High-altitude pulmonary edema: current concepts

An insilico approach to high altitude pulmonary edema - Molecular modeling of human beta2 adrenergic receptor and its interaction with Salmeterol & Nifedipine

Knowledge of the three-dimensional structures of protein targets from genomic data has the potential to accelerate researches pertaining to drug discovery. Human beta(2) adrenergic receptor is a G-protein-coupled receptor with seven transmembrane helices, and is important in pharmaceutical targeting on pulmonary and cardiovascular diseases. The human beta(2) adrenergic receptor has been found to play a very important role in the pathogenesis of high altitude pulmonary edema (HAPE). In the present study, a high quality of protein 3D structure has been predicted for the human beta(2) adrenergic receptor sequence with primary accession number P07550. Homologous template protein sequence with known 3D structure was identified and the template-query protein sequence validation was done by multiple sequence alignment method. The homology model was performed through Modeller and depended on the quality of the sequence alignment by BLAST, template structure and the consolidated result performed by Gene silico meta-server. The statistical verification of the generated model was evaluated by PROCHECK which revealed that the structure modeled through Modeller to be of good quality with 84.1% of residues in the most favored region. Docking studies were carried out after modeling with two well known ligands namely Salmeterol and Nifedipine, and the fitness score revealed that Salmeterol has a higher fitness score than Nifedipine. Estimation of binding affinity by X-Score revealed that Salmeterol had -10.40 binding affinity while Nifedipine showed -9.62 binding affinity. From the present study, it can be concluded that the generated model of human beta(2) adrenergic receptor can be used for further studies related to this receptor and Salmeterol was found to have a high binding affinity with human beta(2) adrenergic receptor.

Alveolar edema fluid clearance and acute lung injury

Although lung-protective ventilation strategies have substantially reduced mortality of acute lung injury patients there is still a need for new therapies that can further decrease mortality in patients with acute lung injury. Studies of epithelial ion and fluid transport across the distal pulmonary epithelia have provided important new concepts regarding potential new therapies for acute lung injury. Overall, there is convincing evidence that the alveolar epithelium is not only a tight epithelial barrier that resists the movement of edema fluid into the alveoli, but it is also actively involved in the transport of ions and solutes, a process that is essential for edema fluid clearance and the resolution of acute lung injury. The objective of this article is to consider some areas of recent progress in the field of alveolar fluid transport under normal and pathologic conditions. Vectorial ion transport across the alveolar and distal airway epithelia is the primary determinant of alveolar fluid clearance. The general paradigm is that active Na(+) and Cl(-) transport drives net alveolar fluid clearance, as demonstrated in several different species, including the human lung. Although these transport processes can be impaired in severe lung injury, multiple experimental studies suggest that upregulation of Na(+) and Cl(-) transport might be an effective therapy in acute lung injury. We will review mechanisms involved in pharmacological modulation of ion transport in lung injury with a special focus on the use of beta-adrenergic agonists which has generated considerable interest and is a promising therapy for clinical acute lung injury.

Transient myoclonic jerks and restless legs during periodic tachypnea in acute mountain sickness

A 46-year-old man with lower airway infection developed acute mountain sickness (AMS) at a 5,100 m high base camp. AMS was associated with myoclonic jerks (7-8/h) and restless legs. AMS with neurological manifestations could be relieved only upon descent to 3,500 m. To avoid pulmonary or neurological problems at high altitude, adequate acclimatization is a prerequisite.

Pathogenesis of pulmonary edema: learning from high-altitude pulmonary edema

Pulmonary edema is a problem of major clinical importance resulting from a persistent imbalance between forces that drive water into the airspace of the lung and the biological mechanisms for its removal. Here, we will review the fundamental mechanisms implicated in the regulation of alveolar fluid homeostasis. We will then describe the perturbations of pulmonary fluid homeostasis implicated in the pathogenesis of pulmonary edema in conditions associated with increased pulmonary capillary pressure, namely cardiogenic pulmonary edema and high-altitude pulmonary edema (HAPE), with particular emphasis on the latter that has provided important new insight into underlying mechanisms of pulmonary edema. We will provide evidence that impaired pulmonary endothelial and epithelial nitric oxide synthesis and/or bioavailability may represent a central underlying defect predisposing to exaggerated hypoxic pulmonary vasoconstriction, and, in turn, capillary stress failure and alveolar fluid flooding. We will then demonstrate that exaggerated pulmonary hypertension, while possibly a prerequisite, may not always be sufficient to cause HAPE, and how defective alveolar fluid clearance may represent a second important pathogenic mechanism. Finally, we will outline, how this new insight gained from studies in HAPE, may be translated into the management of pulmonary edema and hypoxemia related disease states in general.

