Office and Ambulatory Arterial Hypertension in Highlanders: HIGHCARE-ANDES Highlanders Study

Altitude illnesses

Millions of people visit high-altitude regions annually and more than 80 million live permanently above 2,500 m. Acute high-altitude exposure can trigger high-altitude illnesses (HAIs), including acute mountain sickness (AMS), high-altitude cerebral oedema (HACE) and high-altitude pulmonary oedema (HAPE). Chronic mountain sickness (CMS) can affect high-altitude resident populations worldwide. The prevalence of acute HAIs varies according to acclimatization status, rate of ascent and individual susceptibility. AMS, characterized by headache, nausea, dizziness and fatigue, is usually benign and self-limiting, and has been linked to hypoxia-induced cerebral blood volume increases, inflammation and related trigeminovascular system activation. Disruption of the blood-brain barrier leads to HACE, characterized by altered mental status and ataxia, and increased pulmonary capillary pressure, and related stress failure induces HAPE, characterized by dyspnoea, cough and exercise intolerance. Both conditions are progressive and life-threatening, requiring immediate medical intervention. Treatment includes supplemental oxygen and descent with appropriate pharmacological therapy. Preventive measures include slow ascent, pre-acclimatization and, in some instances, medications. CMS is characterized by excessive erythrocytosis and related clinical symptoms. In severe CMS, temporary or permanent relocation to low altitude is recommended. Future research should focus on more objective diagnostic tools to enable prompt treatment, improved identification of individual susceptibilities and effective acclimatization and prevention options.

Association between high-altitude polycythemia and hypertension: a cross-sectional study in adults at Tibetan ultrahigh altitudes

The study aimed to evaluate the association between high-altitude polycythemia and hypertension in adults residing on Anduo County's plateau, which is located 4700 meters above sea level. A total of 387 individuals participated in the cross-sectional survey conducted between April and May of 2021. Interviews, physical inspections, and laboratory tests were employed to gather information about all of the subjects. The association between high-altitude polycythemia and hypertension was assessed using multivariable logistic regression models. The average age of the 387 participants was 32.6 ± 6.3 years. Of these participants, 260 (67%) were male. The overall prevalence of hypertension was 27.1% (57/380). When stratified by gender, the prevalence was 12.6% (16/127) in females and 34.2% (89/260) in males. The overall prevalence of high-altitude polycythemia was 19.6% (76/387). When stratified by gender, the prevalence was 26.2% (68/260) in males and 6.3% (8/127) in females. During logistic regression analysis, we found that participants with elevated hemoglobin per 10 g/L had a 26% greater risk of hypertension (adjusting for odds ratio [OR], 1.26; 95% confidence interval [CI], 1.11-1.44). Additionally, high-altitude polycythemia greatly increased the risk of hypertension in comparison to non-high-altitude polycythemia (OR, 3.01; 95% CI, 1.66-5.44, P < 0.001). The consistency of the results was further demonstrated by stratified and interaction analyses, showing that Hans individuals had a higher risk of hypertension. High-altitude polycythemia is positively associated with hypertension in adults residing at Tibetan ultrahigh altitudes. The results of the investigation may aid in the planning of future research and guide the development of targeted healthcare practices for high-altitude populations, particularly among Han Chinese residents of the Tibetan Plateau.

Hypertension subtypes at high altitude in Peru: Analysis of the Demographic and Family Health Survey 2016-2019

BACKGROUND

The prevalence of hypertension in Peru has increased over the years. Approximately one third of the Peruvian population lives at high altitudes. This population presents particular physiological, genetic and environmental characteristics that could be related to the prevalence of hypertension and its subtypes.

OBJECTIVE

To assess the association between altitude and hypertension in the Peruvian population through an analysis of a nationally representative survey.

METHODS

We conducted a cross-sectional analysis of the Demographic and Family Health Survey for the period 2016-2019. We included 122,336 individuals aged 18 years and older. Hypertension was defined according to the JNC-7 guidelines. High-altitude location was defined as a residential cluster located above 2,500 meters above sea level. We utilized generalized linear models from the Poisson family with a log-link function to assess the magnitude of the association between high altitude and hypertension. Additionally, we employed multinomial regression models to analyze the association between high altitude and subtypes of hypertension, including isolated systolic hypertension (ISH), isolated diastolic hypertension (IDH), and systolic-diastolic hypertension (SDH).

