Figure 10. Conceptual framework depicting the temporal sequence of influence of the key cardiorespiratory factors on .

Note the regions of influence of lung volume (), cardiac output () and blood volume (), each with respect to metabolic O₂ consumption (). Hemoglobin content (Hb) influences the latter phase of stage 1 as well as stage 2. The impact of reduced is limited to stage 1, and blood volume to stage 2. Reduced causes a leftward shift in the desaturation trajectory. Note that the point of inflection at the transition between stages reveals the resting .