Autoregulation of Blood Supply to the Brain

What is autoregulation of blood supply to the brain?

It is the ability of the brain to maintain a relatively constant blood flow despite changes in systemic blood pressure.

What is the normal rate of cerebral blood flow?

Approximately 50 mL per 100 grams of brain tissue per minute.

How does autoregulation control cerebral blood flow?

It maintains a relatively constant blood flow to the brain despite changes in systemic blood pressure.

What are the factors that can affect cerebral blood flow?

blood pressure

carbon dioxide levels, and metabolic demand.

What is the Monro-Kellie doctrine?

It states that the total volume inside the skull must remain constant

What are the effects of impaired cerebral blood circulation?

Impaired brain function, stroke, and other neurological deficits.

What is the normal rate of cerebral blood flow (CBF) in ml/100 g of brain tissue/min?

Approximately 50 to 65 ml/100 g of brain tissue/min.

What is the normal rate of cerebral blood flow (CBF) in ml/min?

750 to 900 ml/min.

Is the flow of cerebral blood normally greater in gray matter or white matter?

Greater in gray matter.

What percentage of the resting cardiac output does the cerebral blood flow receive?

15%.

What does CBF stand for in relation to the brain?

Cerebral Blood Flow.

What does MAP stand for in relation to the brain?

Mean Arterial Pressure.

What does ICP stand for in relation to the brain?

Intracranial Pressure.

What does CVR stand for in relation to the brain?

Cerebrovascular Resistance.

What is the formula for cerebral perfusion pressure (CPP)?

CPP = MAP - ICP

What is autoregulation in the context of cerebral blood flow?

The intrinsic capacity of resistance vessels in the brain to dilate and constrict in response to dynamic perfusion pressure changes, maintaining blood flow relatively constant.

What range of mean arterial pressure (MAP) does autoregulation maintain a constant cerebral blood flow?

65 mmHg – 140 mmHg.

What happens to cerebral blood flow in people with normal autoregulation when mean arterial pressure is reduced to 65 mmHg?

Acute reductions to as low as 65 mmHg do not cause major changes in cerebral blood flow.

What happens to cerebral blood flow in people with normal autoregulation when mean arterial pressure is increased to 140 mmHg?

Increases to as high as 140 mmHg do not cause major changes in cerebral blood flow.

What happens to the cerebral blood flow (CBF) curve in patients with chronic hypertension?

It is shifted to the right side.

How does the shift of the CBF curve in chronic hypertension partially protect the brain?

It shifts to higher blood pressures, protecting the brain from damaging effects of high blood pressure.

What are the factors that affect cerebral blood flow?

Autoregulation

chemoregulation,

neuronal regulation

endothelium-dependent regulation.

What is the myogenic response?

The initial dilation of the vessel in response to an increase in transmural pressure, followed by induction of vascular smooth muscle contraction due to Ca2+ influx because of muscle stretching and reduction in vessel diameter to eventually restore CBF.

What happens to the vascular smooth muscle (VSM) during the myogenic response?

It is stretched and leads to an influx of Ca2+ that induces VSM contraction.

How does an increase in transmural pressure affect vessel diameter initially?

It leads to the initial dilation of the vessel.

What is the ultimate effect of the myogenic response on vessel diameter?

A reduction in vessel diameter to restore CBF to its original level.

What effect does an increase in CO2 concentration in the arterial blood have on cerebral blood flow?

It greatly increases cerebral blood flow.

By how much does a 70% increase in arterial partial pressure of CO2 (Pco2) approximately affect cerebral blood flow?

It approximately doubles cerebral blood flow.

What is sympathetic supply?

The part of the autonomic nervous system that is responsible for the 'fight or flight' response.

What is the effect of sympathetic stimulation on cerebral autoregulation?

Sympathetic stimulation can override cerebral autoregulation, leading to vasoconstriction and increased cerebral blood flow.

What are the mechanisms that influence cerebral blood flow?

• Arterial blood gases (PaCO2 and PaO2)

• central hemodynamics

• cerebral metabolism

• neural mechanisms

What are the components of central hemodynamics that affect cerebral blood flow?

Blood pressure, including effects of hydrostatic pressure gradients.

What are the neural mechanisms that affect cerebral blood flow?

Extrinsic autonomic and sensory nerves

intrinsic neurons in close association with the vasculature within the brain parenchyma

How do the regulators of cerebral blood flow interact with each other?

There are strong interactions between these regulators.

What is the Monro-Kellie doctrine?

It states that the volume of intracranial components remains nearly constant due to the enclosure within the non-expandable skull.

What components does the Monro-Kellie doctrine refer to?

Brain, blood, and cerebrospinal fluid (CSF).

Why must there be an equilibrium between the volumetric components of the brain?

Because the brain is enclosed in the skull.

What happens to the volume of intracranial components after the closure of the fontanelles?

It remains nearly constant.

What are the different types of stroke related to impaired cerebral blood circulation?

