Lung liquid production rates and volumes do not decrease before
labor in healthy fetal sheep.
Lines, A., S. B. Hooper, and R. Harding.
Department of Physiology, Monash University, Clayton, 3168,
Victoria, Australia
APStracts 3:0134L, 1996.
Previous studies have suggested that the volume and production rate of
fetal lung liquid decrease late in gestation, before the onset of
labor, in preparation for the clearance of lung liquid at birth. In
contrast, our earlier studies have not shown a decrease in lung
liquid volume near term, although these studies were not continued to
the onset of labor. Our aim was to determine the changes in lung
liquid volume and production rate in fetal sheep during the last two
weeks of gestation up to the onset of labor at term (147 days). In 8
chronically catheterised fetal sheep, the volume and production rate
of fetal lung liquid was measured on days 130, 135, and 140 of
gestation and then on every second day until the onset of labor.
Labor was detected by monitoring uterine muscle activity and intra
-uterine pressure changes. The gestational age of fetuses at the onset
of labor was 147 +/- 1 days and fetal body weights were 5.0 +/- 0.2
kg. The volume of fetal lung liquid was 40.4 +/- 2.7 ml/kg at 19 +/-
1 days before labor onset and had not significantly changed by 0.7
+/- 0.2 days (44.8 +/- 5.1 ml/kg) before labor onset. Similarly, lung
liquid production rates at 19 +/- 1 days before labor (5.1 +/- 1.8
ml/hr/kg) were not significantly different from those at 0.7 +/- 0.2
days before labor (3.4 +/- 0.7 ml/hr/kg). We conclude that, in
healthy ovine fetuses, lung liquid volumes and production rates do
not decrease prior to the onset of labor. Our results indicate that
the entire volume (approximately 222.5 +/- 36.6 mls) of fetal lung
liquid must be cleared after the onset of labor.
Received 19 April 1996; accepted in final form 26 July 1996.
APS Manuscript Number L124-6.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996