Magnetic Resonance Imaging of Uneven Pulmonary Perfusion in Hypoxia in Humans

RATIONALE

Inhomogeneous hypoxic pulmonary vasoconstriction causing regional overperfusion and high capillary pressure is postulated for explaining how high pulmonary artery pressure leads to high-altitude pulmonary edema in susceptible (HAPE-S) individuals.

OBJECTIVE

Because different species of animals also show inhomogeneous hypoxic pulmonary vasoconstriction, we hypothesized that inhomogeneity of lung perfusion in general increases in hypoxia, but is more pronounced in HAPE-S. For best temporal and spatial resolution, regional pulmonary perfusion was assessed by dynamic contrast-enhanced magnetic resonance imaging.

METHODS

Dynamic contrast-enhanced magnetic resonance imaging and echocardiography were performed during normoxia and after 2 h of hypoxia (Fi(O2) = 0.12) in 11 HAPE-S individuals and 10 control subjects. As a measure for perfusion inhomogeneity, the coefficient of variation for two perfusion parameters (peak signal intensity, time-to-peak) was determined for the whole lung and isogravitational slices.

RESULTS

There were no differences in perfusion inhomogeneity between the groups in normoxia. In hypoxia, analysis of coefficients of variation indicated a greater inhomogeneity in all subjects, which was more pronounced in HAPE-S compared with control subjects. Discrimination between HAPE-S and control subjects was best in gravity-dependent lung areas. Pulmonary artery pressure during hypoxia increased from 22 +/- 3 to 53 +/- 9 mm Hg in HAPE-S and 24 +/- 4 to 33 +/- 6 mm Hg in control subjects (mean +/- SD; p < 0.001), respectively.

CONCLUSION

This study shows that hypoxic pulmonary vasoconstriction is inhomogeneous in hypoxia in humans, particularly in HAPE-S individuals where it is accompanied by a greater increase in pulmonary artery pressure compared with control subjects. These findings support the hypothesis of exaggerated and uneven hypoxic pulmonary vasoconstriction in HAPE-S individuals.

Heterozygotes of NOS3 Polymorphisms Contribute to Reduced Nitrogen Oxides in High-Altitude Pulmonary Edema

STUDY OBJECTIVES

High-altitude pulmonary edema (HAPE), which develops on exertion under hypoxic conditions, aggravates due to endothelial dysfunction. Repeat events of the disorder suggests of genetic susceptibility. Endothelial nitric oxide synthase gene (NOS3), a regulator of vasodilation, has emerged as a strong candidate marker. In the present study, we investigated G894T, 27-base-pair 4b/4a (variable number of tandem repeat), -922A/G, and -786T/C polymorphisms of NOS3, individually or in combination, for an association with HAPE.

DESIGN

A cross-sectional case control study.

SETTINGS

Blood samples of HAPE-resistant lowlanders (HAPE-r) were obtained at sea level, and blood samples of patients with HAPE (HAPE-p) were obtained at Sonam Norboo Memorial Hospital, Leh, at 3,500 m.

PARTICIPANTS

The study groups consisted of 60 HAPE-r inducted two to three times to altitudes > 3,600 m; and 72 HAPE-p, who had HAPE on their first visit to high altitude.

RESULTS

Nitrogen oxides (NOx) at 77.9 +/- 28.6 micromol/L were significantly elevated in HAPE-r as compared to 42.39 +/- 12.93 micromol/L in HAPE-p (p < 0.0001). Genotype distribution of G894T and 4b/4a polymorphisms was significantly different in the two groups (p = 0.001 and 0.009, respectively). Haplotype analysis revealed -922A/G and -786T/C polymorphisms in complete linkage disequilibrium. The wild-type haplotypes G-b (G894T, 4b/4a), G-A (G894T, -922A/G), and G-b-A (G894T, 4b/4a, -922A/G) were significantly overrepresented in HAPE-r (p < 0.0001, p = 0.03, and p = 0.02, respectively). The heterozygote genotype combination GTba as compared to wild-type combination GGbb was significantly higher in HAPE-p (chi2 = 18.62, p = 0.00009; odds ratio, 7.20; 95% confidence interval, 2.82 to 18.38). The combination of four heterozygotes GTbaAGTC was overrepresented in HAPE-p (p = 0.04), whereas the wild-type genotype combination GGbbAATT was overrepresented in HAPE-r (p = 0.002). Furthermore, the GGbb combination correlated with significantly elevated NOx as compared to remaining combinations as a whole in both HAPE-r and HAPE-p (p = 0.01 and 0.004, respectively).

