Exercise-induced dynamic hyperinflation in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is an inflammatory lung disease caused by inhalation of noxious particles, most commonly cigarette smoking. The consequent changes in airways, lung parenchyma and pulmonary vasculature lead to increased resistive, elastic and threshold loads and impaired capacity of the respiratory muscle pump. COPD is characterized by progressive expiratory flow limitation. During exercise, increases in respiratory rate lead to shortening of expiratory time with consequent gas trapping. The resultant increase in end-expiratory lung volume is referred to as dynamic hyperinflation. Dynamic hyperinflation leads to further load-capacity imbalance with consequent increased neural respiratory drive to maintain ventilatory homeostasis, which is closely related to exertional breathlessness intensity. Neuromechanical dissociation, resulting in uncoupling of increased neural respiratory drive from ventilatory output, develops due to mechanical limitations on tidal volume expansion and reduced force-generating capacity of the diaphragm as dynamic hyperinflation progresses during exercise. This review provides an overview of methods of measuring dynamic hyperinflation in COPD and clinical interventions that aim to alleviate lung hyperinflation and improve exercise tolerance.