We tested the hypothesis that increased lymph flow from the abdominal
organs would increase the pressure within the thoracic duct at the tho
racic duct-lung lymphatic junction. Cannulas were placed into the thor
acic duct via the caudal mediastinal (lung) node efferent lymphatics i
n 4 sheep. After the sheep recovered from the surgery, we monitored th
e thoracic duct pressure with pressure transducers. To increase lymph
flow from the lower body, we infused Ringers solution (59 +/- 19 [mean
+/- SD] ml/kg body weight in 30 min.) intravenously into the sheep an
d we inflated a balloon in the inferior vena cava. This technique caus
es substantial increases in lymph flow from the lower body (mainly fro
m the liver and intestines) through the thoracic duct. During the infu
sions, the thoracic duct pressure increased significantly from 4.1 +/-
2.9 cm H2O (baseline) to 6.8 +/- 1.7 cm H2O. The neck vein pressure (
pressure at the outflow of the thoracic duct) did not increase from ba
seline (3.0 +/- 2.6 cm H2O) Thus our results support the hypotheses th
at increased flow through the thoracic duct causes increased thoracic
duct pressure.