Thoracic duct lymph flow and protein flux dynamics: responses to intravascular saline

Fluid and protein flux responses in the left thoracic duct and vasculature were measured in pentobarbital-anesthetized, nephrectomized, adult dogs before and after four successive intravascular saline infusions of 2% of body weight each. We found three main characteristics of the thoracic lymph flow and protein flux responses to the intravenous saline: 1) lymph flow reached a peak and then decreased by approximately 40% after each infusion; 2) the maximum lymph flow occurred 5-7 min after terminating each infusion; and 3) the lymph-to-plasma protein concentration ratio fell more than may be expected from the distribution of the infused saline. We were unable to explain these experimental data with a simple two-compartment mathematical model representing the vascular and interstitial spaces. To adequately explain the data, the model had to be expanded to four compartments representing a vascular compartment, two interstitial compartments each with different capillary protein permeabilities, and a lymphatic compartment. We also found it necessary to include interstitial stress relaxation, a nonlinear function curve for lymph flow versus interstitial fluid pressure, and a complaint lymphatic system.