THORACIC-DUCT FUNCTION IN FETAL, NEWBORN, AND ADULT SHEEP

We measured thoracic duct lymph flow rate versus outflow pressure in 7 chronically catheterized adult sheep and in 6 newborn lambs and compa red our results to data previously obtained from 10 fetal sheep. In fe tal sheep the thoracic duct lymph flow rate was 34.5+/-17.2 ml/hr or 1 1.7+/-6.0 ml/kg/hr. Fetal thoracic duct lymph flow deviated from basel ine between 8 and 12 torr outflow pressure and lymph stopped at 18+/-2 .5 torr. In newborn lambs the thoracic duct lymphs flow rate was 49.5/-22.0 ml/hr or 7.4+/-2.5 ml/kg/hr. The range of outflow pressures ove r which newborn lymph flow deviated from baseline was between 15 and 1 8 torr 130+/-74 ml/hr or 2.3+/-1.3 ml/kg/hr. Adult lymph flow deviated from baseline between 25 and 35 torr and stopped at an outflow pressu re of 41.7+/-6.7 torr. The ability of the thoracic duct to return lymp h against an outflow pressure improves with maturation. However, lymph flow rate corrected for body weight is greatest in immature animals. The higher corrected lymph flow rate in conjunction with the decreased ability to pump against an outflow pressure may help account for imma ture animals predisposition for edema.