Differences between cerebral and cerebellar autoregulation during progressive hypotension in rats.

Autoregulation in the brain is essential to the maintenance of perfusion and hence to the normal functioning of the organism in the face of various hemodynamic challenges. The existence of prodromal symptoms preceding fainting suggests that cerebellar autoregulation could be altered earlier than cerebral autoregulation during the development of hypotension. The purpose of this study was to compare cerebral and cerebellar autoregulatory responses to hypotension induced by two rates of hemorrhage 1.5 and 2.0 ml/min. Cortical blood flows were measured simultaneously using laser Doppler flowmetry in rats. With increasing rate of hemorrhage, the kinetics of autoregulation were maintained in the cerebrum, whereas it caused a progressive loss in the efficacy of autoregulation in the cerebellum.