High-altitude Pulmonary Edema Susceptibility Research Articles

TNF-α and RPLP0 drive the apoptosis of endothelial cells and increase susceptibility to high-altitude pulmonary edema

High-altitude pulmonary edema (HAPE) is a fatal threat for sojourners who ascend rapidly without sufficient acclimatization. Acclimatized sojourners and adapted natives are both insensitive to HAPE but have different physiological traits and molecular bases. In this study, based on GSE52209, the gene expression profiles of HAPE patients were compared with those of acclimatized sojourners and adapted natives, with the common and divergent differentially expressed genes (DEGs) and their hub genes identified, respectively. Bioinformatic methodologies for functional enrichment analysis, immune infiltration, diagnostic model construction, competing endogenous RNA (ceRNA) analysis and drug prediction were performed to detect potential biological functions and molecular mechanisms. Next, an array of in vivo experiments in a HAPE rat model and in vitro experiments in HUVECs were conducted to verify the results of the bioinformatic analysis. The enriched pathways of DEGs and immune landscapes for HAPE were significantly different between sojourners and natives, and the common DEGs were enriched mainly in the pathways of development and immunity. Nomograms revealed that the upregulation of TNF-α and downregulation of RPLP0 exhibited high diagnostic efficiency for HAPE in both sojourners and natives, which was further validated in the HAPE rat model. The addition of TNF-α and RPLP0 knockdown activated apoptosis signaling in endothelial cells (ECs) and enhanced endothelial permeability. In conclusion, TNF-α and RPLP0 are shared biomarkers and molecular bases for HAPE susceptibility during the acclimatization/adaptation/maladaptation processes in sojourners and natives, inspiring new ideas for predicting and treating HAPE.

Preliminary study of identified novel susceptibility loci for HAPE risk in a Chinese male Han population.

High altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema. In recent years, association studies have become the main method for identifying HAPE genetic loci. A genome-wide association study (GWAS) of HAPE risk-associated loci was performed in Chinese male Han individuals (164 HAPE cases and 189 healthy controls) by the Precision Medicine Diversity Array Chip with 2,771,835 loci (Applied Biosystems Axiom™). Eight overlapping candidate loci in CCNG2, RP11-445O3.2, NUPL1 and WWOX were finally selected. In silico functional analyses displayed the PPI network, functional enrichment and signal pathways related to CCNG2, NUPL1, WWOX and NRXN1. This study provides data supplements for HAPE susceptibility gene loci and new insights into HAPE susceptibility.

Asymmetric and symmetric dimethylarginine in high altitude pulmonary hypertension (HAPH) and high altitude pulmonary edema (HAPE)

Introduction: High altitude exposure may lead to high altitude pulmonary hypertension (HAPH) and high altitude pulmonary edema (HAPE). The pathophysiologic processes of both entities have been linked to decreased nitric oxide (NO) availability.Methods: We studied the effect of acute high altitude exposure on the plasma concentrations of asymmetric (ADMA) and symmetric dimethylarginine (SDMA), L-arginine, L-ornithine, and L-citrulline in two independent studies. We further investigated whether these biomarkers involved in NO metabolism were related to HAPH and HAPE, respectively. Fifty (study A) and thirteen (study B) non-acclimatized lowlanders were exposed to 4,559 m for 44 and 67 h, respectively. In contrast to study A, the participants in study B were characterized by a history of at least one episode of HAPE. Arterial blood gases and biomarker concentrations in venous plasma were assessed at low altitude (baseline) and repeatedly at high altitude. HAPE was diagnosed by chest radiography, and HAPH by measuring right ventricular to atrial pressure gradient (RVPG) with transthoracic echocardiography. AMS was evaluated with the Lake Louise Score (LLS) and the AMS-C score.Results: In both studies SDMA concentration significantly increased at high altitude. ADMA baseline concentrations were higher in individuals with HAPE susceptibility (study B) compared to those without (study A). However, upon high altitude exposure ADMA only increased in individuals without HAPE susceptibility, while there was no further increase in those with HAPE susceptibility. We observed an acute and transient decrease of L-ornithine and a more delayed but prolonged reduction of L-citrulline during high altitude exposure. In both studies SDMA positively correlated and L-ornithine negatively correlated with RVPG. ADMA was significantly associated with the occurrence of HAPE (study B). ADMA and SDMA were inversely correlated with alveolar PO2, while L-ornithine was inversely correlated with blood oxygenation and haemoglobin levels, respectively.Discussion: In non-acclimatized individuals ADMA and SDMA, two biomarkers decreasing endothelial NO production, increased after acute exposure to 4,559 m. The observed biomarker changes suggest that both NO synthesis and arginase pathways are involved in the pathophysiology of HAPH and HAPE.

