Journal of Applied Physiology, Vol 70, Issue 1 293-299, Copyright © 1991 by American Physiological Society
Fetal breathing and pressures in the trachea and amniotic sac during oligohydramnios in sheep
K. A. Dickson and R. Harding
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Oligohydramnios commonly leads to fetal lung hypoplasia, but the mechanisms
are not fully understood. Our aim was to determine, in fetal sheep, the
effects of prolonged oligohydramnios on the incidence and amplitude of
tracheal pressure fluctuations associated with fetal breathing movements
(FBM), on tracheal flow rate during periods of FBM (VtrFBM) and periods of
apnea (Vtrapnea), on tracheal pressure relative to amniotic sac pressure,
and on amniotic sac pressure relative to atmospheric pressure. In five
sheep, oligohydramnios was induced by draining amniotic and allantoic
fluids from 107 to 135 days of gestation (411.8 +/- 24.4 ml/day), resulting
in fetal lung hypoplasia. In five control sheep, amniotic fluid volume was
732.3 +/- 94.4 ml. Oligohydramnios increased the incidence of FBM by 14% at
120 and 125 days and the amplitude of FBM by 30-34% at 120-130 days
compared with controls. From 120 days onward, VtrFBM was 35-55% lower in
experimental fetuses than in controls. Influx of lung liquid during FBM was
87% lower in experimental fetuses than in controls. Vtrapnea, tracheal
pressure, and amniotic sac pressure were not significantly altered by
oligohydramnios. Our tracheal flow rate data suggest that transient changes
in lung liquid volume during periods of FBM and periods of apnea were
diminished by oligohydramnios. We conclude that the primary factor in the
etiology of oligohydramnios-induced lung hypoplasia is not an inhibition of
FBM (as measured by tracheal pressure fluctuations) or a reduction in
amniotic fluid pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
