Functional EPAS1/HIF2A missense variant is associated with hematocrit in Andean highlanders.

Hypoxia-inducible factor pathway genes are linked to adaptation in both human and nonhuman highland species. EPAS1, a notable target of hypoxia adaptation, is associated with relatively lower hemoglobin concentration in Tibetans. We provide evidence for an association between an adaptive EPAS1 variant (rs570553380) and the same phenotype of relatively low hematocrit in Andean highlanders. This Andean-specific missense variant is present at a modest frequency in Andeans and absent in other human populations and vertebrate species except the coelacanth. CRISPR-base-edited human cells with this variant exhibit shifts in hypoxia-regulated gene expression, while metabolomic analyses reveal both genotype and phenotype associations and validation in a lowland population. Although this genocopy of relatively lower hematocrit in Andean highlanders parallels well-replicated findings in Tibetans, it likely involves distinct pathway responses based on a protein-coding versus noncoding variants, respectively. These findings illuminate how unique variants at EPAS1 contribute to the same phenotype in Tibetans and a subset of Andean highlanders despite distinct evolutionary trajectories.

Impact of Oxygen Supplementation on Brachial Artery Hemodynamics and Vascular Function During Ascent to 5,050 m.

Vizcardo-Galindo, Gustavo A., Connor A. Howe, Ryan L. Hoiland, Howard H. Carter, Christopher K. Willie, Philip N. Ainslie, and Joshua C. Tremblay. Impact of oxygen supplementation on brachial artery hemodynamics and vascular function during ascent to 5,050 m. High Alt Med Biol. 24:27-36, 2023.-High-altitude trekking alters upper limb hemodynamics and reduces brachial artery vascular function in lowlanders. Whether these changes are reversible with the removal of hypoxia is unknown. We investigated the impact of 20 minutes of oxygen supplementation (O2) on brachial artery hemodynamics, reactive hyperemia (RH; microvascular function), and flow-mediated dilation (FMD; endothelial function). Participants (aged 21-42 years) were examined before and with O2 at 3,440 m (n = 7), 4,371 m (n = 7), and 5,050 m (n = 12) using Duplex ultrasound (days 4, 7, and 10 respectively). At 3,440 m, O2 decreased brachial artery diameter (-5% ± 5%; p = 0.04), baseline blood flow (-44% ± 15%; p < 0.001), oxygen delivery (-39 ± 16; p < 0.001), and peak RH (-8% ± 8%; p = 0.02), but not RH normalized for baseline blood flow. Elevated FMD (p = 0.04) with O2 at 3,440 m was attributed to the reduction in baseline diameter. At 5,050 m, a reduction in brachial artery blood flow (-17% ± 22%; p = 0.03), but not oxygen delivery, diameter, RH, or FMD occurred with O2. These findings suggest that during early trekking at high altitude, O2 causes vasoconstriction in the upper limb along the arterial tree (conduit and resistance arteries). With incremental high-altitude exposure, O2 reduces blood flow without compromising oxygen delivery, RH, or FMD, suggesting a differential impact on vascular function modulated by the duration and severity of high-altitude exposure.

Lifelong exposure to high-altitude hypoxia in humans is associated with improved redox homeostasis and structural-functional adaptations of the neurovascular unit.

High-altitude (HA) hypoxia may alter the structural-functional integrity of the neurovascular unit (NVU). Herein, we compared male lowlanders (n = 9) at sea level (SL) and after 14 days acclimatization to 4300 m (chronic HA) in Cerro de Pasco (CdP), Péru (HA), against sex-, age- and body mass index-matched healthy highlanders (n = 9) native to CdP (lifelong HA). Venous blood was assayed for serum proteins reflecting NVU integrity, in addition to free radicals and nitric oxide (NO). Regional cerebral blood flow (CBF) was examined in conjunction with cerebral substrate delivery, dynamic cerebral autoregulation (dCA), cerebrovascular reactivity to carbon dioxide (CVRCO2 ) and neurovascular coupling (NVC). Psychomotor tests were employed to examine cognitive function. Compared to lowlanders at SL, highlanders exhibited elevated basal plasma and red blood cell NO bioavailability, improved anterior and posterior dCA, elevated anterior CVRCO2 and preserved cerebral substrate delivery, NVC and cognition. In highlanders, S100B, neurofilament light-chain (NF-L) and T-tau were consistently lower and cognition comparable to lowlanders following chronic-HA. These findings highlight novel integrated adaptations towards regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia. KEY POINTS: High-altitude (HA) hypoxia has the potential to alter the structural-functional integrity of the neurovascular unit (NVU) in humans. For the first time, we examined to what extent chronic and lifelong hypoxia impacts multimodal biomarkers reflecting NVU structure and function in lowlanders and native Andean highlanders. Despite lowlanders presenting with a reduction in systemic oxidative-nitrosative stress and maintained cerebral bioenergetics and cerebrovascular function during chronic hypoxia, there was evidence for increased axonal injury and cognitive impairment. Compared to lowlanders at sea level, highlanders exhibited elevated vascular NO bioavailability, improved dynamic regulatory capacity and cerebrovascular reactivity, comparable cerebral substrate delivery and neurovascular coupling, and maintained cognition. Unlike lowlanders following chronic HA, highlanders presented with lower concentrations of S100B, neurofilament light chain and total tau. These findings highlight novel integrated adaptations towards the regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia.

