuals without HAPO. We examined the plasma levels of interleukin 6 (IL-6), interleukin 1 receptor antagonist (IL-1ra) and C-reactive protein (CRP) in two independent studies: study A, Jungfraujoch, Switzerland, three overnight stays at 3458 m, n=12; study B: Capanna Regina Margherita, Italy, 3 overnight stays at 3647 m and one overnight stay at 4559 m, n=10. In both studies, probands showed symptoms of acute mountain sickness but no signs of HAPO. At the Jungfraujoch, IL-6 increased from 0.1+/-0.03 pg/ml to 2. 0+/-0.5 pg/ml (day 2, P=0.03), IL-1ra from 101+/-21 to 284+/-73 pg/ml (day 2, P=0.01), and CRP from 1.0+/-0.4 to 5.8+/-1.5 micrograms/ml (day 4, P=0.01). At the Capanna Margherita, IL-6 increased from 0. 5+/-0.2 pg/ml to 2.0+/-0.8 pg/ml (P=0.02), IL-1ra from 118+/-25 to 213+/-28 pg/ml (P=0.02), and CRP from 0.4+/-0.03 to 3.5+/-1.1 micrograms/ml (P=0.03). IL-8 was below the detection limit of the ELISA (<25 pg/ml) in both studies. The increase of IL-6 and IL-1ra in response to high altitude was delayed and preceded the increase of CRP. We conclude that: (1) circulating IL-6, IL-1ra and CRP are upregulated in response to hypobaric hypoxic conditions at high altitude, and (2) the moderate systemic increase of these inflammatory markers may reflect considerable local inflammation. The existence and the kinetics of high altitude-induced cytokines found in this study support the hypothesis that inflammation is involved in the development of HAPO.

Serial scintigraphic assessment of iodine-123 metaiodobenzylguanidine lung uptake in a patient with high-altitude pulmonary edema

Iodine-123 metaiodobenzylguanidine ((123)I-MIBG) can be considered an indicator of pulmonary endothelial cell function. Serial (123)I-MIBG images of the chest were acquired in a patient with high altitude pulmonary edema (HAPE). The initial evaluation was performed 7 days after admission. The lung to upper mediastinum ratios (LMRs) of (123)I-MIBG uptake were 1.33 (for the right lung) and 1.12 (for the left lung). The second examination of (123)I-MIBG lung uptake, which was performed 2 months later, showed LMRs of 1.39 (right lung) and 1.33 (left lung). We speculated that the decreased lung uptake of (123)I-MIBG at the early recovery stage could reflect an impairment in pulmonary endothelial cell metabolic function in the development of HAPE.

Impairment of transalveolar fluid transport and lung Na(+)-K(+)-ATPase function by hypoxia in rats

We examined whether hypoxic exposure in vivo would influence transalveolar fluid transport in rats. We found a significant decrease in alveolar fluid clearance of the rats exposed to 10% oxygen for 48 h. Terbutaline did not stimulate alveolar fluid clearance, and alveolar fluid cAMP levels were lower than those determined in normoxia experiment. Hypoxia did not influence the alveolar fluid lactate dehydrogenase levels, Evans blue dye fluid-to-serum concentration ratio, or lung wet-to-dry weight ratio, indicating no significant change in the permeability of alveolar-capillary barrier. Histological examination showed no significant fluid accumulation into the interstitium and the alveolar space. Hypoxia did not reduce lung ATP content; however, we found significant decrease in Na(+)-K(+)-ATPase hydrolytic activity in lung tissue preparations and isolated alveolar type II cells. Our data indicate that hypoxic exposure in vivo impairs transalveolar fluid transport, and this impairment is related to the decrease in alveolar epithelial Na(+)-K(+)-ATPase hydrolytic activity but is not secondary to the alteration of cellular energy source.

Altitude-related pulmonary disorders

The major physiologic stress encountered at high altitude is caused by the occurrence of hypobaric hypoxia. In this article, acute and chronic pulmonocardiac adaptation to altitude is reviewed, including possible genetic differences among highlanders from the Himalayan versus the Andean Mountains. The origin, symptoms, and treatment of acute mountain sickness and high altitude pulmonary edema are outlined. In addition, the prediction and prevention of pulmonary complications that may be encountered or exacerbated during commercial airflight are noticed.

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.

Sustained submaximal exercise does not alter the integrity of the lung blood-gas barrier in elite athletes

The extreme thinness of the pulmonary blood-gas barrier results in high mechanical stresses in the capillary wall when the capillary pressure rises during exercise. We have previously shown that, in elite cyclists, 6-8 min of maximal exercise increase blood-gas barrier permeability and result in higher concentrations of red blood cells, total protein, and leukotriene B4 in bronchoalveolar lavage (BAL) fluid compared with results in sedentary controls. To test the hypothesis that stress failure of the barrier only occurs at the highest level of exercise, we performed BAL in six healthy athletes after 1 h of exercise at 77% of maximal O2 consumption. Controls were eight normal nonathletes who did not exercise before BAL. In contrast with our previous study, we did not find higher concentrations of red blood cells, total protein, and leukotriene B4 in the exercising athletes compared with control subjects. However, higher concentrations of surfactant apoprotein A and a higher surfactant apoprotein A-to-phospholipid ratio were observed in the athletes performing prolonged exercise, compared with both the controls and the athletes from our previous study. These results suggest that, in elite athletes, the integrity of the blood-gas barrier is altered only at extreme levels of exercise.

