High altitude pulmonary edema

Effect of furosemide in the treatment of high-altitude pulmonary edema

BACKGROUND

High-altitude pulmonary edema (HAPE) refers to the onset of breathlessness, cough, and fever at rest after arriving at high altitudes. It is a life-threatening illness caused by rapid ascent to high altitudes. Furosemide is controversial in HAPE treatment but is routinely used in China. Further research is needed to assess its efficacy and impact on HAPE management and prognosis. The aim of this study is to determine the effectiveness of furosemide for HAPE.

METHODS

A retrospective was conducted to analysis of patients with HAPE admitted to the People's Hospital of Shigatse City from January 2018 to September 2023. Patients were divided into furosemide group and non-furosemide group for further analysis. Clinical variables including demographic information, comorbidities, vital signs, inflammatory markers, biochemical analysis, CT severity score and prognostic indicators were collected.

RESULTS

A total of 273 patients were enrolled, with 209 patients in the furosemide group and 64 patients in the non-furosemide group. The furosemide group showed a significantly decrease in CT severity scores compared to the non-furosemide group. Subgroup analysis showed that the longer the duration of furosemide use, the more pronounced the improvement in lung CT severity scores. But there were no significant differences in length of hospital stay and in-hospital mortality between the two groups.

CONCLUSION

Furosemide helps alleviate pulmonary edema in HAPE patients, but further research is needed to clarify its impact on prognosis.

Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update

To provide guidance to clinicians about best practices, the Wilderness Medical Society (WMS) convened an expert panel to develop evidence-based guidelines for prevention, diagnosis, and treatment of acute mountain sickness, high altitude cerebral edema, and high altitude pulmonary edema. Recommendations are graded based on the quality of supporting evidence and the balance between the benefits and risks/burdens according to criteria put forth by the American College of Chest Physicians. The guidelines also provide suggested approaches for managing each form of acute altitude illness that incorporate these recommendations as well as recommendations on how to approach high altitude travel following COVID-19 infection. This is an updated version of the original WMS Consensus Guidelines for the Prevention and Treatment of Acute Altitude Illness published in Wilderness & Environmental Medicine in 2010 and the subsequently updated WMS Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness published in 2014 and 2019.

An Unusual Presentation of Pulmonary Edema During an Ice Dive at Altitude

Military diving operations occur in a wide range of austere environments, including high-altitude environments and cold weather environments; however, rarely do both conditions combine. Ice diving at altitude combines the physiologic risks of diving, a hypothermic environment, and a high-altitude environment all in one. Careful planning and consideration of the potential injuries and disease processes affiliated with the aforementioned physiologic risks must be considered. In this case report, we describe a Navy diver who became obtunded secondary to hypoxia during an ice dive at 2,987 m (9,800 ft) elevation and was subsequently diagnosed with high-altitude pulmonary edema. Further consideration of the environment, activities, and history does not make this a clear case, and swimming-induced pulmonary edema which physiologically possesses many overlaps with high-altitude pulmonary edema may have contributed or been the ultimate causal factor for the diver's acute response.

A century of exercise physiology: lung fluid balance during and following exercise

PURPOSE

This review recalls the principles developed over a century to describe trans-capillary fluid exchanges concerning in particular the lung during exercise, a specific condition where dyspnea is a leading symptom, the question being whether this symptom simply relates to fatigue or also implies some degree of lung edema.

METHOD

Data from experimental models of lung edema are recalled aiming to: (1) describe how extravascular lung water is strictly controlled by "safety factors" in physiological conditions, (2) consider how waning of "safety factors" inevitably leads to development of lung edema, (3) correlate data from experimental models with data from exercising humans.

RESULTS

Exercise is a strong edemagenic condition as the increase in cardiac output leads to lung capillary recruitment, increase in capillary surface for fluid exchange and potential increase in capillary pressure. The physiological low microvascular permeability may be impaired by conditions causing damage to the interstitial matrix macromolecular assembly leading to alveolar edema and haemorrhage. These conditions include hypoxia, cyclic alveolar unfolding/folding during hyperventilation putting a tensile stress on septa, intensity and duration of exercise as well as inter-individual proneness to develop lung edema.

CONCLUSION

Data from exercising humans showed inter-individual differences in the dispersion of the lung ventilation/perfusion ratio and increase in oxygen alveolar-capillary gradient. More recent data in humans support the hypothesis that greater vasoconstriction, pulmonary hypertension and slower kinetics of alveolar-capillary O2 equilibration relate with greater proneness to develop lung edema due higher inborn microvascular permeability possibly reflecting the morpho-functional features of the air-blood barrier.

Pathophysiology and Therapy of High-Altitude Sickness: Practical Approach in Emergency and Critical Care

High altitude can be a hostile environment and a paradigm of how environmental factors can determine illness when human biological adaptability is exceeded. This paper aims to provide a comprehensive review of high-altitude sickness, including its epidemiology, pathophysiology, and treatments. The first section of our work defines high altitude and considers the mechanisms of adaptation to it and the associated risk factors for low adaptability. The second section discusses the main high-altitude diseases, highlighting how environmental factors can lead to the loss of homeostasis, compromising important vital functions. Early recognition of clinical symptoms is important for the establishment of the correct therapy. The third section focuses on high-altitude pulmonary edema, which is one of the main high-altitude diseases. With a deeper understanding of the pathogenesis of high-altitude diseases, as well as a reasoned approach to environmental or physical factors, we examine the main high-altitude diseases. Such an approach is critical for the effective treatment of patients in a hostile environment, or treatment in the emergency room after exposure to extreme physical or environmental factors.

