Maintenance of a constant blood flow despite alteration in arterial blood pressure. Probably due to a myogenic response but mechanism not known, Sympathetic nerves not necessary for response but may modify the position of the curve. Normotensives autoregulate between about 60 and 130 mean arterial pressure. Trauma and ischaemia reduce ability to autoregulate and these areas become extremely sensitive to high pressure. Additionally low pressure has more marked reduction in flow than normal because of microvascular changes.
Sympathetic nerves accompany the carotid arteries.
No sympathetic vasodilator fibres identified. Reset the autoregulation set point to the right. This effect similar in magnitude to a change in pCO2 of 1-2 mm Hg. These fibres innnervate mainly the large diameter vessels and hence may have more to do with cerebral blood volume than flow regulation. Chemical control - oxygen and carbon dioxide.