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CVS II > Haemodynamics > Flashcards

Haemodynamics Flashcards

1
Q

Define haemodynamics

A

relationship between blood flow, BP, resistance to flow

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2
Q

Steps of haemodynamics?

A

Force : Contraction
Work : Isovolumetric contraction / ejection
Pressure : Diff aorta to veins
Compliance : Arterial stretch
Resistance : Arterioles
Flow : Vital parameter
Velocity : slowing down blood flow in capillaries

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3
Q

Features of low pressure reservoir system?

A

majority of blood in the venous system + can be used to increase CO - Starling’s law

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4
Q

Define Darcy’s law

A 
role of pressure energy in flow
Q = P1 - P2 / R
Q : flow
P1 - P2 : pressure diff
R : resistance to flow
Flow = Pa - CVP / TPR
Pa : arterial presure
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5
Q

Define Bernoulli’s law

A 
Role of pressure, kinetic, potential energies in flow
Flow = PV + (ρV²/2) + ρgh
PV : pressure (Pa -CVP)
ρV²/2 : kinetic (momentum of blood)
ρgh : potential (effect of gravity)
ρ : fluid mass
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6
Q

Define blood flow

A

Volume of blood flowing in a given time (ml/min)

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7
Q

Define perfusion

A

Blood flow per given mass of tissue (ml/min/g)

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8
Q

Define velocity of blood flow

A

Blood flow divided by cross sectional area where blood flows (cm/s)

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9
Q

Define velocity

A

velocity = volume flow/area

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10
Q

Define volume flow

A

velocity x area

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11
Q

Describe blood flow relationship with velocity

A
  • high velocity of blood flow in aorta
  • arteries branching slows velocity
  • greater the cross sectional area, slower blood flow
  • slowest in capillaries
  • increasing velocity with veins coming together
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12
Q

Where’s laminar blood flow?

A

Most arteries, arterioles, venules, veins

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13
Q

Where’s turbulent blood flow?

A

Ventricles (mixing), aorta (peak flow), atheroma (bruits)

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14
Q

Where’s bolus blood flow?

A

Capillaries

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15
Q

Describe laminar blood flow

A

Concentric shells
0 velocity at walls (molecular interactions between blood + wall)
Max velocity at centre so🔴towards centre
Speeds up blood flow via narrow vessels

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16
Q

Describe turbulent blood flow

A

Blood doesn’t flow linearly + smoothly in adjacent layers –> whirlpools, eddies, vortices due to changes in velocity

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17
Q

Describe bolus blood flow

A

🔴diameter > capillaries – single file
Plasma columns trapped between 🔴
Uniform velocity
Little internal friction - low resistance

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18
Q

Define Reynold’s number (Re)

A 
Describes what determines change from laminar to turbulent flow
Re = ρVD/μ
ρ : density
V : velocity
D : diameter
μ = viscosity
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19
Q

What happens when Re > 2000?

A

Turbulence occurs when Reynold’s number exceeds critical value
eg bruits, ejection murmur – increased blood velocity

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20
Q

Equation for blood flow?

A

Arterial BP/ TPR

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21
Q

Equation for blood flow?

A

Arterial BP/TPR

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22
Q

What’s the highest systolic pressure in aorta?

A

120 mmHg

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23
Q

What’s the highest diastolic pressure in aorta?

A

80 mmHg

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24
Q

How does arterial BP change?

A

falls steadily in systemic circulation with distance from left ventricle

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25
Q

Factors that affect arterial BP?

A

CO : Starling’s/Laplaces’s laws, contractility, HR
Properties of arteries : aorta
Peripheral resistance : arterioles, Haem-arterioles+veins
Blood viscosity : haemocrit, Haem-arterioles+veins

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26
Q

What does arterial BP involve?

A

Systolic, diastolic, pulse + mean blood pressure

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27
Q

Why have elastic fibres in aorta?

A

makes aorta compliant - can stretch under p to propel blood into circulation

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28
Q

How much SV is stored in aorta during LV ejection?

A

60-80% as these structures expand

Energy stored in stretched elastin

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29
Q

What sustains diastolic BP + blood flow when heart’s relaxed?

A

in LV diastole energy returned to blood as aorta walls contract

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30
Q

Equations for pulse p

A

Systolic pressure-Diastolic pressure = Pulse pressure
120 - 80 = 40
Pulse pressure = SV/compliance

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31
Q

Describe pressure profile

A 
1 – Ejection
2 – Peak Systolic
3 – Systolic decline (aorta compliance)
4 – Incisura/dicrotic notch (aortic valve closes)
5 – Diastolic run off,
6 – Peak Diastolic
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32
Q

What is pulse p + what does it tell you?

