AEROSOL DEPOSITION IN INFANTS WITH CYSTIC-FIBROSIS

Twenty asymptomatic infants with cystic fibrosis (CF) were studied to determine the amount of radiolabeled aerosol [99m technetium diethylen etriamine penta acetic acid (Tc99m DTPA)] deposited in the respiratory system and its distribution. Aerosols were generated by jet nebulizat ion systems that were used in the wards and the laboratory. Subjects w ere studied in three groups: group A (n = 10) was sedated with chloral hydrate; children inhaled an aerosol of 7.7 mu m mass median diameter (MMD); group B (n = 5) was not sedated, using the same nebulization s ystem (same aerosol particle size as group A); and group C (n = 5) was not sedated; these children inhaled an aerosol with an MMD of 3.6 mu m. Normal saline plus 4 mCi of Tc99m bound to DTPA was added to each n ebulizer. A closed system was used to collect the expired aerosol. Rad ioactivity in each infant and in the equipment was measured with a gam ma camera on completion of nebulization. In groups A and B, the percen tages of the total dose deposited in the lung were 0.97 +/- 0.35% and 0.76 +/- 0.36%, respectively. In group C, 2.0 +/- 0.71% was deposited in the lung (P < 0.01). Deposition in the nose, mouth, and pharynx was least in group C (P < 0.01). In groups A and B, the intrathoracic dep osition occurred predominantly in the trachea and main bronchi, wherea s in group C, significantly more aerosol was deposited in the lung reg ion. There was marked inter-subject variability in the percentage of a erosol deposition within the three groups. There was no correlation be tween percentage of aerosol deposited in the respiratory system and ag e, height, or weight. Sedation did not have a significant effect on de position of aerosol in infants. This study indicates that only a small proportion of nebulized solution is deposited in the lungs of infants and that this proportion is influenced by the particle size of the ae rosol. The smaller particle size (3.6 mu m MMD) was deposited in the l ung better than large particles. (C) 1996 Wiley-Liss, Inc.