The effect of external pressure on the flow rate and recovery time of the terminal lymphatic system

Abstract

The effects of external pressure on the relative terminal lymphatic flow rate following occlusion of the lymph 99m system were studied. Sulfur colloid tagged with ^[99m]Tc was injected into the thigh of dogs. Initially, the lymphatic clearance of the tracer was measured for approximately 40 minutes with no applied external pressure. The lymphatic system was then occluded for 30 minutes by an applied external pressure of 75 mmHg. Finally, the lymphatic clearance rate following occlusion was measured for an applied external pressure of 0, 30, or 45 mmHg. A two compartment model was defined to determine the terminal lymphatic clearance rate per unit volume of subcutaneous tissue (F/V) from the experimental data for each pressure phase. Values for F/V obtained from the application of the model to the experimental data were statistically compared. The experimental results indicated that the lymphatic clearance did not recover until the external pressure was reduced below 45 mmHg . The relative lymphatic clearance rate at an external pressure of 30 mmHg following occlusion was 54 % of the clearance rate determined for a 0 mmHg applied pressure prior to lymph occlusion. For a 0 mmHg external pressure following occlusion the relative lymphatic clearance rate was 23 % of the rate measured for a 0 mmHg applied pressure prior to occlusion. Tissue deformation caused by the external load increased the impedance to fluid flow of the terminal lymphatic system, and this increased impedance was not fully relieved when the occlusive load was reduced. Moderate external pressure aided lymph flow following occlusion by increasing the hydrostatic pressure of the interstitial fluid which drives lymphatic clearance.