RESULTS

In the adjusted Poisson regression model, we found that the prevalence of hypertension among participants living at high altitudes was lower compared to those living at low altitudes (aPR: 0.89; 95% CI: 0.86-0.93). In the adjusted multinomial regression model, we observed a lower prevalence rate of ISH among participants residing at high altitudes (aRPR: 0.68; 95% CI: 0.61-0.73) and a higher prevalence rate of IDH among participants residing at high altitudes (aRPR: 1.60; 95% CI: 1.32-1.94).

CONCLUSIONS

Residents at high altitudes in Peru have a lower prevalence rate of ISH and a higher prevalence rate of IDH compared to those living at low altitudes. Further studies are needed to determine the influence of other biological, environmental, and healthcare access factors on this relationship.

Association between hemoglobin concentration and hypertension risk in native Tibetans at high altitude

Previous studies examining the association between hemoglobin concentration and hypertension have yielded inconsistent results. There is still a lack of evidence regarding the association between hemoglobin concentration and hypertension risk in native Tibetans at high altitude. We performed this cross-sectional study in Luhuo County of Ganzi Tibetan Autonomous Prefecture (average altitude of 3500 m). In this study, we enrolled 1547 native Tibetans. The association between hemoglobin concentration and hypertension risk was examined by multivariate binary logistic regression and smooth curve fitting. Native Tibetans with hypertension had significantly higher hemoglobin concentrations than those without hypertension (165.9 ± 21.5 g/L vs. 157.7 ± 19.2 g/L, P < 0.001). An increase in hemoglobin concentration of 1 g/L was associated with hypertension (odds ratio [OR] 1.02, 95% confidence interval [CI] 1.01-1.02) after confounder adjustment. The highest hemoglobin concentration group (exceeding 173 g/L) was associated with an increased hypertension risk compared with the bottom quartile of hemoglobin concentration (OR 2.39, 95% CI 1.48-3.85). Hemoglobin concentration (per 1 g/L change) exceeding 176 g/L was significantly associated with an increased hypertension risk (OR 1.04, 95% CI 1.03-1.06). Additionally, high-altitude polycythemia significantly increased the hypertension risk compared with a normal hemoglobin concentration (OR 2.92, 95% CI 1.25-6.86). A similar result was observed for mild polycythemia (OR 1.74, 95% CI 1.29-2.34). In conclusion, hemoglobin concentration was associated with hypertension risk in native Tibetans. When the hemoglobin concentration exceeded a certain value (approximately 176 g/L), the risk of hypertension was significantly increased.

More severe initial manifestations and worse short-term functional outcome of intracerebral hemorrhage in the plateau than in the plain

Intracerebral hemorrhage (ICH) is one of the most devastating forms of stroke. However, studies on ICH at high altitude are insufficient. We aimed to compare the initial manifestations, imaging features and short-term functional outcomes of ICH at different altitudes, and further explore the effect of altitude on the severity and prognosis of ICH. We retrospectively recruited ICH patients from January 2018 to July 2021 from two centers at different altitudes in China. Information regarding to clinical manifestations, neuroimages, and functional outcomes at discharge were collected and analyzed. Association between altitude and initial severity, neuroimages, and short-term prognosis of ICH were also investigated. A total of 724 patients with 400 lowlanders and 324 highlanders were enrolled. Compared with patients from the plain, those at high altitude were characterized by more severe preliminary manifestations (P < 0.0001), larger hematoma volume (P < 0.001) and poorer short-term functional outcome (P < 0.0001). High altitude was independently associated with dependency at discharge (adjusted P = 0.024), in-hospital mortality (adjusted P = 0.049) and gastrointestinal hemorrhage incidence (adjusted P = 0.017). ICH patients from high altitude suffered from more serious initial manifestations and worse short-term functional outcome than lowlanders. Control of blood pressure, oxygen supplementation and inhibition of inflammation may be critical for ICH at high altitude.

Prevalence of hypertension in adults living at altitude in Latin America and the Caribbean: A systematic review and meta-analysis

OBJECTIVE

The objective of this systematic review and meta-analysis was to assess the prevalence of hypertension in populations living at altitude in Latin America and the Caribbean.

