Neuroscience: Cerebral Blood Flow Concepts
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Questions and Answers

What percentage of cardiac output is taken by cerebral blood flow?

  • 15% (correct)
  • 10%
  • 20%
  • 25%

    • At what cerebral blood flow level is ischemia most likely to occur?

  • 25 mL/100g
  • 10 mL/100g
  • 20 mL/100g (correct)
  • 15 mL/100g

    • Which statement regarding the distribution of blood flow in the brain is true?

  • Greater blood flow occurs in the subcortex compared to the cortex
  • Blood flow is equal in gray and white matter
  • Cortex (gray matter) receives greater blood flow than subcortex (white matter) due to higher metabolism (correct)
  • Cortex and subcortex receive no blood flow

    • What is the consequence of an increase in the intracranial blood volume concerning the Monroe-Kellie hypothesis?

    <p>It results in a decrease in either brain volume or cerebrospinal fluid volume.</p> Signup and view all the answers

    How does a decreased pH (increase in H+ ions) affect cerebral blood flow?

    <p>Increases CBF - vasodilation</p> Signup and view all the answers

    What is the Monroe-Kellie hypothesis? (select 2)

    <p>It states that the total volume of the skull contents (brain, CSF, and intracranial blood) is fixed and must remain constant.</p> Signup and view all the answers

    Match the critical thresholds for cerebral blood flow:

    <p>Normal = 50 ml/100g Ischemia = 20 ml/100g Cortical suppression = ~15 ml/100g Cell death = &lt;15 ml/100g</p> Signup and view all the answers

    Which arterial structures primarily supply blood flow to the brain?

    <p>2 internal Carotid arteries (70%)</p> Signup and view all the answers

    CBF = CPP/CVR

    <p>True</p> Signup and view all the answers

    CPP= MAP-ICP or CVP The higher the ICP, the lower the CPP if MAP is stable

    <p>True</p> Signup and view all the answers

    How does Ohm's Law relate to cerebral blood flow (CBF)?

    <p>It defines the relationship between pressure, flow, and resistance. flow = pressure difference/resistance</p> Signup and view all the answers

    How does Poiseuille's law relate to cerebral vascular resistance? (select 2)

    <p>It shows the resistance is directly proportional to vessel length and viscosity</p> Signup and view all the answers

    Which of the following statements accurately describes Poiseuille's law?

    <p>It relates blood flow to vessel radius, length, and viscosity.</p> Signup and view all the answers

    Which of the following factors affect cerebral blood flow (CBF)? (Select all that apply)

    <p>Cerebral metabolic rate (CMR)</p> Signup and view all the answers

    Which of the following factors reduce cerebral metabolic rate of oxygen (CMRO2)? (Select all that apply)

    <p>Hypothermia</p> Signup and view all the answers

    What does it mean that cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) are coupled?

    <p>Brain flow varies to match metabolic activity</p> Signup and view all the answers

    How does age affect cerebral metabolic rate of oxygen (CMRO2)?

    <p>CMRO2 decreases with age due to reduced brain activity.</p> Signup and view all the answers

    Which of the following factors increase cerebral metabolic rate of oxygen (CMRO2)? (Select all that apply)

    <p>Hyperthermia</p> Signup and view all the answers

    What is the breakdown of oxygen utilization in the brain?

    <p>60% electrical activity, 40% cellular integrity</p> Signup and view all the answers

    What is the normal range for cerebral metabolic rate of oxygen (CMRO2) in adults?

    <p>3.0 - 3.5 mL/100g</p> Signup and view all the answers

    What is the effect of altitude on cerebral blood flow (CBF)?

    <p>CBF increases at high altitudes</p> Signup and view all the answers

    What is the mechanism behind high altitude cerebral edema?

    <p>Hypoxia leading to blood-brain barrier disruption and fluid accumulation</p> Signup and view all the answers

    Which physiological mechanisms contribute to compensation for increased cerebral blood flow (CBF) at high altitudes? (Select all that apply)

    <p>Increased respiratory rate</p> Signup and view all the answers

    At what temperature does cerebral blood flow cease due to protein denaturation and cellular death?

    <p>42 degrees Celsius</p> Signup and view all the answers

    What is cerebral autoregulation?

    <p>A homeostatic process that maintains constant cerebral blood flow (CBF) within the mean arterial pressure (MAP) range of 50-150 mmHg.</p> Signup and view all the answers

    Which of these factors is directly related to cerebral autoregulation? select 2

    <p>Cerebral metabolic rate</p> Signup and view all the answers

    What happens to the brain at mean arterial pressures (MAPs) above 150 mmHg?

