High altitude pulmonary edema: a pressure-induced leak

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

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

The Telomere-Telomerase System Is Detrimental to Health at High-Altitude

The hypobaric-hypoxia environment at high-altitude (HA, >2500 m) may influence DNA damage due to the production of reactive molecular species and high UV radiation. The telomere system, vital to chromosomal integrity and cellular viability, is prone to oxidative damages contributing to the severity of high-altitude disorders such as high-altitude pulmonary edema (HAPE). However, at the same time, it is suggested to sustain physical performance. This case-control study, comprising 210 HAPE-free (HAPE-f) sojourners, 183 HAPE-patients (HAPE-p) and 200 healthy highland natives (HLs) residing at ~3500 m, investigated telomere length, telomerase activity, and oxidative stress biomarkers. Fluidigm SNP genotyping screened 65 single nucleotide polymorphisms (SNPs) in 11 telomere-maintaining genes. Significance was attained at p ≤ 0.05 after adjusting for confounders and correction for multiple comparisons. Shorter telomere length, decreased telomerase activity and increased oxidative stress were observed in HAPE patients; contrarily, longer telomere length and elevated telomerase activity were observed in healthy HA natives compared to HAPE-f. Four SNPs and three haplotypes are associated with HAPE, whereas eight SNPs and nine haplotypes are associated with HA adaptation. Various gene-gene interactions and correlations between/among clinical parameters and biomarkers suggested the presence of a complex interplay underlining HAPE and HA adaptation physiology. A distinctive contribution of the telomere-telomerase system contributing to HA physiology is evident in this study. A normal telomere system may be advantageous in endurance training.

Initial Treatment of High-Altitude Pulmonary Edema: Comparison of Oxygen and Auto-PEEP

BACKGROUND

Improvement of oxygenation is the aim in the therapy of high-altitude pulmonary edema (HAPE). However, descent is often difficult and hyperbaric chambers, as well as bottled oxygen, are often not available. We compare Auto-PEEP (AP-Pat), a special kind of pursed lips breathing, against the application of bottled oxygen (O₂-Pat) in two patients suffering from HAPE.

METHODS

We compare the effect of these two different therapies on oxygen saturation measured by pulse oximetry (SpO₂) over time.

RESULT

In both patients SpO₂ increased significantly from 65-70% to 95%. Above 80% this increase was slower in AP-Pat compared with O₂-Pat. Therapy started immediately in AP-Pat but was delayed in O₂-Pat because of organizational and logistic reasons.

CONCLUSIONS

The well-established therapies of HAPE are always the option of choice, if available, and should be started as soon as possible. The advantage of Auto-PEEP is its all-time availability. It improves SpO₂ nearly as well as 3 L/min oxygen and furthermore has a positive effect on oxygenation lasting for approximately 120 min after stopping. Auto-PEEP treatment does not appear inferior to oxygen treatment, at least in this cross-case comparison. Its immediate application after diagnosis probably plays an important role here.

Mean corpuscular haemoglobin concentration (MCHC): a new biomarker for high-altitude pulmonary edema in the Ecuadorian Andes

Ascent to high altitude (> 3000 m height above sea level or m.a.s.l) exposes people to hypobaric atmospheric pressure and hypoxemia, which provokes mountain sickness and whose symptoms vary from the mild acute mountain sickness to the life-threatening, high-altitude pulmonary edema (HAPE). This study analysed the risk factors underlying HAPE in dwellers and travellers of the Ecuadorian Andes after sojourning over 3000 m height. A group of HAPE patients (N = 58) was compared to a NO HAPE group (N = 713), through demographic (ethnicity, sex, and age), red blood cell parameters (erythrocytes counts, hematocrit, median corpuscular volume, median corpuscular haemoglobin, and median corpuscular haemoglobin concentration (MCHC)), altitude (threshold: 3000 m.a.s.l.), and health status (vital signs) variables. Analysis of Deviance for Generalised Linear Model Fits (logit regression) revealed patterns of significant associations. High-altitude dwellers, particularly children and elder people, were HAPE-prone, while women were more tolerant of HAPE than men. Interestingly, HAPE prevalence was strongly related to an increment of MCH. The residence at middle altitude was inversely related to the odds of suffering HAPE. Ethnicity did not have a significant influence in HAPE susceptibility. Elevated MCHC emerges like a blood adaptation of Andean highlanders to high altitude and biomarker of HAPE risk.

