Airway Resistance and Lung Compliance

Lung compliance may be defined as the volume change per unit pressure change.8 It is an expression of the elastic-like properties of the lung if it is measured at points on a pressure-volume curve at which air is not moving into or out of the lung. These points of no air-flow occur near the end of inspiration and again near the end of expiration. Compliance does not include air resistive changes which are the results of friction between the airstream and bronchial wall, turbulance, and other aerodynamic factors. However, studies of lung compliance should yield information about changes in pulmonary mechanics which, although separate from airway resistance, may be influenced by it. The present study represents an attempt deliberately to alter airway resistance by using a known bronchoconstrictor (histamine) in normal subjects and in patients with chronic lung diseases. The influence of this bronchoconstriction on compliance was observed and compared to the effect of hyperventilation.