Starling forces and lymphatic drainage in pleural liquid and protein exchanges

Abstract

Pleural liquid volume and protein concentration (C) were determined in rabbits 60 min after a 2 ml hydrothorax with various albumin concentrations in Ringer, homologous serum or plasma. The absorption rate of the hydrothorax decreased with the increase in colloid osmotic pressure of the pleural liquid ( π), being 0.56 ± 0.03, 0.32 ± 0.02 and 0.17 ± 0.05 ml/h with Ringer, 1.1 and 3% albumin, respectively, and nil with 5% albumin, serum or plasma. C increased with Ringer and 1.1% albumin, did not change with 3% albumin, and decreased with 5% albumin, serum or plasma. The protein content in the pleural liquid increased with Ringer, did not change with 1.1% albumin, and decreased with the other hydrothoraces. These findings indicate that with hydrothoraces of this size: (1) the Starling forces plus the solute-coupled liquid absorption [Agostoni and Zocchi (1990) Respir. Physiol. 81: 19–28] provide most of the pleural liquid absorption when π is ≤ physiological ; (2) the lymphatic drainage increases with π, providing most of the liquid outflow when π is similar to that of plasma. This increase in lymphatic drainage, however, does not compensate for the effects of the changes in Starling forces produced by the increased π.