Blood pressure at high altitude: physiology and clinical implications

Comprehensive viewpoints on heart rate variability at high altitude

OBJECTIVES

Hypoxia is a physiological state characterized by reduced oxygen levels in organs and tissues. It is a common clinicopathological process and a major cause of health problems in highland areas.  Heart rate variability (HRV) is a measure of the balance in autonomic innervation to the heart. It provides valuable information on the regulation of the cardiovascular system by neurohumoral factors, and changes in HRV reflect the complex interactions between multiple systems. In this review, we provide a comprehensive overview of the relationship between high-altitude hypoxia and HRV. We summarize the different mechanisms of diseases caused by hypoxia and explore the changes in HRV across various systems. Additionally, we discuss relevant pharmaceutical interventions. Overall, this review aims to provide research ideas and assistance for in-depth studies on HRV. By understanding the intricate relationship between high-altitude hypoxia and HRV, we can gain insights into the underlying mechanisms and potential therapeutic approaches to mitigate the effects of hypoxia on cardiovascular and other systems.

METHODS

The relevant literature was collected systematically from scientific database, including PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), Baidu Scholar, as well as other literature sources, such as classic books of hypoxia.

RESULTS

There is a close relationship between heart rate variability and high-altitude hypoxia. Heart rate variability is an indicator that evaluates the impact of hypoxia on the cardiovascular system and other related systems. By improving the observation of HRV, we can estimate the progress of cardiovascular diseases and predict the impact on other systems related to cardiovascular health. At the same time, changes in heart rate variability can be used to observe the efficacy of preventive drugs for altitude related diseases.

CONCLUSIONS

HRV can be used to assess autonomic nervous function under various systemic conditions, and can be used to predict and monitor diseases caused by hypoxia at high altitude. Investigating the correlation between high altitude hypoxia and heart rate variability can help make HRV more rapid, accurate, and effective for the diagnosis of plateau-related diseases.

Expedition 5300: limits of human adaptations in the highest city in the world

Exposure to chronic hypobaric hypoxia imposes a significant physiological burden to more than 80 million humans living above 2500 m throughout the world. Among them, 50 000 live in the world's highest city, La Rinconada, located at 5000-5300 m in southern Peru. Expedition 5300 is the first scientific and medical programme led in La Rinconada to investigate the physiological adaptations and altitude-related health issues in this unique population. Dwellers from La Rinconada have very high haemoglobin concentration (20.3 ± 2.4 g/dL; n = 57) and those with chronic mountain sickness (CMS) exhibit even higher concentrations (23.1 ± 1.7 g/dL; n = 150). These values are associated with large total haemoglobin mass and blood volume, without an associated iron deficit. These changes in intravascular volumes lead to a substantial increase in blood viscosity, which is even larger in CMS patients. Despite these large haematological changes, 24 h blood pressure monitoring is essentially normal in La Rinconada, but some results suggest impaired vascular reactivity. Echocardiography revealed large right heart dilatation and high pulmonary arterial pressure as well as left ventricle concentric remodelling and grade I diastolic dysfunction. These changes in heart dimension and function tend to be more severe in highlanders with CMS. Polygraphy evaluations revealed a large reduction in nocturnal pulse oxygen saturation (median SpO2  = 79%), which is even more severe in CMS patients who also tended to show a higher oxygen desaturation index. The population of La Rinconada offers a unique opportunity to investigate the human responses to chronic severe hypoxia, at an altitude that is probably close to the maximum altitude human beings can permanently tolerate without presenting major health issues.

Effect of acute altitude exposure on physiological parameters and glucose metabolism in healthy lowland Peruvians

BACKGROUND

High altitude exposure triggers a series of physiological changes to maintain homeostasis. Although longer-term (days to years) acclimatization processes are well studied, less is known about the physiological changes upon rapid ascent. We took advantage of Peru's geography to measure the first physiological changes following rapid transport from a low to a high-altitude environment among lowlanders.

METHODS

Blood glucose, insulin, C-peptide, and salivary cortisol among healthy lowland Peruvians were measured before and after glucose ingestion at 40 m and upon arrival at 3470 m. Resting heart rate, blood oxygen saturation, and blood pressure were also monitored.

RESULTS

At high altitude, we find a significant ( p<0.05) increase in heart rate and a decrease in blood oxygen saturation and salivary cortisol. Additionally, baseline levels of blood glucose, plasma C-peptide, and cortisol were reduced ( p<0.05). Blood glucose, plasma insulin, and plasma C-peptide returned to baseline or below faster at high altitude after glucose ingestion.

CONCLUSIONS

Although many overlapping environmental and physiological factors are present in the high-altitude environment, the first steps of acclimatization in this population appear to be caused by increased energy expenditure and glucose metabolism to maintain oxygen homeostasis until the longer-term acclimatization mechanisms become more significant.

