Importance of cloud motion on cigarette smoke deposition in lung airways

Deposition patterns of mainstream cigarette smoke were studied in casts of human extrathoracic and lung airways. The laboratory tests were designed to simulate smoking (ie., the behavior of undiluted cigarette smoke in smoker s' lungs), not secondary exposures to non-smokers. The experimental data re vealed concentrated deposits at well-defined sites, particularly at bifurca tions (most notably at inclusive carinal ridges) and certain segments of tu bular airways. The measurements suggest the occurrence of cloud motion wher ein particles are not deposited by their individual characteristics but beh ave as an entity. The observed behavior is consistent with the theory of Ma rtonen (1992), where it was predicted that cigarette smoke could behave aer odynamically as a large cloud (e.g., 20 mum diameter) rather than as submic rometer constituent particles. The effects of cloud motion on deposition ar e pronounced. For example, an aerosol with a mass median aerodynamic diamet er (MMAD) of 0.443 mum and geometric standard deviation (GSD) of 1.44 (i.e. , published cigarette smoke values) will have the following deposition frac tions: lung (TB + P) = 0.14, tracheobronchial (TB) = 0.03, and pulmonary (P ) = 0.11. When cloud motion is simulated, total deposition increases to 0.9 9 and is concentrated in the TB compartment especially the upper bronchi; p ulmonary deposition is negligible. Cloud motion produces heterogeneous depo sition resulting in increased exposures of underlying airway cells to toxic and carcinogenic substances. The deposition sites correlated with incidenc e of cancers in vivo. At present, cloud motion concentration effects per se are not addressed in federal regulatory standards. The experimental and th eoretical data suggest that concentrations of particulate matter may be an important factor to be integrated into U.S. Environmental Protection Agency (EPA) risk assessment protocols.