Cardiovascular adjustments for life at high altitude

Vhl deletion in Dmp1 -expressing cells alters MEP metabolism and promotes stress erythropoiesis

In recent years, general hypoxia-inducible factor (HIF)-prolyl hydroxylase (PHD) enzyme inhibitors have been developed for the treatment of anemia due to renal disease and osteoporosis. However, it remains a challenge to target the HIF signaling pathway without dysregulating the skeletal and hematopoietic system. Here, we examined the effects of Vhl deletion in bone by performing longitudinal analyses of Vhl cKO mice at 3, 6, 10, and 24 weeks of age, where at 10 and 24 weeks of age, high bone mass and splenomegaly are present. Using flow cytometry, we observed increased frequency (%) of CD71 lo TER119 hi FSC lo orthochromatophilic erythroblasts and reticulocytes in 10- and 24-week-old Vhl cKO bone marrow (BM), which correlated with elevated erythropoietin levels in the BM and increased number of red blood cells in circulation. The absolute numbers of myeloerythroid progenitors (MEPs) in the BM were significantly reduced at 24 weeks. Bulk RNA-Seq of the MEPs showed upregulation of Epas1 ( Hif1a) and Efnb2 ( Hif2a) in Vhl cKO MEPs, consistent with a response to hypoxia, and genes involved in erythrocyte development, actin filament organization, and response to glucose. Additionally, histological analysis of Vhl cKO spleens revealed red pulp hyperplasia and the presence of megakaryocytes, both of which are features of extramedullary hematopoiesis (EMH). EMH in the spleen was correlated with the presence of mature stress erythroid progenitors, suggesting that stress erythropoiesis is occurring to compensate for the BM microenvironmental irregularities. Our studies implicate that HIF-driven alterations in skeletal homeostasis can accelerate erythropoiesis.

Key Points

• Dysregulation of HIF signaling in Dmp1+ bone cells induces stress erythropoiesis.• Skeletal homeostasis modulates erythropoiesis.

Tensions in Taxonomies: Current Understanding and Future Directions in the Pathobiologic Basis and Treatment of Group 1 and Group 3 Pulmonary Hypertension

In the over 100 years since the recognition of pulmonary hypertension (PH), immense progress and significant achievements have been made with regard to understanding the pathophysiology of the disease and its treatment. These advances have been mostly in idiopathic pulmonary arterial hypertension (IPAH), which was classified as Group 1 Pulmonary Hypertension (PH) at the Second World Symposia on PH in 1998. However, the pathobiology of PH due to chronic lung disease, classified as Group 3 PH, remains poorly understood and its treatments thus remain limited. We review the history of the classification of the five groups of PH and aim to provide a state-of-the-art review of the understanding of the pathogenesis of Group 1 PH and Group 3 PH including insights gained from novel high-throughput omics technologies that have revealed heterogeneities within these categories as well as similarities between them. Leveraging the substantial gains made in understanding the genomics, epigenomics, proteomics, and metabolomics of PAH to understand the full spectrum of the complex, heterogeneous disease of PH is needed. Multimodal omics data as well as supervised and unbiased machine learning approaches after careful consideration of the powerful advantages as well as of the limitations and pitfalls of these technologies could lead to earlier diagnosis, more precise risk stratification, better predictions of disease response, new sub-phenotype groupings within types of PH, and identification of shared pathways between PAH and other types of PH that could lead to new treatment targets. © 2023 American Physiological Society. Compr Physiol 13:4295-4319, 2023.

Microevolutionary mechanism of high-altitude adaptation in Tibetan chicken populations from an elevation gradient

As an indigenous breed, the Tibetan chicken is found in highland regions and shows physiological adaptations to high altitude; however, the genetic changes that determine these adaptations remain elusive. We assumed that the microevolution of the Tibetan chicken occurred from lowland to highland regions with a continuous elevation range. In this study, we analyzed the genome of 188 chickens from lowland areas to the high-altitude regions of the Tibetan plateau with four altitudinal levels. Phylogenetic analysis revealed that Tibetan chickens are significantly different from other altitude chicken populations. Reconstruction of the demographic history showed that the migration and admixture events of the Tibetan chicken occurred at different times. The genome of the Tibetan chicken was also used to analyze positive selection pressure that is associated with high-altitude adaptation, revealing the well-known candidate gene that participates in oxygen binding (HBAD), as well as other novel potential genes (e.g., HRG and ANK2) that are related to blood coagulation and cardiovascular efficiency. Our study provides novel insights regarding the evolutionary history and microevolution mechanisms of the high-altitude adaptation in the Tibetan chicken.

Genetic variation in HIF-2α attenuates ventilatory sensitivity and carotid body growth in chronic hypoxia in high-altitude deer mice

KEY POINTS

High-altitude natives of many species have experienced natural selection on the gene encoding HIF-2α, Epas1, including high-altitude populations of deer mice. HIF-2α regulates ventilation and carotid body growth in hypoxia, so the genetic variants in Epas1 in high-altitude natives may underlie evolved changes in control of breathing. Deer mice from controlled crosses between high- and low-altitude populations were used to examine the effects of Epas1 genotype on an admixed genomic background. The high-altitude variant was associated with reduced ventilatory chemosensitivity and carotid body growth in chronic hypoxia, but had no effects on haematology. The results help us better understand the genetic basis for the unique physiological phenotype of high-altitude natives.

ABSTRACT

The gene encoding HIF-2α, Epas1, has experienced a history of natural selection in many high-altitude taxa, but the functional role of mutations in this gene are still poorly understood. We investigated the influence of the high-altitude variant of Epas1 in North American deer mice (Peromyscus maniculatus) on control of breathing and carotid body growth during chronic hypoxia. We created hybrids between high- and low-altitude populations of deer mice to disrupt linkages between genetic loci so physiological effects of Epas1 alleles (Epas1^H and Epas1^L , respectively) could be examined on an admixed genomic background. In general, chronic hypoxia (4 weeks at 12 kPa O₂ ) enhanced ventilatory chemosensitivity (assessed as the acute ventilatory response to hypoxia), increased total ventilation and arterial O₂ saturation during progressive poikilocapnic hypoxia, and increased haematocrit and blood haemoglobin content across genotypes. However, effects of chronic hypoxia on ventilatory chemosensitivity were attenuated in mice that were homozygous for the high-altitude Epas1 allele (Epas1^H/H ). Carotid body growth and glomus cell hyperplasia, which was strongly induced in Epas1^L/L mice in chronic hypoxia, was not observed in Epas1^H/H mice. Epas1 genotype also modulated the effects of chronic hypoxia on metabolism and body temperature depression in hypoxia, but had no effects on haematological traits. These findings confirm the important role of HIF-2α in modulating ventilatory sensitivity and carotid body growth in chronic hypoxia, and show that genetic variation in Epas1 is responsible for evolved changes in the control of breathing and metabolism in high-altitude deer mice. Abstract figure legend ventilation and carotid body growth in hypoxia, so we investigated the role genetic variants in Epas1 in highaltitude deer mice on the control of breathing. In the lab, hybrids between high- and lowaltitude populations of deer mice were created to disrupt linkages between genetic loci so physiological effects of Epas1 alleles (Epas1H and Epas1L, respectively) could be examined on an admixed genomic background. The high-altitude variant was associated with reduced ventilatory chemosensitivity and carotid body growth after 4 weeks of chronic hypoxia, compared to mice homozygous for the low-altitude allele (Epas1LL). These results help us better understand the genetic basis for the unique physiological phenotype of high-altitude natives. This article is protected by copyright. All rights reserved.

The heart-brain axis: A proteomics study of meditation on the cardiovascular system of Tibetan Monks

Background

There have been mixed reports on the beneficial effects of meditation in cardiovascular disease (CVD), which is widely considered the leading cause of death worldwide.

Methods

To clarify the role of meditation in modulating the heart-brain axis, we implemented an extreme phenotype strategy, i.e., Tibetan monks (BMI > 30) who practised 19.20 ± 7.82 years of meditation on average and their strictly matched non-meditative Tibetan controls. Hypothesis-free advanced proteomics strategies (Data Independent Acquisition and Targeted Parallel Reaction Monitoring) were jointly applied to systematically investigate and target the plasma proteome underlying meditation. Total cholesterol, low-density lipoprotein cholesterol  (LDL-C), apolipoprotein B (Apo B) and lipoprotein (a) [Lp(a)] as the potential cardiovascular risk factors were evaluated. Heart rate variability (HRV) was assessed by electrocardiogram.

Findings

Obesity, hypertension, and reduced HRV is offset by long-term meditation. Notably, meditative monks have blood pressure and HRV comparable to their matched Tibetan controls. Meditative monks have a protective plasma proteome, related to decreased atherosclerosis, enhanced glycolysis, and oxygen release, that confers resilience to the development of CVD. In addition, clinical risk factors in plasma were significantly decreased in monks compared with controls, including total cholesterol, LDL-C, Apo B, and Lp(a).

