Effects of autonomic blockade on pulmonary and systemic circulation before and after birth

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Abstract
The effects of autonomic blockade on pulmonary and systemic hemo-dynamics were studied in the fetal lamb before and after lung expansion and umbilical cord clamping. In the fetal state, ganglionic blockade resulted in inconsistent changes in pulmonary and systemic vascular resistances mainly because of the erratic behavior of ductus arteriosus flow. Lung expansion with air or oxygen in the presence of autonomic blockade promptly decreased pulmonary vascular resistance in a manner similar to that observed in fetal lambs with intact nervous system. This indicates that mechanical factors play a prominent role in pulmonary vascular resistance before and after birth. Systemic vascular resistance increased markedly after lung expansion and cord clamping. The increment was comparable to that of fetal lambs with intact autonomic nervous system. This suggests that the various vascular shunts and placental circulation are the major regulators of systemic vascular resistance before and after birth.