Methamphetamine exacerbates pathophysiology of traumatic brain injury at high altitude. Neuroprotective effects of nanodelivery of a potent antioxidant compound H-290/51

Military personnel are often exposed to high altitude (HA, ca. 4500-5000m) for combat operations associated with neurological dysfunctions. HA is a severe stressful situation and people frequently use methamphetamine (METH) or other psychostimulants to cope stress. Since military personnel are prone to different kinds of traumatic brain injury (TBI), in this review we discuss possible effects of METH on concussive head injury (CHI) at HA based on our own observations. METH exposure at HA exacerbates pathophysiology of CHI as compared to normobaric laboratory environment comparable to sea level. Increased blood-brain barrier (BBB) breakdown, edema formation and reductions in the cerebral blood flow (CBF) following CHI were exacerbated by METH intoxication at HA. Damage to cerebral microvasculature and expression of beta catenin was also exacerbated following CHI in METH treated group at HA. TiO2-nanowired delivery of H-290/51 (150mg/kg, i.p.), a potent chain-breaking antioxidant significantly enhanced CBF and reduced BBB breakdown, edema formation, beta catenin expression and brain pathology in METH exposed rats after CHI at HA. These observations are the first to point out that METH exposure in CHI exacerbated brain pathology at HA and this appears to be related with greater production of oxidative stress induced brain pathology, not reported earlier.

Hypoxia and Inflammation: Insights From High-Altitude Physiology

The key regulators of the transcriptional response to hypoxia and inflammation (hypoxia inducible factor, HIF, and nuclear factor-kappa B, NF-κB, respectively) are evolutionarily conserved and share significant crosstalk. Tissues often experience hypoxia and inflammation concurrently at the site of infection or injury due to fluid retention and immune cell recruitment that ultimately reduces the rate of oxygen delivery to tissues. Inflammation can induce activity of HIF-pathway genes, and hypoxia may modulate inflammatory signaling. While it is clear that these molecular pathways function in concert, the physiological consequences of hypoxia-induced inflammation and how hypoxia modulates inflammatory signaling and immune function are not well established. In this review, we summarize known mechanisms of HIF and NF-κB crosstalk and highlight the physiological consequences that can arise from maladaptive hypoxia-induced inflammation. Finally, we discuss what can be learned about adaptive regulation of inflammation under chronic hypoxia by examining adaptive and maladaptive inflammatory phenotypes observed in human populations at high altitude. We aim to provide insight into the time domains of hypoxia-induced inflammation and highlight the importance of hypoxia-induced inflammatory sensitization in immune function, pathologies, and environmental adaptation.

Pulmonary Hypertension in Acute and Chronic High Altitude Maladaptation Disorders

Alveolar hypoxia is the most prominent feature of high altitude environment with well-known consequences for the cardio-pulmonary system, including development of pulmonary hypertension. Pulmonary hypertension due to an exaggerated hypoxic pulmonary vasoconstriction contributes to high altitude pulmonary edema (HAPE), a life-threatening disorder, occurring at high altitudes in non-acclimatized healthy individuals. Despite a strong physiologic rationale for using vasodilators for prevention and treatment of HAPE, no systematic studies of their efficacy have been conducted to date. Calcium-channel blockers are currently recommended for drug prophylaxis in high-risk individuals with a clear history of recurrent HAPE based on the extensive clinical experience with nifedipine in HAPE prevention in susceptible individuals. Chronic exposure to hypoxia induces pulmonary vascular remodeling and development of pulmonary hypertension, which places an increased pressure load on the right ventricle leading to right heart failure. Further, pulmonary hypertension along with excessive erythrocytosis may complicate chronic mountain sickness, another high altitude maladaptation disorder. Importantly, other causes than hypoxia may potentially underlie and/or contribute to pulmonary hypertension at high altitude, such as chronic heart and lung diseases, thrombotic or embolic diseases. Extensive clinical experience with drugs in patients with pulmonary arterial hypertension suggests their potential for treatment of high altitude pulmonary hypertension. Small studies have demonstrated their efficacy in reducing pulmonary artery pressure in high altitude residents. However, no drugs have been approved to date for the therapy of chronic high altitude pulmonary hypertension. This work provides a literature review on the role of pulmonary hypertension in the pathogenesis of acute and chronic high altitude maladaptation disorders and summarizes current knowledge regarding potential treatment options.

Mechanisms of Pulmonary Hypertension in Acute Respiratory Distress Syndrome (ARDS)

Background: Acute respiratory distress syndrome (ARDS) is a severe and often fatal disease. The causes that lead to ARDS are multiple and include inhalation of salt water, smoke particles, or as a result of damage caused by respiratory viruses. ARDS can also arise due to systemic complications such as blood transfusions, sepsis, or pancreatitis. Unfortunately, despite a high mortality rate of 40%, there are limited treatment options available for ARDS outside of last resort options such as mechanical ventilation and extracorporeal support strategies. Aim of review: A complication of ARDS is the development of pulmonary hypertension (PH); however, the mechanisms that lead to PH in ARDS are not fully understood. In this review, we summarize the known mechanisms that promote PH in ARDS. Key scientific concepts of review: (1) Provide an overview of acute respiratory distress syndrome; (2) delineate the mechanisms that contribute to the development of PH in ARDS; (3) address the implications of PH in the setting of coronavirus disease 2019 (COVID-19).

[Travelling to High Altitude Destinations after Recovery from COVID-19-infection: New Aspects of Medical Advice in Altitude Medicine]

After loosening of travel restrictions due to the COVID-19 pandemic, tourism to high-altitude destinations over 2500 metres is expected to increase again.In line with this trend, it can be expected that patients after recovery from COVID-19 infection will seek advice from specialists on altitude or travel medicine before travelling to high altitudes.Here, the physician on altitude medicine is faced with major challenges, as such a question has not been raised so far.In addition to the basics of altitude sickness and high altitude pulmonary edema, this article deals with the current studies on pulmonological pathologies and disease course of COVID-19 infections and, in accordance with the current state of knowledge, provides recommendations for advice in altitude medicine for patients after COVID-19 infection.