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.

Cerebral endothelium-dependent function and reactivity to hypercapnia: the role of α1-adrenoreceptors.

We assessed hypercapnic cerebrovascular reactivity (CVR) and endothelium-dependent function [cerebral shear-mediated dilation (cSMD)] in the internal carotid artery (ICA) with and without systemic α1-adrenoreceptor blockade via Prazosin. We hypothesized that CVR would be reduced, whereas cSMD would remain unchanged, after Prazosin administration when compared with placebo. In 15 healthy adults (3 female, 26 ± 4 years), we conducted ICA duplex ultrasound during CVR [target +10 mmHg partial pressure of end-tidal carbon dioxide ([Formula: see text]) above baseline, 5 min] and cSMD (+9 mmHg [Formula: see text] above baseline, 30 s) using dynamic end-tidal forcing with and without α1-adrenergic blockade (Prazosin; 0.05 mg/kg) in a placebo-controlled, double-blind, and randomized design. The CVR in the ICA was not different between placebo and Prazosin (P = 0.578). During CVR, the reactivities of mean arterial pressure and cerebrovascular conductance to hypercapnia were also not different between conditions (P = 0.921 and P = 0.664, respectively). During Prazosin, cSMD was lower (1.1 ± 2.0% vs 3.8 ± 3.0%; P = 0.032); however, these data should be interpreted with caution due to the elevated baseline diameter (+1.3 ± 3.6%; condition: P = 0.0498) and lower shear rate (-14.5 ± 23.0%; condition: P < 0.001). Therefore, lower cSMD post α1-adrenoreceptor blockade might not indicate a reduction in cerebral endothelial function per se, but rather, that α1-adrenoreceptors contribute to resting cerebral vascular restraint at the level of the ICA.NEW & NOTEWORTHY We assessed steady-state hypercapnic cerebrovascular reactivity and cerebral endothelium-dependent function, with and without α1-adrenergic blockade (Prazosin), in a placebo-controlled, double-blind, and randomized study, to assess the contribution of α1-adrenergic receptors to cerebrovascular CO2 regulation. After administration of Prazosin, cerebrovascular reactivity to CO2 was not different compared with placebo despite lower blood flow, whereas cerebral endothelium-dependent function was reduced, likely due to elevated baseline internal carotid arterial diameter. These findings suggest that α1-adrenoreceptor activity does not influence cerebral blood flow regulation to CO2 and cerebral endothelial function.

Brachial artery responses to acute hypercapnia: The roles of shear stress and adrenergic tone.

NEW FINDINGS: What is the central question of this study? What are the contributions of shear stress and adrenergic tone to brachial artery vasodilatation during hypercapnia? What is the main finding and its importance? In healthy young adults, shear-mediated vasodilatation does not occur in the brachial artery during hypercapnia, as elevated α1-adrenergic activity typically maintains vascular tone and offsets distal vasodilatation controlling flow. ABSTRACT: We aimed to assess the shear stress dependency of brachial artery (BA) responses to hypercapnia, and the α1-adrenergic restraint of these responses. We hypothesized that elevated shear stress during hypercapnia would cause BA vasodilatation, but where shear stress was prohibited (via arterial compression), the BA would not vasodilate (study 1); and, in the absence of α1-adrenergic activity, blood flow, shear stress and BA vasodilatation would increase (study 2). In study 1, 14 healthy adults (7/7 male/female, 27 ± 4 years) underwent bilateral BA duplex ultrasound during hypercapnia (partial pressure of end-tidal carbon dioxide, +10.2 ± 0.3 mmHg above baseline, 12 min) via dynamic end-tidal forcing, and shear stress was reduced in one BA using manual compression (compression vs. control arm). Neither diameter nor blood flow was different between baseline and the last minute of hypercapnia (P = 0.423, P = 0.363, respectively) in either arm. The change values from baseline to the last minute, in diameter (%; P = 0.201), flow (ml/min; P = 0.234) and conductance (ml/min/mmHg; P = 0.503) were not different between arms. In study 2, 12 healthy adults (9/3 male/female, 26 ± 4 years) underwent the same design with and without α1-adrenergic receptor blockade (prazosin; 0.05 mg/kg) in a placebo-controlled, double-blind and randomized design. BA flow, conductance and shear rate increased during hypercapnia in the prazosin control arm (interaction, P < 0.001), but in neither arm during placebo. Even in the absence of α1-adrenergic restraint, downstream vasodilatation in the microvasculature during hypercapnia is insufficient to cause shear-mediated vasodilatation in the BA.

