High altitude retinopathy: An overview and new insights

High altitude retinopathy (HAR) is a common ocular disorder that occurs on ascent to high altitude. There are many clinical symptoms, retinal vascular dilatation, retinal edema and hemorrhage are common. These usually do not or slightly affect vision; rarely, severe cases develop serious or permanent vision loss. At present, the research progress of HAR mainly focuses on hemodynamic changes, blood-retinal barrier damage, oxidative stress and inflammatory response. Although the related studies on HAR are limited, it shows that HAR still belongs to hypoxia, and hypobaric hypoxia plays an aggravating role in promoting the development of the disease. Various studies have demonstrated the correlation of HAR with acute mountain sickness (AMS) and high-altitude cerebral edema (HACE), so a deeper understanding of HAR is important. The slow ascent rates and ascent altitude are the key to preventing any altitude sickness. Research on traditional chinese medicine (TCM) and western medicine has been gradually carried out. Further exploration of the pathogenesis and prevention strategies of HAR will provide better guidance for doctors and high-altitude travelers.

The Effect of High-Altitude Hypoxia on Neuropsychiatric Functions

Liu, Bo, Minlan Yuan, Mei Yang, Hongru Zhu, and Wei Zhang. The effect of high-altitude hypoxia on neuropsychiatric functions. High Alt Med Biol. 25:26-41, 2024. Background: In recent years, there has been a growing popularity in engaging in activities at high altitudes, such as hiking and work. However, these high-altitude environments pose risks of hypoxia, which can lead to various acute or chronic cerebral diseases. These conditions include common neurological diseases such as acute mountain sickness (AMS), high-altitude cerebral edema, and altitude-related cerebrovascular diseases, as well as psychiatric disorders such as anxiety, depression, and psychosis. However, reviews of altitude-related neuropsychiatric conditions and their potential mechanisms are rare. Methods: We conducted searches on PubMed and Google Scholar, exploring existing literature encompassing preclinical and clinical studies. Our aim was to summarize the prevalent neuropsychiatric diseases induced by altitude hypoxia, the potential pathophysiological mechanisms, as well as the available pharmacological and nonpharmacological strategies for prevention and intervention. Results: The development of altitude-related cerebral diseases may arise from various pathogenic processes, including neurovascular alterations associated with hypoxia, cytotoxic responses, activation of reactive oxygen species, and dysregulation of the expression of hypoxia inducible factor-1 and nuclear factor erythroid 2-related factor 2. Furthermore, the interplay between hypoxia-induced neurological and psychiatric changes is believed to play a role in the progression of brain damage. Conclusions: While there is some evidence pointing to pathophysiological changes in hypoxia-induced brain damage, the precise mechanisms responsible for neuropsychiatric alterations remain elusive. Currently, the range of prevention and intervention strategies available is primarily focused on addressing AMS, with a preference for prevention rather than treatment.

Transient Central Facial Palsy at High Altitude: A Case Report

Allado, Edem, Bruno Chenuel, Jean-Charles Vauthier, Oriane Hily, Sébastien Richard, and Mathias Poussel. Transient central facial palsy at high altitude: a case report. High Alt Med Biol. 25:100-102, 2024.-High altitude cerebral edema (HACE) is a severe form of acute mountain sickness (AMS). Besides this life-threatening condition, other neurological disorders may develop at high altitude, even if the precise pathophysiological mechanisms generally remain undetermined and are often debated. We report the case of a 34-year-old woman presenting with moderate AMS during an ascent of Mount Kilimanjaro. While descending from the summit, she suddenly experienced focal neurological symptoms of visual blurring, tinnitus, lightheadedness, and the findings of left-sided central facial palsy (flattened nasolabial fold, fall of labial commissure, dysarthria, difficulty in whistling, and facial dysesthesia). These symptoms and signs were confirmed in the field by a physician. Her symptoms regressed spontaneously and completely while continuing to descend. The etiology of this neurological episode at high altitude is discussed. The most probable diagnosis is a transient ischemic attack based on personal and familial vascular history, confirmed unilateral transient central facial palsy and normal results on standard blood work and cerebral magnetic resonance imaging. In this case, migraine should also be considered based on association of headache and transient focal neurological impairment. Overall, special attention should be given to mountaineers presenting with neurological conditions at altitude. Not only HACE should be considered but also the wide spectrum of other neurological conditions that fall outside the usual definition of altitude sickness.

Acute changes in cardiac dimensions, function, and longitudinal mechanics in healthy individuals with and without high-altitude induced pulmonary hypertension at 4559 m

BACKGROUND

High-altitude pulmonary hypertension (HAPH) has a prevalence of approximately 10%. Changes in cardiac morphology and function at high altitude, compared to a population that does not develop HAPH are scarce.

METHODS

Four hundred twenty-one subjects were screened in a hypoxic chamber inspiring a FiO2  = 12% for 2 h. In 33 subjects an exaggerated increase in systolic pulmonary artery pressure (sPAP) could be confirmed in two independent measurements. Twenty nine of these, and further 24 matched subjects without sPAP increase were examined at 4559 m by Doppler echocardiography including global longitudinal strain (GLS).

RESULTS

SPAP increase was higher in HAPH subjects (∆ = 10.2 vs. ∆ = 32.0 mm Hg, p < .001). LV eccentricity index (∆ = .15 vs. ∆ = .31, p = .009) increased more in HAPH. D-shaped LV (0 [0%] vs. 30 [93.8%], p = .00001) could be observed only in the HAPH group, and only in those with a sPAP ≥50 mm Hg. LV-EF (∆ = 4.5 vs. ∆ = 6.7%, p = .24) increased in both groups. LV-GLS (∆ = 1.2 vs. ∆ = 1.1 -%, p = .60) increased slightly. RV end-diastolic (∆ = 2.20 vs. ∆ = 2.7 cm2 , p = .36) and end-systolic area (∆ = 2.1 vs. ∆ = 2.7 cm2 , p = .39), as well as RA end-systolic area index (∆ = -.9 vs. ∆ = .3 cm2 /m2 , p = .01) increased, RV-FAC (∆ = -2.9 vs. ∆ = -4.7%, p = .43) decreased, this was more pronounced in HAPH, RV-GLS (∆ = 1.6 vs. ∆ = -.7 -%, p = .17) showed marginal changes.

CONCLUSIONS

LV and LA dimensions decrease and left ventricular function increases at high-altitude in subjects with and without HAPH. RV and RA dimensions increase, and RV longitudinal strain increases or remains unchanged in subjects with HAPH. Changes are negligible in those without HAPH.

Exercise and hypoxia-induced hypercoagulability is counterbalanced in women in part by decreased platelet reactivity

Hypoxia plays an important role in several pathologies, e.g. chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, and is linked to an increased thrombosis risk. Furthermore, oxygen deprivation is associated with hypercoagulability. In this study, we investigated the effect of gender and exercise on the coagulation potential under hypoxic conditions at high altitude by assessing thrombin generation (TG) and platelet activation. Hereto, ten healthy volunteers were included (50 % male, median age of 27.5 years). The measurements were conducted first at sea level and then twice at high altitude (3883 m), first after a passive ascent by cable car and second after an active ascent by a mountain hike. As expected, both the passive and active ascent resulted in a decreased oxygen saturation and an increased heart rate at high altitude. Acute mountain sickness symptoms were observed independently of the ascent method. After the active ascent, platelet, white blood cell and granulocyte count were increased, and lymphocytes were decreased, without a gender-related difference. FVIII and von Willebrand factor were significantly increased after the active ascent for both men and women. Platelet activation was reduced and delayed under hypobaric conditions, especially in women. TG analysis showed a prothrombotic trend at high altitude, especially after the active ascent. Women had a hypercoagulable phenotype, compared to men at all 3 timepoints, indicated by a higher peak height and endogenous thrombin potential (ETP), and shorter lag time and time-to-peak. In addition, ETP and peak inhibition by thrombomodulin was lower in women after the active ascent, compared to men. Interestingly, data normalisation for subject baseline values indicated an opposing effect of altitude-induced hypoxia on α2-macroglobulin levels and TG lag time between men and women, decreasing in men and increasing in women. We conclude that hypoxia increases TG, as well as FVIII and VWF levels in combination with exercise. In contrast, platelets lose their responsiveness at high altitude, which is most pronounced after heavy exercise. Women had a more pronounced prothrombotic phenotype compared to men, which we theorize is counterbalanced under hypobaric conditions by decreased platelet activation.

Does Lake Louise questionnaire interpret high-altitude headache as acute mountain sickness? Experience in the western Himalayas

BACKGROUND OBJECTIVES

High-altitude headache (HAH) and headache in acute mountain sickness (AMS) are common among lowlanders ascending to the high altitude and are often confused with one another. A pilot study was undertaken to analyze HAH and AMS cases in Indian lowlanders ascending to Leh city (3500 m) in western Himalayas.

METHODS

A total number of 1228 Indian lowlanders, who ascended (fresh and re-inductees) by air and acclimatized, participated in this pilot study. The intensity of headache was assessed by the Visual Analogue Score. The parameters of HAH as per the International Classification of Headache Disorders-3 and 2018 Revised Lake Louise Questionnaire (LLQ) were used to differentiate HAH and AMS.