Interpretation

To our knowledge, this work is the first well-controlled proteomics investigation of long-term meditation, which opens up a window for individuals characterized by a sedentary lifestyle to improve their cardiovascular health with an accessible method practised for more than two millennia.

Funding

See the Acknowledgements section.

Global Reach 2018: sympathetic neural and hemodynamic responses to submaximal exercise in Andeans with and without chronic mountain sickness

Andeans with chronic mountain sickness (CMS) and polycythemia have similar maximal oxygen uptakes to healthy Andeans. Therefore, this study aimed to explore potential adaptations in convective oxygen transport, with a specific focus on sympathetically mediated vasoconstriction of nonactive skeletal muscle. In Andeans with (CMS+, n = 7) and without (CMS-, n = 9) CMS, we measured components of convective oxygen delivery, hemodynamic (arterial blood pressure via intra-arterial catheter), and autonomic responses [muscle sympathetic nerve activity (MSNA)] at rest and during steady-state submaximal cycling exercise [30% and 60% peak power output (PPO) for 5 min each]. Cycling caused similar increases in heart rate, cardiac output, and oxygen delivery at both workloads between both Andean groups. However, at 60% PPO, CMS+ had a blunted reduction in Δtotal peripheral resistance (CMS-, -10.7 ± 3.8 vs. CMS+, -4.9 ± 4.1 mmHg·L-1·min-1; P = 0.012; d = 1.5) that coincided with a greater Δforearm vasoconstriction (CMS-, -0.2 ± 0.6 vs. CMS+, 1.5 ± 1.3 mmHg·mL-1·min-1; P = 0.008; d = 1.7) and a rise in Δdiastolic blood pressure (CMS-, 14.2 ± 7.2 vs. CMS+, 21.6 ± 4.2 mmHg; P = 0.023; d = 1.2) compared with CMS-. Interestingly, although MSNA burst frequency did not change at 30% or 60% of PPO in either group, at 60% Δburst incidence was attenuated in CMS+ (P = 0.028; d = 1.4). These findings indicate that in Andeans with polycythemia, light intensity exercise elicited similar cardiovascular and autonomic responses compared with CMS-. Furthermore, convective oxygen delivery is maintained during moderate-intensity exercise despite higher peripheral resistance. In addition, the elevated peripheral resistance during exercise was not mediated by greater sympathetic neural outflow, thus other neural and/or nonneural factors are perhaps involved.NEW & NOTEWORTHY During submaximal exercise, convective oxygen transport is maintained in Andeans suffering from polycythemia. Light intensity exercise elicited similar cardiovascular and autonomic responses compared with healthy Andeans. However, during moderate-intensity exercise, we observed a blunted reduction in total peripheral resistance, which cannot be ascribed to an exaggerated increase in muscle sympathetic nerve activity, indicating possible contributions from other neural and/or nonneural mechanisms.

Adrenergic control of the cardiovascular system in deer mice native to high altitude

Studies of animals native to high altitude can provide valuable insight into physiological mechanisms and evolution of performance in challenging environments. We investigated how mechanisms controlling cardiovascular function may have evolved in deer mice (Peromyscus maniculatus) native to high altitude. High-altitude deer mice and low-altitude white-footed mice (P. leucopus) were bred in captivity at sea level, and first-generation lab progeny were raised to adulthood and acclimated to normoxia or hypoxia. We then used pharmacological agents to examine the capacity for adrenergic receptor stimulation to modulate heart rate (f_H) and mean arterial pressure (P_mean) in anaesthetized mice, and used cardiac pressure-volume catheters to evaluate the contractility of the left ventricle. We found that highlanders had a consistently greater capacity to increase f_H via pharmacological stimulation of β₁-adrenergic receptors than lowlanders. Also, whereas hypoxia acclimation reduced the capacity for increasing P_mean in response to α-adrenergic stimulation in lowlanders, highlanders exhibited no plasticity in this capacity. These differences in highlanders may help augment cardiac output during locomotion or cold stress, and may preserve their capacity for α-mediated vasoconstriction to more effectively redistribute blood flow to active tissues. Highlanders did not exhibit any differences in some measures of cardiac contractility (maximum pressure derivative, dP/dt_max, or end-systolic elastance, E_es), but ejection fraction was highest in highlanders after hypoxia acclimation. Overall, our results suggest that evolved changes in sensitivity to adrenergic stimulation of cardiovascular function may help deer mice cope with the cold and hypoxic conditions at high altitude.

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High-altitude deer mice have evolved increased aerobic capacity in hypoxia.

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Cardiovascular regulation was examined in normoxia and chronic hypoxia.

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Highland mice had increased capacity for β₁-adrenergic stimulation of heart rate.

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Hypoxia reduced vascular α-adrenergic sensitivity in lowland but not highland mice.

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Cardiac ejection fraction was elevated in highland mice in chronic hypoxia.

Salt supplementation in the management of orthostatic intolerance: Vasovagal syncope and postural orthostatic tachycardia syndrome

Salt supplementation is a common non-pharmacological approach to the management of recurrent orthostatic syncope or presyncope, particularly for patients with vasovagal syncope (VVS) or postural orthostatic tachycardia syndrome (POTS), although there is limited consensus on the optimal dosage, formulation and duration of treatment. Accordingly, we reviewed the evidence for the use of salt supplementation to reduce susceptibility to syncope or presyncope in patients with VVS and POTS. We found that short-term (~3 months) salt supplementation improves susceptibility to VVS and associated symptoms, with little effect on supine blood pressure. In patients with VVS, salt supplementation is associated with increases in plasma volume, and an increase in the time taken to provoke a syncopal event during orthostatic tolerance testing, with smaller orthostatic heart rate increases, enhanced peripheral vascular responses to orthostatic stress, and improved cerebral autoregulation. Responses were most pronounced in those with a baseline sodium excretion <170 mmol/day. Salt supplementation also improved symptoms, plasma volume, and orthostatic responses in patients with POTS. Salt supplementation should be considered for individuals with recurrent and troublesome episodes of VVS or POTS without cardiovascular comorbidities, particularly if their typical urinary sodium excretion is low, and their supine blood pressure is not elevated. The efficacy of the response, in terms of the improvement in subjective and objective markers of orthostatic intolerance, and any potential deleterious effect on supine blood pressure, should be routinely monitored in individuals on high salt regimes.

A novel echocardiographic parameter to identify individuals susceptible to acute mountain sickness

BACKGROUND

Acute mountain sickness (AMS) may cause life-threatening conditions. This study aimed to screen echocardiographic parameters at sea level (SL) to identify predictors of AMS development.

METHODS

Overall, 106 healthy men were recruited at SL and ascended to 4100 m within 7 days by bus. Basic characteristics, physiological data, and echocardiographic parameters were collected both at SL and 4100 m above SL. AMS was identified by 2018 Lake Louise Questionnaire Score.

RESULTS

After acute high altitude exposure (AHAE), 33 subjects were diagnosed with AMS and exhibited lower lateral mitral valve tissue motion annular displacement (MV TMAD_lateral) at SL than AMS-free subjects (13.09 vs. 13.89 mm, p = 0.022). MV TMAD_lateral at SL was significantly correlated with AMS occurrence (OR = 0.717, 95% CI: 0.534-0.964, p = 0.028). The MV TMAD_lateral<13.30-mm group showed over 4-fold risk for AMS development versus the MV TMAD_lateral≥13.30-mm group. After AHAE, the MV TMAD_lateral<13.30-mm group had increased HR (64 vs. 74 bpm, p = 0.001) and right-ventricular myocardial performance index (0.54 vs. 0.69, p = 0.009) and decreased left ventricular global longitudinal strain (-21.50 vs. -20.23%, p = 0.002), tricuspid valve E/A ratio (2.11 vs. 1.89, p = 0.019), and MV E-wave deceleration time (169.60 vs. 156.90 ms, p = 0.035).

CONCLUSION

MV TMAD_lateral at SL was a potential predictor of AMS occurrence and might be associated with differential alterations of ventricular systolic and diastolic functions in subjects with different MV TMAD_lateral levels at SL after AHAE.

Cardiovascular Indicators of Systemic Circulation and Acute Mountain Sickness: An Observational Cohort Study

Background: Acute high-altitude (HA) exposure results in blood pressure (BP) and cardiac function variations in most subjects, some of whom suffer from acute mountain sickness (AMS). Several previous studies have found that cardiovascular function indicators are potentially correlated with AMS.

Objectives: This study aims to examine HA-induced cardiovascular adaptations in AMS patients and compare them with healthy subjects. It also aims to investigate the relationship between cardiovascular function indicators and AMS, as well as to provide some insightful information about the prevention and treatment of AMS.

Methods: Seventy-two subjects were enrolled in this cohort study. All the subjects ascended Litang (4,100 m above sea level). They were monitored by a 24-h ambulatory blood pressure (ABP) device and underwent echocardiography examination within 24 h of altitude exposure. The 2018 Lake Louise questionnaire was used to evaluate AMS.

