DIFFERENCES IN AEROSOL OUTPUT AND AIRWAYS RESPONSIVENESS BETWEEN THE DEVILBISS-40 AND DEVILBISS-45 HAND-HELD NEBULIZERS

Background - The DeVilbiss 40 glass hand held nebulisers have been wid ely used for airways responsiveness testing in epidemiological surveys of asthma. These nebulisers have been superseded in some recent studi es by the DeVilbiss 45 plastic hand held nebulisers with the assumptio n that they are interchangeable. This study compared the aerosol outpu ts of the DeVilbiss 40 and DeVilbiss 45 nebulisers and investigated wh ether there was any difference in the in vivo measurements of airways responsiveness when using the two nebuliser types. Methods - The aeros ol output of six DeVilbiss 40 and six DeVilbiss 45 nebulisers was calc ulated by weight loss per actuation, the usual method of calibrating n ebuliser output, and compared with the true amount of aerosol obtained measured by a fluoride tracer technique. Airways responsiveness was m easured twice in 13 asthmatic patients under identical conditions by t he Yan protocol using DeVilbiss 40 and 45 nebulisers in random order. Results - Weight loss overestimated the true aerosol output of both ty pes of nebulisers. Weight loss was similar for the DeVilbiss 40 and 45 nebulisers but the true aerosol output of the DeVilbiss 45 was nearly twice that of the DeVilbiss 40 nebuliser. The geometric mean PD20 val ues with the DeVilbiss 40 nebuliser was a mean 1.7 doubling doses of h istamine higher than that obtained with the DeVilbiss 45 nebuliser. Co nclusions - The Devilbiss 40 and 45 nebulisers should not be used inte rchangeably far airways responsiveness testing merely because their ou tputs based on weight loss are similar. Artefactual differences in the prevalence rates of airways responsiveness could occur in longitudina l studies if a change was inadvertently made from using DeVilbiss 40 t o DeVilbiss 45 nebulisers.