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Cardiovascular > SM 134 Coronary Blood Flow > Flashcards

SM 134 Coronary Blood Flow Flashcards

1
Q

What determines Oxygen Demand?

A

Hemodynamic factors such as:

Wall Stress
Heart Rate
Contractility

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2
Q

What is the Double Product?

A

An index of Oxygen Demand defined as:

HR * Peak Systolic BP

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3
Q

How does oxygen demand relate to coronary flow?

A

Changes in Myocardial demand require changes in coronary flow

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4
Q

What percent of coronary flow is used at rest in a healthy individual?

A

6%

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5
Q

What are the components of Resistance to coronary flow?

A

Total coronary resistance is the sum of:

Condiut Artery Resistance (R1)
Microcirculatory Resistance (R2)
Compressive Resistance (R3)
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6
Q

What is Conduit Artery Resistance?

A

Resistance in the Conduit Arteries found on the surface of the heart

Normally small and affected by endothelial and autonomic factors as well as atherosclerosis

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7
Q

Where are Conduit Arteries found?

A

Conduit Arteries are found on the surface of the heart

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8
Q

How are Conduit Arteries, Microcirculation, and the Muscle of the heart related?

A

Conduit Arteries on the surface of the heart project into the muscle of the heart using Microcirculation Arteries

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9
Q

What is Microcirculatory Resistance?

A

Primary mechanism by which flow adjusts to demand and how flow is kept constant when arterial pressure changes

Normally high, relates the caliber of arterial microvessels and open capillaries

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10
Q

What is Poiseuille’s Law Significance?

A

Says resistance is inversely proportional to radius to the fourth power

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11
Q

How is R2 regulated?

A

On a local basis, at each given artery branch

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12
Q

What types of factors regulate R2?

A

R2 is regulated by Metabolic, Endothelial, and Neurohumoral factors

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13
Q

Which Metabolic Factors regulate R2?

A

Metabolic regulators of R2 include:

Adenosine, PO2

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14
Q

Which Endothelial Factors regulate R2?

A

Endothelial regulators of R2 include:

EDRF/Nitric Oxide
Endothelial Derived Hyperpolarizing Factor (EDHF)
Prostacyclins
Endothelins

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15
Q

What is EDRF?

A

Endothelial Derived Relaxing Factor = Nitric Oxide

Made continuously in Endothelial cells, rate varies directly with flow

Vasodilator

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16
Q

How does coronary flow related to EDRF levels?

A

EDRF/Nitric Oxide levels scale directly with flow

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17
Q

What is EDHF?

A

Endothelial Derived Hyperpolarizing Factor = EDHF

Flow-induced vasodilation

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18
Q

What are Prostacyclins?

A

Continuously made by the COX pathway

Vasodilators

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19
Q

Which Neurohumoral agents regulate R2?

A

Autonomic Nervous System and circulating vasoactive agents, alpha adrenergic vasoconstriction and beta adrenergic vasodilation

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20
Q

What effects do alpha adrenergic agonists have on circulation?

A

Alpha = vasoconstrict

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21
Q

What effects do beta adrenergic agonists have on circulation?

A

Beta = vasodilate

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22
Q

What causes Compressive Resistance (R3)?

A

Compression of coronary blood vessels during Systole

23
Q

How does Compressive Resistance set the perfusion of the heart?

A

Compressive Resistance rises so greatly in Systole that perfusion of the heart during Systole is a fraction of what occurs during Diastole

24
Q

How does Compressive Resistance vary?

A

Compressive Resistance is greatest in the innermost portion of the ventricular wall and decreases across the wall

25
Q

How does Compressive Resistance affect Microcirculatory Resistance?

A

Compressive Resistance is greatest in the innermost portion of the ventricular wall, which forces Microcirculatory Resistance to compensate by decreasing via vasodilation to ensure adequate blood flow

26
Q

What is Coronary Autoregulation?

A

Idea that Coronary Microvascular Resistance adjusts to keep flow at the level appropriate to Myocardial demand

27
Q

What is Reactive Hyperemia?

A

Increase in coronary flow that follows a brief period of coronary artery occlusion

28
Q

What is the Coronary Flow Reserve?

A

Ratio of flow during Maximum coronary vasodilation to flow during resting conditions

29
Q

To what extent can coronary flow increase during periods of demand?

A

Coronary flow can increase via the coronary flow reserve to 4-5 times its resting value

30
Q

What is the “Bruce” Protocol?