Effects of acetazolamide on pulmonary artery pressure and prevention of high altitude pulmonary edema after rapid active ascent to 4,559 m

Acetazolamide prevents acute mountain sickness (AMS) by inhibition of carbonic anhydrase. Since it reduces acute hypoxic pulmonary vasoconstriction (HPV), it may also prevent high-altitude pulmonary edema (HAPE) by lowering pulmonary artery pressure. We tested this hypothesis in a randomized, placebo-controlled, double-blind study. Thirteen healthy, non-acclimatized lowlanders with a history of HAPE ascended (<22h) from 1,130 to 4,559m with one overnight stay at 3,611m. Medications started 48h before ascent (acetazolamide: n=7, 250mg 3x/d; placebo: n=6, 3x/d). HAPE was diagnosed by chest radiography, and pulmonary artery pressure by measurement of right ventricular to atrial pressure gradient (RVPG) by transthoracic echocardiography. AMS was evaluated with the Lake Louise Score (LLS) and AMS-C Score. Incidence of HAPE was 43% vs. 67% (acetazolamide vs. placebo, p=0.39). Ascent to altitude increased RVPG from 20±5 to 43±10mmHg (p<0.001) without a group difference (p=0.68). Arterial PO₂ fell to 36±9mmHg (p<0.001) and was 8.5mmHg higher with acetazolamide at high altitude (p=0.025). At high altitude, the LLS and AMS-C score remained lower in those taking acetazolamide (both p<0.05). Although acetazolamide reduced HAPE incidence by 35%, this effect was not statistically significant, and considerably less than reductions of about 70-100% with prophylactic dexamethasone, tadalafil, and nifedipine performed with the same ascent profile at the same location. We could not demonstrate a reduction in RVPG compared to placebo treatment despite reductions in AMS severity and better arterial oxygenation. Limited by a small sample size, our data do not support recommending acetazolamide for prevention of HAPE in mountaineers ascending rapidly to over 4,500m.

Lung transcriptome analysis for the identification of genes involved in the hypoxic adaptation of plateau pika (Ochotona curzoniae)

The plateau pika, a typical hypoxia-tolerant mammal lives 3000-5000 m above sea level on the Qinghai-Tibet Plateau, has acquired many physiological and morphological characteristics and strategies in its adaptation to sustained, high-altitude hypoxia. Blunted hypoxic pulmonary vasoconstriction is one such strategy, but the genes involved in this strategy have not been elucidated. Here, we investigated the genes involved and their expression profiles in the lung transcriptome of plateau pikas subjected to different hypoxic conditions (using low-pressure oxygen cabins). A slight, right ventricular hypertrophy was observed in pikas of the control group (altitude: 3200 m) vs. those exposed to 5000 m altitude conditions for one week. Our assembly identified 67,774 genes; compared with their expression in the control animals, 866 and 8364 genes were co-upregulated and co-downregulated, respectively, in pikas subjected to 5000 m altitude conditions for 1 and 4 w. We elucidated pathways that were associated with pulmonary vascular arterial pressure, including vascular smooth muscle contraction, HIF-1 signalling, calcium signalling, cGMP-PKG signalling, and PI3K-Akt signalling based on the differentially expressed genes; the top-100 pathway enrichments were found between the control group and the group exposed to 5000 m altitude conditions for 4 w. The mRNA levels of 18 candidate gene showed that more than 83% of genes were expressed and the number of transcriptome The up-regulated genes were EPAS1, Hbα, iNOS, CX40, CD31, PPM1B, HIF-1α, MYLK, Pcdh12, Surfactant protein B, the down-regulated genes were RYR2, vWF, RASA1, CLASRP, HIF-3α. Our transcriptome data are a valuable resource for future genomic studies on plateau pika.

