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Cardiovascular > SM 134 Coronary Blood Flow > Flashcards

SM 134 Coronary Blood Flow Flashcards

(54 cards)

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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)?

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A

Compression of coronary blood vessels during Systole

23
Q

How does Compressive Resistance set the perfusion of the heart?

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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?

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A

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

25
How does Compressive Resistance affect Microcirculatory Resistance?
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
What is Coronary Autoregulation?
Idea that Coronary Microvascular Resistance adjusts to keep flow at the level appropriate to Myocardial demand
27
What is Reactive Hyperemia?
Increase in coronary flow that follows a brief period of coronary artery occlusion
28
What is the Coronary Flow Reserve?
Ratio of flow during Maximum coronary vasodilation to flow during resting conditions
29
To what extent can coronary flow increase during periods of demand?
Coronary flow can increase via the coronary flow reserve to 4-5 times its resting value
30
What is the "Bruce" Protocol?
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
How is the increase in coronary flow calculated at each stage of the Bruce protocol?
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
What findings on a stress test indicate that the coronary reserve has been exhausted?
Development of Chest Pain and/or ST segment depression on an EKG indicate coronary reserve has been exhausted
33
Compare and contrast Imaging to Exercise testing?
Imaging can reveal regional limitations in flow reserve, but exercise testing can provide quantitative values for flow reserve Use both together
34
When would cardiac radionuclide imaging be performed?
In patients who cannot be physically active enough for an exercise stress test
35
How does cardiac radionuclide imaging work?
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
What are endothelium independent components of coronary flow reserve?
Increased metabolic demand of exercise and vasodilatory effects of adenosine dilate microvasculature without Endothelial cell contributions
37
What are endothelium dependent components of coronary flow reserve?
Increases in production of Nitric Oxide and other endothelial cell vasodilators affect microvasculature resistance
38
Which component of coronary flow reserve is affected by disease?
Endothelium dependent component of microvasculature resistance is reduced by diabetes, hypercholesterolemia, and smoking Reduces maximum flow response to exercise or adenosine
39
What are the causes of Angina Pectoris and Myocardial Ischemia?
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
What is the effect of a coronary artery stenosis?
Abnormal increase in resistance
41
Why does the pressure drop across a stenosed artery decrease alinearly?
Due to separation losses
42
How can coronary flow be maintaned at rest with stenosis?
Increased conduit resistance offered by stenosis is compensated for by microvascular vasodilation, at the cost of coronary reserve flow
43
How does coronary flow reserve change with increasing stenosis?
As the severity of stenosis increases, microvascular coronary flow reserve is exhausted producing exertional angina
44
Why is the subendocardium most susceptible to ischemic injury?
Microvascular coronary flow reserves are exhausted first here, so ischemia damages the subendocardium first
45
How can coronary collateral flow develop?
Develops frequently as stenosis becomes critical and offers modest degree of perfusion to areas in jeopardy
46
What are the goals of treating obstructions to coronary blood flow?
Limit increases in Myocardial O2 demand and augment flow to ischemic areas
47
How can increases in Myocardial O2 demand be limited?
Minimize increases in systolic blood pressure, heart rate
48
How can flow to ischemic areas be augmented?
Counter increases in stenosis severity, endothelial dysfunction, and abnormal vasoconstriction Increase collateral flow or use PTCA/CABG
49
Which component of coronary resistance is most readily manipulated?
R2 = Microvascular resistance; can contract or dilate vessels easily
50
In deeper layers of the heart, such as the subendocardium, how do the components of coronary resistance change?
In the subendocardium and other deep layers, compressive resistance is high while microvasculature resistance is low to compensate; conduit resistance stays constant
51
How do abnormalities alter the slope of the Coronary Flow vs Coronary Pressure graph?
Abnormalities such as hypertrophy and tachycardia decrease the slope, reflecting a lower coronary reserve
52
What are the major factors that affect the extent of pressure decrease across a stenosis in an artery?
Degree of stenosis, flow rate and length of stenosis all increase the pressure decrease due to a stenosis
53
What is the %stenosis cutoff for serious loss of flow?
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
By what factor does coronary flow need to expand to during exercise?
Coronary flow rises to approximately 3x the resting value

Cardiovascular (25 decks)

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