    <p>Hyperemia raising intracranial pressure (ICP), causing compression and damage to the brain tissue, blood-brain barrier disruption, and cerebral edema</p> Signup and view all the answers

    What happens to the brain at mean arterial pressures (MAPs) below 50?

    <p>Ischemia (vasomotor paralysis), Loss of autoregulation, and cellular death</p> Signup and view all the answers

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

    <p>Autoregulation is shifted to the right, e.g., range can be from 80-180</p> Signup and view all the answers

    What is CPP?

    <p>The pressure at which vessels autoregulate CBF via vasodilation and vasoconstriction depending on MAP</p> Signup and view all the answers

    What effect do volatile anesthetics have on cerebral blood flow?

    <p>They increase CBF despite decreasing CMRO2 (uncoupling)</p> Signup and view all the answers

    What is the general effect of vasodilation on cerebral blood flow (CBF)?

    <p>Increase CBF</p> Signup and view all the answers

    What is the general effect of vasoconstriction on cerebral blood flow (CBF)?

    <p>Decrease in CBF</p> Signup and view all the answers

    What can cause increased cerebral blood flow (CBF) due to vasodilation? (Select all that apply)

    <p>Eicosanoids</p> Signup and view all the answers

    Which agents can cause decreased cerebral blood flow (CBF) due to vasoconstriction? (Select all that apply)

    <p>Calcium</p> Signup and view all the answers

    What is the relationship between PaCO2 and cerebral blood flow (CBF)? (select 2)

    <p>Directly proportional</p> Signup and view all the answers

    At what range does maximal cerebral vasodilation in response to PaCO2 occur?

    <p>80-100 mmHg</p> Signup and view all the answers

    At what range does maximal cerebral vasoconstriction in response to PaCO2 occur?

    <p>20-25 mmHg</p> Signup and view all the answers

    What mechanism directly controls cerebral vascular resistance?

    <p>pH of the cerebrospinal fluid around the arterioles</p> Signup and view all the answers

    Why does metabolic acidosis not directly affect cerebral blood flow (CBF)?

    <p>H+ in the blood does not cross the BBB</p> Signup and view all the answers

    Which scenario exemplifies the classic steal phenomenon?

    <p>Increased flow &quot;stolen&quot; from ischemic to a healthy area during vasodilation</p> Signup and view all the answers

    What is the clinical implication of using hyperventilation to cause vasoconstriction and inverse steal? (select 2)

    <p>Increased blood flow in hypoperfused areas</p> Signup and view all the answers

    What is the goal range for permissive hypocapnia?

    <p>30 mmHg</p> Signup and view all the answers

    What is the relationship between paO2 and cerebral blood flow (CBF)?

    <p>If paO2 is less than 50 mmHg, it results in vasodilation and increased CBF (inversely proportional).</p> Signup and view all the answers

    Why does a PaO2 level of less than 50mmHg of brain tissue result in immediate vasodilation?

    <p>To normalize cerebral blood flow (CBF) and promote oxygen supply to tissues as a protective mechanism</p> Signup and view all the answers

    What is the difference between hypoxia and hypoxemia?

    <p>Hypoxia is a deficiency of oxygen at the tissue level, while hypoxemia is a deficiency of oxygen in the blood.</p> Signup and view all the answers

    What is considered a normal cerebral perfusion pressure (CPP)?

    <p>80-100 mmHg</p> Signup and view all the answers

    CPP = MAP-ICP or CVP Higher CVP with a normal MAP will reduce CPP

    <p>True</p> Signup and view all the answers

    Match the cerebral perfusion pressure (CPP) values with their corresponding clinical results:

    <p>50 mmHg = EEG slowing 25-40 mmHg = Flat EEG &lt;20 mmHg = Irreversible tissue damage at normothermia</p> Signup and view all the answers

    How does an increased pH (a decrease in H+) affect cerebral blood flow (CBF)?

    <p>Decreases CBF - vasoconstriction</p> Signup and view all the answers

    What is the Circle of Willis?

    <p>A vascular structure that encircles the stalk of the pituitary gland and provides a collateral route for blood flow to the brain.</p> Signup and view all the answers

    What is considered normal intracranial pressure (ICP)?

    <p>10-20 mmHg</p> Signup and view all the answers

    What is defined as intracranial hypertension (HTN)?

    <p>Pressure greater than 20 mmHg</p> Signup and view all the answers

    What is Cushing's triad?