Suggestive evidence of CYP4F2 gene polymorphisms with HAPE susceptibility in the Chinese Han population.

High altitude pulmonary edema (HAPE) is a common respiratory disease in the high altitude area, which is rapid and harmful. We firstly conducted a case-control study to assess the potential association of CYP4F2 gene polymorphisms with HAPE susceptibility in the Chinese Han population. The study recruited 238 patients with HAPE and 230 healthy controls in Northwest China. Genomic DNA was extracted from blood samples, and gene polymorphisms were detected using the Agena MassARRAY platform. Odds ratios (ORs), 95% confidence intervals (95% CIs), and P-value were used to evaluate the relationship between HAPE risk and CYP4F2 gene polymorphisms. Multi-factor dimension reduction (MDR) was used to assess the optimal interaction of CYP4F2 gene polymorphisms on HAPE risk. We found rs3093193 was shown to reduce the risk of HAPE (OR = 0.70, 95% CI = 0.52-0.93, P = 0.014), while rs12459936 was increased the susceptibility to HAPE (OR = 2.08, 95% CI = 1.33-3.26, P = 0.001). Age stratified analysis revealed that rs3093193 and rs12459936 were correlated with HAPE risk in people at age > 32 years old, and rs3093193 and rs3093110 were correlated with the HAPE risk in people at age ≤ 32 years old. Gender stratification analysis was found that rs3093193, rs12459936, and rs3093110 were all related to HAPE risk in males. A combination of rs12459936 and rs3093110 was the best multi-loci model with the highest testing accuracy. Our study is the first to provide the association between CYP4F2 gene polymorphisms and HAPE risk in the Chinese Han population.

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.

Unique mutations in mitochondrial DNA and associated pathways involved in high altitude pulmonary edema susceptibility in Indian lowlanders

High altitude pulmonary edema (HAPE) is a life threatening non-cardiogenic pulmonary edema that occurs in an otherwise healthy individuals travelling to altitude above 2500 m. Earlier studies have reported association of mutations in nuclear (nDNA) and mitochondrial DNA (mtDNA) with HAPE susceptibility. However, the molecular mechanisms involved in the pathobiology of HAPE have not been fully understood. The present study investigates the genetic predisposition to HAPE by analyzing the mtDNA mutations in HAPE susceptibles (n = 23) and acclimatized controls (n = 23) using next generation sequencing. Structural analysis of mutations was done using SWISS Model server and stability was determined using ΔΔG values. Meta-analysis of GSE52209 dataset was done to identify differentially expressed genes (DEGs) in HAPE susceptibles and acclimatized controls. Fourteen non-synonymous, conserved and pathogenic mutations were predicted using SIFT and PolyPhen scoring in protein coding genes, whereas six mutations in mt-tRNA genes showed association with HAPE (p ≤ 0.05). The structural analysis of these mutations revealed conformational changes in critical regions in Complexes I–V which are involved in subunit assembly and proton pumping activity. The protein–protein interaction network analysis of DEGs showed that HIF1α, EGLN2, EGLN3, PDK1, TFAM, PPARGC1α and NRF1 genes form highly interconnected cluster. Further, pathway enrichment analysis using DAVID revealed that “HIF-1 signaling”, “oxidative phosphorylation” and “Metabolic pathways” had strong association with HAPE. Based on the findings it appears that the identified mtDNA mutations may be a potential risk factor in development of HAPE with the associated pathways providing mechanistic insight into the understanding of pathobiology of HAPE and sites for development of therapeutic targets. Communicated by Ramaswamy H. Sarma

MIR17HG polymorphisms contribute to high-altitude pulmonary edema susceptibility in the Chinese population

