Effect of maternal hypoxemia on behavior in unanesthetized normoxic or mildly hyperoxic fetal lambs

Abstract

To determine whether hypoxemia inhibits fetal activity by substances from the mother or placenta, six fetal lambs were chronically instrumented at 128-132 days gestation for extra-corporeal membrane oxygenation (ECMO). Severe maternal hypoxemia (arterial PO2 decreased to 6.00 +/- 0.60 kPa) was produced while fetal arterial PO2 was maintained normoxic or mildly hyperoxic using ECMO. The incidences of fetal breathing movements were 34.8 +/- 3.1% (SE) during baseline before ECMO, 36.8 +/- 3.4% during baseline with ECMO, and 21.4 +/- 3.5% (P < 0.05 compared with baseline with ECMO) during maternal hypoxemia. The durations of periods of breathing were 9.8 +/- 1.2 min before ECMO, 9.3 +/- 1.1 min with ECMO, and 10.5 +/- 1.7 min (P = NS) during maternal hypoxemia. In 7 of 14 maternal hypoxemia experiments, breathing activity stopped too late (7-23 min) to be attributed to maternal hypoxemia. Fetal electrocorticographic activity (P = NS), nuchal electromyographic activity (P = NS), and eye movements were normal before ECMO, with ECMO, and during maternal hypoxemia. Fetal blood pressure and heart rate did not change. We conclude that the inhibition of fetal activity during maternal hypoxemia does not seem to be mediated by release of factors from the maternal side of the placenta or the ewe.

Effect Of Hypoxia On Respiratory Activity In The Foetus

“…7 Large-bore catheters placed in the superior vena cava and ascending aorta make it possible for approximately 20% of the cardiac output of the foetus to be passed through an externally located membrane gas exchanger; this provides a means of maintaining foetal blood gases and pH within the normal range while the ewe is exposed to hypoxic atmospheres. The only fraction that significantly decreased the incidence of FBM was a 1-10 kDa subfraction.…”

“…The possibility that this, or other inhibitory substances, is released from the placenta during hypoxia has been examined using extracorporeal membrane oxygen (ECMO) exchange to maintain the foetal PO2 in the normal range while making the mother (and placenta) hypoxaemic. 7 Large-bore catheters placed in the superior vena cava and ascending aorta make it possible for approximately 20% of the cardiac output of the foetus to be passed through an externally located membrane gas exchanger; this provides a means of maintaining foetal blood gases and pH within the normal range while the ewe is exposed to hypoxic atmospheres. Under such conditions, FBM, electro-ocular activity and the electromyographic (EMG) activity of the neck muscles remain more or less normal in incidence and amplitude, 7 indicating that maternal (and uteroplacental) hypoxaemia do not cause the release of substances that directly inhibit the respiratory centres in the foetal brain.…”