Pulmonary function during the first year of life in healthy infants born prematurely.

Premature birth is associated with increased respiratory morbidity. We investigated cross-sectionally, in 69 healthy infants who had never had cardiorespiratory problems, whether premature birth is associated with diminished pulmonary function. The study comprised 26 healthy infants born prematurely (PT), median gestational age 32 (26-36) weeks, and 43 healthy controls born full-term (FT), median gestational age 40 (37-42) weeks. Static respiratory system compliance (Crs) was assessed by weighted spirometry, combined with the measurement of the functional residual capacity by closed circuit helium dilution (FRCHe) and with assessment of ventilation distribution from the mixing index (MI). Repeatability of these indices was also assessed. Premature and full-term infants had the same length-corrected FRCHe; their Crs was different, but the difference disappeared when gestational age was taken into account. Mixing index was unrelated to body size and was not different between full-term and premature infants. Crown-heel length and lung volume were not different for any postconceptional age. However, infants born prematurely were smaller and had smaller lung volume at any postnatal age compared to those born at term. Repeatability of the indices was fair. These findings suggest that gestational age < 37 weeks is associated with normal respiratory system mechanics for body size, and normal distribution of ventilation in healthy infants who never had cardiorespiratory problems.