Exercise-induced air trapping is referred to as dynamic hyperinflation. Patients with chronic obstructive pulmonary disease (COPD) are particularly susceptible to dynamic hyperinflation. Common questions include:
- What causes dynamic hyperinflation?
- What are its clinical manifestations?
- How is it diagnosed?
- What is the treatment?
The pathophysiology, clinical presentation, diagnosis, and treatment of dynamic hyperinflation in patients with COPD are reviewed here. The diagnosis and treatment of COPD are discussed separately. (See "Chronic obstructive pulmonary disease: Definition, clinical manifestations, diagnosis, and staging" and "Management of stable chronic obstructive pulmonary disease".)
Lung volumes remain stable when the tidal volume is completely exhaled prior to the initiation of the next breath. Tidal volume increases during exercise (figure 1). Therefore, maintenance of stable lung volumes requires that expiratory muscles be recruited to elevate pleural and alveolar pressure, increase expiratory flow, and force the increased tidal volume to be completely exhaled prior to the next breath.
Hyperinflation — Hyperinflation exists when the end-expiratory lung volume is increased, usually due to an airflow limitation. Hyperinflation acts as a compensatory mechanism. At higher lung volumes, there is decreased airway resistance and increased elastic recoil, resulting in improved expiratory flow. Two types of hyperinflation can be distinguished: static and dynamic.