Results: Acute mountain sickness group consisted of more women (17 [60.7%] vs. 10 [22.7%], p = 0.001) and fewer smokers (5 [17.9%] vs. 23 [52.3%], p = 0.003). Compared with subjects without AMS, subjects with AMS had lower pulse pressure (PP) (daytime PP, 45.23 ± 7.88 vs. 52.14 ± 4.75, p < 0.001; nighttime PP, 42.81 ± 5.92 vs. 49.39 ± 7.67, p < 0.001) and lower effective arterial elastance (Ea) (1.53 ± 0.24 vs. 1.73 ± 0.39, p = 0.023). Multivariate regression indicated that female sex (OR = 0.23, p = 0.024), lower daytime PP (OR = 0.86, p = 0.004), and lower Ea (OR = 0.03, p = 0.015) at low altitude (LA) were independent risk factors for AMS. Combined daytime PP and Ea at LA had a high predictive value for AMS (AUC = 0.873; 95% CI: 0.789–0.956). Correlation analysis showed that AMS-induced headache correlated with daytime PP (R = −0.401, p < 0.001) and nighttime PP at LA (R = −0.401, p < 0.001).

Conclusion: Our study demonstrated that AMS patients had a lower PP and Ea at LA. These baseline indicators of vasodilation at LA were closely associated with AMS, which may explain the higher headache severity in subjects with higher PP at LA.

Seasonal Effects of High-Altitude Forest Travel on Cardiovascular Function: An Overlooked Cardiovascular Risk of Forest Activity

Cardiovascular physiological responses involving hypoxemia in low temperature environments at high altitude have yet to be adequately investigated. This study aims to demonstrate the health effects of hypoxemia and temperature changes in cardiovascular functions (CVFs) by comparing intra-individual differences as participants ascend from low (298 m, 21.9 °C) to high altitude (2729 m, 9.5 °C). CVFs were assessed by measuring the arterial pressure waveform according to cuff sphygmomanometer of an oscillometric blood pressure (BP) device. The mean ages of participants in winter and summer were 43.6 and 41.2 years, respectively. The intra-individual brachial systolic, diastolic BP, heart rate, and cardiac output of participants significantly increased, as participants climbed uphill from low to high altitude forest. Following the altitude increase from 298 m to 2729 m, with the atmosphere gradually reducing by 0.24 atm, the measured average SpO₂ of participants showed a significant reduction from 98.1% to 81.2%. Using mixed effects model, it is evident that in winter, the differences in altitude affects CVFs by significantly increases the systolic BP, heart rate, left ventricular dP/dt max and cardiac output. This study provides evidence that cardiovascular workload increased significantly among acute high-altitude travelers as they ascend from low to high altitude, particularly in winter.

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.

Association of age and blood pressure among 3.3 million adults: insights from China PEACE million persons project

OBJECTIVE

To assess the association between blood pressure (BP) with age and its heterogeneity across various sociodemographic subgroups in China.

METHODS

In this cross-sectional study, we analysed the data from nearly 3.3 million individuals aged 35-75 years from all 31 provinces in mainland China collected from September 2014 through August 2019. On the basis of possible combinations of eight characteristics and antihypertensive status, subgroups of at least 10 000 individuals were created and the age--blood pressure relationship was determined for each group.

RESULTS

The study included 3 291 058 participants (59.6% women), with a mean age of 55.8 ± 9.8 years. The prevalence of hypertension was 47.6%, of which 30.0% were taking antihypertensive medications. The mean SBP was 135.9 ± 20.2 mmHg. SBP increased at a mean unadjusted rate of 0.639 ± 0.001 mmHg/year. For 95% of the 25 145 subgroups, the SBP increased by 0.28--0.85 mmHg/year. The most common characteristics in the subgroups with the steepest association were female sex, rural area, low education, low-income family, Tibet region, and farmer occupation. The increase in SBP ranged from 0.13 to 0.41 mmHg/year for 95% of the treated subgroups and from 0.33 to 0.82 mmHg/year for 95% of the untreated subgroups.

CONCLUSION

Blood pressure is positively associated with age in this study, with almost three-fold variation across subgroups, indicating subgroup differences in biology, behaviour, or exposures. Antihypertension strongly blunts the association of age and blood pressure and diminishes the variation.

Sex-Dependent Association Between Early Morning Ambulatory Blood Pressure Variations and Acute Mountain Sickness

Background

Acute high altitude (HA) exposure elicits blood pressure (BP) responses in most subjects, and some of them suffer from acute mountain sickness (AMS). However, a 24-h ambulatory BP (ABP) change and the correlation with the occurrence of AMS in different sexes are still unclear.

Objectives

This prospective study aimed to investigate HA induced BP responses in males and females and the relationship between AMS and 24-h ABP.

Methods

Forty-six subjects were matched according to demographic parameters by propensity score matching with a ratio of 1:1. All the subjects were monitored by a 24-h ABP device; the measurement was one period of 24 h BP. 2018 Lake Louise questionnaire was used to evaluate AMS.

Results

Both the incidence of AMS (14 [60.9%] vs. 5 [21.7%], P = 0.007) and headache (18 [78.3%] vs. 8 [34.8%], P = 0.003) were higher in females than in males. All subjects showed an elevated BP in the early morning [morning systolic BP (SBP), 114.72 ± 13.57 vs. 120.67 ± 11.10, P = 0.013]. The elevation of morning SBP variation was more significant in females than in males (11.95 ± 13.19 vs. −0.05 ± 14.49, P = 0.005), and a higher morning BP surge increase (4.69 ± 18.09 vs. −9.66 ± 16.96, P = 0.005) was observed after acute HA exposure in the female group. The increase of morning SBP was associated with AMS occurrence (R = 0.662, P < 0.001) and AMS score (R = 0.664, P = 0.001). Among the AMS symptoms, we further revealed that the incidence (R = 0.786, P < 0.001) and the severity of headache (R = 0.864, P < 0.001) are closely correlated to morning SBP.

Conclusions

Our study demonstrates that females are more likely to suffer from AMS than males. AMS is closely associated with elevated BP in the early morning period, which may be correlated to higher headache incidence in subjects with higher morning SBP.

Effect of exercise training in rats exposed to chronic hypoxia: Application for Monge's disease

Physical exercise may improve hematological conditions in high altitude dwellers suffering from Chronic Mountain Sickness (CMS), in reducing hemoglobin concentration. Therefore, the present study aimed to characterize the effects of 1-month exercise training session in a model of rats exposed to chronic hypoxia. Four groups of male rats were studied: normoxic sedentary (NS, n = 8), normoxic training (NT, n = 8), hypoxic sedentary (HS, n = 8), and hypoxic training group (HT, n = 8). Hypoxic groups were exposed to hypobaric hypoxia for one month (PB =433 Torr). Training intensity was progressively increased from a running speed of 10.4 to 17.8 m/min. Chronic hypoxia led to an increase in hematocrit (HCT) associated with a decrease in plasma volume despite an increase in water intake. Training led to a reduction in HCT (p < 0.01), with a non-significant increase in plasma volume and weight gain. Hypoxia and training had inhibitory effects on haptoglobin (NS group: 379 ± 92; HT: 239 ± 34 µg/ml, p < 0.01). Chronic hypoxia and exercise training increased SpO2 measured after acute hypoxic exposure. Training blunted the decrease in V ˙ O2 peak, time of exhaustion, and maximum speed associated with chronic exposure to hypoxia. Chronic hypoxia led to a right ventricular hypertrophy, which was not corrected by 1-month exercise training. Altogether, by decreasing hematocrit, reducing body weight, and limiting performance decrease, training in hypoxia may have a beneficial effect on excessive erythropoiesis in chronic hypoxia. Therefore, regular exercise training might be beneficial to avoid worsening of CMS symptoms in high altitude dwellers and to improve their quality of life.

Blood pressure and left ventricular function changes in different ambulatory blood pressure patterns at high altitude

Acute high‐altitude (HA) exposure induces physiological responses of the heart and blood pressure (BP). However, few studies have investigated the responses associated with dipper and non‐dipper BP patterns. In this prospective study, 72 patients underwent echocardiography and 24‐h ambulatory BP testing at sea level and HA. Patients were divided into dipper and non‐dipper groups according to BP at sea level. Acute HA exposure elevated 24‐h systolic and diastolic BP and increased BP variability, particularly in the morning. Moreover, acute exposure increased left ventricular torsion, end‐systolic elastance, effective arterial elastance, and untwisting rate, but reduced peak early diastolic velocity/late diastolic velocity and peak early diastolic velocity/early diastolic velocity, implying enhanced left ventricular systolic function but impaired filling. Dippers showed pronounced increases in night‐time BP, while non‐dippers showed significant elevation in day‐time BP, which blunted differences in nocturnal BP fall, and lowest night‐time and evening BP. Dippers had higher global longitudinal strain, torsion, and untwisting rates after acute HA exposure. Variations in night‐time systolic BP correlated with variations in torsion and global longitudinal strain. Our study firstly demonstrates BP and cardiac function variations during acute HA exposure in different BP patterns and BP increases in dippers at night, while non‐dippers showed day‐time increases. Furthermore, enhanced left ventricular torsion and global longitudinal strain are associated with BP changes. Non‐dippers showed poor cardiac compensatory and maladaptive to acute HA exposure. However, the exact mechanisms involved need further illumination.