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.

Acid-base balance at high altitude in lowlanders and indigenous highlanders.

High-altitude exposure results in a hyperventilatory-induced respiratory alkalosis followed by renal compensation (bicarbonaturia) to return arterial blood pH (pHa) toward sea-level values. However, acid-base balance has not been comprehensively examined in both lowlanders and indigenous populations-where the latter are thought to be fully adapted to high altitude. The purpose of this investigation was to compare acid-base balance between acclimatizing lowlanders and Andean and Sherpa highlanders at various altitudes (∼3,800, ∼4,300, and ∼5,000 m). We compiled data collected across five independent high-altitude expeditions and report the following novel findings: 1) at 3,800 m, Andeans (n = 7) had elevated pHa compared with Sherpas (n = 12; P < 0.01), but not to lowlanders (n = 16; 9 days acclimatized; P = 0.09); 2) at 4,300 m, lowlanders (n = 16; 21 days acclimatized) had elevated pHa compared with Andeans (n = 32) and Sherpas (n = 11; both P < 0.01), and Andeans had elevated pHa compared with Sherpas (P = 0.01); and 3) at 5,000 m, lowlanders (n = 16; 14 days acclimatized) had higher pHa compared with both Andeans (n = 66) and Sherpas (n = 18; P < 0.01, and P = 0.03, respectively), and Andean and Sherpa highlanders had similar blood pHa (P = 0.65). These novel data characterize acid-base balance acclimatization and adaptation to various altitudes in lowlanders and indigenous highlanders.NEW & NOTEWORTHY Lowlander, Andean, and Sherpa arterial blood data were combined across five independent high-altitude expeditions in the United States, Nepal, and Peru to assess acid-base status at ∼3,800, ∼4,300, and ∼5,000 m. The main finding was that Andean and Sherpa highlander populations have more acidic arterial blood, due to elevated arterial carbon dioxide and similar arterial bicarbonate compared with acclimatizing lowlanders at altitudes ≥4,300 m.

Global Research Expedition on Altitude-related Chronic Health 2018 Iron Infusion at High Altitude Reduces Hypoxic Pulmonary Vasoconstriction Equally in Both Lowlanders and Healthy Andean Highlanders.

BACKGROUND: Increasing iron bioavailability attenuates hypoxic pulmonary vasoconstriction in both lowlanders and Sherpas at high altitude. In contrast, the pulmonary vasculature of Andean individuals with chronic mountain sickness (CMS) is resistant to iron administration. Although pulmonary vascular remodeling and hypertension are characteristic features of CMS, the effect of iron administration in healthy Andean individuals, to our knowledge, has not been investigated. If the interplay between iron status and pulmonary vascular tone in healthy Andean individuals remains intact, this could provide valuable clinical insight into the role of iron regulation at high altitude. RESEARCH QUESTION: Is the pulmonary vasculature in healthy Andean individuals responsive to iron infusion? STUDY DESIGN AND METHODS: In a double-blinded, block-randomized design, 24 healthy high-altitude Andean individuals and 22 partially acclimatized lowlanders at 4,300 m (Cerro de Pasco, Peru) received an IV infusion of either 200 mg of iron (III)-hydroxide sucrose or saline. Markers of iron status were collected at baseline and 4 h after infusion. Echocardiography was performed in participants during room air breathing (partial pressure of inspired oxygen [Pio2] of approximately 96 mm Hg) and during exaggerated hypoxia (Pio2 of approximately 73 mm Hg) at baseline and at 2 and 4 h after the infusion. RESULTS: Iron infusion reduced pulmonary artery systolic pressure (PASP) by approximately 2.5 mm Hg in room air (main effect, P < .001) and by approximately 7 mm Hg during exaggerated hypoxia (main effect, P < .001) in both lowlanders and healthy Andean highlanders. There was no change in PASP after the infusion of saline. Iron metrics were comparable between groups, except for serum ferritin, which was 1.8-fold higher at baseline in the Andean individuals than in the lowlanders (95% CI, 74-121 ng/mL vs 37-70 ng/mL, respectively; P = .003). INTERPRETATION: The pulmonary vasculature of healthy Andean individuals and lowlanders remains sensitive to iron infusion, and this response seems to differ from the pathologic characteristics of CMS.

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 V̇O2peak 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 V̇O2peak 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.

