Deposition of inhaled aerosols in the human lung: From infancy to adulthood.

This narrative review discusses the effects that healthy aging has on particle deposition in the lungs. The lung structure and its size, breathing patterns and minute ventilation are all affected by age, from infancy through adulthood. These age-dependent variations in turn affect total and regional deposition in the healthy lung. While, for age-specific breathing patterns, overall deposition of inhaled particles tends to be higher in children than in adults, regional deposition is age- and particle size-dependent. For aerosols in the 1-5 µm size range, typical of pharmaceutical aerosols, deposition fraction in the upper respiratory tract is higher in children (<15 year old) than in adults while the opposite is observed in the intrathoracic lungs where deposition fraction is lower in children than in adults. However, compared to adults, children have smaller lung surface area over which the deposited dose is distributed. Consequently, the deposition rate per lung surface area is higher in the intrathoracic lungs of children than of adults. In adulthood, aging appears to have little effect on overall deposition during tidal breathing. However, for deep aerosol inhalation, studies suggest an increased deposition in the lung periphery with aging due to airway closure occurring at higher lung volume in the elderly than in young adults. These observations suggest that both therapeutic aerosol delivery and the adverse effects of particle matter exposure may be altered with age through the lifespan.