ESTIMATION OF EXPIRATORY COLLAPSE OF INTRATHORACIC AIRWAYS - A COMPARATIVE STUDY OF VALUE OF FORCED EXPIROGRAMS AND FLOW CURVES IN HEALTH AND IN OBSTRUCTIVE LUNG DISEASE

Abstract

The influence of bronchodilating and bronchoconstricting drugs on the force expiration was analyzed in patients with severe airway obstruction by simultaneous registration of flow-rate volume and esophageal pressure. A corresponding analysis was performed in normal subjects. Forced expiration was started at various lung-volume levels. The contours of a forced expirogram are drug dependent: a "typical" inflected notched expirogram can be provoked by bronchoconstriction, whereas, in other patients, such a curve can be made smooth by bronchodila-tion. A notched expirogram was also observed in normal subjects when forced expiration was started at low lung-volume levels. The inflected notched shape of the expirogram is pathognomonic neither for patients with emphysema, nor for abnormal collapsibility of the airways. The expiratory-collapse volume of the intrathoracic airways was estimated from flow curves. The surface area of a flow curve can be divided into a bronchial component, which represents the gas expulsion from the bronchial tree by the initial tracheobronchial collapse, and an alveolar component, which represents the volume displacement from the alveolar space. The alveolar-component volume can be changed by drugs and depends upon the lung-volume level at which forced expiration is started. The bronchial-component volume is almost independent of these factors, and amounts to about 1/2 the anatomic dead space.