Pulmonary extravascular fluid accumulation in recreational climbers: a prospective study

Physiopathology of High-Altitude Pulmonary Edema

Miserocchi, Giuseppe. Physiopathology of high-altitude pulmonary edema. High Alt Med Biol. 26:1-12, 2025.-The air-blood barrier is well designed to accomplish the matching of gas diffusion with blood flow. This function is achieved by maintaining its thickness at ∼0.5 µm, a feature implying to keep extravascular lung water to the minimum. Exposure to hypobaric hypoxia, especially when associated with exercise, is a condition potentially leading to the development of the so-called high-altitude pulmonary edema (HAPE). This article presents a view of the physiopathology of HAPE by merging available data in humans exposed to high altitude with data from animal experimental approaches. A model is also presented to characterize HAPE nonsusceptible versus susceptible individuals based on the efficiency of alveolar-capillary oxygen uptake and estimated morphology of the air-blood barrier.

Lung function parameters are associated with acute mountain sickness and are improved at high and extreme altitude

At altitude, factors such as decreased barometric pressure, low temperatures, and acclimatization might affect lung function. The effects of exposure and acclimatization to high-altitude on lung function were assessed in 39 subjects by repetitive spirometry up to 6022 m during a high-altitude expedition. Subjects were classified depending on the occurrence of acute mountain sickness (AMS) and summit success to evaluate whether lung function relates to successful climb and risk of developing AMS. Peak expiratory flow (PEF), forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) increased with progressive altitude (max. +20.2 %pred, +9.3 %pred, and +6.7 %pred, all p<0.05). Only PEF improved with acclimatization (BC1 vs. BC2, +7.2 %pred, p=0.044). At altitude FEV1 (p=0.008) and PEF (p<0.001) were lower in the AMS group. The risk of developing AMS was associated with lower baseline PEF (p<0.001) and longitudinal changes in PEF (p=0.008) and FEV1 (p<0.001). Lung function was not related to summit success (7126 m). Improvement in PEF after acclimatization might indicate respiratory muscle adaptation.

Effectiveness of Continuous Positive Airway Pressure in Alleviating Hypoxemia and Improving Exertional Capacity at Altitude

Strickland, Brian, Elan Small, Mary Ryan, and Ryan Paterson. Effectiveness of continuous positive airway pressure in alleviating hypoxemia and improving exertional capacity at altitude. High Alt Med Biol. 25:319-325, 2024. Introduction: Decreased oxygen saturation and exercise tolerance are commonly experienced at high altitude. Continuous positive airway pressure (CPAP) devices have become increasingly portable and battery powered, providing a potentially unique new therapeutic modality for treatment of altitude-related illnesses. This study evaluated the potential use of CPAP devices to improve and maintain oxygen saturation at altitude, both at rest and with exertion, to evaluate the feasibility of using this device at altitude. Methods: Subjects were taken to Mount Blue Sky and monitored while they hiked to the summit (4,350 m), maintaining a consistent level of exertion. Subjects hiked for 0.7 km both with and without CPAP set to 10 cmH2O pressure. Continuous vital signs were collected during the hike and recovery period. Results: All subjects completed the hike wearing CPAP devices at a vigorous level of exertion. Mean oxygen saturation of the CPAP group (M = 83.8%, SD = 3.72) was significantly higher than that of the control group during exertion (M = 78.7%, SD = 2.97); p = 0.005. Recovery after exertion was quicker in the CPAP group than the control group. Three subjects experienced claustrophobia requiring a brief pause, but were able to complete their exercise trial without removing equipment or experiencing adverse events. When pauses from claustrophobia were excluded, there was no difference in completion time between the groups (p = 0.06). Conclusion: CPAP reliably improved oxygen saturation at rest and during vigorous exertion at high altitude. Its ability to correct hypoxemia, even with physical exertion, may prove useful after further study as a portable self-carried device to prevent and treat altitude-related illness, or to improve safety in high-altitude rescues.

Baroreflex and chemoreflex interaction in high-altitude exposure: possible role on exercise performance

The hypoxic chemoreflex and the arterial baroreflex are implicated in the ventilatory response to exercise. It is well known that long-term exercise training increases parasympathetic and decreases sympathetic tone, both processes influenced by the arterial baroreflex and hypoxic chemoreflex function. Hypobaric hypoxia (i.e., high altitude [HA]) markedly reduces exercise capacity associated with autonomic reflexes. Indeed, a reduced exercise capacity has been found, paralleled by a baroreflex-related parasympathetic withdrawal and a pronounced chemoreflex potentiation. Additionally, it is well known that the baroreflex and chemoreflex interact, and during activation by hypoxia, the chemoreflex is predominant over the baroreflex. Thus, the baroreflex function impairment may likely facilitate the exercise deterioration through the reduction of parasympathetic tone following acute HA exposure, secondary to the chemoreflex activation. Therefore, the main goal of this review is to describe the main physiological mechanisms controlling baro- and chemoreflex function and their role in exercise capacity during HA exposure.

Review of Athletic Guidelines for High-Altitude Training and Acclimatization

Ramchandani, Rashi, Ioana Tereza Florica, Zier Zhou, Aziz Alemi, and Adrian Baranchuk. Review of athletic guidelines for high-altitude training and acclimatization. High Alt Med Biol. 00:000-000, 2024. Introduction: Exposure to high altitude results in hypobaric hypoxia with physiological acclimatization changes that are thought to influence athletic performance. This review summarizes existing literature regarding implications of high-altitude training and altitude-related guidelines from major governing bodies of sports. Methods: A nonsystematic review was performed using PubMed and OVID Medline to identify articles regarding altitude training and guidelines from international governing bodies of various sports. Sports inherently involving training or competing at high altitude were excluded. Results: Important physiological compensatory mechanisms to high-altitude environments include elevations in blood pressure, heart rate, red blood cell mass, tidal volume, and respiratory rate. These responses can have varying effects on athletic performance. Governing sport bodies have limited and differing regulations for training and competition at high altitudes with recommended acclimatization periods ranging from 3 days to 3 weeks. Discussion: Physiological changes in response to high terrestrial altitude exposure can have substantial impacts on athletic performance. Major sport governing bodies have limited regulations and recommendations regarding altitude training and competition. Existing guidelines are variable and lack substantial evidence to support recommendations. Additional studies are needed to clarify the implications of high-altitude exposure on athletic ability to optimize training and competition.

