Sympathetic modulation of blood flow and O2 uptake in rhythmically contracting human forearm muscles

and David 0. Warner. Sympathetic modulation of blood flow and 0, uptake in rhythmically contracting human forearm mus-cles. Am. J. Physiol. 263 (Heart Circ. Physiol. 32): Hl078-H1083, 1992.-This study tested the effects of sympathetically mediated changes in blood flow to active muscles on muscle O2 uptake (vo2) in humans. Four minutes of graded (1580 % of maximum voluntary contraction, MVC) rhythmic handgrip ex-ercise were performed. Forearm blood flow (FBF) (plethysmog-raphy) and deep vein 0, saturation were measured each minute. Forearm 0, uptake was calculated using the Fick principle. In protocol 1, exercise was performed while supine and again while upright to augment sympathetic outflow to the active muscles. Standing reduced FBF at rest from 3.6 to 2.2 ml 100 ml- ’ l rein- ’ (P < 0.05). During light exercise (1540 % MVC) FBF was unaffected by body position. Standing reduced FBF (