    <p>Late sign of increased ICP - Wide pule pressure, bradycardia, irregular respiratory patterns</p> Signup and view all the answers

    What causes hypertension in response to increased intracranial pressure (ICP)?

    <p>SNS activation to increase MAP and therefore CPP</p> Signup and view all the answers

    Why does bradycardia occur in increased intracranial pressure (ICP)?

    <p>As a result of PSNS activation in response to increased BP to maintain CPP</p> Signup and view all the answers

    Why do irregular respirations occur during increased intracranial pressure (ICP)?

    <p>Increased pressure on the brain affects the brainstem's respiratory centers.</p> Signup and view all the answers

    What are immediate ways to reduce intracranial pressure (ICP)? (Select all that apply)

    <p>Elevate head of bed (HOB)</p> Signup and view all the answers

    What methods can be used to reduce intracranial pressure (ICP)?

    <p>CSF drainage and surgical decompression</p> Signup and view all the answers

    What is the mechanism of action of mannitol?

    <p>Creates hyperosmolar environment in the blood (increase intravascular volume) so water is drawn down its gradient out of the brain cells into the blood stream</p> Signup and view all the answers

    How does Positive End-Expiratory Pressure (PEEP) affect cerebral blood flow (CBF)?

    <p>Increases CBF due to increased intrathoracic pressure and decreased venous drainage from the brain</p> Signup and view all the answers

    How does mannitol affect cerebral autoregulation to reduce intracranial pressure (ICP)?

    <p>It causes a transient increase in CBF due to hyperosmolality which triggers autoregulation to vasoconstrict and decrease CBF</p> Signup and view all the answers

    What are the complications associated with mannitol use? (Select all that apply)

    <p>Rebound ICP</p> Signup and view all the answers

    How does hypertonic saline reduce intracranial pressure (ICP) more effectively than mannitol?

    <p>By increasing systemic blood pressure to improve CPP</p> Signup and view all the answers

    What are complications associated with hypertonic saline treatment for increased intracranial pressure (ICP)? (Select all that apply)

    <p>Hypernatremia</p> Signup and view all the answers

    What effect does hypertonic saline have on glutamate release?

    <p>It decreases the release of glutamate from presynaptic terminals resulting in decreased excitotoxicity</p> Signup and view all the answers

    What is the relationship between intracranial compliance and intracranial elastance?

    <p>They are inversely related - as compliance increases, elastance decreases</p> Signup and view all the answers

    What is a consequence of high elastance?

    <p>A rigid system that is less able to accommodate volume changes without a sharp rise in ICP, posing a risk for conditions like herniation.</p> Signup and view all the answers

    Which of the following factors can increase intracranial volume? (Select all that apply)

    <p>Increased cerebrospinal fluid (CSF)</p> Signup and view all the answers

    What causes vasogenic brain edema?

    <p>Blood-brain barrier disruption</p> Signup and view all the answers

    What is the blood-brain barrier?

    <p>A tight junctional wall of endothelial cells, pericytes, and astrocyte end-feet that separates CSF from plasma.</p> Signup and view all the answers

    In which of the following structures is the blood-brain barrier (BBB) absent? (Select all that apply)

    <p>Posterior pituitary</p> Signup and view all the answers

    What can cause the blood-brain barrier (BBB) to become dysfunctional? (Select all that apply)

    <p>Tumor</p> Signup and view all the answers

    What is unique about the blood-brain barrier (BBB) in neonates?

    <p>It is poorly developed and more permeable compared to adults.</p> Signup and view all the answers

    Match the agent with its permeability to the blood-brain barrier (BBB):

    <p>Water and gases = Permeable Polarized, hydrophilic substances = Non-permeable Lipophilic substances = Permeable Proteins = Non-permeable</p> Signup and view all the answers

    What is a space occupying lesion?

    <p>Any abnormal tissue found on or in the brain due to disease or trauma</p> Signup and view all the answers

    Where is a supratentorial tumor located?

    <p>Above the tentorium cerebelli in the cerebrum</p> Signup and view all the answers

    Where is an infratentorial tumor located?

    <p>Below the tentorium cerebelli in the cerebellum</p> Signup and view all the answers

    Which types of cancers commonly spread to the brain when they metastasize? (Select all that apply)

    <p>Lung cancer</p> Signup and view all the answers

    What state is considered the beginning of loss of consciousness?

    <p>Disorientation</p> Signup and view all the answers

    What state indicates the deepest level of consciousness that is still responsive to stimulus?

    <p>Stupor</p> Signup and view all the answers

    What type of breathing indicates a rapidly deteriorating condition due to a medullary lesion?