Pressure-sensitive multivesicular liposomes as a smart drug-delivery system for high-altitude pulmonary edema

Changes in bodily fluid pressures, such as pulmonary artery pressure, play key roles in high-altitude pulmonary edema (HAPE) and other disorders. Smart delivery systems releasing a drug in response to these pressures might facilitate early medical interventions. However, pressure-responsive delivery systems are unavailable. We here constructed hydrostatic pressure-sensitive multivesicular liposomes (PSMVLs) based on the incomplete filling of the internal vesicle space with neutral lipids. These liposomes were loaded with amlodipine besylate (AB), a next-generation calcium channel inhibitor, to treat HAPE on time. AB-loaded PSMVLs (AB-PSMVLs) were destroyed, and AB was released through treatment under hydrostatic pressure of at least 25 mmHg. At 25 mmHg, which is the minimum pulmonary artery pressure value in HAPE, 38.8% of AB was released within 1 h. In a mouse HAPE model, AB-PSMVLs concentrated in the lung and released AB to diffuse into the vascular wall. Intravenously injected AB-PSMVLs before HAPE modeling resulted in a stronger protection of lung tissues and respiratory function and lower occurrence of pulmonary edema than treatment with free drug or non-pressure-sensitive AB-loaded liposomes. This study offers a new strategy for developing smart drug delivery systems that respond to changes in bodily fluid pressures.

High Altitude

With ascent to high altitude, barometric pressure declines, leading to a reduction in the partial pressure of oxygen at every point along the oxygen transport chain from the ambient air to tissue mitochondria. This leads, in turn, to a series of changes over varying time frames across multiple organ systems that serve to maintain tissue oxygen delivery at levels sufficient to prevent acute altitude illness and preserve cognitive and locomotor function. This review focuses primarily on the physiological adjustments and acclimatization processes that occur in the lungs of healthy individuals, including alterations in control of breathing, ventilation, gas exchange, lung mechanics and dynamics, and pulmonary vascular physiology. Because other organ systems, including the cardiovascular, hematologic and renal systems, contribute to acclimatization, the responses seen in these systems, as well as changes in common activities such as sleep and exercise, are also addressed. While the pattern of the responses highlighted in this review are similar across individuals, the magnitude of such responses often demonstrates significant interindividual variability which accounts for subsequent differences in tolerance of the low oxygen conditions in this environment.

Lung "Comet Tails" in Healthy Individuals: Accumulation or Clearance of Extravascular Lung Water?

Parks, Jordan K, Courtney M. Wheatley-Guy, Glenn M. Stewart, Caitlin C. Fermoyle, Bryan J. Taylor, Jesse Schwartz, Briana Ziegler, Kay Johnson, Alice Gavet, Loïc Chabridon, Paul Robach, and Bruce D. Johnson. Lung "Comet Tails" in healthy individuals: accumulation or clearance of extravascular lung water? High Alt Med Biol. 24:230-233, 2023-Ultrasound lung comet tails (or B-lines) tend to be limited in number (<5) or absent under ultrasound examination, and the appearance of diffuse B-lines with lung sliding has been suggested to identify pulmonary edema. Clinical evaluation of B-lines has been utilized as a bedside test to assess pulmonary congestion in patients with heart failure. Exposure to altitude or prolonged exercise can alter fluid regulation and can lead to pulmonary congestion or edema. As such, B-lines have been utilized in the field to monitor for pathological lung fluid accumulation. However, ultrasound lung comet lines might not be as reliable for identifying extravascular lung water (EVLW) as previously thought in healthy individuals exercising at altitude where an increase in the number of ultrasound lung comets would reflect fluid buildup in the interstitial space of the alveoli and pulmonary capillaries. This report will focus on reviewing the literature and our data from a group of ultraendurance runners that completed the Ultra Trail Mont Blanc race that demonstrates that lung comet tails may not always be evidence of pathological fluid accumulation in healthy individuals and as such should be used to assess EVLW in concert with other diagnostic testing.

Coronary Syndromes and High-Altitude Exposure—A Comprehensive Review

The aim of this review is to identify a preventive strategy in order to minimize the risk of adverse events in patients with coronary syndromes and acute exposure to high-altitude. For this purpose we searched the electronic database of PubMed, EMBASE, and Web of Science for studies published in the last 30 years in this field. The conclusions of this review are: patients with stable coronary artery disease on optimal treatment and in a good physical condition can tolerate traveling to high altitude up to 3500 m; on the other hand, patients with unstable angina or recent myocardial infarction no older than 6 months should take less interest in hiking or any activity involving high altitude. Air-traveling is contraindicated for patients with myocardial infarction within previous 2 weeks, angioplasty or intracoronary stent placement within previous 2 weeks, and unstable angina or coronary artery bypass grafting within previous 3 weeks. The main trigger for sudden cardiac death is the lack of gradual acclimatization to high-altitude and to the exercise activity, and the most important risk factor is prior myocardial infarction.

Application of Point-of-care Ultrasound for Screening Climbers at High Altitude for Pulmonary B-lines

Introduction: High-altitude pulmonary edema (HAPE) occurs as a result of rapid ascent to altitude faster than the acclimatization processes of the body. Symptoms can begin at an elevation of 2,500 meters above sea level. Our objective in this study was to determine the prevalence and trend of developing B-lines at 2,745 meters above sea level among healthy visitors over four consecutive days. Methods: We performed a prospective case series on healthy volunteers at Mammoth Mountain, CA, USA. Subjects underwent pulmonary ultrasound for B-lines over four consecutive days. Results: We enrolled 21 male and 21 female participants. There was an increase in the sum of B-lines at both lung bases from day 1 to day 3, with a subsequent decrease from day 3 to day 4 (P<0.001). By the third day at altitude, B-lines were detectable at base of lungs of all participants. Similarly, B-lines increased at apex of lungs from day 1 to day 3 and decreased on day 4 (P=0.004). Conclusion: By the third day at 2,745 meters altitude, B-lines were detectable in the bases of both lungs of all healthy participants in our study. We assume that increasing the number of B-lines could be considered an early sign of HAPE. Point-of-care ultrasound could be used to detect and monitor B-lines at altitude to facilitate early detection of HAPE, regardless of pre-existing risk factors.

A systematic review of electrocardiographic changes in populations temporarily ascending to high altitudes

High altitudes can cause hypobaric hypoxia, altering human physiology and the corresponding electrocardiogram (ECG). As part of the Altitude Nondifferentiated ECG Study (ANDES), this paper reviews ECG changes in subjects ascending to high altitudes. This review was conducted following PRISMA guidelines. PubMed, EMBASE, OVID Medline, and Web of Science were searched. 19 studies were ultimately included. Notable ECG changes at high altitudes include T wave inversion in the precordial leads and rightward QRS axis deviation in leads I, II and aVF. Less common findings were increases in P wave amplitude, QRS amplitude, and QTc interval. These ECG deviations typically self-resolved within 2-6 weeks following return to sea level. Consideration must be taken when interpreting ECG changes in individuals during ascent to, at, or upon return from high altitudes. Further large-scale studies are needed to elucidate temporal and altitude-dependent ECG patterns and establish reference standards for clinicians.

