title: Permeability of the canine visceral pleura.
abstract: Fluid and protein movement across the pulmonary endothelial membrane (PEM) and adjacent mesothelial layer of the visceral pleura was quantitatively analyzed in terms of a two-compartment model of fluid exchange. The left lungs of 13 spontaneously breathing anesthetized dogs were enclosed in a water-impermeable membrane, creating a visceral pleural space; fluid flux was determined as the filtration or reabsorption of water and protein in the visceral pleural space. Aortic, pulmonary arterial, left atrial, and pleural pressures were monitored; oncotic pressure was calculated from the protein concentration of plasma and pleural fluid. To determine the hydraulic conductivity (Lp), diffusional permeability (Pd), and the solute and solvent drag reflection coefficients for protein (sigma d and sigma f, respectively), fluid exchange was monitored during two or more experimental periods during which the visceral pleural space contained saline and plasma. The permeability coefficients determined for the PEM of the visceral pleura, Lp = 7.7 (+/- 0.3) X 10(-7) ml X s-1 X mmHg-1 X cm-2, sigma d = 0.93, sigma f = 0.61, and Pd = 2.4 (+/- 1.0) X 10(-6) cm/s, are more restrictive than those previously reported for the devascularized visceral pleura in vitro. We conclude that it is the pulmonary endothelial membrane that determines the rate and composition of visceral pleural fluid flux in response to hydrostatic and oncotic gradients in the intact animal.
mesh_terms: D000818:Animals; D002196:Capillaries / Q000502:physiology; D002199:Capillary Permeability; D004285:Dogs; D004727:Endothelium / Q000502:physiology; D006874:Hydrostatic Pressure; D008168:Lung / Q000098:blood supply / Q000502:physiology; D010994:Pleura / Q000502:physiology*; D014882:Water-Electrolyte Balance