New strategy for rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments

High-altitude hypoxic environments have critical implications on cardiovascular system function as well as blood pressure regulation. Such environments place patients with hypertension at risk by activating the sympathetic nervous system, which leads to an increase in blood pressure. In addition, the high-altitude hypoxic environment alters the in vivo metabolism and antihypertensive effects of antihypertensive drugs, which changes the activity and expression of drug-metabolizing enzymes and drug transporters. The present study reviewed the pharmacodynamics and pharmacokinetics of antihypertensive drugs and its effects on patients with hypertension in a high-altitude hypoxic environment. It also proposes a new strategy for the rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments. The increase in blood pressure on exposure to a high-altitude hypoxic environment was mainly dependent on increased sympathetic nervous system activity. Blood pressure also increased proportionally to altitude, whilst ambulatory blood pressure increased more than conventional blood pressure, especially at night. High-altitude hypoxia can reduce the activities and expression of drug-metabolizing enzymes, such as CYP1A1, CYP1A2, CYP3A1, and CYP2E1, while increasing those of CYP2D1, CYP2D6, and CYP3A6. Drug transporter changes were related to tissue type, hypoxic degree, and hypoxic exposure time. Furthermore, the effects of high-altitude hypoxia on drug-metabolism enzymes and transporters altered drug pharmacokinetics, causing changes in pharmacodynamic responses. These findings suggest that high-altitude hypoxic environments affect the blood pressure, pharmacokinetics, and pharmacodynamics of antihypertensive drugs. The optimal hypertension treatment plan and safe and effective medication strategy should be formulated considering high-altitude hypoxic environments.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

PROSPERO

CRD42021275229.

Associations of socioeconomic status and obesity with hypertension in tibetan adults in a Chinese plateau area

BACKGROUND

Previous studies have identified that socioeconomic status (SES) and obesity are associated with hypertension. However, their interaction on hypertension risk has not yet been assessed.

METHODS

The study used data from 6,069 Tibetan residents in Chengguan District in Lhasa, the Chinese Tibetan autonomous region's capital, based on a cohort study conducted from May 2018 to September 2019 in five provinces in southwest China. We used logistic regression models to assess the complex relations of SES and obesity with hypertension.

RESULTS

Compared with individuals of high SES, low and moderate SES were positively associated with high risk of hypertension. SES and obesity have significant additive interaction on hypertension (general obesity by BMI: RERI = 1.33, P < 0.001; abdominal obesity by WC: RERI = 0.76, P < 0.001; abdominal obesity by WHtR: RERI = 0.96, P < 0.001). In people from the low and moderate SES segments, obesity was linked to an increased risk of hypertension, but the correlations were stronger in people from the moderate SES category. Compared with people of high SES and non obese, those with moderate SES and obesity had a higher risk of hypertension, and ORs were 4.38 (2.80, 6.84) for general obesity by BMI, 3.38 (2.05, 5.57) for abdominal obesity by WC, and 3.18 (1.57, 6.42) for abdominal obesity by WHtR.

CONCLUSION

There is an independent and additive interaction effect of obesity and SES on the risk of hypertension. People with obesity, especially those of moderate and low SES, should reduce weight and waist circumference, and pay more attention to blood pressure. Moreover, the government, health administration departments, and society should prioritize improving the socioeconomic status of the Tibetan population and addressing risk factors like obesity.

Coronary Syndromes and High-Altitude Exposure—A Comprehensive Review

The aim of this review is to identify a preventive strategy in order to minimize the risk of adverse events in patients with coronary syndromes and acute exposure to high-altitude. For this purpose we searched the electronic database of PubMed, EMBASE, and Web of Science for studies published in the last 30 years in this field. The conclusions of this review are: patients with stable coronary artery disease on optimal treatment and in a good physical condition can tolerate traveling to high altitude up to 3500 m; on the other hand, patients with unstable angina or recent myocardial infarction no older than 6 months should take less interest in hiking or any activity involving high altitude. Air-traveling is contraindicated for patients with myocardial infarction within previous 2 weeks, angioplasty or intracoronary stent placement within previous 2 weeks, and unstable angina or coronary artery bypass grafting within previous 3 weeks. The main trigger for sudden cardiac death is the lack of gradual acclimatization to high-altitude and to the exercise activity, and the most important risk factor is prior myocardial infarction.

Molecular Mechanisms of High-Altitude Acclimatization

High-altitude illnesses (HAIs) result from acute exposure to high altitude/hypoxia. Numerous molecular mechanisms affect appropriate acclimatization to hypobaric and/or normobaric hypoxia and curtail the development of HAIs. The understanding of these mechanisms is essential to optimize hypoxic acclimatization for efficient prophylaxis and treatment of HAIs. This review aims to link outcomes of molecular mechanisms to either adverse effects of acute high-altitude/hypoxia exposure or the developing tolerance with acclimatization. After summarizing systemic physiological responses to acute high-altitude exposure, the associated acclimatization, and the epidemiology and pathophysiology of various HAIs, the article focuses on molecular adjustments and maladjustments during acute exposure and acclimatization to high altitude/hypoxia. Pivotal modifying mechanisms include molecular responses orchestrated by transcription factors, most notably hypoxia inducible factors, and reciprocal effects on mitochondrial functions and REDOX homeostasis. In addition, discussed are genetic factors and the resultant proteomic profiles determining these hypoxia-modifying mechanisms culminating in successful high-altitude acclimatization. Lastly, the article discusses practical considerations related to the molecular aspects of acclimatization and altitude training strategies.

Metabolic Syndrome and Its Components are Associated with In-Hospital Complications after Thoracic Endovascular Aortic Repair for Acute Type B Aortic Dissection

BACKGROUND

This study aimed to explore whether and to what extent metabolic syndrome (MetS) and its components are associated with in-hospital complications in patients with acute type B aortic dissection after thoracic endovascular aortic repair (TEVAR).

METHODS

We retrospectively enrolled 684 patients who had undergone TEVAR. Demographic and clinical data were collected and subgroup analysis, mixed-model regression analysis, scoring systems, and receiver operating characteristic (ROC) curve analyses were performed.

