Pulmonary hemodynamics: implications for high altitude pulmonary edema (HAPE). A review

COVID-19 and Pneumolysis Simulating Extreme High-altitude Exposure with Altered Oxygen Transport Physiology; Multiple Diseases, and Scarce Need of Ventilators: Andean Condor's-eye-view

BACKGROUND

Critical hypoxia in this COVID-19 pandemic results in high mortality and economic loss worldwide. Initially, this disease' pathophysiology was poorly understood and interpreted as a SARS (Severe Acute Respiratory Syndrome) pneumonia. The severe atypical lung CAT scan images alerted all countries, including the poorest, to purchase lacking sophisticated ventilators. However, up to 88% of the patients on ventilators lost their lives. It was suggested that COVID-19 could be similar to a High-Altitude Pulmonary Edema (HAPE). New observations and pathological findings are gradually clarifying the disease.

METHODS

As high-altitude medicine and hypoxia physiology specialists working and living in the highlands for over 50 years, we perform a perspective analysis of hypoxic diseases treated at high altitudes and compare them to Covid-19. Oxygen transport physiology, SARS-Cov-2 characteristics, and its transmission, lung imaging in COVID-19, and HAPE, as well as the causes of clinical signs and symptoms, are discussed.

RESULTS

High-altitude oxygen transport physiology has been systematically ignored. COVID-19 signs and symptoms indicate a progressive and irreversible failure in the oxygen transport system, secondary to pneumolysis produced by SARS-Cov-2's alveolar-capillary membrane "attack". HAPE's pulmonary compromise is treatable and reversible. COVID-19 is associated with several diseases, with different individual outcomes, in different countries, and at different altitudes.

CONCLUSIONS

The pathophysiology of High-altitude illnesses can help explain COVID-19 pathophysiology, severity, and management. Early diagnosis and use of EPO, acetylsalicylic-acid, and other anti-inflammatories, oxygen therapy, antitussives, antibiotics, and the use of Earth open-circuit- astronaut-resembling suits to return to daily activities, should all be considered. Ventilator use can be counterproductive. Immunity development is the only feasible long-term survival tool.

Polymorphisms of the tissue inhibitor of metalloproteinase 3 gene are associated with resistance to high-altitude pulmonary edema (HAPE) in a Japanese population: a case control study using polymorphic microsatellite markers

Introduction

High-altitude pulmonary edema (HAPE) is a hypoxia-induced, life-threatening, high permeability type of edema attributable to pulmonary capillary stress failure. Genome-wide association analysis is necessary to better understand how genetics influence the outcome of HAPE.

Materials and Methods

DNA samples were collected from 53 subjects susceptible to HAPE (HAPE-s) and 67 elite Alpinists resistant to HAPE (HAPE-r). The genome scan was carried out using 400 polymorphic microsatellite markers throughout the whole genome in all subjects. In addition, six single nucleotide polymorphisms (SNPs) of the gene encoding the tissue inhibitor of metalloproteinase 3 (TIMP3) were genotyped by Taqman® SNP Genotyping Assays.

Results

The results were analyzed using case-control comparisons. Whole genome scanning revealed that allele frequencies in nine markers were statistically different between HAPE-s and HAPE-r subjects. The SNP genotyping of the TIMP3 gene revealed that the derived allele C of rs130293 was associated with resistance to HAPE [odds ratio (OR) = 0.21, P = 0.0012) and recessive inheritance of the phenotype of HAPE-s (P = 0.0012). A haplotype CAC carrying allele C of rs130293 was associated with resistance to HAPE.

Discussion

This genome-wide association study revealed several novel candidate genes associated with susceptibility or resistance to HAPE in a Japanese population. Among those, the minor allele C of rs130293 (C/T) in the TIMP3 gene was linked to resistance to HAPE; while, the ancestral allele T was associated with susceptibility to HAPE.

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.

