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1419 A PROTEIN INHIBITOR OF SURFACTANT IN THE AIRWAY SUCTION SAMPLES OF RDS INFANTS

RDS is precipitated by a surfactant deficiency. However, once ventilation has been initiated a complex pathophysiologic sequence of factors seems to influence disease severity. The lungs of the premature with surfactant deficiency are abnormally permeable to protein, and a specific protein from the vascular space of preterm lambs can enter the air spaces and disrupt surfactant function. We have previously demonstrated the presence of a similar inhibitor protein in the airways of infants with RDS. We have now developed a radioimmunoassay for the inhibitor from the human. We collected daily airway samples (AS) by deep suctioning from infants with RDS and from infants without RDS who were being ventilated for other reasons. Blood gas and respiratory assistance variables were recorded with collection of each AS. We then measured the amount of inhibitor by radioimmunoassay and the amount of phosphatidylcholine (PC), and expressed the results as the ratio of inhibitor to PC. Soon after intubation for RDS, the ratio was 6.4±0.5; the ratio decreased to 1.1±0.5 by 2 to 4 days before extubation and to 0.6±0.1 on the day of extubation. The ratio of inhibitor to PC was only 0.25±0.03 in samples from infants without RDS. The ventilatory pressures required to normalize PcO2 values correlated well with corresponding inhibitor to PC ratios from infants with RDS (r=0.85). This study documents a relationship between the severity of RDS and the ratio of inhibitor to PC in airway samples.