auto-regulation of cerebralblood flow takes place at ?

Autoregulation Cerebral blood flow is "autoregulated" extremely well between aerial pressure limits of 60 and 140 mm Hg. That is, mean aerial pressure can be decreased acutely to as low as 60 mm Hg or increased to as high as 140 mm Hg without significant change in cerebral blood flow. And, in people who have hypeension, autoregulation of cerebral blood flow occurs even when the mean aerial pressure rises to as high as160 to 180 mm Hg. If the aerial pressure falls below 60 mm Hg, cerebral blood flow then becomes severely decreased. ref : guyton and hall