SKELETAL-MUSCLE VASCULAR-RESPONSES IN HUMAN LIMBS TO ISOMETRIC HANDGRIP

Studies of whole limb blood flow have shown that static handgrip elici ts a vasodilatation in the resting forearm and vasoconstriction in the resting leg. We asked if these responses occur in the skeletal muscle vascular bed, and if so, what is the relative contribution of local m etabolic versus other mechanisms to these vascular responses. Blood fl ow recordings were made simultaneously in the skeletal muscle of the r esting arm and leg using the Xenon-washout method in ten subjects duri ng 3 min of isometric handgrip at 30% of maximal voluntary contraction . In the arm, skeletal muscle vascular resistance (SMVR) decreased tra nsiently at the onset of exercise followed by a return to baseline lev els at the end of exercise. In the leg SMVR remained unchanged during the 1st min of handgrip, but had increased to exceed baseline levels b y the end of exercise. During exercise electromyography (EMG) recordin gs from nonexercising limbs demonstrated a progressive 20-fold increas e in activity in the arm, but remained at baseline in the leg. During EMG-signal modelled exercise performed to mimic the inadvertent muscle activity, decreases in forearm SMVR amounted to 57% of the decrease s een with controlateral handgrip. The present study would seem to indic ate that vascular tone in nonexercising skeletal muscle in the arm and leg are controlled differently during the early stages of static hand grip. Metabolic vasodilatation due to involuntary contraction could si gnificantly modulate forearm skeletal muscle vascular responses, but o ther factors, most likely neural vasodilator mechanisms, must make maj or contributions. During the later stages of contralateral sustained h andgrip, vascular adjustments in resting forearm skeletal muscle would seem to be the final result of reflex sympathetic vasoconstricter dri ve, local metabolic vasodilator forces and possibly neurogenic vasodil ator mechanisms.