Relationships between cerebral blood flow velocities and arterial pressures during intra-aortic counterpulsation

Abstract

Objective: To determine the effects of intra-aortic counter-pulsation (IABP) on cerebral blood flow velocity. Design: Prospective self-controlled study. Setting: University hospital surgical intensive care unit. Participants: Nineteen cardiac surgical patients requiring perioperative IABP assistance. Interventions: Simultaneous recording of transcranial Doppler middle cerebral artery blood flow velocity and arterial pressure in response to changes in the magnitude of augmentation and trigger ratio. Measurements and Main Results: Instantaneous cerebral blood flow velocities correlated with arterial pressures during IABP ( r = 0.650) at different magnitudes of augmentation and trigger ratios. The increase in arterial pressure during balloon inflation was associated with an increase in cerebral blood flow velocity, and the decrease in arterial pressure in response to balloon deflation was associated with a decrease in cerebral blood flow velocity that was dependent on the magnitude of augmentation. Different magnitudes of augmentation or trigger ratios had no effect on peak systolic cerebral blood flow velocity, mean cerebral blood flow velocity, mean arterial pressure, or the mean velocity-to-pressure ratio. Instantaneous cerebral blood flow velocity to arterial pressure ratios were lowest in response to balloon deflation at the time of pre-ejection. Conclusions: IABP modified the phasic profile of cerebral blood flow to reflect the arterial pressure waveform without affecting mean cerebral blood flow velocity. Peak systolic cerebral blood flow velocity was maintained in augmented beats despite the decreased systolic arterial pressure associated with afterload reduction. The acute decrease in cerebral blood flow velocity at pre-ejection was balanced by increased cerebral blood flow velocity during balloon inflation in diastole.