High-altitude pulmonary edema (HAPE) is a common acute altitude sickness. This study was designed to investigate the effect of MIR17HG polymorphisms on HAPE risk in the Chinese population. The Agena MassARRAY platform was used to genotype six single-nucleotide polymorphisms (SNPs) in the MIR17HG gene in 244 HAPE patients and 243 non-HAPE controls. The odds ratio (OR) and 95% confidence interval were used to evaluate the association between each MIR17HG polymorphisms and the risk of HAPE under a polygenetic model. Statistical analysis was performed using the χ2 test. Multifactor dimensionality reduction (MDR) analysis was used to analyze the impacts of SNP–SNP interactions on the risk of HAPE. According to the allele model, the HAPE risk of people with the rs7318578 A allele of MIR17HG was lower than that of people with the C allele (OR 0.74, p = 0.036).Logistic regression analysis of four models for all selected MIR17HG SNPs showed significant differences in the frequencies of rs7318578 (OR 0.74, p = 0.037) and rs17735387 (OR 1.51, p = 0.036) between cases and controls. The results of the sex stratification analysis showed that among males, rs17735387 in the MIR17HG gene is associated with an increased risk of HAPE. MDR analysis showed that the best combination model was a three-locus model incorporating rs72640334, rs7318578, and rs7336610. This study revealed the correlations between rs7318578 and rs17735387 on the MIR17HG gene and the risk of HAPE in the Chinese population, providing a theoretical basis for the early screening, prevention, and diagnosis of HAPE in high-risk populations.

Association Between the Polymorphism of Steroid Hormone Metabolism Genes and High-Altitude Pulmonary Edema in the Chinese Han Population.

PurposeSteroid hormone metabolism plays an essential role in high-altitude pulmonary edema (HAPE) progression. This study aimed to investigate the association between polymorphism in seven steroid hormone metabolism genes (STAR, HSD3B1, HSD3B2, CYP17A1, CYP21A2, CYP11B1, and CYP11B2) and HAPE susceptibility among Han Chinese.Patients and MethodsA total of 41 tagSNPs in the seven genes were genotyped using Sequenom MassARRAY SNP assays from 169 HAPE patients (HAPE-p) and 309 matched Han Chinese individuals resistant to HAPE (HAPE-r). The genotypic and allele frequencies, odds ratios (ORs), and 95% confidence intervals (95% CIs) were calculated.ResultsFour SNPs, including the allele C of rs6203 (p = 0.034, OR [95% CI] = 1.344 [1.022−1.767]) in HSD3B1, allele G of rs3740397 (p = 0.044, OR [95% CI] = 1.314 [1.007−1.714]) and allele C of rs10786712 (p = 0.039, OR [95% CI] = 0.751 [0.572−0.986]) in CYP17A1, and allele T of rs6402 (p = 0.006, OR [95% CI] = 0.504 [0.306−0.830]) in CYP11B1, were significantly associated with HAPE. The distribution of the genotypes of these SNPs also significantly differed between the HAPE-p and HAPE-r groups. Moreover, six haplotypes (the linkage disequilibrium block including rs10883783, rs4919686, rs3740397, rs3824755, and rs10786712) of CYP17A1 were also significantly associated with HAPE.ConclusionThe four SNPs located in HSD3B1 (rs6203), CYP17A1 (rs3740397 and rs10786712), and CYP11B1 (rs6402) and the six haplotypes of CYP17A1 are likely to have an effect on HAPE.

Mitochondrial DNA mutations contribute to high altitude pulmonary edema via increased oxidative stress and metabolic reprogramming during hypobaric hypoxia

High altitude pulmonary edema (HAPE) is experienced by non-acclimatized sea level individuals on exposure to high altitude hypoxic conditions. Available evidence suggests that genetic factors and perturbed mitochondrial redox status may play an important role in HAPE pathophysiology. However, the precise mechanism has not been fully understood. In the present study, sequencing of mitochondrial DNA (mtDNA) from HAPE subjects and acclimatized controls was performed to identify pathogenic mutations and to determine their role in HAPE. Hypobaric hypoxia induced oxidative stress and metabolic alterations were also assessed in HAPE subjects. mtDNA copy number, mitochondrial oxidative phosphorylation (mtOXPHOS) activity, mitochondrial biogenesis were measured to determine mitochondrial functions. The data revealed that the mutations in Complex I genes affects the secondary structure of protein in HAPE subjects. Further, increased oxidative stress during hypobaric hypoxia, reduced mitochondrial biogenesis and mtOXPHOS activity induced metabolic reprogramming appears to contribute to mitochondrial dysfunctions in HAPE individuals. Haplogroup analysis suggests that mtDNA haplogroup H2a2a1 has potential contribution in the pathobiology of HAPE in lowlanders. This study also suggests contribution of altered mitochondrial functions in HAPE susceptibility.

