Geometric and Dimensional Airway Models of Conductive, Transitory and Respiratory Zones of the Human Lung

Abstract

The rational analysis of the physical events associated with the movement of gases in the lung makes use of relatively refined models which reflect some of the properties of the airway system. Some investigators used simple airway models which did not need to be dimensionally defined (Otis et al., 1956; Fry and Hyatt, 1960; and others). Roher (1915) measured diameter and length of the elements of the bronchial tree (see p. 135) and constructed a dimensional model on which he based his reasoning on flow resistance in the human airways. In his study on the deposition of airborne particles in the lung, Findeisen (1935) proposed and used a dimensional airway model which has been widely applied subsequently (Landahl, 1959; and others) since it appeared to be the most complete information available (cf. Dittmer and Grebe, 1958). Unfortunately, Findeisens’ model conveys much erroneous information. It was not based on sufficient actual data and thus the dimensions of even the most proximal airways are not correct. In addition, the grouping of subsequent airways into nine categories with different “branching factors” is entirely inadequate to represent the pulmonary architecture. In studying the distribution of ventilation in the dog’s lung Ross (1957) measured the dimensions of a bronchial tree and designed a model which took special account of the irregular features of the dog’s airway system. This model is not directly applicable to the human lung because of significant architectural and dimensional differences in the two species.