AEROSOL BOLUS DISPERSION AND EFFECTIVE AIRWAY DIAMETERS IN MILDLY ASTHMATIC-CHILDREN

The contribution of aerosol techniques, the estimation of aerosol bolu s dispersion and effective airway dimensions, to the clinical diagnosi s of paediatric asthma was studied. In 47 children, aged 11+/-2 yrs, w ith mild asthma (forced expiratory volume in one second (FEV,) 83+/-9% of forced vital capacity (FVC)) effective airway diameters were deriv ed from the recovery of inhaled 1 mu m sebacate droplets. Intrapulmona ry dispersion of inhaled boluses of 0.4 mu m droplets was studied, by characterizing the concentration distributions of droplets in the exha led air by their standard deviation and skewness. Effective airway dia meters increased in asthmatic subjects with increasing body size, and did not differ from those obtained in 16 healthy children of similar a ge and height. Standard deviation and skewness of particle boluses exh aled from shallow lung depths were higher in the asthmatic children th an the healthy children (e.g. standard deviation 91+/-17 ml vs 79+/-15 ml, skewness 0.38+/-0.16 vs 0.23+/-0.16, respectively, for boluses in 140 ml lung depth). The sensitivity and specificity of bolus dispersi on to detect alterations in lung function was comparable to that of FE V(1)/FVC, the most sensitive conventional lung function parameter in t he present study. There was no correlation between body height or lung function and bolus parameters. We conclude that aerosol measurements do not provide an obvious benefit for the clinical diagnosis of mild p aediatric asthma, but bolus dispersion supplies additional information on alterations in convective gas transport in the diseased lung.