The role of hypoxia-induced modulation of alveolar epithelial Na+- transport in hypoxemia at high altitude

Reabsorption of excess alveolar fluid is driven by vectorial Na⁺-transport across alveolar epithelium, which protects from alveolar flooding and facilitates gas exchange. Hypoxia inhibits Na⁺-reabsorption in cultured cells and in-vivo by decreasing activity of epithelial Na⁺-channels (ENaC), which impairs alveolar fluid clearance. Inhibition also occurs during in-vivo hypoxia in humans and laboratory animals. Signaling mechanisms that inhibit alveolar reabsorption are poorly understood. Because cellular adaptation to hypoxia is regulated by hypoxia-inducible transcription factors (HIF), we tested whether HIFs are involved in decreasing Na⁺-transport in hypoxic alveolar epithelium. Expression of HIFs was suppressed in cultured rat primary alveolar epithelial cells (AEC) with shRNAs. Hypoxia (1.5% O₂, 24 h) decreased amiloride-sensitive transepithelial Na⁺-transport, decreased the mRNA expression of α-, β-, and γ-ENaC subunits, and reduced the amount of αβγ-ENaC subunits in the apical plasma membrane. Silencing HIF-2α partially prevented impaired fluid reabsorption in hypoxic rats and prevented the hypoxia-induced decrease in α- but not the βγ-subunits of ENaC protein expression resulting in a less active form of ENaC in hypoxic AEC. Inhibition of alveolar reabsorption also caused pulmonary vasoconstriction in ventilated rats. These results indicate that a HIF-2α-dependent decrease in Na⁺-transport in hypoxic alveolar epithelium decreases alveolar reabsorption. Because susceptibles to high-altitude pulmonary edema (HAPE) have decreased Na⁺-transport even in normoxia, inhibition of alveolar reabsorption by hypoxia at high altitude might further impair alveolar gas exchange. Thus, aggravated hypoxemia might further enhance hypoxic pulmonary vasoconstriction and might subsequently cause HAPE.

Emerging Mechanisms of Pulmonary Vasoconstriction in SARS-CoV-2-Induced Acute Respiratory Distress Syndrome (ARDS) and Potential Therapeutic Targets

The 1918 influenza killed approximately 50 million people in a few short years, and now, the world is facing another pandemic. In December 2019, a novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused an international outbreak of a respiratory illness termed coronavirus disease 2019 (COVID-19) and rapidly spread to cause the worst pandemic since 1918. Recent clinical reports highlight an atypical presentation of acute respiratory distress syndrome (ARDS) in COVID-19 patients characterized by severe hypoxemia, an imbalance of the renin-angiotensin system, an increase in thrombogenic processes, and a cytokine release storm. These processes not only exacerbate lung injury but can also promote pulmonary vascular remodeling and vasoconstriction, which are hallmarks of pulmonary hypertension (PH). PH is a complication of ARDS that has received little attention; thus, we hypothesize that PH in COVID-19-induced ARDS represents an important target for disease amelioration. The mechanisms that can promote PH following SARS-CoV-2 infection are described. In this review article, we outline emerging mechanisms of pulmonary vascular dysfunction and outline potential treatment options that have been clinically tested.

NOD-like receptors mediate inflammatory lung injury during plateau hypoxia exposure

Background

The lung is an important target organ for hypoxia treatment, and hypoxia can induce several diseases in the body.

Methods

We performed transcriptome sequencing for the lungs of rats exposed to plateau hypoxia at 0 day and 28 days. Sequencing libraries were constructed, and enrichment analysis of the differentially expressed genes (DEGs) was implemented using the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Subsequently, experimental validation was executed by quantitative real-time PCR (qRT-PCR) and western blot.

Results

The results showed that the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) signaling pathway that was involved in immunity may play a crucial function in lung injury caused by plateau hypoxia. And the expressions of NOD1, NOD2, IL-1β, TNF-α, IL-6, and IL-18 were higher at 28 days of exposure to plateau hypoxia than that at 0 day. Similarly, CARD9, MYD88, p38 MAPK, and NF-κB p65, which are related to the NF-κB and MAPK signaling pathways, also demonstrated increased expression at 28 days exposure to plateau hypoxia than at 0 day.

Conclusions

Our study suggested that the NF­κBp65 and p38 MAPK signaling pathways may be activated in the lungs of rats during plateau hypoxia. Upregulated expression of NF­κBp65 and p38 MAPK can promote the transcription of downstream inflammatory factors, thereby aggravating the occurrence and development of lung tissue remodeling.

The Hen or the Egg: Impaired Alveolar Oxygen Diffusion and Acute High-altitude Illness?

Individuals ascending rapidly to altitudes >2500 m may develop symptoms of acute mountain sickness (AMS) within a few hours of arrival and/or high-altitude pulmonary edema (HAPE), which occurs typically during the first three days after reaching altitudes above 3000-3500 m. Both diseases have distinct pathologies, but both present with a pronounced decrease in oxygen saturation of hemoglobin in arterial blood (SO₂). This raises the question of mechanisms impairing the diffusion of oxygen (O₂) across the alveolar wall and whether the higher degree of hypoxemia is in causal relationship with developing the respective symptoms. In an attempt to answer these questions this article will review factors affecting alveolar gas diffusion, such as alveolar ventilation, the alveolar-to-arterial O₂-gradient, and balance between filtration of fluid into the alveolar space and its clearance, and relate them to the respective disease. The resultant analysis reveals that in both AMS and HAPE the main pathophysiologic mechanisms are activated before aggravated decrease in SO₂ occurs, indicating that impaired alveolar epithelial function and the resultant diffusion limitation for oxygen may rather be a consequence, not the primary cause, of these altitude-related illnesses.

L-arginine Attenuates Hypobaric Hypoxia-Induced Increase in Ornithine Decarboxylase 1

BACKGROUND

Chronic hypoxia-induced pulmonary hypertension and vascular remodeling have been shown to be associated with ornithine decarboxylase 1 (ODC1). However, few animal studies have investigated the role of ODC1 in acute hypoxia.