Global REACH 2018: volume regulation in high-altitude Andeans with and without chronic mountain sickness.

The high-altitude maladaptation syndrome known as chronic mountain sickness (CMS) is characterized by polycythemia and is associated with proteinuria despite unaltered glomerular filtration rate. However, it remains unclear if indigenous highlanders with CMS have altered volume regulatory hormones. We assessed NH2-terminal pro-B-type natriuretic peptide (NT pro-BNP), plasma aldosterone concentration, plasma renin activity, kidney function (urinary microalbumin, glomerular filtration rate), blood volume, and estimated pulmonary artery systolic pressure (ePASP) in Andean males without (n = 14; age = 39 ± 11 yr) and with (n = 10; age = 40 ± 12 yr) CMS at 4,330 m (Cerro de Pasco, Peru). Plasma renin activity (non-CMS: 15.8 ± 7.9 ng/mL vs. CMS: 8.7 ± 5.4 ng/mL; P = 0.025) and plasma aldosterone concentration (non-CMS: 77.5 ± 35.5 pg/mL vs. CMS: 54.2 ± 28.9 pg/mL; P = 0.018) were lower in highlanders with CMS compared with non-CMS, whereas NT pro-BNP was not different between groups (non-CMS: 1394.9 ± 214.3 pg/mL vs. CMS: 1451.1 ± 327.8 pg/mL; P = 0.15). Highlanders had similar total blood volume (non-CMS: 90 ± 15 mL·kg-1 vs. CMS: 103 ± 18 mL·kg-1; P = 0.071), but Andeans with CMS had greater total red blood cell volume (non-CMS: 46 ± 10 mL·kg-1 vs. CMS: 66 ± 14 mL·kg-1; P < 0.01) and smaller plasma volume (non-CMS: 43 ± 7 mL·kg-1 vs. CMS: 35 ± 5 mL·kg-1; P = 0.03) compared with non-CMS. There were no differences in ePASP between groups (non-CMS: 32 ± 9 mmHg vs. CMS: 31 ± 8 mmHg; P = 0.6). A negative correlation was found between plasma renin activity and glomerular filtration rate in both groups (group: r = -0.66; P < 0.01; non-CMS: r = -0.60; P = 0.022; CMS: r = -0.63; P = 0.049). A smaller plasma volume in Andeans with CMS may indicate an additional CMS maladaptation to high altitude, causing potentially greater polycythemia and clinical symptoms.

Global Reach 2018: Nitric oxide-mediated cutaneous vasodilation is reduced in chronic, but not acute, hypoxia independently of enzymatic superoxide formation.

We tested the hypotheses that 1) cutaneous microvascular function is impaired by acute normobaric and chronic hypobaric hypoxia and 2) that the superoxide free radical (via NADPH oxidase or xanthine oxidase) contributes to this impairment via nitric oxide (NO) scavenging. Local heating-induced cutaneous hyperemia (39 °C) was measured in the forearm of 11 male lowlanders at sea level (SL) and following 14-18 days at high altitude (HA; 4340 m in Cerro de Pasco, Peru), and compared to 11 highlanders residing permanently at this elevation. Cutaneous vascular conductance (CVC; laser-Doppler flux/mean arterial pressure) was not different during 39 °C [control site: 73 (19) vs. 71 (18)%max; P = 0.68] between normoxia and acute normobaric hypoxia (FIO2 = 0.125; equivalent to HA), respectively. At HA, CVC was reduced during 39 °C in lowlanders compared to SL [control site: 54 (14) vs. 73 (19)%max; P < 0.01] and was lower in Andean highlanders compared to lowlanders at HA [control site: 50 (24) vs. 54 (14)%max; P = 0.02]. The NO contribution to vasodilation during 39 °C (i.e., effect of NO synthase inhibition) was reduced in lowlanders at HA compared to SL [control site: 41 (11) vs 49 (10)%max; P = 0.04] and in Andean highlanders compared to lowlanders at HA [control site: 32 (21) vs. 41 (11)%max; P = 0.01]. Intradermal administration (cutaneous microdialysis) of the superoxide mimetic Tempol, inhibition of xanthine oxidase (via allopurinol), or NADPH oxidase (via apocynin) had no influence on cutaneous endothelium-dependent dilation during any of the conditions (all main effects of drug P > 0.05). These results suggest that time at HA impairs NO-mediated cutaneous vasodilation independent of enzymatic superoxide formation.

Global REACH 2018: Influence of excessive erythrocytosis on coagulation and fibrinolytic factors in Andean highlanders.

