The maximal flow–volume curve. The isovolume flow–pressure curve (left) is created from measurements of pleural pressure and expiratory flow at different volumes of forced expiration. These measurements can be extrapolated to show a maximal flow–volume curve (right). Note that, at a volume specific pleural pressure, the maximal expiratory flow will be limited. VC, vital capacity. Reprinted from  with permission from Elsevier.