Sleep loss effects on physiological and cognitive responses to systemic environmental hypoxia

In the course of their missions or training, alpinists, but also mountain combat forces and mountain security services, professional miners, aircrew, aircraft and glider pilots and helicopter crews are regularly exposed to altitude without oxygen supplementation. At altitude, humans are exposed to systemic environmental hypoxia induced by the decrease in barometric pressure (<1,013 hPa) which decreases the inspired partial pressure of oxygen (PIO₂), while the oxygen fraction is constant (equal to approximately 20.9%). Effects of altitude on humans occur gradually and depend on the duration of exposure and the altitude level. From 1,500 m altitude (response threshold), several adaptive responses offset the effects of hypoxia, involving the respiratory and the cardiovascular systems, and the oxygen transport capacity of the blood. Fatigue and cognitive and sensory disorders are usually observed from 2,500 m (threshold of prolonged hypoxia). Above 3,500 m (the threshold for disorders), the effects are not completely compensated and maladaptive responses occur and individuals develop altitude headache or acute altitude illness [Acute Mountain Sickness (AMS)]. The magnitude of effects varies considerably between different physiological systems and exhibits significant inter-individual variability. In addition to comorbidities, the factors of vulnerability are still little known. They can be constitutive (genetic) or circumstantial (sleep deprivation, fatigue, speed of ascent.). In particular, sleep loss, a condition that is often encountered in real-life settings, could have an impact on the physiological and cognitive responses to hypoxia. In this review, we report the current state of knowledge on the impact of sleep loss on responses to environmental hypoxia in humans, with the aim of identifying possible consequences for AMS risk and cognition, as well as the value of behavioral and non-pharmacological countermeasures.

A comparative analysis of lung function and spirometry parameters in genotype-controlled natives living at low and high altitude

BACKGROUND

The reference values for lung function are associated to anatomical and lung morphology parameters, but anthropometry it is not the only influencing factor: altitude and genetics are two important agents affecting respiratory physiology. Altitude and its influence on respiratory function has been studied independently of genetics, considering early and long-term acclimatization.

OBJECTIVE

The objective of this study is to evaluate lung function through a spirometry study in autochthonous Kichwas permanently living at low and high-altitude.

METHODOLOGY

A cross-sectional study of spirometry differences between genetically matched lowland Kichwas from Limoncocha (230 m) at Amazonian basin and high-altitude Kichwas from Oyacachi (3180 m) in Andean highlands. The sample size estimates permitted to recruited 118 patients (40 men and 78 women) from Limoncocha and 95 (39 men and 56 women) from Oyacachi. Chi-square method was used to analyze association or independence of categorical variables, while Student's t test was applied to comparison of means within quantitative variables. ANOVA, or in the case that the variables didn't meet the criteria of normality, Kruskal Wallis test were used to compare more than two groups.

RESULTS

The FVC and the FEV1 were significantly greater among highlanders than lowlanders (p value < 0.001), with a proportion difference of 15.2% for men and 8.5% for women. The FEV1/FVC was significantly higher among lowlanders than highlanders for men and women. A restrictive pattern was found in 12.9% of the participants.

CONCLUSION

Residents of Oyacachi had greater FVC and FEV1 than their peers from Limoncocha, a finding physiologically plausible according to published literature. Lung size and greater ventilatory capacities could be an adaptive mechanism developed by the highlander in response to hypoxia. Our results support the fact that this difference in FVC and FEV1 is a compensatory mechanism towards lower barometric and alveolar partial pressure of oxygen pressure.

Exposomes to Exosomes: Exosomes as Tools to Study Epigenetic Adaptive Mechanisms in High-Altitude Humans

Humans on earth inhabit a wide range of environmental conditions and some environments are more challenging for human survival than others. However, many living beings, including humans, have developed adaptive mechanisms to live in such inhospitable, harsh environments. Among different difficult environments, high-altitude living is especially demanding because of diminished partial pressure of oxygen and resulting chronic hypobaric hypoxia. This results in poor blood oxygenation and reduces aerobic oxidative respiration in the mitochondria, leading to increased reactive oxygen species generation and activation of hypoxia-inducible gene expression. Genetic mechanisms in the adaptation to high altitude is well-studied, but there are only limited studies regarding the role of epigenetic mechanisms. The purpose of this review is to understand the epigenetic mechanisms behind high-altitude adaptive and maladaptive phenotypes. Hypobaric hypoxia is a form of cellular hypoxia, which is similar to the one suffered by critically-ill hypoxemia patients. Thus, understanding the adaptive epigenetic signals operating in in high-altitude adjusted indigenous populations may help in therapeutically modulating signaling pathways in hypoxemia patients by copying the most successful epigenotype. In addition, we have summarized the current information about exosomes in hypoxia research and prospects to use them as diagnostic tools to study the epigenome of high-altitude adapted healthy or maladapted individuals.

Cardiopulmonary response to high-altitude mountaineering in lung transplant recipients-The Jebel Toubkal experience

OBJECTIVES

Only a small proportion of lung transplant recipients achieve a physical status comparable to healthy individuals in the long term. It is reasonable to hypothesize that the necessary cardiopulmonary adaptation required for strenuous physical exercise may be impaired. Exposure to high altitude provides an optimal platform to study the physiological cardiopulmonary adaptation in lung transplant recipients under aerobic conditions. To gain a deeper understanding, 14 healthy lung transplant recipients and healthcare professionals climbed the highest peak in North Africa (Mount Jebel Toubkal; 4167 m) in September 2019.

METHODS

Monitoring included daily assessment of vital signs, repeated transthoracic echocardiography, pulmonary function tests, and capillary blood sampling throughout the expedition.

RESULTS

Eleven out of fourteen lung transplant recipients reached the summit. All recipients showed a stable lung function and vital parameters and physiological adaptation of blood gases. Similar results were found in healthy controls. Lung transplant recipients showed worse results in the 6-minute walk test at low and high altitude compared to controls (day 1: 662 m vs. 725 m, p < 0.001, day 5: 656 m vs. 700 m, p = 0.033) and a lack of contractile adaptation of right ventricular function with increasing altitude as measured by tricuspid plane systolic excursion on echocardiography (day 2: 22 mm vs. 24 mm, p = 0.202, day 5: 23 mm vs. 26 mm, p = 0.035).

CONCLUSIONS

Strenuous exercise in healthy lung transplant recipients is safe. However, the poorer cardiopulmonary performance in the 6-minute walk test and the lack of right ventricular cardiac adaptation may indicate underlying autonomic dysregulation.

