Hemodynamics

Question 1

Answer 1

Veins

Question 2

How do you determine the systemic pressure difference that drives blood flow (Q)?

Answer 2

Question 3

Why is turbulent flow bad in the systemic vasculature?

Answer 3

• Can cause endothelial damage –> inflammation, dysfunction of endothelium (important for local vasodilation and autoregulation of CV system) –> can lead to atherosclerosis and / or thrombus formation
• Local pockets of static blood that’s not moving as much –> more likely to clot

Question 4

In the CV system, what determines compliance?

Answer 4

Question 5

• Changes in […] alter peripheral venous pressure
• How can venous pressure be altered?
• Nitroglycerin is a selective venodilator. What affect will this drug have on pre-load and oxygen demand?

Answer 5

• Blood volume
• Changes in venous tone via SNS activation
• It will vasodilate veins, increasing blood in veins, thereby decreasing blood that is returned to heart so decrease pre-load and decrease oxygen demand

Question 6

Answer 6

Question 7

Answer 7

Capillaries are arranged in parallel. This allows the body to alter local vasoconstriction and vasodilation to alter blood flow locally to tissues without changing total resistance. If total resistance is unchanged and flow is constant, then pressure will not change.

Question 8

What must be the relationship between the pressure gradient and vascular resistance in order for blood flow to occur?

Answer 8

Pressure gradient must be high enough to overcome TPR

Question 9

Normally the viscosity of blood does not change. However, there are circumstances that can change viscosity. When would this happen?

Answer 9

Polycythemia = genetic condition, too many RBCs

Question 10

Answer 10

Question 11

What 4 factors determine the resistance to blood flow?

Answer 11

Question 12

Answer 12

Question 13

Answer 13

2. decreased

Question 14

Answer 14

Capillaries

Question 15

Answer 15

Question 16

Answer 16

Decrease; increase

Question 17

With compliance in mind, explain why the BP measured at the brachial artery is not the same as the BP of the actual aorta.

Answer 17

The aorta is more compliant that the systemic arteries. Therefore, blood in the aorta will display a lower increase in pressure for a given change in volume or distention of the vessel. The systemic arteries distend less than the aorta, so for the same level of distention, there will be a larger change in pressure. Therefore, the pressure measured at the brachial artery is actually higher than it is in the aorta. The systolic pressure increases, while the diastolic pressure decreases leading to a greater pulse pressure in the BA vs. aorta.

Question 18

• What does aortic pulse pressure tell you?
• How is it calculated?
• What 2 things determine PP?

Answer 18

• See image
• See image
• Compliance and stroke volume output

Question 19

Answer 19

Increase, right

Question 20

Answer 20

Venules

Question 21

What is the equation for flow rate?

Answer 21

A * v

v = velocity

A = Cross-sectional area

Therefore, v = Q / A

Question 22

• When the left ventricle ejects blood into the aorta, the aortic pressure […].
• What is systolic pressure?
• As the left ventricle is relaxing and refilling, the pressure in the aorta […].
• What is diastolic pressure?

Answer 22

• Rises
• The maximal aortic pressure following ejection is systolic pressure
• Falls
• The lowest pressure in the aorta, which occurs just before the ventricle ejects blood into the aorta, is diastolic pressure

Question 23

Answer 23

1. decrease, decrease

Question 24

Answer 24

Decreased

Question 25

Answer 25

Question 26

What is central venous pressure?

Answer 26

BP in the thoracic vena cava near right atrium. This determines the filling pressure of the right ventricle and ventricular stroke volume and CO.

Question 27

What is hemodynamics?

Answer 27

Question 28

Let's say a person is exercising. SNS is going to increase HR, increase contractility to increase CO. This will also increase oxygen consumption throughout the whole body, including the heart. Part of the response of the SNS is vasoconstriction. If the vessels that deliver blood to the myocardium constricted, then there would be insufficient oxygen delivered to the heart muscle to meet increased demand. How does the heart overcome the order to vasoconstrict by the SNS?

Answer 28

Increase in coronary blood flow (active hyperemia) triggers local vasodilatory molecules (NO and adenosine) that act counter to the order to constrict by SNS

Question 29

Decreasing compliance [...] pulse pressure. Decreasing SV [...] pulse pressure.

Answer 29

Increases Decreases

Question 30

Failure of what system to drain excess fluid leads to edema?

Answer 30

Lymphatic system

Question 31

Answer 31

Arterioles

Question 32

What is the single most important factor that affects resistance, and thus flow?

Answer 32

radius Decrease in r --\> increase in R, decrease in Q

Question 33

The capillary beds cover a large area. What implications does this have for flow and velocity?

Answer 33

Flow will remain unchanged because the CV system is a closed system, so flow must be constant. However, V = Q/A and if Q is staying the same and A is increasing then V is decreasing when blood moves into the capillaries. This is important because this maximizes the time blood spends in the capillaries to exchange nutrients and waste.

Question 34

Blood flow (Q) is determined by two factors. What are they?

Answer 34

Note that although Q = A \* v, these factors do not **determine** the blood flow necesscarily. If surface area changes, a corresponding change in velocity happens to keep flow constant. However, changes in pressure and resistance can actually change the value of Q in the CV system.

Question 35

* Mechanisms that cause vasoconstriction of resistance vessels SVR * Mechanisms that cause vasodilation of resistance vessels will [...] SVR

Answer 35

* Increase * Decrease

Question 36

What factors aid venous return to the heart?

Answer 36

* Structural factors inherent to the veins themselvs * Large lumen, one way valves preventing backflow * Skeletal muscle compression of nearby surrounding muscles * Functional adaptations * Innervation by SNS