A study of systemic blood flow in the fetus with cardiac failure using a sheep fetus model

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There are two main factors, neurological and serological, involved iii circulatory control in the fetus. These factors play an important role in redistribution of blood flow, increasing blood flow to the vital organs such as brain, heart and adrenal gland, when the fetus fell in distress. This study clarified that not only cardiac but peripheral regulation should maintain fetal circulation.Canulation to fetal femoral artery and vein was performed in the sheep fetus in 120-135 gestational days. Transit-time ultrasonic flow meters were placed around ascending aorta and pulmonary artery and then a pacing lead wire was attached with some stitches at the ventricle. Atrio-vetricular block was completed by the injection of 10% formalin solution at intraventricula septum. Artificial A-V block decreased fetal heart rate from 168 to 81 bpm and, -cardiac outpu-L, to 40 % of normal condition. Returning -fetal heart rate at 180 bpm by pacing and the decreasing it stepwise, stroke volume increased up to the period of 100 bpm heart rate. When the heart rate was stepwise decreased by pacing, fetal arterial pressure fluctuated with a characteristic wave in a 20-30 second cycle. This waving pattern of arterial pressure disappeared soon, but reappeared when the heart rate was changed down further. This pattern was not affected by parasympathetic or sympathetic blockades.In conclusion, fetus has own not only cardiac but peripheral vascular regulation to maintain circulation.