RESULTS

Overall, 684 inpatients were assigned to the poor outcome (n = 90) or no complications (n = 594) group. Compared to the no complications group, the poor outcome group had a higher incidence of MetS (44 [48.9%] vs. 120 [20.2%], P < 0.05). In the subgroup analysis, in-hospital complications were present in 3.1%, 6.6%, 11.9%, 20.7%, 40.0%, and 62.5% of patients in the 6 groups who met the 0, 1, 2, 3, 4, and 5 MetS diagnostic criteria, respectively. On multivariable logistic regression, hypertension (odds ratio [OR]: 2.680; 95% confidence interval [CI]: 1.571-4.570), type 2 diabetes (OR: 2.135; 95% CI: 1.192-3.824), quartiles of body mass index (OR: 1.801; 95% CI: 1.415-2.291), high-density lipoprotein cholesterol (OR: 0.763; 95% CI: 0.611-0.953), and systolic blood pressure (OR: 1.894; 95% CI: 1.486-2.413) were independent factors for in-hospital complications after adjustment for other risk factors. After adjusting for potential confounding factors, MetS was an independent risk factor for in-hospital complications. We established a scoring system for each component and the area under the ROC curve was 0.664 (95% CI: 0.618-0.710) in all patients, 0.672 (95% CI: 0.595-0.749) in patients with MetS, and 0.610 (95% CI: 0.552-0.667) in patients without MetS, as determined by ROC analysis.

CONCLUSIONS

MetS, especially the blood pressure component, confers a greater risk of in-hospital complications in patients with acute type B aortic dissection after TEVAR.

Effects of altitude on the gut microbiome and metabolomics of Sanhe heifers

Introduction

Extreme environments at high altitudes pose a significant physiological challenge to animals. We evaluated the gut microbiome and fecal metabolism in Sanhe heifers from different altitudes.

Methods

Twenty Sanhe heifers (body weight: 334.82 ± 13.22 kg, 15-month-old) selected from two regions of China: the Xiertala Cattle Breeding Farm in Hulunbeier, Inner Mongolia [119°57' E, 47°17' N; approximately 700 m altitude, low altitude (LA)] and Zhizhao Dairy Cow Farm in Lhasa, Tibet [91°06' E, 29°36' N; approximately 3,650 m altitude, high altitude (HA)], were used in this study. Fecal samples were collected and differences in the gut microbiota and metabolomics of Sanhe heifers were determined using 16S rRNA gene sequencing and metabolome analysis.

Results and discussion

The results showed that altitude did not significantly affect the concentrations of fecal volatile fatty acids, including acetate, propionate, butyrate, and total volatile fatty acids (p > 0.05). However, 16S rRNA gene sequencing showed that altitude significantly affected gut microbial composition. Principal coordinate analysis based on Bray-Curtis dissimilarity analysis revealed a significant difference between the two groups (p = 0.001). At the family level, the relative abundances of Peptostreptococcaceae, Christensenellaceae, Erysipelotrichaceae, and Family_XIII were significantly lower (p < 0.05) in LA heifers than in HA heifers. In addition, the relative abundances of Lachnospiraceae, Domibacillus, Bacteroidales_S24-7_group, Bacteroidales_RF16_group, Porphyromonadaceae, and Spirochaetaceae were significantly higher in HA heifers than in LA heifers (p < 0.05). Metabolomic analysis revealed the enrichment of 10 metabolic pathways, including organismal systems, metabolism, environmental information processing, genetic information processing, and disease induction. The genera Romboutsia, Paeniclostridium, and g_unclassified_f_Lachnospiraceae were strongly associated with the 28 differential metabolites. This study is the first to analyze the differences in the gut microbiome and metabolome of Sanhe heifers reared at different altitudes and provides insights into the adaptation mechanism of Sanhe heifers to high-altitude areas.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Review of the relationship and underlying mechanisms between the Qinghai-Tibet plateau and host intestinal flora

The intestinal microbial community is the largest ecosystem in the human body, in which the intestinal flora plays a dominant role and has a wide range of biological functions. However, it is vulnerable to a variety of factors, and exposure to extreme environments at high altitudes, as seen on the Qinghai-Tibet plateau, may cause changes in the structure and function of the host intestinal flora. Conversely, the intestinal flora can help the host adapt to the plateau environment through a variety of ways. Herein, we review the relationship and underlying mechanism between the host intestinal flora and the plateau environment by discussing the characteristics of the plateau environment, its influence on the intestinal flora, and the important role of the intestinal flora in host adaptation to the plateau environment. This review aimed to provide a reference for maintaining the health of the plateau population.

