Published ahead of print on August 6, 2003, doi:10.1164/rccm.200304-479OC Am. J. Respir. Crit. Care Med., Volume 168, Number 9, November 2003, 1123-1128 A more recent version of this article appeared on November 1, 2003
Submitted on April 3, 2003 Surfactant Protein Profile of Pulmonary Surfactant in Premature InfantsPhilip L Ballard1*,1 Neonatology, Pediatrics, Anesthesiology and Critical Care, University of Pennsylvania School of Medicine, Children's Hospital of Philadelphia, Philadelphia, PA, USA, 2 Pediatrics, The Mercy Children's Hospital, The University of Missouri-Kansas City School of Medicine, Kansas City, MO, USA * To whom correspondence should be addressed. E-mail: ballardp{at}email.chop.edu.
Although premature infants are known to be deficient in pulmonary surfactant, there is limited information regarding surfactant protein composition. To assess the postnatal profile of surfactant proteins, tracheal aspirate samples were collected from 35 intubated infants of 23-31 weeks gestation between 8 and 80 days of age. In 71 large aggregate surfactant samples that had a normal in vitro function (minimum surface tension <1 mN/m by pulsating bubble surfactometry) mean±SEM content of surfactant protein-A, -B, -C (3.7 kDa) were 7.1± 1.4%, 1.8±0.2%, and 4.6±0.6%, respectively, of phospholipid. To assess surfactant proteins in the first week of life, we analyzed samples from additional infants receiving only synthetic replacement surfactant. On the second day of life, content of surfactant protein-A, -B, and -C was 13.4, 8.4 and 0.1%, respectively, of the mean levels for day 8-80 samples. The major postnatal increases for SP-A, -B and -C occured during the first, second and third weeks, respectively. We conclude that surfactant of newborn premature infants is markedly deficient in surfactant proteins, in particular surfactant protein-C. Despite continuing lung disease, some infants >1 week of age have surfactant with normal in vitro function that contains surfactant proteins at levels comparable to adult surfactant. Key words: surface tension, tracheal aspirate, bronchopulmonary dysplasia
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