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Oxygen consumption (VO2) was measured during controlled and spontaneous ventilation with continuous positive airway pressure in newborn infants in whom chronic lung disease later developed. The oxygen cost of breathing (the difference in VO2 between spontaneous and controlled ventilation) was significantly higher in infants with chronic lung disease than in control infants (20.1% +/- 7.5% and 4.8% +/- 4.9% of VO2 during spontaneous ventilation (p < 0.05), respectively).

The passive compliance of the total respiratory system (CRS) was measured by the occlusion technique in 34 preterm newborn infants with respiratory distress syndrome. Gestational age ranged from 27 to 33 weeks. Preterm newborn infants were divided into four groups on the basis of clinical criteria. Group 1 consisted of 10 infants tested during the first postnatal days (1 to 3 days) while acutely ill and requiring ventilation and oxygen therapy. After the acute phase of respiratory distress syndrome, two groups were tested: group 2 consisted of nine infants (5 to 22 days of age) who no longer required ventilation, and group 3 consisted of six infants (7 to 28 days of age) who subsequently had bronchopulmonary dysplasia. Group 4 consisted of nine infants older than 1 month of age with confirmed bronchopulmonary dysplasia. Group 1 had significantly lower CRS and CRS normalized for body weight (CRS/BW) than group 2 had (P less than 0.001). In groups 3 and 4 CRS was significantly lower than in group 2 (P less than 0.001), as was CRS/BW (P less than 0.001). There was no significant difference in CRS and CRS/BW values between groups 3 and 4. This cross-sectional study in preterm infants with respiratory distress syndrome suggests that CRS may have predictive value in regard to development of bronchopulmonary dysplasia after the acute phase of respiratory distress syndrome.