Adaptive Responses to Hypoxia and/or Hyperoxia in Humans

Significance: Oxygen is indispensable for aerobic life, but its utilization exposes cells and tissues to oxidative stress; thus, tight regulation of cellular, tissue, and systemic oxygen concentrations is crucial. Here, we review the current understanding of how the human organism (mal-)adapts to low (hypoxia) and high (hyperoxia) oxygen levels and how these adaptations may be harnessed as therapeutic or performance enhancing strategies at the systemic level. Recent Advances: Hyperbaric oxygen therapy is already a cornerstone of modern medicine, and the application of mild hypoxia, that is, hypoxia conditioning (HC), to strengthen the resilience of organs or the whole body to severe hypoxic insults is an important preparation for high-altitude sojourns or to protect the cardiovascular system from hypoxic/ischemic damage. Many other applications of adaptations to hypo- and/or hyperoxia are only just emerging. HC-sometimes in combination with hyperoxic interventions-is gaining traction for the treatment of chronic diseases, including numerous neurological disorders, and for performance enhancement. Critical Issues: The dose- and intensity-dependent effects of varying oxygen concentrations render hypoxia- and/or hyperoxia-based interventions potentially highly beneficial, yet hazardous, although the risks versus benefits are as yet ill-defined. Future Directions: The field of low and high oxygen conditioning is expanding rapidly, and novel applications are increasingly recognized, for example, the modulation of aging processes, mood disorders, or metabolic diseases. To advance hypoxia/hyperoxia conditioning to clinical applications, more research on the effects of the intensity, duration, and frequency of altered oxygen concentrations, as well as on individual vulnerabilities to such interventions, is paramount. Antioxid. Redox Signal. 37, 887-912.

Matrix metalloproteinase-9 and substance-P as predictors for early-stage diagnosis of acute mountain sickness

INTRODUCTION

Although acute mountain sickness (AMS) can be a life-threatening condition, early diagnosis is difficult due to vague and non-specific symptoms. The aim of this study is to investigate biochemical markers that can detect high-altitude diseases in advance. Eight different biomarkers (BNP, HIF-1α, NGAL, MMP-3, MMP-9, SESN2, substance P (SP), and U-II) were studied, and their relationship with AMS was investigated.

METHODS

Of the 84 mountaineers who participated in the mountaineering training organized by the Turkish Mountaineering Federation in the Rize Kaçkar Mountains in 2018, 52 volunteered to participate in the study. Twelve hours after the participants reached an altitude of 2200 m (exposed to moderate hypoxia), their vital parameters were measured, and blood samples were taken for biochemistry tests. Vital signs and Lake Louise (LL) AMS scores were recorded every 24 h during the following 72 h. The participants were divided into two groups according to their LL scores: those with AMS and those without (AMS+ and AMS -), and the vital parameters and biomarker levels of both groups were compared and evaluated.

RESULTS

Of the volunteers participating in the study, 35 (67.3%) were male and 17 (32.7%) were female, although there was no gender difference in terms of susceptibility to AMS. Among the investigated markers in the AMS + group, MMP-9 and SP were statistically significantly higher (p = 0.037 and p = 0.038, respectively). There were no statistical differences between AMS- and AMS+ groups with regard to heart rate, oxygen saturation, and systolic and diastolic blood pressure values (p = 0.507, p = 0.929, p = 0.955, p = 0.572, respectively).

CONCLUSION

There were significant differences between the AMS- and AMS+ groups in terms of MMP-9 and SP. However, differences in physical indexes between the groups were not statistically significant. This could provide objective indexes for scanning and screening individuals susceptible to AMS in the early stages of rapid ascending.

Metabolic syndrome and its components are associated with hypoxemia after surgery for acute type A aortic dissection: an observational study

Background

The aim of this study was to explore whether or to what extent metabolic syndrome (METs) and its components were associated with hypoxemia in acute type A aortic dissection (ATAAD) patients after surgery.

Methods

This study involved 271 inpatients who underwent surgery. Demographic and clinical data were collected. Subgroup analysis, mixed model regression analysis, and receiver operating characteristic (ROC) curve analysis were performed, and a scoring system was evaluated.

Results

The 271 inpatients were assigned to the hypoxemia group (n = 48) or no hypoxemia group (n = 223) regardless of METs status. Compared to the no hypoxemia group, the hypoxemia group had a higher incidence of METs. Hypoxemia was present in 0%, 3.7%, 19.8%, 51.5%, 90.0% and 100% in the groups of individuals who met the diagnostic criteria of MetS 0, 1, 2, 3, 4 and 5 times, respectively. In the multivariable logistic regression analysis, BMI quartile was still a risk factor for hypoxemia after adjustment for other risk factors. After adjustment for potential confounding factors, METs was an independent risk factor for hypoxemia in several models. After assigning a score for each METs component present, the AUCs were 0.852 (95% CI 0.789–0.914) in all patients, 0.728 (95% CI 0.573–0.882) in patients with METs and 0.744 (95% CI 0.636–0.853) in patients without METs according to receiver operating characteristic analysis.

Conclusions

METs, especially body mass index, confers a greater risk of hypoxemia in ATAAD after surgery.

Magnetic resonance imaging study of normal cranial bone marrow conversion at high altitude

BACKGROUND

To use conventional magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI) to investigate the effects of long-term hypoxia on cranial bone marrow conversion in healthy people at high altitudes.

METHODS

A total of 1,130 individuals were selected from altitudinal areas of 2,000-3,000, 3,100-4,000, and >4,100 m. Each altitude range was divided into 5 age groups: 0-5, 6-14, 15-29, 30-49, and ≥50 years. Firstly, cranial bone marrow typing of the participants in each altitude range was performed on sagittal T1-weighted images (T1WI) according to the average diploe thickness and signal intensity of the normal skull, and the relationship between bone marrow conversion and age was analyzed. Secondly, the apparent diffusion coefficient (ADC) values of the frontal bone, parietal bone, occipital bone, and temporal bone were measured in the DWI post-processing workstation and statistical methods were used to analyze whether different altitudinal gradients and long-term hypoxic environment had any effect on cranial bone marrow conversion.

