Cerebral Blood Flow, Energy Metabolism, And Metabolic Imaging

Front 1

if cerebral bloodflow is inhibited, how long will it take to lose consciousness? have irreversible damage?

Back 1

10 seconds. 3-5 minutes

Front 2

circulation through the brain depends upon what?

Back 2

perfusion pressure (difference between mean arterial pressure and the intracranial pressure) and the resistance to flow.

Front 3

what is the functional perfusion pressure of the brain?

Back 3

the mean arterial blood pressure, but under certain pathological conditions, the venous pressure and the intracranial pressure may raise, thus reducing the effective perfusion pressure

Front 4

cerebrovascular resistance depends upon what factors? what about functionally?

Back 4

viscosity of blood and vascular factors such as vessel diameter, length, and number of connecting vessels. functionally only the diameter of the vessels matter

Front 5

autoregulation keeps a constant CBF as long as the mean blood pressure does not drop to what? how does it accomplish this?

Back 5

60 mmHg or less, it accomplishes this by dilating the blood vessels in the brain over various BP ranges.

Front 6

when the blood pressure is too high, what does autoregulation do?

Back 6

constricts vessels to regulate CBF

Front 7

autoregulation of CBF is important for protection from and against what?

Back 7

against extracranial cerebrovascular disease, increased intracranial pressure, and decreased cardiac output. protection from changes in perfusion pressure due to changes in body posture

Front 8

physiologically, what is the major regulator of CBF?

Back 8

pCO2 in blood and cerebral tissues

Front 9

increased pCO2 will do what to the CBF?

Back 9

increase it via vasodilation

Front 10

how do temperature and oxygen affect CBF?

Back 10

not as much as CO2 does, but increasing PO2 generally decreases CBF and vice versa, while significantly increasing temp will increase CBF and vice versa

Front 11

cerebral vein blood is what compared to the bulk of venous blood

Back 11

less oxygenated

Front 12

oxygen to the brain is primarilly used for what?

Back 12

synthesis of ATP, the brain cannot perform anaerobic metabolism like most other organs

Front 13

does oxygen demand of the brain ever change?

Back 13

no, not even during sleep

Front 14

high energy consumption of the brain seems to be related to what?

Back 14

transport of ions to maintain electrical potentials, synthesize NT, enzyme replacement, and structural replacement

Front 15

what is the energy equation for the brain?

Back 15

glucose + O2 -> CO2, H2O, pyruvate and lactate

Front 16

the glucose dependence of the CNS is due to what?

Back 16

the blood brain barrier will not allow other substances in, not from an inability of the neural tissue to metabolize other things

Front 17

what does the brain do in states of hypoglycemia?

Back 17

it uses any available free glucose, then switches to the small amount of stored, slow moving glycogen stored in the glia. free amino acids are used next (especially aspartate and glutamate). Finally protein and lipid are degraded, but by this time irreversible damage will have occured.

Front 18

what is insulin's effect on the brain in terms of glucose uptake?

Back 18

none, but if hypoglycemia is due to increased insulin, the brain must compete with the muscles and liver for the glucose, thus intensifying the problem

Front 19

cerebral metabolic rate will fall when what occurs?

Back 19

brain function is impaired, before the metabolic rate is reduced by half, a coma will ensue

Front 20

how can seizures cause brain damage?

Back 20

the high energy demand of all those firing neurons complicated by possible ischemia due to lack of respiration leads to depletion of energy from the brain

Front 21

what compound can be used as a partial substitute for glucose in the brain during periods of starvation and suckling?

Back 21

ketone bodies

Front 22

what molecule is used to image metabolism in humans for PET scans?

Back 22

fluoro-2-deoxyglucose.

Front 23

how do PET scans and autoradiograms of cerebral blood flow give an indication of metabolic activity?

Back 23

autoregulation alters CBF in response to changes in local metabolism of tissues, BUT note that they do not correlate perfectly

Front 24

locations of epileptic foci and tumors in the brain usually show what in terms of CBF and GU (glucose uptake)?

Back 24

increases in both

Front 25

give a clinically important example of when the small dissociation between GU and CBF is important?

Back 25

dead tissue has no metabolic activity, but blood will flow through it, thus these levels maybe checked in damage heart tissue to determine the most appropriate surgery

Front 26

how does BOLD fMRI work?

Back 26

apparently when brain activity increases, GU increases, but O2 uptake from blood actually declines, thus there are reduced hemoglobin concentrations in veins draining metabolically active areas, and there is a magnetic difference between oxy hemoglobin and hemoglobin and this shows up on MRI