RESULTS

Out of 1228 cases, 78 (6.4%) cases had headache, of which 24 (1.95%) cases were HAH only, 40 (3.25%) cases AMS only and 14 (1.14%) cases were defined as both HAH and AMS. There was a significant difference in heart rate [F (2,51) = (4.756), P =0.01] between these groups. It also showed a difference in the correlation between the parameters within the groups. The Odd's Ratio of AMS in fresh and re-inductees was found to be 4.5 and for HAH it was 4.33.

INTERPRETATION CONCLUSIONS

The findings of this study suggest that LLQ has a tendency of overestimating AMS by including HAH cases. Furthermore differential parameters exhibit differences when AMS and HAH are considered separately. Re-inductees showed a lower incidence of HAH and AMS.

[Mechanism of IL-17 Signaling Pathway in Spleen Inflammatory Response Induced by Altitude Hypoxia in Mice]

Objective

To explore the mechanism of spleen tissue inflammatory response induced by altitude hypoxia in mice.

Methods

C57BL/6 mice were randomly assigned to a plain, i.e., low-altitude, normoxia group and an altitude hypoxia group, with 5 mice in each group. In the plain normoxia group, the mice were kept in a normoxic environment at the altitude of 400 m above sea level (with an oxygen concentration of 19.88%). The mice in the altitude hypoxia group were kept in an environment at the altitude of 4200 m above sea level (with an oxygen concentration of 14.23%) to establish the animal model of altitude hypoxia. On day 30, spleen tissues were collected to determine the splenic index. HE staining was performed to observe the histopathological changes in the spleen tissues of the mice. Real time fluorogenic quantitative PCR (RT-qPCR) and Western blot were conducted to determine the mRNA and protein expressions of interleukin (IL)-6, IL-12, and IL-1β in the spleen tissue of the mice. High-throughput transcriptome sequencing was performed with RNA sequencing (RNA-seq). KEGG enrichment analysis was performed for the differentially expressed genes (DEGs). The DEGs in the key pathways were verified by RT-qPCR.

Results

Compared with the plain normoxia group, the mice exposed to high-altitude hypoxic environment had decreased spleen index (P<0.05) and exhibited such pathological changes as decreased white pulp, enlarged germinal center, blurred edge, and venous congestion. The mRNA and protein expression levels of IL-6, IL-12, and IL-1β in the spleen tissue of mice in the altitude hypoxia group were up-regulated (P<0.05). According to the results of transcriptome sequencing and KEGG pathway enrichment analysis, 4218 DEGs were enriched in 178 enrichment pathways (P<0.05). DEGs were significantly enriched in multiple pathways associated with immunity and inflammation, such as T cell receptor signaling pathway, TNF signaling pathway, and IL-17 signaling pathway (P<0.05) in the spleen of mice exposed to high-altitude hypoxic environment. Among them, IL-17 signaling pathway and the downstream inflammatory factors were highly up-regulated (P<0.05). Compared with the plain normoxia group, the mRNA expression levels of key genes in the IL-17 signaling pathway, including IL-17, IL-17R, and mitogen-activated protein kinase genes (MAPKs), and the downstream inflammatory factors, including matrix metallopeptidase 9 (MMP9), S100 calcium binding protein A8 gene (S100A8), S100 calcium binding protein A9 gene (S100A9), and tumor necrosis factor α (TNF-α), were up-regulated or down-regulated (P<0.05) in the altitude hypoxia group. According to the validation of RT-qPCR results, the mRNA expression levels of DEGs were consistent with the RNA-seq results.

Conclusion

Altitude hypoxia can induce inflammatory response in the mouse spleen tissue by activating IL-17 signaling pathway and promoting the release of downstream inflammatory factors.

Respiratory tract infection: an unfamiliar risk factor in high-altitude pulmonary edema

The dramatic changes in physiology at high altitude (HA) as a result of the characteristic hypobaric hypoxia condition can modify innate and adaptive defense mechanisms of the body. As a consequence, few sojourners visiting HA with mild or asymptomatic infection may have an enhanced susceptibility to high-altitude pulmonary edema (HAPE), an acute but severe altitude sickness. It develops upon rapid ascent to altitudes above 2500 m, in otherwise healthy individuals. Though HAPE has been studied extensively, an elaborate exploration of the HA disease burden and the potential risk factors associated with its manifestation are poorly described. The present review discusses respiratory tract infection (RTI) as an unfamiliar but important risk factor in enhancing HAPE susceptibility in sojourners for two primary reasons. First, the symptoms of RTI s resemble those of HAPE. Secondly, the imbalanced pathways contributing to vascular dysfunction in HAPE also participate in the pathogenesis of the infectious processes. These pathways have a crucial role in shaping host response against viral and bacterial infections and may further worsen the clinical outcomes at HA. Respiratory tract pathogenic agents, if screened in HAPE patients, can help in ascertaining their role in disease risk and also point toward their association with the disease severity. The microbial screenings and identifications of pathogens with diseases are the foundation for describing potential molecular mechanisms underlying host response to the microbial challenge. The prior knowledge of such infections may predict the manifestation of disease etiology and provide better therapeutic options.

High-Altitude Pulmonary Edema Combined with Spontaneous Pneumomediastinum: A Case Report

Background

High-altitude pulmonary edema (HAPE) is a serious life-threatening disease that occurs after rapid ascent to high altitude; its main early-stage presentations include fatigue, headache, low-grade fever, dyspnea, and cough. X-ray and computed tomography (CT) images show pulmonary shadows and patches, which may be localized (initial right lung field predomination) or generalized to the bilateral lung base.

Case Presentation

In this report, we present a case of a 25-year-old man diagnosed with HAPE combined with spontaneous pneumomediastinum. After a quick descent and effective medical treatment, this patient made a full recovery. The case may provide helpful information for the prevention and treatment of this disease since an increased number of people, especially young men, currently travel and work at high altitudes.

Conclusion

After accurate clinical diagnosis with the help of CT or X-ray, immediate descent and appropriate oxygen supplementation are the most effective treatments for HAPE at high altitude.

High-Altitude Pulmonary Edema in Women: A Scoping Review-UIAA Medical Commission Recommendations

Pichler Hefti, Jacqueline, Dominique Jean, Alison Rosier, Mia Derstine, David Hillebrandt, Lenka Horakova, Linda E. Keyes, Kastė Mateikaitė-Pipirienė, Peter Paal, Marija Andjelkovic, Beth Beidlemann, and Susi Kriemler. High-altitude pulmonary edema in women: a scoping review-UIAA Medical Commission Recommendations. High Alt Med Biol. 24:268-273, 2023. Background: High-altitude pulmonary edema (HAPE) can occur >2,500-3,000 m asl and is a life-threatening medical condition. This scoping review aims to summarize the current data on sex differences in HAPE. Methods: The International Climbing and Mountaineering Federation (UIAA) Medical Commission convened an international author team to review women's health issues at high altitude. Pertinent literature from PubMed and Cochrane was identified by keyword search combinations (including HAPE), with additional publications found by hand search. The primary search focus was for original articles that included minimum one woman and at least a rudimentary subgroup analysis. Results: The literature search yielded 7,165 articles, 416 of which were relevant for HAPE, and 7 of which were ultimately included here. Six were case series, consistently reporting a lower HAPE prevalence in women. The one retrospective case-control study reported male HAPE prevalence at 10/100,000 and female at 0.74/100,000. No studies were identified that directly compared sex differences in the prevalence of HAPE. No published data was found for topics other than epidemiology. Conclusions: Few studies and associated methodological limitations allow few conclusions to be drawn. Incidence of HAPE may be lower in women than in men. We speculate that besides physiological aspects, behavioral differences may contribute to this potential sex difference.

Appetite, Hypoxia, and Acute Mountain Sickness: A 10-Hour Normobaric Hypoxic Chamber Study

Barclay, Holly, Saptarshi Mukerji, Bengt Kayser, and Jui-Lin Fan. Appetite, hypoxia and acute mountain sickness: A 10-hour normobaric hypoxic chamber study. High Alt Med Biol. 24:329-335, 2023. Background: The effects of hypoxia and acute mountain sickness (AMS) on appetite and food preferences are moot, especially during the early phase of hypoxic exposure. We examined the effects of a 10-hour hypoxic exposure on appetite and food preference. Methods: We assessed appetite (hunger, satisfaction, fullness, perceived appetite, and lost appetite), food preferences (sweet, salty, savory, and fatty), and AMS (Lake Louise score) with questionnaires in 27 healthy individuals (13 women) across 10-hour exposures to normobaric normoxia (fraction of inspired O2 [FiO2]: 0.21) and normobaric hypoxia (FiO2: 0.12, equivalent of 5,000 m) in a randomized, single-blinded manner. Results and Conclusions: Compared with normoxia, hypoxia decreased hunger and appetite (p = 0.040 and <0.001, respectively), which was mediated by a decreased desire for sweet, salty, and fatty foods (p < 0.05 for all). AMS was associated with a decreased desire for sweet (R = -0.438, p = 0.032) and salty foods (R = -0.460, p = 0.024) and greater loss of appetite (R = -0.619, p = 0.018). Our findings suggest that acute hypoxia rapidly suppresses appetite and that AMS development further amplifies anorexia. Clinical Trial Registration Number: ACTRN12618000548235.

