Dynamic Changes in Splanchnic Blood Flow and Blood Volume in Dogs during Activation of Sympathetic Nerves

Arterial inflow to and venous outflow from the vascularly isolated splanchnic region were measured simultaneously by using cannulating electromagnetic square-wave flow transducers in 25 anesthetized dogs with intact abdomens. Change in splanchnic blood volume (SBV) was calculated as the instantaneous difference between inflow and outflow. Addition of the respective increases and decreases in SBV induced by changing carotid sinus pressure from the control value (mean, 136 mm Hg) to 200 or to 40 mm Hg gave an average total volume of 93 ml of blood ( SD , ±21.7) that could be mobilized reflexly from the splanchnic circulation, Electrical stimulation (15 v, 2 cps, 3 msec duration) of the left thoracic splanchnic nerve for 2 to 10 minutes decreased SBV by 159 ml of blood ( SD , ±84). These mean values represent 32 and 48%, respectively, of the calculated total SBV. In both situations the translocation of blood was rapid, 50% of the total change in splanchnic blood flow and SBV occurring within 30 seconds. During a 2-minute hemorrhage (7.2 ml/kg), a mean volume of 56 ml of blood ( SD , ±16) was mobilized from the splanchnic region. This represented 54% of the total volume bled. Under these circumstances, blood moved out of the splanchnic circulation at a fairly constant rate.