Exam 3 Kirk 8: Special Circulation (Cerebral and Pulmonary) Flashcards
Brain only constitutes 2% of body weight but uses 15% of resting cardiac output
Because brain primarily uses aerobic metabolism of glucose it needs _____ supply of O2 and glucse
Brain is most _______ in the body
Of all tissues, brain is ______ to ischemia
Because brain primarily uses aerobic metabolism of glucose, it needs steady and large arterial supply of O2 and glucose
Brain is most metabolically active tissue in the bodu
Of all tissues, brain is LEAST tolerant to ischemia
The brain ____ have lymphatics
Brain does have lympatics
________ is an ring of cessels formed from two internal carotid arteries and two vertebral basilar system.
The two ______ are major blood supply to the circle
Three large paired vessels originate from the circle of Willis: ____, ____and ____
Circle of willis
the two internal carotid arteries are major blood supply to the circle
antetior, posteriar and middle cerebral arteries
What does the BBB do?
What can pass through it>
BBB limits transport of sunstances from the systemic circulation and the brain parenchyma
Lipid soluble substances (o2 co2 ethanol steroid hormones) and glucose can pass BBB
Most drugs and substances over 500 daltons can’t pass
_______ maintains a constant blood flow to the brain
However, regional blood flow is associated with _______ Therefore flow rates vary dependent upon
Autoregulation maintains constant blood flow to the brain
Regional blood flow is associated with regional neural activity, flow rates are dependent upon which part of brain is active at any given time
Cerebral perfusion pressure is normally between ______ mmHG
How does the brain compensate if
IF CPP falls….
If CPP rises…
What is the range for autoregulation?
Cerebral perfusion pressure is normally between 80-100 mmHg
If CPP falls, the brain will vasodilate
If CPP rises, brain will vasoconstrict
Autoregulation is normally seen between 70-140 mmHG. In hypertension, curve is shifted to the right in order to maintain normal blood flow at higher pressures
An increase in CSF pressure will _____ vascular resistance and _____ cerebral blood flow
What is normal CSF pressure.
As CSF pressure increases, cerebral blood flow ____ and metabolically activated ________ will dilate the arteries to maintain blood flow
BUT what happens when CSF increases above arterial pressure?
Increase in CSF pressure (pushing down on vasculature) will increase vascular resistance and decrease cerebral blood flow
Normal CSF pressure is at 12 mmHg. Therefore CSF pressure and venous pressure are the same.
As CSF pressure increases, cerebral flow decreases SO autoregulation will cause metabolically activated vasodilation to maintain the blood flow.
BUT at CSF pressure higher than arterial pressure (so higher than 100mmHg), cerebral blood flow decreases rapidly.
Monroe Kellie Doctrine says that the brain is within a compacted compartment, so which three things are added together to a constant volume?
What does that mean if one of the compartments increases in volume?
An intracranial hemmorhage will have an “effective” increase in brain volume, causing a _____ in vascular volume and a _____ in CSF. This will cause a ______ in pressure.
brain volume + CSF volume + vasculature volume = constant
If something increases, there must be a decrease somewhere else to compensate for it
Hemmorhage: effective increase in brain volume causes a decrease in vasculature volume and CSF volume… this will increase both vascular and CSF pressure
Cerebral blood blow is very sensitive to ____
Blood flow is normally effected by pH but pH ___ affect cerebral blood flow.
But changes in CO2 causes changes in cerebral blood flow because _____
Cerebral blood flow sensitive to Pco2
Blood flow normally affected by pH (pH causes vasodilation) BUT doesn’t affect brain because h+ can’t cross BBB
CO2 can cross BBB so it can affect cerebral blood flow
Inhalation of CO2 (high Co2 low pH) causes ______
Conversely, hyperventilation _____ Co2, causing ______.
Inhalation of CO2 causes vasodilation
(think about when you feel light headed, you’re supposed to breathe into and out of a bag, this increases Co2 you’re breathing in and causes vasodilation in you’re brain)
Hyperventilation causes DECREASE in Co2, causing vasoconstriction (which decreases blood flow, resulting in diziness or fainting)
Patients with high intracranial pressures due to head injury are treated by _________
There is a trade off though, what happens
Patients with cerebral edema are hyperventilation, which causes a decrease in PCo2 and therefore causes vasoconstriction
This decreases cerebral blood flow (that’s the trade off) which helos decrease the pressure but still a trade off
How is fMRI useful in determining which sides of your brain are working/doing metabolic activity?
Explain the Cushing Response
Cerebral ischemia activates both the ___ and the ___
What does each do?
Cushing response is what happens when you get an elevated intracranial pressure causing decreased cerebral perfusion and therefore ischemia
That ischemia results in activation of SNS and PSNS
The SNS (medulla) increases the blood pressure by vasoconstriction (alpha 1 receptors)
The PSNS acts on the heart to decrease HR
So patients with head trauma have an increase in BP but a decrease in HR