NEW FINDINGS: What is the central question of this study? Are coagulation and fibrinolytic factors disrupted in Andean highlanders with excessive erythrocytosis? What is the main finding and its importance? Excessive erythrocytosis is not associated with prothombotic disruptions in coagulation or the fibrinolytic system in Andean highlanders. Impairments in coagulation and fibrinolysis may not contribute to the increased vascular risk associated with excessive erythrocytosis. ABSTRACT: Increased coagulation and reduced fibrinolysis are central factors underlying thrombotic risk and events. High altitude-induced excessive erythrocytosis (EE) is prevalent in Andean highlanders, contributing to increased cardiovascular risk. Disruption in the coagulation-fibrinolytic axis resulting in uncontrolled fibrin deposition might underlie the increased thrombotic risk associated with high-altitude EE. The experimental aim of this study was to determine whether EE is associated with a prothrombotic blood coagulation and fibrinolytic profile in Andean highlanders. Plasma coagulation factors (von Willebrand factor and factors VII, VIII and X), fibrinolytic factors [tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1)] and D-dimer levels were determined in 26 male residents of Cerro de Pasco, Peru (4340 m a.s.l.): 12 without EE (age, 40 ± 13 years; haemoglobin, 17.4 ± 1.9 g/dl) and 14 with EE (age, 43 ± 15 years; haemoglobin, 24.4 ± 1.6 g/dl). There were no significant differences in von Willebrand factor (40.5 ± 24.8 vs. 45.5 ± 22.4%), factor VII (77.0 ± 14.5 vs. 72.5 ± 8.9%), factor VIII (55.6 ± 19.8 vs. 60.7 ± 26.8%) and factor X (73.9 ± 8.3 vs. 67.3 ± 10.9%) between the Andean highlanders without or with EE. The t-PA antigen (8.5 ± 3.6 vs. 9.6 ± 5.4 ng/ml), t-PA activity (5.5 ± 2.4 vs. 5.8 ± 1.6 IU/ml), PAI antigen (45.0 ± 33.8 vs. 40.5 ± 15.8 ng/ml), PAI-1 activity (0.24 ± 0.09 vs. 0.25 ± 0.11 IU/ml) and the molar concentration ratio of active t-PA to active PAI-1 (1:0.051 ± 0.034 vs. 1:0.046 ± 0.021 mmol/l) were also similar between the groups, as were D-dimer levels (235.0 ± 126.4 vs. 268.4 ± 173.7 ng/ml). Collectively, the results of the present study indicate that EE is not associated with a hypercoagulable, hypofibrinolytic state in Andean highlanders.

Global REACH 2018: dysfunctional extracellular microvesicles in Andean highlander males with excessive erythrocytosis.

High altitude-related excessive erythrocytosis (EE) is associated with increased cardiovascular risk. The experimental aim of this study was to determine the effects of microvesicles isolated from Andean highlanders with EE on endothelial cell inflammation, oxidative stress, apoptosis, and nitric oxide (NO) production. Twenty-six male residents of Cerro de Pasco, Peru (4,340 m), were studied: 12 highlanders without EE (age: 40 ± 4 yr; BMI: 26.4 ± 1.7; Hb: 17.4 ± 0.5 g/dL, Spo2: 86.9 ± 1.0%) and 14 highlanders with EE (43 ± 4 yr; 26.2 ± 0.9; 24.4 ± 0.4 g/dL; 79.7 ± 1.6%). Microvesicles were isolated, enumerated, and collected from plasma by flow cytometry. Human umbilical vein endothelial cells were cultured and treated with microvesicles from highlanders without and with EE. Microvesicles from highlanders with EE induced significantly higher release of interleukin (IL)-6 (89.8 ± 2.7 vs. 77.1 ± 1.9 pg/mL) and IL-8 (62.0 ± 2.7 vs. 53.3 ± 2.2 pg/mL) compared with microvesicles from healthy highlanders. Although intracellular expression of total NF-κB p65 (65.3 ± 6.0 vs. 74.9 ± 7.8.9 AU) was not significantly affected in cells treated with microvesicles from highlanders without versus with EE, microvesicles from highlanders with EE resulted in an ∼25% higher (P < 0.05) expression of p-NF-κB p65 (173.6 ± 14.3 vs. 132.8 ± 12.2 AU). Cell reactive oxygen species production was significantly higher (76.4.7 ± 5.4 vs. 56.7 ± 1.7% of control) and endothelial nitric oxide synthase (p-eNOS) activation (231.3 ± 15.5 vs. 286.6 ± 23.0 AU) and NO production (8.3 ± 0.6 vs. 10.7 ± 0.7 µM/L) were significantly lower in cells treated with microvesicles from highlanders with versus without EE. Cell apoptotic susceptibility was not significantly affected by EE-related microvesicles. Circulating microvesicles from Andean highlanders with EE increased endothelial cell inflammation and oxidative stress and reduced NO production.NEW & NOTEWORTHY In this study, we determined the effects of microvesicles isolated from Andean highlanders with excessive erythrocytosis (EE) on endothelial cell inflammation, oxidative stress, apoptosis, and NO production. Microvesicles from highlanders with EE induced a dysfunctional response from endothelial cells characterized by increased cytokine release and expression of active nuclear factor-κB and reduced nitric oxide production. Andean highlanders with EE exhibit dysfunctional circulating extracellular microvesicles that induce a proinflammatory, proatherogenic endothelial phenotype.

