The estimation of cerebral metabolic rate of O2 from Near Infra-Red Spectroscopy

The accurate estimation of cerebral metabolic rate of O2 (CMRO2) is still an unavailable but highly desired clinical tool. The addition of a further experimental variable to near infra-red spectroscopy (NIRS) allows more information to be gained than has previously been possible. A physiological model is presented here that can be used to estimate CMRO2 from measurements of oxy- and deoxy- haemoglobin and oxygen saturation. It is shown that under steady state conditions, CMRO2 can be estimated accurately, despite the system of equations being underdetermined, partly since the parameters that have to be provided are physiologically meaningful and thus unlikely to vary over a wide range. Initial simulations under dynamic conditions seem to support the hypothesis that dynamic changes in CMRO2 can also be estimated accurately, although this is still work in progress