Low-dose theophylline reduces symptoms of acute mountain sickness

OBJECTIVE

Headache, nausea, and sleeplessness at altitude [acute mountain sickness (AMS)] are major health problems for several million mountain recreationists who ascend to high altitudes each year. We aimed to test the efficacy of low-dose, slow-release theophylline for the prevention of AMS in a placebo-controlled, double-blind, randomized trial.

METHODS

Twenty healthy male volunteers (mean age 34.7 y) were randomized (random allocation) to receive either 300 mg theophylline daily or placebo 5 days prior, during ascent, and during a stay at 4,559 m altitude. AMS symptoms were collected using the Lake Louise Score on each day during ascent and at high altitude. A 12-channel sleep recorder recorded sleep and breathing parameters during the first night at 4,559 m. Theophylline serum levels were drawn prior to the sleep study.

RESULTS

Seventeen completed the entire study. Theophylline (n = 9) compared to placebo (n = 8) significantly reduced AMS symptoms at 4,559 m (Lake Louise Score: 1.5 +/- 0.5 vs placebo 2.3 +/- 2.37; p < 0.001), events of periodic breathing (34.3/h vs placebo 74.2/h; p < 0.05), and oxygen desaturations (62.3/h vs placebo 121.6/h; p < 0.01). No significant differences in sleep efficiency or sleep structure were present in the two groups. No adverse drug effects were reported.

CONCLUSIONS

Low-dose, slow-release theophylline reduces symptoms of AMS in association with alleviation of events of periodic breathing and oxygen desaturations.

Pathogenesis of high altitude pulmonary edema: does alveolar epithelial lining fluid vascular endothelial growth factor exacerbate capillary leak?

Vascular endothelial growth factor (VEGF) is a potent mediator of capillary leak if it gains access to its receptors on the capillary endothelium. We have observed that there are high levels of VEGF compartmentalized in the alveolar epithelial lining fluid of normal humans at levels 500-fold greater than plasma. The potential for high altitude to result in compromise of alveolar epithelial tight junctions and experimental animal studies in which pulmonary edema is induced when VEGF is overexpressed in the alveolar epithelium, suggest a mechanism. We hypothesize that when the epithelial barrier is compromised at high altitude the normally high level of VEGF in the alveolar epithelial fluid has access to the pulmonary endothelium, where it acutely alters permeability, markedly exacerbating the high permeability pulmonary edema that characterizes high altitude pulmonary edema. If correct, this paradigm opens the possibility of testing available anti-VEGF therapies to treat this potentially fatal disorder.

High altitude headache: efficacy of acetaminophen vs. ibuprofen in a randomized, controlled trial

Ibuprofen has been shown to be more effective than placebo in the treatment of high altitude headache (HAH), but nonsteroidal anti-inflammatory agents have been linked to increased incidence of gastrointestinal (GI) side effects and high-altitude pulmonary edema (HAPE). We postulated that acetaminophen, which does not share ibuprofen's theorized causal link to GI side effects or HAPE, could provide effective HAH therapy. We conducted a prospective, randomized, double-blind, clinical trial of ibuprofen vs. acetaminophen in the Solu Khumbu, Nepal: Mt. Everest Base Camp, Pheriche, Dingboche (4240 m to 5315 m). Seventy-four consecutive patients (ages 13 to 61 years) were randomized, were assessed with the Lake Louise Acute Mountain Sickness (AMS) criteria, and received a physical examination (which included vital signs, oxygen saturation as measured by pulse oximetry (SpO(2)), and assessment of clinical Lake Louise AMS criteria). Patients then received either 400 mg of ibuprofen (IBU) or 1000 mg of acetaminophen (ACET), and were asked to rate their cephalgia using a 10-cm visual analog scale (VAS). Thirty-nine patients received IBU, and 35 received ACET. Baseline Lake Louise AMS scores were identical in the two groups (mean = 5.9). No differences in mean VAS scores between IBU and ACET groups were noted at time 0 (presentation), 30, 60, or 120 min. No cases of HAPE or high altitude cerebral edema were noted during the study period. In this study population, acetaminophen was as effective as ibuprofen in relieving the pain of HAH.