The 2018 Global Research Expedition on Altitude Related Chronic Health (Global REACH) to Cerro de Pasco, Peru: an Experimental Overview.

NEW FINDINGS: What is the central question of this study? Herein, a methodological overview of our research team's (Global REACH) latest high altitude research expedition to Peru is provided. What is the main finding and its importance? The experimental objectives, expedition organization, measurements and key cohort data are discussed. The select data presented in this manuscript demonstrate the haematological differences between lowlanders and Andeans with and without excessive erythrocytosis. The data also demonstrate that exercise capacity was similar between study groups at high altitude. The forthcoming findings from our research expedition will contribute to our understanding of lowlander and indigenous highlander high altitude adaptation. ABSTRACT: In 2016, the international research team Global Research Expedition on Altitude Related Chronic Health (Global REACH) was established and executed a high altitude research expedition to Nepal. The team consists of ∼45 students, principal investigators and physicians with the common objective of conducting experiments focused on high altitude adaptation in lowlanders and in highlanders with lifelong exposure to high altitude. In 2018, Global REACH travelled to Peru, where we performed a series of experiments in the Andean highlanders. The experimental objectives, organization and characteristics, and key cohort data from Global REACH's latest research expedition are outlined herein. Fifteen major studies are described that aimed to elucidate the physiological differences in high altitude acclimatization between lowlanders (n = 30) and Andean-born highlanders with (n = 22) and without (n = 45) excessive erythrocytosis. After baseline testing in Kelowna, BC, Canada (344 m), Global REACH travelled to Lima, Peru (∼80 m) and then ascended by automobile to Cerro de Pasco, Peru (∼4300 m), where experiments were conducted over 25 days. The core studies focused on elucidating the mechanism(s) governing cerebral and peripheral vascular function, cardiopulmonary regulation, exercise performance and autonomic control. Despite encountering serious logistical challenges, each of the proposed studies was completed at both sea level and high altitude, amounting to ∼780 study sessions and >3000 h of experimental testing. Participant demographics and data relating to acid-base balance and exercise capacity are presented. The collective findings will contribute to our understanding of how lowlanders and Andean highlanders have adapted under high altitude stress.

Global REACH 2018: Andean highlanders, chronic mountain sickness and the integrative regulation of resting blood pressure.

NEW FINDINGS: What is the central question of this study? Does chronic mountain sickness (CMS) alter sympathetic neural control and arterial baroreflex regulation of blood pressure in Andean (Quechua) highlanders? What is the main finding and its importance? Compared to healthy Andean highlanders, basal sympathetic vasomotor outflow is lower, baroreflex control of muscle sympathetic nerve activity is similar, supine heart rate is lower and cardiovagal baroreflex gain is greater in mild CMS. Taken together, these findings reflect flexibility in integrative regulation of blood pressure that may be important when blood viscosity and blood volume are elevated in CMS. ABSTRACT: The high-altitude maladaptation syndrome chronic mountain sickness (CMS) is characterized by excessive erythrocytosis and frequently accompanied by accentuated arterial hypoxaemia. Whether altered autonomic cardiovascular regulation is apparent in CMS is unclear. Therefore, during the 2018 Global REACH expedition to Cerro de Pasco, Peru (4383 m), we assessed integrative control of blood pressure (BP) and determined basal sympathetic vasomotor outflow and arterial baroreflex function in eight Andean natives with CMS ([Hb] 22.6 ± 0.9 g·dL-1 ) and seven healthy highlanders ([Hb] 19.3 ± 0.8 g·dL-1 ). R-R interval (RRI, electrocardiogram), beat-by-beat BP (photoplethysmography) and muscle sympathetic nerve activity (MSNA; microneurography) were recorded at rest and during pharmacologically induced changes in BP (modified Oxford test). Although [Hb] and blood viscosity (7.8 ± 0.7 vs. 6.6 ± 0.7 cP; d = 1.7, P = 0.01) were elevated in CMS compared to healthy highlanders, cardiac output, total peripheral resistance and mean BP were similar between groups. The vascular sympathetic baroreflex MSNA set-point (i.e. MSNA burst incidence) and reflex gain (i.e. responsiveness) were also similar between groups (MSNA set-point, d = 0.75, P = 0.16; gain, d = 0.2, P = 0.69). In contrast, in CMS the cardiovagal baroreflex operated around a longer RRI (960 ± 159 vs. 817 ± 50 ms; d = 1.4, P = 0.04) with a greater reflex gain (17.2 ± 6.8 vs. 8.8 ± 2.6 ms·mmHg-1 ; d = 1.8, P = 0.01) versus healthy highlanders. Basal sympathetic vasomotor activity was also lower compared to healthy highlanders (33 ± 11 vs. 45 ± 13 bursts·min-1 ; d = 1.0, P = 0.08). In conclusion, our findings indicate adaptive differences in basal sympathetic vasomotor activity and heart rate compensate for the haemodynamic consequences of excessive erythrocyte volume and contribute to integrative blood pressure regulation in Andean highlanders with mild CMS.