Polysomnographic indicators of restorative sleep and body mass trajectories in the Wisconsin Sleep Cohort Study

STUDY OBJECTIVES

Previous research suggests that reductions in restorative, slow-wave (N3), and rapid eye movement (REM) sleep are associated with weight gain and obesity in mid-to-late life. We extend prior work by examining how within-person (WP) changes and between-person (BP) differences in restorative sleep over several years are associated with body mass trajectories among participants in the Wisconsin Sleep Cohort Study (WSCS).

METHODS

We used data from 4,862 polysomnographic (PSG) sleep studies and physical exams collected from 1,187 WSCS participants over an average duration of 14.9 years. Primary measures of interest included body mass index (BMI = kg/m2) and the percentages of time spent in N3 and REM sleep. We estimated a series of linear mixed regression models to examine how WP changes and BP differences in N3 and REM sleep affected BMI trajectories, controlling for other sleep measures, demographic characteristics, and health behaviors as potential confounders.

RESULTS

Women in the WSCS experienced more rapid BMI gain than men. With some variation by sex, we found that (1) below-average N3 and REM sleep is associated with above-average BMI, and (2) within-person decreases in N3 and REM sleep over time are associated with gains in BMI. These findings persisted after adjustment for sleep duration and other potential confounders.

CONCLUSIONS

Our findings highlight the importance of PSG indices of restorative sleep in mid-to-late life, suggesting that future clinical treatments and public health policies will benefit from heightened attention to sleep quality.

Rate-Pressure Product Responses to Static Contractions Performed at Various Altitudes

Simmonds, Michael J., Surendran Sabapathy, and Jean-Marc Hero. Rate-pressure product responses to static contractions performed at various altitudes. High Alt Med Biol. 22: 166-173, 2021. Background: Adventure tourism has led to an unprecedented number of individuals being exposed to altitude, including those with subclinical cardiometabolic disorders. The disproportionate hemodynamic challenge associated with small-muscle static activities is potentially dangerous at altitude as these may compound the risk for cardiac events. We thus examined the cardiovascular response to, and during recovery from, static exercise performed at altitude. Methods: Eighteen individuals completed this study at three altitudes (sea level; ∼1,500 m; ∼3,000 m) in central Nepal. At each altitude, individuals performed two handgrip contractions for 2 minutes at the same intensity (30% maximal voluntary contraction [MVC]), with two distinct recovery periods: during control recovery was completed quietly at rest, while during ischemic challenge recovery was conducted with a cuff occluding the upper limb. Results: Oxygen saturation decreased during ascent to 1,500 m (-2%) and 3,000 m (-8%), compared with sea level. Handgrip MVC was not affected by altitude, although heart rate at rest (∼70 beat/min), during static exercise (range ∼90-95 beat/min), and during recovery in both conditions (each ∼70 beat/min) was significantly increased by ∼15% at 3,000 m, but not 1,500 m. The magnitude of the muscle metaboreflex during recovery from static exercise was unaffected by altitude; however, the rate-pressure product was significantly elevated by ∼10% during and following static exercise at 3,000 m. Conclusions: A significant increase in the rate-pressure product during static exercise was observed at altitude, which persisted during recovery. Individuals at risk for cardiac events should use awareness of static contractions while at altitude, especially considering that stress induced by static exercise is additive to that of dynamic activities such as hiking.

Might a high hemoglobin mass be involved in non-cardiogenic pulmonary edema? The case of the chronic maladaptation to high-altitude in the Andes

Exposure to hypoxic environments when ascending at high altitudes may cause life-threatening pulmonary edema (HAPE) due to a rapid accumulation of extracellular fluid flooding in the pulmonary alveoli. In Andeans, high-altitude adaptation occurs at the expense of being more prone to chronic mountain sickness: relative hypoventilation, excess pulmonary hypertension, and secondary polycythemia. Because HAPE prevalence is high in the Andes, we posit the hypothesis that a high hemoglobine mass may increase HAPE risk. In support of it, high intrapulmonary hypertension along with hyperviscosity produced by polycytemia may enhance sear forces and intravascular hemolysis, thus leading to increased acellular hemoglobin and the subsequent damage of the alveolar and endothelial barrier. It is proposed to investigate the relationship between the vaso-endothelial homeostasis and erythropoiesis in the maladaptation to high altitude and HAPE. This research is especially important when reentry HAPE, since rheologic properties of blood changes with rapid ascent to high altitudes.

Does arterial stiffness affect orthostatic hypotension among high-altitude Tibetans?

OBJECTIVE

This study aimed to investigate the association between arterial stiffness and orthostatic hypotension (OH) and orthostatic blood pressure (BP) changes among Tibetans living at high altitude.

METHODS

A total of 630 high-altitude Tibetans were included (56.53 ± 10.16 years; 246 men). Arterial stiffness was assessed by brachial-ankle pulse wave velocity (baPWV). OH was defined as a decrease in systolic BP (SBP) >20 mmHg or a decrease in diastolic BP (DBP) >10 mmHg after 1 min or 3 min of moving from supine to standing position.

RESULTS

The prevalence of OH in this population was 6.3%. Compared with subjects without OH, the subjects with OH had a higher baPWV (P < 0.001). Multiple logistical regression found that baPWV was significantly associated with the occurrence of OH (OR 1.147, CI 95% 1.028-1.280, P = 0.014). Spearman correlation analysis showed that baPWV was negatively associated with orthostatic changes in SBP and DBP(r = -0.256, P < 0.001 and r = -0.194, P < 0.001, respectively). Further multiple stepwise linear regression analysis showed that baPWV was independently correlated with orthostatic BP changes (SBP: β = -0.599, P < 0.001; DBP: β = -0.333, P < 0.001). Moreover, increased baPWV was correlated with attenuation of orthostatic heart rate changes. No significant association was observed between hematocrit or hemoglobin concentration and OH.

CONCLUSION

BaPWV was significantly associated with the occurrence of OH and orthostatic changes in the SBP and DBP, which suggests that arterial stiffness may be a potential mechanism of impaired hemodynamic response to orthostatic challenges among high-altitude Tibetans.

Latin American Consensus on the management of hypertension in the patient with diabetes and the metabolic syndrome

: The prevalence of hypertension, type 2 diabetes mellitus (DM2) and the metabolic syndrome continues to increase in Latin America, while the rates of diagnosis, treatment and control of these disorders remain low. The frequency of the risk factors that constitute the metabolic syndrome and are associated with an increased risk of cardiovascular disease has not diminished since the publication of the previous consensus. This document discusses the socioeconomic, demographic, environmental and cultural characteristics of most associated Latin American countries and partially explains the lack of better results in improving clinical and public health actions that allow high morbidity and mortality rates caused by cardiovascular diseases and DM2 to be reduced through programs aligned with the so-called precision medicine, which should be predictive, preventive, personalized and participatory. The Consensus ratifies the diagnostic criteria expressed in the previous consensus to define hypertension and DM2 but, for the metabolic syndrome, and in the absence of evidence, the recommendation is to implement a cohort study that determines the abdominal perimeter value associated with hard outcomes, such as DM2 and CVD. Meanwhile, we recommend modifying the criterion to more than 94 cm in men and more than 84 cm in women according to WHO recommendations. We also recommend the carrying out of a study that identifies the situation of hypertension and DM2 in people of African ancestry who, in Latin America, exceed 75 million and whose epidemiology does not include solid studies. With respect to the proposed therapeutic targets, we recommended maintaining those defined in the previous consensus, but insisting that early pharmacological management of prediabetes with metformin should be introduced, as should the treatment of diabetic hypertensive patients with a combination therapy of two fixed-dose antihypertensive drugs and management with statins. To increase adherence, the use of different drugs combined in a single pill (polypill) is recommended. The simplification of the therapeutic regimen is accompanied by greater control of cardiovascular risk factors, both in primary and secondary prevention, and has been shown to be cost-effective. The consensus recommends the use of the currently available polypill combining an angiotensin-converting enzyme inhibitor, a statin and aspirin for secondary cardiovascular prevention and in patients with a high cardiovascular risk, such as hypertension patients with DM2.

Global REACH: Assessment of Brady-Arrhythmias in Andeans and Lowlanders During Apnea at 4330 m

Background: Ascent to altitude increases the prevalence of arrhythmogenesis in low-altitude dwelling populations (Lowlanders). High altitude populations (i.e., Nepalese Sherpa) may have arrhythmias resistant adaptations that prevent arrhythmogenesis at altitude, though this has not been documented in other High altitude groups, including those diagnosed with chronic mountain sickness (CMS). We investigated whether healthy (CMS-) and CMS afflicted (CMS +) Andeans exhibit cardiac arrhythmias under acute apneic stress at altitude.

