The goal of this study was to determine whether racial differences exist in the functional behavior of conduit vessels.

Compared with Caucasians, African Americans have a higher prevalence of cardiovascular disease and its complications, which may be related to reduced nitric oxide (NO)-dependent and -independent vasodilation of the microvasculature. However, whether a similar impairment is also present at the level of the conductance arteries is unknown.

To this end, we studied endothelium-dependent (posthyperemia flow-mediated dilation) and -independent (nitroglycerin) vascular responses of the brachial artery by high-resolution ultrasound imaging. There were 46 black subjects (23 men and 23 women; age 37 ± 8 years and 38 ± 9 years, respectively) and 46 white subjects (23 men and 23 women; age 38 ± 11 years and 36 ± 9 years, respectively) in this study.

Baseline diameter was similar in blacks and in whites (4.4 ± 0.9 mm and 4.1 ± 0.7 mm, respectively). Mean reactive hyperemia after cuff deflation was similar in the two groups (793 ± 653% in black and 852 ± 734% in white subjects, respectively; p = 0.5). Flow-mediated dilation was significantly lower in black compared with white individuals (4.79 ± 3.5% vs. 8.87 ± 4.5%, respectively; p < 0.0001). Nitroglycerin-mediated dilation was also significantly lower in black individuals compared with white individuals (10.99 ± 4.6% vs. 14.98 ± 5.4%, respectively; p = 0.0002).

African Americans show reduced responsiveness of conductance vessels to both endogenous and exogenous NO compared with Caucasian Americans. These findings expand our understanding of racial differences in vascular function and suggest a mechanistic explanation for the increased incidence and severity of cardiovascular disease observed in African Americans.