SWALLOWING AND URINE FLOW RESPONSES OF OVINE FETUSES TO 24 H OF HYPOXIA

The aim of this study was to determine the effects of 24 h of hypoxia on fetal swallowing and urine flow rates. The study design included successive 24-h control, hypoxia, and recovery periods. To induce hypoxia, we infused nitrogen into the trachea of late-gestation pregnant sheep. During hypoxia, there were decreases in fetal arterial oxygen saturation [from 62.7 +/- 2.2 to 30.9 +/- 2.9% (SE)] and PO2 (from 21.1 +/- 1.0 to 14.1 +/- 0.9 mmHg) (n = 7). Fetal arterial pH decreased maximally by 0.04 +/- 0.01 at 6 h and returned to control thereafter. Fetal swallowing decreased from 13.4 +/- 2.1 to 0.6 +/- 0.2 ml.h(-1).kg fetal wt(-1) with the onset of hypoxia and gradually increased, but only to one-half control levels, during the last 12 h of hypoxia. Fetal urine flow gradually decreased from 9.6 +/- 1.6 ml.h(-1).kg(-1) to a minimum of 5.3 +/- 0.5 ml.h(-1).kg(-1) at 2-3 h of hypoxia and returned to control thereafter. During the first hour of the recovery period, fetal swallowing transiently increased to twice control levels before returning to control. This was followed by a delayed, transient increase in urine flow to 63% above control levels at 2-6 h after hypoxia. We conclude that the fetal swallowing and urine flow responses to prolonged hypoxia in the absence of acidemia are distinctly different from the initial inhibitory responses, in that swallowing partially and urine flow fully recovers from the initial suppression.