• Haemorrhagic

• ischaemic

• transient ischaemic attacks

Which disease is associated with chronic reduction in cerebral blood flow?

Alzheimer's disease.

What condition involves the accumulation of cerebrospinal fluid in the brain?

Hydrocephalus.

Which condition is associated with cerebral oedema?

Impaired cerebral blood circulation.

What is stroke?

A neurological deficit due to an acute focal injury of the central nervous system (CNS) by a vascular cause.

What are the types of stroke caused by a vascular injury?

• Cerebral infarction

• intracerebral hemorrhage (ICH)

• subarachnoid hemorrhage (SAH)

In which types of strokes is autoregulation impaired?

Both ischaemic and haemorrhagic strokes.

What is the pial artery associated with in ischaemic stroke?

Penetrating vessel (intracerebral arteries) and its intraparenchymal components.

What happens after vessel occlusion in ischaemic stroke?

There is a vasodilatory response with flow diversion and inflammatory process in the ischemic area.

What occurs if the ischemic process is prolonged?

Inflammatory response increases

What happens when there is an interruption of blood flow within a specific territory?

It leads to a fall in cerebral perfusion pressure and a vasodilatory response.

What is the role of collateral circulation activation response in the case of impaired blood flow?

It promotes flow diversion to the ischemic region.

What is the penumbral region in the context of impaired blood flow and ischemic stroke?

It is the area of interest of many reperfusion therapies in acute ischemic stroke and represents potentially viable tissue that may be salvageable.

What factors determine the salvageability of tissue in the penumbral region?

The duration the tissue has been underperfused, the extent of collateral supply, and the integrity of cerebral autoregulation.

What are the consequences of endothelial dysfunction in impaired blood flow and ischaemic stroke?

Metabolic impairment, energy failure, free radical production, excitotoxicity, loss of calcium ion homeostasis, and activation of proteases.

What adverse events increase oxidative stress and mitochondrial damage in impaired blood flow and ischaemic stroke?

The cascade of adverse consequences such as metabolic impairment, energy failure, free radical production, excitotoxicity, loss of calcium ion homeostasis, and activation of proteases.

What results from oxidative stress and mitochondrial damage in impaired blood flow and ischaemic stroke?

Necrosis and apoptosis-mediated neuronal cell death.

What contributes to reperfusion lesions in the ischemic/penumbral area if reperfused?

Breakdown of the blood-brain barrier function, loss of mechanisms of cerebral autoregulation, and persistent distal microvascular occlusion.

What are the potential outcomes of reperfusion in the ischemic/penumbral area?

Reperfusion lesions such as hemorrhagic transformation, and/or the lack of clinical improvement despite flow restoration (futile recanalization).

What are the benefits of cerebral autoregulation in improving collateral response?

It maintains flow in ischemic surrounding areas and avoids reperfusion lesions.

How does optimal management of blood pressure depend on cerebral autoregulation?

It depends on the integrity of cerebral autoregulation to protect the brain from ischemia or hyperperfusion.

What can cause excessive levels of glutamate?

Ischemia, anoxia, hypoglycemia, or trauma.

How do glutamate and its synthetic agonists cause neuronal cell death?

By producing excessive Ca2+ influx.

What role do excitotoxins play in brain damage from a stroke?

They play a significant role in the damage.

What happens to the cells in the severely ischemic area when a cerebral artery is occluded?

They die.

What happens to the surrounding partially ischemic cells when a cerebral artery is occluded?

They may survive but lose their ability to maintain the transmembrane Na+ gradient.

What prevents the ability of astrocytes to remove glutamate from the brain's extracellular fluid?

Elevated levels of intracellular Na+.

What happens in the penumbra region when glutamate accumulates?

Excitotoxic damage and cell death occurs.

Apart from stroke, what other neurodegenerative diseases may excessive glutamate receptor activation contribute to?

Amyotrophic lateral sclerosis (ALS), Parkinson disease, and Alzheimer disease.

What is cerebral oedema?

Accumulation of extra edema fluid in the brain, compressing blood vessels and causing decreased blood flow and destruction of brain tissue.

How does cerebral oedema affect blood vessels?

It compresses the blood vessels, often causing seriously decreased blood flow.

What does cerebral oedema lead to?

A vicious cycle.

What are the effects of cerebral oedema on vasculature?

Edema compresses the vasculature and decreases blood flow.

What is the consequence of decreased blood flow due to cerebral oedema?

Brain ischaemia.

What happens to capillary pressure with arteriolar dilation in cerebral oedema?

Capillary pressure increases.

How does cerebral oedema affect the delivery of oxygen?

Decreases cerebral blood flow, reduces O2 delivery.

What happens to capillary permeability in cerebral oedema?

It increases, leading to more fluid leakage.

How does cerebral oedema affect the delivery of substrates needed for ATP?

Reduces delivery of substrates needed for ATP.

What is the consequence of decreased function of nerve cell membrane sodium pumps?

It causes decreased function of nerve cells.