Hind-limb vascular-capacitance responses in anaesthetized dogs.

In anaesthetized dogs a hind limb was vascularly isolated, perfused through the femoral artery at either constant flow or constant pressure and drained from the femoral vein at constant pressure. Inflow and outflow were recorded. Vascular-resistance changes were calculated from changes in pressure or flow and volume changes from the differences between inflow and outflow. During constant-flow perfusion, both changes in carotid sinus pressure and direct stimulation of efferent sympathetic nerves resulted in large resistance responses. However, changes in carotid sinus pressure did not result in changes in limb blood volume and only small decreases were obtained in response to direct stimulation. During constant-pressure perfusion, both reflex and direct stimulation resulted not only in significant changes in resistance but also in significant volume changes which were much larger than those obtained during constant-flow perfusion. Similar responses were obtained when the flow rate was changed by altering the pump speed. These results indicate that changes in pressure to carotid baroreceptors do not result in active capacitance responses in the limb circulation and that only very small responses are obtained even to electrical stimulation of sympathetic nerves. The larger responses occurring during constant-pressure perfusion are thought to be secondary to changes in blood flow.