Normal flow volume loop

Flow volume loops may be displayed on an anesthesia machine with inspiration above the horizontal axis, and volume increasing from left to right. When displayed this way, breaths progress in a clockwise direction, as shown by the arrows in this figure. Tidal volume (TV) is represented by the point on the volume axis where the flow curve crosses zero, and peak expiratory flow (PEF) occurs at the lowest point on the expiratory portion of the curve.