What regulates cerebral blood flow (CBF)?

From the Guidelines

Cerebral blood flow is primarily regulated through autoregulation, where cerebral arterioles constrict when blood pressure increases and dilate when blood pressure decreases, maintaining constant perfusion between mean arterial pressures of 60-160 mmHg. This regulation is crucial to ensure the brain receives consistent oxygen and nutrient supply despite changes in systemic blood pressure. Other mechanisms also play important roles, including:

• Chemical factors: increased carbon dioxide (hypercapnia) causes vasodilation, while decreased carbon dioxide (hypocapnia) leads to vasoconstriction 1
• Oxygen levels: hypoxemia triggers vasodilation to increase oxygen delivery
• Neurogenic control: sympathetic innervation provides mild vasoconstriction
• Metabolic coupling: ensures blood flow increases to brain regions with higher activity through mediators like adenosine, nitric oxide, and potassium ions
• Endothelial factors: nitric oxide and endothelin help regulate vascular tone

These mechanisms work together to protect the brain from ischemia during blood pressure fluctuations and ensure active brain regions receive adequate blood supply, which is critical since the brain lacks significant energy reserves and depends on continuous glucose and oxygen delivery 1. The most recent and highest quality study on this topic is not directly provided, but the principles of cerebral blood flow regulation are well-established in the medical literature, with studies such as 1 providing insight into the complex mechanisms involved.

Key factors that can affect cerebral blood flow regulation include:

• Systemic arterial pressure: any factor that decreases cardiac output or total peripheral vascular resistance can diminish cerebral perfusion pressure 1
• Venous filling: excessive pooling of blood in dependent parts of the body or diminished blood volume can predispose to decreased cerebral blood flow 1
• Carbon dioxide levels: low carbon dioxide tension can cause vasoconstriction and decrease cerebral blood flow 1

Overall, maintaining optimal cerebral blood flow is critical to preventing morbidity and mortality, and ensuring good quality of life, particularly in patients with conditions that affect cerebral blood flow regulation, such as aneurysmal subarachnoid hemorrhage 1.

From the Research

Mechanisms Regulating Cerebral Blood Flow

• Cerebral blood flow (CBF) is regulated by various mechanisms, including vasomotor, chemical, metabolic, and neurogenic mechanisms 2
• The regulation of CBF is critical for the maintenance of neural function and hence survival of the organism 3
• Important lipid mediators, such as 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs), act as reciprocal regulators of cerebral artery diameter 3

Role of the Autonomic Nervous System

• The autonomic nervous system, particularly the sympathetic innervation of cerebral arteries, plays a role in regulating CBF 2, 4
• Sympathetic tone helps prevent increases in CBF in humans, which is consistent with the view based on animal studies 2
• Neurogenic control of the cerebral vasculature is an important player in autoregulatory function and acts to buffer surges in perfusion pressure 4

Endothelial Control of Cerebral Blood Flow

• The cerebral endothelium plays a crucial role in regulating CBF through multiple modes, including chemical control of vascular tone, heterotypic and homotypic cell-cell interactions, and second messenger signaling 5
• Endothelial dysfunction is often associated with cerebral small vessel disease and compromised blood-brain barrier, highlighting the importance of understanding endothelial factors in regulating vessel function 5

Other Regulatory Mechanisms

• Cerebral autoregulation, which buffers CBF with changes in blood pressure, is an important mechanism of CBF regulation 4, 6
• The relationship between regulatory mechanisms, including blood gases, neuronal metabolism, and autonomic nervous system, is complex and interconnected 4