The venous admixture–mixed venous oxygen tension relationship. Venous admixture (Q_va/Q_t) plotted against mixed-venous oxygen tension (Pvo₂) during mechanical ventilation (rectangles in A and D), continuous positive airway pressure (diamonds in B and E), and unsupported spontaneous breathing (circles in C and F) with minor (s_min, open symbols in A–C) and major pulmonary shunt (s_maj, solid symbols in D–F). Thick lines represent the fixed effect of PvO₂ (dotted line, nonsignificant regression).