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Cardiovascular System > Cardiovascular mechanics 3 > Flashcards

Cardiovascular mechanics 3 Flashcards

1
Q

What are the two circulatory systems

A

Pulmonary and systemic, coupled together

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2
Q

How is blood propelled through the blood vessels

A

Muscular pump (heart) generates a pressure gradient

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3
Q

Why are capillaries highly branched

A

Diffusion is only effective over short distances

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4
Q

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

A

Regulate diameter and resistance to blood flow

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5
Q

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

A

Veins and venues as they are highly compliant

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6
Q

How is resistance calculated for a fluid circuit

A

Darcy’s law

pressure = volumetric flow x resistance

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7
Q

What are the assumptions made using Darcy’s Law

A

Steady flow
Rigid vessels
Right atrial pressure is negligible

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8
Q

Why may steady flow not occur

A

Intermittent pumping

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9
Q

How is regulation of flow achieved

A

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

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10
Q

Why does pressure fall across the circulation

A

Viscous (frictional) pressure losses

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11
Q

Which vessels present the most resistance to flow

A

Small arteries and arterioles

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12
Q

What does resistance to flow depend on

A

Fluid viscosity
Length of the tube
Inner radius

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13
Q

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

A

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

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14
Q

What is the difference in cardiac output between rest and exercise

A 
rest = 5
exercise = 20
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15
Q

Describe laminar flow

A

Velocity of the fluid is constant at any point

Flow is in layers and is fastest at the centre

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16
Q

Why is velocity greatest in the centre in laminar flow

A

Adhesive forces between the wall and fluids slow the blood

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17
Q

Describe turbulent flow

A

Blood flows erratically to form Eddys

Prone to pooling

18
Q

What is turbulent flow associated with

A

Pathophysiological changes to the endothelial lining of the blood vessels

19
Q

Define shear rate

A

Gradient of the velocity profile at any point

20
Q

How is shear rate calculated

A

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

21
Q

Describe the shear stress in laminar flow

A

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

22
Q

Describe disturbed shear stress

A

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

23
Q

Where is blood pressure usually measured and why

A

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

24
Q

What is pulse pressure

A

Difference between systolic pressure and diastolic pressure

25
Q

What is heard when using a stethoscope to measure blood pressure

A

Turbulent flow as the cuff is slowly deflated

26
Q

How is mean arterial pressure calculated

A

Diastolic blood pressure + 1/3 pulse pressure

27
Q

What causes the dicrotic notch

A

Closure of the aortic valve

28
Q

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

A

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

29
Q

What is the windkessel effect

A

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

30
Q

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

A

40% of blood is “Stored” in elastic arteries

31
Q

Why is blood “stored” in elastic arteries

A

Blood enters the aorta faster than it leaves

32
Q

Define compliance

A

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

33
Q

What is the effect on pulse pressure with age

A

Compliance decreases as the arteries become stiffer so PP increases

34
Q

What is the of gravity effect on pressure and blood flow

A 
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)
35
Q

What is an aneurysm

A

A balloon-like distension in weakened vessel walls

36
Q

What is the effect of an aneurysm

A

Increase in radius

For the same internal pressure, the inward force exerted by the muscle must increase

37
Q

What causes an aneurysm to rupture

A

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

38
Q

What is the purpose of valves

A

Unidirectionality

39
Q

What do incompetent valves cause

A

Dilated superficial veins in the left - varicose veins

40
Q

What is Poiseuille’s equation

A

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

Cardiovascular System (13 decks)

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