Magnetic resonance spectroscopy of isoflurane kinetics in humans .2. Functional localization

We describe the first experiments to relate the kinetics of isoflurane (determined by magnetic resonance spectroscopy) to cerebral function. Using a surface receive coil we found two-compartment kinetics within the head with equilibrium half-rimes of 3.5 min and approximately 1 h with respect to expired isoflurane concentrations. Using critical fusion flicker frequency as an objective measure of the cerebral effect of isoflurane, we found evidence to identify the fast component as the brain. Responsiveness to command was lost at a brain partial pressure of 0.3% isoflurane. We conclude that the measured cerebral kinetics of isoflurane exactly matched the predictions of the classical perfusion-limited model.