Might a high hemoglobin mass be involved in non-cardiogenic pulmonary edema? The case of the chronic maladaptation to high-altitude in the Andes

Exposure to hypoxic environments when ascending at high altitudes may cause life-threatening pulmonary edema (HAPE) due to a rapid accumulation of extracellular fluid flooding in the pulmonary alveoli. In Andeans, high-altitude adaptation occurs at the expense of being more prone to chronic mountain sickness: relative hypoventilation, excess pulmonary hypertension, and secondary polycythemia. Because HAPE prevalence is high in the Andes, we posit the hypothesis that a high hemoglobine mass may increase HAPE risk. In support of it, high intrapulmonary hypertension along with hyperviscosity produced by polycytemia may enhance sear forces and intravascular hemolysis, thus leading to increased acellular hemoglobin and the subsequent damage of the alveolar and endothelial barrier. It is proposed to investigate the relationship between the vaso-endothelial homeostasis and erythropoiesis in the maladaptation to high altitude and HAPE. This research is especially important when reentry HAPE, since rheologic properties of blood changes with rapid ascent to high altitudes.

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.

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.

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.

The plasma level changes of VEGF and soluble VEGF receptor-1 are associated with high-altitude pulmonary edema

Hypoxia-induced plasma levels of VEGF and sFlt-1 are responsible for increased vascular permeability occurred in both brain and pulmonary edema. Currently, it remains unclear the exact roles of VEGF and sFlt-1 in High Altitude Pulmonary Edema (HAPE) pathogenesis. In this study, plasma levels of VEGF and sFlt-1 from 10 HAPE and 10 non-HAPE subjects were measured and compared. The results showed that plasma levels of both VEGF and sFlt-1 in HAPE patients were significantly increased as compared to the non-HAPE group. Interestingly, increased plasma levels of these two protein factors were markedly reduced after treatments. As compared to VEGF, sFlt-1 was much more affected by hypoxia and treatments, suggesting this factor was a key factor contributed to HAPE pathogenesis. Importantly, the ratio of sFlt-1 and VEGF in group of either non-HAPE or HAPE after recovery was significantly lower than the ratio in HAPE patients prior to treatments. Our findings suggested that sFlt-1 was a key factor that involved in HAPE pathogenesis and the sFlt-1/VEGF ratio could be used as a sensitive diagnostic marker for HAPE. J. Med. Invest. 65:64-68, February, 2018.

Remote ischemic preconditioning does not prevent acute mountain sickness after rapid ascent to 3,450 m

Remote ischemic preconditioning (RIPC) has been shown to protect remote organs, such as the brain and the lung, from damage induced by subsequent hypoxia or ischemia. Acute mountain sickness (AMS) is a syndrome of nonspecific neurologic symptoms and in high-altitude pulmonary edema excessive hypoxic pulmonary vasoconstriction (HPV) plays a pivotal role. We hypothesized that RIPC protects the brain from AMS and attenuates the magnitude of HPV after rapid ascent to 3,450 m. Forty nonacclimatized volunteers were randomized into two groups. At low altitude (750 m) the RIPC group (n = 20) underwent 4 × 5 min of lower-limb ischemia (induced by inflation of bilateral thigh cuffs to 200 mmHg) followed by 5 min of reperfusion. The control group (n = 20) underwent a sham protocol (4 × 5 min of bilateral thigh cuff inflation to 20 mmHg). Thereafter, participants ascended to 3,450 m by train over 2 h and stayed there for 48 h. AMS was evaluated by the Lake Louise score (LLS) and the AMS-C score. Systolic pulmonary artery pressure (SPAP) was assessed by transthoracic Doppler echocardiography. RIPC had no effect on the overall incidence (RIPC: 35%, control: 35%, P = 1.0) and severity (RIPC vs.

