Coronary and Systemic Circulation; Vascular Control

Question 1

What coronary arteries branch off of the R coronary artery?

Answer 1

The acute marginal and in a right dominant heart, the posterior descending

Question 2

What coronary arteries branch off of the L coronary artery? What are their branches?

Answer 2

The L circumflex (obtuse marginals and the posterior descending in a L dominant heart), the L anterior descending (diagonal and septal branches)

Question 3

What are thebesian vessels? Are they found in a normal person?

Answer 3

Vessels that do not follow the normal path of flow and may drain into chambers besides the R atrium.
Yes.

Question 4

Why are anastomoses in coronary circulation important?

Answer 4

They allow blood flow (and thus perfusion) to most of the heart, even in cases of significant three vessel coronary artery disease

Question 5

What is a coronary perfusion territory? Why might territories overlap?

Answer 5

The area supplied by a vessel. They overlap in areas that are important to the heart’s function (i.e. the papillary muscles for the mitral valve) so if flow from one artery is compromised, the papillary muscle and thus the valve will still work.

Question 6

What is coronary dominance? Approximately how often are people right dominant? Left dominant? Co-dominant?

Answer 6

Which artery supplies the posterior descending artery. In right dominant people (70%), it’s the R coronary artery. In left dominant people (10%), it’s the left circumflex. In codominant (10%), it’s both.

Question 7

What is the major variable controlling coronary blood flow?

Answer 7

Resistance. (P=QR where Q= coronary blood flow)

Question 8

What are the three components of coronary vascular resistance? When are they significant?

Answer 8

R1- if you push on the artery, it pushes back; significant in pathology, not normally
R2- metabolic resistance; resistance changes based on metabolic needs of tissue
R3- mechanical resistance; arteries travel through the thickness of cardiac muscle. Not much flow during systole

Question 9

What is autoregulation of flow? What is a consequence of this? Give an example of a small molecule involved.

Answer 9

The intrinsic ability of the heart to maintain a constant coronary blood flow across a range of coronary perfusion pressures. Thus, a change in pressure (as long pressure stays between 30 and 150 mm Hg) will not affect flow. NO

Question 10

When does most coronary perfusion occur? Why?

Answer 10

During diastole. Because R3 is really high in systole

Question 11

What clinical diagnostic tests would one use to diagnose impaired myocardial perfusion?

Answer 11

An EKG with a stress test. Then potentially catheterization and an angiogram (inject dye, see where it goes) to identify blockages

Question 12

What is an angioplasty? How does it work?

Answer 12

A procedure to re-open an artery. A catheter is introduced and a stent is placed at the site of occlusion. The stent expands, keeping the artery open and increasing flow and thus downstream perfusion

Question 13

What is coronary artery bypass surgery/grafting?

Answer 13

“replumbing the heart.” Creating new vascular pathways to that areas distal to an occlusion will still be perfused

Question 14

What does an intra-aortic balloon pump do? Why is this important?

Answer 14

It reduces heart pressure just before systole and increases it during diastole (reduces PP). This means the heart does less work. It also improves coronary blood flow and thus the oxygen supply to the heart.

Question 15

Where do most of the cardiac veins drain to? What about the anterior cardiac veins?

Answer 15

Most drain to the coronary sinus just behind the RA. The anterior cardiac veins drain to the RV

Question 16

What are two major endogenous vasodilators?

Answer 16

Adenosine and NO

Question 17

Define vascular compliance. How would you calculate it mathematically? How is it related to elastance?

Answer 17

Compliance is how stiff a vessel is; it is determined by the elastic fiber content and arrangement in a tissue. C= (change in V)/(change in P). Elastance = 1/compliance

Question 18

How does arterial compliance change with age? How does this affect arterial pressure?

Answer 18

Compliance decreases with age. Thus, for a given pressure, a vessel has a smaller increase in volume because arteries are less elastic. Since vessels are more rigid, TPR increases and Blood pressure increases (MAP = CO x TPR)

Question 19

How is tension related to transmural pressure of a vessel? How is tension defined in this context?

Answer 19

Tension= transmural pressure x radius
Tension is the amount of force required to pull apart the walls of a vessel (or how much energy required to hold a slit in the walls of a vessel together)

Question 20

How does increased pressure change the resistance of an elastic vessel?

