[Importance of air-trapping in patients with COPD. Pathophysiological principle].

Exertional dyspnea is the leading symptom in patients with COPD. The main causes are progressive weakness of skeletal muscles, reduction of diffusing capacity in emphysema and above all dynamic hyperinflation as a result of the collapsibility of bronchioli with expiratory flow limitation. The exercise-induced hyperinflation leads to a reduction of inspiratory capacity. Therefore, patients are unable to increase the minute volume under exercise. The inadequate ventilatory answer to an increased ventilatory drive is perceived as dyspnea. The inhalation of long-acting bronchodilators reduces hyperinflation and increases exercise capacity.