CONTROL

P = 0.496 for LLS; P = 0.320 for AMS-C score) of AMS. RIPC also had no significant effect on SPAP [maximum after 10 h at high altitude; RIPC: 33 (SD 8) mmHg; controls: 37 (SD 7) mmHg; P = 0.19]. This study indicates that RIPC, performed immediately before passive ascent to 3,450 m, does not attenuate AMS and the magnitude of high-altitude pulmonary hypertension.NEW & NOTEWORTHY Remote ischemic preconditioning (RIPC) has been reported to improve neurologic and pulmonary outcome following an acute ischemic or hypoxic insult, yet the effect of RIPC for protecting from high-altitude diseases remains to be determined. The present study shows that RIPC, performed immediately before passive ascent to 3,450 m, does not attenuate acute mountain sickness and the degree of high-altitude pulmonary hypertension. Therefore, RIPC cannot be recommended for prevention of high-altitude diseases.

H2S Regulates Hypobaric Hypoxia-Induced Early Glio-Vascular Dysfunction and Neuro-Pathophysiological Effects

Hypobaric Hypoxia (HH) is an established risk factor for various neuro-physiological perturbations including cognitive impairment. The origin and mechanistic basis of such responses however remain elusive. We here combined systems level analysis with classical neuro-physiological approaches, in a rat model system, to understand pathological responses of brain to HH. Unbiased ‘statistical co-expression networks’ generated utilizing temporal, differential transcriptome signatures of hippocampus—centrally involved in regulating cognition—implicated perturbation of Glio-Vascular homeostasis during early responses to HH, with concurrent modulation of vasomodulatory, hemostatic and proteolytic processes. Further, multiple lines of experimental evidence from ultra-structural, immuno-histological, substrate-zymography and barrier function studies unambiguously supported this proposition. Interestingly, we show a significant lowering of H₂S levels in the brain, under chronic HH conditions. This phenomenon functionally impacted hypoxia-induced modulation of cerebral blood flow (hypoxic autoregulation) besides perturbing the strength of functional hyperemia responses. The augmentation of H₂S levels, during HH conditions, remarkably preserved Glio-Vascular homeostasis and key neuro-physiological functions (cerebral blood flow, functional hyperemia and spatial memory) besides curtailing HH-induced neuronal apoptosis in hippocampus. Our data thus revealed causal role of H₂S during HH-induced early Glio-Vascular dysfunction and consequent cognitive impairment.

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Glio-Vascular dysfunction temporally precedes Hypobaric Hypoxia (HH) induced neuro-pathological effects.

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Exposure to HH significantly lowers the levels of H₂S in brain.

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Augmentation of H₂S, utilizing its donor, preserves Glio-Vascular homeostasis and curtails HH-induced memory impairment.

The exposure to Hypobaric Hypoxia (HH) environment (such as that encountered by humans at high altitude) culminates in cognitive impairment in an altitude- and duration-dependent manner. The mechanistic basis for such effects, however, remains elusive. Our present study showed that HH-induced neuro-pathological perturbations are temporally preceded by Glio-Vascular dysfunction and are concomitant with lowered levels of gaseous messenger, H₂S, in brain. The maintenance of H₂S levels (utilizing a specific donor, NaHS) during hypoxia curtailed HH-induced brain-vascular dysfunction and ensuing neuro-pathological effects (on spatial memory). Interestingly, identification of origin of disease in the present study effectively revealed a possible interventional strategy.

Remote ischemic preconditioning for prevention of high-altitude diseases: fact or fiction?

