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Cardio Exam 1 > 4 - Coronary, Pulmonary, Cerebral Circulations > Flashcards

4 - Coronary, Pulmonary, Cerebral Circulations Flashcards

1
Q

Polymorphic ventricular tachycardia can be classified as which of the following:

1 - Anatomically-defined reentrant circuit

2 - Functionally-defined reentrant circuit

3 - Spiral wave reentry

4 - Delayed afterdepolarization

A

Spiral wave reentry

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2
Q

What are the first vessels to branch from the aorta to supply the heart muscle with blood?

A

Left and right coronary arteries

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3
Q

What part of the heart does the right coronary artery supply?

A

The right coronary artery supplies the posterior left ventricle (LV) and right ventricle (RV)

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4
Q

What part of the heart does the left coronary artery supply?

A

The left coronary artery quickly branches into the left anterior descending artery, supplying the anterior LV, and the left circumflex artery, supplying the lateral LV free wall

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5
Q

How variable is this branching pattern from the right and left coronary arteries?

A

HIGHLY variable

Makes it hard to predict vessel of infarction

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6
Q

What are we able to determine in terms of the infarct location?

A

Distinct changes in the surface ECG can pinpoint the location of lesions/injury, just not the responsible vessel

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7
Q

Describe extravascular compression

A

When the major arteries of the heart, which lie on the epicardial surface in order to branch and supply the heart muscle, become compressed during systole altering blood flow

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8
Q

Describe blood flow through the coronary circuit during systole vs diastole

A

Blood flow through the coronary circuit is high during diastole (when extrasystolic pressure is low) and low during systolic muscle contraction, when extrasystolic pressure reaches its peak

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9
Q

What is meant by the terms phasic flow

A

The flow of blood through the coronary circulation is “phasic” meaning that it is high during diastole and low or absent during systole

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10
Q

Which coronary arteries are more sensitive to phasic flow

A

While the whole heart is subject to extravascular compressive forces, the LEFT heart is more severely affected

The subendocardial vessels are especially vulnerable and are a common site of ischemic injury

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11
Q

What other factors contribute to phasic flow?

A

The pressure differential between the aorta and right atrial pressures contribute to the phasic nature of the flow

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12
Q

How does wall tension of the blood vessels play a role in phasic flow?

A

Wall tension exerts an additional force during ventricular muscle contraction

The contracting muscle impeded flow by compressing on the vessel

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13
Q

What pathological condition increases the impact of wall tension or wall stress

A

Cardiac hypertrophy

The expansion of muscle tissue in the heart adds compressive forces and can compromise flow significantly in the setting of pump failure (decompensated heart failure)

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14
Q

What is the equation for blood flow?

A

Flow = ∆P/R

P = pressure
R = resistance

Change in pressure is calculated by (inlet pressure - outlet pressure)

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15
Q

Does resistance to blood flow increase or decrease in most disease states?

A

Increases

This can reduce flow to the subendocardium

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16
Q

What is coronary autoregulation?

A

A regulatory mechanism which aims to maintain a constant flow despite varying perfusion pressures by utilizing metabolic and myogenic mechanisms to influence vascular tone

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17
Q

What are myogenic mechansims that are used?

A

Stretch activated ion channels respond to pressure changes directly

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18
Q

What are metabolic mechanisms that are used?

A

Changes in the generation and release of by-products of cardiac work

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19
Q

How is oxygen an important regulator of vascular tone?

A

Role of oxygen

  • Even at rest, heart tissue has a high extraction rate of oxygen
  • When activity level is increased, a hypoxic signal is sent to increase coronary blood flow
  • The process to increase coronary blood flow is through to involve adenosine
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20
Q

Describe the adenosine hypothesis

A
  • ATP depletion occurs in cardiac myocytes
  • Adenosine is released and diffuses to nearby vascular smooth muscle cells
  • Adenosine binds to the A2 adenosine receptor
  • This acivates an intracellular signal cascade
  • The cascade ends in vasodilation by vascular smooth muscle relazation
  • This is a cAMP-dependent mechanism of vasodilation
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21
Q

What is the other role of adenosine in this situation?

A

Additionally, adenosine will act on A1 receptors on the myocytes to reduce inotropy and therefore metabolic demand.

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22
Q

What is coronary reserve?

A

Coronary reserve is the difference between autoregulation of flow and the capacity of flow to increase upon demand (full vasodilation)

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23
Q

How can disease processes affect coronary reserve?