Inflammatory cytokines in BAL fluid and pulmonary hemodynamics in high-altitude pulmonary edema

To evaluate the pathogenesis of high-altitude pulmonary edema (HAPE), we performed bronchoalveolar lavage (BAL) and pulmonary hemodynamic studies in seven patients with HAPE at its early stage. We measured cell counts, biochemical contents, and concentrations of pro-inflammatory cytokines including interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor (TNF)-alpha and of anti-inflammatory cytokines including IL-1 receptor antagonist (ra) and IL-10 in the BAL fluid (BALF). All patients showed increased counts for total cells, alveolar macrophages, neutrophils and lymphocytes, and markedly elevated concentrations of proteins, lactate dehydrogenase, IL-1beta, IL-6, IL-8, TNF-alpha and IL-1ra. The levels of IL-1alpha and IL-10 were not increased. Patients also showed pulmonary hypertension with normal wedge pressure. Both the driving pressure obtained as pulmonary arterial pressure minus wedge pressure and the PaO2 under room air were significantly correlated with the concentrations of IL-6 and TNF-alpha in the BALF. These findings suggest that the inflammatory cytokines play a role at the early stage of HAPE and might be related to pulmonary hypertension.

Viral respiratory infection increases susceptibility of young rats to hypoxia-induced pulmonary edema

Recent clinical observations of a high incidence of preexisting respiratory infections in pediatric cases of high-altitude pulmonary edema prompted us to ask whether such infections would increase the susceptibility to hypoxia-induced pulmonary edema in young rats. We infected weanling rats with Sendai virus, thus causing a mild respiratory infection. Within 7 days of infection, Sendai virus was essentially undetectable by using viral culture and immunohistochemical techniques. Animals at day 7 of Sendai virus infection were then exposed to normobaric hypoxia (fraction of inspired O2 = 0.1) for 24 h and examined for increases in gravimetric lung water and in vascular permeability, as well as for histological evidence of increased lung water. Bronchoalveolar lavage was performed on a separate series of animals. Compared with control groups, infected hypoxic animals showed significant increases in perivascular cuffing, gravimetric lung water, and lung protein leak. In addition, infected hypoxic animals had increases in lavage fluid cell counts and protein content compared with controls. We conclude that young rats, exposed to moderate hypoxia while recovering from a mild viral respiratory infection, may demonstrate evidence of early pulmonary edema formation, a finding of potential relevance to human high-altitude pulmonary edema.

Endothelial selectins in acute mountain sickness and high-altitude pulmonary edema

STUDY OBJECTIVES

Mechanical or inflammatory injury to pulmonary endothelial cells may cause impaired pulmonary gas exchange in acute mountain sickness (AMS) and noncardiogenic pulmonary edema in high-altitude pulmonary edema (HAPE). This study was designed to determine whether markers of endothelial cell activation or injury, plasma E- and P-selectin, were increased after ascent to high altitude, in AMS or in HAPE.

DESIGN

We collected clinical data and plasma specimens in control subjects at sea level and after ascent to 4,200 m, and in climbers with AMS or HAPE at 4,200 m. Data analysis was performed using standard nonparametric statistical methods, and results reported as mean+/-SD.

SETTING

National Park Service medical camp at 4,200 m on Mt. McKinley (Denali), Alaska.

PATIENTS

Blood samples and clinical data were collected from 17 healthy climbers at sea level and again after ascent to 4,200 m, and from a different group of 13 climbers with AMS and 8 climbers with HAPE at 4,200 m. Climbers with AMS were divided into normoxic (n=7) and hypoxemic (n=6) groups.

MEASUREMENTS AND RESULTS

Using an enzyme immunoassay technique, plasma E-selectin concentrations were found to be increased in the 17 control subjects after ascent to 4,200 m (17.2+/-8.2 ng/mL) as compared to sea level (12.9+/-8.2 ng/mL) (p=0.001). Plasma E-selectin concentrations were also increased in subjects with hypoxemic AMS (30.6+/-13.4 ng/mL) and HAPE (23.3+/-9.1 ng/mL) compared to control subjects at sea level (p=0.009). Increased plasma E-selectin concentration significantly correlated with hypoxemia (p=0.006). Plasma P-selectin concentrations were unchanged after ascent to 4,200 m and in subjects with AMS and HAPE.

CONCLUSION

Because E-selectin is produced only by endothelial cells, increased plasma E-selectin after ascent to high altitude and in hypoxemic climbers with AMS and HAPE provides evidence that endothelial cell activation or injury is a component of hypoxic altitude illness.