Neuroimaging Features of High-Altitude Cerebral Edema: A Case Report

High-altitude cerebral edema (HACE) is serious, sometimes fatal clinical condition visualized in unacclimatized individuals climbing high altitudes. The current case report highlights a 39 year old male with a recent history of high-altitude mountain climbing and presented with memory impairment. The radiological findings revealed edema and microhemorrhages at genu and splenium of corpus callosum. Two months later the subject displayed complete resolution of edema, with persistent microhemorrhages. Herein, we report the radiological features of this rare clinical event. The lack of advanced imaging centers at higher altitudes elicit this clinical condition as less described entity.

Circulating markers of intestinal barrier injury and inflammation following exertion in hypobaric hypoxia

Hypoxia induced intestinal barrier injury, microbial translocation, and local/systemic inflammation may contribute to high-altitude associated gastrointestinal complications or symptoms of acute mountain sickness (AMS). Therefore, we tested the hypothesis that six-hours of hypobaric hypoxia increases circulating markers of intestinal barrier injury and inflammation. A secondary aim was to determine if the changes in these markers were different between those with and without AMS. Thirteen participants were exposed to six hours of hypobaric hypoxia, simulating an altitude of 4572 m. Participants completed two 30-minute bouts of exercise during the early hours of hypoxic exposure to mimic typical activity required by those at high altitude. Pre- and post-exposure blood samples were assessed for circulating markers of intestinal barrier injury and inflammation. Data below are presented as mean ± standard deviation or median [interquartile range]. Intestinal fatty acid binding protein (Δ251 [103-410] pg•mL-1; p = 0.002, d = 0.32), lipopolysaccharide binding protein (Δ2 ± 2.4 μg•mL-1; p = 0.011; d = 0.48), tumor necrosis factor-α (Δ10.2 [3-42.2] pg•mL-1; p = 0.005; d = 0.25), interleukin-1β (Δ1.5 [0-6.7] pg•mL-1 p = 0.042; d = 0.18), and interleukin-1 receptor agonist (Δ3.4 [0.4-5.2] pg•mL-1p = 0.002; d = 0.23) increased from pre- to post-hypoxia. Six of the 13 participants developed AMS; however, the pre- to post-hypoxia changes for each marker were not different between those with and without AMS (p > 0.05 for all indices). These data provide evidence that high altitude exposures can lead to intestinal barrier injury, which may be an important consideration for mountaineers, military personnel, wildland firefighters, and athletes who travel to high altitudes to perform physical work or exercise.

High-Altitude Exposure and Cerebral Venous Thrombosis: An Updated Systematic Review

Kharel, Sanjeev, Suraj Shrestha, Samriddha Raj Pant, Suman Acharya, Amit Sharma, Santosh Baniya, and Sanjeeb S. Bhandari. High-altitude exposure and cerebral venous thrombosis: an updated systematic review. High Alt Med Biol. 24:167-174, 2023. Background: High altitude (HA) may increase the risk of cerebral venous thrombosis (CVT). Differentiating it from other HA illnesses is crucial for prompt treatment and better outcomes. We aimed to summarize the clinical data, etiology, and risk factors of this poorly understood entity at an HA. Materials and Methods: A systematic literature search of various databases, including PubMed, Embase, and Google Scholar, was done using relevant keywords; cerebral venous thrombosis; HA, up to May 1, 2022. Results: A total of nine studies, including 75 cases of CVT at HA (3,000-8,848 m), with 66 males and 9 females, were included in this review. Headache and seizure were the most common clinical presentations. Smoking, drinking habits, and the use of oral contraceptive pills (OCP) were the most common risk factors for the development of CVT. Similarly, various underlying hypercoagulable states were also present among cases of CVT associated with HA exposure. Conclusion: Our review concludes that HA exposure can predispose individuals with risk factors such as preexisting hypercoagulable states, smoking, drinking habits, and use of OCP to an increased risk of CVT.

Prevalence of High-Altitude Polycythemia and Hyperuricemia and Risk Factors for Hyperuricemia in High-Altitude Immigrants

Song Zhen, Anxin Zhang, Jie Luo, Guanghai Xiong, Haibo Peng, Rang Zhou, Yuanfeng Li, Hongqiang Xu, Zhen Li, Wei Zhao, and Haoxiang Zhang. Prevalence of high-altitude polycythemia and hyperuricemia and risk factors for hyperuricemia in high-altitude immigrants. High Alt Med Biol. 24:132-138, 2023. Background: Few studies have investigated the epidemiology of chronic mountain sickness (CMS) in high-altitude immigrants. This study evaluated the prevalence of polycythemia and hyperuricemia (HUA) and risk factors for HUA in high-altitude immigrants. Methods: A cross-sectional study was conducted with 7,070 immigrants 15-45 years of age living on the Tibetan Plateau between January and December 2021. Information from routine physical examinations was obtained from each participant. Binary logistic regression analysis was performed to determine the correlation of several risk factors for HUA. Results: The prevalence of high-altitude polycythemia (HAPC) and HUA was 25.8% (28.7% in males and 9.4% in females) and 54.2% (59.9% in males and 22.5% in females), respectively. The highest prevalence of HAPC in males and females was observed in participants 26-30 and 21-25 years of age, respectively. The highest prevalence of HUA in both males and females was observed in participants 26-30 years of age. Binary logistic regression analysis showed that age, sex, and hemoglobin (Hb) concentration were risk factors for HUA, among which age was a negative factor and male sex and Hb concentration were positive factors. Conclusions: Immigrants are more susceptible to HAPC and HUA. The high prevalence of CMS of immigrants may be associated with Hb concentration, age, and sex.

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.

(-)-Epicatechin gallate prevents inflammatory response in hypoxia-activated microglia and cerebral edema by inhibiting NF-κB signaling

High-altitude cerebral edema (HACE), a potentially lethal disease, is associated with a time-dependent exposure to altitude-related hypobaric hypoxia (HH) and has reportedly been associated with microglia hyperactivation. Catechins are substances with good antioxidant properties, among which (-)-epigallocatechin gallate (EGCG) may play a neuroprotective role through the inhibition of microglia overactivation; however, the function of its analog- (-)-epicatechin gallate (ECG)-requires further elucidation. The aim of the present study was to investigate whether ECG prevented HACE by inhibiting HH-activated microglia. Primary microglia exposed to lipopolysaccharide (LPS)/ATP were co-treated with EGCG, ECG, and (-)-epigallocatechin, and ECG and EGCG exerted significant anti-inflammatory and neuroprotective effects. ECG inhibited the NF-κB pathway to prevent the activation of microglia induced by 1% O₂. In addition, ECG ameliorated the increase in brain water content and aquaporin 4 expression induced by HH in mice. ECG also reduced the number of Iba1⁺ microglia in the brain, the release of proinflammatory factors, and the recruitment of microglia to blood vessels in HH-exposed mice. The outcomes of the present study revealed that ECG alleviated hypoxic hyperactivated microglia, reduced the neuroinflammation and blood-brain barrier permeability, and prevented HACE by inhibiting NF-κB signaling.

Variables Influencing the Pressure and Volume of the Pulmonary Circulation as Risk Factors for Developing High Altitude Pulmonary Edema (HAPE)

BACKGROUND

At altitudes above 2500 m, the risk of developing high altitude pulmonary edema (HAPE) grows with the increases in pulmonary arterial pressure. HAPE is characterized by severe pulmonary hypertension, though the incidence and relevance of individual risk factors are not yet predictable. However, the systolic pulmonary pressure (SPAP) and peak in tricuspid regurgitation velocity (TVR) are crucial factors when diagnosing pulmonary hypertension by echocardiography.

METHODS

The SPAP and TVR of 27 trekkers aged 20-65 years en route to the Solu Khumbu region of Nepal were assessed. Echocardiograph measurements were performed at Lukla (2860 m), Gorak Shep (5170 m), and the summit of Kala Patthar (5675 m). The altitude profile and the participants' characteristics were also compiled for correlation with the measured data.

RESULTS

The results showed a highly significant increase in SPAP and TVR after ascending Kala Patthar. The study revealed a lower increase of SPAP and TVR in the group of older participants, although the respective initial measurements at Gorak Shep were significantly higher for this group. A similar finding occurred in those using Diamox^® as prophylaxis. There was an inverse relationship between TVR and SPAP, the peripheral capillary oxygen saturation, and heart rate.

CONCLUSIONS

The echocardiograph results indicated that older people are an at-risk group for developing HAPE. A conservative interpretation of the basic tactical rules for altitudes should be followed for older trekkers or trekkers with known problems of altitude acclimatization ("slow acclimatizer") as SPAP elevates with age. The prophylactic use of Acetazolamide (Diamox^®) should be avoided where not necessary for acute medical reasons. Acetazolamide leads to an increase of SPAP, and this may potentially enhance the risk of developing HAPE. Arterial oxygen saturation measurements can provide an indicator for the self-assessment for the risk of developing HAPE and a rule of thumb for the altitude profile, but does not replace a HAPE diagnosis. Backpack weight, sex, workload (actual ascent speed), and pre-existing diseases were not statistically significant factors related to SPAP and TVR (p ≤ 0.05).