Association between CYP2C19 gene polymorphisms and susceptibility to high-altitude pulmonary edema.

High-altitude pulmonary edema (HAPE) is caused by the interaction of both genetic and environmental risk factors. In this study, we aimed to explore whether three single nucleotide polymorphisms (SNPs) in CYP2C19 gene influenced the HAPE susceptibility in the Chinese Han population. We recruited 238 cases and 230 controls between January 2018 and October 2018 from the Affiliated Hospital of Xizang Minzu University. The relationship between CYP2C19 gene polymorphisms and HAPE was studied by association analysis. Genotyping was performed using the Agena MassARRAY platform and the statistical analysis was performed using Chi-squared test, independent sample t test, genetic model analysis and haplotype analysis. The main finding of our study showed that rs4494250 in CYP2C19 gene was associated with an increased risk of HAPE at age>32years in the log-additive model (OR=1.80, 95% CI=1.05-3.09, P=0.033). Also, it was observed to be associated with a reduced risk of HAPE at age≤2years in the dominant model (A/G-A/A vs G/G, OR=0.55, 95% CI=0.31-0.97, P=0.038) and in the log-additive model (OR=0.58, 95% CI=0.35-0.96, P=0.033). Our findings demonstrated that CYP2C19 genetic variants were associated with risk of developing HAPE in Han Chinese population.

Mitochondrial DNA sequencing reveals association of variants and haplogroup M33a2\u20323 with High altitude pulmonary edema susceptibility in Indian male lowlanders

High Altitude Pulmonary Edema (HAPE) is a threatening disorder caused due to acute exposure to high altitude above 3000 m. Apart from multiple factors involved, the genetic factors also play an important function in the pathogenesis of HAPE. This study aims to evaluate the role of mtDNA polymorphism and their association with haplogroup in understanding the etiology of HAPE. In this study, all the HAPE susceptible and acclimatized control subjects could be classified into nine haplogroups pertaining mostly to Macrohaplogroup M and U. The frequency of haplogroup M was significantly higher in HAPE susceptibles whereas the haplogroup M33a2′3 was found only in HAPE susceptibles. The variant G4491A and A4944G of MT-ND2, A14002G of MT-ND5, and C8562T of MT-ATP8, were definition site of haplogroup M33a2′3. The frequency of A10398G of MT-ND3, A8701G of MT-ATP6 and C14766T of MT-CYB genes were significantly higher in HAPE susceptibles. mtDNA copy number also plays a significant synergistic role in HAPE susceptibility. Our findings suggests that variants in MT-ND2 and MT-ND5 were predicted to confer decreased protein stability in HAPE susceptibles and in particular, highly conserved variants G4491A, A4944G and A14002G associated with haplogroup M33a2′3 may be the primary cause of susceptibility to HAPE in Indian male lowlanders.

High Altitude Pulmonary Edema in Children: A Single Referral Center Evaluation

To describe the clinical features of children who presented to Children's Hospital Colorado (CHCO) with high-altitude pulmonary edema (HAPE). We performed a retrospective chart review in children discharged from CHCO (an elevation of 1668m) with a clinical diagnosis of HAPE and a chest radiograph consistent with noncardiogenic pulmonary edema. Descriptive statistics were used to describe the demographics, presentations, and treatment strategies. From 2004 to 2014, 50 children presented to CHCO who were found to have a clinical diagnosis of HAPE and a chest radiograph consistent with noncardiogenic pulmonary edema. Most (72%) patients were male, and most (60%) of the children in the study were diagnosed with classic HAPE, 38% with re-entry HAPE, and 2% with high altitude resident pulmonary edema. Elevation at symptom presentation ranged from 1840 to 3536m. Patients were treated with a variety of medications, including diuretics, steroids, and antibiotics. Four patients were newly diagnosed with structural heart findings: 2 patients with patent foramen ovale and 2 with atrial septal defects. Eleven patients had findings consistent with pulmonary hypertension at the time of echocardiography. HAPE symptoms may develop below 2500m, so providers should not rule out HAPE based on elevation alone. Structural heart findings and pulmonary hypertension are associated with HAPE susceptibility and their presence may inform treatment. Inappropriate use of antibiotics and diuretics in children with HAPE suggest that further education of providers is warranted.