Answer 20

As pressure increases, r increases (arteries vasodilator) and R falls

Question 21

What is the slope of a volume v. pressure curve? Of a pressure v. volume curve?

Answer 21

Volume v. pressure: slope= (change in P)/(change in V)= 1/compliance
Pressure v. volume: slope = (change in V)/(change in P)= compliance

Question 22

How does an arterial volume v. pressure curve differ from a venous curve? Why is this important?

Answer 22

The arterial curve has a much steeper slope so for a small change in volume, there is a large change in pressure. The venous curve has a less steep slope and thus is more compliant as a system. This is why the venous system is a reservoir for blood.

Question 23

What happens to arterial and venous volume v. pressure curves if a person has a hemorrhage?

Answer 23

Hemorrhage= decreased volume so both curves shift to the L so that a reasonable pressure can be maintained at the new volume. [Remember, curves can shift based on the ANS control of the blood vessel]

Question 24

How do arteries store energy for blood circulation? Why is this clinically significant?

Answer 24

When blood is pumped into the aorta during systole, some of the energy created by movement distends the elastic walls of the aorta, creating a transmural pressure. When the heart fills during systole, this transmural pressure is converted into movement energy and drives forward flow. This is why we have a diastolic BP and why BP never = 0

Question 25

Describe the aortic pulse contour

Answer 25

When the LV fills and undergoes isovolumic contraction, P(aorta)= 80 mm Hg
When the LV ejects blood, P(aorta) climbs to 120 mm Hg (P(LV) is a little greater than P(aorta)) then falls (P(aorta) is a little greater than P(LV) b/c of energy stored in the walls) to 100. A transient reversal of flow closes the aortic valve (dichrotic notch) and P(aorta) climbs slightly then decreases back to 80 mm Hg as the LV fills again.

Question 26

What is the general mechanism of action of nitrates?

Answer 26

They cause the release of NO in smooth muscle and thus cause venodilation

Question 27

How is cardiac output related to venous return?

Answer 27

They are equal b/c the circulatory system is a closed system

Question 28

What are the two physiologic components of the venous system? How are they connected (in parallel or in series)?

Answer 28

The peripheral venous compartment and the central venous compartment. Connected in series

Question 29

Where is most of the blood contained in the body? Where is the compliance greatest? What about the area with the greatest resistance?

Answer 29

Most blood is contained in the peripheral venous compartment which also has the greatest compliance. Arterioles have the greatest resistance

Question 30

Which compartment determines preload? What about afterload?

Answer 30

Preload- EDV. Central venous compartment

Afterload- P(aorta)- arterioles. They determine resistance and thus pressure in the whole system

Question 31

Jugular venous distention is a barometer for what?

Answer 31

Central venous pressure

Question 32

What would blood pressure be if we stopped the heart? Why is this?

Answer 32

7 mm Hg. It is the mean systemic filling pressure (MSFP) which is the pressure created by the volume of blood in the circulatory system.

Question 33

What drives flow in the venous compartment?

Answer 33

The pressure gradient from the peripheral venous compartment (7 mm Hg) to the central venous compartment (0 mm Hg)

Question 34

How does increased blood volume change central venous pressure? What about venous return? How does increased venous tone change CVP and VR?

Answer 34

Increased volume- increases MSFP which increases the pressure gradient in the veins and increases venous return to the heart.
Same things happen with increased tone

Question 35

How does increased arteriole tone affect VR? MSFP?

Answer 35

Increased arteriole tone means increased total resistance in the body. More blood is trapped on the arterial side of circulation and consequetly, less is on the venous side. This decreases VR for a given CVP. It does not change MSFP though b/c total blood volume does not change

Question 36

How are the cardiac (Frank-starling curve) and venous function curves related?

Answer 36

They both measure how CO or VR changes with changing CVP. Where they intersect is the equilibrium point for the body at that moment

Question 37

How does an increased in inotropy change the cardiac function and venous function curves?

Answer 37

Increased inotropy (i.e. SNS stimulation) will move the cardiac function curve to the left (greater CO at a smaller CVP). This will increase CO by moving along the venous curve to the L. Eventually, to compensate, the body will shift the venous curve to the L to decrease VR and return to the equilibrium point.