A-15R Free Communication/Poster Peripheral Circulation
Debate continues regarding the existence of vasodilatory mechanisms that could contribute to the “immediate” increase (first second following initial contraction release) in blood flow at the on set of exercise.
To test the hypothesis that vasodilation proportional to muscle activation determines the immediate increase in blood flow following the first contraction of exercise. We reasoned that if such vasodilatory mechanisms do exist, we would observe an increase in blood flow during the first heart beat following a single, brief contraction that was proportional to the intensity of the contraction in conditions where the muscle pump was ineffective.
5 healthy young subjects 24.5 ± 2.5 yrs; 2 males, 3 females) lay supine with the forearm above heart level. In this position, veins are virtually empty, and we do not observe any contraction-induced venous emptying, i.e. muscle pump is ineffective (data not shown). 1-s forearm isometric handgrip contractions were performed across a range of %maximal voluntary contraction (%MVC) intensities (5–70%). Beat-by-beat measures of brachial artery diameter and mean blood velocity (BAD,MBV; Doppler ultrasound), heart rate (HR; ECG) and arterial blood pressure (ABP; tonometry) were performed.
Neither HR, BAD nor ABP changed with the first heart beat following contraction, therefore MBV represents forearm blood flow and is reported here. Figure demonstrates the tight linear relationship of %change in MBV with contraction intensity.
These data support the hypothesis that vasodilation proportional to muscle activation determines the immediate blood flow increase at the onset of exercise. Mechanisms responsible remain to be determined. Supported by NSERC; CFI New Opportunities Fund