Methods and Results: Electrocardiograms (lead II) were collected in CMS- (N = 9), CMS + (N = 8), and Lowlanders (N = 13) following several days at 4330 m (Cerro de Pasco, Peru). ECG rhythm and HR were assessed at both rest and during maximal volitional apnea. Both CMS- and CMS + had similar basal HR (69 ± 8 beats/min vs. 62 ± 11 beats/min), while basal HR was higher in Lowlanders (77 ± 18 beats/min; P < 0.05 versus CMS +). Apnea elicited significant bradycardia (nadir −32 ± 15 beats/min; P < 0.01) and the development of arrhythmias in 8/13 Lowlanders (junctional rhythm, 3° atrio-ventricular block, sinus pause). HR was preserved was prior to volitional breakpoint in both CMS- (nadir −6 ± 1 beat/min) and CMS + (1 ± 12 beats/min), with 2/17 Andeans developing arrhythmias (1 CMS+ and 1 CMS-; both Premature atrial contraction) prior to breakpoint.

Conclusion: Andeans showed an absence of arrhythmias and preserved HR response to volitional apnea at altitude, demonstrating that potential cardio-resistant adaptations to arrhythmogenesis exist across permanent HA populations. Acclimatized Lowlanders have further demonstrated an increased prevalence of arrhythmias at altitude.

Parallel Molecular Evolution in Pathways, Genes, and Sites in High-Elevation Hummingbirds Revealed by Comparative Transcriptomics

High-elevation organisms experience shared environmental challenges that include low oxygen availability, cold temperatures, and intense ultraviolet radiation. Consequently, repeated evolution of the same genetic mechanisms may occur across high-elevation taxa. To test this prediction, we investigated the extent to which the same biochemical pathways, genes, or sites were subject to parallel molecular evolution for 12 Andean hummingbird species (family: Trochilidae) representing several independent transitions to high elevation across the phylogeny. Across high-elevation species, we discovered parallel evolution for several pathways and genes with evidence of positive selection. In particular, positively selected genes were frequently part of cellular respiration, metabolism, or cell death pathways. To further examine the role of elevation in our analyses, we compared results for low- and high-elevation species and tested different thresholds for defining elevation categories. In analyses with different elevation thresholds, positively selected genes reflected similar functions and pathways, even though there were almost no specific genes in common. For example, EPAS1 (HIF2α), which has been implicated in high-elevation adaptation in other vertebrates, shows a signature of positive selection when high-elevation is defined broadly (>1,500 m), but not when defined narrowly (>2,500 m). Although a few biochemical pathways and genes change predictably as part of hummingbird adaptation to high-elevation conditions, independent lineages have rarely adapted via the same substitutions.

Life Ascending: Mechanism and Process in Physiological Adaptation to High-Altitude Hypoxia

To cope with the reduced availability of O₂ at high altitude, air-breathing vertebrates have evolved myriad adjustments in the cardiorespiratory system to match tissue O₂ delivery with metabolic O₂ demand. We explain how changes at interacting steps of the O₂ transport pathway contribute to plastic and evolved changes in whole-animal aerobic performance under hypoxia. In vertebrates native to high altitude, enhancements of aerobic performance under hypoxia are attributable to a combination of environmentally induced and evolved changes in multiple steps of the pathway. Additionally, evidence suggests that many high-altitude natives have evolved mechanisms for attenuating maladaptive acclimatization responses to hypoxia, resulting in counter-gradient patterns of altitudinal variation for key physiological phenotypes. For traits that exhibit counteracting environmental and genetic effects, evolved changes in phenotype may be cryptic under field conditions and can only be revealed by rearing representatives of high-and low-altitude populations under standardized environmental conditions to control for plasticity.

Divergent Fine-Scale Recombination Landscapes between a Freshwater and Marine Population of Threespine Stickleback Fish

Meiotic recombination is a highly conserved process that has profound effects on genome evolution. At a fine-scale, recombination rates can vary drastically across genomes, often localized into small recombination "hotspots" with highly elevated rates, surrounded by regions with little recombination. In most species studied, the location of hotspots within genomes is highly conserved across broad evolutionary timescales. The main exception to this pattern is in mammals, where hotspot location can evolve rapidly among closely related species and even among populations within a species. Hotspot position in mammals is controlled by the gene, Prdm9, whereas in species with conserved hotspots, a functional Prdm9 is typically absent. Due to a limited number of species where recombination rates have been estimated at a fine-scale, it remains unclear whether hotspot conservation is always associated with the absence of a functional Prdm9. Threespine stickleback fish (Gasterosteus aculeatus) are an excellent model to examine the evolution of recombination over short evolutionary timescales. Using a linkage disequilibrium-based approach, we found recombination rates indeed varied at a fine-scale across the genome, with many regions organized into narrow hotspots. Hotspots had highly divergent landscapes between stickleback populations, where only ∼15% of these hotspots were shared. Our results indicate that fine-scale recombination rates may be diverging between closely related populations of threespine stickleback fish. Interestingly, we found only a weak association of a PRDM9 binding motif within hotspots, which suggests that threespine stickleback fish may possess a novel mechanism for targeting recombination hotspots at a fine-scale.

Red Cell Distribution Width as a Novel Marker for Different Types of Atrial Fibrillation in Low and High Altitude

Background

Increased red cell distribution width (RDW) can predict the incidence and mortality of cardiovascular diseases. However, there are limited data on the relationship between RDW and altitude and the subtype of atrial fibrillation (AF). We investigated the effects of altitude on RDW in patients with different types of AF.

Methods

A total of 303 patients with nonvalvular AF were included. Of these, 156 lived in low altitude (77 paroxysmal AF, PAF; 79 persistent AF, PeAF) and 147 in high altitude (77 paroxysmal AF, PAF; 70 persistent AF, PeAF). In these groups, baseline characteristics, complete blood counts, serum biochemistry, and echocardiography were evaluated. Multivariate logistic regression analysis was conducted to determine the independent predictors of AF at the different altitudes.

Results

In both low and high altitudes, RDW and left atrial diameter (LAD) were higher in AF than control subjects (P < 0.05) and higher in persistent AF than paroxysmal AF (P < 0.05). Compared with any groups (PAF group, PeAF group, or control group) of low-altitude, RDW and LAD were found higher in high-altitude corresponding groups. Multivariate logistic regression analysis demonstrated that RDW, mean corpuscular volume (MCV), and LAD levels independently associated with AF patients in low altitude (RDW, OR 1.687, 95% CI 1.021–2.789; P < 0.05), while in high altitude, RDW, MCV, creatinine (Cr), and LAD were independent predictors for AF patients (RDW, OR 1.755, 95% CI 1.179–2.613; P < 0.05).

Conclusion

Elevated RDW levels may be an independent risk marker for nonvalvular AF, affected by type of AF and altitude.

Values of heart rate at rest in children and adults living at different altitudes in the Andes

Introduction

The heart rate (HR) is useful for the monitoring of patients, but almost no studies have been found which describe their variations according to different geographic locales and altitudes using centiles in children and adults.

Methodology

Descriptive, cross-sectional study of secondary data. Measurements were taken with a calibrated pulse oximeter; our participants resided in host cities for more than 2 months and underwent clinical evaluations by physicians. The results were categorized according to their age group and the altitude of residence using centile charts.

Results

Our sample size consisted of 6,289 subjects across different villages in Peru. Using Pearson correlation between HR and altitude, it was found in the group of patients aged 1–5 years, a coefficient of -0.118 (p value = 0.012), in the group of patients aged 6–17, 0.047 (p value = 0.025), in the group of patients aged 18–50, -0.044 (p value = 0.041) and for the group of patients aged 51–80, 0.042 (p value = 0.256). In the groups of 1–5, 6–17 and 18–50 years of age, the variations were negligible but statistically significant due to our large sample size. When all of the data was evaluated, HR values were also found to have negligible variations according to the residence altitude, with a Pearson coefficient of -0.033 (p value = 0.009). Centiles charts were used to describe the distribution of HR for different age groups by altitude of residence.

Conclusion

There are minimal variations of the HR according to the altitude of residence in all age groups.

Altitudinal variation of the gut microbiota in wild house mice

The maintenance of oxygen homeostasis in the gut is critical for the maintenance of a healthy gut microbiota. However, few studies have explored how the concentration of atmospheric oxygen affects the gut microbiota in natural populations. High-altitude environments provide an opportunity to study the potential effects of atmospheric oxygen on the composition and function of the gut microbiota. Here, we characterized the caecal microbial communities of wild house mice (Mus musculus domesticus) in two independent altitudinal transects, one in Ecuador and one in Bolivia, from sea level to nearly 4,000 m. First, we found that differences in altitude were associated with differences in the gut microbial community after controlling for the effects of body mass, diet, reproductive status and population of origin. Second, obligate anaerobes tended to show a positive correlation with altitude, while all other microbes tended to show a negative correlation with altitude. These patterns were seen independently in both transects, consistent with the expected effects of atmospheric oxygen on gut microbes. Prevotella was the most-enriched genus at high elevations in both transects, consistent with observations in high-altitude populations of pikas, ruminants and humans, and also consistent with observations of laboratory mice exposed to hypoxic conditions. Lastly, the renin-angiotensin system, a recently proposed microbiota-mediated pathway of blood pressure regulation, was the top predicted metagenomic pathway enriched in high altitudes in both transects. These results suggest that high-altitude environments affect the composition and function of the gut microbiota in wild mammals.