OBJECTIVES

We investigated ODC1 gene expression, morphologic and functional changes, and the effect of L-arginine as an attenuator in lung tissues of rats exposed to acute hypobaric hypoxia at a simulated altitude of 6000 m.

METHODS

Sprague-Dawley rats exposed to simulated hypobaric hypoxia (6000 m) for 24, 48, or 72 hours were treated with L-arginine (L-arginine group, 20 mg/100 g intraperitoneal; n=15) or untreated (non-L-arginine group, n=15). Control rats (n=5) were maintained at 2260 m in a normal environment for the same amount of time but were treated without L-arginine. The mean pulmonary artery pressure was measured by PowerLab system. The morphologic and immunohistochemical changes in lung tissue were observed under a microscope. The mRNA and protein levels of ODC1 were measured by real-time polymerase chain reaction and Western-blot, respectively.

RESULTS

Hypobaric hypoxia induced pulmonary interstitial hyperemia and capillary expansion in the lungs of rats exposed to acute hypoxia at 6000 m. The mean pulmonary artery pressure and the mRNA and protein levels of ODC1 were significantly increased, which could be attenuated by treatment with L-arginine.

CONCLUSIONS

L-arginine attenuates acute hypobaric hypoxia-induced increase in mean pulmonary artery pressure and ODC1 gene expression in lung tissues of rats. ODC1 gene contributes to the development of hypoxic pulmonary hypertension.

High Altitude Pulmonary Edema in a Mining Worker With an Abnormal Rise in Pulmonary Artery Pressure in Response to Acute Hypoxia Without Prior History of High Altitude Pulmonary Edema

High altitude pulmonary edema (HAPE) is a potentially life-threatening form of noncardiogenic pulmonary edema that may develop in otherwise healthy individuals upon ascent to high altitude. A constitutional susceptibility has been noted in some individuals, whereas others appear not to be susceptible at all. In our report, we present a case of HAPE triggered by concurrent respiratory tract infection and strenuous exercise in a mining worker with an abnormal rise in pulmonary artery pressure in response to acute hypoxia, without a prior history of HAPE during almost a year of commuting between high altitude and lowland areas.

Adaptation of iron requirement to hypoxic conditions at high altitude

Adequate acclimatization time to enable adjustment to hypoxic conditions is one of the most important aspects for mountaineers ascending to high altitude. Accordingly, most reviews emphasize mechanisms that cope with reduced oxygen supply. However, during sojourns to high altitude adjustment to elevated iron demand is equally critical. Thus in this review we focus on the interaction between oxygen and iron homeostasis. We review the role of iron 1) in the oxygen sensing process and erythropoietin (Epo) synthesis, 2) in gene expression control mediated by the hypoxia-inducible factor-2 (HIF-2), and 3) as an oxygen carrier in hemoglobin, myoglobin, and cytochromes. The blood hormone Epo that is abundantly expressed by the kidney under hypoxic conditions stimulates erythropoiesis in the bone marrow, a process requiring high iron levels. To ensure that sufficient iron is provided, Epo-controlled erythroferrone that is expressed in erythroid precursor cells acts in the liver to reduce expression of the iron hormone hepcidin. Consequently, suppression of hepcidin allows for elevated iron release from storage organs and enhanced absorption of dietary iron by enterocytes. As recently observed in sojourners at high altitude, however, iron uptake may be hampered by reduced appetite and gastrointestinal bleeding. Reduced iron availability, as observed in a hypoxic mountaineer, enhances hypoxia-induced pulmonary hypertension and may contribute to other hypoxia-related diseases. Overall, adequate systemic iron availability is an important prerequisite to adjust to high-altitude hypoxia and may have additional implications for disease-related hypoxic conditions.

High-altitude pulmonary edema can be prevented by heat shock protein 70-mediated hyperbaric oxygen preconditioning

BACKGROUND

The primary goal of this study was to test whether high-altitude exposure (HAE of 9.7% O2 at 0.47 absolute atmosphere [ATA] for 3 days) was capable of increasing lung edema, neutrophil, and hemorrhage scores as well as decreasing lung levels of both aquaporin 1 (AQP1) and AQP5 proteins and messenger RNA (mRNA) expression in rats, with a secondary goal to test whether a preinduction of heat shock protein 70 (HSP70) by hyperbaric oxygen preconditioning (HBO2P of 100% O2 at 2.0 ATA for 1 hour per day for 5 consecutive days) attenuated the HAE-induced increased lung injury scores and decreased lung AQP1 and AQP5 protein and mRNA expressions.

METHODS

Rats were assigned to (1) non-HBO2P (21% O2 at 1.0 ATA) + non-HAE (21% O2 at 1.0 ATA) group; (2) non-HBO2P + HAE group; (3) HBO2P + HAE group; and HBO2P + HSP70 antibodies (Ab) + HAE group. For the HSP70 Ab group, a neutralizing HSP70 Ab was injected intravenously at 24 hours before HAE. All the physiologic and biochemical parameters were obtained at the end of HAE or the equivalent period of non-HAE. The cardiovascular and blood gas parameters were monitored for all experiments. Bronchoalveolar lavage (BAL) was performed to determine proinflammatory cytokines (interleukin 6, interleukin 1β, and tumor necrosis factor α). Parts of the lung were excised for myeloperoxidase activity measurement, whereas the rest was collected for lung damage score assessments. AQP1 and AQP5 protein and mRAN expressions were also determined in the lung tissues.

RESULTS

In the non-HBO2P + HAE group, the animals displayed higher values of lung myeloperoxidase activity, BAL proinflammatory cytokines, lung water weight, and acute lung injury scores compared with those of the non-HBO2P + non-HAE controls. In contrast, the non-HBO2P + HAE group rats had lower values of lung AQP1 and AQP5 protein and mRNA expressions, mean arterial pressure, heart rate, SO2, Paco2, HCO3, and pH compared with those of non-HBO2P + non-HAE group rats. The increased acute lung edema, neutrophil, and hemorrhage scores; increased BAL levels of proinflammatory cytokines; decreased lung AQP1 and AQP5 protein and mRNA expressions; and hypotension, bradycardia, hypoxia, and acidosis caused by HAE were all significantly attenuated by HBO2P.