RESULTS

There was a positive correlation between bone marrow type and age in the healthy populations at all 3 levels of altitude (P<0.05). The average thickness of the cranial diploe also positively correlated with age (P<0.05); in the age ranges of 30-49 and ≥50 years, the ADC values of the occipital and temporal bone marrow positively correlated with increasing altitude (P<0.05).

CONCLUSIONS

The cranial bone marrow of normal people at high altitudes changes from Type I to Type IV with increasing age and under the influence of long-term chronic hypoxia. The bone marrow of the occipital and temporal bones of healthy people aged 30-49 and ≥50 years showed erythromedularization during the process of Type III and IV bone marrow conversion.

Blood Pressure Variation with Altitudes in Children: A Cross-Sectional Observational Study from Himalayan Hills

OBJECTIVES

We aimed to evaluate blood pressure (BP) in Indian children who had similar demographic characteristics but hailed from different altitudes.

METHODS

BP of school going children, aged 5 to 12 years, at five different locations varying in altitude (near sea level: n = 425; 2000 feet: n = 244; 4000 feet: n = 248; 6000 feet: n = 242 and 8000 feet: n = 250) was measured in a mountainous district in Himalaya. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were recorded by aneroid sphygmomanometer in the sitting posture using a calibrated instrument and four trained resident doctors. The average of three readings was taken.

RESULTS

Of the 1229 children whose data were analyzed, 50.4% were boys. SBP showed a progressive rise from 99.5 (4.00) mmHg [mean (standard deviation)] at near sea level to 106.7 (4.17) mmHg at 8000 feet. Similarly, DBP showed a rise from 60.1 (3.67) mmHg to 66.8 (4.58) mmHg over the same altitude range. Analysis of covariance for BP variation with altitude, with age as covariate, indicated a modest but statistically significant rise in both SBP and DBP with altitude. Higher BP values was noted among children residing at higher than at lower altitude (0.8% at sea level to 18.8% at 8000 feet). Correlations between SBP and DBP values and height and weight, though positive and significant at p < 0.01 level, were weak.

CONCLUSIONS

These data will help in correct interpretation of BP readings in children residing at high altitude.

Cardiac adaptation to high altitudes after short- and long-term exposure among Chinese Han lowlanders

BACKGROUND

Short-term, high altitude (HA) exposure raises pulmonary artery systolic pressure (PASP) and decreases left ventricular volumes. However, relatively little is known of the long-term cardiac consequences of prolonged exposure in Chinese Han lowlanders, a highly adapted HA population.

AIMS

We studied cardiac structure and function by echocardiography to investigate short-term adaptation and potential long-term cardiac remodeling.

METHODS

This study included 301 healthy subjects of short-term exposure (STE), acclimatized Chinese Han lowlanders (AL) at HA, native Tibetans (NT), and sea level residents (SLR) with 75, 77, 69, and 80 participants, respectively. All groups underwent standard echocardiography.

RESULTS

Compared with SLR, systolic blood pressure (SBP) and heart rate of STE and AL did not significantly increase following HA exposure, but SBP in STE was lower than AL. In lowlanders, HA exposure enlarged right heart and pulmonary artery (PA), reduced left ventricular (LV) diastolic function. This decrease in LV diastolic function increased with exposure time. Compared with SLR, ejection fraction did not change significantly in STE, but decreased in AL. Interventricular septal end-diastolic thickness (IVSd) increased both in STE and AL compared with SLR. Compared with NT, AL population had higher SBP and the greater diameter of PA.

CONCLUSIONS

In Chinese Han lowlanders, exposure to HA enlarged right ventricle and decreased the diastolic function of LV. LV systolic function was preserved after short-term HA exposure but decreased after long-term HA exposure. It was possible to speculate that ethnicity contributed to the observed difference in heart.

Blood Pressure Load: An Effective Indicator of Systemic Circulation Status in Individuals With Acute Altitude Sickness

Background: Acute high altitude (HA) exposure results in blood pressure (BP) variations in most subjects. Previous studies have demonstrated that higher BP is potentially correlated with acute mountain sickness (AMS). The BP load may be of clinical significance regarding systemic circulation status.

Objectives: This study aimed to examine HA-induced BP changes in patients with AMS compared to those in healthy subjects. Further, we provided clinical information about the relationship between variations in 24-h ambulatory parameters (BP level, BP variability, and BP load) and AMS.

Methods: Sixty-nine subjects were enrolled and all participants ascended Litang (4,100 m above sea level). They were monitored using a 24-h ambulatory blood pressure device and underwent echocardiography within 24 h of altitude exposure. The 2018 Lake Louise questionnaire was used to evaluate AMS.

Results: The AMS group comprised more women than men [15 (65.2%) vs. 13 (28.3%), P < 0.001] and fewer smokers [4 (17.4%) vs. 23 (50.0%), P = 0.009]. The AMS group exhibited significant increases in 24-h BP compared to the non-AMS group (24-h SBP variation: 10.52 ± 6.48 vs. 6.03 ± 9.27 mmHg, P = 0.041; 24-h DBP variation: 8.70 ± 4.57 vs. 5.03 ± 4.98 mmHg, P = 0.004). The variation of mean 24-h cBPL (cumulative BP load) (mean 24-h cSBPL: 10.58 ± 10.99 vs. 4.02 ± 10.58, P = 0.016; 24-h mean cDBPL: 6.03 ± 5.87 vs. 2.89 ± 4.99, P = 0.034) was also obviously higher in AMS subjects than in non-AMS subjects after HA exposure. 24-h mean cSBPL variation (OR = 1.07, P = 0.024) and 24-h mean cDBPL variation (OR = 1.14, P = 0.034) were independent risk factors of AMS. Moreover, variation of 24-h mean cSBPL showed a good correlation with AMS score (R = 0.504, P < 0.001).

