PULMONARY VASCULAR PRESSURE-FLOW CHARACTERISTICS IN CANINE PULMONARY-EMBOLISM

We tested the hypothesis that, in canine embolic pulmonary hypertension, upstream transmission of increased left atrial pressure (LAP) is inversely related to the level of the pressure intercept (P(I)) obtained by extrapolation from the linear pulmonary vascular pressure-flow (P-Q̇) plot. P-Q̇ coordinates were obtained by varying Q̇ through systemic fistulas. Seven group 1 dogs were embolized with autologous blood clot to produce marked pulmonary hypertension and mean pulmonary arterial pressure (PAP), and P(I) increased from 15 to 41 mmHg (P < 0.001) and from 8.8 to 31 mmHg (P < 0.001), respectively. Before and after embolization we assessed effects of increased LAP, produced by inflation of a left atrial balloon, on PAP at constant Q̇. Embolization depressed the mean slope of this relationship from 0.78 to 0.16 (P < 0.001). Subsequently, six group 2 dogs were embolized to produce moderate pulmonary hypertension with a mean P(I) of 22 mmHg. This value was significantly less than P(I) in group 1 (P < 0.01). After embolization, the slope of the PAP-LAP relationship was greater in group 2 than group 1: 0.47 vs. 0.16 (P < 0.01). We conclude that the upstream transmission of left atrial pressure is inversely related to P(I) and that marked embolic pulmonary hypertension produces an effective vascular waterfall.