CONCLUSIONS

Reduced NOx and combination of heterozygotes associate with the susceptibility to HAPE. The study impels another step toward application of NOx as a diagnostic marker for HAPE. The NOS3 GTba and GTbaAGTC genotype combinations may find application as genetic markers for predicting the risk for HAPE.

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.

High altitude cerebral and pulmonary edema

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

Hypoxic pulmonary vasoconstriction is heterogeneously distributed in the prone dog

Hypoxic pulmonary vasoconstriction (HPV) is thought to protect gas exchange by decreasing perfusion to hypoxic regions. However, with global hypoxia, non-uniformity in HPV may cause over-perfusion to some regions, leading to high-altitude pulmonary edema. To quantify the spatial distribution of HPV and regional PO2 (PRO2) among small lung regions (approximately 2.0 cm3), five prone beagles (approximately 8.3 kg) were anesthetized and ventilated (PEEP approximately 2 cm H2O) with an F1O2 of 0.21, then 0.50, 0.18, 0.15, and 0.12 in random order. Regional blood perfusion (Q), ventilation (VA) and calculated PRO2 were obtained using iv infusion of 15 microm and inhalation of 1 microm fluorescent microspheres. Lung pieces were clustered by their relative blood flow response to each F1O2. Clusters were shown to be spatially grouped within animals and across animals. Lung piece resistance increased as PRO2 decreased to 60-70 mmHg but dropped at PRO2's < 60mmHg. Regional ventilation changed little with hypoxia. HPV varied more in strength of response, rather than PRO2 response threshold. In initially homogeneous VA/Q lungs, we conclude that HPV response is heterogeneous and spatially clustered.

Polymorphisms of renin-angiotensin system genes with high-altitude pulmonary edema in Japanese subjects

STUDY OBJECTIVES

The renin-angiotensin system (RAS), including angiotensin-converting enzyme (ACE) and angiotensin II type 1 receptor (AT(1)R), plays an important role in the pathogenesis of pulmonary hypertension, which is suggested to be critical in the development of high-altitude pulmonary edema (HAPE). Investigating the associations of the polymorphisms in the genes of RAS with HAPE is to elucidate the genetic background underlying this disease.

DESIGN

A cross-sectional, case-control study.

SETTING

Shinshu University Hospital, Matsumoto, Japan.

PARTICIPANTS

Forty-nine HAPE-susceptible (HAPE-s) subjects with a history of HAPE, and 55 healthy climbers with HAPE resistance (HAPE-r).

INTERVENTIONS

Twenty-one of 49 HAPE-s subjects underwent right cardiac catheterization.

MEASUREMENTS AND RESULTS

The insertion/deletion polymorphism in the ACE gene (ACE-I/D) was investigated by polymerase chain reaction (PCR). There was no significant difference of the distribution of the ACE-I/D polymorphism between the HAPE-s and HAPE-r groups. The A(1166)C and G(1517)T single-nucleotide polymorphisms (SNPs) in AT(1)R gene were investigated by the PCR following digested by corresponding restricted endonuclease enzymes. The distribution of the G(1517)T SNP was significantly different between the two groups (p = 0.012). The pulmonary hemodynamics of the 21 HAPE-s subjects were retrospectively examined. The pulmonary artery pressure (PAP), pulmonary vascular resistance (PVR), and PVR index (PVRI) were all significantly increased on hospital admission. Moreover, the PVR and PVRI were significantly higher in the HAPE-s subjects with D positivity than in the HAPE-s subjects with I positivity (PVR, p = 0.015; PVRI, p = 0.028), while the PAP did not show any significant difference between the two subgroups.

