The mechanics of terminal lymph flow

The effects of external pressure on the terminal lymphatic clearance rate are studied. Sulfur colloid tagged with 99mTc is injected into the subcutaneous tissue in the hind thigh of canines. The activity of the tracer is measured over the injection site for 90 min to determine the lymphatic clearance rate of the sulfur colloid. Several experiments are performed at different external pressures applied to the surface of the canine thigh. A two-compartment model is defined to determine both the terminal lymphatic flow rate per unit volume of tissue and the diffusion constant (sulfur colloid/interstitial fluid) from the raw data. Experimental results indicate that increases in the external pressure applied to the skin cause terminal lymphatic clearance rates to increase until the pressure reaches 60 mm Hg. At this level, some test results showed reduced levels of clearance. At 75 mm Hg, the lymphatic clearance of sulfur colloid from the subcutaneous tissue was stopped suggesting occlusion of the vessels resulting from vessel collapse.