CONCLUSION

Our data indicate that HBO2P may attenuate high-altitude acute lung injury by a preinduction of lung HSP70 in rats.

Increased hepcidin levels in high-altitude pulmonary edema

Low iron availability enhances hypoxic pulmonary vasoconstriction (HPV). Considering that reduced serum iron is caused by increased erythropoiesis, insufficient reabsorption, or elevated hepcidin levels, one might speculate that exaggerated HPV in high-altitude pulmonary edema (HAPE) is related to low serum iron. To test this notion we measured serum iron and hepcidin in blood samples obtained in previously published studies at low altitude and during 2 days at 4,559 m (HA1, HA2) from controls, individuals with HAPE, and HAPE-susceptible individuals where prophylactic dexamethasone and tadalafil prevented HAPE. As reported, at 4,559 m pulmonary arterial pressure was increased in healthy volunteers but reached higher levels in HAPE. Serum iron levels were reduced in all groups at HA2. Hepcidin levels were reduced in all groups at HA1 and HA2 except in HAPE, where hepcidin was decreased at HA1 but unexpectedly high at HA2. Elevated hepcidin in HAPE correlated with increased IL-6 at HA2, suggesting that an inflammatory response related to HAPE contributes to increased hepcidin. Likewise, platelet-derived growth factor, a regulator of hepcidin, was increased at HA1 and HA2 in controls but not in HAPE, suggesting that hypoxia-controlled factors that regulate serum iron are inappropriately expressed in HAPE. In summary, we found that HAPE is associated with inappropriate expression of hepcidin without inducing expected changes in serum iron within 2 days at HA, likely due to too short time. Although hepcidin expression is uncoupled from serum iron availability and hypoxia in individuals developing HAPE, our findings indicate that serum iron is not related with exaggerated HPV.

Genome wide expression analysis suggests perturbation of vascular homeostasis during high altitude pulmonary edema

Background

High altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic edema which occurs in unacclimatized but otherwise normal individuals within two to four days after rapid ascent to altitude beyond 3000 m. The precise pathoetiology and inciting mechanisms regulating HAPE remain unclear.

Methodology/Principle findings

We performed global gene expression profiling in individuals with established HAPE compared to acclimatized individuals. Our data suggests concurrent modulation of multiple pathways which regulate vascular homeostasis and consequently lung fluid dynamics. These pathways included those which regulate vasoconstriction through smooth muscle contraction, cellular actin cytoskeleton rearrangements and endothelial permeability/dysfunction. Some notable genes within these pathways included MYLK; rho family members ARGEF11, ARHGAP24; cell adhesion molecules such as CLDN6, CLDN23, PXN and VCAM1 besides other signaling intermediates. Further, several important regulators of systemic/pulmonary hypertension including ADRA1D, ECE1, and EDNRA were upregulated in HAPE. We also observed significant upregulation of genes involved in paracrine signaling through chemokines and lymphocyte activation pathways during HAPE represented by transcripts of TNF, JAK2, MAP2K2, MAP2K7, MAPK10, PLCB1, ARAF, SOS1, PAK3 and RELA amongst others. Perturbation of such pathways can potentially skew vascular homeostatic equilibrium towards altered vascular permeability. Additionally, differential regulation of hypoxia-sensing, hypoxia-response and OXPHOS pathway genes in individuals with HAPE were also observed.

Conclusions/Significance

Our data reveals specific components of the complex molecular circuitry underlying HAPE. We show concurrent perturbation of multiple pathways regulating vascular homeostasis and suggest multi-genic nature of regulation of HAPE.

‘Ome’ on the range: update on high-altitude acclimatization/adaptation and disease

The main physiological challenge in high-altitude plateau environments is hypoxia.

Metabolomic analysis of the plasma of patients with high-altitude pulmonary edema (HAPE) using 1H NMR

Upon rapid ascent to a high altitude, non-acclimatized individuals, although healthy, are highly prone to contracting high-altitude pulmonary edema (HAPE). Early diagnosis is difficult and there is no reliable biomarker available. We used proton ((1)H) NMR metabolomics to profile the altered metabolic patterns of blood plasma from HAPE patients. The plasmas of ten patients with HAPE and ten individuals without HAPE were collected and compared using (1)H NMR spectroscopy. Data were evaluated with several multivariate statistical analyses, including the principal components, the orthogonal partial least-squares discriminant, and the orthogonal signal correction partial least-squares discriminant. Multivariate statistical analyses revealed a significant disparity between subjects with HAPE and those in the control group. Compared to the plasma of the controls, the HAPE patients had significant increases in valine, lysine, leucine, isoleucine, glycerol phosphoryl choline, glycine, glutamine, glutamic acid, creatinine, citrate, and methyl histidine. These were accompanied by decreases in α- and β-glucose, trimethylamine, and the metabolic products of lipids. The data demonstrate that metabolomics may be effective for the diagnosis of HAPE in the future, and can be used for further understanding HAPE pathogenesis.

Reducing pulmonary injury by hyperbaric oxygen preconditioning during simulated high altitude exposure in rats

BACKGROUND

Hyperbaric oxygen preconditioning (HBO₂P + HAE) has been found to be beneficial in preventing the occurrence of ischemic damage to brain, spinal cord, heart, and liver in several disease models. In addition, pulmonary inflammation and edema are associated with a marked reduction in the expression levels of both aquaporin (AQP) 1 and AQP5 in the lung. Here, the aims of this study are first to ascertain whether acute lung injury can be induced by simulated high altitude in rats and second to assess whether HBO2P + HAE is able to prevent the occurrence of the proposed high altitude-induced ALI.