Predictive Capacity of Pulmonary Function Tests for Acute Mountain Sickness

Small, Elan, Nicholas Juul, David Pomeranz, Patrick Burns, Caleb Phillips, Mary Cheffers, and Grant S. Lipman. Predictive capacity of pulmonary function tests for acute mountain sickness. High Alt Med Biol. 22: 193-200, 2021. Background: Pulmonary function as measured by spirometry has been investigated at altitude with heterogenous results, though data focused on spirometry and acute mountain sickness (AMS) are limited. The objective of this study was to investigate the capacity of pulmonary function tests (PFTs) to predict the development of AMS. Materials and Methods: This study was a blinded prospective observational study run during a randomized controlled trial comparing acetazolamide, budesonide, and placebo for AMS prevention on White Mountain, CA. Spirometry measurements of forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), and peak expiratory flow were taken at a baseline altitude of 1,250 m, and the evening of and morning after ascent to 3,810 m. Measurements were assessed for correlation with AMS. Results: One hundred three participants were analyzed with well-matched baseline demographics and AMS incidence of 75 (73%) and severe AMS of 48 (47%). There were no statistically significant associations between changes in mean spirometry values on ascent to high altitude with incidence of AMS or severe AMS. Lake Louise Questionnaire scores were negatively correlated with FVC (r = -0.31) and FEV₁ (r = -0.29) the night of ascent. Baseline PFT had a predictive accuracy of 65%-73% for AMS, with a receiver operating characteristic of 0.51-0.65. Conclusions: Spirometry did not demonstrate statistically significant changes on ascent to high altitude, nor were there significant associations with incidence of AMS or severe AMS. Low-altitude spirometry did not accurately predict development of AMS, and it should not be recommended for risk stratification.

Expression of Aquaporin-1 and Aquaporin-5 in a Rat Model of High-Altitude Pulmonary Edema and the Effect of Hyperbaric Oxygen Exposure

Objective:

To investigate the therapeutic roles of hyperbaric oxygen exposure on high-altitude pulmonary edema and to determine whether aquaporin-1 and aquaporin-5 were involved in the pathogenesis of HAPE in rats.

Methods:

Rats were divided into 5 groups: The control group, the HAPE group (HAPE model), the HBO group (hyperbaric oxygen exposure), the NBO group (normobaric oxygen exposure), and the NA group (normal air exposure). Western blot and real-time PCR were used to analyze the pulmonary expressions of AQP1 and AQP5. The wet-to-dry (W/D) weight ratio and the morphology of the lung were also examined.

Results:

The lung W/D weight ratio in the HAPE group was increased compared with the control group. The injury score in the HBO group was noticeably lower than that in the control group. The mRNA and proteins expressions of AQP1 and AQP5 were significantly downregulated in the HAPE group.

Conclusions:

Oxygen exposure alleviated high-altitude hypobaric hypoxia-induced lung injury in rats. Additionally, HBO therapy had significant advantage on interstitial HAPE.

No Relevant Analogy Between COVID-19 and Acute Mountain Sickness

Berger, Marc Moritz, Peter H. Hackett, and Peter Bärtsch. No relevant analogy between COVID-19 and acute mountain sickness. High Alt Med Biol. 21:315-318, 2020.-Clinicians and scientists have suggested therapies for coronavirus disease-19 (COVID-19) that are known to be effective for other medical conditions. A recent publication suggests that pathophysiological mechanisms underlying acute mountain sickness (a syndrome of nonspecific neurological symptoms typically experienced by nonacclimatized individuals at altitudes >2500 m) may overlap with the mechanisms causing COVID-19. In this short review, we briefly evaluate this mistaken analogy and demonstrate that this concept is not supported by scientific evidence.

Acute mountain sickness: Do different time courses point to different pathophysiological mechanisms?

Acute mountain sickness (AMS) is a syndrome of nonspecific symptoms (i.e., headache, anorexia, nausea, vomiting, dizziness, and fatigue) that may develop in nonacclimatized individuals after rapid exposure to altitudes ≥2,500 m. In field studies, mean AMS scores usually peak after the first night at a new altitude. Analyses of the individual time courses of AMS in four studies performed at 3,450 m and 4,559 m revealed that three different patterns are hidden in the above-described overall picture. In 41% of those who developed AMS (i.e., AMS-C score >0.70), symptoms peaked on day 1, in 39%, symptoms were most prominent on day 2, and in 20%, symptoms were most prominent on day 3. We suggest to name the different time courses of AMS type I, type II, and type III, respectively. Here, we hypothesize that the variation of time courses of AMS are caused by different pathophysiological mechanisms. This assumption could explain why no consistent correlations between an overall assessment of AMS and single pathophysiological factors have been found in a large number of studies over the past 50 yr. In this paper, we will briefly review the fundamental mechanisms implicated in the pathophysiology of AMS and discuss how they might contribute to the three different AMS time courses.

EDN1 gene potentially involved in the development of acute mountain sickness

Previous investigations have indicated that environmental and genetic factors collectively contribute to the development of acute mountain sickness (AMS), but whether the EDN1 gene is involved in AMS remains to be elucidated. A total of 356 healthy male soldiers who had not traveled to high altitudes in the previous 12 months were enrolled in our study. All participants were taken by plane from 500 m (Chengdu in Sichuan Province) to a 3700 m highland (Lhasa) within 2 hours. Clinical data were collected within 24 hours, and pulmonary function parameters were completed simultaneously. Genotypes were obtained by using iMLDR genotyping assays. A total of 237 soldiers (66.57%) presented AMS symptoms, including headache, dizziness, gastrointestinal upset and fatigue. Soldiers with AMS showed an increase in heart rate (HR), plasma tryptophan and serotonin, and a decrease in SaO2, FEV1, PEF, FVC, V75, V50, V25 and MMF (all P < 0.01). Notably, allele T in single nucleotide polymorphism (SNP) rs2070699 showed a positive correlation with the occurrence of AMS. A general linear regression analysis showed that rs2060799, Mean Arterial Pressure (MAP), SaO2, FVC, tryptophan and serotonin were independent predictors for the occurrence of AMS. Importantly, the area under the curve (AUC) values for tryptophan (0.998), serotonin (0.912) and FVC (0.86) had diagnostic specificity and sensitivity. Our results demonstrated that AMS is accompanied by changes in lung function parameters, increased plasma tryptophan and serotonin levels, and that the EDN1 polymorphism is a potential risk factor for AMS.