NR3C2 Gene is Associated with Susceptibility to High-Altitude Pulmonary Edema in Han Chinese

The mineralocorticoid receptor is encoded by the NR3C2 gene and plays an important role in regulating vascular tone in high-altitude pulmonary edema (HAPE). This study aimed to investigate the association of the polymorphisms in the NR3C2 gene with HAPE susceptibility in Han Chinese. We enrolled 133 HAPE patients and 131 matched healthy Han Chinese from the Yushu area in Qinghai, where the altitude is greater than 3500 m. Two single nucleotide polymorphisms (SNPs) of the NR3C2 gene, rs2070951 and rs5522, were genotyped by the Sequenom MassARRAY SNP assay. The genotypic distributions and allele frequencies of NR3C2 SNP rs5522 were significantly different between the HAPE and control groups (P<0.05). The frequency of the A allele of rs5522 was significantly higher in the HAPE group than in the control group (P<0.05) with an odds ratio of 1.7 (95% CI: 1.0-2.8). There were no significant differences in the genotypic distributions and allele frequencies of NR3C2 SNP rs2070951 between the HAPE and control groups. The frequencies of the C-A and C-G haplotypes were significantly higher in the HAPE group than in control group. The rs5522 polymorphism of the NR3C2 gene was associated with HAPE susceptibility in Chinese subjects. The A allele may contribute to the susceptibility to HAPE. The frequency of the C-A and C-G haplotypes of rs2070951 and rs5522 in the NR3C2 gene may increase the risk of HAPE.

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.

Subclinical pulmonary dysfunction contributes to high altitude pulmonary edema susceptibility in healthy non-mountaineers

HAPE susceptible (HAPE-S, had HAPE episode in past) subjects may have subclinical cardio-pulmonary dysfunction. We compared the results of pulmonary function tests in 25 healthy HAPE-S non-mountaineers and 19 matched HAPE resistant (HAPE-R, no HAPE episode in past). Acute normobaric hypoxia (FIo2 0.12) was administered at sea level to confirm hypoxia intolerance in HAPE-S. Unlike HAPE-R, HAPE-S subjects had elevated baseline and post-hypoxia systolic pulmonary arterial pressures (20.9 ± 3 vs 27.3 ± 5 mm Hg during normoxia and 26.2 ± 6 vs 45.44 ± 10 mm Hg during hypoxia, HAPE-R vs HAPE-S). Forced vital capacity (FVC) and single breath alveolar volume (SBVA) were significantly lower in HAPE-S compared to HAPE-R (FVC: 4.33 ± 0.5 vs 4.6 ± 0.4; SBVA: 5.17 ± 1 vs 5.6 ± 1 Lt; HAPE-S vs HAPE-R). Two subgroups with abnormal pulmonary function could be identified within HAPE-S; HAPE-S1 (n = 4) showed DLCO>140% of predicted, suggestive of asthma and HAPE-S2 (n = 12) showed restrictive pattern. Each of these patterns have previously been linked to early small airway disease and may additionally represent a lower cross-sectional area of the pulmonary vascular bed, related to lower lung volumes. HAPE susceptibility in healthy non-mountaineers may be related to sub-clinical pulmonary pathology that limits compensatory rise in ventilation and pulmonary circulation during hypoxic stress.

Genome-wide association study of high-altitude pulmonary edema in a Han Chinese population.

