Effects on cardiac output distribution of propranolol, verapamil and epidural blockade during continuous positive-pressure ventilation : An experimental study in the pig

Sammanfattning: The blood perfusion of all body regions is governed by local vasoregulation, and systemic humoral and neural impulses provide additional tuning of vascular tone. Is the regulation of circulation centralised or, in other words, is the sympathetic nervous system (SNS) superior to local autoregulation of the perfusion of vital organs? Using the microsphere method and acquired data on the body composition of the pig, it was possible to interpret the absolute distribution of cardiac output (CO) and flux changes between organs and tissues. Also, two indirect methods for estimating body composition, dual-energy x-ray absorptiometry (DXA) and underwater weighing (UWW), were validated against carcass analysis. The circulation was challenged by continuous positive-pressure ventilation (CPPV), which reduces venous return and hence CO. The SNS was interfered with in the periphery by the β-receptor blocker propranolol, which acts as a peripheral vasoconstrictor, and at the proximal level by an epidural blockade defined in the pig. We also investigated how the calcium channel blocker verapamil, a peripheral vasodilator, interfered with vasoregulation.The body composition of the 12-week-old pig (20-25-kg) is described. Body components obtained by DXA correlated closely to carcass analysis. DXA overestimated bone mineral mass, lean mass and total weight and underestimated fat mass. The fat estimations by DXA and UWW were significantly affected by the amount of water in lean mass and fat-free mass.The combination of β-blockade and CPPV severely reduced CO. Local vasoregulation seems to outweigh the influence of SNS. The adrenal blood flow increased during CPPV, but this was obviated by epidural blockade.