Preconditioning refers to exposure to brief episodes of potentially adverse stimuli and protects against injury during subsequent exposures. This was first described in the heart, where episodes of ischemia/reperfusion render the myocardium resistant to subsequent ischemic injury, which is likely caused by reactive oxygen species (ROS) and proinflammatory processes. Protection of the heart was also found when preconditioning was performed in an organ different from the target, which is called remote ischemic preconditioning (RIPC). The mechanisms causing protection seem to include stimulation of nitric oxide (NO) synthase, increase in antioxidant enzymes, and downregulation of proinflammatory cytokines. These pathways are also thought to play a role in high-altitude diseases: high-altitude pulmonary edema (HAPE) is associated with decreased bioavailability of NO and increased generation of ROS, whereas mechanisms causing acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) seem to involve cytotoxic effects by ROS and inflammation. Based on these apparent similarities between ischemic damage and AMS, HACE, and HAPE, it is reasonable to assume that RIPC might be protective and improve altitude tolerance. In studies addressing high-altitude/hypoxia tolerance, RIPC has been shown to decrease pulmonary arterial systolic pressure in normobaric hypoxia (13% O2) and at high altitude (4,342 m). Our own results indicate that RIPC transiently decreases the severity of AMS at 12% O2. Thus preliminary studies show some benefit, but clearly, further experiments to establish the efficacy and potential mechanism of RIPC are needed.

KGF-2 targets alveolar epithelia and capillary endothelia to reduce high altitude pulmonary oedema in rats

High altitude pulmonary oedema (HAPE) severely affects non-acclimatized individuals and is characterized by alveolar flooding with protein- rich oedema as a consequence of blood-gas barrier disruption. Limited choice for prophylactic treatment warrants effective therapy against HAPE. Keratinocyte growth factor-2 (KGF-2) has shown efficiency in preventing alveolar epithelial cell DNA damages in vitro. In the current study, the effects of KGF-2 intratracheal instillation on mortality, lung liquid balance and lung histology were evaluated in our previously developed rat model of HAPE. We found that pre-treatment with KGF-2 (5 mg/kg) significantly decreased mortality, improved oxygenation and reduced lung wet-to-dry weight ratio by preventing alveolar-capillary barrier disruption demonstrated by histological examination and increasing alveolar fluid clearance up to 150%. In addition, KGF-2 significantly inhibited decrease of transendothelial permeability after exposure to hypoxia, accompanied by a 10-fold increase of Akt activity and inhibited apoptosis in human pulmonary microvascular endothelial cells, demonstrating attenuated endothelial apoptosis might contribute to reduction of endothelial permeability. These results showed the efficacy of KGF-2 on inhibition of endothelial cell apoptosis, preservation of alveolar-capillary barrier integrity and promotion of pulmonary oedema absorption in HAPE. Thus, KGF-2 may represent a potential drug candidate for the prevention 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.

New insights of aquaporin 5 in the pathogenesis of high altitude pulmonary edema

Background

High altitude pulmonary edema (HAPE) affects individuals and is characterized by alveolar flooding with protein-rich edema as a consequence of blood-gas barrier disruption. In this study, we hypothesized that aquaporin 5 (AQP5) which is one kind of water channels may play a role in preservation of alveolar epithelial barrier integrity in high altitude pulmonary edema (HAPE).

Methods

Therefore, we established a model in Wildtype mice and AQP5 −/− mice were assingned to normoxic rest (NR), hypoxic rest (HR) and hypoxic exercise (HE) group. Mice were produced by training to walk at treadmill for exercising and chamber pressure was reduced to simulate climbing an altitude of 5000 m for 48 hours. Studies using BAL in HAPE mice to demonstrated that edema is caused leakage of albumin proteins and red cells across the alveolarcapillary barrier in the absence of any evidence of inflammation.

Results

In this study, the Lung wet/dry weight ratio and broncholalveolar lavage protein concentrations were slightly increased in HE AQP5 −/− mice compared to wildtype mice. And histologic evidence of hemorrhagic pulmonary edema was distinctly shown in HE group. The lung Evan’s blue permeability of HE group was showed slightly increased compare to the wildtype groups, and HR group was showed a medium situation from normal to HAPE development compared with NR and HE group.

Conclusions

Deletion of AQP5 slightly increased lung edema and lung injury compared to wildtype mice during HAPE development, which suggested that the AQP5 plays an important role in HAPE formation induced by high altitude simulation.

