Developmental changes in the response of the newborn to sustained ventilatory elastic loads.

Postnatal development of the steady-state response to inspiratory elastic loading was studied in eight 48-h-old and eight 24-day-old unanesthetized, tracheostomized monkeys. Both age groups exhibited a fall in minute ventilation (VE) with loads of two to five times baseline respiratory elastance. There was no statistical difference in the ventilatory response between age groups. The response patterns of both groups were characterized by a fall in both tidal volume (VT) and mean inspiratory flow (VT/TI) associated with a prolongation of TI and TI/Ttot. All subjects demonstrated a significant load compensatory response both in terms of neural drive (diaphragmatic EMG output) and force output (inspiratory work production). Arterial CO2 increased significantly during loading in the older subjects in linear correlation with the decline in VE, but the newborns did not exhibit a statistically significant alteration in PaCO2 throughout the range of elastic loads. These data indicate that normal newborns are capable of responding to an external elastic load and that the newborn response is comparable to that of more mature subjects.