Isovolemic hemodilution in chronic mountain sickness acutely worsens nocturnal oxygenation and sleep apnea severity

STUDY OBJECTIVES

Chronic mountain sickness (CMS) is commonly observed among Andean and other highland populations. Sleep-disordered breathing (SDB) is highly prevalent at high altitude, and SDB and nocturnal hypoxemia have been observed in CMS. Phlebotomy is commonly performed to treat CMS, but it is unknown whether reducing hematocrit improves SDB. We hypothesized that isovolemic hemodilution (IVHD) in CMS would reduce SBD severity and improve sleep efficiency.

METHODS

Six participants with CMS and 8 without CMS, all residents of Cerro de Pasco, Peru (altitude 4340 m), completed baseline nocturnal sleep studies. CMS participants then underwent IVHD, and nocturnal sleep studies were repeated 24-48 hours after IVHD. We analyzed sleep apnea severity, nocturnal oxygenation, and sleep quality in those with CMS relative to those without CMS, and the effects of IVHD in CMS participants.

RESULTS

Participants with CMS did not have altered sleep architecture, sleep apnea severity, or nocturnal oxygenation relative to non-CMS participants. However, IVHD in CMS increased apnea-hypopnea index (40.9 ± 6.9 events/h to 61.5 ± 7.7 events/h, P = .009). IVHD increased oxyhemoglobin desaturation index (P = .008) and the percentage of sleep time spent with oxyhemoglobin saturation at or below 80% (P = .012). There was no effect of IVHD on sleep efficiency, arousal index, or sleep staging.

CONCLUSIONS

In this cohort, CMS was not associated with worsened SDB or changes in sleep architecture. IVHD, a putative therapeutic option for participants with CMS, appears to worsen nocturnal oxygenation and SDB within 48 hours post-IVHD.

CITATION

Sanchez-Azofra A, Villafuerte FC, DeYoung PN, et al. Isovolemic hemodilution in chronic mountain sickness acutely worsens nocturnal oxygenation and sleep apnea severity. J Clin Sleep Med. 2022;18(10):2423-2432.

Clinician's Corner: Counseling Patients with Pulmonary Vascular Disease Traveling to High Altitude

Ulrich, Silvia, Mona Lichtblau, Simon R. Schneider, Stéphanie Saxer, and Konrad E. Bloch, Clinician's corner: counseling patients with pulmonary vascular disease traveling to high altitude. High Alt Med Biol. 23:201-208, 2022.-Pulmonary vascular diseases (PVDs) with precapillary pulmonary hypertension (PH), such as pulmonary arterial or chronic thromboembolic PH, impair exercise performance and survival in patients. Vasodilators and other treatments improve quality of life and prognosis to an extent in patients who have PVDs as chronic disorders. Obviously, patients with PVD wish to participate in usual daily activities, including travel to popular settlements and mountainous regions located at high altitude. However, the pulmonary hemodynamic impairment due to PVD leads to blood and tissue hypoxia, particularly during exercise and sleep. It is thus of concern that alveolar hypoxia at higher altitude may exacerbate patients' symptoms and lead to decompensation. Current PH guidelines discourage high-altitude exposure for fear of altitude-related adverse health effects. However, several recent well-designed prospective and randomized trials show that despite altitude-induced hypoxemia, pulmonary hemodynamic changes and impairment of exercise performance in patients with PVD are similar to the responses in healthy people or in patients with mild chronic obstructive pulmonary disease. The vast majority of patients with PVD can tolerate short-term exposure to moderate altitudes up to 2,500 m. For the roughly 10% of patients with stable disease who develop severe hypoxemia when ascending to 2,500 m, they respond well to low-level supplemental oxygen support. The best low-altitude predictors for adverse health effects at high altitude are the known clinical risk factors for PVD such as symptoms, functional class, exercise capacity, and exertional oxygen desaturation, whereas hypoxia altitude simulation testing is of little additive value. In any case, patients should be instructed that altitude-related adverse health effects may be difficult to predict and that in case of worsening symptoms, immediate accompanied descent to lower altitude and oxygen therapy are required. Patients with severe hypoxemia near sea level may safely visit high-altitude regions up to 1,500-2,000 m while continuing oxygen therapy and avoiding strenuous exercise. All PH patients should be counseled before any high-altitude sojourn by doctors with experience in PVD and high-altitude medicine and have an action plan for the occurrence of severe hypoxemia and other altitude-related conditions such as acute mountain sickness.

Treatment of Focal and Segmental Glomerulosclerosis Secondary to High Altitude Polycythemia with Acetazolamide

Vizcarra-Vizcarra, Cristhian A., Eduardo Chávez-Velázquez, Carmen Asato-Higa, and Abdías Hurtado-Aréstegui. Treatment of focal and segmental glomerulosclerosis secondary to high altitude polycythemia with acetazolamide. High Alt Med Biol 00:000-000, 2022.-Focal segmental glomerulosclerosis (FSGS) is a morphological pattern, caused by glomerular injury and is the leading cause of nephrotic syndrome in adults. We present the case of a 59-year-old female patient, resident of a high-altitude city (3,824 m), who had polycythemia and nephrotic syndrome. A renal biopsy was performed, and the findings were compatible with FSGS. The patient received phlebotomy 500 ml three times, which reduced, partially, the hemoglobin concentration. However, she had refractory proteinuria, despite the use of enalapril and spironolactone. We observed that proteinuria worsened with the increase in hemoglobin levels. So, she was treated with acetazolamide 250 mg bid for 4 months, which reduced proteinuria and hemoglobin. During the coronavirus disease 2019 (COVID-19) pandemic, the patient did not take acetazolamide and again, she had an increase in hemoglobin and proteinuria levels. We conclude that acetazolamide may be an effective treatment in FSGS due to high altitude polycythemia.

Severe acute reentry high altitude pulmonary edema in pediatric patients: report of three cases and literature review

BACKGROUND

High Altitude Pulmonary Edema (HAPE) is a fatal form of severe high-altitude illness. It is a form of noncardiogenic, noninfectious pulmonary edema secondary to alveolar hypoxia. The exact incidence of HAPE in children is unknown; however, most literature reports an incidence between 0.5-15%. There are three proposed HAPE types including classic HAPE, reentry HAPE, and high-altitude resident pulmonary edema (HARPE).

CASE

We present three pediatric patients who were diagnosed with re-entry high altitude pulmonary edema and did not have any underlying cardiac abnormalities. All patients reside in areas of high altitude with a history of travelling to places of lower altitude. They had respiratory infections prior to the manifestation of HAPE.

CONCLUSIONS

These are the first reported cases of children with reentry HAPE in Saudi Arabia. Reentry HAPE can occur in otherwise healthy children. Rapid ascent to high altitude and recent respiratory infections are the most commonly reported triggers. Prognosis is very favorable with a very rapid response to oxygen therapy. Education about HAPE is mandatory for families and health care workers working in high altitude areas.

Proteomic analysis reveals proteins and pathways associated with declined testosterone production in male obese mice after chronic high-altitude exposure

OBJECTIVE

Obesity is common in highland areas owing to lifestyle alterations. There are pieces of evidence to suggest that both obesity and hypoxia may promote oxidative stress, leading to hypogonadism in males. These findings indicate an increased risk of hypogonadism in obese males following hypoxia exposure. However, the mechanisms underlying the disease process remain unclear. The current study aims to explore the mechanism of testosterone production dysfunction in obese male mice exposed to a chronic high-altitude hypoxia environment.

METHODS

An obese male mouse model was generated by inducing obesity in mice via a high-fat diet for 14 weeks, and the obese mice were then exposed to a high-altitude hypoxia environment for 24 days. Sera and testicular tissues were collected to detect serum lipids, sex hormone level, and testicular oxidative stress indicators. Morphological examination was performed to assess pathological alterations in testicular tissues and suborganelles in leydig cells. Proteomic alterations in testicular tissues were investigated using quantitative proteomics in Obese/Control and Obese-Hypoxia/Obese groups.

RESULTS

The results showed that chronic high-altitude hypoxia exposure aggravated low testosterone production in obese male mice accompanied by increased testicular oxidative stress and histological damages. In total, 363 and 242 differentially expressed proteins (DEPs) were identified in the two comparison groups, Obese/Control and Obese-Hypoxia/Obese, respectively. Functional enrichment analysis demonstrated that several significant functional terms and pathways related to testosterone production were altered in the two comparison groups. These included cholesterol metabolism, steroid hormone biosynthesis, peroxisome proliferator-activated receptor (PPAR) signaling pathway, oxidative stress responses, as well as retinol metabolism. Finally, 10 representative DEPs were selected for parallel reaction monitoring verification. Among them, StAR, DHCR7, NSDHL, CYP51A1, FDPS, FDX1, CYP11A1, ALDH1A1, and GPX3 were confirmed to be downregulated in the two groups.

