Rapid onset vasodilation during baroreceptor loading and unloading

The purpose of these experiments was to determine if the increase in vascular conductance following a single muscle contraction (50% of maximal voluntary contraction) (6 male and 6 female subjects) was altered during baroceptor loading and unloading. Rapid onset vasodilation (ROV) was determined by measuring brachial artery blood flow (Doppler ultrasound) and blood pressure (Finapress monitor). Brachial artery vascular conductance was calculated by dividing blood flow by mean arterial pressure. ROV was described by the area under the Delta vascular conductance (VC)-time curve during the 30 s following muscle contraction. ROV was determined using chamber pressures of +20, +10, 0, -10, -20, and -40 mmHg (lower body positive and negative pressure, LBPP, and LBNP). We tested the hypothesis that the impact of baroreceptor loading and unloading produces a proportion change in ROV. The level of ROV following each contraction was proportional to the peak force (r(2) = 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<middle dot>mmHg(-1)) was lower than that observed at Control (0.532 +/- 0.284 mL<middle dot>mmHg(-1), P = 0.034) and +20 mmHg LBPP (0.658 +/- 0.364 mL<middle dot>mmHg(-1), P = 0.0008). ROV was linearly related to chamber pressure from -40 to +20 mmHg chamber pressure (r(2) = 0.512, P = 0.022, n = 69) and from -20 to +10 mmHg chamber pressure (r(2)= 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.