Evolved Mechanisms of Aerobic Performance and Hypoxia Resistance in High-Altitude Natives

Comparative physiology studies of high-altitude species provide an exceptional opportunity to understand naturally evolved mechanisms of hypoxia resistance. Aerobic capacity (VO₂max) is a critical performance trait under positive selection in some high-altitude taxa, and several high-altitude natives have evolved to resist the depressive effects of hypoxia on VO₂max. This is associated with enhanced flux capacity through the O₂ transport cascade and attenuation of the maladaptive responses to chronic hypoxia that can impair O₂ transport. Some highlanders exhibit elevated rates of carbohydrate oxidation during exercise, taking advantage of its high ATP yield per mole of O₂. Certain highland native animals have also evolved more oxidative muscles and can sustain high rates of lipid oxidation to support thermogenesis. The underlying mechanisms include regulatory adjustments of metabolic pathways and to gene expression networks. Therefore, the evolution of hypoxia resistance in high-altitude natives involves integrated functional changes in the pathways for O₂ and substrate delivery and utilization by mitochondria.

Citius, Altius, Fortius: Agreement between Perkins and Dynamic Contour Tonometry (Pascal) and the Impact of Altitude

Introduction

To ascertain differences in intraocular pressure (IOP) measurement and their repeatability between dynamic contour tonometry (DCT) and Goldmann/Perkins applanation tonometry (GAT) at two different atmospheric pressures.

Materials and methods

Forty-one eyes of 41 healthy consenting subjects were enrolled for this observational, cross-sectional study. Pachymetry and IOP measurements with DCT and GAT for both eyes of each subject at Acapulco (0 m from sea level) and at Mexico City (2,234 m from sea level) were done by the same observer. The IOP was compared between tonometers at each of the altitudes, and also for repeatability of each tonometer at different altitudes. Pearson's correlation coefficient and Bland-Altman plots were used to assess reliability of measurements and their differences at the two altitudes.

Results

The mean age of patients was 41.7 (28-66 years); 22 were females. Mean IOP with DCT was 16.1 ± 2.2 mm Hg at sea level and 15.9 ± 2.1 mm Hg at 2,234 m above sea level, not a significant difference. Mean GAT IOP at the two altitudes was 13.1 ± 1.8 and 11.5 ± 1.7 mm Hg respectively, a statistically sig -nificant difference. In contrast, central corneal thickness (CCT) was not significantly changed (548.3 to 549.4 μm, p = 0.496).

Conclusion

Repeatability of single-observer measurements with GAT remains clinically acceptable, but not at different altitudes. The DCT seems to more consistently measure a similar IOP at different altitudes in the same subjects. The two tonometers may not be used interchangeably in the serial follow-up of patients at any of the altitudes.How to cite this article: Albis-Donado O, Bhartiya S, Gil-Reyes M, Casale-Vargas G, Arreguin-Rebollar N, Kahook MY. Citius, Altius, Fortius: Agreement between Perkins and Dynamic Contour Tonometry (Pascal) and the Impact of Altitude. J Curr Glaucoma Pract 2018;12(1):40-44.

Combinatorial therapy of exercise-preconditioning and nanocurcumin formulation supplementation improves cardiac adaptation under hypobaric hypoxia

BACKGROUND

Chronic hypobaric hypoxia (cHH) mediated cardiac insufficiencies are associated with pathological damage. Sustained redox stress and work load are major causative agents of cardiac insufficiencies under cHH. Despite the advancements made in pharmacological (anti-oxidants, vasodilators) and non-pharmacological therapeutics (acclimatization strategies and schedules), only partial success has been achieved in improving cardiac acclimatization to cHH. This necessitates the need for potent combinatorial therapies to improve cardiac acclimatization at high altitudes. We hypothesize that a combinatorial therapy comprising preconditioning to mild aerobic treadmill exercise and supplementation with nanocurcumin formulation (NCF) consisting of nanocurcumin (NC) and pyrroloquinoline quinone (PQQ) might improve cardiac adaptation at high altitudes.

METHODS

Adult Sprague-Dawley rats pre-conditioned to treadmill exercise and supplemented with NCF were exposed to cHH (7620 m altitude corresponding to pO2~8% at 28±2°C, relative humidity 55%±1%) for 3 weeks. The rat hearts were analyzed for changes in markers of oxidative stress (free radical leakage, lipid peroxidation, manganese-superoxide dismutase [MnSOD] activity), cardiac injury (circulating cardiac troponin I [TnI] and T [cTnT], myocardial creatine kinase [CK-MB]), metabolic damage (lactate dehydrogenase [LDH] and acetyl-coenzyme A levels, lactate and pyruvate levels) and bio-energetic insufficiency (ATP, p-AMPKα).

RESULTS

Significant modulations (p≤0.05) in cardiac redox status, metabolic damage, cardiac injury and bio-energetics were observed in rats receiving both NCF supplementation and treadmill exercise-preconditioning compared with rats receiving only one of the treatments.

CONCLUSIONS

The combinatorial therapeutic strategy showed a tremendous improvement in cardiac acclimatization to cHH compared to either exercise-preconditioning or NCF supplementation alone which was evident from the effective modulation in redox, metabolic, contractile and bio-energetic homeostasis.

Cardioprotection after acute exposure to simulated high altitude in rats. Role of nitric oxide

AIM

In previous studies, upregulation of NOS during acclimatization of rats to sustained hypobaric hypoxia was associated to cardioprotection, evaluated as an increased tolerance of myocardium to hypoxia/reoxygenation. The objective of the present work was to investigate the effect of acute hypobaric hypoxia and the role of endogenous NO concerning cardiac tolerance to hypoxia/reoxygenation under β-adrenergic stimulation.

METHODS

Rats were submitted to 58.7 kPa in a hypopressure chamber for 48 h whereas their normoxic controls remained at 101.3 kPa. By adding NOS substrate L-arg, or blocker L-NNA, isometric mechanical activity of papillary muscles isolated from left ventricle was evaluated at maximal or minimal production of NO, respectively, under β-adrenergic stimulation by isoproterenol, followed by 60/30 min of hypoxia/reoxygenation. Activities of NOS and cytochrome oxidase were evaluated by spectrophotometric methods and expression of HIF1-α and NOS isoforms by western blot. Eosin and hematoxiline staining were used for histological studies.

RESULTS

Cytosolic expression of HIF1-α, nNOS and eNOS, and NO production were higher in left ventricle of hypoxic rats. Mitochondrial cytochrome oxidase activity was decreased by hypobaric hypoxia and this effect was reversed by L-NNA. After H/R, recovery of developed tension in papillary muscles from normoxic rats was 51-60% (regardless NO modulation) while in hypobaric hypoxia was 70% ± 3 (L-arg) and 54% ± 1 (L-NNA). Other mechanical parameters showed similar results. Preserved histological architecture was observed only in L-arg papillary muscles of hypoxic rats.

CONCLUSION

Exposure of rats to hypobaric hypoxia for only 2 days increased NO synthesis leading to cardioprotection.

Control of breathing and ventilatory acclimatization to hypoxia in deer mice native to high altitudes

AIM

We compared the control of breathing and heart rate by hypoxia between high- and low-altitude populations of Peromyscus mice, to help elucidate the physiological specializations that help high-altitude natives cope with O₂ limitation.

METHODS

Deer mice (Peromyscus maniculatus) native to high altitude and congeneric mice native to low altitude (Peromyscus leucopus) were bred in captivity at sea level. The F1 progeny of each population were raised to adulthood and then acclimated to normoxia or hypobaric hypoxia (12 kPa, simulating hypoxia at ~4300 m) for 5 months. Responses to acute hypoxia were then measured during stepwise reductions in inspired O₂ fraction.

RESULTS

Lowlanders exhibited ventilatory acclimatization to hypoxia (VAH), in which hypoxia acclimation enhanced the hypoxic ventilatory response, made breathing pattern more effective (higher tidal volumes and lower breathing frequencies at a given total ventilation), increased arterial O₂ saturation and heart rate during acute hypoxia, augmented respiratory water loss and led to significant growth of the carotid body. In contrast, highlanders did not exhibit VAH - exhibiting a fixed increase in breathing that was similar to hypoxia-acclimated lowlanders - and they maintained even higher arterial O₂ saturations in hypoxia. However, the carotid bodies of highlanders were not enlarged by hypoxia acclimation and were similar in size to those of normoxic lowlanders. Highlanders also maintained consistently higher heart rates than lowlanders during acute hypoxia.

