Attenuated Rapid-Onset Vasodilation to Forearm Muscle Contraction in Black Men

Abstract

Purpose: Non-Hispanic Black individuals have a blunted ability to vasodilate at rest compared with other racial groups. Limited studies have investigated blood flow responses to exercise in Black individuals. Recently, our laboratory demonstrated that Black men exhibit attenuated increases in forearm vascular conductance (FVC) during steady-state rhythmic handgrip. The mechanisms for this remain unknown. Herein, we used single muscle contractions, a modality that allows for assessment of rapid-onset vasodilation (ROV) independent of major elevations in shear stress, tissue metabolism, and systemic hemodynamics.

Methods: Ten young, healthy Black and White men performed single forearm contractions at 20%, 40%, and 60% maximal voluntary contraction (MVC). In addition, cuff inflations were performed on the forearm to examine the contribution of mechanical compression to ROV. Forearm blood flow (FBF; duplex Doppler ultrasound), heart rate (ECG), and mean arterial pressure (Finometer) were continuously measured. FVC was calculated as FBF/mean arterial pressure.

Results: Baseline FVC (White men vs Black men, 0.75 ± 0.11 vs 0.80 ± 0.09 mL·min-1·mm Hg-1; P = 0.73), FBF, and MVCs (White men vs Black men, 54 ± 2 vs 54 ± 2 kg; P = 0.95) were similar between the groups. After single contractions, both groups exhibited intensity-dependent FVC and FBF increases during ROV; however, these responses were attenuated in the Black group at all intensities (e.g., 60%MVC FVC: White men vs Black men, +371% ± 37% vs +220% ± 23% baseline; P = 0.001). FVC and FBF responses to cuff inflation alone were also attenuated in Black individuals (P < 0.001).

Conclusions: Collectively, these data indicate that Black men have an overall blunted ability to rapidly vasodilate compared with young White men.

Conflict of interest statement

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the authors.

Copyright © 2020 by the American College of Sports Medicine.

Figures

Figure 1:

Mean summary data showing the time course of forearm vascular conductance (FVC; top panel) and forearm blood flow (FBF; bottom panel) responses to single forearm contraction at 20%, 40%, and 60% maximal voluntary contraction (MVC) in non-Hispanic white (grey circles, n=10) and non-Hispanic black (black circles, n=10) men. * P < 0.05 white men versus black men.

Figure 2:

Individual and mean summary data showing the initial response (first cardiac cycle following contraction) and the peak response for forearm vascular conductance (FVC; top panel) and forearm blood flow (FBF; bottom panel) responses to single forearm contraction at 20%, 40% and 60% maximal voluntary contraction (MVC) in non-Hispanic white (grey bars, n=10) and non-Hispanic black (black bars, n=10) men. * P < 0.05 white men versus black men.

Figure 3:

Mean summary data showing forearm vascular conductance (FVC) and forearm blood flow (FBF) responses over 20 cardiac cycles immediately following mechanical cuff inflations on the forearm in non-Hispanic white (grey circles, n=10) and non-Hispanic black (black circles, n=10) men. * P < 0.05 white men versus black men.