A Comparison of Cerebral Hemovelocity and Blood Oxygen Saturation Levels during Vigilance Performance

This study compared measures of cerebral blood flow velocity (CBFV) and blood oxygen saturation (rSO 2 ), during the performance of a 40-min vigilance task. Observers monitored a simulated air-traffic control display for flight path deviations which occurred in a unidirectional or a multidirectional context. CBFV and rSO 2 measures were secured from the medial cerebral arteries in the left and right cerebral hemispheres and from the corresponding frontal lobes, respectively. Performance efficiency was greater in the unidirectional than the multidirectional condition and declined over time in both conditions, more so in the multidirectional condition. This pattern of results was paralleled in different ways by the two hemodynamic measures. A result of this sort challenges the assumption of a close tie between cerebral blood flow and oxygen saturation (Siesjo, 1978) and supports recent findings (Mintun et al., 2001) that cerebral blood flow and oxygen levels are not tightly coupled in active brain states.