Figure 53-7 Normal and absent autoregulation curves. The "absent" curve indicates a pressure-passive condition in which cerebral blood flow (CBF) varies in proportion to cerebral perfusion pressure. This curve is drawn to indicate subnormal CBF values during normotension as have been shown to occur immediately after both head injury^[28] and subarachnoid hemorrhage.^[45] The potential for modest hypotension to cause ischemia is apparent.