Autonomic neural control of intrathoracic airways

Autonomic neural control of the intrathoracic airways aids in optimizing air flow and gas exchange. In addition, and perhaps more importantly, the autonomic nervous system contributes to host defense of the respiratory tract. These functions are accomplished by tightly regulating airway caliber, blood flow, and secretions. Although both the sympathetic and parasympathetic branches of the autonomic nervous system innervate the airways, it is the later that dominates, especially with respect to control of airway smooth muscle and secretions. Parasympathetic tone in the airways is regulated by reflex activity often initiated by activation of airway stretch receptors and polymodal nociceptors. This review discusses the preganglionic, ganglionic, and postganglionic mechanisms of airway autonomic innervation. Additionally, it provides a brief overview of how dysregulation of the airway autonomic nervous system may contribute to respiratory diseases.

Variations in alveolar partial pressure for carbon dioxide and oxygen have additive not synergistic acute effects on human pulmonary vasoconstriction

The human pulmonary vasculature constricts in response to hypercapnia and hypoxia, with important consequences for homeostasis and adaptation. One function of these responses is to direct blood flow away from poorly-ventilated regions of the lung. In humans it is not known whether the stimuli of hypercapnia and hypoxia constrict the pulmonary blood vessels independently of each other or whether they act synergistically, such that the combination of hypercapnia and hypoxia is more effective than the sum of the responses to each stimulus on its own. We independently controlled the alveolar partial pressures of carbon dioxide (Pa_co2) and oxygen (Pa_o2) to examine their possible interaction on human pulmonary vasoconstriction. Nine volunteers each experienced sixteen possible combinations of four levels of Pa_co2 (+6, +1, −4 and −9 mmHg, relative to baseline) with four levels of Pa_o2 (175, 100, 75 and 50 mmHg). During each of these sixteen protocols Doppler echocardiography was used to evaluate cardiac output and systolic tricuspid pressure gradient, an index of pulmonary vasoconstriction. The degree of constriction varied linearly with both Pa_co2 and the calculated haemoglobin oxygen desaturation (1-So₂). Mixed effects modelling delivered coefficients defining the interdependence of cardiac output, systolic tricuspid pressure gradient, ventilation, Pa_co2 and So₂. No interaction was observed in the effects on pulmonary vasoconstriction of carbon dioxide and oxygen (p>0.64). Direct effects of the alveolar gases on systolic tricuspid pressure gradient greatly exceeded indirect effects arising from concurrent changes in cardiac output.

Overexpression of cationic amino acid transporter-1 increases nitric oxide production in hypoxic human pulmonary microvascular endothelial cells

1. The endogenous production of and/or the bioavailability of nitric oxide (NO) is decreased in pulmonary hypertensive diseases. L-arginine (L-arg) is the substrate for NO synthase (NOS). L-arg is transported into cells via the cationic amino acid transporters (CAT), of which there are two isoforms in endothelial cells, CAT-1 and CAT-2. 2. To test the hypothesis that hypoxia will decrease CAT expression and L-arg uptake resulting in decreased NO production in human pulmonary microvascular endothelial cells (hPMVEC), cells were incubated in either normoxia (21% O(2), 5% CO(2), balance N(2)) or hypoxia (1% O(2), 5% CO(2), balance N(2)). 3. The hPMVEC incubated in hypoxia had 80% less NO production than cells incubated in normoxia (P < 0.01). The hPMVEC incubated in hypoxia had significantly lower CAT-2 mRNA levels than normoxic hPMVEC (P < 0.005), and the transport of L-arg was 40% lower in hypoxic than in normoxic hPMVEC (P < 0.01). In hypoxic cells, overexpression of CAT-1 resulted in significantly greater L-arg transport and NO production (P < 0.05). 4. These results demonstrate that in hPMVEC, hypoxia decreased CAT-2 expression, L-arg uptake and NO production. Furthermore, the hypoxia-induced decrease in NO production in hPMVEC can be attenuated by overexpressing CAT in these cells. We speculate that the CAT may represent a novel therapeutic target for treating pulmonary hypertensive disorders.

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.

