Figure 36-24 Flow (ordinate) versus volume (abscissa). A, Closed-chest positive-pressure ventilation under general anesthesia in a patient with severe airways obstruction and hyperinflation before surgery to reduce lung volume. The flow-volume curve shows inspiratory (negative) and expiratory (positive) flow on the ordinate, plotted clockwise from zero volume on the abscissa. Expiratory flow started with a sharp upward peak and then fell immediately to a low flow rate with convexity toward the volume axis, suggesting expiratory flow limitation. expiratory flow rate was so low that inflation of the next positive-pressure breath was initiated before expiratory flow reached zero. Because expiratory flow continued up to this point, there must have been intrinsic positive end-expiratory pressure (PEEPi). B, A similar closed-check flow-volume curve after lung resection shows that the characteristic pattern of expiratory flow limitation has disappeared and that expiratory flow rate fell to zero before inflation started for the next breath (i.e., no suggestion of PEEPi). (Adapted from Dueck R: Assessment and monitoring of flow limitation and other parameters from flow/volume loops. J Clin Monit Comput 16:425, 2000.)