Maximal lymph flow in the ovine fetus

Abstract

This study was designed to determine the maximal left thoracic duct lymph flow rate in late-gestation ovine fetuses. Chronically catheterized sheep fetuses (n = 8) with indwelling left thoracic lymph duct and vascular catheters were studied > or = 5 days after surgery at 136 +/- 1 (SE) days' gestation. To increase lymph flow rate, 4 L of warm lactated Ringer's solution were infused intravenously into the fetus over 4 hours, because this causes mild edema as determined ultrasonographically. During a 1-hour preinfusion period lymph flow rate was 0.53 +/- 0.06 ml/min. During the infusion increases occurred in fetal arterial (7.6 +/- 1.0 mm Hg) and venous (2.4 +/- 0.3 mm Hg) pressures (p < 0.001). Lymph flow rate increased and reached a plateau after 1 hour at 339% +/- 30% of preinfusion values (p < 0.001). When the infusion was terminated, fetal arterial and venous pressures rapidly returned to preinfusion levels. Lymph flow rate gradually decreased during the first 30 minutes and stabilized at 97% +/- 17% above control during the subsequent 30 minutes. Analysis of lymph flow rate as a function of outflow pressure revealed that the increases in flow occurred because of an upward shift in the plateau flow rate with no change in the stop-flow pressure. (1) Fetal left thoracic duct lymph flow rate can increase significantly above basal values and therefore is an important safety factor against fetal edema formation. (2) The maximal lymph flow rate appears to be 3.4 times normal when venous pressure is elevated and two times normal when venous pressure is normal.