Typical flow volume curves at rest and with exercise by disease state. Panel A demonstrates a healthy subject. Panel B demonstrates the leftward shift of the curve with noticeable expiratory flow limitation during exercise (tidal expiratory loop exceeds the maximal expiratory flow envelope) seen in COPD. Panel C demonstrates the rightward shift of the curve but does not reveal expiratory flow limitation characteristic of ILD. Both Panels B and C show decreased IRV compared with the normal response in Panel A. Panel D demonstrates that in PAH, the exercise flow volume loop is similar to that in a normal patient.