METHODS

Rats were randomly divided into the following three groups: the normobaric air (NBA; 21% O₂ at 1 ATA) group, the HBO₂P + high altitude exposure (HAE) group, and the NBA + HAE group. In HBO₂P + HAE group, animals received 100% O₂ at 2.0 ATA for 1 hour per day, for five consecutive days. In HAE groups, animals were exposed to a simulated HAE of 6,000 m in a hypobaric chamber for 24 hours. Right after being taken out to the ambient, animals were anesthetized generally and killed and thoroughly exsanguinated before their lungs were excised en bloc. The lungs were used for both histologic and molecular evaluation and analysis.

RESULTS

In NBA + HAE group, the animals displayed higher scores of alveolar edema, neutrophil infiltration, and hemorrhage compared with those of NBA controls. In contrast, the levels of both AQP1 and AQP5 proteins and mRNA expression in the lung in the NBA + HAE group were significantly lower than those of NBA controls. However, the increased lung injury scores and the decreased levels of both AQP1 and AQP5 proteins and mRNA expression in the lung caused by HAE was significantly reduced by HBO₂P + HAE.

CONCLUSIONS

Our results suggest that high altitude pulmonary injury may be prevented by HBO2P + HAE in rats.

Basic medical advice for travelers to high altitudes

BACKGROUND

High-altitude travel, for mountain climbing, trekking, or sightseeing, has become very popular. Therefore, the awareness of its dangers has increased, and many prospective travelers seek medical advice before setting forth on their trip.

METHODS

We selectively searched the literature for relevant original articles and reviews about acclimatization to high altitude and about high-altitude-related illnesses, including acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE) (search in Medline for articles published from 1960-2010).

RESULTS

High-altitude-related illnesses are caused by hypoxia and the resulting hypoxemia in otherwise healthy persons who travel too high too fast, with too little time to become acclimatized. The individual susceptibility to high-altitude-related illness is a further risk factor that can only be recognized in persons who have traveled to high altitudes in the past. In an unselected group of mountain climbers, 50% had AMS at 4500 meters, while 0.5-1% had HACE and 6% had HAPE at the same altitude. Persons with preexisting illnesses, particularly of the heart and lungs, can develop symptoms of their underlying disease at high altitudes because of hypoxia. Thus, medical advice is based on an assessment of the risk of illness in relation to the intended altitude profile of the trip, in consideration of the prospective traveler's suitability for high altitudes (cardiopulmonary performance status, exercise capacity) and individual susceptibility to high-altitude-related illnesses, as judged from previous exposures. The symptoms and treatment of high-altitude-related illnesses should be thoroughly explained.

CONCLUSION

An understanding of the physiology of adaptation to high altitudes and of the pathophysiology and clinical manifestations of high-altitude-related illnesses provides a basis for the proper counseling of prospective travelers, through which life-threatening conditions can be prevented.

High altitude pulmonary oedema

High altitude pulmonary oedema (HAPE) is an important and preventable cause of death at high altitudes. However, little is known about the global incidence of HAPE, in part because most cases occur in remote environments where no records are kept. Furthermore, despite international efforts to achieve consensus, there is wide disparity in the diagnostic criteria in clinical and research use. We have reviewed the literature on the incidence and epidemiology of HAPE. There is broad agreement between studies that HAPE incidence at 2500m is around 0.01%, and increases to 1.9% at 3600m and 2.5-5% at 4300m. Risk factors for HAPE include rate of ascent, intensity of exercise and absolute altitude attained, although an individual pre-disposition to developing the condition is also well described and suggests an underlying genetic susceptibility. It is increasingly recognised that clinically-detectable HAPE is an extreme of a continuous spectrum of excess pulmonary fluid accumulation, which has been demonstrated in asymptomatic individuals. There is a continued need to ensure awareness of the diagnosis and treatment of HAPE among visitors to high altitude. It is likely that HAPE is preventable in all cases by progressive acclimatisation, and we advocate a pragmatic "golden rules" approach. Our understanding of the epidemiology and underlying genetic susceptibility to HAPE may be advanced if susceptible individuals register with the International HAPE Database: http://www.altitude.org/hape.php. HAPE has direct relevance to military training and operations and is likely to be the leading cause of death at high altitude.

Return to activity at altitude after high-altitude illness

Context:

Sports and other activities at high altitude are popular, yet they pose the unique risk for high-altitude illness (HAI). Once those who have suffered from a HAI recover, they commonly desire or need to perform the same activity at altitude in the immediate or distant future.

Evidence Acquisition:

As based on key text references and peer-reviewed journal articles from a Medline search, this article reviews the pathophysiology and general treatment principles of HAI.

Results:

In addition to the type of HAI experienced and the current level of recovery, factors needing consideration in the return-to-play plan include physical activity requirements, flexibility of the activity schedule, and available medical equipment and facilities. Most important, adherence to prudent acclimatization protocols and gradual ascent recommendations (when above 3000 m, no more than 600-m net elevation gain per day, and 1 rest day every 1 to 2 ascent days) is powerful in its preventive value and thus strongly recommended. When these are not practical, prophylactic medications (acetazolamide, dexamethasone, salmeterol, nifedipine, or phosphodiesterase inhibitors, depending on the type of prior HAI) may be prescribed and can reduce the risk of illness. Athletes with HAI should be counseled that physical and mental performance may be adversely affected if activity at altitude continues before recovery is complete and that there is a risk of progression to a more serious HAI.

Conclusion:

With a thoughtful plan, most recurrent HAI in athletes can be prevented.

