Figure 5.

Tidal volume encroachment by dynamic hyperinflation in COPD. In this figure the effects of respiratory rate and work rate on the end-inspiratory (EILV), end-expiratory lung volume (EELV), tidal volume (ie, EILV–EELV) and minute ventilation in subjects with severe COPD is displayed. While EILV increases with increasing respiratory rate from 20 to 30min⁻¹ (lower left panel), so does EELV resulting in an almost constant (encroached) tidal volume. At respiratory rates higher than 30, though, EILV does not increase any more, however, EELV further increases resulting in a reduced tidal volume and even a drop in ventilation (left upper panel) at respiratory rates higher than 35min⁻¹. In the right lower panel we can see how during progressive exercise tidal volume also decreases at high intensity due again to increase in EELV without parallel increase in EILV (Constructed with data from Puente-Maestu et al 2005).

Abbreviation: COPD, chronic obstructive pulmonary disease; EELV, end-expiratory lung volume; EILV, end-inspiratory lung volume; TLC, total lung capacity.