Fig. 2.

Steady state behaviour of the models under different inputs. Steady state outputs of oxygenated haemoglobin (${\mathit{HbO}}_2$, top row), deoxygenated haemoglobin (HHb, middle) and cerebral metabolic rate of oxygen (CMRO₂, bottom) for varying values of four model inputs: mean arterial pressure (P_a, left column), arterial partial pressure of carbon dioxide (${\mathit{P}}_{\mathit{a}}{\mathit{CO}}_2$, centre left), arterial oxygen saturation (${\mathit{S}}_{\mathit{a}}{\mathit{O}}_2$, centre right) and relative metabolic demand (u, right). Results from previously published model B1M2 correspond well with those of BrainSignals for the first three inputs, but the responses to changes in demand diverge significantly. To better capture these responses, which are important for modelling functional activation, the metabolic submodel in BSX has been modified as described in Eqs. (1), (2), (3) and the accompanying text.