CONCLUSIONS

Chronic hypoxia exposure could exacerbate low testosterone production in obese male mice by influencing the expression of key proteins involved in steroid hormone biosynthesis, cholesterol biosynthesis, oxidative stress responses and retinol metabolism.

A review of the skeletal effects of exposure to high altitude and potential mechanisms for hypobaric hypoxia-induced bone loss

Mountaineering and exposure to high altitude result in physiological adaptations to the reduced inspiratory oxygen availability. Acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE) are well-described harmful effects of exposure to high altitude. Common to AMS, HAPE, and HACE are distinct clinical signs and symptoms of impaired function. However, several studies have suggested that high altitude might result in a substantial bone loss, which usually does not produce any apparent symptoms. This review aims to provide a comprehensive overview of, and map current knowledge of the skeletal effects of hypobaric hypoxia and high altitude. PubMed and Embase were searched from inception to September 6, 2021, to identify studies investigating the skeletal effects of exposure to hypobaric hypoxia and high altitude. Three hundred sixty titles and abstracts were screened, and 20 full-text articles were included (16 in vivo studies and four real-world human studies). In rodents, simulated high altitude up to 2900 m did not result in any adverse skeletal effects. In contrast, studies exposing animals to very high altitude (3500-5500 m) reported substantial reductions in BMD, cortical morphology, and bone strength, as well as deteriorated trabecular microstructure. Detrimental microstructural effects were also reported in rats exposed to simulated extreme altitude (6000 m). Finally, real-world human studies in mountaineers suggested high altitude exposure reduced bone mineral density (BMD) and that the harmful skeletal effects of hypobaric hypoxia were not entirely recovered after 12 months. In conclusion, in vivo and real-world studies demonstrated high altitude exposure results in adverse skeletal effects. The underlying mechanism for hypobaric hypoxia-induced bone loss is not elucidated.

Effects of chronic intermittent hypobaric hypoxia on prostate-specific antigen (PSA) in Chilean miners

OBJECTIVE

The aim was to determine the effects of chronic intermittent hypobaric hypoxia (CIHH) on prostate-specific antigen (PSA) levels in Chilean miners who work at different altitudes.

METHODS

A cross-sectional study was conducted between April and July 2019. Miners from five mines (N=338) at different altitudes were evaluated. We recorded sociodemographic, working and altitude information. Haemoglobin oxygen saturation (SaO2) and haemoglobin (Hb) were measured in situ, while PSA and testosterone were analysed at a low level. Linear mixed-effect models were used to evaluate the association between PSA level and two CIHH exposures: composite CIHH (with four descriptors) and ChileStd-CIHH (CIHH Chilean standard; based on the Chilean technical guide for occupational exposure to CIHH). All models were adjusted by age, body mass index and day of the work the samples were taken.

RESULTS

Highest and lowest PSA levels were found in mines ≥3000 m above sea level (mine 3: median=0.75, IQR=-0.45; mine 4: median=0.46, IQR=-0.35). In the multilevel models, the wider altitude difference between mining operation and camp showed lower PSA levels (model D: βPSA=-0.93 ng/mL, βlogPSA=-0.07, p<0001), adjusted for other CIHH descriptors, SaO2, Hb and testosterone. The descriptors of composite CIHH explained better PSA variations than ChileStd-CIHH (model D: marginal R2=0.090 vs model A: marginal R2=0.016).

CONCLUSIONS

Occupational health regulations and high altitude medicine should consider these results as initial evidence on the inclusion of new descriptors for CIHH and the possible effect of this exposure on PSA levels in this male-dominated occupational sector.

Improved Neuroimaging Findings and Cognitive Function in a Case of High-altitude Cerebral Edema

High-altitude cerebral edema (HACE) is a rare condition of acute mountain sickness that manifests as consciousness disturbance and truncal ataxia. Neuroimaging shows vasogenic edema with microbleeds in the white matter and the corpus callosum. We herein report a case of HACE in which the patient showed widespread hyperintense signals with extensive microbleeds in the white matter and corpus callosum on MRI, as well as cognitive dysfunction. Rehabilitation to improve the higher brain function facilitated the recovery of the patient's cognitive impairment and was accompanied by improved MRI findings.

Establishment of an experimental rat model of high altitude cerebral edema by hypobaric hypoxia combined with temperature fluctuation

High altitude cerebral edema (HACE) is a kind of life threat disease encountered at high altitude, but the precise pathogenesis of it is far more understood. Hypobaic hypoxia (HH) and cold are conditions characteristic of high altitude environment. HH is always considered as the central causative factor for the development of HACE, but the effect of cold stress on HACE has been rarely investigated. The purpose of this study was to investigate the potential role of cold stress in the development of HACE and establish a stable experimental animal model. Male SPF Wistar rats were randomly divided into five groups for this experiment, control group (altitude, 1400 m, temperature, 25 ℃), NC + 2 ℃ group (altitude, 1400 m, temperature, 2 ℃), HH group (altitude, 6000 m, temperature, 25 ℃), HH+2 ℃ group (altitude, 6000 m, temperature, 2 ℃) and HH + 12/2 ℃ (altitude, 6000 m, temperature, 12 ℃/2 ℃ light/dark cycle). After exposure for 72 h, the blood and brain tissues were collected. Brain water content (BWC) and Evans Blue dye extravasation were used to assess the brain edema and blood-brain barrier (BBB) permeability, respectively. The levels of pro-inflammatory cytokines in serum were assessed via enzyme-linked immunosorbent assay. Oxidative stress markers and ATPase activity were determined using commercial kits. Western blotting was used to detect the expression of related proteins. Compared to control, HH+2 ℃ could significantly increase the BWC and BBB permeability, and these changes were further exacerbated by HH + 12/2 ℃. Furthermore, HH+2 ℃ and HH + 12/2 ℃ markedly increased the levels of H₂O₂ and MDA, restrained SOD and GSH levels and decreased Na⁺/K⁺-ATPase activitie compared with the control group. In addition, HH+2 ℃ and HH + 12/2 ℃ enhanced the levels of pro-inflammatory cytokines IL-1β, TNF-α and IL-6 in serum and significantly increased the expression of VEGF in brain compared with the control group, but only HH + 12/2 ℃ could increase the expression of AQP4. However, compared with control group, no significant differences in these parameters were observed in HH and NC+2 ℃groups. These results demonstrated that HH or cold stress alone did not successfully induce brain damage, while HH+2 ℃ could induce the onset of HACE via provoking injury caused by HH. HH + 12/2 ℃ was more obvious and efficient. Collectively, we firstly suggest that cold stress may promote the formation of HACE by aggravating the brain injury induced by HH exposure and supply an effective and reliable experimental rat model of HACE via HH combined with temperature fluctuation.

Interplay between rotational work shift and high altitude-related chronic intermittent hypobaric hypoxia on cardiovascular health and sleep quality in Chilean miners

Mining activities expose workers to diverse working conditions, rotational shifts and high altitude-related hypobaric hypoxia. Separately, each condition has been reported having a negative impact on miners' health risk; however, the combination of both stressors has been poorly explored. The present study aimed to analyse the effects of exposure to rotational work shift (RWS) alone or in combination with high altitude-related chronic intermittent hypobaric hypoxia (CIHH) on cardiometabolic, physical activity and sleep quality related markers in copper miners from Los Pelambres mine in Chile. One hundred and eleven male miners working in RWS with or without CIHH were included. Anthropometrics measures, sleep quality assessment, physical activity level (PAL) and handgrip strength were evaluated. Exposure to CIHH exacerbated the detrimental effects of RWS as miners exposed to the combination of RWS and CIHH where more obese and had a wider neck circumference, reduced PAL at work and worsened sleep quality. Practitioner summary: The purpose was to assess cardiometabolic health and sleep quality markers associated with the combined effects of rotational shift work and high altitude-related intermittent hypobaric hypoxia in miners. Findings showed a wider neck circumference, lower physical activity level and higher prevalence of poor sleep quality in exposed miners. Abbreviations: ANOVA: analysis of variance; BM: body mass; BMI: body mass index; CI: confidence intervals; CIHH: chronic intermittent hypobaric hypoxia; CV: cardiovascular; CVR: cardiovascular risk; HA: high altitude; HACE: high-altitude cerebral edema; HGS: handgrip strength; IPAQ-SF: International Physical Activity Questionnaire - Short Form; LSD: Fisher's least standardized difference; MANCOVA: multivariate general lineal model; MET: metabolic equivalent; PAL: physical activity level; PSQI: Pittsburg sleep quality index; RWS: rotational work shift; WHR: waist-to-hip ratio.

