PHYSIOLOGICAL FACTORS AFFECTING AIRWAY RESISTANCE IN NORMAL SUBJECTS AND IN PATIENTS WITH OBSTRUCTIVE RESPIRATORY DISEASE*

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Abstract
The effects on airway conductance (the reciprocal of airway resistance) of chest strapping, bronchomotor drugs, exercise, forced breathing, O2, CO2, and old age, were measured in normal subjects and compared with similar observations in patients with asthma, bronchitis and emphysema. Airway conductance was found to be dependent upon lung elastic pressure rather than on lung volume. This relationship was altered by bronchomotor drugs. Breathing O2 and different concentrations of CO2 did not alter the airway resistance. In several patients with mild asthma, airway resistance increased after forced breathing or exercise. In normal subjects, airway conductance appeared to depend upon a balance of forces between the tension in the airway walls and the opposing transmural pressure gradient due to the elastic traction of the lung. The airway conductance was found to be reduced and the balance of forces was altered in patients who had lower airway obstruction.