Positive expiratory pressure improves arterial and cerebral oxygenation in acute normobaric and hypobaric hypoxia

Positive expiratory pressure (PEP) has been shown to limit hypoxia-induced reduction in arterial oxygen saturation, but its effectiveness on systemic and cerebral adaptations, depending on the type of hypoxic exposure [normobaric (NH) versus hypobaric (HH)], remains unknown. Thirteen healthy volunteers completed three randomized sessions consisting of 24-h exposure to either normobaric normoxia (NN), NH (inspiratory oxygen fraction, FiO2 = 13.6%; barometric pressure, BP = 716 mmHg; inspired oxygen partial pressure, PiO2 = 90.9 ± 1.0 mmHg), or HH (3,450 m, FiO2 = 20.9%, BP = 482 mmHg, PiO2 = 91.0 ± 0.6 mmHg). After the 6th and the 22nd hours, participants breathed quietly through a facemask with a 10-cmH₂O PEP for 2 × 5 min interspaced with 5 min of free breathing. Arterial (SpO2, pulse oximetry), quadriceps, and cerebral (near-infrared spectroscopy) oxygenation, middle cerebral artery blood velocity (MCAv; transcranial Doppler), ventilation, and cardiovascular responses were recorded continuously. SpO2without PEP was significantly lower in HH (87 ± 4% on average for both time points, P < 0.001) compared with NH (91 ± 3%) and NN (97 ± 1%). PEP breathing did not change SpO2 in NN but increased it similarly in NH and HH (+4.3 ± 2.5 and +4.7 ± 4.1% after 6h; +3.5 ± 2.2 and +4.1 ± 2.9% after 22h, both P < 0.001). Although MCAv was reduced by PEP (in all sessions and at all time points, -6.0 ± 4.2 cm/s on average, P < 0.001), the cerebral oxygenation was significantly improved (P < 0.05) with PEP in both NH and HH, with no difference between conditions. These data indicate that PEP could be an attractive nonpharmacological means to improve arterial and cerebral oxygenation under both normobaric and hypobaric mild hypoxic conditions in healthy participants.

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.

Is it time to revise the acclimatization schedule at high altitude? Evidence from a field trial in Western Himalayas

Background

In Western Himalayas, Indian Army soldiers take 11 days (6 days of acclimatization and 5 days of travel) on a sea-level to high altitude road (SH road) to reach a high altitude location (HAL) situated at an altitude of 11,500 feet from sea-level location (SLL) at an altitude of 1150 feet while following acclimatization schedule (AS). AS has an extra safety margin over the conventional 'mountaineering thumb rule' of not exceeding 500 m sleeping altitude above 3000 m altitude. We carried out this randomised field trial to study the feasibility of moving large number of troops rapidly from SLL to HAL on SH road in western Himalayas in 4 days under pharmaco-prophylaxis.

Methods

Based on the pharmaco-prophylaxis, at SLL 508 healthy lowland soldiers were divided into two groups: 'A' (n = 256) with Acetazolamide + Dexamethasone and 'B' (n = 252) with Acetazolamide + Placebo. They travelled rapidly by road to HAL in 4 days and prevalence of acute mountain sickness (AMS), high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE) during the ascent was measured.

Results

Prevalence of AMS was found to be 1.56% and 1.59% in group 'A' and group 'B' respectively during the ascent with no cases of HAPE and HACE.

Conclusion

At least on SH road, troops can be inducted rapidly to HAL from SLL in 4 days under pharmaco-prophylaxis with Acetazolamide with minimal occurrence of acute high altitude illnesses.

Transthoracic sonographic assessment of B-line scores during ascent to altitude among healthy trekkers

Sonographic B-lines can indicate pulmonary interstitial edema. We sought to determine the incidence of subclinical pulmonary edema measured by sonographic B-lines among lowland trekkers ascending to high altitude in the Nepal Himalaya. Twenty healthy trekkers underwent portable sonographic examinations and arterial blood draws during ascent to 5160 m over ten days. B-lines were identified in twelve participants and more frequent at 4240 m and 5160 m compared to lower altitudes (P < 0.03). There was a strong negative correlation between arterial oxygen saturation and the number of B-lines at 5160 m (ρ = -0.75, P = 0.008). Our study contributes to the growing body of literature demonstrating the development of asymptomatic pulmonary edema during ascent to high altitude. Portable lung sonography may have utility in fieldwork contexts such as trekking at altitude, but further research is needed in order to clarify its potential clinical applicability.

Right Heart-Pulmonary Circulation at High Altitude and the Development of Subclinical Pulmonary Interstitial Edema

Most healthy subjects can develop a subclinical interstitial pulmonary edema that is a complex and multifactor phenomenon, still with unanswered questions, and might be one line of defense against the development of severe symptomatic lung edema. Whether the acute, reversible increase in lung fluid content is really an innocent and benign part of the adaptation to extreme physiologic condition or rather the clinically relevant marker of an individual vulnerability to life-threatening high altitude pulmonary edema remains to be established in future studies. Thus the question if encouraging more conservative habits to climb is right or not remains open.

High altitude trekking after lung transplantation: a prospective study using lung ultrasound to detect comets tails for interstitial pulmonary edema in lung transplant recipients and healthy volunteers

The intensity of physical activity which can be tolerated after lung transplantation and the tolerance to prolonged exercise at high altitude are poorly investigated. Lung ultrasound comet tails have been used in the diagnosis of interstitial pulmonary edema and high pulmonary altitude edema. The aim was to assess the number of lung ultrasound comet tails and to monitor changes in the optic nerve sheath diameter (ONSD) during a climb to the top of Mount Kilimanjaro in 10 lung transplant recipients and 10 healthy controls at three different altitude levels: 1360, 3505, 4900 m. Lung transplant recipients showed a constant increase in comet tail scores with altitude, whereas control subjects only showed an increase at the highest measurement point. Differences between groups (transplant versus control) reached significance only after the first ascend: 0.9 (95% CI: -0.41; 2.21) vs. 0.1 (95% CI: -0.12; 0.32) (P = 0.2; 1360 m), 2.33 (95% CI: 0.64; 4.02) vs. 0.3 (95% CI: -0.18; 0.78) (P = 0.04; 3505 m), and 4.11 (95% CI: 0.13; 0.34) vs. 2.9 (95% CI: 0.49; 5.31) (P = 0.15; 4900 m); ONSD increased significantly in both groups from 3.53 (95% CI: 0.34; 0.66) at 1360 m to 4.11 (95% CI: 0.36; 0.71) at 4900 m (P < 0.05). Lungs of transplant recipients are able to adapt to altitude and capable of performing prolonged exercise at high altitude after slow ascend.

Swallow-breathing coordination during incremental ascent to altitude

Swallow and breathing are highly coordinated behaviors reliant on shared anatomical space and neural pathways. Incremental ascent to high altitudes results in hypoxia/hypocapnic conditions altering respiratory drive, however it is not known whether these changes also alter swallow. We examined the effect of incremental ascent (1045 m, 3440 m and 4371 m) on swallow motor pattern and swallow-breathing coordination in seven healthy adults. Submental surface electromyograms (sEMG) and spirometry were used to evaluate swallow triggered by saliva and water infusion. Swallow-breathing phase preference was different between swallows initiated by saliva versus water. With ascent, saliva swallows changed to a dominate pattern of occurrence during the transition from inspiration to expiration. Additionally, water swallows demonstrated a significant decrease in submental sEMG duration and a shift in submental activity to earlier in the apnea period, especially at 4371 m. Our results suggest that there are changes in swallow-breathing coordination and swallow production that likely increase airway protection with incremental ascent to high altitude. The adaptive changes in swallow were likely due to the exposure to hypoxia and hypocapnia, along with airway irritation.