Vascular endothelial growth factor in patients with high-altitude pulmonary edema

To examine the role of VEGF in the pathogenesis of high-altitude pulmonary edema (HAPE), we measured the concentrations of VEGF in venous serum and bronchoalveolar lavage fluid in patients with HAPE and in healthy volunteers. The VEGF in venous serum of the patients was normal at admission and significantly increased at recovery. Similarly, the VEGF in bronchoalveolar lavage fluid of the patients was increased at recovery compared with admission, but values at both admission and recovery were significantly lower than those of the controls. The present finding suggests that VEGF probably is destroyed in the lung of HAPE, and it appears less likely to have a critical part in the pathogenesis of HAPE but has rather an important role in the repair process for the impaired cell layer.

Characteristics of the ventilatory response in subjects susceptible to high altitude pulmonary edema during acute and prolonged hypoxia

The present study compares the changes in ventilation in response to sustained hypobaric hypoxia and acute normobaric hypoxia between subjects susceptible to high altitude pulmonary edema (HAPE-S) and control subjects (C-S). Seven HAPE-S and five C-S were exposed to simulated high altitude of 4000 m for 23 h in a hypobaric chamber. Resting minute ventilation (V(E)), tidal volume (V(T)), and respiratory frequency (f(R)), as well as the end-tidal partial pressures of oxygen (P(ET(O2))) and carbon dioxide (P(ET(CO2))) were measured in all subjects sitting in a standardized position. Six measurement periods were recorded: ZH1 at 450 m at Zurich level, HA1 on attaining 3600 m altitude, HA2 after 20 min at 4000 m, HA3 after 21 h and HA4 after 23 h at 4000 m altitude, and ZH2 immediately after recompression to Zurich level. At ZH1 and HA3, the measurements were first done in lying, then in sitting, and afterwards in standing. Peripheral arterial oxygen saturation (Sa(O2)) was continuously recorded. All respiratory parameters were also measured during exercise lasting 30 min, the work load being 50% of maximal oxygen consumption (V(O2max)) at Zurich level and 26% of the Zurich V(O2max) at 4000 m. V(E), P(ET(O2)) and P(ET(CO2)) did not significantly differ between HAPE-S and C-S at rest and during exercise periods at Zurich level and at high altitude. However, Sa(O2) was significantly lower in HAPE-S than in C-S at rest and during exercise at 4000 m. Breathing through the mouthpiece during ventilation measurements increased significantly the Sa(O2) in HAPE-S in posture tests at HA3. This effect was most pronounced in the supine posture, in which HAPE-S had the lowest Sa(O2) values. These data provide evidence that (1) gas exchange might be impaired on the level of ventilation-perfusion mismatch or due to diffusion limitation in HAPE-S during the first 23 h of exposure to a simulated altitude of 4000 m, and (2) contrary to C-S, the Sa(O2) in HAPE-S is significantly affected by body position and by mouthpiece breathing.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Response of nitric oxide pathway to L-arginine infusion at the altitude of 4,350 m

It was hypothesized that hypoxia may inhibit nitric oxide (NO) production by reducing the availability of endothelial NO synthase (NOS III) substrate. To evaluate the effect of L-arginine on the NO release in high altitude, 11 subjects were infused with L-arginine (0.5 g x kg(-1)) during 30 min in normoxia and after 36 h at 4,350 m (hypoxia). The L-citrulline and cyclic guanosine monophosphate (cGMP) concentrations were measured to investigate NO synthesis and guanylyl cyclase activity respectively. L-citrulline concentration, arterial oxygen saturation (Sa,O2), systemic blood pressure, heart rate and acute mountain sickness (AMS) score were measured at rest and 15, 30 and 45 min after starting infusion. The results showed that baseline L-citrulline was lower in hypoxia (p<0.05). L-arginine infusion increased L-citrulline concentration in both conditions. However, in hypoxia L-citrulline concentration remained lower than in normoxia (p<0.05). The concentration of cGMP was lower in hypoxia (p<0.05). In hypoxia, Sa,O2 increased from 15 min after the start of the infusion to 45 min (p<0.05). Blood pressure and heart rate were not affected by L-arginine infusion. Subjects who experienced symptoms of AMS showed a slight decrease in AMS score with L-arginine. The decreased L-citrulline suggests a hypoxia-induced impairment of nitric oxide synthase III or a decrease in L-arginine availability. The improvement of arterial oxygen saturation by pretreatment with L-arginine could be ascribed to an enhancement of the ventilation/perfusion ratio. Collectively, these results are consistent with a decrease in nitric oxide production in hypoxia that could be antagonized by supplying nitric oxide synthase cosubstrate.