Conclusions: Our study demonstrated that patients with AMS had higher BP and BP load changes after altitude exposure than healthy subjects. Excessive BP load variations were associated with AMS. Thus, BP load could be an effective indicator regarding systemic circulation status of AMS.

Experimental Modeling of Damaging and Protective Hypoxia of the Mammalian Brain

Currently, there is a new surge of interest in the problem of hypoxia, almost lost in recent decades. Due to the fact that the circle of competent specialists in this field has significantly narrowed, it is necessary to carry out an intensive exchange of knowledge. In order to inform a wide range of interested researchers and doctors, this review summarizes the current understanding of hypoxia, its pathogenic and adaptogenic consequences, as well as key physiological and molecular mechanisms that implement the response to hypoxia at various levels-from cellular to organismic. The review presents a modern classification of forms of hypoxia, the understanding of which is necessary for the formation of a scientifically based approach to experimental modeling of hypoxic states. An analysis of the literature covering the history and current level of hypoxia modeling in mammals and human experiments, including methods for creating moderate hypoxia used to increase the resistance of the nervous system to severe forms of hypoxia and other extreme factors, is carried out. Special attention is paid to the discussion of the features and limitations of various approaches to the creation of hypoxia, as well as the disclosure of the potential for the practical application of moderate hypoxic effects in medicine.

Recommendations for traveling to altitude with neurological disorders

BACKGROUND

Several neurological conditions might worsen with the exposure to high altitude (HA). The aim of this review was to summarize the available knowledge on the neurological HA illnesses and the risk for people with neurological disorders to attend HA locations.

METHODS

A search of literature was conducted for several neurological disorders in PubMed and other databases since 1970. The neurological conditions searched were migraine, different cerebrovascular disease, intracranial space occupying mass, multiple sclerosis, peripheral neuropathies, neuromuscular disorders, epileptic seizures, delirium, dementia, and Parkinson's disease (PD).

RESULTS

Attempts were made to classify the risk posed by each condition and to provide recommendations regarding medical evaluation and advice for or against traveling to altitude. Individual cases should be advised after careful examination and risk evaluation performed either in an outpatient mountain medicine service or by a physician with knowledge of HA risks. Preliminary diagnostic methods and anticipation of neurological complications are needed.

CONCLUSIONS

Our recommendations suggest absolute contraindications to HA exposure for the following neurological conditions: (1) Unstable conditions-such as recent strokes, (2) Diabetic neuropathy, (3) Transient ischemic attack in the last month, (4) Brain tumors, and 5. Neuromuscular disorders with a decrease of forced vital capacity >60%. We consider the following relative contraindications where decision has to be made case by case: (1) Epilepsy based on recurrence of seizure and stabilization with the therapy, (2) PD (± obstructive sleep apnea syndrome-OSAS), (3) Mild Cognitive Impairment (± OSAS), and (4) Patent foramen ovale and migraine have to be considered risk factors for acute mountain sickness.

Angelica archangelica and Ginkgo biloba Extracts Recover Functional Blood Hemoglobin Derivatives in Rabbits Exposed to High Altitude

BACKGROUND

Shortage of oxygen is a common condition for residents of high-altitude (HA) areas. In mammals, hemoglobin (Hb) has four derivatives: oxyhemoglobin (Hb-O2)‎, carboxyhemoglobin (Hb-CO), sulfhemoglobin (Hb-S), and methemoglobin (Met-Hb). In HA areas, aberrant physiological performance of blood hemoglobin is well-established.

OBJECTIVE

The study aimed to investigate the influence of 30 days of HA residence on rabbits' total Hb, Hb derivatives, Hb autooxidation rate, and antioxidant enzymes in comparison to low-altitude control rabbits. Further, the study aimed to investigate the effect of antioxidant-rich Angelica archangelica and/or Ginkgo biloba extracts on the same parameters in HA-resident rabbits.

METHODS

Rabbits subjected to 30 days of HA residence were compared to low-altitude control rabbits. HA-residence rabbits were then orally administered 0.11 g/kg b.wt. of Angelica archangelica and/or Ginkgo biloba extract for 14 days. Hb derivatives and Hb autooxidation rate were measured spectrophotometrically. Antioxidant enzymes were estimated using specialized kits.

RESULTS

Compared to low-altitude rabbits, 30-day HA-residence rabbits showed a noticeable increase (p<0.05) in Hb-O2‎ and Hb-CO concentration. In addition, Met-Hb concentration, autooxidation rate of Hb molecules, and activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) exhibited a remarkable increase in HA-residence rabbits (p<0.01), reflective of rapid ROS generation. In HA-residence rabbits, both individual and combined treatment with antioxidant-rich extracts for 14 days resulted in recovery to near-normal functional levels of Hb-O2‎ and Met-Hb, Hb autooxidation rate, and activities of SOD and GPx, while only combined treatment led to Hb-O2 recovery.

CONCLUSION

The findings suggest that functional Hb levels may be recovered by oral administration of A. archangelica, G. biloba, or combined treatments. In conclusion, oxidative stress due to living in HA areas may be avoided by supplementation with natural antioxidants.

