Effect of age, sex, stature, and smoking habits on human airway conductance.

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Abstract
Regressions for respiratory airflow conductance against age and height have been calculated from measurements made by body plethysmograph in 82 normal subjects aged 17-82 years. The specif ic conductance (conductance /lung volume) was independent of age, height, and sex and a log-normal distribution. The distribution of conductance was also log-normal in both sexes. However, males with the lowest conductance deviated from this pattern, probably because they compensated by increasing their thoracic gas volume during the test. The airway conductance as measured by this technique was lower in old than in young smokers but rose significantly with age in male non-smokers; as a result, the conductance of the group as a whole was maintained in the elderly. This unexpected stability of conductance throughout life may have been partly due to increasing inequality of time constants in the lung and partly to adaptive increase in thoracic-gas volume (TGV). The specific conductance (conductance/TGV) showed a barely significant rise in old nonsmokers and was maintained in the group as a whole. However the correction for TGV is incomplete because of a positive intercept on the conductance versus TGV graph. The forced expiratory volume and, to a lesser extent, the peak flow, fell with age.