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sem 2 CVS > Principles of Haemodynamics > Flashcards

Principles of Haemodynamics Flashcards

1
Q

what is haemodynamics?

A

the relationship between blood flow, blood pressure and resistance to flow (flow of blood through the heart and vessels)

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2
Q

name 6 key factors involved in haemodynamics?

A
  1. Force (cardiac contraction)
  2. Work (isovolumetric contraction-when pressure gets to a certain level ejection occurs, the longer this period, the stronger the contraction)
  3. Pressure (the difference in pressure from the aorta to veins helps blood flow)
  4. Compliance (arterial stretch)
  5. Resistance (in arterioles)
  6. Flow velocity (slowing down blood flow in capillaries, increasing efficiency for gas exchange)
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3
Q

is the CVS is a closed or open system?

A

The CVS is a closed system

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4
Q

where is the majority of blood located?

A

Majority of blood is in the venous system

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5
Q

what is the venous system?

A

Low pressure reservoir system which expands a lot

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6
Q

what can the reservoir of venous blood be used for?

A

The reservoir of venous blood can be used to increase CO by increasing he force of contraction (starlings law). This happens as when more blood is needed, veins can contract to give more blood to the heart.

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7
Q

why do we constrict/dilate arteries?

A

To send blood to different places

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8
Q

what is darcy’s law, and the equation involved with it?

A

The role of pressure in energy flow. The flow in a vessel is equal to the difference in pressure across vessel divided by resistance of flow

Q=(P1-P2)/R
Q= flow
P1-P2= pressure difference. In this case, it is Pa-CVP (arterial pressure-central venous pressure)
R= resistance to flow. In this case it’s TPR (total peripheral resistance)

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9
Q

what is Bernoulli’s Law?

A

As the speed of a moving fluid increases, the pressure within the fluid decreases.

There’s more than just pressure controlling blood flow:
The role of pressure, kinetic and potential energies in flow

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10
Q

Blood is moving so means in terms of energy?

A

Blood is moving and so has kinetic energy and gravity pulling it so also potential energy

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11
Q

Blood having kinetic energy means what?

A

Kinetic energy means blood can travel against the concentration gradient

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12
Q

what is the definition of blood flow?

A

volume of blood flowing in a given time (ml/min, l/min)

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13
Q

what is the definition of perfusion?

A

blood flow per given mass of tissue (ml/min/g). Takes into account mass of tissue.

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14
Q

what is the definition of velocity of blood flow?

A

blood flow (cm/s) affected by the cross-sectional area through which the blood flows, so flow may remain the same but velocity changes if there has been a change in cross sectional area

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15
Q

what is flow determined by?

A

Flow is determined by arterial blood pressure and resistance.

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16
Q

what is the relationship between volume flow, velocity and area

A

Volume flow (Q)= Velocity (V) x Area (A)

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17
Q

Is the velocity of blood flow in the aorta high or low?

A

The velocity of blood flow in the aorta is high

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18
Q

When the blood reaches the arteries what happens to the speed?

A

Speed starts to increase at arteries

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19
Q

What slows the velocity of blood?

A

The branching of arteries into capillaries slows velocity

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20
Q

Describe the capillaries:

A
  • 1 cell thick
  • very narrow
  • in total, they have a large cross-sectional area
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21
Q

what is the relationship between cross-sectional area and flow?

A

The greater the cross-sectional area, the slower the flow

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22
Q

So, where is flow slowest?

A

flow is slowest in the capillaries

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23
Q

veins coming together increases what?

A

veins coming together increases the velocity

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24
Q

name the 3 patterns of blood flow?

A

laminar, turbulent and bolus

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25
Q

laminar flow is present in which vessels?

A

most arteries, arterioles, venues and veins

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26
Q

describe laminar flow:

A

-smooth, layers

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27
Q

with laminar flow, what is the velocity like at the walls compared to the centre and why is this?

A
  • Zero velocity at walls due to friction and molecular interactions, as near the walls of the vessel there is some friction between water molecules in the blood and the walls of the vessel, which slows down the blood
  • Maximum velocity is at centre
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28
Q

(laminar flow) having maximum velocity at the centre means what?

A
  • Moves RBCs towards centre

- speeds up blood flow through narrow vessels

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29
Q

laminar flow can be disrupted to become what?

A

turbulent flow

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30
Q

when does turbulent flow occur (examples)?

A
  • Ventricles (mixing)
  • aorta (peak flow)
  • atheroma (bruits- abnormal sound generated by turbulent flow of blood)
  • with high bp
  • with obstructions
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31
Q

why does turbulent flow happen?

A

Turbulent flow happens when blood flows too quickly above a certain speed, no longer laminar

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32
Q

with turbulent flow, why does the blood not flow linearly and smoothly in adjacent layers?

A

because of increased pressure and velocity

33
Q

(turbulent flow) instead of flowing smoothly how does it flow?

A

whirlpools, eddies, vortices

34
Q

can you hear turbulent flow when listening with a stethoscope?

A

yes

35
Q

name the third type of flow?

A

bolus

36
Q

bolus flow occurs in only 1 type of vessel-which one?

A

capillaries

37
Q

describe bolus flow (efficiency, velocity, friction etc.)

A
  • Very efficient flow
  • uniform velocity
  • little internal friction
  • very low resistance
38
Q

with bolus flow in the capillaries, why do RBC’s move in single file?

A

RBCs have a larger diameter than capillaries and so move in single file, squeezing their way through.

39
Q

what are trapped between the RBC’s in bolus flow?

A

Plasma columns (bolus of fluid) are trapped between RBCs

40
Q

what is Reynolds Number (Re)?

