LYMPH-FLOW IN SHEEP WITH RAPID CARDIAC VENTRICULAR PACING

Increases in systemic venous pressure (P-V) associated with heart fail ure cause an increase in microvascular fluid filtration into the tissu e spaces. By removing this excess filtrate from the tissues, lymphatic vessels help to prevent edema. However, the lymphatics drain into sys temic veins and an increase in P-V may interfere with lymphatic flow. To test this, we cannulated caudal mediastinal node efferent lymphatic s in sheep. We used rapid cardiac ventricular pacing (240-275 beats/mi n) to cause heart failure for 4-7 days. Each day we determined the lym ph flow rate two ways. First, we adjusted the lymph cannula height so that the pressure at the outflow end of the lymphatic was zero. After we determined the lymph flow with zero outflow pressure, we raised the cannula so that outflow pressure was equal to the actual venous press ure. We quantitated the effect of venous pressure on lymph flow rate b y comparing the flow rate with outflow pressure=P-V to the flow rate w ith zero outflow pressure. At baseline, P-V=5.0+/-2.5 (SD) cmH(2)O and we found no difference in the two lymph flow rates. Pacing caused P-V and both lymph flow rates to increase significantly. However for P-V <15 cmH(2)O, we found little difference in the two lymph flow rates. T hus increases in P-V to 15 cmH(2)O at the outflow to the lymphatics ha d little effect on lymph flow. By comparison, P-V >15 cmH(2)O slowed l ymph flow by 55+/-29% relative to the lymph flow rate with zero outflo w pressure. Thus P-V values >15 cmH(2)O interfere with lymph flow from the sheep caudal mediastinal lymph node.