Maturation of eupneic respiration in the neonatal monkey

Comparison between 21 2-day-old infant monkeys and 17 21-day-old infants during non-rapid eye movement sleep demonstrated that minute ventilation (VI) increased from 141 +/- 30 to 257 +/- 65 ml/min secondary to elevations in tidal volume (VT) and mean inspiratory flow (VT/Ti) with little change in respiratory timing. These volumetric parameters of ventilation as well as functional residual capacity remained significantly augmented when standardized for gain in body weight. Dynamic lung compliance increased from 0.69 +/- 0.19 to 0.89 +/- 0.39 ml/cm H2O with age while inspiratory pulmonary resistance did not change. Effective elastance fell significantly with maturation (5.27 +/- 1.51 cm H2O/ml on day 2 versus 4.15 +/- 1.35 cm H2O/ml on day 21) while effective impedance was elevated postnatally. The postnatal ventilatory gain (80% increase in VI) was attributable to increases both in dynamic lung compliance (30%) and inspiratory effort (50%) as determined by esophageal pressure changes. Isometric occlusion pressures (P0.1, P0.2 . . . Pmax) also significantly increased during this time span, suggesting that the increased ventilation resulted from an elevated respiratory drive.