Key result
Single 1-s isometric forearm contractions produced immediate increases in forearm blood flow proportional to intensity, which were greater in below-heart vs above-heart positions (P<0.05).
Why the study?
Does contraction intensity determine immediate exercise hyperemia in healthy subjects?
Does contraction intensity determine immediate exercise hyperemia in healthy subjects?
Effect estimate: slope = 4.4 +/- 0.5%DeltaFBF/%MVC in AH
p-value: p=<0.05
Immediate exercise hyperemia is proportional to contraction intensity, supporting the existence of rapid-acting vasodilatory mechanisms at the onset of human forearm exercise.
Supports rapid vasodilation contributing to immediate hyperemia proportional to intensity; leaves open translation to dynamic exercise or patients.
We tested the hypothesis that rapid vasodilation proportional to contraction intensity contributes to the immediate (first cardiac cycle after initial contraction) exercise hyperemia. Ten healthy subjects performed single 1-s isometric forearm contractions at 5, 10, 15, 20, 30, 50, and 70% maximal voluntary contraction intensity (MVC) in arm above heart (AH) and below heart (BH) positions. Forearm blood flow (FBF; brachial artery mean blood velocity, Doppler ultrasound), mean arterial pressure (arterial tonometry), and heart rate (electrocardiogram) were measured beat by beat. Venous emptying (measured with a forearm strain gauge) was already maximized at 5% MVC, indicating that increases in contraction intensity did not further empty the forearm veins. Immediate increases in FBF were linearly proportional to contraction intensity from 5 to 70% MVC in AH (slope = 4.4 +/- 0.5%DeltaFBF/%MVC). In BH, the immediate increase in FBF demonstrated a curvilinear relationship with increasing contraction intensity and was greater than AH at 15, 20, 30, and 50% MVC (P < 0.05). Peak changes in FBF were greater in BH vs. AH from 10 to 50% MVC, even when venous refilling was complete (P < 0.05). These data support the existence of a rapid-acting vasodilatory mechanism(s) at the onset of human forearm exercise.
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Tschakovsky et al. (2004) studied Healthy (n=10). Single 1-s isometric forearm contractions at varying intensities (5-70% MVC) and arm positions vs. Arm above heart (AH) vs arm below heart (BH) positions was evaluated on Immediate increases in forearm blood flow (FBF) (slope = 4.4 +/- 0.5%DeltaFBF/%MVC in AH, p=<0.05). Single 1-s isometric forearm contractions produced immediate increases in forearm blood flow proportional to intensity, which were greater in below-heart vs above-heart positions (P<0.05).