    <p>Ataxic breathing /Biot's respirations</p> Signup and view all the answers

    What is decerebrate posturing? (select 2)

    <p>An abnormal body posture characterized by extension of the arms and legs.</p> Signup and view all the answers

    What is decorticate posturing? (select 2)

    <p>A rigid posture with arms flexed and legs extended, indicating severe brain damage.</p> Signup and view all the answers

    What does posturing indicate?

    <p>Brain herniation due to large increases in ICP</p> Signup and view all the answers

    What does the progression from decorticate to decerebrate posturing indicate in terms of brain herniation? (select 2)

    <p>Uncal brain herniation</p> Signup and view all the answers

    Which cranial nerves does the oculocephalic reflex assess? (Choose all that apply)

    <p>Cranial Nerve III (Oculomotor)</p> Signup and view all the answers

    What is the alternate name for the oculocephalic reflex?

    <p>Doll's eye reflex</p> Signup and view all the answers

    What is a normal response to the oculocephalic reflex test?

    <p>Eyes move in the opposite direction of head movement</p> Signup and view all the answers

    Which cranial nerves are assessed by the oculovestibular reflex?

    <p>CN 3, 4, 6, 8</p> Signup and view all the answers

    Calorics test eye movement to injection of water COWS = cold opposite, warm same

    <p>True</p> Signup and view all the answers

    Which cranial nerves are used to test the corneal reflex?

    <p>Trigeminal nerve (Cranial Nerve V)</p> Signup and view all the answers

    Which cranial nerves are involved in the gag reflex?

    <p>Cranial Nerve IX and X</p> Signup and view all the answers

    By what mechanism do volatile anesthetics uncouple cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2)? (select 2)

    <p>Vasodilation of cerebral vessels</p> Signup and view all the answers

    What occurs to cerebral blood flow (CBF) at a minimum alveolar concentration (MAC) of 0.5?

    <p>CBF decreases because CMRO2 &gt; vasodilation</p> Signup and view all the answers

    What is the effect of 1.5 MAC on cerebral blood flow (CBF)?

    <p>Increases CBF because vasodilation &gt; CMRO2</p> Signup and view all the answers

    What is an immediate way to balance a reduction in cerebral blood flow (CBF) caused by volatile agents?

    <p>Hyperventilation to cause vasoconstriction</p> Signup and view all the answers

    At what MAC level do the effects of vasodilation balance with cerebral metabolic rate of oxygen consumption (CMRO2)?

    <p>MAC 1</p> Signup and view all the answers

    How should you manage volatile agent delivery for patients with increased intracranial pressure (ICP)?

    <p>Use hyperventilation to cause vasoconstriction, thereby decreasing cerebral blood flow (CBF).</p> Signup and view all the answers

    What is a known negative side effect of enflurane?

    <p>Seizure activity</p> Signup and view all the answers

    What effect do induction agents have on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2)?

    <p>Decrease CBF and CMRO2 due to vasoconstriction</p> Signup and view all the answers

    Which of the following agents are used as anticonvulsants? (Select all that apply)

    <p>Barbiturates (sans methohexital)</p> Signup and view all the answers

    Which induction agent is unique for its cerebral vasodilatory properties?

    <p>Ketamine</p> Signup and view all the answers

    Which anesthetic agent is noted to decrease cerebral blood flow (CBF) without changes in intracranial pressure (ICP) or cerebral metabolic rate of oxygen (CMRO2)?

    <p>Dexmedetomidine</p> Signup and view all the answers

    Which anesthetic agent is noted for its increased concentration and effect with longer infusions?

    <p>Dexmedetomidine</p> Signup and view all the answers

    What effects do opioids have on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2)?

    <p>Minimally decrease CBF and CMRO2</p> Signup and view all the answers

    How do opioids alter intracranial pressure (ICP) through hypercarbia?

    <p>By decreasing respiratory rate</p> Signup and view all the answers

    What is unique about the response of large muscles to non-depolarizing neuromuscular blockade?

    <p>Large muscles are more resistant and therefore recover faster.</p> Signup and view all the answers

    Which induction agent causes the least reduction in cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow (CBF)?

    <p>Midazolam</p> Signup and view all the answers

    What is unique about quaternary amide anticholinergic agents such as glycopyrrolate?

