Dynamic changes in lung volumes during exercise in normal lungs and COPD

Dynamic changes in lung volumes during exercise in normal lungs and COPD. Note that end-expiratory lung volume (EELV) remains relatively constant in normal lungs as minute ventilation increases. Tidal volume (VT) is able to expand, since inspiratory volume (IC) remains constant. In COPD, increases in EELV force VT closer to the total lung capacity (TLC) and IC is reduced even at rest. Dynamic hyperinflation further increases EELV and reduces IC as minute ventilation increases. VT is unable to expand and patients cannot achieve high minute ventilations before breathing becomes so restricted that patients have to stop activity.