CONCLUSIONS

The ACE-I/D polymorphism is not associated with HAPE susceptibility in Japanese subjects. The AT(1)R gene polymorphisms may likely associate with HAPE susceptibility. The D allele of the ACE-I/D polymorphism probably contributes to the hyperresponsive PVR and PVRI to acute hypoxia.

High-altitude illness

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

Spatial distribution of hypoxic pulmonary vasoconstriction in the supine pig

Hypoxic pulmonary vasoconstriction (HPV) serves to maintain optimal gas exchange by decreasing perfusion to hypoxic regions. However, global hypoxia and nonuniform HPV may result in overperfusion of poorly constricted regions leading to local edema seen in high-altitude pulmonary edema. To quantify the spatial distribution of HPV and its response to regional Po2 (Pr(O2)) among small lung regions, five pigs were anesthetized and mechanically ventilated in the supine posture. The animals were ventilated with an inspired O2 fraction (Fi(O2)) of 0.50 and 0.21 and then (in random order) 0.15, 0.12, and 0.09. Regional blood flow (Q) and alveolar ventilation (Va) were measured by using intravenous infusion of 15 microm and inhalation of 1-microm fluorescent microspheres, respectively. Pr(O2) was calculated for each piece at each Fi(O2). Lung pieces differed in their Q response to hypoxia in a manner related to their initial Va/Q with Fi(O2) = 0.21. Reducing Fi(O2) < 0.15 decreased Q to the initially high Va/Q (higher Pr(O2)) regions and forced Q into the low Va/Q (dorsal-caudal) regions. Resistance increased in most lung pieces as Pr(O2) decreased, reaching a maximum resistance when Pr(O2) is between 40 and 50 Torr. Local resistance decreased at PrO2 < 40 Torr. Pieces were statistically clustered with respect to their relative Q response pattern to each Fi(O2). Some clusters were shown to be spatially organized. We conclude that HPV is spatially heterogeneous. The heterogeneity of Q response may be related, in part, to the heterogeneity of baseline Va/Q.

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.

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

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

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

STUDY OBJECTIVES

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

DESIGN

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

SETTING

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

PATIENTS

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

MEASUREMENTS AND RESULTS

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

CONCLUSION

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

Positive association of the endothelial nitric oxide synthase gene polymorphisms with high-altitude pulmonary edema

BACKGROUND

A defect of nitric oxide (NO) synthesis in the lung of high-altitude pulmonary edema (HAPE) has been suggested to contribute to its exaggerated pulmonary hypertension. Several polymorphisms have been identified in the gene encoding endothelial nitric oxide synthase (eNOS), which is a key enzyme responsible for NO synthesis, some of which were reported to be associated with vascular disorders.

METHODS AND RESULTS

We studied 41 HAPE-susceptible subjects (HAPE-s) and 51 healthy climbers (control group) in a Japanese population. We examined 2 polymorphisms of the eNOS gene, including the Glu298Asp variant and 27-base pair (bp) variable numbers of tandem repeats using polymerase chain reaction followed by restriction fragment length polymorphism. The Asp allelic frequency of the Glu298Asp variant was 25.6% in the HAPE-s and 9.8% in the controls, which was significantly different between the two groups (P=0.0044). The eNOS4a allelic frequency of 27-bp variable numbers of tandem repeats was 23.2% in the HAPE-s, significantly higher than that of 6.9% in the controls (P=0.0016). In HAPE-s group, 11 of 41 (26.8%) subjects possessed simultaneously both of the two significant alleles, but among the controls, none did, which showed a high statistical difference between the two groups (P=0.000059).

CONCLUSIONS

Both polymorphisms of the eNOS gene were significantly associated with HAPE. A genetic background may underlie the impaired NO synthesis in the pulmonary circulation of HAPE-s. These polymorphisms could be genetic markers for predicting the susceptibility to HAPE.

