Effects of progressive vascular occlusion on slope and intercept of the pulmonary artery pressure-flow relationship.

Abstract

Pulmonary hemodynamics may be described by mean pulmonary arterial pressure (PAP)-cardiac output (CO) plots. The slope of the PAP-CO relationship may define the incremental resistance (IR), and the extrapolated pressure intercept (P(I)), the effective outflow pressure. The authors investigated the effects of progressive pulmonary vascular occlusion on the IR and P(I) of the PAP-CO plot. Nine experimental and nine time control dogs were studied. In the former group, PAP-CO plots were obtained in three conditions: (1) Baseline, (2) following occlusion of the right pulmonary artery, and (3) following occlusion of the right pulmonary artery and blood flow to the left upper lobe. Following progressive occlusion, there was a corresponding increase in the IR of the PAP-CO plot, from 1.95 to 3.62 to 5.16 mmHg.1-1.min (all P < 0.05). In contrast to the increase in IR, P(I) remained constant. Over the same interval, there were no changes in IR or P(I) in the time control group. These findings indicate that changes in the slope of the PAP-CO plot correspond to changes in the number of parallel vascular units.