Figure 9.

Typical flow-volume curves in (A): a healthy subject and patients with (B) COPD, (C) ILD, and (D) PAH. In the patient with COPD, there is a leftward shift of the curve with noticeable expiratory flow limitation during exercise (i.e., tidal loops at peak exercise exceed maximal expiratory envelope). In the patient with ILD, there is a rightward shift of the curve with no expiratory flow limitation and adequate reserves of inspiratory and expiratory flow at end exercise. Note the markedly reduced inspiratory reserve volume (IRV) in both ILD and COPD patients compared with healthy subject (IRV, TLC-end-inspiratory lung volume). In PAH; the flow-volume curve is close to the healthy subject due to absence of respiratory mechanical problem in most classical cases. Solid lines, maximal and tidal loops at rest; dashed lines, tidal loops at peak exercise; dotted lines, predicted normal maximal expiratory loop. COPD, chronic obstructive pulmonary disease; ILD, interstitial lung disease; TLC, total lung capacity; RV, residual volume; IC, inspiratory capacity; PAH, pulmonary arterial hypertension. Reproduced with permission from the publisher (O'Donnell et al., 1997, 1998).