Tracings of volume (obtained by integration of the flow signal), flow, airway pressure (P_aw), and esophageal pressure (P_oes) in a representative patient with chronic obstructive pulmonary disease (COPD) during an end-inspiratory occlusion followed by an end-expiratory occlusion. Dashed lines indicate timing of occlusions. P_max, maximum value; P1, zero flow value; P2, plateau value; PEEPi, intrinsic positive end-expiratory pressure is the static end-expiratory recoil pressure of the respiratory system; P_plat, plateau value of P_oes after end- expiratory occlusion. Values of P_aw, P_max, used for calculations were corrected for the resistive pressure drop due to the artificial airway.