Hyperinflation is one of the most important pathophysiological mechanisms responsible for shortness of breath in COPD patients. Hyperinflation may be assessed in body pletysmography in which residual volume (RV) and total lung capacity (TLC) are measured. These parameters are considered to precisely reflect the degree of hyperinflation. In patients with COPD, an increased breathing frequency, e.g. during exercise or disease exacerbation, leads to dynamic hyperinflation which further increases shortness of breath.