Study for the development of physiological function in extremely immature fetus by using extrauterine fetal incubation system

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The aim of our was to evidence the physiological mechanisms to regulate blood gas exchange and circulation in extremely premature fetus. The materials we used were premature goat fetuses during extra uterine incubation by using A-V ECMO,the system of which was developed by our group. It was essential to maintain fetal goats in stable condition during extra uterine incubation. Our previous study revealed that extremely premature goat fetus (95 gestational days, 500 gm) could be incubated for 8 days.However it was issued that the goat fetus lapsed into cardiac failure during extra uterine incubation. So in the first year, the purpose of our study was to examine the feasibility of long time extra uterine incubation of premature goat fetuses without cardiac failure. In consequence, long time extrauterine incubation more than 20 days could be achieved by suppression of the fetal movement and swallowing with diazepam and pancronium bromide administered into blood circuit. In the second year, the purpose was to assess the mechanism of distribution of circulation under the fetal hypoxia. In consequence, it was revealed that intra cranial circulation was influenced by hypercapnia rather than by hypoxemia.Because the blood flow volume of the fetal carotid artery was more increased under the normoxemic hypercapnia than under the isocapnic hypoxemia. Dexamethasone was clinically used to make the fetal lung mature, however the pharmacological functions of the dexamethasone for the premature fetuses were not revealed. In the last year the purpose was to assess the influence of the dexamethasone on the fetal central nervous system. Changes of the short term variability (STV) and long term variability (LTV) of the fetal heart rate were observed after dexamethasone injection. STV and LTV were increased after the administration of the dexamethasone. Therefore it was considered that dexamethasone did not suppress the fetal central nervous system during extra uterine incubation.