Dynamic lung hyperinflation and its clinical implication in COPD

Static lung hyperinflation is defined as the elevation of end-expiratory lung volume above its predicted value, with no increase in end-expiratory alveolar pressure, which remains equal to atmospheric pressure. Dynamic hyperinflation is the transient increase of this volume above the relaxation volume. In patients with COPD, dynamic hyperinflation is mainly determined by the mechanical properties of the respiratory system. Its measurement relies on plethysmography and, during exercise, inspiratory capacity. During exercise, dynamic hyperinflation attenuates expiratory flow limitation but increases the inspiratory loading and induces functional weakness of the diaphragm. It also has haemodynamic consequences and results in more rapid, shallow breathing and progressive reduction in dynamic lung compliance. These events explain exercise intolerance. Several approaches may help combat dynamic hyperinflation and its deleterious clinical effects: bronchodilators, hyperoxia, helium-oxygen mixtures, lung volume reduction surgery...