Relationship between pericardial pressure and lymphatic pericardial fluid transport in sheep

We investigated the relationship between pericardial pressure and the volum etric lymphatic clearance rate of pericardial fluid in sheep. A single cath eter perfusion system was established to deliver tracer to the pericardial cavity and control pericardial pressure. In addition, catheters were placed into the thoracic duct and into the jugular vein at the base of the neck. I-125-human serum albumin (HSA) was administered into the pericardial perfu sate to serve as the lymph flow marker and its concentration monitored in t he effluent from the outflow end of the perfusion system. I-131- HSA was in jected intravenously to permit calculation of plasma tracer loss and tracer recirculation into lymphatics. From mass balance equations, estimates of t otal pericardial clearance into lymphatics increased significantly as peric ardial pressures were elevated in 2.4 cm H2O increments from 2.5 to 12.5 cm H2O (P = 0.018). Pericardial lymph transport ranged from 0.89 +/- 0.10 to 3.09 +/- 0.66 ml/h at 2.5 and 12.5 cm H2O pericardial pressure, respectivel y. The majority of transport occurred through mediastinal vessels with a sm all proportion (10.3 to 23.9%) being cleared into lymphatics leading to the thoracic duct. We conclude that lymphatic pericardial fluid transport incr eases similar to 3.5-fold over a pericardial pressure range that encompasse s the transition between the shallow and steep portions of the pericardial pressure-volume relationship. (C) 2000 Academic Press.