Static mechanical properties of bronchi in normal excised human lungs.

Bronchographic studies were performed on 22 normal human lungs at transpulmonary pressures between 20 and 0 cmH2O. Pressure-diameter behavior of 322 bronchi was evaluated. In younger (less than 40 yr) subjects, the airways of males showed greater recoil than those of females. No difference between sexes was seen in older (greater than 40 yr) subjects. Bronchi less than 2.1 mm diam had a significant decrease in recoil with increasing age in males but not in females. Small bronchi had greater recoil than large bronchi in both sexes in the younger group but not in the older group. The younger group had evidence of anisotropic behavior of the bronchi not seen in the older group. The percentage decrease in lung volume for a given decrease in transpulmonary pressure was less in the older than in the younger subjects in both sexes. Measurements of the cube root of lung volume, bronchial length, and the position of markers attached to the pleura indicated that the lungs deflated in an overall, isotropic manner down to a pressure of 3 cmH2O.