A

BP and HR measured over 4 stages at the end of each 3 minute stage, with gradually increasing speed on a treadmill

Increased speed = More METS

Monitor EKG continually

31
Q

How is the increase in coronary flow calculated at each stage of the Bruce protocol?

A

Increase in coronary flow is calculated by taking the ratio of Double Product (SBP * HR) at the end of the stage to the Double Product at the beginning, to infer what factor of vasodilation had to occur to support the activity

32
Q

What findings on a stress test indicate that the coronary reserve has been exhausted?

A

Development of Chest Pain and/or ST segment depression on an EKG indicate coronary reserve has been exhausted

33
Q

Compare and contrast Imaging to Exercise testing?

A

Imaging can reveal regional limitations in flow reserve, but exercise testing can provide quantitative values for flow reserve

Use both together

34
Q

When would cardiac radionuclide imaging be performed?

A

In patients who cannot be physically active enough for an exercise stress test

35
Q

How does cardiac radionuclide imaging work?

A

Adenosine is infused via IV so that a cardiac radionuclide imaging procedure can be performed with maximum Microvascular dilation

Identifies differences in regional flow, but like all imaging studies, cannot provide quantitative values of flow

36
Q

What are endothelium independent components of coronary flow reserve?

A

Increased metabolic demand of exercise and vasodilatory effects of adenosine dilate microvasculature without Endothelial cell contributions

37
Q

What are endothelium dependent components of coronary flow reserve?

A

Increases in production of Nitric Oxide and other endothelial cell vasodilators affect microvasculature resistance

38
Q

Which component of coronary flow reserve is affected by disease?

A

Endothelium dependent component of microvasculature resistance is reduced by diabetes, hypercholesterolemia, and smoking

Reduces maximum flow response to exercise or adenosine

39
Q

What are the causes of Angina Pectoris and Myocardial Ischemia?

A

Imbalance between O2 demand and O2 supply:

Inability to increase coronary flow sufficiently when O2 demand rises = exertional angina

Primary reduction in O2 supply from thrombus formation or vasoconstriction of a stenosed epicardial artery

40
Q

What is the effect of a coronary artery stenosis?

A

Abnormal increase in resistance

41
Q

Why does the pressure drop across a stenosed artery decrease alinearly?

A

Due to separation losses

42
Q

How can coronary flow be maintaned at rest with stenosis?

A

Increased conduit resistance offered by stenosis is compensated for by microvascular vasodilation, at the cost of coronary reserve flow

43
Q

How does coronary flow reserve change with increasing stenosis?

A

As the severity of stenosis increases, microvascular coronary flow reserve is exhausted producing exertional angina

44
Q

Why is the subendocardium most susceptible to ischemic injury?

A

Microvascular coronary flow reserves are exhausted first here, so ischemia damages the subendocardium first

45
Q

How can coronary collateral flow develop?

A

Develops frequently as stenosis becomes critical and offers modest degree of perfusion to areas in jeopardy

46
Q

What are the goals of treating obstructions to coronary blood flow?

A

Limit increases in Myocardial O2 demand and augment flow to ischemic areas

47
Q

How can increases in Myocardial O2 demand be limited?

A

Minimize increases in systolic blood pressure, heart rate

48
Q

How can flow to ischemic areas be augmented?

A

Counter increases in stenosis severity, endothelial dysfunction, and abnormal vasoconstriction

Increase collateral flow or use PTCA/CABG

49
Q

Which component of coronary resistance is most readily manipulated?

A

R2 = Microvascular resistance; can contract or dilate vessels easily

50
Q

In deeper layers of the heart, such as the subendocardium, how do the components of coronary resistance change?

A

In the subendocardium and other deep layers, compressive resistance is high while microvasculature resistance is low to compensate; conduit resistance stays constant

51
Q

How do abnormalities alter the slope of the Coronary Flow vs Coronary Pressure graph?

A

Abnormalities such as hypertrophy and tachycardia decrease the slope, reflecting a lower coronary reserve

52
Q

What are the major factors that affect the extent of pressure decrease across a stenosis in an artery?

A

Degree of stenosis, flow rate and length of stenosis all increase the pressure decrease due to a stenosis

53
Q

What is the %stenosis cutoff for serious loss of flow?

A

70% stenosis leads to serious loss of flow that can cause ischemic damage during periods of activity

90% stenosis borders on insufficient for resting function

54
Q

By what factor does coronary flow need to expand to during exercise?

A

Coronary flow rises to approximately 3x the resting value

Cardiovascular (25 decks)

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