Answer to Question 1
ANS: A
The newborn infant is stimulated by new tactile and thermal stimuli, all of which stimulate breathing. In addition, as placental gas transfer is suddenly interrupted, the newborn quickly be-comes hypoxemic, hypercapnic, and acidotic.
Answer to Question 2
ANS: D
Figure 9-9 summarizes the major cardiopulmonary changes that take place during the transition from the fluid-filled lung to an air-filled lung. As the lung expands with air and gas exchange starts within the lung, pulmonary blood PO2 increases, PCO2 decreases, and the pH rises. This results in pulmonary vasodilation, lower pulmonary vascular resistance, and constriction of the ductus arteriosus. This facilitates greater blood flow through the pulmonary circulation. Ductus arteriosus closure is further stimulated by the loss of maternal prostaglandins. The combination of increasing alveolar air content and constriction of the ductus arteriosus promotes progressive im-provement in the matching of ventilation and blood flow, which, in turn, increases the PO2 and decreases the PCO2 of blood leaving the lungs. Cessation of umbilical and placental blood flow, following the clamping of the umbilical cord, causes closure of the ductus venosus and a rapid rise in systemic vascular resistance. The combination of the above events establishes a normal ex-trauterine circulatory pattern.
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