Incremental pulmonary vascular resistance increases with elevation of pulmonary venous pressure

The aim of this study was to determine whether elevation of pulmonary venous pressure affects incremental pulmonary vascular resistance. We vascularly isolated the left lower lobe of the lung and perfused with blood using a pulsatile pump. Blood flow to the isolated lobe was decreased in 6 to 7 steps from about 8 to 1 ml/kg/min. Incremental pulmonary vascular resistance was estimated from the slope of the pressure-flow relationship between pulmonary arteriovenous pressure difference and pulmonary blood flow at different pulmonary venous pressures. Incremental pulmonary vascular resistance increased as pulmonary venous pressure was elevated. This result suggests that an increase in cardiac output, i.e., an increase in pulmonary blood flow, results in a larger increase of pulmonary arterial pressure in high pulmonary venous pressure than in low pulmonary venous pressure.