Cerebral autoregulation
Cerebral autoregulation is a process in mammals that aims to maintain adequate and stable
Cerebral autoregulation refers to the
This regulation of cerebral blood flow is achieved primarily by small arteries, arterioles, which either dilate or contract under the influence of multiple complex
Physiological mechanisms
Three different mechanisms are thought to contribute to the process of cerebral autoregulation. These are
Metabolic regulation
Metabolic regulation is driven by the difference between cerebral metabolism (demand) and oxygen delivery through cerebral blood flow (supply) and acts by means of a vasoactive substance. In principle, this is a negative feedback control system that seeks to balance blood flow to its demand.
Myogenic regulation
The effect of transmural blood pressure changes is directly detected by the vascular smooth muscle in arterioles, probably via a stress sensing mechanism. Then, the calibers are adjusted accordingly to keep blood flow constant.
Neurogenic regulation
The vascular smooth muscle actuators in the resistance arterioles are controlled via sympathetic innervation, receiving the input from the appropriate brainstem autonomous control center. Nitric oxide released by parasympathetic fibers may also play a role.
Assessment of cerebral autoregulation
In order to assess cerebral autoregulation one must at least continuously measure arterial blood pressure and cerebral blood flow. Because CO2 levels are of great influence to cerebral autoregulation it is recommended to also continuously measure CO2.
Measuring arterial blood pressure
Measuring cerebral blood flow
Quantification of cerebral autoregulation
The quantification of cerebral autoregulation always involves variation seen in cerebral blood flow in relation to changes in blood pressure. This blood pressure variation can either be evoked or spontaneous. Evoked blood pressure changes can be the result of:
- releasing leg cuffs that were inflated above systolic pressure
- breathing at a fixed rate
- performing a Valsalva maneuver
- performing squat-stand or sit-stand maneuvers
- lower body negative pressure
- pharmaceutical methods to raise or lower blood pressure
The quantification depends on the experimental setup and can involve methods such as regression, cross-correlation, transfer function analysis or fitting mathematical models.
Measuring and understanding cerebral autoregulation remains a big challenge. Despite great clinical interest and much research effort, benefit to patients has so far been limited.
See also
References
- ^ "CV Physiology | Autoregulation of Organ Blood Flow". www.cvphysiology.com.
- PMID 2201348.