Influence of alterations in Starling forces on visceral pleural fluid movement

The influence of alterations in hydrostatic and oncotic pressure gradients on fluid movement across the visceral pleura was examined in 16 spontaneously breathing anesthetized dogs. The left lung was enclosed in a water-impermeable polyethylene membrane, creating a visceral pleural space; visceral fluid movement was determined as the formation or reabsorption of fluid in this space. Aortic, pulmonary arterial, right and left atrial, and pleural pressures were monitored; oncotic pressure was calculated from the protein concentration of plasma and pleural fluid. Left atrial pressure was varied from 0 to 30 mmHg and pulmonary arterial pressure from 15 to 36 mmHg by inflating atrial balloon catheters; the plasma-to-pleural fluid oncotic gradient was varied from 6.8 to 19.3 mmHg by infusing saline. The movement of fluid across the visceral pleura was significantly (P less than 0.001) related to the effective (transmural hydrostatic pressure minus oncotic gradient) pulmonary arterial (r = 0.87) and left atrial pressures (r = 0.92). The filtration coefficient of the visceral pleura estimated by our technique was 1.1 x 10(-6) ml.s-1.cmH2O-1.cm-2. These results not only confirm the concept that fluid flux across the visceral pleura is determined by the action of Starling forces across this membrane but also provide an estimate of the filtration coefficient for the visceral pleura.