Abdominal lymph flow response to intraperitoneal fluid in awake sheep.

Lymphatic vessels are important in draining excess fluid from the abdominal space and preventing ascites. In sheep, diaphragmatic lymph vessels draining the abdominal space run to the caudal mediastinal lymph node and efferent vessels from the node drain into veins in the neck. To estimate the lymph flow response to excess intraperitoneal fluid in sheep, we cannulated a caudal mediastinal node efferent lymphatic in 5 sheep. After the sheep recovered from the surgery, the lymph flow (QL) was 154 +/- 161 (SD) microliters/min and the lymph protein concentration (CL) was 3.7 +/- 9 g/dl. Lymph flow decreased linearly with increases in lymphatic outflow pressure greater than 6 cmH2O. From this linear QL vs. outflow pressure relationship, we estimated the effective pressure driving lymph flow as the outflow pressure at which QL = 0. At baseline, the driving pressure was 24.7 +/- 14.0 cmH2O. After we infused Ringers solution (10% body weight) into the abdominal space, QL increased significantly to 7.0 +/- 4.1 times baseline and CL decreased significantly to 0.7 +/- 0.6 g/dl. Although the abdominal pressure increased significantly from 10.6 +/- 2.8 cmH2O to 15.8 +/- 2.1 cmH2O, we found no increase in lymphatic driving pressure.