METHODS

We conducted a systematic search from January 1, 2000 to January 10, 2023 in Web of Science (WoS)/Core Collection, WoS/Medline, WoS/Scielo, Scopus, PubMed and Embase databases. We included studies that assessed the prevalence of hypertension in altitude populations (>1500 m.a.s.l.) and these were meta-analyzed using a random-effects model. To assess the sources of heterogeneity, we performed subgroup and meta-regression analyses.

RESULTS

Thirty cross-sectional studies (117 406 participants) met the inclusion criteria. Studies used different cut-off points. The prevalence of hypertension in the studies that considered the cut-off point of ≥ 140/90 mmHg in the general population was 19.1%, ≥ 130/85 mmHg was 13.1%, and ≥ 130/80 mmHg was 43.4%. There was a tendency for the prevalence of hypertension to be higher in men. In meta-regression analyses, no association was found between altitude, mean age, year of publication, risk of bias and prevalence of hypertension.

CONCLUSION

The prevalence of hypertension in the altitude population of Latin America and the Caribbean is lower than that reported in populations living at sea level and lower than other altitude populations such as Tibetans.

PROSPERO

CRD42021275229.

Preserved peak exercise capacity in Andean highlanders with excessive erythrocytosis both before and after isovolumic hemodilution

In chronic mountain sickness (CMS), increased blood oxygen (O₂)-carrying capacity due to excessive erythrocytosis (EE, [Hb] ≥ 21 g/dL) could be offset, especially during exercise by both impaired cardiac output (Q̇t) and O₂ diffusion limitation in lungs and muscle. We hypothesized that EE results in reduced peak V̇o₂ despite increased blood O₂-carrying capacity, and that isovolumic hemodilution (IVHD) improves exercise capacity. In 14 male residents of Cerro de Pasco, Peru (4,340 m), six with and eight without EE, we measured peak cycle-exercise capacity, V̇o₂, Q̇t, arterial blood gas parameters, and (resting) blood volume. This was repeated for participants with EE after IVHD, reducing hematocrit by 20% (from 67% to 53%). From these data, we quantified the major O₂ transport pathway components (ventilation, pulmonary alveolar-capillary diffusion, Q̇t, and blood-muscle mitochondria diffusion). Participants with EE had similar peak V̇o₂, systemic O₂ delivery, and O₂ extraction as non-EE controls, however, with lower Q̇t and higher arterial [O₂]. After IVHD, peak V̇o₂ was preserved (but not enhanced), with lower O₂ delivery (despite higher Q̇t) balanced by greater O₂ extraction. The considerable variance in exercise capacity across the 14 individuals was explained essentially completely by differences in both pulmonary and muscle O₂ diffusional conductances and not by any differences in ventilation, [Hb], nor Q̇t. In conclusion, EE does not result in lower peak V̇o₂ in Andean males, and IVHD maintains, but does not enhance, exercise capacity.NEW & NOTEWORTHY Male Andean highlanders with and without excessive erythrocytosis (EE) have similar peak V̇o₂ at 4,340 m, with higher arterial [O₂] in EE and lower cardiac output (Q̇t), thus maintaining similar O₂ delivery. Peak V̇o₂ in participants with EE was unaffected by isovolumic hemodilution (hematocrit reduced from 67% to 53%), with lower O₂ delivery balanced by slightly increased Q̇t and greater O₂ extraction. Differences in lung and muscle diffusing capacity, and not hematocrit variation, accounted for essentially all interindividual variance in peak V̇o₂.

Cardiac remodelling in the highest city in the world: effects of altitude and chronic mountain sickness

AIMS

A unique Andean population lives in the highest city of the world (La Rinconada, 5100 m, Peru) and frequently develops a maladaptive syndrome, termed chronic mountain sickness (CMS). Both extreme altitude and CMS are a challenge for the cardiovascular system. This study aims to evaluate cardiac remodelling and pulmonary circulation at rest and during exercise in healthy and CMS highlanders.

