- The autoregulatory vessel calibre changes are mediated by interplay between myogenic, neurogenic, metabolic and endothelial mechanisms:
Myogenic Tone
- Thought to be the primary mechanism behind cerebral autoregulation
- Cerebral vascular smooth muscle vasoconstricts in response to increased wall tension and vasodilates in response to decreased wall tension
- Results in change of vessel calibre to maintain a constant cerebral blood flow
Metabolic Response
- Decreased perfusion due to a fall in perfusion pressure can lead to accumulation of metabolic products in tissue (H+/K+/adenosine/nitric oxide/CO2)
- Mediate cerebral vasodilatation and thus increased cerebral blood flow
- Important mechanism in smaller vessels that are subject to changes in the local environment
Neurogenic Response
- Vascular smooth muscle is under autonomic control and mediates vasoreactivity in small and medium sized vessels
- Thought to play minor role in autoregulation in health
- Differences in regional innervation in the brain may contribute to the pathophysiology of certain conditions such as PRES
Endothelial Response
- Endothelial tissue secretes a number of vasodilators and vasoconstrictors in a paracrine manner
- Thought to play a minor role in cerebral autoregulation