    <p>They do not cross the blood-brain barrier.</p> Signup and view all the answers

    What is the effect of hyperthermia on the brain? (Select all that apply)

    <p>Increase cerebral blood flow (CBF)</p> Signup and view all the answers

    What is the endothelial mechanism of cerebral autoregulation? (select 2)

    <p>Endothelial cells release nitric oxide in response to increased blood flow.</p> Signup and view all the answers

    What is the primary way in which cerebral autoregulation is maintained?

    <p>Myogenic activity via variations of smooth muscle diameter</p> Signup and view all the answers

    Which channel primarily regulates membrane potential?

    <p>K+ channels</p> Signup and view all the answers

    What are the results of K+ channel inhibition? (select 2)

    <p>Decreased CBF</p> Signup and view all the answers

    What is the result of hyperpolarization on cerebral blood flow (CBF)? (select 2)

    <p>Vasodilation due to closure of Ca++ channels</p> Signup and view all the answers

    Which of the following would cause vasoconstriction and therefore decreased cerebral blood flow (CBF)?

    <p>Endothelin-1 (ET-1)</p> Signup and view all the answers

    What is the effect of hyperbaric oxygen therapy on cerebral blood flow (CBF)?

    <p>Increases cerebral blood flow.</p> Signup and view all the answers

    Which arteries are part of the anterior circle of Willis? (Select all that apply)

    <p>Anterior cerebral artery</p> Signup and view all the answers

    What effect does nitrous oxide have on CMRO2 and ICP?

    <p>Increases CMRO2 and ICP due to SNS activation</p> Signup and view all the answers

    Why do certain induction agents cause cerebral vasoconstriction?

    <p>Decreased CRMO2 resulting in decreased CO2 leading to vasoconstriction</p> Signup and view all the answers

    At what level does MAC amnesia occur?

    <p>0.2-0.4</p> Signup and view all the answers

    Which of the following factors increase intracranial compliance? (Select all that apply)

    <p>Hypocarbia</p> Signup and view all the answers

    Which of the following factors decreases intracranial compliance? (Select all that apply)

    <p>Hypercarbia</p> Signup and view all the answers

    How do astrocytes affect cerebral blood flow (CBF)?

    <p>They promote local vasodilation of arterioles</p> Signup and view all the answers

    What causes cytotoxic brain edema?

    <p>Swelling of neuronal or glial components from ischemia</p> Signup and view all the answers

    Which type of neoplasm is noted for its rapid growth?

    <p>Glial cell tumor</p> Signup and view all the answers

    Study Notes

    Monroe-Kellie Hypothesis

    • The sum of brain, CSF, and intracranial blood volumes remains constant.
    • An increase in one volume requires a decrease in one or both of the others.

    Cerebral Blood Flow (CBF)

    • Normal range is 50mL/100g of brain tissue.
    • Greater blood flow in the cortex (gray matter) compared to the subcortex (white matter).
    • CBF represents 15% of the body's cardiac output.
    • It is influenced by blood supply, perfusion, and cerebral vascular resistance.

    CBF Critical Thresholds

    • Ischemia occurs at 20mL/100g of brain tissue per minute.
    • Cortical suppression occurs at approximately 15mL/100g per minute.
    • Cell death can result from prolonged CBF below critical thresholds.

    Cerebral Blood Flow

    • The volume of the brain, cerebrospinal fluid (CSF), and intracranial blood is constant. If one volume increases, one or both of the other volumes must decrease.
    • Cerebral blood flow (CBF) is typically 50mL/100g of brain tissue.
    • The cortex (grey matter) receives more blood flow than the subcortex (white matter).
    • CBF receives 15% of the total cardiac output.
    • Factors influencing CBF include blood supply, perfusion, and cerebral vascular resistance.
    • Ischemia (restriction of blood flow) occurs at CBF of 20mL/100g.
    • CBF of approximately 15mL/100g leads to cortical suppression.
    • Cell death occurs when CBF falls below a certain threshold.

    Steal Phenomena

    • Cerebral vessels supplying ischemic areas are already maximally dilated.
    • Situations causing cerebral vasodilation, such as hypercapnia, can divert blood flow from ischemic areas to healthy areas, worsening ischemia.
    • Inverse steal is the concept that situations causing cerebral vasoconstriction, such as hypocapnia, can redirect blood flow from healthy areas to ischemic areas, potentially improving perfusion in the ischemic region.

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    Description

    This quiz covers key concepts related to the Monroe-Kellie Hypothesis and Cerebral Blood Flow (CBF). Understand how the volumes of brain, CSF, and blood interact, and learn the critical thresholds for ischemia and cell death. Test your knowledge of the normal CBF ranges and factors influencing cerebral circulation.

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