Prevalence, awareness, treatment and control of hypertension among Ngawa Tibetans in China: a cross-sectional study

OBJECTIVES

To explore the prevalence, awareness, treatment and control rate of hypertension and analyse the potential social environment factors among Ngawa Tibetans in China.

DESIGN

This was a cross-sectional observational study.

SETTING

The investigation based on a multistage stratified cluster sampling was conducted in the Ngawa area, Sichuan Province, Southwest China. Tibetan residents were selected by random sampling method from one city and six counties in Ngawa.

METHODS

Basic demographical information, physical activity and blood pressure were collected. In addition, the participants completed the questionnaire. A multivariate logistic regression analysis was used to examine the association between the prevalence, awareness, treatment and control rate of hypertension and the potential risk factors.

PARTICIPANTS

The sample comprised 2228 Ngawa Tibetan residents (age 18-80 years) from September 2018 to June 2019.

RESULTS

The prevalence rate of hypertension was 24.6%. The control rate was 6.2%, while the awareness rate (32.3%) and treatment rate (21.7%) of hypertension had been significantly improved.

CONCLUSION

The prevalence of hypertension among Ngawa Tibetans was high. The awareness and treatment were improved in recent years. But the control rate was low. The government needs to strengthen the basic medical care and health education for Ngawa Tibetans.

Hypoxic Exercise Exacerbates Hypoxemia and Acute Mountain Sickness in Obesity: A Case Analysis

Acute mountain sickness (AMS) is a common syndrome characterized by headache, dizziness, loss of appetite, weakness, and nausea. As a major public health issue, obesity has increased in high altitude urban residents and intermittent commuters to high altitudes. The present study investigated acute hypoxic exposure and hypoxic exercise on hypoxemia severity and AMS symptoms in a physically active obese man. In this case analysis, peripheral oxygen saturation (SpO₂) was used to evaluate hypoxemia, heart rate (HR) and blood pressure (BP) were used to reflect the function of autonomic nervous system (ANS), and Lake Louise scoring (LLS) was used to assess AMS. The results showed that acute hypoxic exposure led to severe hypoxemia (SpO₂ = 72%) and tachycardia (HRrest = 97 bpm), and acute hypoxic exercise exacerbated severe hypoxemia (SpO₂ = 59%) and ANS dysfunction (HRpeak = 167 bpm, SBP/DBP = 210/97 mmHg). At the end of the 6-h acute hypoxic exposure, the case developed severe AMS (LLS = 10) symptoms of headache, gastrointestinal distress, cyanosis, vomiting, poor appetite, and fatigue. The findings of the case study suggest that high physical activity level appears did not show a reliable protective effect against severe hypoxemia, ANS dysfunction, and severe AMS symptoms in acute hypoxia exposure and hypoxia exercise.

Oxidative Stress, Kinase Activation, and Inflammatory Pathways Involved in Effects on Smooth Muscle Cells During Pulmonary Artery Hypertension Under Hypobaric Hypoxia Exposure

High-altitude exposure results in hypobaric hypoxia, which affects organisms by activating several mechanisms at the physiological, cellular, and molecular levels and triggering the development of several pathologies. One such pathology is high-altitude pulmonary hypertension (HAPH), which is initiated through hypoxic pulmonary vasoconstriction to distribute blood to more adequately ventilated areas of the lungs. Importantly, all layers of the pulmonary artery (adventitia, smooth muscle, and endothelium) contribute to or are involved in the development of HAPH. However, the principal action sites of HAPH are pulmonary artery smooth muscle cells (PASMCs), which interact with several extracellular and intracellular molecules and participate in mechanisms leading to proliferation, apoptosis, and fibrosis. This review summarizes the alterations in molecular pathways related to oxidative stress, inflammation, kinase activation, and other processes that occur in PASMCs during pulmonary hypertension under hypobaric hypoxia and proposes updates to pharmacological treatments to mitigate the pathological changes in PASMCs under such conditions. In general, PASMCs exposed to hypobaric hypoxia undergo oxidative stress mediated by Nox4, inflammation mediated by increases in interleukin-6 levels and inflammatory cell infiltration, and activation of the protein kinase ERK1/2, which lead to the proliferation of PASMCs and contribute to the development of hypobaric hypoxia-induced pulmonary hypertension.

Methamphetamine exacerbates pathophysiology of traumatic brain injury at high altitude. Neuroprotective effects of nanodelivery of a potent antioxidant compound H-290/51

Military personnel are often exposed to high altitude (HA, ca. 4500-5000m) for combat operations associated with neurological dysfunctions. HA is a severe stressful situation and people frequently use methamphetamine (METH) or other psychostimulants to cope stress. Since military personnel are prone to different kinds of traumatic brain injury (TBI), in this review we discuss possible effects of METH on concussive head injury (CHI) at HA based on our own observations. METH exposure at HA exacerbates pathophysiology of CHI as compared to normobaric laboratory environment comparable to sea level. Increased blood-brain barrier (BBB) breakdown, edema formation and reductions in the cerebral blood flow (CBF) following CHI were exacerbated by METH intoxication at HA. Damage to cerebral microvasculature and expression of beta catenin was also exacerbated following CHI in METH treated group at HA. TiO2-nanowired delivery of H-290/51 (150mg/kg, i.p.), a potent chain-breaking antioxidant significantly enhanced CBF and reduced BBB breakdown, edema formation, beta catenin expression and brain pathology in METH exposed rats after CHI at HA. These observations are the first to point out that METH exposure in CHI exacerbated brain pathology at HA and this appears to be related with greater production of oxidative stress induced brain pathology, not reported earlier.

