Rapid onset vasodilatation is blunted in obese humans

Abstract

Aim: Conduit artery function in obese humans is frequently assessed at rest, but very little is known about resistance artery function in response to muscle contraction. We tested the hypothesis that obese adults will exhibit reduced contraction-induced rapid onset vasodilatation. Single and brief forearm contractions were used to isolate the local effects of muscle contraction on the forearm vasodilatory response, independent of systemic haemodynamic and sympathetic neural influence.

Methods: We measured forearm blood flow (Doppler ultrasound), blood pressure (finger photoplethysmography) and heart rate (electrocardiogram) on a beat-by-beat basis in 14 obese (body mass index = 36.2 ± 1.7 kg m(-2)) and 14 lean (body mass index = 21.6 ± 0.7 kg m(-2)) young (18-40 years) adults. Percent changes from baseline in forearm vascular conductance (FVC(%) ) were calculated in response to single, brief forearm contractions performed in random order at 15, 20, 25, 30, 40 and 50% of maximal voluntary contraction (MVC).

Results: In both groups, each single contraction evoked a significant (P < 0.05), immediate (within one cardiac cycle) and graded FVC(%) increase from one up to six cardiac cycles post-contraction. Immediate (20-50% MVC), peak (15-50% MVC) and total (area under the curve, 20-50% MVC) vasodilatory responses were reduced with obesity. The degree of impaired vasodilatation increased with increasing workloads.

Conclusions: These novel findings demonstrate a blunted contraction-induced rapid onset vasodilatation with obesity that is exercise intensity dependent. Impaired rapid onset vasodilatation may negatively impact haemodynamic responses to everyday intermittent activities performed by obese humans.

Figure 1

Representative arterial blood pressure (top) and blood velocity (bottom) pre- and post-contraction a lean subject at 50% of maximal voluntary contraction. Note the marked response in velocity despite any change in the blood pressure time course.

Figure 2

Time course of the vasodilatory response following single, brief forearm muscle contractions at different workloads, in lean (□) and obese (■) adults. Significant rapid vasodilatation impairments were observed in obese adults at all workloads. MVC: maximal voluntary contraction. Data are presented as mean ± SE from 14 lean and 14 obese adults. *P < 0.05 vs. obese adults.

Figure 3

Responses to single, brief forearm muscle contractions at different absolute (left panel) and relative (right panel) workloads (WL) in lean (□) and obese (■) adults. (a) Immediate (first unimpeded cardiac cycle post-contraction) forearm vascular conductance (FVC) responses. (b) Peak (mean of the three consecutive greatest FVC_%) FVC responses. (c) Total (area under dynamic response curve of FVC_% post-contraction) FVC responses. Linear regression analysis of vasodilatory responses to both absolute and relative workloads shows obese adults exhibit significantly lower slopes when compared to lean controls. MVC: maximal voluntary contraction. Data are presented as mean ± SE from 14 lean and 14 obese adults.