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. 2022 Nov 29;309:104000. doi: 10.1016/j.resp.2022.104000

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Fig. 5 — Changes in gas exchange according to ventilation perfusion after increasing FiO₂. This figure depicts changes in gas exchange according to ventilation (V’)/perfusion (Q’) alterations after increasing the fraction of inspired oxygen (FiO₂). Above, venous admixture with three possible conditions: 1) low V’/Q’ with normal alveolar ventilation and increased capillary perfusion that rising FiO₂ will determine marked increase of PaO₂ and P_AO₂; 2) low V’/Q’ with decreased alveolar ventilation and normal capillary perfusion that rising FiO₂ will determine increase of PaO₂ and marked increase of P_AO₂; and 3) true shunt with absent alveolar ventilation and variable capillary perfusion not modified by FiO₂. Below, wasted ventilation with three possible conditions: 1) high V’/Q’ with normal alveolar ventilation and decreased capillary perfusion that rising FiO₂ will determine marked increase of P_AO₂; 2) high V’/Q’ with normal capillary perfusion that rising FiO₂ will determine marked increase of P_AO₂, and 3) dead space with normal alveolar ventilation but absent capillary perfusion that with FiO₂ will not change.