High-altitude retinopathy after climbing Mount Aconcagua in a group of experienced climbers

BACKGROUND

Visual disturbances after high-altitude exposure were first reported in 1969. Manifestations may include retinal hemorrhage, papilledema, and vitreous hemorrhage.

METHODS

We observed a group of 6 experienced climbers who ascended Mt Aconcagua to an altitude of 6,962 m in February 2007. Visual acuity study, intraocular pressure study, visual field study, nerve fiber layer analysis, eye Doppler, laboratory studies, fundus photography, and intravenous fluorescein angiography were performed on the climbers before and after their exposures to high altitude.

RESULTS

In all six study subjects, retinal vascular engorgement and tortuosity were present in varying degrees in both eyes. One of the climbers had both retinal hemorrhage and pulmonary edema. Of the two subjects who had visual field defects, one had severe nerve fiber layer defects of both eyes. Furthermore, laboratory studies of this climber showed a high level of antiphospholipid antibody. Significant reduction of the left ocular blood flow was also noted on this subject's eye Doppler examination after the Mt Aconcagua expedition.

CONCLUSION

Various high-altitude retinopathies were observed in the experienced climbers of this study. As high-altitude pursuits become more popular, attention should be paid to the increasing prevalence of high-altitude retinopathy.

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.

Evidence for a genetic basis for altitude illness: 2010 update

Altitude illness refers to a group of environmentally mediated pathophysiologies. Many people will suffer acute mountain sickness shortly after rapidly ascending to a moderately hypoxic environment, and an unfortunate few will develop potentially fatal conditions such as high altitude pulmonary edema or high altitude cerebral edema. Some individuals seem to be predisposed to developing altitude illness, suggesting an innate contribution to susceptibility. The implication that there are altitude-sensitive and altitude-tolerant individuals has stimulated much research into the contribution of a genetic background to the efficacy of altitude acclimatization. Although the effect of altitude attained and rate of ascent on the etiology of altitude illness is well known, there are only tantalizing, but rapidly accumulating, clues to the genes that may be involved. In 2006, we reviewed what was then known about the genetics of altitude illness. This article updates that review and attempts to tabulate all the available genetic data pertaining to these conditions. To date, 58 genes have been investigated for a role in altitude illness. Of these, 17 have shown some association with the susceptibility to, or the severity of, these conditions, although in many cases the effect size is small or variable. Caution is recommended when evaluating the genes for which no association was detected, because a number of the investigations reviewed in this article were insufficiently powered to detect small effects. No study has demonstrated a clear-cut altitude illness gene, but the accumulating data are consistent with a polygenic condition with a strong environmental component. The genes that have shown an association affect a variety of biological pathways, suggesting that either multiple systems are involved in altitude pathophysiology or that gene-gene interactions play a role. Although numerous studies have been performed to investigate specific genes, few have looked for evidence of heritability or familial transmission, or for epidemiological patterns that would be consistent with genetically influenced conditions. Future trends, such as genome-wide association studies and epigenetic analysis, should lead to enhanced understanding of the complex interactions within the genome and between the genome and hypoxic environments that contribute to an individual's capacity to acclimatize rapidly and effectively to altitude.

High-altitude disorders: pulmonary hypertension: pulmonary vascular disease: the global perspective

Globally, it is estimated that > 140 million people live at a high altitude (HA), defined as > 2,500 m (8,200 ft), and that countless others sojourn to the mountains for work, travel, and sport. The distribution of exposure to HA is worldwide, including 35 million in the Andes and > 80 million in Asia, including China and central Asia. HA stress primarily is due to the hypoxia of low atmospheric pressure, but dry air, intense solar radiation, extreme cold, and exercise contribute to acute and chronic disorders. The acute disorders are acute mountain sickness (also known as soroche), HA cerebral edema, and HA pulmonary edema (HAPE). Of these, HAPE is highly correlated with acute pulmonary hypertension. The first chronic syndrome described in HA dwellers in Peru was chronic mountain sickness (Monge disease), which has a large component of relative hypoventilation and secondary erythrocytosis. The prevalence of chronic mountain sickness in HA dwellers ranges from 1.2% in native Tibetans to 5.6% in Chinese Han; 6% to 8% in male residents of La Paz, Bolivia; and 15.6% in the Andes. Subacute mountain sickness is an exaggerated pulmonary hypertensive response to HA hypoxia occurring over months, most often in infants and very young children. Chronic pulmonary hypertension with heart failure but without hypoventilation is seen in Asia. Not only does HA pulmonary hypertension exact health consequences for the millions affected, but also the mechanisms of disease relate to pulmonary hypertension associated with multiple other disorders. Genetic understanding of these disorders is in its infancy.

