MAXIMAL LYMPH-FLOW IN THE OVINE FETUS

OBJECTIVE: This study was designed to determine the maximal left thora cic duct lymph flow rate in late-gestation ovine fetuses. STUDY DESIGN : Chronically catheterized sheep fetuses (n = 8) with indwelling left thoracic lymph duct and vascular catheters were studied greater-than-o r-equal-to 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. RESULTS: During a 1-ho ur 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 prein fusion values (p < 0.001). When the infusion was terminated, fetal art erial and venous pressures rapidly returned to preinfusion levels. Lym ph flow rate gradually decreased during the first 30 minutes and stabi lized at 97% +/- 17% above control during the subsequent 30 minutes. A nalysis 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. CONCLUSION S: (1) Fetal left thoracic duct lymph flow rate can increase significa ntly above basal values and therefore is an important safety factor ag ainst fetal edema formation. (2) The maximal lymph flow rate appears t o be 3.4 times normal when venous pressure is elevated and two times n ormal when venous pressure is normal.