The effect of intermittent hypoxia on bodyweight, serum glucose and cholesterol in obesity mice

This article tests mice's indicators of body nutritional metabolism under tolerable hypoxic conditions, in order to explore the effects of moderate intermittent hypoxia on the bodyweight, blood sugar and blood cholesterol of obese mice and to identify the role of leptin in these effects; this study applies high-fat diet to establish Mice Obesity Models and observes the intervention effects of intermittent hypoxic training in this Model. Small healthy mice are classified in 4 groups at random, that is, Group A (Normal), Group B (Normal Hypoxia) fed with normal foods and undergoing Intermittent Hypoxic Training (IHT), Group C (Fatty-diet) fed with High-Fat and High-Sugar (HFHS) foods without IHT and Group D (Fatty-diet and Hypoxia) fed with HFHS foods with IHT. After 40 days of feeding and hypoxic training, weigh the mice, measure the levels of blood sugar and blood cholesterol with a full automatic biochemical analyzer, measure serum leptin concentration by enzyme-linked immunosorbent assay (ELISA) technique, inspect liver leptin receptor expression and liver fat slice by immunohistochemistry. It is found that compared to control group, after experiment, the average bodyweight, blood sugar, blood cholesterol and serum leptin concentration in Group C is increased significantly and numerous fat cells are distributed in the liver, which indicates that hyperlipemia model has been successfully established; after intermittent hypoxic training, the average bodyweight, blood sugar, blood cholesterol and liver fat cells distribution density and scope in Group B and D are lower than those in Group A and C, while serum leptin concentration is increased significantly; liver leptin receptor expression in Group D is higher than that in Group C. And hypoxia groups have no trauma conclusion. Moderate intermittent hypoxia can reduce bodyweight by increasing leptin concentration and enhancing liver leptin expression and it can also reduce the level of blood sugar and blood cholesterol and meanwhile prevent steatosis in liver cells effectively.

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.

Effects of sildenafil on the human response to acute hypoxia and exercise

We examined the effects of the 5-phosphodiesterase (5-PDE) inhibitor sildenafil on pulmonary arterial pressure and some oxygen transport and cardiopulmonary parameters in humans during exposure to hypobaric hypoxia at rest and after exercise. In a double-blind study, 100 mg sildenafil or placebo was administered orally to 14 healthy volunteers 45 min before exposure to 5,000 m of simulated altitude. Arterial oxygen saturation (SaO2), heart rate (HR), tidal volume (VT), respiratory rate (RR), left ventricular ejection fraction (EF), and pulmonary arterial pressure (PAP) were measured first at rest in normoxia, at rest and immediately after exercise during hypoxia, and after exercise in normoxia. The increase in systolic PAP produced by hypoxia was significantly decreased by sildenafil at rest from 40.9 +/- 2.6 to 34.9 +/- 3.0 mmHg (-14.8%; p = 0.0046); after exercise, from 49.0 +/- 3.9 to 42.9 +/- 2.6 mmHg (-12.6%; p = 0.003). No significant changes were found in normoxia either at rest or after exercise. Measurements of the effect of sildenafil on exercise capacity during hypoxia did not provide conclusive data: a slight increase in SaO2 was observed with exercise during hypoxia, and sildenafil did not cause significant changes in ventilatory parameters under any condition. Sildenafil diminishes the pulmonary hypertension induced by acute exposure to hypobaric hypoxia at rest and after exercise. Further studies are needed to determine the benefit from this treatment and to further understand the effects of sildenafil on exercise capacity at altitude.

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.

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.

Airline Chair-Rest Deconditioning

Air passenger miles will likely double by year 2020. The altered and restrictive environment in an airliner cabin can influence haematological homeostasis in passengers and crew. Flight-related deep venous thromboemboli (DVT) have been associated with at least 577 deaths on 42 of 120 airlines from 1977 to 1984 (25 deaths/million departures), whereas many such cases go unreported. However, there are four major factors that could influence formation of possible flight-induced DVT: sleeping accommodations (via sitting immobilisation); travellers' medical history (via tissue injury); cabin environmental factors (via lower partial pressure of oxygen and lower relative humidity); and the more encompassing chair-rest deconditioning (C-RD) syndrome. There is ample evidence that recent injury and surgery (especially in deconditioned hospitalised patients) facilitate thrombophlebitis and formation of DVT that may be exacerbated by the immobilisation of prolonged air travel. In the healthy flying population, immobilisation factors associated with prolonged (>5 hours) C-RD such as total body dehydration, hypovolaemia and increased blood viscosity, and reduced venous blood flow (pooling) in the legs may facilitate formation of DVT. However, data from at least four case-controlled epidemiological studies did not confirm a direct causative relationship between air travel and DVT, but factors such as a history of vascular thromboemboli, venous insufficiency, chronic heart failure, obesity, immobile standing position, more than three pregnancies, infectious disease, long-distance travel, muscular trauma and violent physical effort were significantly more frequent in DVT patients than in controls. Thus, there is no clear, direct evidence yet that prolonged sitting in airliner seats, or prolonged experimental chair-rest or bed-rest deconditioning treatments cause DVT in healthy people.

Exercise delays the hypoxic thermal response in rats

Exercise exacerbates acute mountain sickness. In infants and small mammals, hypoxia elicits a decrease in body temperature (Tb) [hypoxic thermal response (HTR)], which may protect against hypoxic tissue damage. We postulated that exercise would counteract the HTR and promote hypoxic tissue damage. Tb was measured by telemetry in rats (n = 28) exercising or sedentary in either normoxia or hypoxia (10% O2, 24 h) at 25 degrees C ambient temperature (Ta). After 24 h of normoxia, rats walked at 10 m/min on a treadmill (30 min exercise, 30 min rest) for 6 h followed by 18 h of rest in either hypoxia or normoxia. Exercising normoxic rats increased Tb ( degrees C) vs. baseline (39.68 +/- 0.99 vs. 38.90 +/- 0.95, mean +/- SD, P < 0.05) and vs. sedentary normoxic rats (38.0 +/- 0.09, P < 0.05). Sedentary hypoxic rats decreased Tb (36.15 +/- 0.97 vs. 38.0 +/- 0.36, P < 0.05) whereas Tb was maintained in the exercising hypoxic rats during the initial 6 h of exercise (37.61 +/- 0.55 vs. 37.72 +/- 1.25, not significant). After exercise, Tb in hypoxic rats reached a nadir similar to that in sedentary hypoxic rats (35.05 +/- 1.69 vs. 35.03 +/- 1.32, respectively). Tb reached its nadir significantly later in exercising hypoxic vs. sedentary hypoxic rats (10.51 +/- 1.61 vs. 5.36 +/- 1.83 h, respectively; P = 0.002). Significantly greater histopathological damage and water contents were observed in brain and lungs in the exercising hypoxic vs. sedentary hypoxic and normoxic rats. Thus exercise early in hypoxia delays but does not prevent the HTR. Counteracting the HTR early in hypoxia by exercise exacerbates brain and lung damage and edema in the absence of ischemia.

