Figure 6. Impact of metabolic O₂ consumption () on .

Panel (A) shows the effect of doubling on arterial () and mixed venous () O₂ during apnea; (i) 10 ml min⁻¹kg⁻¹, (ii) 20 ml min⁻¹kg⁻¹ with cardiac compensation (CC), and (iii) 20 ml min⁻¹kg⁻¹ with no CC (nCC). Note that with CC, increased , from (i) to (ii), elevated uniformly at all levels of during both stages 1 and 2; note that the level of at the inflection point (shown by short black lines) is unchanged. With nCC (iii), increased caused a reduced resting and lower inflection, and greater during stage 1, compared to (ii). (B) Sensitivity of to changes in . Note that with increased : a uniform increase in occurred with CC, and a more-than-proportional increase was seen with nCC; is elevated in both cases, but more so with nCC; a uniform increase in is shown regardless of CC. n = ‘normal’ values; S1, stage 1 slope; S2, stage 2 slope.