Regional Deposition: Targeting

Patterns of regional aerosol deposition within the lungs are known to vary in a predictable manner with a number of factors, most notably aerodynamic particle size and inhalation pattern. Targeting deposition involves the intentional manipulation of one or more of these factors to promote aerosol deposition in certain locations within the respiratory tract. This section will begin by exploring existing evidence supporting the need to target regional deposition. Thereafter, various approaches to targeting will be introduced. In addition to control of aerodynamic particle size and inhalation pattern, a collection of approaches are available through which to passively target deposition to more central or peripheral lung regions. These include the delivery of short aerosol boluses at prescribed time points in inhalation, control of transient hygroscopic aerosol size changes during transport through the respiratory tract, and use of alternative carrier gas mixtures such as helium/oxygen mixtures. Comparatively, targeting aerosol deposition locally to very precise, spatially-defined lung regions is in its infancy. Early, exploratory techniques used for local targeting will be described. The continued evolution of deposition targeting towards ever more specific locations within the lungs is required to explore fundamental research questions in aerosol medicine: namely, how precise does targeting need to be before additional refinement fails to produce appreciably different therapeutic effects, and which nascent applications of aerosols in medicine might benefit from more selective regional targeting?