Fig 4. Hemoglobin saturation response at the capillary outlet for m = (ΔCBv/CBv)/(ΔCMR_O2/CMR_O2) = 2.

The lower plot depicts hemoglobin saturation following neural activation, mimicked by the four discrete physiological cases, namely, A to D. Once stimulation occurs, CMR_O2 increases, from its resting (basal) state, from 200 to 250 μmol/100g/min (case A) causing a drop in sO₂. Subsequently, CBv increases from 0.6 to 0.9 mm/s resulting in a steep increase in saturation (case B). Next, CMR_O2 reverts back to its basal level of 200 μmol/100g/min leading to a further increase in sO₂ (case C). Finally, CBv transitions to its resting state (case D) with the concomitant asymptotic drop in sO₂ to its basal value. The top and middle plots illustrate the duration of the activated and basal oxygen metabolic and blood velocity transitions, respectively. “Asym” stands for asymptotic values.