The Processes Involved in the Biologic Aspects of Pulmonary Deposition, Clearance, and Retention of Insoluble Aerosols

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Abstract
Inhaled insoluble particulates remain in the lungs and cause a tissue reaction only when and where the self cleaning mechanism of these organs becomes inadequate relative to the burden imposed. The pulmonary clearance mechanism is not too well understood; it has two components and both must work together. The upper respiratory tract components consists of a mucous blanket transported by the whipping action of cilia. The alveolar components also consists of a moving film of fluid which ultimately joins the mucous blanket. The pulmonary tissue reaction to insoluble particulates is located on the alveolar wall and serves to sequester the foreign material within nodules or plaques. This containment, however, is not necessarily permanent and the particulates may be mobilized under certain conditions. Such mobilization leads to the destruction of some of the nodules or plaques and to further clearance via the mucous blanket. Although a small portion of the particulates is capable of penetrating the alveolar membrane directly, then being transported via tissue fluid to lymphatic vessels and thence to lymph nodes; most of the dust that is ultimately transported to lymph nodes emanates from the sequestered exogenous material within nodules or plaques. The explanation of this transport is based upon conjecture but has some experimental support.

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