A

finger senses radial artery which tells you about SV + arterial compliance (stretchiness)

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33
Q

Describe relationship between volume of blood in elastic arteries vs arterial p

A

exponential

when SV raised bigger pulse p

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34
Q

Why’s there a greater systolic p when there’s a greater SV?

A

as eject more blood it stretches aortic wall more, finite amount can stretch, aorta loses compliance creating more pressure

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35
Q

Describe elderly graph of volume of blood in elastic arteries vs arterial p

A

steeper exponential because, decreased compliance, increase in afterload, to increase SV

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36
Q

Equation for compliance?

A

compliance = change in v/change in p

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37
Q

Why decreased compliance with age?

A

stiffer arteries (arteriosclerosis)

38
Q

Why does pulse p increase down arterial tree?

A

Tapering of vessels + increased stiffness of distal arteries

39
Q

What happens to pulse p at arterioles?

A

At arterioles pulse pressure disappears – drop of pressure means flow more continuous

40
Q

What’s aortic stenosis?

A

narrowing of aortic valve which narrows exit from heart so slower upstroke, smaller peak indicating poorer ejection

41
Q

What’s aortic regurgitation?

A

Leaky aortic valve

fast upstroke, larger peak, poor diastolic run off indicating blood entering aorta/ventricles during diastolic

42
Q

How to calculate mean BP?

A

diastolic pressure + 1/3 [pulse pressure]

43
Q

What controls mean BP?

A

age, disease, distance along arterial tree, blood volume (SV,CO), exercise (SV,CO), emotion (stress, anger, fear, apprehension, pain), wake/Sleep (80/50 mmHg)

44
Q

Equation of blood flow?

A 
blood flow = arterial blood p / TPR
CO = (Pa - CVP) / TPR
blood flow = Pa - CVP x G
G because TPR = 1/conductance
G : conductance
CO : bloow flow, cardiac output
Pa = blood pressure
45
Q

Equation of blood pressure (Pa)?

A

Pa = CO x TPR

46
Q

What’s used in Darcy’s law of flow states?

A

Arterial p (Pa – mean BP 90 mmHg)
TPR (Total Peripheral Resistance of vasculature)
CVP (Central Venous Pressure)

47
Q

Role of TPR?

A

controls blood flow + BP so when increased resistance, increase in pressure to keep constant flow

48
Q

What controls TPR?

A

Poiseuille’s law
Myogenic response
Blood viscosity

49
Q

How does vasodilation affect blood flow?

A

lower BP in artery, lower TPR in arterioles so increased blood flow

50
Q

How does constriction affect blood flow?

A

higher BP in artery, higher TPR in arterioles so decreased blood flow

51
Q

How does hypertension happen?

A

over constriction of arterioles –> reduction in blood flow – harmful –> end organ damage

52
Q

Why does pressure drop from arteries to capillaries?

A

increased resistance

53
Q

Define Poiseuille’s law

A

describes parameters that govern TPR

54
Q

Equation of resistance?

A 
resistance = 8ηL / πr⁴
r = Radius of vessel
η = Blood viscosity
L = Vessel length
55
Q

Equation of conductance?

A 
conductance = πr⁴ / 8ηL
r = Radius of vessel
η = Blood viscosity
L = Vessel length
56
Q

What’s the equation of Darcy’s + Poiseullie’s law?

A

blood flow = Pa - CVP x (πr⁴ / 8ηL)
r = Radius of vessel
η = Blood viscosity
L = Vessel length

57
Q

eg of r⁴ effect?

A

radius 1 vs radius 2

2 has increased flow by 16x + exerts 1/16th of the resistance of radius 1

58
Q

What’s TPR in arterioles controlled by?

A

r⁴
pressure diff across vessels P1 - P2
length L

59
Q

What’s arteriole radius controlled by?

A

ANS release NA - vascular tone

60
Q

Why do arterioles control TPR and not capillaries?

A

-Radius
No sympathetic innervation/smooth muscle
-Pressure drop
Less pressure drop across capillaries (20-30mmHg) than arterioles (40-50 mmHg) ∵ less resistance to blood flow in capillaries
-Length short

61
Q

Why’s there less resistance in capillaries?

A

-Bolus flow reduces viscosity (η)
-Capillaries arranged in parallel RTotal = 1/R1 + 1/R2
but arterioles in series with arteries, arterioles,capillaries
RTotal = R1 + R2

62
Q

What’s local blood flow mainly controlled by?