A

Determines at what point the flow will change from laminar to turbulent flow

41
Q

what does Re measure?

A

Flow against pressure, providing there is constant resistance and area

42
Q

what does an increase in pressure subsequently increase?

A

Increase in pressure increases flow up to a point where it becomes turbulent – after that, further increase in pressure doesn’t increase flow but just goes to turbulent state

43
Q

when does turbulence occur (in terms of Re)?

A

Turbulence occurs when Reynolds number exceeds a critical value (>2000)

44
Q

give reasons why this value could be exceeded?

A
  • bruits
  • ejection murmur
  • increased blood velocity
45
Q

how does diameter affect Re?

A

Bigger diameter = bigger Reynolds number

46
Q

does Re have units?

A

Reynolds number doesn’t have units

47
Q

minor clotting can occur due to changes in what?

A

changes in viscosity

48
Q

where is blood flow highest?

A

Blood flow is highest in aorta

49
Q

what is the pressure in aorta during systole and diastole?

A

120mmHg during systole 80mmHg during diastole

50
Q

when does arterial pressure fall?

A

Arterial pressure falls steadily in systemic circulation with distance from LV

51
Q

Resistance occurs in arterioles by what?

A

constriction

52
Q

name some factors that affect arterial blood pressure

A
  • Cardiac output (SV, HR)
  • Properties of arteries
  • Peripheral resistance
  • Blood viscosity (increase in viscosity, increases blood pressure)
53
Q

Arterial blood pressure involves interaction between which 4 key relationships?

A

o Systolic pressure – pressure when ejecting

o Diastolic pressure – pressure when relaxing

o Pulse pressure – difference between diastolic and systolic pressure (radial artery for pulse is difference)

o Mean blood pressure – average pressure (as when measuring blood pressure)

54
Q

why can’t you detect a pulse in veins?

A

You can’t detect a pulse by the time you get to veins because its smooth flow, and there isn’t much change to the pressure

55
Q

role of elastic fibres in the movement of blood?

A
  • The recoil of elastic fibres of the aorta and larger arteries helps to propel the blood into the circulation
  • Maintains blood pressure even during diastole
56
Q

during LV ejection, where is SV and energy stored?

A
  • 60-80% of stroke volume is stored in aorta and arteries as these structures expand
  • Energy stored in stretched elastin
57
Q

during LV diastole what happens?

A
  • Energy is returned to the blood at the walls of the aorta and arteries contract
  • This sustains diastolic blood pressure and blood flow when the heart is relaxed
58
Q

what is compliance?

A

how much the aorta is stretched

59
Q

what is pulse pressure?

A

what the finger senses, eg. at the wrist (radial artery).

60
Q

what does the pulse pressure tell you about?

A

Tells you about stroke volume and arterial compliance (stretchiness)

61
Q

how is pulse pressure affected when there is a higher SV?

A

With a higher stroke volume, pulse pressure goes up

62
Q

how will a less compliant aorta affect pulse pressure?

A

A less compliant aorta will give higher pulse pressure for the same cardiac output

63
Q

Rest Vs Exercise- compare the SV, stretch, compliance and systolic volume

A 
exercise:
o	Greater SV
o	Greater stretch of arteries
o	Less compliant
o	Relatively greater systolic pressure
64
Q

how does exercise affect the SV?

A

During exercise the stroke volume increases. Each time the heart beats, we expel more blood. Squeezing the blood in the legs and veins so more is going back to the heart

65
Q

when the brain lacks o2 what does it do?

A

sends sympathetic messages to veins, which squeeze in so more blood goes back to the heart.

66
Q

increasing CO does what to the aorta?

A

aorta stretches more

67
Q

why is there greater stretch of the arteries?

A

because more blood is ejected

68
Q

greater stretch of the arteries causes what?

A

Greater stretch of the arteries as more blood is ejected causes less compliance and less recoil and the difference between systole and diastole increases i.e. pulse pressure increases

69
Q

at a normal SV, there is a linear relationship between what?

A

pulse pressure has a linear relationship with stroke volume

70
Q

is there a limit to how much the aorta can stretch?

A

yes

71
Q

given there is a limit to how much the aorta can stretch, how does this affect the curve?

A

Increase SV, increase in steepness of curve

– caused as reaching upper limits as it is how much aorta can stretch

72
Q

as you get older how is arterial compliance affected?

A

there is a decrease in arterial compliance because the arteries get stiffer

73
Q

when you have a decrease compliance, SV increases which pressures disproportionally?

A

Stroke volume now increases systolic and pulse pressure disproportionally

74
Q

having a high pulse and a low compliance increases what?

A

increases after-load

75
Q

having a high pressure means what?

A

damages vessel but also reduces CO

76
Q

what is the consequence of reducing CO?

A

makes it harder for the heart to eject blood, so it now needs more oxygen, pumps harder, heart muscles grow to match demand
-hypertrophy of the ventricle wall

77
Q

age increases the stiffness of vessels (particularly the aorta) how does this affect the arterial tree?

A

it means the large pulse pressure is present throughout arterial tree, usually this pulse will decrease

78
Q

when looking at the arterial tree, when can the pulse pressure no longer be detected?

A
  • once you get into the arterioles the pulse pressure can’t be detected
  • the flow is more continuous
79
Q

what controls mean blood pressure?

A
  • Age
  • Disease
  • Distance along arterial tree
  • Blood volume – SV, CO
  • Exercise – SV, CO
  • Emotion, - stress, anger, fear, apprehension, pain
  • Wake/sleep – Decrease in BP 80/50mmHg

sem 2 CVS (17 decks)

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