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

Millions of people worldwide live at high altitude, being chronically exposed to hypobaric hypoxia. Hypertension is a major cardiovascular risk factor but data on its prevalence and determinants in highlanders are limited, and systematic studies with ambulatory blood pressure monitoring are not available. Aim of this study was to assess the prevalence of clinic and ambulatory hypertension and the associated factors in a sample of Andean highlanders. Hypertension prevalence and phenotypes were assessed with office and ambulatory blood pressure measurement in a sample of adults living in Cerro de Pasco, Peru (altitude 4340 m). Basic clinical data, blood oxygen saturation, hematocrit, and Qinghai Chronic Mountain Sickness score were obtained. Participants were classified according to the presence of excessive erythrocytosis and chronic mountain sickness diagnosis. Data of 289 participants (143 women, 146 men, mean age 38.3 years) were analyzed. Office hypertension was present in 20 (7%) participants, while ambulatory hypertension was found in 58 (20%) participants. Masked hypertension was common (15%), and white coat hypertension was rare (2%). Among participants with ambulatory hypertension, the most prevalent phenotypes included isolated nocturnal hypertension, isolated diastolic hypertension, and systodiastolic hypertension. Ambulatory hypertension was associated with male gender, age, overweight/obesity, 24-hour heart rate, and excessive erythrocytosis. Prevalence of hypertension among Andean highlanders may be significantly underestimated when based on conventional blood pressure measurements, due to the high prevalence of masked hypertension. In highlanders, ambulatory hypertension may be independently associated with excessive erythrocytosis.

Highs and lows of sympathetic neurocardiovascular transduction: influence of altitude acclimatization and adaptation.

High-altitude (>2,500 m) exposure results in increased muscle sympathetic nervous activity (MSNA) in acclimatizing lowlanders. However, little is known about how altitude affects MSNA in indigenous high-altitude populations. Additionally, the relationship between MSNA and blood pressure regulation (i.e., neurovascular transduction) at high-altitude is unclear. We sought to determine 1) how high-altitude effects neurocardiovascular transduction and 2) whether differences exist in neurocardiovascular transduction between low- and high-altitude populations. Measurements of MSNA (microneurography), mean arterial blood pressure (MAP; finger photoplethysmography), and heart rate (electrocardiogram) were collected in 1) lowlanders (n = 14) at low (344 m) and high altitude (5,050 m), 2) Sherpa highlanders (n = 8; 5,050 m), and 3) Andean (with and without excessive erythrocytosis) highlanders (n = 15; 4,300 m). Cardiovascular responses to MSNA burst sequences (i.e., singlet, couplet, triplet, and quadruplet) were quantified using custom software (coded in MATLAB, v.2015b). Slopes were generated for each individual based on peak responses and normalized total MSNA. High altitude reduced neurocardiovascular transduction in lowlanders (MAP slope: high altitude, 0.0075 ± 0.0060 vs. low altitude, 0.0134 ± 0.080; P = 0.03). Transduction was elevated in Sherpa (MAP slope, 0.012 ± 0.007) compared with Andeans (0.003 ± 0.002, P = 0.001). MAP transduction was not statistically different between acclimatizing lowlanders and Sherpa (MAP slope, P = 0.08) or Andeans (MAP slope, P = 0.07). When resting MSNA is accounted for (ANCOVA), transduction was inversely related to basal MSNA (bursts/minute) independent of population (RRI, r = 0.578 P < 0.001; MAP, r = -0.627, P < 0.0001). Our results demonstrate that transduction is blunted in individuals with higher basal MSNA, suggesting that blunted neurocardiovascular transduction is a physiological adaptation to elevated MSNA rather than an effect or adaptation specific to chronic hypoxic exposure.NEW & NOTEWORTHY This study has identified that sympathetically mediated blood pressure regulation is reduced following ascent to high-altitude. Additionally, we show that high altitude Andean natives have reduced blood pressure responsiveness to sympathetic nervous activity (SNA) compared with Nepalese Sherpa. However, basal sympathetic activity is inversely related to the magnitude of SNA-mediated fluctuations in blood pressure regardless of population or condition. These data set a foundation to explore more precise mechanisms of blood pressure control under conditions of persistent sympathetic activation and hypoxia.

