Shifting concepts of autoregulation: Commentary to 'Static autoregulation in humans'

Abstract

Advances in imaging techniques have transformed our understanding of cerebral autoregulation. Older imaging techniques provided measurements of cerebral blood flow (CBF) that reflected the average CBF over a window of 10-20 minutes. A key finding, dating back to 1959, was that CBF remained more or less stable over a remarkably wide range of changes in blood pressure. Modern techniques can measure changes in CBF within the time frame of a heartbeat. They have revealed, paradoxically, a remarkable instability of CBF. This commentary attempts to reconcile these seemingly contradictory observations.

Keywords: Brain imaging; cerebral autoregulation; cerebral blood flow; hypertension.

Figure 1.

Static versus dynamic cerebral autoregulation. A schematic explanation of how Lassen’s classical autoregulation curve relates to the more recent curves derived from faster measurements of cerebral blood flow (CBF) and blood pressure (BP). Faster measurements allow us to study faster changes in BP and CBF. For slow changes, there is a wide plateau where CBF is relatively stable over a range of change in BP. As changes in BP become faster, the plateau shrinks, and in addition directional sensitivity may be revealed (different changes for decreases versus increases in BP). When changes in BP occur faster than the response time needed for autoregulation, there is an almost linear relationship between changes in BP and CBF.