A

changes in radius of arterioles supplying a given organ/tissue

63
Q

eg of intrinsic control of arteriole radius?

A

Factors entirely within an organ or tissue:

neural, humoral

64
Q

eg of extrinsic control of arteriole radius?

A

Factors outside the organ or tissue:

bayliss myogenic response, tissue metabolites, local hormones, endothelial factors

65
Q

What’s bayliss myogenic response?

A
  • Increase pressure
  • distended vessel
  • feedbacks to constrict
  • controls flow
  • Decrease pressure
  • dilate vessel
  • maintain blood flow in presence of low BP
66
Q

When does the bayliss myogenic response not work?

A

critical point below 60mmHg

67
Q

Importance of bayliss myogenic response?

A
  • Maintains local blood flow when changes in local BP (renal, coronary, cerebral circulation)
  • Protective – low BP, still good flow + high BP, less flow/damage
68
Q

Define viscosity

A

measure of internal friction opposing the separation of the lamina

69
Q

What does blood viscosity depend on?

A

Velocity of blood
Vessel diameter
Haematocrit

70
Q

What’s normal haematocrit?

A

45%

71
Q

What’s typical blood η relative to water?

A

4-5

72
Q

Clinical implications of polycythaemia?

A
  • high η
  • high TPR/BP
  • low BF
73
Q

Clinical implications of anaemia?

A
  • low η
  • low TPR/BP
  • high HR (baroreceptor reflex)
74
Q

Clinical implications of tube diameter (Fahraeus-Lindqvist effect)?

A
  • η falls in small vessels (< 100 µm) due to bolus flow
  • low resistance
  • high BF in microvessels
75
Q

Clinical implications of 🔴deformability?

A
  • high η
  • low BF
  • sickle cell crises (pain)
76
Q

Clinical implications of blood velocity?

A

slow venous flow in immobile legs – increased η

77
Q

How much blood volume is in systemic veins + venules?

A

60%

78
Q

Describe veins

A

Thin-walled, collapsible, voluminous vessels
Contain 2/3ths of blood volume
Contractile – has smooth muscle, innervated by sympathetic nerves
Control radius

79
Q

What does the contraction of veins do?

A

Expels blood into central veins
Increases venous return/CVP/end-diastolic volume
Increases stroke volume (Starling’s law)

80
Q

What’s the typical venous pressure of limb vein, heart level?

A

5-10 mmHg

81
Q

What’s the typical CVP?

A

0-5 mmHg

82
Q

What’s the typical venous pressure of foot vein, standing?

A

90 mmHg

83
Q

Why do veins collapse when hand above heart?

A

gravity

84
Q

What happens when you stimulate sympathetic nerves of veins?

A 
Venoconstriction
Shifts blood centrally
Increases venous return/CVP/end-diastolic pressure
Increased SV (Starling’s law)
85
Q

How do veins return blood back to heart?

A

pressure gradient
thoracic pump
skeletal muscle pump

86
Q

How does pressure gradient cause venous return?

A

Pressure in veins between 10 (supine) – 90 (standing) mm Hg
IVC/SVC/right atrium < 5 mm Hg
Venous return = Venous Pressure – Pressure right atrium / Venous resistance

87
Q

How does thoracic pump cause venous return?

A
  • inhalation
  • thoracic cavity expands
  • increased abdominal pressure
  • increased pressure on IVC (squeezes it)
  • forcing blood upward towards heart
  • increased right ventricular SV
  • blood flows faster with inhalation
  • take more O2
  • reduce CVP in RA
  • increases pressure diff
88
Q

How does skeletal muscle pump cause venous return?

A
  • leg muscles contract
  • returns blood into RA
  • retrograde flow prevented by valves
  • reduce high local venous pressures when upright position
  • reduces swelling of feet from lower venous pressures, lower capillary pressure, less filtration
  • lower CVP + SV during exercise
89
Q

Why can standing for a long time cause you to faint?

A

-pooling blood
-decrease starlings low
-decrease SV
-decrease CO
-poor perfusion of brain
gravity, heat-induced vasodilatation, lack of muscle use

90
Q

How does blood flow with very little pressure difference?

A
  • ejected blood has greater kinetic energy at heart than feet (more velocity, V) + potential energy (more height, h)
  • greater kinetic/potential energies overcome pressure gradient to maintain flow
  • pressure + potential gradients cancel each other but KINETIC ENERGY
91
Q

What’s Bernoulli theory?

A

mechanical energy of flow is determined by
pressure, kinetic, potential energies
Pressure (PV) + Kinetic (ρV2/2) + potential (ρgh)
ρ: fluid mass

CVS II (19 decks)

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