Quantitative aspects of perinatal lung growth

Weight, DNA, protein, hydroxyproline and disaturated phosphatidylcholine (DSPC) content were investigated in lungs of 97 normally formed infants over an age range from 22 to 75 postconceptional weeks, including 25 cases of hyaline membrane disease (HMD) and 13 small-for-dates infants (SFD). Lung weight and lung DNA relative to body weight were markedly lower in infants who died at 37-41 weeks than in those who died at shorter gestations or in early infancy. Total lung DSPC and DSPC concentration had a narrow peak at 36-41 weeks. The DSPC concentration per milligram of lung DNA in the first few months of infant life was similar to that in infants at 24 weeks gestation. Lung protein concentrations increased steadily but were variable at all ages. SFD infants had significantly higher concentrations of hydroxyproline and showed a peak DSPC concentration at an earlier gestation than the normals. Lungs of HMD infants showed some increase in hydroxyproline concentration but little other quantitative evidence of difference from the normals. We suggest that the relatively small lung size in many infants who die near term may result from recurrent intrauterine stress. Lung changes in small for dates infants are compatible with an advance in lung maturation, while the increased hydroxyproline concentration in the lungs of cases of HMD implies an early proliferative response to lung injury.