Pathological features of the lung in fatal high altitude pulmonary edema occurring at moderate altitude in Japan

In order to characterize the pathological features of high altitude pulmonary edema (HAPE) occurring at moderate altitude in Japan, we performed routine hematoxylin and eosin (HE) staining in lung materials from HAPE autopsied cases. We also undertook advanced immunohistochemical staining for observation of type II pneumocytes, pulmonary surfactant (PS), and mast cells in the lung of HAPE cases to examine the biological changes within the lung parenchyma. The pathological findings of HAPE were characterized by alveolar edema, congestion of pulmonary vessels, alveolar hyaline membranes, alveolar hemorrhage, and multithrombi and fibrin clots, but maintained alveolar structure. The immunostaining results showed that the type II pneumocytes were cellular fusion, deformity, and exfoliation from the walls of alveoli; the PS not only lined the alveolar surface, but was also patchily distributed within alveoli; and the number of mast cells were increased (9.0 +/- 0.9 cells/mm(2)) compared to that in controls (1.1 +/- 0.4 cells/mm(2)) (p < 0.01). We conclude that the pathological features of HAPE at moderate altitude in Japan are similar to others reported worldwide, and that the type II pneumocytes, PS, and mast cells may contribute to some extent to pathophysiological parts in the development and progression of HAPE.

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.

[Acute mountain sickness: the clinical characteristics of a cohort of 615 patients]

OBJECTIVE

To study the acute mountain sickness (AMS) and the influence the altitude has on individuals according to time of exposure, age and place of residence. Study cohort prospective in the shelters of Cotopaxi and Chimborazo (4,800 and 5,000 m), in the Ecuatorian Andes.

SUBJECTS AND METHODS

Tourists from 8 to 51 years of age, residents of the coastal and mountain regions, exposed suddenly to the altitude. Signs and symptoms were recorded at 2, 8, 20 and 24 h of exposure and categorized according to the degree of acute mountain sickness found: AMS 1 [4 to 7 points (light), AMS 2 [8 to 11 points (moderate)] and AMS 3 [more than 12 points (severe)].

RESULTS

The study, consisted of 615 patients, was completed by 564. Neurological symptoms are prevalent (headache in the 81.7% of patients) over cardiopulmonary symptoms (cardiac frequency over 100/min in the 25.6%). At 20 h (after one night), the signs and symptoms are more intense and affect a greater number of people (p < 0.0001). Patients from 8 to 22 years of age and residents of the coast have a greater risk of developing AMS 2 (p < 0.01). Overweight, a sedentary life style and a previous incidence of altitude sickness are factors which contribute to the development of AMS 2 (p < 0.001).

CONCLUSIONS

AMS is an important neurological affection. Young people, individuals from sea-level, as well as those whose are overweight, sedentary or who have previously experienced AMS, have a higher risk of developing AMS 2 after a sudden exposure to altitudes between 4,800 and 5,000 meters. Lack of balance and coordination, and shortness of breath at rest imply AMS 3 and the presence of high altitude cerebral or pulmonary edema.

A tragic report of probable high-altitude pulmonary edema in the Himalayas: preventive implications

High-altitude pulmonary edema (HAPE) is a well-recognized disease entity in trekkers to the Nepal Himalayas. We present the case of a patient who had clinical features consistent with HAPE but did not descend the mountain on time, which contributed to his death. The important factors of the diagnosis, the descent, and the follow-up in Kathmandu are examined.

Hypoxia-induced pulmonary blood redistribution in subjects with a history of high-altitude pulmonary edema

BACKGROUND

Pulmonary hypertension has been suggested to play an important role in development of high-altitude pulmonary edema (HAPE), and individual susceptibility has been suggested to be associated with enhanced pulmonary vascular response to hypoxia. We hypothesized that much greater pulmonary vasoconstriction would be induced by acute alveolar hypoxia in HAPE-susceptible (HAPE-s) subjects and that changes in pulmonary blood flow distribution could be demonstrated by radionuclide study.

METHODS AND RESULTS

We performed ventilation-perfusion scintigraphy in 8 HAPE-s subjects and 5 control subjects while each was in the supine position and acquired functional images of pulmonary blood flow and ventilation under separate normoxic and hypoxic (arterial oxygen saturation, 70%) conditions. We also measured acceleration time/right ventricular ejection time (AcT/RVET) with Doppler echocardiography under each condition in both groups. Moreover, we assayed human leukocyte antigen (HLA) alleles serologically in the HAPE-s group. Pulmonary blood flow was significantly shifted from the basal lung region to the apical lung region under hypoxia in HAPE-s subjects, although no significant change in regional ventilation was observed. With Doppler echocardiography, HAPE-s subjects showed increased pulmonary arterial pressure during hypoxia compared with control subjects. The magnitude of cephalad redistribution of lung blood flow was significantly higher in the HLA-DR6-positive than in HLA-DR6-negative HAPE-s subjects.

