Validating deposition models in disease: what is needed?

To develop theoretical deposition models, assumptions are introduced to make the models computationally affordable. For this reason, experimental (in vivo) validation of such models is needed to give confidence to the assumptions being made. However, for an in vivo deposition experiment to be considered useful for validation of a model, a number of parameters must be measured in the experiment for input to the model. Ideally, these parameters would include time-dependent breathing flow rates during aerosol exposure, properties of the inhaled aerosol as a function of time during the breath (including particle size distribution, aerosol mass fraction, as well as hygroscopic properties, inhaled temperature and humidity if hygroscopicity is important), in addition to anatomical regional deposition data and detailed lung geometry measurements. Furthermore, because of the dependence of extrathoracic filtering on the inlet conditions at the mouth and the complexity of modeling deposition in this region, experimental data on the filtering properties of the mouth-throat are needed. Although some of the above parameters are impractical to measure with current experimental techniques, it would greatly aid the development of deposition models if as many of these parameters as possible were measured in future in vivo deposition experiments. Data exemplifying the importance of measuring the above parameters is discussed.