Sizing Evaporative Aerosols: The 'Man with Too Many Watches' Dilemma

摘要

Three of the articles in this issue(1-3) describe and compare various methods for sizing nebulized, evaporative aerosols, either by cascade impaction or laser diffraction. They all show differences between nebulizers and sizing techniques depending on the degree of evaporation that is allowed to occur before or during the sizing process itself. Although some of these methods seem better than others for distinguishing between different nebulizers, it is not clear which technique and measured size best reflects in vivo regional deposition in the respiratory tract (or to use the watch analogy, which gives the correct time?). As Abdelrahim and Chrystyn acknowledge "No large scale robust attempt has been made to investigate in vitro/in vivo correlations. Although the task to develop such robust correlations is not easy, it will help understand the clinical significance of different in vitro results as well as nebuliser comparability." Such studies are certainly needed, but it is our opinion that the most realistic in vivo size (and method for determining that size) should be assessed by comparing regional deposition studies for various nebulizers, sized with the proposed methods, to experimental findings for the regional deposition of radiolabeled nonhygroscopic (i.e., nonevaporative) aerosols.