The Multinational Andean Genetic and Health Program,--IV. Altitude and the blood pressure of the Aymara

Blood Pressure in Andean Adults Living Permanently at Different Altitudes

Vinueza Veloz, Andrés Fernando, Aymaru Kailli Yaulema Riss, Chris I. De Zeeuw, Tannia Valeria Carpio Arias, and María Fernanda Vinueza Veloz. Blood pressure in Andean adults living permanently at different altitudes. High Alt Med Biol. 21:360-369, 2020. Aims: To estimate the association between blood pressure (BP) and chronic exposure to altitude in nonhypertensive Andean adults, while taking ethnicity into consideration. Materials and Methods: Sample included 10,041 nonhypertensive adults with indigenous or mixed ethnic background (the latter also referred to as mestizos), who permanently lived at different altitudes. BP was measured following international recommendations. Altitude was measured in meters above the sea level (masl) using a global positioning system. Data were analyzed through linear regression models with restricted cubic splines. Results: A significant nonlinear relation between altitude and systolic blood pressure (SBP) as well as diastolic blood pressure (DBP) was found (both p < 0.001). BP described a j-shaped curve, where the minimum was observed between 750 and 1250 masl, from where both SBP and DBP rose as altitude increased. These associations were independent from sex, age, index of economic wellbeing, body mass index, and years of education. Interestingly, at all altitudes indigenous people had lower SBP and DBP in comparison to mestizos (both p < 0.001). Conclusions: Living permanently at altitudes ≥750 masl is associated with higher SBP and DBP in Andean dwellers and this association is modulated by their ethnic background.

Blood pressure level increase with altitude in three argentinean indigenous communities

Objective

To compare blood pressure (BP) levels in three groups of Argentinean Indigenous schoolchildren from similar ethnic backgrounds but living at three different altitudes.

Methods

A cross-sectional study compared 185 (83 females) children aged 5–14 years from San Antonio de los Cobres (SAC), 3750 m above sea level; 46 (23 females) from Cobres, 3450 m; and 167 (83 females) from Chicoana (CH), 1400 m. Anthropometric and BP measurements were performed.

Results

The prevalence of overweight/obesity was lower in SAC (6.5% [12]) and Cobres (4.3% [2]) than in CH (24% [24]) (BMI > 85 percentile per CDC norms). Systolic BP increased significantly with altitude: (SAC 86 mm Hg, Cobres 77 mm Hg, and CH 69 mm Hg). Similar results were obtained with diastolic BP (SAC 57 mm Hg, Cobres 51 mm Hg, and CH 47 mm Hg) and with median arterial pressure (MAP) (SAC 67 mm Hg, Cobres 60 mm Hg, and CH 55 mm Hg). Multiple linear regression analyses showed that altitude was significantly and independently associated with children's systolic BP (beta 10.56; R² = 0.40), diastolic BP (beta 6.27; R² = 0.25) and MAP (beta 7.69; R² = 0.32); adjusted for age, sex, and BMI.

Conclusions

We found that as altitude increased, BP levels increased significantly in indigenous children from similar backgrounds living permanently at different altitudes.

Prevalence, awareness, treatment, and control of hypertension among herdsmen living at 4,300 m in Tibet

BACKGROUND

Studies on blood pressure (BP) in high-altitude areas are scarce and the results are controversial. Tibetans live in regions at high altitudes, and data on the prevalence of hypertension in this population is not currently well known.

METHODS

All Tibetans aged 40 years and older living in the township of Yangbajing (4,300 m) in Tibet, China were invited to participate in the 2009 survey. BP was measured with electronic sphygmomanometers (calibrated by the results of a previous study). Histories of hypertension and medication use were collected through face-to-face interviews. Hypertension was defined as systolic BP (SBP) ≥140 mm Hg and/or diastolic BP (DBP) ≥90 mm Hg, or antihypertensive medication use in the past 2 weeks.

RESULTS

A total of 701 adults (aged 40-89, 42.9% male, 94.9% herdsmen) were recruited. The mean (s.d.) SBP/DBP was 146.6 (31.3)/92.0 (15.7) mm Hg and the prevalence of hypertension was 55.9%. Of note, 61.2% of those with hypertension had stage 2 hypertension (SBP ≥160 or DBP ≥100 mm Hg). At age 70 years and older, the mean (s.d.) SBP/DBP were 182.8 (30.9)/102.6 (13.4) mm Hg. Among those with hypertension (n = 392), only 19.9% were aware of their condition, 2.6% were taking medication, and only one participant had controlled BP.