Incidence of decompression sickness in hypobaric hypoxia training

Simulated flight in a hypobaric chamber is a fundamental component in the physiological training of aviators. Although rare, there is always a risk of decompression sickness (DCS) in trainees during hypobaric hypoxia training. In this study we aimed to determine the incidence of altitude-induced DCS and the symptoms manifested in trainees and inside chamber observers (ICOs) during the training sessions. We retrospectively reviewed the records of DCS cases during the period of January 1, 2011, and October 1, 2018. The records of 6,657 trainees and 615 ICOs were evaluated. The gender distribution in 6,657 trainees was 6,578 (98.81%) male and 79 (1.19%) female. The numbers of DCS cases in trainees and ICOs were six (0.09%) and two (0.33%), respectively [(ICOs versus trainees - odds ratio (OR): 3.574; 95% CI 0.720-17.744; (p > 0.05)]. All ICOs were male; no DCS incident was observed among female trainees. Recompression treatments were applied on site, and complete recovery was achieved in all cases. Overall DCS incidence was found to be 0.11% among the 7,193 male subjects, which included trainees and ICOs. The higher incidence of DCS in ICOs was attributed to the physical activities performed at altitudes by ICOs. In such training, established instructions have to be strictly followed by physicians, ICOs and trainees. All trainees and ICOs should be aware of the symptoms and signs of DCS, and medical support including a recompression facility, should be provided on site during hypobaric hypoxia training.

[Research progress on mechanism in adaptation of hemoglobin to plateau hypoxia]

Low oxygen partial pressure is the main cause of acute mountain sickness.Hemoglobin plays a crucial physiological role in the binding, utilization, transportation and release of oxygen in the body. To increase the capacity of oxygen binding of hemoglobin or the capacity of oxygen supply in tissues can help alleviate altitude sickness. However, increasing hemoglobin content has certain limitations. Using techniques from molecular biology, researchers are looking for endogenous or exogenous substances that can regulate the conformation of hemoglobin to increase oxygen uptake in the alveoli, or the availability of alveolar oxygen in the tissues. At present, the research on allosteric modulators to improve the affinity of hemoglobin has made some progress, and research on applying this mechanism to plateau hypoxia is also underway. This article reviews the relationship between hemoglobin and hypoxia, the structure of hemoglobin and the role of various allosteric modulators in hypoxia, which would provide information for finding new substances regulating the conformation of hemoglobin.

Pharmacological activation of peroxisome proliferator-activated receptor γ (PPAR-γ) protects against hypoxia-associated fetal growth restriction

The hypoxia of high-altitude (HA) residence increases the risk of intrauterine growth restriction (IUGR) and preeclampsia 3-fold, augmenting perinatal morbidity and mortality and the risk for childhood and adult disease. Currently, no effective therapies exist to prevent these vascular disorders of pregnancy. The peroxisome proliferator-activated receptor γ (PPAR-γ) is an important regulator of uteroplacental vascular development and function and has been implicated in the pathogenesis of IUGR and preeclampsia. Here, we used a model of HA pregnancy in mice to determine whether hypoxia-induced fetal growth restriction reduces placental PPAR-γ protein expression and placental vascularization and, if so, to evaluate the effectiveness of the selective PPAR-γ agonist pioglitazone (PIO) for preventing hypoxia-induced IUGR. Hypoxia resulted in asymmetric IUGR, placental insufficiency, and reduced placental PPAR-γ expression; PIO prevented approximately half of the fetal growth restriction and attenuated placental insufficiency. PIO did not affect fetal growth under normoxia. Although PIO was beneficial for fetal growth, PIO treatment reduced placental vascular density of the labrynthine zone in normoxic and hypoxic (Hx) conditions, and mean vascular area was reduced in the Hx group. Our results suggest that pharmacological PPAR-γ activation is a potential strategy for preventing IUGR in pregnancies complicated by hypoxia, although further studies are needed to identify its likely metabolic or vascular mechanisms.-Lane, S. L., Dodson, R. B., Doyle, A. S., Park, H., Rathi, H., Matarrazo, C. J., Moore, L. G., Lorca, R. A., Wolfson, G. H., Julian, C. G. Pharmacological activation of peroxisome proliferator-activated receptor γ (PPAR-γ) protects against hypoxia-associated fetal growth restriction.

The Effect of Hypoxia on Cardiovascular Disease: Friend or Foe?

Savla, Jainy J., Benjamin D. Levine, and Hesham A. Sadek. The effect of hypoxia on cardiovascular disease: Friend or foe? High Alt Med Biol. 19:124-130, 2018.-Over 140 million people reside at altitudes exceeding 2500 m across the world, resulting in exposure to atmospheric (hypobaric) hypoxia. Whether this chronic exposure is beneficial or detrimental to the cardiovascular system, however, is uncertain. On one hand, multiple studies have suggested a protective effect of living at moderate and high altitudes for cardiovascular risk factors and cardiovascular disease (CVD) events. Conversely, residence at high altitude comes at the tradeoff of developing diseases such as chronic mountain sickness and high-altitude pulmonary hypertension and worsens outcomes for diseases such as chronic obstructive pulmonary disease. Interestingly, recently published data show a potential role for severe hypoxia as a unique and unexpected therapy after myocardial infarction. In this review, we will discuss the current literature evaluating the effects of altitude exposure and the accompanying hypoxia on health and the potential therapeutic applications of hypoxia on CVD.

Lung Ultrasound Is Accurate for the Diagnosis of High-Altitude Pulmonary Edema: A Prospective Study

Objective

The aim of this study was to assess the diagnostic accuracy of lung ultrasonography (LUS) for high-altitude pulmonary edema (HAPE).

Background

LUS has proven to be a reliable tool for the diagnosis of pulmonary diseases, including pneumonia, acute respiratory distress syndrome (ARDS), and pneumothorax. LUS also has potential for the diagnosis of HAPE. However, the actual diagnostic value of LUS for HAPE is still unknown. Our objective was to determine the feasibility of using LUS for the diagnosis of HAPE.

Materials and Methods

A prospective clinical research study of adult HAPE patients was conducted. LUS and chest X-ray (CXR) were performed in patients with suspected HAPE before and after treatment, and pulmonary moist rales were recorded concurrently. The diagnostic value of LUS, CXR, and moist rales for HAPE (i.e., their sensitivity, specificity, and positive and negative predictive values) were assessed, and the results were compared. The gold standard was the final diagnosis.

Results

In total, 148 patients were enrolled in the study, 126 of which were diagnosed with HAPE (85.14%). Before treatment, the diagnostic accuracy of LUS for HAPE was as follows: sensitivity, 98.41% (95% confidence interval (CI) 100.60-96.23%); specificity, 90.91% (95% CI 102.92-78.90%). LUS had higher sensitivity (0.98 vs. 0.81, P < 0.01 using the McNemar test) than moist rales for the diagnosis of HAPE. LUS also had higher sensitivity than CXR (0.98 vs. 0.93, P < 0.05 using the McNemar test). After treatment, LUS was consistent with CXR in 96.55% of HAPE patients, and the concordance between LUS and CXR was high (k statistic = 0.483 P ≤ 0.001; 95% CI -0.021 to -0.853).

Conclusion

The results indicate that LUS is a reliable method for the diagnosis and surveillance of HAPE. This trial is registered with Chinese Clinical Trial Registry (No. ChiCTR-DDD-16009841).

Isolated psychosis during exposure to very high and extreme altitude - characterisation of a new medical entity

BACKGROUND

Psychotic episodes during exposure to very high or extreme altitude have been frequently reported in mountain literature, but not systematically analysed and acknowledged as a distinct clinical entity.

METHODS

Episodes reported above 3500 m altitude with possible psychosis were collected from the lay literature and provide the basis for this observational study. Dimensional criteria of the Diagnostic and Statistical Manual of Mental Disorders were used for psychosis, and the Lake Louise Scoring criteria for acute mountain sickness and high-altitude cerebral oedema (HACE). Eighty-three of the episodes collected underwent a cluster analysis to identify similar groups. Ratings were done by two independent, trained researchers (κ values 0.6-1).FindingsCluster 1 included 51% (42/83) episodes without psychosis; cluster 2 22% (18/83) cases with psychosis, plus symptoms of HACE or mental status change from other origins; and cluster 3 28% (23/83) episodes with isolated psychosis. Possible risk factors of psychosis and associated somatic symptoms were analysed between the three clusters and revealed differences regarding the factors 'starvation' (χ2 test, p = 0.002), 'frostbite' (p = 0.024) and 'supplemental oxygen' (p = 0.046). Episodes with psychosis were reversible but associated with near accidents and accidents (p = 0.007, odds ratio 4.44).

CONCLUSIONS

Episodes of psychosis during exposure to high altitude are frequently reported, but have not been specifically examined or assigned to medical diagnoses. In addition to the risk of suffering from somatic mountain illnesses, climbers and workers at high altitude should be aware of the potential occurrence of psychotic episodes, the associated risks and respective coping strategies.

Physiological, hematological and biochemical factors associated with high-altitude headache in young Chinese males following acute exposure at 3700 m

BACKGROUND

High-altitude headache (HAH) is the most common sickness occurred in healthy people after rapid ascending to high altitude, and its risk factors were still not well understood. To investigate physiological, hematological and biochemical risk factors associated with high-altitude headache (HAH) after acute exposure to 3700 m, we conducted a two-stage, perspective observational study. In 72 h, total 318 young Han Chinese males ascended from sea level (altitude of 50 m) to altitude of 3700 m by train. Demographic data, physiological, hematological and biochemical parameters of all participants were collected within one week prior to the departure, and within 24 h after arrival.