CONCLUSIONS

Our results suggest that highland deer mice have evolved high rates of alveolar ventilation and respiratory O₂ uptake without the significant enlargement of the carotid bodies that is typical of VAH in lowlanders, possibly to adjust the hypoxic chemoreflex for life in high-altitude hypoxia.

Endothelial markers in high altitude induced systemic hypertension (HASH) at moderate high altitude

Background

Chronic intermittent hypoxia is known to induce systemic arterial hypertension whereas chronic hypoxia causes pulmonary arterial hypertension. High altitude (HA) induced systemic hypertension (HASH) in previously normotensive lowlanders following acclimatisation and prolonged stay at moderate HA is a commonly encountered medical problem. HASH has been attributed to increased sympathetic discharge. Endothelial dysfunction (ED) is implicated in hypertension in the plains hence this study was conducted in HA. This is relevant especially because of the established role of ED in the aetiopathogenesis of HA illnesses. Since hypoxia may induce ED, we aimed at studying the association of endothelial dysfunction with HASH in temporary residents at HA.

Methods

In this case-control single-centre study, we evaluated ED, by measuring endothelial molecular markers, soluble intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (VCAM-1), vascular endothelial growth factor (VEGF) and endothelial selectin (E-Selectin) in 24 cases with HASH and 25 age, sex matched normotensive controls at moderate high altitude (11,500 ft).

Results

The levels of sICAM-1 (patients: 214.3 ± 34.2 μg/L, controls: 196.2 ± 28.5 μg/L; p = 0.049) and VCAM-1 (patients 766.1 ± 123.4 ng/mL, controls: 668.6 + 117.6 ng/mL; p = 0.007) were statistically higher in the patient group. However, VEGF and E-Selectin were not significantly different between the groups. sICAM-1 significantly correlated with levels of systolic and diastolic blood pressure (r = 0.401, p = 0.003 and 0.486, p = 0.000) respectively.

Conclusion

HASH is associated with endothelial dysfunction in form of raised levels of sICAM-1 and VCAM-1.

Discordance of metabolic syndrome and abdominal obesity prevalence according to different criteria in Andean highlanders: A community-based study

AIMS

There is no consensus as to which Metabolic Syndrome (MetS) definition to use for South-American populations. The aim of this study is to compare the prevalence of MetS and abdominal obesity using different criteria in Andean adults aged 40 and older living permanently at high altitude.

METHODS

We conducted a cross-sectional study in Chivay (Andean highlands). 237 participants were included. Anthropometric measurements, glucose and lipid assessments were done in all subjects. Adult Treatment Panel III (ATPIII) and International Diabetes Federation (IDF) criteria for MetS were used. Abdominal obesity prevalence was determined using the American Diabetes Association (ADA), IDF, and PREVENCION Study criteria. Cohen's Kappa coefficient (κ) was analyzed to assess agreement level between different criteria. Multiple regression analyses were performed to find predictors for waist circumference.

RESULTS

MetS was identified in 28.7% (95%CI=23.8-33.5) using ATPIII criteria, and 37.9% (95%CI=32.7-43.0) using IDF criteria, with higher prevalence in women. The κ statistics for agreement between both criteria was 0.775 (95%CI=0.690-0.859). Abdominal obesity prevalence according to ADA, IDF, and PREVENCION criteria was 35.9% (95%CI=29.7-42.0), 75.9% (95%CI=70.5-81.4), and 42.6% (95%CI=36.3-49.0), respectively. Agreement between ADA and PREVENCION criteria was highest (κ=0.859, 95%CI=0.792-0.925). The strongest predictors for higher waist circumference values were triglycerides and BMI in women, and systolic blood pressure, triglycerides, fasting plasma glucose, and HDL-cholesterol in men.

CONCLUSIONS

MetS according to ATP III and IDF criteria was highly prevalent. IDF criteria identified a larger number of subjects with MetS. Different abdominal obesity criteria tended to show variation when applied to our sample population.

Evidence of Early-Stage Selection on EPAS1 and GPR126 Genes in Andean High Altitude Populations

The aim of this study is to identify genetic variants that harbour signatures of recent positive selection and may facilitate physiological adaptations to hypobaric hypoxia. To achieve this, we conducted whole genome sequencing and lung function tests in 19 Argentinean highlanders (>3500 m) comparing them to 16 Native American lowlanders. We developed a new statistical procedure using a combination of population branch statistics (PBS) and number of segregating sites by length (nSL) to detect beneficial alleles that arose since the settlement of the Andes and are currently present in 15–50% of the population. We identified two missense variants as significant targets of selection. One of these variants, located within the GPR126 gene, has been previously associated with the forced expiratory volume/forced vital capacity ratio. The other novel missense variant mapped to the EPAS1 gene encoding the hypoxia inducible factor 2α. EPAS1 is known to be the major selection candidate gene in Tibetans. The derived allele of GPR126 is associated with lung function in our sample of highlanders (p < 0.05). These variants may contribute to the physiological adaptations to hypobaric hypoxia, possibly by altering lung function. The new statistical approach might be a useful tool to detect selected variants in population studies.

Cooperative Oxygen Sensing by the Kidney and Carotid Body in Blood Pressure Control

Oxygen sensing mechanisms are vital for homeostasis and survival. When oxygen levels are too low (hypoxia), blood flow has to be increased, metabolism reduced, or a combination of both, to counteract tissue damage. These adjustments are regulated by local, humoral, or neural reflex mechanisms. The kidney and the carotid body are both directly sensitive to falls in the partial pressure of oxygen and trigger reflex adjustments and thus act as oxygen sensors. We hypothesize a cooperative oxygen sensing function by both the kidney and carotid body to ensure maintenance of whole body blood flow and tissue oxygen homeostasis. Under pathological conditions of severe or prolonged tissue hypoxia, these sensors may become continuously excessively activated and increase perfusion pressure chronically. Consequently, persistence of their activity could become a driver for the development of hypertension and cardiovascular disease. Hypoxia-mediated renal and carotid body afferent signaling triggers unrestrained activation of the renin angiotensin-aldosterone system (RAAS). Renal and carotid body mediated responses in arterial pressure appear to be synergistic as interruption of either afferent source has a summative effect of reducing blood pressure in renovascular hypertension. We discuss that this cooperative oxygen sensing system can activate/sensitize their own afferent transduction mechanisms via interactions between the RAAS, hypoxia inducible factor and erythropoiesis pathways. This joint mechanism supports our view point that the development of cardiovascular disease involves afferent nerve activation.

Effects of various acute hypoxic conditions on metabolic parameters and cardiac function during exercise and recovery

Purpose

Evaluation of metabolic parameters and cardiac function is important to determine the decrease in aerobic exercise capacity under hypoxic conditions. However, the variations in metabolic parameters and cardiac function and the reasons for the decrease in aerobic exercise capacity under hypoxic conditions have not been clearly explained. The purpose of this study was to compare the responses between sea level and various acute normobaric hypoxic conditions on metabolic parameters and cardiac function during exercise and recovery in order to evaluate aerobic exercise capacity.

Methods

Ten healthy male participants (21.3 ± 3.06 y) performed submaximal bicycle exercise (116.7 ± 20.1 W and 60 rpm) at sea level (20.9 % O₂) and under various normobaric hypoxic conditions (16.5 % O₂, 14.5 % O₂, 12.8 % O₂, and 11.2 % O₂) in a random order. Metabolic parameters (arterial oxygen saturation; S_PO₂, oxygen consumption; VO₂, blood lactate level) and cardiac function (heart rate; HR, stroke volume; SV, end-systolic volume; ESV, end-diastolic volume; EDV, ejection fraction; EF, cardiac output; CO) were measured at rest, during exercise (30 min), and recovery (30 min). We compared the responses on metabolic parameters and cardiac function between the different oxygen partial pressure conditions during exercise and recovery.

Results

The various acute normobaric hypoxic conditions did not affect VO₂ and SV during exercise and recovery. S_PO₂ decreased (p < .05) and blood lactate level increased (p < .05) as the oxygen partial pressure decreased. HR, EF, CO increased (p < .05) and EDV, ESV decreased (p < .05) at oxygen partial pressures of 14.5 % O₂ and below compared with 20.9 and 16.5 % O₂ during exercise and recovery.

Conclusion

A decrease in the oxygen partial pressure to 14.5 % O₂ and below might be associated with significant changes in metabolic parameters and cardiac function during exercise and recovery. These changes are an acute compensation response to reduced aerobic exercise capacity by decreased oxygen delivering and utilizing capacities under hypoxic conditions.