A

The vasodilator capacity can be diminished by disease processes

  • Obstruction (thrombus, plaque) reduces vasodilatory potential
  • Heart failure and diabetes may cause an impaired vascular response to vasodilators by changes in expression of receptors and intracellular signalling molecules
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24
Q

What is the consequence of decreased coronary reserve

A

During diseases that severely limit the coronary reserve, even low intensity exercise like walking can strain the heart and cause anginal symptoms

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25
Q

What is another factor which can alter coronary blood flow?

A

Autonomic influence

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26
Q

What does it mean that sympathetic stimulation has a biphasic effect?

A
  • First phase of the response is constriction (due to adrenergic receptors)
  • Second phase of the response is vasodilation (to a much greater extent through the INDIRECT effect of oxygen demand)
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27
Q

Describe pulmonary circulation

A

The pulmonary circulation is the circulation that stems from the right ventricle through the pulmonary artery into the smaller arteries and arterioles

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28
Q

Where does the pulmonary circulation go from there? How does it get back to the heart?

A

Next, the pulmonary blood flow surrounds individual alveoli to optimize the surface area for gas exchange

Then, the blood reaches the venule and venous vessels which flow into two main pulmonary veins

The blood flows from the two main pulmonary veins into the left atrium

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29
Q

Is the resistance in the pulmonary circulation higher or lower than in the systemic circulation?

A

The resistance of the pulmonary circulation is much lower than the systemic circulation

30
Q

What contributes to the decreased resistance in the pulmonary circulation?

A
  • Vessels contain more elastic and less smooth muscle
  • Vessel lumens are larger than those in the periphery
  • Vessels are shorter, allowing resistance to be dramatically lowered
31
Q

Why is increased elastic and decreased smooth muscle useful for the pulmonary circulation?

A

Because the pulmonary circulation must accommodate the entire cardiac output with each ventricular ejection

These vessels have a greatly lowered or even absent myogenic response (vasodilation/constriction)

32
Q

What behavioral factor has an effect on the distribution of blood flow in the pulmonary circuit?

A

Upright posture

33
Q

How does upright posture effect pulmonary circulation?

A

Blood has to flow against gravity to perfuse the highest portion of the lung and can easily fall to perfuse the lower regions of the lung

34
Q

What does regional perfusion contribute to?

A

The development of differences in Starling forces to influence lung edema as the base of the lung is subject to higher capillary hydrostatic pressure

This means that the base of the lung requires optimal lymphatic drainage to maintain transcapillary exchange

35
Q

How does the pulmonary circulation passively regulate its circulation?

A
  • Recruitment: opening of previously closed capillaries
  • Distention: accommodation of increased blood volume

Both mechanisms can be present throughout the lung tissue at the same time to account for regional differences such as the effects of gravity

36
Q

How does the pulmonary circulation actively regulate blood flow?

A
  • Hypoxic vasoconstriction (most important)

- Ventilation-perfusion

37
Q

What is ventilation-perfusion?

A

Ventilation-perfusion is the term used to describe the processes by which the lung vasculature responds to the partial pressure of oxygen in the alveoli

38
Q

What is hypoxic vasoconstriction?

A

Hypoxic vasoconstriction denotes the very specific and particular effect in the lungs that alveolar hypoxia evokes a vasoconstriction to shunt blood away from poorly perfused regions; elsewhere in the body hypoxia elicits vasodilation

39
Q

If this short-term adaptation is implicated in the long-term, what are the consequences?

A

This short-term mechanism can cause pathological adaptions if activated long-term, as severe or prolonged hypoxia causes increased pulmonary vascular resistance and pulmonary arterial hypertension

40
Q

What are the two main blood supplies to the brain?

A
  • Internal carotids (branches of the common carotid arteries)
  • Vertebral arteries (branches of the subclavian arteries)
41
Q

What do the internal carotids supply?

A

Most of the forebrain

42
Q

What do the internal carotids become?

A

Branches off into the ophthalmic artery then becomes the middle and anterior cerebral arteries

43
Q

What do the vertebral arteries supply?

A
  • Brainstem
  • Cerebellum
  • Occipital lobe
  • Part of the thalamus
44
Q

What do the vertebral arteries branch into?

A

Branches into the posterior cerebral arteries and then contributes to the middle cerebral arteries and anterior cerebral arteries

45
Q

What does the posterior cerebral artery supply?

