Lymphatic system or hydro-oncotic forces. Which is more significant in drainage of pleural fluid?

Abstract

Artificial pleural fluids, containing plasma protein from 0.1 to 9.0 g per 100 ml, indocyanine green (ICG) and para-aminohippurate (PAH), were injected into the pleural cavity of dogs. The concentration of these two indicators were measured at a regular time interval, and the lymphatic and non-lymphatic flows and PAH clearance were calculated by Stewart's and Takashina's equations. When the protein concentration in the pleural fluid was less than 4 g per 100 ml, the pleural fluid volume decreased at a rate of 0.20 ml/kg/hour. The decrease was due to pleural fluid drainage by the lymphatic flow, because the inward and outward non-lymphatic flows due to hydro-oncotic forces balanced each other and the net non-lymphatic flow was essentially zero. When the protein concentration was 6 g per 100 ml or more, the decrease of pleural fluid was remarkably attenuated, because of an increase of the inward non-lymphatic flow due to an increase of protein concentration in the pleural fluid. Even in these situations, the lymphatic flow was kept at the rate of 0.20 ml/kg/hour, similarly with the former conditions. From these results, it may be concluded that the lymphatic system is a principal factor, and that factors governed by hydro-oncotic elements have additive effect to that of the lymphatic system in the regulation of pleural fluid dynamics.