METHODS AND RESULTS

Highlanders living permanently at 3800 m (n = 23) and 5100 m (n = 55) with (n = 38) or without CMS (n = 17) were compared with 18 healthy lowlanders. Rest and exercise echocardiography were performed to describe cardiac remodelling, pulmonary artery pressure (PAP), and pulmonary vascular resistance (PVR). Total blood volume (BV) and haemoglobin mass were determined in all people. With the increase in the altitude of residency, the right heart dilated with an impairment in right ventricle systolic function, while the left heart exhibited a progressive concentric remodelling with Grade I diastolic dysfunction but without systolic dysfunction. Those modifications were greater in moderate-severe CMS patients. The mean PAP was higher both at rest and during exercise in healthy highlanders at 5100 m. The moderate-severe CMS subjects had a higher PVR at rest and a larger increase in PAP during exercise. The right heart remodelling was correlated with PAP, total BV, and SpO2.

CONCLUSION

Healthy dwellers at 5100 m exhibit both right heart dilatation and left ventricle concentric remodelling with diastolic dysfunction. Those modifications are even more pronounced in moderate-severe CMS subjects and could represent the limit of the heart's adaptability before progression to heart failure.

Nocturnal hypoxemia, blood pressure, vascular status and chronic mountain sickness in the highest city in the world

INTRODUCTION

Chronic mountain sickness (CMS) is a condition characterized by excessive erythrocytosis in response to chronic hypobaric hypoxia. CMS frequently triggers cardiorespiratory diseases such as pulmonary hypertension and right or left heart failure. Ambient hypoxia might be further amplified night-time by intermittent hypoxia related to sleep-disordered breathing (SDB) so that sleep disturbance may be an important feature of CMS. Our aim was to characterize in a cross-sectional study nocturnal hypoxaemia, SDB, blood pressure (BP), arterial stiffness and carotid intima-media thickness (CIMT) in highlanders living at extreme altitude.

METHODS

Men aged 18 to 55 years were prospectively recruited. Home sleep apnoea test, questionnaires (short-form health survey; Montreal cognitive assessment; Pittsburgh Sleep Questionnaire Index and the Insomnia severity index), 24-h ambulatory BP monitoring, CIMT and arterial stiffness were evaluated in 3 groups: i) Andean lowlanders (sea-level); ii) highlanders living at 3,800 m and iii) highlanders living at 5,100 m. Analyses were conducted in sub-groups according to 1) CMS severity 2) healthy subjects living at the three different altitude.

RESULTS

Ninety-two males were evaluated at their living altitudes. Among the 54 highlanders living at 5,100 m, subjects with CMS showed lower mean nocturnal oxygen saturation (SpO₂), SpO₂ nadir, lower pulse wave velocity and higher nocturnal BP variability than those with no-CMS. Lower nocturnal SpO₂ nadir was associated with higher CMS severity (ß= -0.14, p=.009). Among the 55 healthy subjects, healthy highlanders at 5,100 m were characterized by lower scores on quality of life and sleep quality scales and lower mean SpO₂ compared to lowlanders.

CONCLUSIONS

Lower nocturnal SpO₂ and higher nocturnal BP variability are associated with CMS severity in individuals living permanently at high altitude. The role of lower SpO₂ and higher nocturnal BP variability in the cardiovascular progression of CMS and in the overall prognosis of the disease need to be evaluated in further studies.

High-Altitude Erythrocytosis: Mechanisms of Adaptive and Maladaptive Responses

Erythrocytosis, or increased production of red blood cells, is one of the most well-documented physiological traits that varies within and among in high-altitude populations. Although a modest increase in blood O₂-carrying capacity may be beneficial for life in highland environments, erythrocytosis can also become excessive and lead to maladaptive syndromes such as chronic mountain sickness (CMS).

Prevalence of hypertension and its relationship with altitude in highland areas: a systematic review and meta-analysis

