Racial Differences in Hemodynamic Responses to Environmental Thermal Stress Among Adolescents

Abstract

Background-Previous studies by our laboratory and others have shown that blood pressure (BP) responses to many short-term laboratory stressors are greater in black than in white children. We sought to determine the cardiac and vascular contributions to these differences in BP reactivity and whether racial differences in vascular reactivity involve excessive vasoconstriction or deficient vasodilation. Methods and Results-We evaluated BP, heart rate, and impedance cardiographic measures of preejection period (PEP) and total peripheral resistance (TPR) in healthy black (nϭ76) and white (nϭ60) adolescents (mean age, 14.8 years) during passive exposure to a vasoconstrictive cold chamber (8°C to 10°C) and a vasodilatory heat chamber (40°C to 42°C). Results indicated greater decreases in PEP and increases in TPR in blacks than whites during cold exposure (PϽ0.05) but no group differences during heat exposure. Covariance analyses indicated that the racial differences during cold exposure probably reflected greater ␤-adrenergic cardiac reactivity and ␣-adrenergic vasoconstrictive reactivity in blacks than whites. Conclusions-Blacks and whites exhibited comparable myocardial and vasodilatory responses to heat stress, but blacks exhibited heightened myocardial and vasoconstrictive reactivity to cold stress. These results suggest that the locus of racial differences in vascular reactivity involves vasoconstrictive rather than vasodilatory function. The pattern of racial differences during cold stress raises the possibility that both myocardial and vasoconstrictive mechanisms may contribute to the increased risk of hypertension in blacks.

Ethnic Differences in Arterial Responses and Inflammatory Markers in Afro-Caribbean and Caucasian Subjects

“…These findings are consistent with studies showing few atherosclerotic changes in the large arteries of patients with small vessel disease 23 and hyperinsulinaemia in black, but not white, hypertensive subjects with end organ damage. 15 Increased carotid intima media thickness 24 and attenuated vascular reactivity 10,14 but better large vessel function [25][26][27][28] have been described in Afro-Caribbeans previously, but this is the first study in which all of these aspects have been examined together in community settings. Explanations for population differences in disease susceptibility must be sought in representative samples of the general population to ensure unbiased and generalizable comparisons.…”

Phenylephrine-induced elevations in arterial blood pressure are attenuated in heat-stressed humans

“…Cardiac output, TPR, and TPC were estimated with thoracic impedance using the Kubicek equation (13). This method of estimating cardiac output has previously been used under heat-stressed condition (11,19). We recognize that this method of cardiac output measurement, and thus the calculation of TPR and TPC, has a number of limitations.…”

“…Impedance cardiograph and phonocardiography (models EBI 100C and DA 100, Biopac System, Santa Barbara, CA) were used to measure transthoracic impedance (Zo) and left ventricular ejection time for the estimation of stroke volume. This noninvasive method to measure stroke volume has been widely used under both normothermic and heat stress conditions (3,11,13,19). Forearm skin blood flow was indexed by laser-Doppler flowmetry (Perimed, North Royalton, OH) from an area not covered by the tube-lined suit.…”

Racial differences in albuminuria, kidney function, and risk of stroke

“…In support of this, prior studies showed that endothelium-dependent vasodilatation was impaired in black individuals as compared to white individuals, even in young, otherwise healthy adults. [27][28][29][30][31] Further, individuals of African descent may be at higher risk for renal sodium retention, resistant hypertension, and vascular injury due to a number of factors such as a higher prevalence of primary aldosteronism or activating polymorphisms in renal tubular epithelial sodium channels. These factors, in turn, may partially explain racial differences in the association between albuminuria and stroke in this study.…”