Global REACH 2018: The carotid artery diameter response to the cold pressor test is governed by arterial blood pressure during normoxic but not hypoxic conditions in healthy lowlanders and Andean highlanders.

NEW FINDINGS: What is the central question of this study? What is the impact of oxygen on the circulatory responses to an isocapnic cold pressor test (CPT) in lowlanders and Andean highlanders? What is the main finding and its importance? Overall, the circulatory responses to an isocapnic CPT were largely unaltered with acute normobaric hypoxia and chronic hypobaric hypoxia exposure in lowlanders. However, the relationship between mean arterial pressure and common carotid artery diameter was dampened in hypoxic conditions. Furthermore, there were no differences in the circulatory responses to the CPT between lowlanders and Andean highlanders with lifelong exposure to high altitude. ABSTRACT: The impact of oxygen on the circulatory responses to a cold pressor test (CPT) in lowlanders and Andean highlanders remains unknown. Our hypotheses were as follows: (i) in lowlanders, acute normobaric and hypobaric hypoxia would attenuate the common carotid artery (CCA) diameter response to the CPT compared with normobaric normoxia; (ii) Andean highlanders would exhibit a greater CCA diameter response compared with lowlanders; and (iii) a positive relationship between CCA diameter and blood pressure in response to the CPT would be present in both lowlanders and highlanders. Healthy lowlanders (n = 13) and Andean highlanders (n = 8) were recruited and conducted an isocapnic CPT, which consisted of a 3 min foot immersion into water at 0-1°C. Blood pressure (finger photoplethysmography) and CCA diameter and blood flow (Duplex ultrasound) were recorded continuously. The CPT was conducted in lowlanders at sea level in isocapnic normoxic and hypoxic conditions and after 10 days of acclimatization to 4300 m (Cerro de Pasco, Peru) in hypoxic and hyperoxic conditions. Andean highlanders were tested at rest at high altitude. The main findings were as follows: (i) in lowlanders, normobaric but not hypobaric hypoxia elevated CCA reactivity to the CPT; (ii) no differences in response to the CPT were observed between lowlanders and highlanders; and (iii) although hypobaric hypoxaemia reduced the relationship between CCA diameter and blood pressure compared with normobaric normoxia (P = 0.132), hypobaric hyperoxia improved this relationship (P = 0.012), and no relationship was observed in Andean highlanders (P = 0.261). These data demonstrate that the circulatory responses to a CPT were modified by oxygen in lowlanders, but were unaltered with lifelong hypoxic exposure.

Relationships Between Chemoreflex Responses, Sleep Quality, and Hematocrit in Andean Men and Women.

Andean highlanders are challenged by chronic hypoxia and many exhibit elevated hematocrit (Hct) and blunted ventilation compared to other high-altitude populations. While many Andeans develop Chronic Mountain Sickness (CMS) and excessive erythrocytosis, Hct varies markedly within Andean men and women and may be driven by individual differences in ventilatory control and/or sleep events which exacerbate hypoxemia. To test this hypothesis, we quantified relationships between resting ventilation and ventilatory chemoreflexes, sleep desaturation, breathing disturbance, and Hct in Andean men and women. Ventilatory measures were made in 109 individuals (n = 63 men; n = 46 women), and sleep measures in 45 of these participants (n = 22 men; n = 23 women). In both men and women, high Hct was associated with low daytime SpO2 (p < 0.001 and p < 0.002, respectively) and decreased sleep SpO2 (mean, nadir, and time <80%; all p < 0.02). In men, high Hct was also associated with increased end-tidal PCO2 (p < 0.009). While ventilatory responses to hypoxia and hypercapnia did not predict Hct, decreased hypoxic ventilatory responses were associated with lower daytime SpO2 in men (p < 0.01) and women (p < 0.009) and with lower nadir sleep SpO2 in women (p < 0.02). Decreased ventilatory responses to CO2 were associated with more time below 80% SpO2 during sleep in men (p < 0.05). The obstructive apnea index and apnea-hypopnea index also predicted Hct and CMS scores in men after accounting for age, BMI, and SpO2 during sleep. Finally, heart rate response to hypoxia was lower in men with higher Hct (p < 0.0001). These data support the idea that hypoventilation and decreased ventilatory sensitivity to hypoxia are associated with decreased day time and nighttime SpO2 levels that may exacerbate the stimulus for erythropoiesis in Andean men and women. However, interventional and longitudinal studies are required to establish the causal relationships between these associations.