Racial differences in hemodynamic responses to environmental thermal stress among adolescents

Background-Previous studies by our laboratory and others have shown that bl ood pressure (BP) responses to many short-term laboratory stressors are gre ater in black than in white children. We sought to determine the cardiac an d vascular contributions to these differences in BP reactivity and whether racial differences in vascular reactivity involve excessive vasoconstrictio n or deficient vasodilation. Methods and Results-We evaluated BP, heart rate, and impedance cardiographi c measures or preejection period (PEP) and total peripheral resistance (TPR ) in healthy black (n=76) and white (n=60) adolescents (mean age, 14.8 year s) during passive exposure to a vasoconstrictive Cold chamber (8 degrees C to 10 degrees C) and a vasodilatory heat chamber (40 degrees C to 42 degree s C). Results indicated greater decreases in PEP and increases in TPR in bl acks than whites Juring cold exposure (P<0.05) but no group differences dur ing heat exposure. Covariance analyses indicated that the racial difference s during cold exposure probably reflected greater beta-adrenergic cardiac r eactivity and alpha-adrenergic vasoconstrictive reactivity in blacks than w hites. Conclusions-Blacks and whites exhibited comparable myocardial and vasodilat ory responses to heat stress, but blacks exhibited heightened myocardial an d vasoconstrictive reactivity to cold stress. These results suggest that th e locus of racial differences in vascular reactivity involves vasoconstrict ive rather than vasodilatory function. The pattern of racial differences du ring cold stress raises the possibility that both myocardial and vasoconstr ictive mechanisms may contribute to the increased risk of hypertension in b lacks.