This systematic review and meta-analysis synthesized the pooled prevalence of hypertension at high altitudes and explored its correlation with altitude using studies published in Chinese and English from database inception to February 2021. A systematic literature search was conducted among bibliographic databases (PubMed, Embase, and Web of Science) and three Chinese databases (CNKI, VIP, and Wanfang data) to identify eligible studies. A random-effects model was used to calculate the overall pooled prevalence of hypertension. The I² statistic was used to assess heterogeneity across studies. Random-effects meta-regression was conducted to investigate covariates that may have influenced between-study heterogeneity. The pooled prevalence of hypertension among the general population in high-altitude areas was 33.0% (95% CI: 29.0-38.0%), with high between-study heterogeneity (I² = 99.4%, P < 0.01). Subgroup analyses showed the pooled prevalence of hypertension in Tibetan individuals was significantly higher than that in non-Tibetan individuals living in the Himalayas and Pamir Mountains (41% vs. 18%). A trend toward an increase in the prevalence of hypertension was found with every 100-m increase in elevation (coefficient: 0.012, 95% CI: -0.001 to 0.025, P = 0.069) only in Tibetan individuals. In addition, in these individuals, we found an increase in mean diastolic BP with each 100-m increase in altitude (coefficient: 0.763, 95% CI: 0.122-1.403, P = 0.025). Our meta-analysis suggests that the pooled prevalence of hypertension among the general population in high-altitude areas is 33.0%. Subjects of Tibetan ethnicity were more prone to developing hypertension at high altitudes. However, a very weak relationship between altitude and the prevalence of hypertension was found only in Tibetan individuals.

Association between Altitude and the Framingham Risk Score: A Cross-Sectional Study in the Peruvian Adult Population

To determine the association between altitude and the Framingham risk score in the Peruvian population, we performed a cross-sectional analytical study of data collected by the 2017–2018 Food and Nutrition Surveillance by Life Stages survey. The outcome of this study was the Framingham 10-year cardiovascular disease event risk prediction, which is composed of six modifiable and non-modifiable coronary risk factors. A generalized linear model (GLM) of the gamma family and log link function was used to report the crude and adjusted β coefficients. Several sensitivity analyses were performed to assess the association of interest. Data from a total of 833 surveyed participants were included. After adjusting for educational level, poverty level, alcohol consumption, physical activity level, the presence of any limitation, obesity, and area of residence, it was observed that altitude ≥ 2500 m above sea level (β = −0.42 [95% CI: −0.69 to −0.16]) was negatively and significantly associated with a decrease in the Framingham 10-year risk score. High altitude was significantly and negatively associated with Framingham 10-year risk scores. Our results will allow prevention strategies considering modifiable risk factors to avoid the development of cardiovascular diseases, especially in people living at low altitudes.

Effect of acetazolamide on obstructive sleep apnoea in highlanders: protocol for a randomised, placebo-controlled, double-blinded crossover trial

INTRODUCTION

Obstructive sleep apnoea (OSA) is a highly prevalent disease that causing systemic hypertension. Furthermore, altitude-dependent hypobaric hypoxic condition and Tibetan ethnicity have been associated with systemic hypertension independent of OSA, therefore patients with OSA living at high altitude might be at profound risk to develop systemic hypertension. Acetazolamide has been shown to decrease blood pressure, improve arterial oxygenation and prevent high altitude periodic breathing in healthy volunteers ascending to high altitude and decrease blood pressure in patients with systemic hypertension at low altitude. However, the effect of acetazolamide on 24-hour blood pressure, sleep-disordered disturbance and daytime cognitive performance in patients with OSA permanently living at high altitude has not been studied.

METHODS AND ANALYSIS

This study protocol describes a randomised, placebo-controlled, double-blinded crossover trial. Highland residents of both sexes, aged 30-60 years, Tibetan ethnicity, living at an elevation of 3650 m and apnoea-hypopnoea index over 15/hour will be included. Participants will be randomly assigned to a 2×2 week treatment period starting with 750 mg/day acetazolamide followed by placebo treatment or vice versa, separated by a 1-week wash-out phase. Clinical assessments, 24-hour ambulatory blood pressure monitoring (ABPM), polysomnography (PSG), near-infrared spectroscopy, nocturnal fluid shift and cognitive performance will be assessed before and at the end of each treatment period. The primary outcome will be the difference in 24-hour mean blood pressure between acetazolamide therapy and placebo; secondary outcomes will be the difference in other 24-hour ABPM-derived parameters, PSG-derived parameters, cognitive performance and overnight change in different segments of fluid volume between acetazolamide therapy and placebo. Accounting for potential dropouts, 40 participants will be recruited.

ETHICS AND DISSEMINATION

The protocol was approved by the West China Hospital of Sichuan University Biomedical Research Ethics Committee. Recruitment will start in spring 2022. Dissemination of the results include presentations at conferences and publications in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ChiCTR2100049304.

Sub-maximal aerobic exercise training reduces haematocrit and ameliorates symptoms in Andean highlanders with chronic mountain sickness

New Findings

What is the central question of this study?

