Factors That Affect Aerosol Targeting

Particles that penetrate beyond the oropharynx and enter the lower airways may deposit in two broad regions of the lungs the tracheobronchial zone and the pulmonary zone, as shown in Fig. 3 (13). Anatomically, it is assumed that the tracheobronchial zone is composed of the trachea and the larger conducting airways, whereas the pulmonary zone contains the smaller airways and alveoli. The extent to which particles deposit in either region is dependent on particle size, inspiratory flow rate, and lung volume at the time of inhalation (14). Whether a particle will impact or sediment also depends on the value of these parameters. For example, a small particle can deposit by impaction mechanisms when inhaled fast or by sedimentation when inhaled slowly. 

Several investigators have modeled deposition within the Inng as a function of particle size. Gerrity related particle size and regional deposition on a per airway generation basis, as shown in Fig. 4 (15). His calculations took into account the Landahl equations (9) and the Weibel-A lung model (16). This model 

Yeh and Shum developed a model for regional deposition on a per lobe basis instead of per airway generation. Airway dimensions to the terminal bronchioles were obtained from measurements of the cast of the lungs from a human cadaver. Information for generations beyond the terminal bronchioles 

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The model also predicts that regional deposition in the tracheobronchial region will be greatest in the lower left lobe for 1-, 2-, and 3-pm particles whereas deposition in the pulmonary region will be greatest in the lower right lobe for these same particles (17). 

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