1212 INDUCTION OF BREATHING IN THE FETAL SHEEP WITH AMMONUM CHLORIDE INFUSION

Abstract

Eight sheep fetuses (125-140 days old) were chronically catheterized and infused with 20-25 mEq/Kg of NH₄ C1 in order to study the effects of acute metabolic acidemia on the fetal circulation. The fetal arterial pH decreased from 7.4-7.35 to 6.8-6.9. Regional blood flows before and during acidemia were measured by means of a microsphere method. During NH₄ C1 acidemia, 8/9 animals showed increased blood flow to the diaphragm and to the intercostal muscles. In subsequent preparations, tracheal and amniotic catheters were placed and these showed that NH₄ C1 induced regular respirations (60-90/min) generating negative tracheal pressures of 20-30 torr. Regular breathing began 1-2 hours after stopping the infusion of NH₄C1 and continued for 12-24 hours -after blood ammonia concentrations had returned to normal. Repeated infusions of NH₄C1 elicited the same response. Pulmonary blood flows were higher at similar right ventricular PO₂'s during NH₄C1-induced acidemia. All fetuses had normal blood pressure and heart rate, and all recovered completely.

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