Figure 17-13 Lung volume plotted against transpulmonary pressure in a pressure-volume diagram for an healthy awake (normal) and an anesthetized patient. The lung compliance of the awake patient (slope of line AB = 100 mL/cm H₂ O) equals that shown for the small dependent alveoli in Figure 17-3 . The lung compliance of the anesthetized patient (slope of line AB' = 50 mL/cm H₂ O) equals that shown for the medium midlung alveoli in Figure 17-3 and for the anesthetized patient in Figure 17-12 . The total area within the oval and triangles has the dimensions of pressure multiplied by volume and represents the total work of breathing. The hatched area to the right of lines AB and AB' represents the active inspiratory work necessary to overcome resistance to airflow during inspiration (INSP). The hatched area to the left of the triangle AB'C represents the active expiratory work necessary to overcome resistance to airflow during expiration (EXP). Expiration is passive in the healthy subject because sufficient potential energy is stored during inspiration to produce expiratory airflow. The fraction of total inspiratory work necessary to overcome elastic resistance is shown by the triangles ABC and AB'C. The anesthetized patient has decreased compliance and increased elastic resistance work (triangle AB'C) when compared with the healthy patient's compliance and elastic resistance work (triangle ABC). The anesthetized patient shown in this figure has increased airway resistance to both inspiratory and expiratory work.