A new hemodynamic model shows that temporal perturbations of cerebral blood flow and metabolic rate of oxygen cannot be measured individually using functional near-infrared spectroscopy.

A recent dynamic model relates the functional near-infrared spectroscopy (fNIRS) measurements to hemodynamic and metabolic parameters. This note reports modified expressions of the new model in terms of cerebral blood volume (CBV), blood flow (CBF) and metabolic rate of oxygen (CMRO2). On the basis of these modified expressions, the new model reproduces known steady state relationships between hemoglobin concentration, CBF and CMRO2, and yields time-dependent relationships that describe transient changes. This new model allows for the translation of the fNIRS measurements into dynamic measures of ΔCBV/CBV0 and the difference ΔCBF/CBF0 - ΔCMRO2/CMRO2|0, provided that some baseline physiological parameters and a relationship between overall, arterial and venous blood volume changes are assumed.