Contribution of Starling and lymphatic flows to pleural liquid exchanges in anesthetized rabbits

We studied the time course of volume and protein reabsorption of a 2-ml hydrothorax using whole (WP) or diluted (DP) homologous plasma injected into the right pleural cavity in anesthetized spontaneously breathing supine rabbits. Animals were killed at 5 (WP, n = 4; DP, n = 3), 36 (WP, n = 3; DP, n = 4), 55 (WP, n = 4), 90 (WP, n = 8; DP, n = 4), and 150 (WP, n = 4; DP, n = 5) min after the injection. The volume and protein content of the pleural liquid in control conditions (n = 12) amounted to 0.35 +/- 0.015 (SE) ml/kg and 1.8 +/- 0.27 g/100 ml, respectively, which are not significantly different at 90 min (n = 7). Pleural liquid volume decreased at a similar rate during WP or DP reabsorption according to the equation V = 0.84 +/- 0.05 X e-0.02t, with net reabsorptive flow expressed as dV/dt. The globulin quantity (Q) of the pleural liquid for WP and DP, respectively, decreased according to the equations Qwp = 1 + 1.5 X e-0.04t and Qdp = 0.7 + 0.6 X e-0.03t. Assuming a major lymphatic globulin clearance and no filtration into the cavity, we obtained lymph flow using the equation VL = dQ/dt X l/C where dQ/dt is calculated from the equations for Qwp and Qdp and C represents globulin concentration. The Starling flow (Vs) was then calculated by the equation Vs = dV/dt-VL. With increasing time, lymph flow was found to decrease progressively and was not significantly different from net flow with DP, which implied a Starling flow value of zero. During WP reabsorption, lymph flow initially exceeded the net flow, with the difference disappearing at approximately 60 min; accordingly, Starling filtration flow decreased progressively, becoming zero at the same time.