Influence of respiratory air space dimensions on aerosol deposition

Models used to estimate both total and regional deposition of aerosols in the human respiratory tract have been proposed by a number of individuals and groups. Although the values chosen by different investigators for dimensions of airways or other air spaces may differ significantly from each other, there is the common assumption that the normal human respiratory tract is structurally uniform and that dimensions and branching patterns may be considered as constants in the deposition equations. There has been, therefore, considerable emphasis on estimating the effects of particle size, size dispersion, tidal volume and respiratory frequency. Much less attention has been paid to the normal intersubject variability of the size of air spaces in spite of the obvious influence this would have on aerosol deposition. Work on deposition from our own laboratories, as well as published results of others on pulmonary anatomy, has lead to the conclusion that there is considerable anatomic variability among normal subjects. Aerosol deposition in individuals examined under nearly identical conditions has also shown considerable variability. This paper will discuss the similarity in range of anatomical differences and differences in deposition and the probable relationship between the two.