Circulation 7

Question 1

Breakdown of coronary artery dominance in humans

Answer 1

Right-sided dominant: 50%
Left-sided dominant: 20%
Non-dominance: 30%

Question 2

Ratio of myocardial capillaries to myocytes

Answer 2

1:1 (not usually all active simultaneously)

Question 3

When are more myocardial capillaries likely to be recruited?

Answer 3

During episodes of ischemia

Question 4

What is the primary determinant of coronary blood flow?

Answer 4

Aortic pressure

Question 5

Primary regulation of coronary blood flow is due to wat?

Answer 5

Metabolic activity and changes in arteriolar resistance

Question 6

Highest myocardial tissue pressures occur when, and what does this cause?

Answer 6

During early systole; left coronary blood flow may actually reverse during systole

Question 7

When does maximal left coronary blood flow occur?

Answer 7

Early diastole, when tissue pressure falls to approximately 0

Question 8

Percentages of diastolic vs systolic perfusion of myocardium

Answer 8

60-65% occurs during diastole, 25-30% during systole

Question 9

Which layer of heart tissue is the ventricular diastolic pressure greatest?

Answer 9

In the endocardium; least near the epicardium

Question 10

Consequences of endocardium enduring greater pressure

Answer 10

More likely to be compressed; more likely to undergo ischemic event than the epicardium

Question 11

Regulation of endocardial vessels under normal conditions

Answer 11

Due to larger compression forces, the vessels are more dilated to accommodate

Question 12

Diseases that can cause subendocardial infarction

Answer 12

Aortic valve stenosis
Aortic valve regurgitation
Congestive heart failure

Question 13

Consequences of decreased coronary blood pressure

Answer 13

Endocardial blood flow will be restricted more than epicardial blood flow because of the normally greater endocardial tissue (occurs during sever hypotension or partial coronary occlusion)

Question 14

Sympathetic adrenergic stimulation activates what receptors?

Answer 14

Alpha receptors in the coronaries, inducing weak vasoconstriction

Question 15

Beta-1 adrenergic receptors - location in the heart and effect

Answer 15

Present on pacemaker cells and myocardium. During sympathetic stimulation, coronary vasodilation will override alpha receptors due to increases in metabolism

Question 16

Beta-2 adrenergic receptors - location in the heart and effect

Answer 16

Coronary smooth muscle; mediate vasodilation, but are less sensitive to sympathetic stimulation

Question 17

Vagal stimulation can be blocked by __ suggesting . . .

Answer 17

atropine; an acetylcholine effect is probably mediated by release of nitric oxide from endothelial cells

Question 18

__ is the major factor in the regulation of coronary blood flow

Answer 18

Metabolism

Question 19

Graphical relationship of coronary blood flow and myocardial metabolic activity

Answer 19

Linear relationship

Question 20

Metabolic substrates for the heart

Answer 20

1. Fatty acids - 60%
2. Carbohydrates - 35-40%
3. Others (ketones, lactate, proteins)

Question 21

How is oxygen supply to the heart limited?

Answer 21

Flow-limited, because most of the oxygen (~80%) is removed from blood during its one passage through the heart

Question 22

Oxygen consumption is directly related to the __ of the heart.

Answer 22

work

Question 23

Cardiac work equation

Answer 23

Mean arterial pressure x systolic stroke volume

Question 24

__ work consumes much more oxygen than __ work

Answer 24

Pressure, volume

Question 25

Myocardial oxygen supply equation

Answer 25

Myocardial blood flow x arterial oxygen content

Question 26

Myocardial blood flow is dependent upon . . .

Answer 26

Diastolic perfusion pressure and coronary vascular resistance

Question 27

Myocardial oxygen demand depends on these three things

Answer 27

Afterload, heart rate, and contractility

Question 28

Myocardial ischemia results from this

Answer 28

An imbalance in the ratio of oxygen supply to oxygen demand, creating a relative lack of blood flow

Question 29

This is NEVER a primary cause of ischemia

Answer 29

Excessive oxygen demand

Question 30

Collateral circulation

Answer 30

Normal human heart has collateral vessels, but they are insufficient to prevent sudden infarction; can respond to gradual obstruction

Question 31

Process of gradual collateral circulation

Answer 31

Involves a complex sequence of vessel injury, inflammation, and cellular proliferation

Question 32

Coronary "steal"

Answer 32

Under certain conditions, an increase in blood flow in one region of the heart can cause a decrease in blood flow in another region

Question 33

No coronary "steal"

Answer 33

Arteriole resistance in the non-obstructed vessel vasodilates to keep the same amount of resistance in both vessels, keeping a good flow through the obstructed vessel as well

Question 34

When does coronary steal usually become an issue?

Answer 34

During exercise, when the non-obstructed vessel becomes vasodilated and the obstructed vessel remains at a higher resistance

Question 35

Clinical manifestations of coronary steal

Answer 35

- Exercise-induced ischemia - Stress-testing with adenosine - Peripheral arterial disease that causes caludication

Question 36

How much cardiac output goes to skeletal muscle during rest?

Answer 36

20% (muscle makes up 40% of body mass)

Question 37

What is the resting flow of skeletal muscle as compared to brain and kidneys?

Answer 37

3 mL/min per 100g, compared to 50 and 400 mL/min per 100g

Question 38

What does skeletal muscle's large flow reserve indicate?

Answer 38

Vasculature in resting muscle has a high degree of vascular tone

Question 39

What happens to the vessels with dynamic exercise?

Answer 39

Alternation between extravascular compression and free flow, but overall, there is a profound reduction in resistance to blood flow due to metabolic vasodilation

Question 40

Consequences of isometric tensions of ~70% of max or above

Answer 40

Blood flow through the contracting muscle approaches zero, so the tensions cannot be sustained for more than 1-2 min

Question 41

Innervation of skeletal muscle arteries

Answer 41

Sympathetic cholinergic receptors that induce vasodilation by acting on mucarinic receptors coupled to NO production

Question 42

Epinephrine with vascular control

Answer 42

Causes vasodilation at low concentrations through beta-2 adrenergic receptors, but at high concentrations, binds to alpha adrenergic receptors and vasoconstricts