Sodium nitroprusside and regional arterial haemodynamics in the dog

Blood flow to functionally different vascular beds was examined during a sodium nitroprusside infusion in 10 dogs anaesthetized with halothane (1 MAC) in oxygen. Blood flows were measured in the ascending aorta, and the coeliac, superior mesenteric, renal and iliac arteries. In two dogs, regional vascular impedance and related power were calculated. Regional pressure-flow relationships were measured at systemic pressure reductions of approximately 15, 35 and 55% of control. At pressure reductions of 15-35%, coeliac, mesenteric and aortic blood flow exceeded control values (P less than 0.025); renal and iliac blood flows were reduced, but not significantly. At pressure reductions of 55% a more significant reduction of iliac, renal and aortic blood flow occurred (P less than 0.05). All vascular resistances showed significant monotonic reductions (P less than 0.01) over the entire range of pressure reduction. Total power dissipation was reduced in all beds with a reduction of characteristic impedance in the coeliac, renal and iliac beds; aortic oscillatory pressure power increased.