Prevalence and Risk Factors of Diabetes, Hypertension and Other Non-Communicable Diseases in a Tribal Population in South India

INTRODUCTION

The prevalence of non-communicable diseases is increasing in tribal areas of India owing to the development and adoption of modern lifestyle. This study was done to assess the prevalence and risk factors of obesity, diabetes and hypertension in a tribal area in South India.

MATERIALS AND METHODS

A cross-sectional study was conducted among all men and women 40 years and above in ten randomly selected villages in three village panchayats located in a hilly area in Vellore district, Tamil Nadu. Minimum sample size calculated was 370. Data collection was done using a pretested questionnaire, clinical examination, and capillary blood glucose measurement. Prevalence and 95% confidence interval were estimated for diabetes and hypertension. By univariate and multivariate logistic regression, the Odds Ratio was calculated to identify the risk factors. SPSS version 16.0 was used. A value of P < 0.05 was considered statistically significant.

RESULTS

The study included 502 subjects, 212 (42.2%) males and 290 (57.8%) females. The proportion of generalized and abdominal obesity was 21% and 36.5%. The prevalence of diabetes and hypertension among the tribal population was 7.4% and 36.5%. Approximately 62% of diabetes and 68% of hypertension were newly diagnosed during this study. Higher age, female sex, generalized and abdominal obesity, and diabetes were risk factors for hypertension and abdominal obesity and hypertension were risk factors for diabetes.

CONCLUSION

The prevalence of diabetes and hypertension is high with two-thirds being newly diagnosed during study in this tribal population mandating early screening, awareness campaigns for early health-seeking and improvement in health access.

The Impact of Temporary Stay at High Altitude on the Circulatory System

In recent times many people stay temporarily at high altitudes. It is mainly associated with the growing popularity of regular air travel, as well as temporary trips to mountain regions. Variable environmental conditions, including pressure and temperature changes, have an impact on the human body. This paper analyses the physiological changes that may occur while staying at high altitude in healthy people and in people with cardiovascular diseases, such as arterial hypertension, pulmonary hypertension, heart failure, ischemic heart disease, or arrhythmias. Possible unfavourable changes were underlined. Currently recognized treatment recommendations or possible treatment modifications for patients planning to stay at high altitudes were also discussed.

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.

Carbohydrate and Glutamine Supplementation Attenuates the Increase in Rating of Perceived Exertion during Intense Exercise in Hypoxia Similar to 4200 m

The rating of perceived exertion (RPE) indicates the feeling of fatigue. However, hypoxia worsens the condition and can worsen RPE. We evaluated whether carbohydrate and glutamine supplementation alters RPE and physiological markers in running at 70% peak oxygen uptake until exhaustion in a simulated altitude of 4500 m. Nine volunteers underwent three running tests at 70% peak oxygen uptake until exhaustion: (1) hypoxia and placebo, (2) hypoxia and 8% maltodextrin, and (3) hypoxia after six days of glutamine supplementation (20 g/day) and 8% maltodextrin. The exercise and supplementation were randomized and double-blinded. Lactate, heart rate, haemoglobin O₂ saturation (SpO₂%), and RPE (6-20 scale) were analyzed at the 15th and 30th min. The level of significance was set at p ≤ 0.05. SpO₂% decreased at the 15th and 30th minutes compared to resting in placebo, carbohydrate, and glutamine supplementation. RPE increased at the 30th minute compared to the 15th minute in placebo and carbohydrate supplementation; however, there was no difference in the glutamine supplementation condition. Heart rate and lactate increased after the 15th and 30th minutes compared to resting, similar to the three conditions studied. We conclude that previous supplementation with glutamine and carbohydrate during intense exercise in hypoxia similar to 4500 m can attenuate the increase in RPE by the increase in glycemia and can be a useful strategy for people who exercise in these conditions.

Oxidative Stress, Kinase Activity and Inflammatory Implications in Right Ventricular Hypertrophy and Heart Failure under Hypobaric Hypoxia

High altitude (hypobaric hypoxia) triggers several mechanisms to compensate for the decrease in oxygen bioavailability. One of them is pulmonary artery vasoconstriction and its subsequent pulmonary arterial remodeling. These changes can lead to pulmonary hypertension and the development of right ventricular hypertrophy (RVH), right heart failure (RHF) and, ultimately to death. The aim of this review is to describe the most recent molecular pathways involved in the above conditions under this type of hypobaric hypoxia, including oxidative stress, inflammation, protein kinases activation and fibrosis, and the current therapeutic approaches for these conditions. This review also includes the current knowledge of long-term chronic intermittent hypobaric hypoxia. Furthermore, this review highlights the signaling pathways related to oxidative stress (Nox-derived O₂^.- and H₂O₂), protein kinase (ERK5, p38α and PKCα) activation, inflammatory molecules (IL-1β, IL-6, TNF-α and NF-kB) and hypoxia condition (HIF-1α). On the other hand, recent therapeutic approaches have focused on abolishing hypoxia-induced RVH and RHF via attenuation of oxidative stress and inflammatory (IL-1β, MCP-1, SDF-1 and CXCR-4) pathways through phytotherapy and pharmacological trials. Nevertheless, further studies are necessary.