Chest Ultrasonography in Modern Day Extreme Settings: From Military Setting and Natural Disasters to Space Flights and Extreme Sports

Chest ultrasonography (CU) is a noninvasive imaging technique able to provide an immediate diagnosis of the underlying aetiology of acute respiratory failure and traumatic chest injuries. Given the great technologies, it is now possible to perform accurate CU in remote and adverse environments including the combat field, extreme sport settings, and environmental disasters, as well as during space missions. Today, the usage of CU in the extreme emergency setting is more likely to occur, as this technique proved to be a fast diagnostic tool to assist resuscitation manoeuvres and interventional procedures in many cases. A scientific literature review is presented here. This was based on a systematic search of published literature, on the following online databases: PubMed and Scopus. The following words were used: "chest sonography," " thoracic ultrasound," and "lung sonography," in different combinations with "extreme sport," "extreme environment," "wilderness," "catastrophe," and "extreme conditions." This manuscript reports the most relevant usages of CU in the extreme setting as well as technological improvements and current limitations. CU application in the extreme setting is further encouraged here.

The influence of thoracic gas compression and airflow density dependence on the assessment of pulmonary function at high altitude

The purpose of this report was to illustrate how thoracic gas compression (TGC) artifact, and differences in air density, may together conflate the interpretation of changes in the forced expiratory flows (FEFs) at high altitude (>2400 m). Twenty-four adults (10 women; 44 ± 15 year) with normal baseline pulmonary function (>90% predicted) completed a 12-day sojourn at Mt. Kilimanjaro. Participants were assessed at Moshi (Day 0, 853 m) and at Barafu Camp (Day 9, 4837 m). Typical maximal expiratory flow-volume (MEFV) curves were obtained in accordance with ATS/ERS guidelines, and were either: (1) left unadjusted; (2) adjusted for TGC by constructing a "maximal perimeter" MEFV curve; or (3) adjusted for both TGC and differences in air density between altitudes. Forced vital capacity (FVC) was lower at Barafu compared with Moshi camp (5.19 ± 1.29 L vs. 5.40 ± 1.45 L, P < 0.05). Unadjusted data indicated no difference in the mid-expiratory flows (FEF25-75% ) between altitudes (∆ + 0.03 ± 0.53 L sec-1 ; ∆ + 1.2 ± 11.9%). Conversely, TGC-adjusted data revealed that FEF25-75% was significantly improved by sojourning at high altitude (∆ + 0.58 ± 0.78 L sec-1 ; ∆ + 12.9 ± 16.5%, P < 0.05). Finally, when data were adjusted for TGC and air density, FEFs were "less than expected" due to the lower air density at Barafu compared with Moshi camp (∆-0.54 ± 0.68 L sec-1 ; ∆-10.9 ± 13.0%, P < 0.05), indicating a mild obstructive defect had developed on ascent to high altitude. These findings clearly demonstrate the influence that TGC artifact, and differences in air density, bear on flow-volume data; consequently, it is imperative that future investigators adjust for, or at least acknowledge, these confounding factors when comparing FEFs between altitudes.

The Influence of CO2 and Exercise on Hypobaric Hypoxia Induced Pulmonary Edema in Rats

Introduction: Individuals with a known susceptibility to high altitude pulmonary edema (HAPE) demonstrate a reduced ventilation response and increased pulmonary vasoconstriction when exposed to hypoxia. It is unknown whether reduced sensitivity to hypercapnia is correlated with increased incidence and/or severity of HAPE, and while acute exercise at altitude is known to exacerbate symptoms the effect of exercise training on HAPE susceptibility is unclear.

Purpose: To determine if chronic intermittent hypercapnia and exercise increases the incidence of HAPE in rats.

Methods: Male Wistar rats were randomized to sedentary (sed-air), CO₂ (sed-CO₂,) exercise (ex-air), or exercise + CO₂ (ex-CO₂) groups. CO₂ (3.5%) and treadmill exercise (15 m/min, 10% grade) were conducted on a metabolic treadmill, 1 h/day for 4 weeks. Vascular reactivity to CO₂ was assessed after the training period by rheoencephalography (REG). Following the training period, animals were exposed to hypobaric hypoxia (HH) equivalent to 25,000 ft for 24 h. Pulmonary injury was assessed by wet/dry weight ratio, lung vascular permeability, bronchoalveolar lavage (BAL), and histology.

Results: HH increased lung wet/dry ratio (HH 5.51 ± 0.29 vs. sham 4.80 ± 0.11, P < 0.05), lung permeability (556 ± 84 u/L vs. 192 ± 29 u/L, P < 0.001), and BAL protein (221 ± 33 μg/ml vs. 114 ± 13 μg/ml, P < 0.001), white blood cell (1.16 ± 0.26 vs. 0.66 ± 0.06, P < 0.05), and platelet (16.4 ± 2.3, vs. 6.0 ± 0.5, P < 0.001) counts in comparison to normobaric normoxia. Vascular reactivity was suppressed by exercise (−53% vs. sham, P < 0.05) and exercise+CO₂ (−71% vs. sham, P < 0.05). However, neither exercise nor intermittent hypercapnia altered HH-induced changes in lung wet/dry weight, BAL protein and cellular infiltration, or pulmonary histology.

Conclusion: Exercise training attenuates vascular reactivity to CO₂ in rats but neither exercise training nor chronic intermittent hypercapnia affect HH- induced pulmonary edema.

Inhaled Budesonide Does Not Affect Hypoxic Pulmonary Vasoconstriction at 4559 Meters of Altitude

Berger, Marc Moritz, Franziska Macholz, Peter Schmidt, Sebastian Fried, Tabea Perz, Daniel Dankl, Josef Niebauer, Peter Bärtsch, Heimo Mairbäurl, and Mahdi Sareban. Inhaled budesonide does not affect hypoxic pulmonary vasoconstriction at 4559 meters of altitude. High Alt Med Biol 19:52-59, 2018.-Oral intake of the corticosteroid dexamethasone has been shown to lower pulmonary artery pressure (PAP) and to prevent high-altitude pulmonary edema. This study tested whether inhalation of the corticosteroid budesonide attenuates PAP and right ventricular (RV) function after rapid ascent to 4559 m. In this prospective, randomized, double-blind, and placebo-controlled trial, 50 subjects were randomized into three groups to receive budesonide at 200 or 800 μg twice/day (n = 16 and 17, respectively) or placebo (n = 17). Inhalation was started 1 day before ascending from 1130 to 4559 m within 20 hours. Systolic PAP (SPAP) and RV function were assessed by transthoracic echocardiography at low altitude (423 m) and after 7, 20, 32, and 44 hours at 4559 m. Ascent to high altitude increased SPAP about 1.7-fold (p < 0.001), whereas RV function was preserved. There was no difference in SPAP and RV function between groups at low and high altitude (all p values >0.10). Capillary partial pressure of oxygen (PO₂) and carbon dioxide as well as the alveolar to arterial PO₂ difference were decreased at high altitude but not affected by budesonide. Prophylactic inhalation of budesonide does not attenuate high-altitude-induced pulmonary vasoconstriction and RV function after rapid ascent to 4559 m.

