Cardiovascular mechanics 3

Question 1

What are the two circulatory systems

Answer 1

Pulmonary and systemic, coupled together

Question 2

How is blood propelled through the blood vessels

Answer 2

Muscular pump (heart) generates a pressure gradient

Question 3

Why are capillaries highly branched

Answer 3

Diffusion is only effective over short distances

Question 4

What is the function of the smooth muscle in small arteries and arterioles

Answer 4

Regulate diameter and resistance to blood flow

Question 5

Which blood vessel acts as a reservoir for blood volume and why

Answer 5

Veins and venues as they are highly compliant

Question 6

How is resistance calculated for a fluid circuit

Answer 6

Darcy’s law

pressure = volumetric flow x resistance

Question 7

What are the assumptions made using Darcy’s Law

Answer 7

Steady flow
Rigid vessels
Right atrial pressure is negligible

Question 8

Why may steady flow not occur

Answer 8

Intermittent pumping

Question 9

How is regulation of flow achieved

Answer 9

Variation in resistance in the vessels as blood pressure remains relatively constant

Question 10

Why does pressure fall across the circulation

Answer 10

Viscous (frictional) pressure losses

Question 11

Which vessels present the most resistance to flow

Answer 11

Small arteries and arterioles

Question 12

What does resistance to flow depend on

Answer 12

Fluid viscosity
Length of the tube
Inner radius

Question 13

How is vascular tone and blood flow related and which equation reflects this

Answer 13

Small changes in vascular tone (e.g. by vasoconstriction/ vasodilation) may produce large changes in flow
Poiseuille’s

Question 14

What is the difference in cardiac output between rest and exercise

Answer 14

rest = 5
exercise = 20

Question 15

Describe laminar flow

Answer 15

Velocity of the fluid is constant at any point

Flow is in layers and is fastest at the centre

Question 16

Why is velocity greatest in the centre in laminar flow

Answer 16

Adhesive forces between the wall and fluids slow the blood

Question 17

Describe turbulent flow

Answer 17

Blood flows erratically to form Eddys

Prone to pooling

Question 18

What is turbulent flow associated with

Answer 18

Pathophysiological changes to the endothelial lining of the blood vessels

Question 19

Define shear rate

Answer 19

Gradient of the velocity profile at any point

Question 20

How is shear rate calculated

Answer 20

Shear rate x velocity = shear stress (shear rate = shear stress/velocity)

Question 21

Describe the shear stress in laminar flow

Answer 21

High shear stress
Cells are aligned in the direction of flow
Secretions promote vasodilation and anticoagulation

Question 22

Describe disturbed shear stress

Answer 22

Low shear stress due to promotion of endothelial proliferation, apoptosis and shape change
Secretions promote vasoconstriction, coagulation and platelet aggregation.

Question 23

Where is blood pressure usually measured and why

Answer 23

Upper arm as it is easily accessed and at the level of the heart

Question 24

What is pulse pressure

Answer 24

Difference between systolic pressure and diastolic pressure

Question 25

What is heard when using a stethoscope to measure blood pressure

Answer 25

Turbulent flow as the cuff is slowly deflated

Question 26

How is mean arterial pressure calculated

Answer 26

Diastolic blood pressure + 1/3 pulse pressure

Question 27

What causes the dicrotic notch

Answer 27

Closure of the aortic valve

Question 28

What causes the difference in rate of pressure reduction in the ventricles vs aorta

Answer 28

aorta pressure decreases slowly due to its elasticity, buffering the change in pressure

Question 29

What is the windkessel effect

Answer 29

pumps of water through a solid tube produces separate pumps of water out. Replacing a section of the tube with a balloon will produce a continuous stream of water out, despite a pumping input

Question 30

What is the effect of the blood entering the aorta faster than it leaves

Answer 30

40% of blood is "Stored" in elastic arteries

Question 31

Why is blood "stored" in elastic arteries

Answer 31

Blood enters the aorta faster than it leaves

Question 32

Define compliance

Answer 32

Relationship between the transmural pressure and the vessel volume, depending on vessel elasticity

Question 33

What is the effect on pulse pressure with age

Answer 33

Compliance decreases as the arteries become stiffer so PP increases

Question 34

What is the of gravity effect on pressure and blood flow

Answer 34

``` Hydrostatic pressure in the legs increases so blood pools in the veins due to their high compliance Reduced venous return Reduced pressure (without compensatory mechanisms) ```

Question 35

What is an aneurysm

Answer 35

A balloon-like distension in weakened vessel walls

Question 36

What is the effect of an aneurysm

Answer 36

Increase in radius | For the same internal pressure, the inward force exerted by the muscle must increase

Question 37

What causes an aneurysm to rupture

Answer 37

Muscle fibre weakening so that the force needed to counteract the increase in radius cannot be produced Expansion until rupture

Question 38

What is the purpose of valves

Answer 38

Unidirectionality

Question 39

What do incompetent valves cause

Answer 39

Dilated superficial veins in the left - varicose veins

Question 40

What is Poiseuille's equation

Answer 40

R = 8L x fluid viscosity / pi x r^4