Effects of lung inflation on longitudinal distribution of pulmonary vascular resistance.

A low-viscosity bolus technique was employed to determine the influence of lung inflation on the distribution of pulmonary vascular resistance in isolated cat lungs. When the lungs were collapsed, the longitudinal distribution of resistance was concentrated near the proximal (arterial) part of the vascular bed. As the lungs were inflated, the resistance became more evenly distributed with the maximum located close to the midpoint of the total blood volume. The fraction of total pressure drop across the lung which occurred proximal to the midpoint of the total lung blood volume decreased from 0.69 in the collapsed lung to 0.43 at a transpulmonary pressure of 16 cmH2O.