A two-stage genome-wide association study (GWAS) was performed to identify and analyze genes and single nucleotide polymorphisms (SNPs) associated with high-altitude pulmonary edema (HAPE) in a Han Chinese patient population. In the first stage, DNA samples from 68 patients with recurrent HAPE were scanned using Affymetrix SNP Array 6.0 Chips, and allele frequencies were compared to those of 84 HapMap CHB samples to identify candidate SNPs. In the second stage, the 77 identified candidate SNPs were examined in an independent cohort of samples from 199 HAPE patients and 304 controls. Associations between SNPs and HAPE risk were tested using various genetic models. Of the 77 original SNPs, 7 were found to be associated with HAPE susceptibility in the second stage of the study. GO and pathway enrichment analysis of the 7 SNPs revealed 5 adjacent genes involved in various processes, including regulation of nucleoside diphosphate metabolism, thyroid hormone catabolism, and low-density lipoprotein receptor activity. These results suggest the identified SNPs and genes may contribute to the physiopathology of HAPE.

Susceptibility to high-altitude pulmonary edema is associated with a more uniform distribution of regional specific ventilation.

High-altitude pulmonary edema (HAPE) is a potentially fatal condition affecting high-altitude sojourners. The biggest predictor of HAPE development is a history of prior HAPE. Magnetic resonance imaging (MRI) shows that HAPE-susceptible (with a history of HAPE), but not HAPE-resistant (with a history of repeated ascents without illness) individuals develop greater heterogeneity of regional pulmonary perfusion breathing hypoxic gas (O2 = 12.5%), consistent with uneven hypoxic pulmonary vasoconstriction (HPV). Why HPV is uneven in HAPE-susceptible individuals is unknown but may arise from regionally heterogeneous ventilation resulting in an uneven stimulus to HPV. We tested the hypothesis that ventilation is more heterogeneous in HAPE-susceptible subjects (n = 6) compared with HAPE-resistant controls (n = 7). MRI specific ventilation imaging (SVI) was used to measure regional specific ventilation and the relative dispersion (SD/mean) of SVI used to quantify baseline heterogeneity. Ventilation heterogeneity from conductive and respiratory airways was measured in normoxia and hypoxia (O2 = 12.5%) using multiple-breath washout and heterogeneity quantified from the indexes Scond and Sacin, respectively. Contrary to our hypothesis, HAPE-susceptible subjects had significantly lower relative dispersion of specific ventilation than the HAPE-resistant controls [susceptible = 1.33 ± 0.67 (SD), resistant = 2.36 ± 0.98, P = 0.05], and Sacin tended to be more uniform (susceptible = 0.085 ± 0.009, resistant = 0.113 ± 0.030, P = 0.07). Scond was not significantly different between groups (susceptible = 0.019 ± 0.007, resistant = 0.020 ± 0.004, P = 0.67). Sacin and Scond did not change significantly in hypoxia (P = 0.56 and 0.19, respectively). In conclusion, ventilation heterogeneity does not change with short-term hypoxia irrespective of HAPE susceptibility, and lesser rather than greater ventilation heterogeneity is observed in HAPE-susceptible subjects. This suggests that the basis for uneven HPV in HAPE involves vascular phenomena.NEW & NOTEWORTHY Uneven hypoxic pulmonary vasoconstriction (HPV) is thought to incite high-altitude pulmonary edema (HAPE). We evaluated whether greater heterogeneity of ventilation is also a feature of HAPE-susceptible subjects compared with HAPE-resistant subjects. Contrary to our hypothesis, ventilation heterogeneity was less in HAPE-susceptible subjects and unaffected by hypoxia, suggesting a vascular basis for uneven HPV.

Elevated pulmonary artery pressure and brain natriuretic peptide in high altitude pulmonary edema susceptible non-mountaineers.

Exaggerated pulmonary pressor response to hypoxia is a pathgonomic feature observed in high altitude pulmonary edema (HAPE) susceptible mountaineers. It was investigated whether measurement of basal pulmonary artery pressure (Ppa) and brain natriuretic peptide (BNP) could improve identification of HAPE susceptible subjects in a non-mountaineer population. We studied BNP levels, baseline hemodynamics and the response to hypoxia (FIo2 = 0.12 for 30 min duration at sea level) in 11 HAPE resistant (no past history of HAPE, Control) and 11 HAPE susceptible (past history of HAPE, HAPE-S) subjects. Baseline Ppa (19.31 ± 3.63 vs 15.68 ± 2.79 mm Hg, p < 0.05) and plasma BNP levels (52.39 ± 32.9 vs 15.05 ± 9.6 pg/ml, p < 0.05) were high and stroke volume was less (p < 0.05) in HAPE-S subjects compared to control. Acute hypoxia produced an exaggerated increase in heart rate (p < 0.05), mean arterial pressure (p < 0.05) and Ppa (28.2 ± 5.8 vs 19.33 ± 3.74 mm Hg, p < 0.05) and fall in peripheral oxygen saturation (p < 0.05) in HAPE-S compared to control. Receiver operating characteristic (ROC) curves showed that Ppa response to acute hypoxia was the best variable to identify HAPE susceptibility (AUC 0.92) but BNP levels provided comparable information (AUC 0.85). BNP levels are easy to determine and may represent an important marker for the determination of HAPE susceptibility.

