Normal pressure volume loop during positive pressure ventilation

During positive pressure ventilation, breaths progress on a pressure volume loop in a counterclockwise direction, with inspiration curving upward, and expiration curving downward, as shown by the arrows in this figure. Thus the upper right point on the graph represents peak inspiratory pressure and tidal volume. The lower left point of the loop appears at zero volume, and the set level of positive end expiratory pressure (PEEP). In this example, PEEP is set at zero.