AVERAGE BLOOD-FLOW AND OXYGEN-UPTAKE IN THE HUMAN BRAIN DURING RESTING WAKEFULNESS - A CRITICAL-APPRAISAL OF THE KETY-SCHMIDT TECHNIQUE

The Kety-Schmidt technique can be regarded as the reference method for measurement of global average cerebral blood flow (average CBF) and g lobal average cerebral metabolic rate of oxygen (average CMRO2). Howev er, in the practical application of the method, diffusion equilibrium for inert gas tracer between the brain and its venous blood is not rea ched. As a consequence, normal values for CBF and CMRO2 of 54 ml 100 g -1 min-1 and 3.5 ml 100 g-1 min-1 obtained with the Kety-Schmidt techn ique are an overestimation of the true values. Using the Kety-Schmidt technique we have performed 57 measurements of CBF and CMRO2 during EE G-verified wakeful rest in young normal adults. In order to estimate t he equilibrium values for CBF and CMRO2, a simple computer-based simul ation model was employed to quantitate the systematic overestimation c aused by incomplete tracer equilibrium. When correcting the measured d ata, we find that the true average values for CBF and CMRO2 in the hea lthy young adult are approximately 46 ml 100 g-1 min 1 and approximate ly 3.0 ml 100 g-1 min-1. Previous studies have suggested that some of the variation in' CMRO2 values could be ascribed to differences in cer ebral venous anatomy. However in the present study, no correlation bet ween CMRO2 and cerebral venous anatomy as imaged by magnetic resonance angiography could be established. Our data show that the interindivid ual variation of CMRO2 is 11% (coefficient of variation).