REGIONAL DEPOSITION OF NEBULIZED HYPODENSE NONISOTONIC SOLUTIONS IN THE HUMAN RESPIRATORY-TRACT

Deposition of nonisotonic therapeutic and diagnosis aerosols can cause changes in airway fluid composition and bronchoconstriction in sensit ive subjects. ''Hypodense'' aerosols containing a relatively low conce ntration of droplets in the carrier air were used in the studies of re gional deposition of radiolabelled nebulized solutions of hypo- and hy pertonic saline, in order to investigate whether the number of droplet s per volume of carrier can affect deposition. Solutions with and with out 0.5% nedocromil sodium were nebulized in order to examine the effe cts of a potential modifier of the rates of heat and mass transfer. Th e deposition was quantified using penetration index (PI) calculated fr om images obtained by single photon emission computerized tomography ( SPECT) in 11 healthy volunteers per study. There was an increase in th e penetration index (10.9%, for the saline only; 15.5%, for the nedocr omil study) of the hypotonic compared to the hypertonic aerosol, altho ugh the initial size distribution of both types of aerosols was very s imilar (mass median aerodynamic diameter (MMAD) 3.7 and 3.8 mu m; geom etric standard deviation (GSD) 1.8 and 1.5 for the hypo- and hypertoni c aerosols, respectively). The present results confirm the effects of tonicity on deposition of aerosols found in a parallel study reported in this issue of the Journal. They also give support to the theory tha t, in addition to the concentration of the nebulized solutions, the nu mber of droplets per volume of the carrier air is a factor affecting d eposition of aqueous aerosols. The presence of 0.5% nedocromil sodium in the solutions did not appear to interfere with the processes of hea t and water transfer in the airways.