[The FHR variability of "Shiba goats" in acute hypoxic state].

Fetal heart rate variability in an experimentally induced acute hypoxic state was investigated using chronically prepared fetal goats. FHR variability was calculated using a microcomputer with the R-R intervals of the direct fetal ECG signal measured with a peak detector. The accuracy of the peak detector was 0.1 msec. The formula for FHR variability was as follows: (Formula: see text) A fetal acute hypoxic state was induced by maternal inhalation of a gas mixture low in O2 concentration. The fetal condition was evaluated by blood gas analysis of the fetal carotid artery. In mild fetal hypoxemia due to the maternal inhalation of a gas mixture including 8-10% of O2, both STV and LTV were increased at 10-20 minutes after the beginning of the experiment. Subsequently, both were decreased at 30-40 minutes, but maintained a level higher than that of the control. When severe fetal hypoxemia was induced by the maternal inhalation of the gas mixture containing 4-6% of O2, both STV and LTV increased at 10-20 minutes after induction, then decreased to a level lower than that of the control at 30-40 minutes. No significant difference in fetal PO2 was observed between the 10-20 min. period and the 30-40 min. period of the severe hypoxemic state. But significant differences in pH and BE values were found when the 10-20 min. period and the 30-40 min. period were compared. When data showing the fetal arterial pH and BE to be significantly lower than those of the control at 30-40 min. of the severe hypoxemic state were excluded, significant negative correlations were found between PO2 and STV and between PO2 and LTV . It appeared that FHR variability, both STV and LTV , would increase during the acute hypoxemic state and that they would decrease to a level lower than that of the control after metabolic acidosis occurred due to continuing hypoxemia.