Figure 3.
A, Data from Weibel11 showing the average airway diameter at each generation of branching measured directly from an airway cast. The red square with error bars shows the mean diameter of the terminal bronchioles measured by McDonough et al9 using microCT scan. B, Comparison of the total cross-sectional area of all the airways in each generation of airway branching measured by Weibel11 to the total cross-sectional area of the terminal bronchioles measured from microCT images by McDonough et al.9 C, A retrograde catheter (arrow) placed in a small airway approximately 2 mm in diameter in the manner described in References 7 and 13. D, Chest radiograph from a living human with normal lung function where the bronchial pressure-measuring device developed by Yanai and colleagues14 was put in place through a bronchoscope. The direct measurement of the resistance of the small airways <2 mm in diameter provided in both postmortem human lungs7,13 and in living humans14 are consistent with Weibel’s measurements of a rapidly increasing total cross sectional area of the distal airways.