The Relationship Between Airway Resistance, Airway Conductance and Lung Volume in Subjects of Different Age and Body Size12

Abstract

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 re- sistance to airflow, lengthening increasing resist- ance 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 tech- nique for comparing changes in airway resistance with changes in lung volume in an individual, since each measurement of airway resistance in- cludes 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. METHODSAirway resistance was measured by the method previously described by DuBois, Botelho and Comroe (7).The method has the advantage that the pressure changes in the body plethysmograph reflect changes in alveolar pressure rather than changes in pleural or esophageal pressure.The resulting measurements are therefore assessments of pure airway resistance uncomplicated by the effects of tissue viscosity which are included with 1 This investigation was supported in part under a contract between the Army Chemical Center and the Graduate School of Medicine, University of Pennsylvania.