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Although surfactant deficiency at birth is the major cause of respiratory distress syndrome (RDS), there is insufficient data on surfactant and surfactant inhibitors after birth. In the present study, a total of 345 airway specimens (AS) from 61 neonates of gestational age of 24 to 29 wk (54 with RDS) were analyzed for concentrations of phosphatidylcholine (PC), saturated PC (SPC), surfactant protein A (SP-A), nonsedimentable protein, and free amino acids in epithelial lining fluid (ELF). The relationship between surfactant indices, surface activity, and severity of RDS was studied. Treatment with human surfactant containing SP-A increased PCELF and SPCELF to levels found in infants without RDS. In placebo-treated infants similar concentrations were first reached between Days 4 and 7. Surfactant treatment increased the low SP-A/SPC ratio, although this ratio remained lower than that in exogenous surfactant. In RDS, the concentrations of free amino acids in ELF were 6 to 31 times higher than in infants without RDS. The nonsedimentable proteins of AS and cationic amino acids increased the minimum surface tension of SP-A-deficient surfactant from AS. Addition of SP-A improved the surface activity. According to multiple regression analysis, In PCELF (p less than 0.0001), SPC/PC ratio (p less than 0.0001), In SP-A/SPC ratio (p less than 0.0002), and proteinELF (p less than 0.01) correlated with alveolar-arterial oxygen pressure gradient. Of the infants weighing less than 1,000 g, those who were going to die or develop bronchopulmonary dysplasia had a strikingly lower SP-A/SPC ratio during the first week (less than 25 ng/nmol) than those surviving without BPD.(ABSTRACT TRUNCATED AT 250 WORDS)
Hallman et al. (Sun,) studied this question.