RESULTS

The incidence of HAH was 74.84%. For parameters measured at sea level, participants with HAH exhibited significantly higher age and lower BUN (p < 0.05). For parameters measured at 3700 m, participants with HAH exhibited significantly lower blood oxygen saturation (SpO2), higher resting heart rate (HR), higher systolic blood pressure at resting (SBP) and lower blood urea nitrogen (BUN) (all p < 0.05). At 3700 m, the severity of HAH associated with SpO2, HR and BUN significantly (all p < 0.05). Multivariate logistic regression revealed that for parameters at sea level, BUN was associated with HAH [BUN (OR:0.77, 95% CI:0.60-0.99)] and for parameters at 3700 m, SpO2, HR and BUN were associated with HAH independently [SpO2 (OR:0.84, 95% CI:0.76-0.93); HR (OR:1.03, 95% CI:1.00-1.07); BUN (OR:0.64, 95% CI:0.46-0.88)]. No association between hematological parameters and HAH was observed.

CONCLUSION

We confirmed that higher HR, lower SpO2 are independent risk factors for HAH. Furthermore, we found that at both 50 m and 3700 m, lower BUN is a novel independent risk factor for HAH, providing new insights for understanding the pathological mechanisms.

Long-term exposure to high altitude hypoxia during pregnancy increases fetal heart susceptibility to ischemia/reperfusion injury and cardiac dysfunction

BACKGROUND

High altitude hypoxia (HAH) exposure affects fetal development. However, the fetal cardiovascular responses to the HAH are not well understood. We have tested the hypothesis that long-term HAH exposure alters the hypoxia/ischemia-sensitive gene expressions, leading to an increase in fetal heart susceptibility to ischemia/reperfusion (I/R) injury and cardiac dysfunction.

METHODS

Time-dated pregnant sheep were exposed to high-altitude (3820 m) or were maintained at sea level (~300 m) for 110 days. Fetal hearts were isolated from the near-term ewes and subjected to I/R in a Langendorff preparation.

RESULTS

HAH decreased the fetal body and heart weights in the female but not male fetuses. HAH had no effect on the left ventricle (LV) function at baseline, but increased the LV infarct size and attenuated the post-ischemic recovery of LV function in both male and female fetuses, as compared with the normoxic groups. HAH increased the protein levels of hypoxia-inducible factor (HIF)-1α and DNA methyltransferases type 3b (DNMT3b), but attenuated protein kinase C epsilon (PKCε) levels in the fetal hearts. AHA induced a 4.3 fold increase of miR-210 in the males and a 2.9 fold increase in female hearts. In addition, HAH had no effect on mTOR protein and phosphorylation levels but increased the autophagy biomarker, LC3B-II protein levels and LC3B-II/LC3B-I ratio in the fetal hearts.

CONCLUSION

The results suggest that gestational HAH exposure induces in utero programming of the hypoxia/ischemia-sensitive gene expression pattern in the developing heart and increases cardiac susceptibility to I/R injury.

The relationship between anxiety and acute mountain sickness

Introduction

Whilst the link between physical factors and risk of high altitude (HA)-related illness and acute mountain sickness (AMS) have been extensively explored, the influence of psychological factors has been less well examined. In this study we aimed to investigate the relationship between ‘anxiety and AMS risk during a progressive ascent to very HA.

Methods

Eighty health adults were assessed at baseline (848m) and over 9 consecutive altitudes during a progressive trek to 5140m. HA-related symptoms (Lake Louise [LLS] and AMS-C Scores) and state anxiety (State-Trait-Anxiety-Score [STAI Y-1]) were examined at each altitude with trait anxiety (STAI Y-2) at baseline.

Results

The average age was 32.1 ± 8.3 years (67.5% men). STAI Y-1 scores fell from 848m to 3619m, before increasing to above baseline scores (848m) at ≥4072m (p = 0.01). STAI Y-1 scores correlated with LLS (r = 0.31; 0.24–0.3; P<0.0001) and AMS-C Scores (r = 0.29; 0.22–0.35; P<0.0001). There was significant main effect for sex (higher STAI Y-1 scores in women) and altitude with no sex-x-altitude interaction on STAI Y-1 Scores. Independent predictors of significant state anxiety included female sex, lower age, higher heart rate and increasing LLS and AMS-C scores (p<0.0001). A total of 38/80 subjects (47.5%) developed AMS which was mild in 20 (25%) and severe in 18 (22.5%). Baseline STAI Y-2 scores were an independent predictor of future severe AMS (B = 1.13; 1.009–1.28; p = 0.04; r² = 0.23) and STAI Y-1 scores at HA independently predicted AMS and its severity.

Conclusion

Trait anxiety at low altitude was an independent predictor of future severe AMS development at HA. State anxiety at HA was independently associated with AMS and its severity.

How Can Acute Mountain Sickness be Quantified at Moderate Altitude?

Reports of acute mountain sickness (AMS) at moderate altitude show a wide variability, possibly because of different investigation methods. The aim of our study was to investigate the impact of investigation methods on AMS incidence. Hackett's established AMS score (a structured interview and physical examination), the new Lake Louise AMS score (a self-reported questionnaire) and oxygen saturation were determined in 99 alpinists after ascent to 2.94 km altitude. AMS incidence was 8% in Hackett's AMS score and 25% in the Lake Louise AMS score. Oxygen saturation correlated inversely with Hackett's AMS score with no significant correlation with the Lake Louise AMS score. At moderate altitude, the new Lake Louise AMS score overestimates AMS incidence considerably. Hackett's AMS score remains the gold standard for evaluating AMS incidence.

Interventions for preventing high altitude illness: Part 1. Commonly-used classes of drugs

BACKGROUND

High altitude illness (HAI) is a term used to describe a group of cerebral and pulmonary syndromes that can occur during travel to elevations above 2500 metres (8202 feet). Acute hypoxia, acute mountain sickness (AMS), high altitude cerebral oedema (HACE) and high altitude pulmonary oedema (HAPE) are reported as potential medical problems associated with high altitude. In this review, the first in a series of three about preventive strategies for HAI, we assess the effectiveness of six of the most recommended classes of pharmacological interventions.

OBJECTIVES

To assess the clinical effectiveness and adverse events of commonly-used pharmacological interventions for preventing acute HAI.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OVID), Embase (OVID), LILACS and trial registries in January 2017. We adapted the MEDLINE strategy for searching the other databases. We used a combination of thesaurus-based and free-text terms to search.

SELECTION CRITERIA

We included randomized-controlled and cross-over trials conducted in any setting where commonly-used classes of drugs were used to prevent acute HAI.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as expected by Cochrane.

MAIN RESULTS

We included 64 studies (78 references) and 4547 participants in this review, and classified 12 additional studies as ongoing. A further 12 studies await classification, as we were unable to obtain the full texts. Most of the studies were conducted in high altitude mountain areas, while the rest used low pressure (hypobaric) chambers to simulate altitude exposure. Twenty-four trials provided the intervention between three and five days prior to the ascent, and 23 trials, between one and two days beforehand. Most of the included studies reached a final altitude of between 4001 and 5000 metres above sea level. Risks of bias were unclear for several domains, and a considerable number of studies did not report adverse events of the evaluated interventions. We found 26 comparisons, 15 of them comparing commonly-used drugs versus placebo. We report results for the three most important comparisons: Acetazolamide versus placebo (28 parallel studies; 2345 participants)The risk of AMS was reduced with acetazolamide (risk ratio (RR) 0.47, 95% confidence interval (CI) 0.39 to 0.56; I² = 0%; 16 studies; 2301 participants; moderate quality of evidence). No events of HAPE were reported and only one event of HACE (RR 0.32, 95% CI 0.01 to 7.48; 6 parallel studies; 1126 participants; moderate quality of evidence). Few studies reported side effects for this comparison, and they showed an increase in the risk of paraesthesia with the intake of acetazolamide (RR 5.53, 95% CI 2.81 to 10.88, I² = 60%; 5 studies, 789 participants; low quality of evidence). Budenoside versus placebo (2 parallel studies; 132 participants)Data on budenoside showed a reduction in the incidence of AMS compared with placebo (RR 0.37, 95% CI 0.23 to 0.61; I² = 0%; 2 studies, 132 participants; low quality of evidence). Studies included did not report events of HAPE or HACE, and they did not find side effects (low quality of evidence). Dexamethasone versus placebo (7 parallel studies; 205 participants)For dexamethasone, the data did not show benefits at any dosage (RR 0.60, 95% CI 0.36 to 1.00; I2 = 39%; 4 trials, 176 participants; low quality of evidence). Included studies did not report events of HAPE or HACE, and we rated the evidence about adverse events as of very low quality.

AUTHORS' CONCLUSIONS

Our assessment of the most commonly-used pharmacological interventions suggests that acetazolamide is an effective pharmacological agent to prevent acute HAI in dosages of 250 to 750 mg/day. This information is based on evidence of moderate quality. Acetazolamide is associated with an increased risk of paraesthesia, although there are few reports about other adverse events from the available evidence. The clinical benefits and harms of other pharmacological interventions such as ibuprofen, budenoside and dexamethasone are unclear. Large multicentre studies are needed for most of the pharmacological agents evaluated in this review, to evaluate their effectiveness and safety.

