Effect of respiratory acidosis on body movements in the chronically instrumented fetal lamb

Abstract

In respiratory acidosis, it is reported that the fetal breathing movements as well as the fetal heart rate variability increase. As the increase of these two kinds of fetal activities is occasionally observed in normal conditions, it is difficult to distinguish respiratory acidosis and normal conditions by mere observation of these activities. As the third diagnostic variable, if a different fetal body movement response to respiratory acidosis is observed, it would be helpful for better diagnosis in combination with other activities. We investigated the effect of respiratory acidosis on body movements in the chronically instrumented fetal lamb. A total of four experiments were performed on four ewes. Respiratory acidosis was induced in the fetus by maternal administration of a high carbon dioxide gas mixture for 1 hour. Fetal body movements were observed by real-time ultrasonography. The frequency of body movements was expressed as the number of each movement in a 30-minute period. The mean pCO2 increased from 42.9 +/- 4.9 mmHg to 62.9 +/- 14.8 mmHg, and the mean pH decreased from 7.368 +/- 0.04 to 7.209 +/- 0.04 during the experiments. The frequency of fetal body movements significantly decreased. The percentage reduction of these movements of the same fetus during the experiments as compared to the control periods were as follows; the high-frequency movements, 89.2 +/- 9.7%; the rolling movements, 55.6 +/- 13.5%; the simple movements, 78.3 +/- 18.4%. Normoxemic respiratory acidosis, which is reported to increase fetal breathing movements, caused a marked reduction in fetal body movements. These findings suggest that the ultrasonographic dissociation of fetal behaviors in respiratory acidosis would be potentially helpful in the diagnosis of impending fetal jeopardy.