Serial changes in spirometry during an ascent to 5,300 m in the Nepalese Himalayas

The aims of the present study were to determine the changes in forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1) and peak expiratory flow (PEF), during an ascent to 5,300 m in the Nepalese Himalayas, and to correlate the changes with arterial oxygen saturation measured by pulse oximetry (SpO2) and symptoms of acute mountain sickness (AMS). Forty-six subjects were studied twice daily during an ascent from 2,800 m (mean barometric pressure 550.6 mmHg) to 5,300 m (mean barometric pressure 404.3 mmHg) during a period of between 10 and 16 days. Measurements of FVC, FEV1, PEF, SpO2, and AMS were recorded. AMS was assessed using a standardized scoring system. FVC fell with altitude, by a mean of 4% from sea level values [95% confidence intervals (CI) 0.9% to 7.4%] at 2,800 m, and 8.6% (95% CI 5.8 to 11.4%) at 5,300 m. FEV1 did not change with increasing altitude. PEF increased with altitude by a mean of 8.9% (95% CI 2.7 to 15.1%) at 2,800 m, and 16% (95% CI 9 to 23%) at 5,300 m. These changes were not significantly related to SpO2 or AMS scores. These results confirm a progressive fall in FVC and increase in PEF with increasing hypobaric hypoxia while FEV1 remains unchanged. The increase in PEF is less than would be predicted from the change in gas density. The fall in FVC may be due to reduced inspiratory force producing a reduction in total lung capacity; subclinical pulmonary edema; an increase in pulmonary blood volume, or changes in airway closure. The absence of a correlation between the spirometric changes and SpO2 or AMS may simply reflect that these measurements of pulmonary function are not sufficiently sensitive indicators of altitude-related disease. Further studies are required to clarify the effects of hypobaric hypoxia on lung volumes and flows in an attempt to obtain a unifying explanation for these changes.

Chronic hypoxia decreases K(V) channel expression and function in pulmonary artery myocytes

Activity of voltage-gated K+ (KV) channels regulates membrane potential (E(m)) and cytosolic free Ca2+ concentration ([Ca2+](cyt)). A rise in ([Ca2+](cyt))in pulmonary artery (PA) smooth muscle cells (SMCs) triggers pulmonary vasoconstriction and stimulates PASMC proliferation. Chronic hypoxia (PO(2) 30-35 mmHg for 60-72 h) decreased mRNA expression of KV channel alpha-subunits (Kv1.1, Kv1.5, Kv2.1, Kv4.3, and Kv9.3) in PASMCs but not in mesenteric artery (MA) SMCs. Consistently, chronic hypoxia attenuated protein expression of Kv1.1, Kv1.5, and Kv2.1; reduced KV current [I(KV)]; caused E(m) depolarization; and increased ([Ca2+](cyt)) in PASMCs but negligibly affected KV channel expression, increased I(KV), and induced hyperpolarization in MASMCs. These results demonstrate that chronic hypoxia selectively downregulates KV channel expression, reduces I(KV), and induces E(m) depolarization in PASMCs. The subsequent rise in ([Ca2+](cyt)) plays a critical role in the development of pulmonary vasoconstriction and medial hypertrophy. The divergent effects of hypoxia on KV channel alpha-subunit mRNA expression in PASMCs and MASMCs may result from different mechanisms involved in the regulation of KV channel gene expression.