Environmental and infectious conditions in sports

The hearts and lungs of athletes are subject to damage from a wide array of infections and environmental factors. Mild to moderate exercise has been shown to be beneficial to overall health, and strenuous exercise simply requires proper rest and rehabilitation to ensure its beneficial effects as well. Simple colds and URTIs are very common in athletes and do not usually require significant intervention. Any suspected cardiac infection mandates a thorough evaluation and proper management to prevent catastrophic consequences. High altitudes can be helpful in enhancing performance, but caution must be exercised at even modest altitude to prevent serious complications. With diving, participants should know their time limits and ascend properly to avoid serious complications. Keeping the heart and lungs in a good state of health is a major priority for the weekend warrior and world-class athletes alike. A thorough knowledge of infections and environmental issues in the cardiopulmonary health of athletes should always be of highest priority.

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.

Hypoxia decreases active Na transport across primary rat alveolar epithelial cell monolayers

Hypoxia has been reported to inhibit activity and expression of ion transporters of alveolar epithelial cells. This study extended those observations by investigating the mechanisms underlying inhibition of active Na transport across primary cultured adult rat alveolar epithelial cell monolayers grown on polycarbonate filters. Cell monolayers were exposed to normoxia and hypoxia (1.5% and 5% O(2), 5% CO(2)), and resultant changes in bioelectric properties [i.e., short-circuit current (I(sc)) and transepithelial resistance (R(t))] were measured in Ussing chambers. Results showed that I(sc) decreased with duration of exposure to hypoxia, while relatively little change was observed for R(t). In normoxia, amiloride inhibited approximately 70% of I(sc). The amiloride-sensitive portion of I(sc) decreased over time of exposure to hypoxia, whereas the magnitude of the amiloride-insensitive portion of I(sc) was not affected. Na pump capacity measured after permeabilization of the apical plasma membrane with amphotericin B decreased in monolayers exposed to 1.5% O(2) for 24 h, as did the capacity of amiloride-sensitive Na uptake measured after imposing an apical to basolateral Na gradient and permeabilization of the basolateral membrane. These results demonstrate that exposure to hypoxia inhibits alveolar epithelial Na reabsorption by reducing the rates of both apical amiloride-sensitive Na entry and basolateral Na extrusion.

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.

Inhibition of active sodium absorption leads to a net liquid secretion into in vivo rabbit lung at two levels of alveolar hypoxia

Active sodium transport across alveolar epithelium is known to contribute to the resolution of pulmonary oedema. We have attempted to assess whether sodium transport is essential to prevent liquid accumulation in healthy pulmonary alveoli exposed to mild hypoxia, and whether its contribution to liquid absorption differs between mild and moderate levels of hypoxia. In twenty-four anaesthetized adult rabbits we used direct bronchial cannulation to measure liquid movement from the liquid-filled left lung over 3.5 h. Half of the rabbits were studied at a level of mixed venous (and alveolar) oxygen partial pressure, PVO2, of 6.5 kPa and half at 4.5 kPa. PVO2 was altered by changing the inspired oxygen fraction in the ventilated right lung. Alveolar hydrostatic pressure was 0.3 kPa. In each group of 12, six animals with inhibitors of sodium transport in the isosmotic instillate were compared with six controls. We have shown an alveolar liquid secretion (approximately 0.6 microl min(-1) (kg body weight)(-1)) in the presence of inhibitors of active transport and an absorption (approximately 4 microl min(-1) (kg body weight)(-1)) in controls. Changing PVO2 had no influence on these movements. We conclude that, in this model of pulmonary oedema, active sodium transport appears to be essential for prevention of alveolar liquid accumulation via secretion. Furthermore, the contribution of active sodium transport to liquid absorption remains constant at oxygen tensions between 4.5 and 6.5 kPa.

Assessment of high altitude tolerance in healthy individuals

The most reliable prediction of high altitude tolerance can be derived from the clinical history of previous comparable exposures. Unfortunately, there are no reliable tests for prediction prior to first-time ascents. Although susceptibility to AMS is usually associated with a low hypoxic ventilatory response (HVR), there is too much overlap with the range of normal values, which precludes measuring HVR or O(2) saturation during brief hypoxia for reliable identification of susceptibility to AMS. A low HVR and an exaggerated rise in pulmonary artery pressure with (prolonged) hypoxia, or exercise in normoxia, are markers of susceptibility to high altitude pulmonary edema (HAPE). These tests can not be recommended for routinely determining high altitude tolerance because the prevalence of susceptibility to HAPE is low and because specificity and sensitivity of these tests are not sufficiently established. On the other hand, HAPE may be avoided in susceptible individuals by ascent rates of 300 m per day above an altitude of 2000 m. Since prediction of risk of mountain sickness is difficult, it is important during the physician consultation prior to ascent to consider the altitude profile, the type of ascent, the performance capacity, the history of previous exposures, and the medical infrastructure of the area.

Energy and water balance at high altitude

Many studies have shown that subjects lose significant amounts of body mass, fat mass as well as fat-free mass, during a climb to and/or a stay at high altitude. Altitude-induced weight loss is mainly caused by malnutrition due to hypoxia-related satiety, independent of acute mountain sickness.