Soluble Urokinase-Type Plasminogen Activator Receptor Plasma Concentration May Predict Susceptibility to High Altitude Pulmonary Edema.

Introduction. Acute exposure to high altitude induces inflammation. However, the relationship between inflammation and high altitude related illness such as high altitude pulmonary edema (HAPE) and acute mountain sickness (AMS) is poorly understood. We tested if soluble urokinase-type plasminogen activator receptor (suPAR) plasma concentration, a prognostic factor for cardiovascular disease and marker for low grade activation of leukocytes, will predict susceptibility to HAPE and AMS. Methods. 41 healthy mountaineers were examined at sea level (SL, 446 m) and 24 h after rapid ascent to 4559 m (HA). 24/41 subjects had a history of HAPE and were thus considered HAPE-susceptible (HAPE-s). Out of the latter, 10/24 HAPE-s subjects were randomly chosen to suppress the inflammatory cascade with dexamethasone 8 mg bid 24 h prior to ascent. Results. Acute hypoxic exposure led to an acute inflammatory reaction represented by an increase in suPAR (1.9 ± 0.4 at SL versus 2.3 ± 0.5 at HA, p < 0.01), CRP (0.7 ± 0.5 at SL versus 3.6 ± 4.6 at HA, p < 0.01), and IL-6 (0.8 ± 0.4 at SL versus 3.3 ± 4.9 at HA, p < 0.01) in all subjects except those receiving dexamethasone. The ascent associated decrease in PaO2 correlated with the increase in IL-6 (r = 0.46, p < 0.001), but not suPAR (r = 0.27, p = 0.08); the increase in IL-6 was not correlated with suPAR (r = 0.16, p = 0.24). Baseline suPAR plasma concentration was higher in the HAPE-s group (2.0 ± 0.4 versus 1.8 ± 0.4, p = 0.04); no difference was found for CRP and IL-6 and for subjects developing AMS. Conclusion. High altitude exposure leads to an increase in suPAR plasma concentration, with the missing correlation between suPAR and IL-6 suggesting a cytokine independent, leukocyte mediated mechanism of low grade inflammation. The correlation between IL-6 and PaO2 suggests a direct effect of hypoxia, which is not the case for suPAR. However, suPAR plasma concentration measured before hypoxic exposure may predict HAPE susceptibility.

Hypoxia-Induced Inflammatory Chemokines in Subjects with a History of High-Altitude Pulmonary Edema.

High altitude hypoxia is known to induce an inflammatory response in immune cells. Hypoxia induced inflammatory chemokines may contribute to the development of high altitude pulmonary edema (HAPE) by causing damage to the lung endothelial cells and thereby capillary leakage. In the present study, we were interested to know whether chronic inflammation may contribute to HAPE susceptibility. We examined the serum levels of macrophage inflammatory protein-1α (MIP-1α), monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 in group (1) HAPE Susceptible subjects(n=20) who had past history of HAPE and group (2) Control (n=18) consist of subjects who had stayed at high altitude for 2years without any history of HAPE. The data obtained confirmed that circulating MCP-1, MIP-1α were significantly upregulated in HAPE-S individuals as compared to the controls suggestive of chronic inflammation. However, it is not certain whether chronic inflammation is cause or consequence of previous episode of HAPE. The moderate systemic increase of these inflammatory markers may reflect considerable local inflammation. The existence of enhanced level of inflammatory chemokines found in this study support the hypothesis that subjects with past history of HAPE have higher baseline chronic inflammation which may contribute to HAPE susceptibility.