What is the effect of sub‐maximal aerobic exercise training on signs and symptoms of chronic mountain sickness (CMS) in Andean highlanders?

What is the main finding and its importance?

Aerobic exercise training (ET) effectively reduces haematocrit, ameliorates symptoms and improves aerobic capacity in CMS patients, suggesting that a regular aerobic ET programme might be used as a low‐cost non‐invasive/non‐pharmacological management strategy of this syndrome.

Abstract

Excessive erythrocytosis is the hallmark sign of chronic mountain sickness (CMS), a debilitating syndrome associated with neurological symptoms and increased cardiovascular risk. We have shown that unlike sedentary residents at the same altitude, trained individuals maintain haematocrit within sea‐level range, and thus we hypothesise that aerobic exercise training (ET) might reduce excessive haematocrit and ameliorate CMS signs and symptoms. Eight highlander men (38 ± 12 years) with CMS (haematocrit: 70.6 ± 1.9%, CMS score: 8.8 ± 1.4) from Cerro de Pasco, Peru (4340 m) participated in the study. Baseline assessment included haematocrit, CMS score, pulse oximetry, maximal cardiopulmonary exercise testing and in‐office plus 24 h ambulatory blood pressure (BP) monitoring. Blood samples were collected to assess cardiometabolic, erythropoietic, and haemolysis markers. ET consisted of pedalling exercise in a cycloergometer at 60% of V˙O2peak for 1 h/day, 4 days/week for 8 weeks, and participants were assessed at weeks 4 and 8. Haematocrit and CMS score decreased significantly by week 8 (to 65.6 ± 6.6%, and 3.5 ± 0.8, respectively, P < 0.05), while V˙O2peak and maximum workload increased with ET (33.8 ± 2.4 vs. 37.2 ± 2.0 ml/min/kg, P < 0.05; and 172.5 ± 9.4 vs. 210.0 ± 27.8 W, P < 0.01; respectively). Except for an increase in high‐density lipoprotein cholesterol, other blood markers and BP showed no differences. Our results suggest that reduction of haematocrit and CMS symptoms results mainly from haemodilution due to plasma volume expansion rather than to haemolysis. In conclusion, we show that ET can effectively reduce haematocrit, ameliorate symptoms and improve aerobic capacity in CMS patients, suggesting that regular aerobic exercise might be used as a low‐cost non‐invasive and non‐pharmacological management strategy.

Blood Pressure Response in Miners Exposed to Chronic Intermittent Hypoxia in Chile

Introduction: Limited information is available on blood pressure (BP) behavior in workers exposed to chronic intermittent hypoxia (CIH), and even less is known regarding effects of CIH on 24-h ambulatory BP in those affected by arterial hypertension at sea level (SL). The aims of this study were to assess clinic and 24-h ambulatory BP at SL and at high altitude (HA; 3,870 m above SL) in workers exposed to CIH, and to compare BP response to HA exposure between normotensive and hypertensive workers.

Methods: Nineteen normotensive and 18 pharmacologically treated hypertensive miners acclimatized to CIH were included, whose work was organized according to a “7 days-on−7 days-off” shift pattern between SL and HA. All measurements were performed on the second and seventh day of their HA shift and after the second day of SL sojourn.

Results: Compared to SL, 24-h systolic BP (SBP) and diastolic BP (DBP) increased at HA [+14.7 ± 12.6 mmHg (p < 0.001) and +8.7 ± 7.2 mmHg (p < 0.001), respectively], and SBP nocturnal fall decreased consistently (−4.1 ± 9.8%; p < 0.05) in all participants, with hypertensives showing higher nocturnal DBP than normotensives (p < 0.05) despite the current therapy. Also, heart rate (HR) nocturnal fall tended to be reduced at HA. In addition, the 24-h SBP/DBP hypertension threshold of ≥130/80 mmHg was exceeded by 39% of workers at SL and by 89% at HA. Clinic HR, SBP, and DBP were significantly higher on the second day of work at HA compared with SL, the increase being more pronounced for SBP in hypertensives (p < 0.05) and accompanied by, on average, mild altitude sickness in both groups. These symptoms and the values of all cardiovascular variables decreased on the seventh day at HA (p < 0.05) regardless of CIH exposure duration.

