Fig. 4.

Changes in gas exchange according to ventilation/ perfusion. This figure depicts changes in gas exchange according to ventilation (V’)/perfusion (Q’) alterations. On the left, normal gas exchange with normal V’/Q’. Above, venous admixture with three possible conditions: 1) low V’/Q’ with normal alveolar ventilation and increased capillary perfusion; 2) low V’/Q’ with decreased alveolar ventilation and normal capillary perfusion; and 3) true shunt with absent alveolar ventilation and variable capillary perfusion. Below, wasted ventilation with three possible conditions: 1) high V’/Q’ with normal alveolar ventilation and decreased capillary perfusion; 2) high V’/Q’ with normal capillary perfusion, and 3) dead space with normal capillary ventilation but absent perfusion.