Low pulmonary artery flush perfusion pressure combined with high positive end-expiratory pressure reduces oedema formation in isolated porcine lungs

Flush perfusion of the pulmonary artery with organ protection solution is a standard procedure before lung explantation. However, rapid flush perfusion may cause pulmonary oedema which is deleterious in the lung transplantation setting. In this study we tested the hypotheses that high pulmonary perfusion pressure contributes to the development of pulmonary oedema and positive end-expiratory pressure (PEEP) counteracts oedema formation. We expected oedema formation to increase weight and decrease compliance of the lungs on the basis of a decrease in alveolar volume as fluid replaces alveolar air spaces. The pulmonary artery of 28 isolated porcine lungs was perfused with a low-potassium dextrane solution at low (mean 27 mmHg) or high (mean 40 mmHg) pulmonary artery pressure (PAP) during mechanical ventilation at low (4 cmH(2)O) or high (8 cmH(2)O) PEEP, respectively. Following perfusion and storage, relative increases in lung weight were smaller (p < 0.05) during perfusion at low PAP (62 +/- 32% and 42 +/- 26%, respectively) compared to perfusion at high PAP (133 +/- 54% and 87 +/- 30%, respectively). Compared to all other PAP-PEEP combinations, increases in lung weight were smallest (44 +/- 9% and 27 +/- 12%, respectively), nonlinear intratidal lung compliance was largest (46% and 17% respectively, both p < 0.05) and lung histology showed least infiltration of mononuclear cells in the alveolar septa, and least alveolar destruction during the combination of low perfusion pressure and high PEEP. The findings suggest that oedema formation during pulmonary artery flush perfusion in isolated and ventilated lungs can be reduced by choosing low perfusion pressure and high PEEP. PAP-PEEP titration to minimize pulmonary oedema should be based on lung mechanics and PAP monitoring.

Polymorphisms of human vascular endothelial growth factor gene in high-altitude pulmonary oedema susceptible subjects

BACKGROUND AND OBJECTIVE

Based on the reported biological properties and function of vascular endothelial growth factor (VEGF) in hypoxic conditions, many investigations have studied the hypothesis that VEGF has an important role in the pathogenesis of high altitude sicknesses, including high-altitude pulmonary oedema (HAPE). Unfortunately, the results are inconsistent. Therefore, the association of VEGF gene single nucleotide polymorphisms (SNP) with being susceptible to HAPE was investigated.

METHODS

The study included 53 HAPE-susceptible subjects (HAPE-s) and 69 HAPE-resistant mountaineer controls (HAPE-r). Subjects were Japanese and the two groups were comparable in terms of age and gender. The SNP of the VEGF gene, namely C-2578A, G-1154A and T-460C in the promoter, G + 405C in the 5'-untranslated region and C936T in the 3'-untranslated region, were examined by allele discrimination experiments. In addition, arterial oxygen tension (PaO(2)) and pulmonary haemodynamic data were available for 21 of the HAPE-s subjects.

RESULTS

There were no statistically significant differences in the allele frequencies, genotype distributions or haplotype frequencies of VEGF SNP between the HAPE-s and HAPE-r groups. Furthermore, neither PaO(2) nor pulmonary haemodynamic parameters were associated with the VEGF SNP in the 21 HAPE-s subjects.

CONCLUSIONS

This genetic study did not provide evidence that functional SNP of the VEGF gene are associated with susceptibility to HAPE in a Japanese population.