Regional Deposition of 3.6μm Particles in Subjects with Mild to Moderately Severe Asthma

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Abstract
Regional deposition of 3.6 μm (aerodynamic diameter) monodisperse Teflon particles labelled with 111In was studied twice in ten mild to moderately severe asthmatics. The subjects inhaled the particles with maximally deep inhalations at 0.51/sec. Lung retention was measured after 0,6,24 and 48 hrs using a profile scanner equipped with two 13 x 5 cm NaI crystals. The retentions after 24 hrs (Ret24) and 48 hrs (Ret48) were highly correlated, r = 0.98. Also Ret24 and Ret6 were well correlated, r = 0.85. There was a significant negative correlation between Ret24 and airway resistance (Raw). Ret24 tended to be lower in the asthmatics than in healthy subjects earlier studied at comparable Raw -values. In contrast to an earlier similar investigation in healthy subjects there was a rather poor reproducibility of the Ret24 values, also after standardizing for differences in Raw (r = 0.58). The study indicates that regional deposition can be studied by measurements of lung retention after 24 hrs and probably also after 6 hrs in mild to moderately severe asthmatics. This means that repeated measurements can be performed within rather short time periods with very low radiation doses.