The relationship between airway resistance, airway conductance and lung volume in subjects of different age and body size.

The resistance of the airways to the airflow through them depends on the radius, length and number of the airways. It has long been apparent (1, 2) that the bronchi are distended as well as lengthened in the inspiratory position of the lung. These two changes in the dimensions of these airways would have opposite effects on their resistance to airflow, lengthening increasing resistance and widening reducing it. More recent measurements of airway resistance have shown that it is reduced in the inspiratory position of the lung (3, 4, 5) and is more in individuals with small lungs (6). The body plethysmograph affords a good technique for comparing changes in airway resistance with changes in lung volume in an individual, since each measurement of airway resistance includes as an essential stage in its derivation, a measurement of intrathoracic gas volume. It therefore seemed desirable to explore further the relationship between airway resistance and lung volume at different degrees of inflation of the lung in normal subjects.