CONCLUSIONS

These findings suggest that acute hypoxia induces much greater cephalad redistribution of pulmonary blood flow that results from exaggerated vasoconstriction in the basal lung in HAPE-s subjects. Furthermore, pulmonary vascular hyperreactivity to hypoxia may be associated with HLA-DR6.

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.

Blood pressure and plasma catecholamines in acute and prolonged hypoxia: effects of local hypothermia

This study measured the pressor and plasma catecholamine response to local hypothermia during adaptation to hypobaric hypoxia. Eight healthy men were studied at rest and after 10 and 45 min of local cooling of one hand and forearm as well as after 30 min of rewarming at sea level and again 24 h and 5 days after rapid, passive transport to high altitude (4,559 m). Acute mountain sickness scores ranged from 5 to 16 (maximal attainable score: 20) on the first day but were reduced to 0-8 by the fifth day. Systolic blood pressure, heart rate, and plasma epinephrine increased on day 1 at altitude compared with sea level but declined again on day 5, whereas diastolic and mean blood pressures continued to rise in parallel with plasma norepinephrine. With local cooling, an increased vasoactive response was seen on the fifth day at altitude. Very high pressures were obtained, and the pressure elevation was prolonged. Heart rate increased twice as much on day 5 compared with the other two occasions. Thoracic fluid index increased with cooling on day 5, suggesting an increase in pulmonary vascular resistance. In conclusion, prolonged hypoxia seems to elicit an augmented pressor response to local cooling in the systemic and most likely also the pulmonary circulation.

Hypoxia/Hypoxemia-Induced activation of the procoagulant pathways and the pathogenesis of ischemia-associated thrombosis

Although oxygen deprivation has long been associated with triggering of the procoagulant pathway and venous thrombosis, blood hypoxemia and stasis by themselves do not lead to fibrin formation. A pathway is outlined through which diminished levels of oxygen activate the transcription factor early growth response-1 (Egr-1) leading to de novo transcription/translation of tissue factor in mononuclear phagocytes and smooth muscle cells, which eventuates in vascular fibrin deposition. The procoagulant response is magnified by concomitant suppression of fibrinolysis by hypoxia-mediated upregulation of plasminogen activator inhibitor-1. These data add a new facet to the biology of thrombosis associated with hypoxemia/stasis and imply that interference with mechanisms causing Egr-1 activation in response to oxygen deprivation might prevent vascular fibrin deposition occurring in ischemia without directly interfering with other pro/anticoagulant pathways.

Hypoxia and hyperoxia both transiently affect distribution of pulmonary perfusion but not ventilation in awake sheep

Despite a remarkable gravity independent heterogeneity in both local pulmonary ventilation and perfusion, the two are closely correlated at rest and during exercise in the normal lung. These observations strongly indicate that there is a mechanism for coupling of the two so that local V/Q-ratio is kept fairly uniform throughout the lung. This is also necessary to achieve adequate gas exchange in the lung. It was recently suggested that oxygen-induced vasoconstriction has a slow and intense component that might contribute to the matching of ventilation and perfusion also under normal conditions (Vejlstrup & Dorrington 1993). We therefore simultaneously determined distribution of local ( approximately 1(1/2) cm3 lung pieces) ventilation and perfusion in eight sheep at normoxia (FiO2 21%) and after 10 min and 2(1/2) h exposure to hypoxia (FiO2 12%; four sheep) or hyperoxia (FiO2 40%; four sheep). We used a approximately 1 microm wet fluorescent aerosol and 15 microm radioactive microspheres i.v. to measure local ventilation and perfusion, respectively. Neither hypoxia nor hyperoxia caused changes in the distribution of ventilation. After 10 min exposure to hypoxia or hyperoxia, distribution of perfusion was altered so that the correlation between values for local ventilation and perfusion decreased. After 2(1/2) h exposure to either hypoxia or hyperoxia, distributions of perfusion and V/Q-ratio had returned to baseline. These results show that distribution of perfusion is influenced by acute changes in oxygen tension, so that local matching of ventilation and perfusion is affected. Apparently, some mechanism restores the matching during extended exposure to the altered oxygen tension.

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.

Prevention of common travel ailments

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

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.