Attenuated forearm vascular conductance responses to rhythmic handgrip in young African-American compared with Caucasian-American men

Abstract

Previous studies have demonstrated that African-American (AA) individuals have heightened vasoconstrictor and reduced vasodilator responses under resting conditions compared with Caucasian-American (CA) individuals. However, potential differences in vascular responses to exercise remain unclear. Therefore, we tested the hypothesis that, compared with CA subjects, AA subjects would present an attenuated increase in forearm vascular conductance (FVC) during rhythmic handgrip exercise. Forearm blood flow (FBF; duplex Doppler ultrasound) and mean arterial pressure (MAP; finger photoplethysmography) were measured in healthy young CA ( n = 10) and AA ( n = 10) men during six trials of rhythmic handgrip performed at workloads of 4, 8, 12, 16, 20, and 24 kg. FVC (calculated as FBF/MAP), FBF, and MAP were similar between groups at rest (FVC: 63 ± 7 ml·min^-1·100 mmHg^-1 in CA subjects vs. 62 ± 7 ml·min^-1·100 mmHg^-1 in AA subjects, P = 0.862). There was an intensity-dependent increase in FVC during exercise in both groups; however, AA subjects presented lower FVC (interaction P < 0.001) at 8-, 12-, 16-, 20-, and 24-kg workloads (e.g., 24 kg: 324 ± 20 ml·min^-1·100 mmHg^-1 in CA subjects vs. 241 ± 21 ml·min^-1·100 mmHg^-1 in AA subjects, P < 0.001). FBF responses to exercise were also lower in AA subjects (interaction P < 0.001), whereas MAP responses did not differ between groups (e.g., ∆MAP at 24 kg: +19 ± 2 mmHg in CA subjects vs. +19 ± 2 mmHg in AA subjects, interaction P = 0.950). These findings indicate lower hyperemic responses to rhythmic handgrip exercise in AA men compared with CA men. NEW & NOTEWORTHY It is known that African-American individuals have heightened vasoconstriction and reduced vasodilation under resting conditions compared with Caucasian-American individuals. Here, we identified that the hyperemic response to moderate and high-intensity rhythmic handgrip exercise was lower in healthy young African-American men.

Keywords: black; blood velocity; brachial artery; diameter; dynamic exercise; racial differences; white.

Fig. 1.

Forearm vascular conductance, forearm blood flow, and mean arterial pressure in healthy young male Caucasian-American (CA) and African-American (AA) subjects at rest [baseline (BL)] and the end of rhythmic handgrip trials with incremental absolute workloads from 4 to 24 kg. *P < 0.05 for group comparison.

Fig. 2.

Forearm vascular conductance, forearm blood flow, and mean arterial pressure in healthy young male Caucasian-American (CA; mean: gray columns and individuals: white circles) and African-American (AA; mean: black columns and individuals: white triangles) subjects at rest [baseline (BL)] and the end of rhythmic handgrip trials from 15% to 45% MVC. *P < 0.05 for group comparison.