Extensive Microhemorrhages of the Cerebellar Peduncles After High-Altitude Cerebral Edema

Pichler Hefti, Jacqueline, Philipp Hoigné-Perret, and Raimund Kottke. Extensive microhemorrhages of the cerebellar peduncles after high-altitude cerebral edema. High Alt Med Biol. 18:182-184, 2017.-Neuromagnetic resonance imaging (MRI) of subjects who suffered from high-altitude cerebral edema (HACE) typically shows cerebral microhemorrhages (MH) of the corpus callosum, in particular the splenium, and supratentorial white matter. This is a case report of a 43-year-old male, who suffered from unusually prolonged severe ataxia and amnesia after having been rescued during the ascent to Mount Everest at 6400 m. MRI of the brain 63 days after the incident showed the typical MH in the corpus callosum, but, in addition, extensive MH were found in the middle cerebellar peduncles. These infratentorial MH might reflect the pronounced atactic gait disorder. This case describes the first HACE-associated MH in the cerebellar peduncles in a high-altitude mountaineer indicating a potential vulnerability of infratentorial brain areas to hypobaric hypoxia.

[Mountain medicine. II]

Travelling to high altitudes is an increasingly popular form of recreational holiday. Individual medical advice may be essential for certain groups of individuals such as patients with chronic disorders, pregnant women or children. This is the second part in a series of two articles on mountain medicine. The first part covered high-altitude physiology and medical aspects of objective alpine dangers and the increased exposure to ultraviolet radiation. This part covers altitude sickness, fluid balance, nutrition, and precautions for patients with pre-existing medical conditions, pregnant women and children.

Lipid Subhyaloid Maculopathy and Exposure to High Altitude

BACKGROUND

High altitude retinopathy (HAR) includes a number of diseases related to high altitude such as acute mountain sickness (AMS), high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). High altitude retinopathy is mainly characterized by retinal hemorrhages, usually sparing the macular region, a condition specifically known as high altitude retinal hemorrhages (HARH). The pathogenesis of HARH is unclear. Many studies show that lack of oxygen causes an inadequate autoregulation of retinal circulation, causing vascular incompetence. Other retinal changes described in HAR have been reported, such as optical disk edema, optic disc hyperemia, cotton wool exudates, venous occlusions, and macular edema.

CASE REPORT

In this paper we present a case of an aviator who developed a unilateral maculopathy through subhyaloid lipid accumulation on a climb to the top of Mt. Everest. The clinical findings are suggestive of an apparent case of temporary altitude-induced visual disruption maybe by the same presumable pathogenesis of HARH. Right eye visual loss was perceived at 5150 m when he was trying to take a photograph 40 d into the expedition.

DISCUSSION

The maculopathy developed by this patient adds to the discussion on the pathogenesis of HARH, especially the aspect of this maculopathy and its complete resolution. It seems that autoregulation failure could lead to exudation and lipid deposits in the foveal area. Although macular damage is not a common signal in HARH, checking visual acuity during high altitude expeditions remains an important procedure to avoid late diagnosis as unilateral blindness may not be detected early. Rosas Petrocinio R, Gomes ED. Lipid subhyaloid maculopathy and exposure to high altitude. Aerosp Med Hum Perform. 2016; 87(10):898-900.

Low-Dose Gabapentin in Treatment of High-Altitude Headache

Headache is the most prevalent symptom of acute mountain sickness. We conducted a pilot clinical trial at an altitude of 3500 m to evaluate the efficacy of gabapentin in treatment of high-altitude headache (HAH). Twenty-four adult HAH patients (10 female, 14 male; age 18–50 years) were randomly assigned to receive either 300 mg of gabapentin capsule or identical placebo. After 1 h the presence of HAH and need to receive supplementary analgesic were assessed. The duration of the HAH-free phase after taking additional analgesic was also registered. Four patients in the gabapentin group asked for additional analgesics, whereas nine placebo recipients did not find primary medication satisfactory after the first hour of treatment ( P = 0.04). The mean HAH-free period was 17.10 h in the gabapentin group, which was significantly higher than in the placebo group with a mean of 10.08 h ( P = 0.02). This preliminary observation indicates that gabapentin is effective in treatment and alleviation of HAH.

No Evidence of Cerebral Oedema in Severe Acute Mountain Sickness

In a randomized, double-blind cross-over study 10 subjects were exposed to a simulated altitude of 4500 m for 10 h after administration of placebo, acetozolamide (250 mg bid) or theophylline (250 mg bid). T2-weighted magnetic resonances images (MRI) and diffusion weighted MRI were obtained directly after exposure to altitude under hypoxic conditions. Although eight of 10 subjects had moderate to severe acute mountain sickness (AMS), we found no evidence of cerebral oedema, irrespective of the medication taken. Almost all subjects showed a decrease in inner cerebrospinal fluid (iCSF) volumes (placebo −10.3%, P = 0.02; acetazolamide −13.2%, P = 0.008, theophylline −12.2%, n.s.). There was no correlation between AMS symptoms and fluid shift. However, we found a significantly positive correlation of large (>10 ml) iCSF volume and more severe AMS after administration of placebo ( r = 0.76, P = 0.01). Moderate to severe AMS after high altitude exposure for 10 h is associated with a decreased iCSF-volume independent of AMS severity or medication without signs of cerebral oedema.

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.

•

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

•

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

•

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.

[Pediatric gastrointestinal disorders at hight altitude. Report of two cases and review of literature.]

Upon ascending above 2500 meters sea level, the human body undergoes a series of physiological changes that have been studied during years. These changes undertake various systems including gastrointestinal tract, with diverse clinical manifestations, most mild and therefore little reported and are underdiagnosed. Two pediatric patients who atended to the Pediatric Unit of Gastroenterolog, Hepatolog and Nutrition (Gastronutriped) in Bogota, in whose we documented symptoms affecting gastrointestinal tract associated with high altitude.Regarding to these cases, a review of the available literature focusing on physiolog, clinical manifestations and feasible treatment was made. The final aim of this article is to sensitize to health care professionals working in cities located at high altitudes, to consider this entity as a differential diagnosis in children from places with lower altitude.

High-Altitude Medicine

Individuals may seek the advice of medical providers when considering travel to high altitude. This article provides a basic framework for counseling and evaluating such patients. After defining "high altitude" and describing the key environmental features at higher elevations, the physiologic changes that occur at high altitude and how these changes are experienced by the traveler are discussed. Clinical features and strategies for prevention and treatment of the main forms of acute altitude illness are outlined, and frameworks for approaching the common clinical scenarios that may be encountered regarding high-altitude travelers are provided.

Acute and Chronic Altitude-Induced Cognitive Dysfunction in Children and Adolescents

OBJECTIVE

To assess whether exposure to high altitude induces cognitive dysfunction in young healthy European children and adolescents during acute, short-term exposure to an altitude of 3450 m and in an age-matched European population permanently living at this altitude.

STUDY DESIGN

We tested executive function (inhibition, shifting, and working memory), memory (verbal, short-term visuospatial, and verbal episodic memory), and speed processing ability in: (1) 48 healthy nonacclimatized European children and adolescents, 24 hours after arrival at high altitude and 3 months after return to low altitude; (2) 21 matched European subjects permanently living at high altitude; and (3) a matched control group tested twice at low altitude.

RESULTS

Short-term hypoxia significantly impaired all but 2 (visuospatial memory and processing speed) of the neuropsychological abilities that were tested. These impairments were even more severe in the children permanently living at high altitude. Three months after return to low altitude, the neuropsychological performances significantly improved and were comparable with those observed in the control group tested only at low altitude.

CONCLUSIONS

Acute short-term exposure to an altitude at which major tourist destinations are located induces marked executive and memory deficits in healthy children. These deficits are equally marked or more severe in children permanently living at high altitude and are expected to impair their learning abilities.

New genetic and physiological factors for excessive erythrocytosis and Chronic Mountain Sickness

In the last few years, genetic and functional studies have provided important insight on the pathophysiology of excessive erythrocytosis (EE), the main sign of Chronic Mountain Sickness (CMS). The recent finding of the association of the CMS phenotype with a single-nucleotide polymorphism (SNP) in the Sentrin-specific Protease 1 (SENP1) gene, and its differential expression pattern in Andean highlanders with and without CMS, has triggered large interest in high-altitude studies because of the potential role of its gene product in the control of erythropoiesis. The SENP1 gene encodes for a protease that regulates the function of hypoxia-relevant transcription factors such as Hypoxia-Inducible Factor (HIF) and GATA, and thus might have an erythropoietic regulatory role in CMS through the modulation of the expression of erythropoietin (Epo) or Epo receptors. The different physiological patterns in the Epo-EpoR system found among Andeans, even among highlanders with CMS, together with their different degrees of erythropoietic response, might indicate specific underlying genetic backgrounds, which in turn might reflect different levels of adaptation to lifelong high-altitude hypoxia. This minireview discusses recent genetic findings potentially underlying EE and CMS, and their possible physiological mechanisms in Andean highlanders.