PULMONARY MECHANICS AND ENERGETICS OF NORMAL, NONVENTILATED LOW-BIRTH-WEIGHT INFANTS

Pulmonary mechanics and energetics were determined in 33 healthy low birthweight infants (< 1,500 g, 28–34 weeks gestation) who had never received ventilatory support. Tidal volume, dynamic pulmonary compliance, pulmonary resistance, pressure‐volume relationships, and tidal flow‐volume measurements were obtained by pneumotachography and the esophageal balloon technique. Standardized data collection and software data analysis by least mean squares technique yielded data at 0.5, 1, 2, and 4 weeks postnatally, as a function of gestational age (<30, 30–32, and >32 weeks gestation). Relatively stable values were obtained for tidal volume and minute ventilation (normalized for body weight); these were associated with values of peak‐to‐peak esophageal pressure significantly (P < 0.001) increasing from 4.4 ± 0.3 SEM cmH2O at 0.5 weeks to 8.1 ± 0.8 SEM cmH2O at 4 weeks of age. Dynamic pulmonary compliance ranged from 2.0 to 2.4 mL/cmH2O in the first 4 weeks of life. When normalized for weight, compliance decreased with age, which may suggest a slower pulmonary maturation as compared to increase of body weight. Mean pulmonary resistance decreased from 62.9 cmH2O/L/s at <30 weeks gestation to 32.5 cmH2O/L/s at >32 weeks gestation, 0.5 weeks postnatally. Pulmonary resistance peaked at 2 weeks postnatally (P < 0.05), at all gestational ages, then decreased. Changes in pulmonary mechanics resulted in increasing resistive work of breathing. Our findings suggest a postnatal retardation of pulmonary and airway growth, relative to gestation maturation. These data can provide an objective base of comparison for data in sick, low birthweight neonates. Pediatr Pulmonol 1990; 8:89‐95. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company