EFFECTS OF ENDOTOXIN INFUSION ON MEAN SYSTEMIC FILLING PRESSURE AND FLOW RESISTANCE TO VENOUS RETURN

Mean systemic filling pressure (P-sf) is an indicator of the filling s tate of the systemic circulation. Cardiac output (Q') is related linea rly to the difference between P-sf and central venous pressure (Pcv), according to: Q' = (P-sf - P-cv)/R(sf), where R(sf) is the flow resist ance downstream from the sites where blood pressure is equal to P-sf. In 16 anaesthetized pigs we evaluated P-sf, R(sf) and Q' during baseli ne conditions, continuous endotoxin infusion and after subsequent flui d loading. P-sf and R(sf) were determined from simultaneous measuremen ts of Q' and P-sf at seven levels of lung inflation. The following res ults were obtained. P-sf was 8.1 +/- 1.8 mm Hg (mean +/- SD) during ba seline conditions, increased after endotoxin infusion to 9.9 +/- 3.2 m m Hg (P = 0.04) and remained the same after infusion of 18 ml . kg(-1) of Ringer's lactate. R(sf) increased from 0.34 +/- 0.07 to 0.80 +/- 0 .34 mm Hg . ml(-1) s by endotoxin and decreased after fluid infusion t o 0.58 +/- 0.14. Q' changed inversely proportional to R(sf) (P = 0.001 ). R(sf) changes were highly correlated with the changes in total syst emic flow resistance (R(s)) (P < 0.001). Endotoxin caused haemoconcent ration and a decrease in plasma volume. The stability of P-sf during e ndotoxin infusion and after volume loading indicate that the stressed volume was well maintained and changes in blood volume are compensated by changes in nonstressed volume. The increase in R(sf) can be attrib uted to arteriolar vasoconstriction, venous vasoconstriction and haemo concentration.