CONCLUSION

According to our survey in Yangbajing, Tibetan adults aged 40 years and older living at high altitudes had high BP and prevalence of hypertension with low awareness, treatment, and control. Future studies are needed to clarify the association between BP, altitude, and other possible causes.

Intermittent hypoxia: cause of or therapy for systemic hypertension?

During acute episodes of hypoxia, chemoreceptor-mediated sympathetic activity increases heart rate, cardiac output, peripheral resistance and systemic arterial pressure. However, different intermittent hypoxia paradigms produce remarkably divergent effects on systemic arterial pressure in the post-hypoxic steady state. The hypertensive effects of obstructive sleep apnea (OSA) vs. the depressor effects of therapeutic hypoxia exemplify this divergence. OSA, a condition afflicting 15-25% of American men and 5-10% of women, has been implicated in the pathogenesis of systemic hypertension and is a major risk factor for heart disease and stroke. OSA imposes a series of brief, intense episodes of hypoxia and hypercapnia, leading to persistent, maladaptive chemoreflex-mediated activation of the sympathetic nervous system which culminates in hypertension. Conversely, extensive evidence in animals and humans has shown controlled intermittent hypoxia conditioning programs to be safe, efficacious modalities for prevention and treatment of hypertension. This article reviews the pertinent literature in an attempt to reconcile the divergent effects of intermittent hypoxia therapy and obstructive sleep apnea on hypertension. Special emphasis is placed on research conducted in the nations of the former Soviet Union, where intermittent hypoxia conditioning programs are being applied therapeutically to treat hypertension in patients. Also reviewed is evidence regarding mechanisms of the pro- and anti-hypertensive effects of intermittent hypoxia.

Genetic polymorphisms in the Renin-Angiotensin system in high-altitude and low-altitude Native American populations

Cardiovascular disease (CVD) is reportedly less common in high-altitude native populations than in lowlanders. To some extent, this is due to cultural and demographic factors; however, increased cardiovascular efficiency contributing to hypoxia adaptation may also be involved. Numerous genetic variants have been associated with cardiovascular health. If the decreased incidence of CVD in modern high-altitude populations reflects selective pressures having favoured the transmission of these alleles in their antecedents, it would be expected that these alleles would be more common in highlanders than in lowlanders. We tested this hypothesis by determining the allele frequencies of five polymorphic loci in genes encoding components of the renin-angiotensin system (RAS) that have alleles associated with hypertension and cardiovascular disease in a high-altitude native Andean population, Quechua from the Peruvian altiplano, and in a lowland Amerindian population, Maya from the Yucatan peninsula. The polymorphisms examined were 1) the insertion/deletion polymorphism in intron 16 of the angiotensin converting enzyme (ACE) gene; 2) the A/G2350 transition (ACE-8) in intron 17 of the ACE gene; 3) the A/C1166 transversion in the 3' untranslated region of the angiotensin II receptor (type 1) gene (AGTR1); 4) the G/AI9-83 transition in intron 8 of the renin gene (REN); and 5) the T/C704 (Met235Thr) transition mutation in angiotensinogen (AGT). There was no evidence for an over-representation of the RAS alleles associated with cardiovascular fitness in the high-altitude Amerindian population when compared to the lowland Amerindian population.

No evidence for an association between genetic polymorphisms of beta(2)- and beta(3)-adrenergic receptor genes with body mass index in Aymara natives from Chile

OBJECTIVE

We assessed the association between Gln27Glu and Trp64Arg genetic polymorphisms of the beta(2) (ADRB2) and beta(3) (ADRB3) adrenergic receptor genes with body mass index and other cardiovascular risk factors.

METHODS

In a cross-sectional study, adult Aymara subjects (n = 152) living in the Andean regions of northern Chile were characterized with respect to their ADRB2 and ADRB3 genotypes, body mass index, plasma leptin and insulin levels, fasting glucose concentration, blood pressure, and plasma lipid profile.

RESULTS

The frequency of the Glu27 allele of the ADRB2 gene was estimated to be 0.04, and the allele frequency of the Arg64 variant of the ADRB3 gene was estimated as 0.13. No associations were found between the Trp64Arg polymorphism of the ADRB3 gene and body mass index or other cardiovascular risk factors. The small number of subjects with the allele encoding Glu27 in the ADRB2 gene seriously limited the analysis of the association between genotype and phenotype with the use of this polymorphism, although no clear associations were found.

CONCLUSION

We found insufficient evidence to support an association between polymorphisms Gln27Glu and Trp64Arg of the ADRB2 and ADRB3 genes, respectively, with body mass index and other cardiovascular risks in the rural Aymara population from Chile.