Altitude training for elite endurance athletes: A review for the travel medicine practitioner

High altitude training is regarded as an integral component of modern athletic preparation, especially for endurance sports such as middle and long distance running. It has rapidly achieved popularity among elite endurance athletes and their coaches. Increased hypoxic stress at altitude facilitates key physiological adaptations within the athlete, which in turn may lead to improvements in sea-level athletic performance. Despite much research in this area to date, the exact mechanisms which underlie such improvements remain to be fully elucidated. This review describes the current understanding of physiological adaptation to high altitude training and its implications for athletic performance. It also discusses the rationale and main effects of different training models currently employed to maximise performance. Athletes who travel to altitude for training purposes are at risk of suffering the detrimental effects of altitude. Altitude illness, weight loss, immune suppression and sleep disturbance may serve to limit athletic performance. This review provides an overview of potential problems which an athlete may experience at altitude, and offers specific training recommendations so that these detrimental effects are minimised.

SENP1, but not fetal hemoglobin, differentiates Andean highlanders with chronic mountain sickness from healthy individuals among Andean highlanders

Chronic mountain sickness (CMS) results from chronic hypoxia. It is unclear why certain highlanders develop CMS. We hypothesized that modest increases in fetal hemoglobin (HbF) are associated with lower CMS severity. In this cross-sectional study, we found that HbF levels were normal (median = 0.4%) in all 153 adult Andean natives in Cerro de Pasco, Peru. Compared with healthy adults, the borderline elevated hemoglobin group frequently had symptoms (headaches, tinnitus, cyanosis, dilatation of veins) of CMS. Although the mean hemoglobin level differed between the healthy (17.1 g/dL) and CMS (22.3 g/dL) groups, mean plasma erythropoietin (EPO) levels were similar (healthy, 17.7 mIU/mL; CMS, 12.02 mIU/mL). Sanger sequencing determined that single-nucleotide polymorphisms in endothelial PAS domain 1 (EPAS1) and egl nine homolog 1 (EGLN1), associated with lower hemoglobin in Tibetans, were not identified in Andeans. Sanger sequencing of sentrin-specific protease 1 (SENP1) and acidic nuclear phosphoprotein 32 family, member D (ANP32D), in healthy and CMS individuals revealed that non-G/G genotypes were associated with higher CMS scores. No JAK2 V617F mutation was detected in CMS individuals. Thus, HbF and other classic erythropoietic parameters did not differ between healthy and CMS individuals. However, the non-G/G genotypes of SENP1 appeared to differentiate individuals with CMS from healthy Andean highlanders.

Novel Insights into Cardiovascular Regulation in Patients with Chronic Mountain Sickness

Studies of high-altitude populations, and in particular of maladapted subgroups, may provide important insight into underlying mechanisms involved in the pathogenesis of hypoxemia-related disease in general. Chronic mountain sickness (CMS) is a major public health problem in mountainous regions of the world affecting many millions of high-altitude dwellers. It is characterized by exaggerated chronic hypoxemia, erythrocytosis, and mild pulmonary hypertension. In later stages these patients often present with right heart failure and are predisposed to systemic cardiovascular disease, but the underlying mechanisms are poorly understood. Here, we present recent new data providing insight into underlying mechanisms that may cause these complications.

Responses of peripheral blood mononuclear cells to moderate exercise and hypoxia

The purpose of this study was to analyze the physiological features of peripheral blood mononuclear cells (PBMCs) isolated from healthy female trekkers before and after physical activity carried out under both normoxia (low altitude, < 2000 m a.s.l.) and hypobaric hypoxia (high altitude, > 3700 m a.s.l.). The experimental design was to differentiate effects induced by exercise and those related to external environmental conditions. PBMCs were isolated from seven female subjects before and after each training period. The PBMCs were phenotypically and functionally characterized using fluorimetric and densitometric analyses, to determine cellular activation, and their intracellular Ca(2+) levels and oxidative status. After a period of normoxic physical exercise, the PBMCs showed an increase in fully activated T lymphocytes (CD3(+) CD69(+) ) and a reduction in intracellular Ca(2+) levels. On the other hand, with physical exercise performed under hypobaric hypoxia, there was a reduction in T lymphocytes and an increase in nonactivated B lymphocytes, accompanied by a reduction in O2 (-) levels in the mitochondria. These outcomes reveal that in women, low- to moderate-intensity aerobic trekking induces CD69 T cell activation and promotes anti-stress effects on the high-altitude-induced impairment of the immune responses and the oxidative balance.

Cardiovascular System Response to Carbon Dioxide and Exercise in Oxygen-Enriched Environment at 3800 m

Background: This study explores the responses of the cardiovascular system as humans exercise in an oxygen-enriched room at high altitude under various concentrations of CO₂. Methods: The study utilized a hypobaric chamber set to the following specifications: 3800 m altitude with 25% O₂ and different CO₂ concentrations of 0.5% (C1), 3.0% (C2) and 5.0% (C3). Subjects exercised for 3 min three times, separated by 30 min resting periods in the above-mentioned conditions, at sea level (SL) and at 3800 m altitude (HA). The changes of heart rate variability, heart rate and blood pressure were analyzed. Results: Total power (TP) and high frequency power (HF) decreased notably during post-exercise at HA. HF increased prominently earlier the post-exercise period at 3800 m altitude with 25% O₂ and 5.0% CO₂ (C3), while low frequency power (LF) changed barely in all tests. The ratios of LF/HF were significantly higher during post-exercise in HA, and lower after high intensity exercise in C3. Heart rate and systolic blood pressure increased significantly in HA and C3. Conclusions: Parasympathetic activity dominated in cardiac autonomic modulation, and heart rate and blood pressure increased significantly after high intensity exercise in C3.

Endogenous Asymmetric Dimethylarginine Pathway in High Altitude Adapted Yaks

Hypoxia-induced and high altitude pulmonary hypertension are a major problem in the mountain areas of the world. The asymmetric methylarginines (ADMA) inhibit nitric oxide (NO) synthesis by competing with L-arginine, and high levels of plasma ADMA predict adverse outcomes in pulmonary hypertension. However, little is known about the regulation of the ADMA-NO pathway in animals adapted to high altitudes. We measured the plasma ADMA concentration, endothelial NO synthase (eNOS), dimethylarginine dimethylaminohydrolases (DDAH) protein expression, and DDAH activities in the lungs from yaks. Although the yaks are hypoxemic, cardiac function and pulmonary arterial pressures are almost normal, and we found decreased DDAH expression and activity in association with reduced plasma ADMA concentrations. The eNOS expression was significantly higher in yaks. These results indicate that augmented endogenous NO activity in yaks through the ADMA-DDAH pathway and eNOS upregulation account for the low pulmonary vascular tone observed in high altitude adapted yaks.

Heart rate variability during sleep at high altitude: effect of periodic breathing

BACKGROUND

Heart rate variability (HRV) during sleep in normal subjects at high altitude shows a decrease in parasympathetic tone associated with an increase in the sympathetic one, which tends to be reversed with acclimatization. However, periodic breathing (PB) during sleep may influence this effect detected by HRV spectral analysis.

PURPOSE

The aim of our study was to investigate HRV during sleep periodic breathing (PB) at high altitude in normal subjects at two different times of acclimatization, i.e., two different levels of hypoxemia.

METHODS

Recordings of six healthy climbers (aged between 33 and 40 years), at sea level (SL) and at Everest North Base Camp (5180 m), during the first (BC1) and the tenth (BC2) overnight unattended polygraphy, were analyzed. PB was commonplace in all subjects at high altitude to a variable extent. At SL and at BC1 and BC2, HRV was evaluated overnight and separately during clear regular breathing (RB) and PB.

RESULTS

A mean overnight beat-by-beat series interval (RR) reduction at acute environmental hypoxic exposure that resumed to SL values after 10-day sojourn was observed. This reduction was mostly due to RR during RB, while during PB, RR values were not different from SL. Higher peaks of tidal volume were associated with higher HRV.

CONCLUSIONS

The present study shows that in healthy subjects, PB with central apneas increases the amplitude of RR oscillations, and these oscillations are tightly related to respiratory amplitude. Oxygenation does not influence this phenomenon. Therefore, oscillations in ventilation itself should be taken into account when investigating HRV.

Role of p53 in lung tissue remodeling

The tumor suppressor gene p53 regulates a wide range of cellular processes including cell cycle progression, proliferation, apoptosis and tissue development and remodeling. Lung cell apoptosis and tissue remodeling have critical roles in many lung diseases. Abnormal proliferation or resistance to apoptosis of lung cells will lead to structural changes of many lung tissues, including the pulmonary vascular wall, small airways and lung parenchyma. Among the many lung diseases caused by vascular cell apoptosis and tissue remodeling are chronic obstructive pulmonary disease, bronchial asthma and pulmonary arterial hypertension. Recent advances in biology and medicine have provided new insights and have resulted in new therapeutic strategies for tissue remodeling in human and animal models. This review is focused on lung disease susceptibility associated with the p53 pathway and describes molecular mechanisms upstream and downstream of p53 in lung tissue remodeling. Improved understanding of structural changes associated with pulmonary vascular remodeling and lung cell apoptosis induced by the p53 pathway may new provide therapeutic targets.