Lung pathology in high-altitude pulmonary edema

Autopsy findings in 10 cases of high-altitude pulmonary edema have been collected from published articles and personal observations. All cases were males with a mean age of 37 years (22-62). The altitude of occurrence was from 8400 to 17 500 feet. The mean combined lung weight in nine cases was 1682 g (1200-3000 g). Cerebral edema was present in five of eight cases. The most frequency pulmonary findings in addition to diffuse edema consisted of leukocyte infiltrates, alveolar hemorrhages, thrombi in small pulmonary arteries, and alveolar hyaline membranes. Pulmonary infarction was present in only one case. Right ventricular dilatation was commonly present. The left ventricle was normal. No significant coronary disease was present.

Inhibition of histamine release by nedocromil sodium reduces exercise-induced hypoxemia in master athletes

During exercise in highly-trained older master athletes (MA), the impairment of pulmonary gas exchanges has been shown to be associated with a concomitant increase in histamine release (2). To determine the role of the histamine released (% H) during exercise-induced hypoxemia, seven MA (age 63.2 yr +/- 1.9), all of whom were known to develop exercise-induced hypoxemia, performed two maximal incremental exercise tests at a one-month interval after administration of nedocromil sodium (which inhibits histamine and other mediator release) or placebo in random double-blind order. During exercise testing, blood samples for arterial blood gas analysis and histamine assay were drawn at rest, exercise and recovery. Nedocromil sodium induced an inhibition in % H (0.57 +/- 0.03 at maximal load (Pmax) with placebo vs 0.24 +/- 0.02 with nedocromil sodium) linked with an improvement of pulmonary gas exchange (PaO2: 71.1 +/- 1.4 at Pmax with placebo vs 83.4 +/- 3 with nedocromil sodium; D(Ai-a)O2: 37.5 +/- 1.4 at Pmax vs 19.1 +/- 3.1, respectively). These results confirm the link established between the increase in histamine and exercise-induced hypoxemia in master athletes.

Evidence against an increase in capillary permeability in subjects exposed to high altitude

A potential pathogenetic cofactor for the development of acute mountain sickness and high-altitude pulmonary edema is an increase in capillary permeability, which could occur as a result of an inflammatory reaction and/or free radical-mediated injury to the lung. We measured the systemic albumin escape by intravenously injecting 5 muCi of 125I-labeled albumin and the plasma concentrations of cytokines, F2-isoprostanes (products of lipid peroxidation), and acute-phase proteins in 24 subjects exposed to 4,559 m. Ten subjects developed acute mountain sickness, and four subjects developed high-altitude pulmonary edema. The transcapillary escape rate of albumin was 6.9 +/- 2.0%/h (SD) at low (550 m) and 6.3 +/- 1.9%/h at high (4,559 m) altitude (P = 0.23; n = 24). The subjects with high-altitude pulmonary edema had a modest but insignificant increase in the transcapillary escape rate of albumin (4.6 +/- 1.9%/h at low vs. 5.7 +/- 1.9%/h at high altitude; P = 0.42; n = 4). Plasma concentrations of fibrinogen, alpha 1-acid glycoprotein, C-reactive protein, and interleukin-6 were unchanged in the early phases and significantly increased by the end of the observation period in the subjects with high-altitude pulmonary edema, whereas tumor necrosis factor-alpha and F2-isoprostanes did not change at all. This suggests that the inflammatory reaction was rather a consequence than a causative factor of high-altitude pulmonary edema. In summary, these data argue against a dominant role for increased systemic capillary permeability in the development of acute mountain sickness and high-altitude pulmonary edema.

Sensitive and specific immunoassays to detect rabbit IL-8 and MCP-1: cytokines that mediate leukocyte recruitment to the lungs

The alpha- and beta-chemokines such as IL-8 and MCP-1 direct the recruitment of neutrophils and monocytes into the lungs and other tissues. In order to study the roles of IL-8 and MCP-1 in animals models, specific reagents are required that provide accurate measurements of these cytokines in biological fluids. Here we describe the development of sensitive and specific immunoassays for rabbit IL-8 and rabbit MCP-1, and the validation of these assays in rabbit plasma and bronchoalveolar lavage fluid. The sensitivity of each assay in 0.25 ng/ml for IL-8 and 0.1 ng/ml for MCP-1. The rabbit IL-8 assay does not crossreact with rabbit GRO, another alpha-chemokine, and crossreacts only weakly with human IL-8. The rabbit MCP-1 assay does not crossreact with human MCP-1. Anticoagulants interfere with the detection of IL-8 and MCP-1 in plasma, although. EDTA has the least inhibitory effect. Heat-sensitive inhibitors in normal rabbit serum interfere with the detection of IL-8 and MCP-1, although autoantibodies to IL-8 and MCP-1 were not detected. Rabbit erythrocytes bind IL-8 and MCP-1, but erythrocyte contamination of bronchoalveolar lavage fluid causes only a small error in the detection of IL-8 and MCP-1, unless the number of erythrocytes approaches the number found in blood. These assays provide sensitive and specific means to detect IL-8 and MCP-1 in rabbit plasma and bronchoalveolar lavage fluid, and demonstrate the importance of using species-specific reagents in animal studies.