Pulmonary vascular pressure-flow relationship in canine oleic acid pulmonary edema

We tested the hypothesis that the increased impedance to flow in canine oleic acid (OA) lung injury is predominantly due to an increase in effective downstream pressure (EDP), obtained by extrapolating to zero flow the linear portion of the pulmonary artery pressure (PAP)/flow (Q) relationship. PAP-Q coordinates were obtained in eight anesthetized, O2-ventilated dogs by varying Q through systemic arteriovenous fistulae. PAP-Q lines were obtained before and approximately 5 h after injection of OA. A second group of six dogs served as a time control (TC) group. There was a linear relationship between PAP and Q in both experimental and control groups (mean r value 0.948). The presence of pulmonary edema in the OA group caused the EDP to almost double, from 7 to 12 mmHg (P less than 0.01). In contrast, EDP remained constant in TCs. Incremental vascular conductance (IVC), slope of the PAP/Q line, decreased (P less than 0.05) a similar amount in both groups. The above findings are consistent with the modeling of the pulmonary circulation according to a Starling resistor in that large amounts of edema changed EDP but not incremental conductance.