STAT3-RXR-Nrf2 activates systemic redox and energy homeostasis upon steep decline in pO2 gradient

Hypobaric hypoxia elicits several patho-physiological manifestations, some of which are known to be lethal. Among various molecular mechanisms proposed so far, perturbation in redox state due to imbalance between radical generation and antioxidant defence is promising. These molecular events are also related to hypoxic status of cancer cells and therefore its understanding has extended clinical advantage beyond high altitude hypoxia. In present study, however, the focus was to understand and propose a model for rapid acclimatization of high altitude visitors to enhance their performance based on molecular changes. We considered using simulated hypobaric hypoxia at some established thresholds of high altitude stratification based on known physiological effects. Previous studies have focused on the temporal aspect while overlooking the effects of varying pO₂ levels during exposure to hypobaric hypoxia. The pO₂ levels, indicative of altitude, are crucial to redox homeostasis and can be the limiting factor during acclimatization to hypobaric hypoxia. In this study we present the effects of acute (24h) exposure to high (3049m; pO₂: 71kPa), very high (4573m; pO₂: 59kPa) and extreme altitude (7620m; pO₂: 40kPa) zones on lung and plasma using semi-quantitative redox specific transcripts and quantitative proteo-bioinformatics workflow in conjunction with redox stress assays. It was observed that direct exposure to extreme altitude caused 100% mortality, which turned into high survival rate after pre-exposure to 59kPa, for which molecular explanation were also found. The pO₂ of 59kPa (very high altitude zone) elicits systemic energy and redox homeostatic processes by modulating the STAT3-RXR-Nrf2 trio. Finally we posit the various processes downstream of STAT3-RXR-Nrf2 and the plasma proteins that can be used to ascertain the redox status of an individual.

Interstitial lung fluid balance in healthy lowlanders exposed to high-altitude

We aimed to assess lung fluid balance before and after gradual ascent to 5150m. Lung diffusion capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (Dm_CO) and ultrasound lung comets (ULCs) were assessed in 12 healthy lowlanders at sea-level, and on Day 1, Day 5 and Day 9 after arrival at Mount Everest Base Camp (EBC). EBC was reached following an 8-day hike at progressively increasing altitudes starting at 2860m. DLCO was unchanged from sea-level to Day 1 at EBC, but increased on Day 5 (11±10%) and Day 9 (10±9%) vs. sea-level (P≤0.047). Dm_CO increased from sea-level to Day 1 (9±6%), Day 5 (12±8%), and Day 9 (17±11%) (all P≤0.001) at EBC. There was no change in ULCs from sea-level to Day 1, Day 5 and Day 9 at EBC. These data provide evidence that interstitial lung fluid remains stable or may even decrease relative to at sea-level following 8days of gradual exposure to high-altitude in healthy humans.

Acute high-altitude sickness

At any point 1–5 days following ascent to altitudes ≥2500 m, individuals are at risk of developing one of three forms of acute altitude illness: acute mountain sickness, a syndrome of nonspecific symptoms including headache, lassitude, dizziness and nausea; high-altitude cerebral oedema, a potentially fatal illness characterised by ataxia, decreased consciousness and characteristic changes on magnetic resonance imaging; and high-altitude pulmonary oedema, a noncardiogenic form of pulmonary oedema resulting from excessive hypoxic pulmonary vasoconstriction which can be fatal if not recognised and treated promptly. This review provides detailed information about each of these important clinical entities. After reviewing the clinical features, epidemiology and current understanding of the pathophysiology of each disorder, we describe the current pharmacological and nonpharmacological approaches to the prevention and treatment of these diseases.

Lack of acclimatisation is the main risk factor for acute altitude illness; descent is the optimal treatmenthttp://ow.ly/45d2305JyZ0

Reappraisal of DLCO adjustment to interpret the adaptive response of the air-blood barrier to hypoxia

DLCO measured in hypoxia must be corrected due to the higher affinity (increase in coefficient θ) of CO with Hb. We propose an adjustment accounting for individual changes in the equation relating DLCO to subcomponents Dm (membrane diffusive capacity) and Vc (lung capillary volume): 1/DLCO=1/Dm+1/θVc. We adjusted the individual DLCO measured in hypoxia (HA, 3269m) by interpolating the 1/DLCO to the sea level (SL) 1/θ value. Nineteen healthy subjects were studied at SL and HA. Based on the proposed adjustment, DLCO increased in HA in 53% of subjects, reflecting the increase in Dm that largely overruled the decrease in Vc. We hypothesize that a decrease in Vc (buffering microvascular filtration) and the increase in Dm (possibly resulting from a decrease in thickness of the air-blood barrier) represent the anti-edemagenic adaptation of the lung to hypoxia exposure. The efficiency of this adaptation varied among subjects as DLCO did not change in 31% of subjects and decreased in 16%.

Novel Insights into Cardiovascular Regulation in Patients with Chronic Mountain Sickness

Studies of high-altitude populations, and in particular of maladapted subgroups, may provide important insight into underlying mechanisms involved in the pathogenesis of hypoxemia-related disease in general. Chronic mountain sickness (CMS) is a major public health problem in mountainous regions of the world affecting many millions of high-altitude dwellers. It is characterized by exaggerated chronic hypoxemia, erythrocytosis, and mild pulmonary hypertension. In later stages these patients often present with right heart failure and are predisposed to systemic cardiovascular disease, but the underlying mechanisms are poorly understood. Here, we present recent new data providing insight into underlying mechanisms that may cause these complications.

Incidence of high altitude pulmonary edema in low-landers during re-exposure to high altitude after a sojourn in the plains

BACKGROUND

There is uncertainty whether acclimatized low-landers who return to high altitude after a sojourn at low altitude have a higher incidence of pulmonary edema than during the first exposure to high altitude.

METHODS

This was a prospective cohort study consisting of men ascending to 3400 m by road (N = 1003) or by air (N = 4178). The study compared the incidence of high altitude pulmonary edema during first exposure vs the incidence during re-exposure in each of these cohorts.

