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FHB exam one > Circulation 8 > Flashcards

Circulation 8 Flashcards

1
Q

Brain mass vs. blood demand

A

2% total body weight, but 15% of resting cardiac output

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2
Q

What is the brain’s main energy source?

A

Aerobic metabolism of glucose (needs a relatively large amount of oxygen and glucose)

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3
Q

What distance of capillaries does the brain contain?

A

400 miles

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4
Q

Blood brain barrier is due to what four things?

A

Endothelial cell tight junctions, basement membranes, neuroglial processes, metabolic enzymes

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5
Q

What types of substances can cross the BBB?

A

Lipid soluble substances such as oxygen, carbon dioxide, ethanol, and steroids, as well as those with transporters

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6
Q

What is the molecular weight cutoff for the BBB?

A

> 500 daltons (which includes most drugs)

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7
Q

Five factors affecting cerebral blood flow

A
  1. Autoregulation
  2. Tissue pressure (Monro-Kellie doctrine)
  3. Metabolism
  4. Autonomic nervous system
  5. Cushing’s response
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8
Q

Autoregulation of brain bloodflow

A

Maintains a consistent blood flow to the brain, but flow rates in differing areas of the brain will be dependent upon which part of the brain is active

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9
Q

CPP during normal states

A

80-100 mmHg

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10
Q

What happens with fluctuations in CPP?

A

If it falls - cerebral vasodilation

If it rises - cerebral vasoconstriction

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11
Q

Consequences of cranial rigidity on cerebral blood flow

A

Elevations in intracranial pressure will cause vascular compression, resulting in ischemia

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12
Q

Calculation of CPP

A

MAP minus intracranial venous pressure

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13
Q

Monro-Kellie doctrine equation

A

Brain volume + cerebral vascular volume + cerbrospinal fluid volume = constant

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14
Q

Monro-Kellie Doctrine

A

When the volume of one compartment increases, there must be a corresponding compensatory decrease in the volume of the other compartments

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15
Q

To what metabolite is cerebral blood flow very sensitive?

A

Arterial PCO2 (indirectly, pH)

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16
Q

Metabolic pH changes and blood flow

A

Decreased pH causes vasodilation and an increase in blood flow
Increased pH causes vasoconstriction and a decrease in blood flow

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17
Q

What effect does change in blood pH have on cerebral circulation?

A

Very little; H+ does not easily cross the BBB

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18
Q

Indirect effect of change of blood pH on cerebral blood flow

A

pH will change the amount of CO2 in the blood, which CAN cross the BBB and will rapidly change the amount of blood flow in the brain

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19
Q

How are patients with high intracranial pressures treated differently?

A

They are artificially ventilated at high rates to lower PCO2 levels, which vasoconstricts cerebral blood vessels and thereby decreases cerebral edema

20
Q

For what is O2 in cerebral flow mostly used?

A

It may have some play in cerebral vasodilation at decreased levels, but it mostly helps with metabolism changes during fMRIs

21
Q

When is adenosine formed?

A

In response to ischemia, hypoxia, hypotension, electrical stimulation of the brain, and seizures

22
Q

Timeframe of adenosine intervention

A

In situations that either reduce O2 supply or increase O2 demand, adenosine is formed within 5 seconds and remains elevated throughout event

23
Q

Mechanism of action of adenosine

A

Acts on purinergic receptors on vascular smooth muscle cells to activate ATP-sensitive potassium current, causing hyperpolarization, turning off calcium current and lowering intracellular calcium

24
Q

Mechanism of action of potassium ions

A

EC potassium concentrations increase in response to electrical stimulation of the brain and during seizures, hyperpolarizing and vasodilating vessels by stimulating Na/K-ATPase pump

25
Q

Parasympathetic cerebral control

A

A division of the facial nerve carries parasympathetic innervation to some cerebral vessels to cause vasodilation

26
Q

Sympathetic cerebral control

A

Exerts minimal vasoconstriction to increase cerebral vascular resistance

27
Q

Cushing response

A

An elevation of intracranial pressure can cause a decrease in cerebral perfusion

28
Q

What does cerebral ischmia stimulate?

A

Vasomotor centers in the medulla that increase sympathetic nerve activity, elevating systemic blood pressure

29
Q

Percentage of blood received: pulmonary vs bronchial circulation

A

100% - pulmonary

1% - bronchial

30
Q

Compliance in pulmonary vessels

A

7 times more compliant than systemic arteries due to minimal smooth muscle

31
Q

Mean pressure gradient in the lungs

A

6 mmHg

32
Q

What is different about the capillaries in the lungs than in the systemic circuit?

A

They have a major influence on vascular resistance: represent about 40% of resistance

33
Q

How is flow regulated in the pulmonary circuit?

A

Recruitment of new vessels; they do NOT autoregulate

34
Q

Effect of inspiration on the extra-alveolar vessels

A

Negative intrapleural pressure distends the vessels, decreasing resistance

35
Q

Effect of inspiration on the alveolar microvessels

A

Inflation of alveoli compresses and elongates the vessels, increasing resistance

36
Q

Net effect o inspiration

A

Slight increase or no change in pulmonary peripheral resistance

37
Q

Hydrostatic pressure in the lungs

A

Gravity and anatomy’s influence on distribution of pulmonary blood flow

38
Q

A change in 1 cm of height is equivalent to a change in hydrostatic pressure of __ mmHg.

A

0.74

39
Q

Vascular “waterfall” effect

A

In an upright person, height divides the pulmonary vascular system and blood flow into 3 “zones”

40
Q

Zone 1

A

Alveolar pressure exceeds both arterial and venous pressures, causing capillaries to collapse
DOES NOT EXIST UNDER NORMAL CONDITIONS

41
Q

Conditions under which zone 1 can be met

A

During hypotension or positive pressure mechanical ventilation

42
Q

Zone 2

A

Alveolar pressure exceeds venous pressure, but not arterial pressure, causing partial collapse of capillaries

43
Q

Conditions of zone 2

A

Upper third of the lung in a normal person

44
Q

Zone 3

A

Both arterial and venous pressures are greater than the alveolar pressure; flow determined by that gradient

45
Q

Conditions of zone 3

A

Primarily in the bottom third of the lung

FHB exam one (23 decks)

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