Lung volumes and expiratory flow during bronchoconstriction in asthma

Abstract

Bronchial asthma is characterized by excessive airway narrowing and hyperinflation. In this review, the mechanisms linking the increases of functional residual capacity (FRC) and residual volume (RV) to reduced airway calibre are analysed. The authors have shown that the increase in FRC is closely associated with the occurrence of flow limitation, i.e. the achievement of maximum flow during tidal volume; whereas, the increase in RV can be modulated by the magnitude of the bronchodilator effect of the deep inhalation during induced bronchoconstriction. It can be speculated that flow limitation contributes to the increase in FRC through a reflex mechanism; whereas, the increase in RV depends on the site of airway narrowing, which in turn determines the relationship between airway and parenchymal properties.