RESULTS

Pulmonary edema occurred in 13 of the 4178 entries by air (Incidence: 0.31%, 95% CI: 0.18%-0.53%). The incidence during first exposure was 0.18% (0.05%-0.66%) and 0.36% (0.2%-0.64%) during re-exposure (Fisher Exact Test for differences in the incidence (two-tailed) p = 0.534). The relative risk for the re-exposure cohort was 1.95 (95% CI, 0.43%-8.80%). Pulmonary edema occurred in 3 of the 1003 road entrants (Incidence: 0.30%, 95% CI: 0.08%-0.95%). All three cases occurred in the re-exposure cohort.

CONCLUSION

The large overlap of confidence intervals between incidence during first exposure and re-exposure; the nature of the confidence interval of the relative risk; and the result of the Fisher exact test, all suggest that this difference in incidence could have occurred purely by chance. We did not find evidence for a significantly higher incidence of HAPE during re-entry to HA after a sojourn in the plains.

Factors associated with B-lines after exposure to hypobaric hypoxia

AIMS

Increased extravascular lung water (EVLW) is seen as B-lines on chest ultrasonography. In lowlanders ascending to altitude the time course, relationship with the patient's clinical status and factors affecting B-lines are still unclear. The aim was to monitor B-lines, clinical status and N-terminal B-type natriuretic peptide (NT-proBNP) during exposure to high altitude.

METHODS AND RESULTS

Chest ultrasonography, blood samples, cardiovascular parameters, and signs and symptoms of high altitude pulmonary oedema (HAPE) were prospectively assessed in 19 participants at baseline and after ascent to 3830 m (9, 24, 48, 72 h, and 8 days) by blinded investigators. Potential confounding factors (e.g. altitude variations, physical effort) were minimized. Generalized estimating equations were used to analyse factors associated with B-lines. B-lines changed with exposure to altitude (P = 0.006) in a parabolic-like pattern within the first 72 h; 10 of 18 participants (55.6%) had >5 B-lines at 24 h. B-lines were correlated with the number of signs and symptoms (partial coefficient = 0.372, P = 0.001). B-lines were associated with time (P = 0.038), sex (P = 0.013), and SpO2 (P = 0.042), but not with NT-proBNP (P = 0.546). The participant with a clinical diagnosis of HAPE had 23 B-lines.

CONCLUSION

B-lines during exposure to altitude seem to reflect the individual response to hypobaric hypoxia and represent clinically relevant alterations at high altitude, also in patients with HAPE. Similar to previous studies, our results support a non-cardiogenic aetiology of B-lines.

Physiology in Medicine: A physiologic approach to prevention and treatment of acute high-altitude illnesses

With the growing interest in adventure travel and the increasing ease and affordability of air, rail, and road-based transportation, increasing numbers of individuals are traveling to high altitude. The decline in barometric pressure and ambient oxygen tensions in this environment trigger a series of physiologic responses across organ systems and over a varying time frame that help the individual acclimatize to the low oxygen conditions but occasionally lead to maladaptive responses and one or several forms of acute altitude illness. The goal of this Physiology in Medicine article is to provide information that providers can use when counseling patients who present to primary care or travel medicine clinics seeking advice about how to prevent these problems. After discussing the primary physiologic responses to acute hypoxia from the organ to the molecular level in normal individuals, the review describes the main forms of acute altitude illness--acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema--and the basic approaches to their prevention and treatment of these problems, with an emphasis throughout on the physiologic basis for the development of these illnesses and their management.

Serious altitude illness in travelers who visited a pre-travel clinic

BACKGROUND

Few data are available on the incidence and predictors of serious altitude illness in travelers who visit pre-travel clinics. Travel health consultants advise on measures to be taken in case of serious altitude illness but it is not clear if travelers adhere to these recommendations.

METHODS

Visitors to six travel clinics who planned to travel to an altitude of ≥3,000 m were asked to complete a diary from the first day at 2,000 m until 3 days after reaching the maximum sleeping altitude. Serious altitude illness was defined as having symptoms of serious acute mountain sickness (AMS score ≥ 6) and/or cerebral edema and/or pulmonary edema.

RESULTS

The incidence of serious altitude illness in the 401 included participants of whom 90% reached ≥4,000 m, was 35%; 23% had symptoms of serious AMS, 25% symptoms of cerebral edema, and 13% symptoms of pulmonary edema. Independent predictors were young age, the occurrence of dark urine, travel in South America or Africa, and lack of acclimatization between 1,000 and 2,500 m. Acetazolamide was brought along by 77% of the responders of whom 41% took at least one dose. Of those with serious altitude illness, 57% had taken at least one dose of acetazolamide, 20% descended below 2,500 m on the same day or the next, and 11% consulted a physician.

CONCLUSIONS

Serious altitude illness was a very frequent problem in travelers who visited pre-travel clinics. Young age, dark urine, travel in South America or Africa, and lack of acclimatization nights at moderate altitude were independent predictors. Furthermore, we found that seriously ill travelers seldom followed the advice to descend and to visit a physician.

Long-term monitoring of oxygen saturation at altitude can be useful in predicting the subsequent development of moderate-to-severe acute mountain sickness

OBJECTIVE

The use of pulse oximetry (Spo2) to identify subjects susceptible to acute mountain sickness (AMS) is the subject of debate. To obtain more reliable data, we monitored Spo2 for 24 hours at altitude to investigate the ability to predict impending AMS.

METHODS

The study was conducted during the climb from Alagna (1154 m) to Capanna Regina Margherita (4559 m), with an overnight stay in Capanna Gnifetti (3647 m). Sixty subjects (11 women) were recruited. Each subject was fitted with a 24-hour recording finger pulse oximeter. The subjects rode a cable car to 3275 m and climbed to 3647 m, where they spent the night.

RESULTS

In the morning, 24 subjects (6 women) had a Lake Louise Questionnaire score (LLS) ≥ 3 (AMS(+)), and 15 subjects (4 women) exhibited moderate-to-severe disease (LLS ≥ 5 = AMS(++)). At Alagna, Spo2 did not differ between the AMS(-) and AMS(+) subjects. At higher stations, all AMS(+) subjects exhibited a significantly lower Spo2 than did the AMS(-) subjects: at 3275 m, 85.4% vs 87.7%; resting at 3647 m, 84.5% vs 86.4%. The receiver operating characteristics curve analysis resulted in a rather poor discrimination between the AMS(-) subjects and all of the AMS(+) subjects. With the cutoff LLS ≥ 5, the sensitivity was 86.67%, the specificity was 82.25%, and the area under the curve was 0.88 (P < .0001) for Spo2 ≤ 84% at 3647 m.

CONCLUSIONS

We conclude that AMS(+) subjects exhibit a more severe and prolonged oxygen desaturation than do AMS(-) subjects starting from the beginning of altitude exposure, but the predictive power of Spo2 is accurate only for AMS(++).