Low prevalence of type 2 diabetes despite a high average body mass index in the Aymara natives from Chile

The aim of this study was to estimate the prevalence of type 2 diabetes mellitus (DM2), impaired glucose tolerance (IGT), and the frequency of dyslipidemia, obesity, and hypertension in the rural Aymara population from Northern Chile. In this cross-sectional study, 196 Aymara adult subjects were characterized with respect to their reported physical activity, fasting plasma glucose levels, insulin concentrations, blood pressures, body mass indexes, and plasma lipid profiles. The participants also underwent a 2-h oral glucose tolerance test. The diagnostic criteria for DM2 and IGT followed those of the World Health Organization. The overall prevalence of DM2 was estimated as 1.5% (95% confidence interval: 0.3--4.5). Overall prevalence of IGT was calculated as 3.6% (1.5--7.3). The occurrence of obesity and dyslipidemia was relatively high in the Aymara population, although the frequency of sedentary habits, and the prevalence of hypertension were low. In conclusion, the prevalence of DM2 in the rural Aymara population living at high altitudes in Northern Chile, was much lower than that of other Amerindian groups that adopted lifestyles from industrialized Western societies. Despite a relatively high prevalence of a body mass index of at least 30 kg/m(2), especially in women (23.5%), high physical activity levels and low plasma-insulin concentrations may have been responsible in part for the low prevalence of DM2 in the Aymara population.

Body size, composition, and blood pressure of high-altitude Quechua from the Peruvian Central Andes (Huancavelica, 3,680 m)

Although much information is available about the effects of high altitude on physiological characteristics, less is know about its effect on body composition. In the present study, anthropometric and body composition variables were investigated in a sample of 77 adult Quechua males from the Peruvian Central Andes (Huancavelica, 3,680 m). The subjects are shorter in relation to body weight than other ethnic groups, whereas body proportions are macrocormic (indicating a long trunk relative to the lower extremities), with intermediate values of the acromial-iliac index. All skinfold thicknesses are low (approximately 15th percentiles of NHANES reference values for the triceps and subscapular skinfolds), but tend to be higher than in the other Quechua populations. Similar results are obtained when percentage fat is estimated. Somatotypes are dominant in mesomorphy with very low ectomorphy. Comparison with a sample of high-altitude Kirghiz (3,200 m), previously studied with the same methods, shows higher values in the Peruvian sample for all variables related to adiposity. The presence of low adiposity in the Quechua population could be associated with stresses of the high-altitude environment. Mean values of blood pressure are very low and there is no correlation with age.

Changes in the renin-angiotensin-aldosterone system in 2 kidney -2 clip Goldblatt hypertensive rats of both sexes submitted to chronic hypobaric hypoxia

The effect of chronic hypobaric hypoxia (CHH) on the development of 2k-2c Goldblatt renovascular hypertension has been analyzed in rats of both sexes. Results have shown lower values of blood pressure (BP) in all the animals exposed to CHH compared with their normoxic control (P < 0.001). Haematocrit was increased by adaptation to CHH (P < 0.001), and was larger in male than in female hypoxic rats, both normotensive (P < 0.05) and hypertensive (P < 0.01). Plasma renin activity was higher in normoxic and hypoxic hypertensive female rats than in their normotensive controls (P < 0.05). Plasma angiotensinogen concentration was higher in normoxic control male rats than in all the other groups. This difference disappeared after adaptation to CHH or development of hypertension. Plasma aldosterone concentration was lowest in normoxic control male rats and the difference also disappeared after CHH or renal ischemia. Present data indicate that CHH blunts the hypertensive response to bilateral renal ischemia in male and female rats. Sexual differences related to the mechanisms that could be involved in hypertension development have been observed. The renin-angiotensin-aldosterone system might be modulated by gonadal hormones during the development of hypertension.

Altitude and blood pressure in children

People living at high altitude are generally observed to have lower blood pressure than those residing at sea level. To investigate whether low pO2 or low body weight accounts for this, blood pressure, weight, height and pulse rate were measured in 847 Peruvian children residing at 3500 m and compared to previously collected data in 3924 Dutch children living at sea level. In the two study populations the same protocol for measurement of blood pressure was used by observers who showed no systematic differences in average blood pressure readings during training sessions. Systolic as well as diastolic blood pressure was found to increase with age in both Peruvian and Dutch children. Systolic blood pressure by age was 5-10 mmHg lower in Peruvian boys and girls than in their Dutch counterparts. However, virtually no differences in systolic blood pressure, and to a lesser extent diastolic blood pressure, by body weight or height between Peruvian and Dutch subjects were found. These findings are in agreement with the hypothesis that differences in body weight, rather than in pO2, explain most of the observed differences in blood pressure between children of the same age living at different altitudes.