Pressure-flow relationships of the canine iliac periphery and systemic hemodynamics: effects of sodiumnitroprusside and adenosine

Abstract

It has been reported that sodiumnitroprusside (SNP) decreases mean systemic pressure and simultaneously increases pressure pulse amplification towards the iliac periphery (Kenner and van Zwieten 1982). This unexpected finding was suggested to be due to a decrease in iliac peripheral resistance but an increase in iliac differential resistance. In order to investigate this apparent contradiction, the iliac periphery was hemodynamically isolated from the rest of the circulation and perfused with the dog's own blood by means of a pump. Perfusion pressure (P) and flow (F), femoral venous pressure (Pv), systemic pressure (Ps) and cardiac output (CO) were measured. Steady state pressure-flow relations of the isolated bed were obtained during control and during various i.v. infusion rates of SNP and adenosine (ADS) and were found to be straight (mean r = 0.99). Their slope (delta P/delta F) was defined as differential resistance (Rd). Peripheral resistance (Rp) of the iliac bed was defined as Rp = (P-Pv)/F, calculated at the flow value where perfusion pressure equalled the prevailing systemic pressure. Total peripheral resistance (TPR) was defined as TPR = Ps/CO. The changes of Rd, Rp, Ps, CO and TPR with respect to control show that during low SNP infusion rates Rd and Rp were both increased while TPR was decreased. During all infusion rates of SNP CO did not change while Ps decreased. During low infusion rates of adenosine CO increased while Ps, Rd and Rp did not change and TPR decreased.(ABSTRACT TRUNCATED AT 250 WORDS)