Abstract
The purpose of these experiments was to determine if the increase in vascular conductance following a single muscle contraction (50% MVC) (6 male & 6 female subjects) was altered by baroceptor loading and unloading. Rapid onset vasodilation (ROV) was determined by measuring brachial artery blood flow (Doppler ultrasound), and blood pressure (Finapress). Brachial artery vascular conductance was calculated dividing blood flow by mean arterial pressure. ROV was described by the area under the ∆VC-time curve during the 30 s following muscle contraction. ROV was determined using chamber pressures of +20, +10, 0, -10, -20, & -40 mmHg chamber pressure (lower body positive and negative pressure, LBPP and LBNP) . We tested the hypothesis that the impact of baroreceptor loading and unloading produce a proportion change in ROV. The level of ROV following each contraction was proportional to the peak force ( r2 = 0.393, p = 0.0001). Peak force was therefore used as a covariate in further analysis. ROV during application of -40 mmHg LBNP (0.345 ± 0.229 ml • mmHg-1) was lower than during Control (0.532 ± 0.284 ml • mmHg-1, p=0.034) and +20 mmHg LBPP ( 0.658 ± 0.364 ml • mmHg-1, p=0.0008). ROV was linearly related to chamber pressure from -40 to +20 mmHg chamber pressure (r2 = 0.512, p = 0.022, n = 69) and from -20 to +10 mmHg chamber pressure (r2= 0.973, p < 0.0425, n=45), Overall, vasoconstrictor tone altered with physiologically relevant baroreceptor loading and unloading resulted in a proportion change in ROV.
Published Version
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