Bidimensional VMR pattern for 4 healthy subjects. Bidimensional reactivity pattern as derived by the NIRS signals for four healthy subjects. Each red circle represents the instantaneous concentration of CO2Hb (horizontal axis) and O2Hb (vertical axis). All the values are normalized with respect to the maximum. The dotted lines depict the first and third quadrants bisectors. All the graphs present characteristics of the VMR pattern of healthy subjects and are almost always comprises into the region delimited by the two bisectors. 15 subjects showed patterns similar to A and B, 4 subjects showed a pattern similar to graph C, whereas graph D is relative to the subject that showed the shorter plateau region.