Breathless Babies: Preemies' Lung Function Shows Prolonged Impairment

"We have shown that healthy preterm infants have reduced lung function in the first months of life that persists into the second year of life," said principle investigator of the research, Marcus Herbert Jones, M.D., Ph.D., professor in the Department of Pediatrics at Pontificia Universidade Catolica do Rio Grande do Sul in Brazil. "Healthy infants born prematurely may have smaller sized airways relative to the lung volume," he explained.

That premature infants have less well developed lungs than their full term counterparts is well established, but researchers were unsure if preemies underwent a "catch-up" period of lung function development. To determine if that was the case, Dr. Jones and colleagues recruited 26 preterm infants born between 30 and 34 weeks' gestation and compared their lung development and function to that of full term infants at about 10 weeks of age, then again at an average age of 15 months.

They found that lung capacity and development relative to body size was similar between the groups, but airway function was consistently lower in the premature infants at both evaluations.

"We were unable to detect a catch-up period during the study. There was no change in the rate of increase of lung function when compared to full term infants," said Dr. Jones.

Remarkably, the researchers also found that premature infants who had more fully developed lungs, thus less need for supplemental oxygen after birth, actually faced greater respiratory problems than those who required prolonged supplemental oxygen.

"It is a counterintuitive finding," said Dr. Jones. "My interpretation is that in preterm infants, supplemental oxygen may be a marker of a less mature lung, which may have a better long term respiratory prognosis than infants with accelerated maturation due to prenatal events such as infection and inflammation."

Maternal tobacco smoking was also associated with lower lung function in both premature and full term infants in both evaluations, suggesting a long lasting effect of smoke exposure on infant lung growth and development. The finding supports a number of other studies that have similarly found that maternal smoking adversely affects lung function in both full term and preterm infants.

While Dr. Jones and colleagues postulate that the preterm infants' reduced lung function may be due to airways that do not develop at the same rate as their lung volume, they also highlight other possible explanations, including more compliant airways, increased bronchial tone, or decreased pulmonary elastic recoil, and advocate further research to determine why preterm infants face persistent deficits in lung function.

"These subjects have decreased airway function not only in the first few months of life, but also at the one year follow-up evaluation," wrote Dr. Jones. "The persistence of reduced expiratory flows in healthy preterm infants may contribute to their increased risk of respiratory illnesses early in life."

The research was published in the second issue for December of the American Journal of Respiratory and Critical care medicine, published by the American Thoracic Society.