Maturation of hypoxic ventilatory response of the newborn lamb

The ventilatory response to acute hypoxia was studied in unanesthetized newborn lambs before and after carotid body denervation. Animals studied immediately following operative delivery were compared with a second group who were studied in the 2nd wk of postnatal life. Response time was defined as the interval between the decrease in oxygen saturation in the aortic arch and an increase in tidal volume or ventilatory rate. Animals in the older group demonstrated a significantly shorter response time than those studied immediately following delivery (1.8 s vs. 5.7 s). A ventilatory response was also elicited in carotid body-denervated animals in both study groups. Mean response time following denervation was 29.5 s for the younger and 12.5 s for the older animals. The data suggest that the development of a rapid, carotid body-mediated hypoxic ventilatory response occurs gradually during the first days of postnatal life, and that the central hypoxic response of the fetus (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42:630-635, 1977) persists into postnatal life.