Conclusion: Long history of work at HA according to scheduled CIH did not prevent the occurrence of acute cardiovascular changes at HA during the first days of exposure. The BP response to HA tended to be more pronounced in hypertensive than in normotensive workers despite being already treated; the BP changes were more evident for 24-h ambulatory BP. Twenty-four-hour ABP monitoring is a useful tool for an appropriate evaluation of BP in CIH workers.

Global REACH 2018: the adaptive phenotype to life with chronic mountain sickness and polycythaemia

KEY POINTS

Humans suffering from polycythaemia undergo multiple circulatory adaptations including changes in blood rheology and structural and functional vascular adaptations to maintain normal blood pressure and vascular shear stresses, despite high blood viscosity. During exercise, several circulatory adaptations are observed, especially involving adrenergic and non-adrenergic mechanisms within non-active and active skeletal muscle to maintain exercise capacity, which is not observed in animal models. Despite profound circulatory stress, i.e. polycythaemia, several adaptations can occur to maintain exercise capacity, therefore making early identification of the disease difficult without overt symptomology. Pharmacological treatment of the background heightened sympathetic activity may impair the adaptive sympathetic response needed to match local oxygen delivery to active skeletal muscle oxygen demand and therefore inadvertently impair exercise capacity.

ABSTRACT

Excessive haematocrit and blood viscosity can increase blood pressure, cardiac work and reduce aerobic capacity. However, past clinical investigations have demonstrated that certain human high-altitude populations suffering from excessive erythrocytosis, Andeans with chronic mountain sickness, appear to have phenotypically adapted to life with polycythaemia, as their exercise capacity is comparable to healthy Andeans and even with sea-level inhabitants residing at high altitude. By studying this unique population, which has adapted through natural selection, this study aimed to describe how humans can adapt to life with polycythaemia. Experimental studies included Andeans with (n = 19) and without (n = 17) chronic mountain sickness, documenting exercise capacity and characterizing the transport of oxygen through blood rheology, including haemoglobin mass, blood and plasma volume and blood viscosity, cardiac output, blood pressure and changes in total and local vascular resistances through pharmacological dissection of α-adrenergic signalling pathways within non-active and active skeletal muscle. At rest, Andeans with chronic mountain sickness had a substantial plasma volume contraction, which alongside a higher red blood cell volume, caused an increase in blood viscosity yet similar total blood volume. Moreover, both morphological and functional alterations in the periphery normalized vascular shear stress and blood pressure despite high sympathetic nerve activity. During exercise, blood pressure, cardiac work and global oxygen delivery increased similar to healthy Andeans but were sustained by modifications in both non-active and active skeletal muscle vascular function. These findings highlight widespread physiological adaptations that can occur in response to polycythaemia, which allow the maintenance of exercise capacity.

Impact of High Altitude on Cardiovascular Health: Current Perspectives

Globally, about 400 million people reside at terrestrial altitudes above 1500 m, and more than 100 million lowlanders visit mountainous areas above 2500 m annually. The interactions between the low barometric pressure and partial pressure of O2, climate, individual genetic, lifestyle and socio-economic factors, as well as adaptation and acclimatization processes at high elevations are extremely complex. It is challenging to decipher the effects of these myriad factors on the cardiovascular health in high altitude residents, and even more so in those ascending to high altitudes with or without preexisting diseases. This review aims to interpret epidemiological observations in high-altitude populations; present and discuss cardiovascular responses to acute and subacute high-altitude exposure in general and more specifically in people with preexisting cardiovascular diseases; the relations between cardiovascular pathologies and neurodegenerative diseases at altitude; the effects of high-altitude exercise; and the putative cardioprotective mechanisms of hypobaric hypoxia.

[Blood pressure and high altitude: physiological response and clinical management]

High altitude is an extreme environment that challenges human beings exposed because of work, recreational activities, or habitat. Exposure to hypobaric hypoxia results in physiological adaptations in response to the geography and the associated extreme environmental conditions. These acclimatization responses can be diverse and result from evolutionary changes and comorbidities. In this context, this review aims to identify the available evidence on the effects of high altitude on blood pressurefrom the physiological to clinical aspects at rest and during exerciseand the underlying mechanisms and possible clinical implications of acute and chronic intermittent hypoxia.