Roles of the visceral pleura in the production of pleural effusion in permeability pulmonary edema.

We investigated the roles of the mesothelium of the visceral pleura on hydraulic conductivity in dogs under normal conditions and condition of permeability pulmonary edema. Nineteen mongrel dogs were divided into following 4 groups: thoracotomy alone (control group, n = 7); thoracotomy and striping of the mesothelium using Gelfilm (C + G group, n = 4); injection of oleic acid to increase the permeability of the pulmonary vessels (OA group, n = 4); injection of oleic acid and striping of the mesothelium (OA + G group, n = 4). A hemispherical capsule filled with physiological saline was attached to the visceral pleura. The transpleural fluid flow (delta V) was measured at given incremental or decremental hydrostatic pressures (delta Pcap) in the capsule. Hydraulic conductivity was calculated from the slope of linear regression line obtained from relationship between delta Pcap and the fluid flow rate (v) according to the Starling's equation. The conductivity obtained were 1.49 +/- 0.69 (nl.min-1.cmH2O-1.cm-2) in the control group, 1.37 +/- 0.88 in the C + G group, 3.75 +/- 0.74 in the OA + G group, and 7.07 +/- 2.49 in the OA + G group. The hydraulic conductivity was not increased by striping of the mesothelium (1.49 +/- 0.69 [nl.min-1.cmH2O-1.cm-2] vs. 1.37 +/- 0.88, in the control group vs. C + G group, respectively). Visceral pleural hydraulic conductivity following OA injection was increased by striping of the mesothelium (3.75 +/- 0.74 vs. 7.07 +/- 2.49 in OA group vs. OA + G group, respectively). These findings suggest that the wall of pulmonary vessels acts as a barrier to movement of pleural effusion under normal conditions, whereas the mesothelium of the visceral pleura acts as that under condition of permeability pulmonary edema.