A

The occipital lobe and the choroid plexuses of the 3rd and 4th lateral ventricles and lower temporal lobe

46
Q

What does the middle cerebral artery supply?

A

deep structures of the brain

47
Q

What does the anterior cerebral artery supply?

A

frontal lobe and medial regions of cortex

48
Q

What is the role of the carotid sinus in regulating cerebral blood flow?

A

The carotid sinus has both mechanosensitive baroreceptor sensory nerve fibers and chemosensitive sensory nerve fibers

49
Q

What are the two categories of differences we see between capillaries in the CNS and capillaries in the systemic circulation?

A
  • Cellular differences

- Structural differences

50
Q

What are the cellular differences between capillaries in the CNS and capillaries in the systemic circulation?

A

In the CNS…

  • Capillary endothelial cells are enclosed by the endfeet processes of astrocytes
  • These astrocytes are in contact with neuronal cells
  • The capillaries are also in closer proximity to neurons, so the diffusion distance is shorter
51
Q

What are the structural differences between capillaries in the CNS and capillaries in the systemic circulation?

A

In the CNS…

  • Spaces between capillary endothelial cells are small
  • Neighboring endothelial cells are tethered together by a cytoskeletal complex
52
Q

How does dye act when injected into the systemic circulation? What about when its injected into the CNS?

A
  • Dye injected into CNS does NOT travel to the rest of the body
  • Dye injected into the systemic circulation goes everywhere EXCEPT the CNS

This phenomenon is called the blood-brain barrier

53
Q

What implication does the blood brain barrier have on medications meant to reach the CNS?

A

ONLY very small, lipid-soluble substances can diffuse through the CNS capillary endothelial cells

All other molecules require carrier-mediated transport

54
Q

What is meant by a circumventricular organ?

A

A brain structure which is said to be “outside” of the blood brain barrier

55
Q

Which brainstructures are circumventricular?

A
  • Subforical organ
  • Organum vasculosum of the lamina terminalis
  • Area postrema
  • Neurophysis
56
Q

What is unique about the CVOs or circumventricular organs?

A

these regions contain “sensory” machinery (e.g. ion channel distribution) that allow them to “taste” the peripheral circulation and refine neurotransmitter activity and hormone release to maintain equilibrium

57
Q

What is the result of some disease states on the blood-brain barrier?

A

The blood-brain barrier can become altered with disease and the transport of substances becomes dependent primarily on hydrostatic pressure

58
Q

What is the predominant level of regulation in the CNS?

A

The LOCAL level

59
Q

What does local regulation mean in the CNS?

A

Most regulation occurs in an autocrine/paracrine fashion rather than the extensive neural regulation seen in some organs

60
Q

What does autoregulation mean in the CNS?

A

Autoregulation is the maintainence of constant blood flow in the presence of changing perfusion pressure

61
Q

What factors affect (or can affect) autoregulation?

A

Arterial pressure is the main driving force to perfuse cerebral circulation

Intracranial pressure is usually low, so it is negligible

62
Q

What is the range of arterial pressures that autoregualtion can counteract in order to keep cerebral blood flow constant?

A

60 - 140 mmHg

This range is termed the “autoregulatory zone”

63
Q

What can happen to the autoregulation mechanism over a period of sustained hypertension?

A

It can “reset” so that both the upper and lower limits are elevated

64
Q

What is the clinical implication of this “resetting”

A

This is important when starting or stopping hypertension medication because periods of syncope (fainting) can occur with blood pressures lower than the “reset” range of autoregulation

65
Q

What is the metabolic mechanism of dealing with a high partial pressure of CO2 in the brain?

A

A high Pa of CO2 indicates high metabolism and the brain will increase cerebral blood flow

66
Q

What else has a similar effect?

A

Hypoxia, but much less of an effect is elicited than is in the case of carbon dioxide

67
Q

What is the myogenic (mechanical) response to stretch in the brain?

A

Vasoconstriction in order to maintain a constant flow

68
Q

What is the effect of intracranial pressure increasing?

A

Cerebral blood flow will steadily decline and brain activity will be impaired or cease - can cause blood vessels to be compressed

Examples are with trauma or edema

69
Q

What is the effect of temperature on cerebral blood flow?

A

Temp goes down, CBF goes down

Temp goes up, CBF goes up

70
Q

What is the effect of blood viscocity (hematocrit) and cerebral blood flow?

A

Viscocity goes down, CBF goes up

Viscocity goes up, CBF goes down

Cardio Exam 1 (15 decks)

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