CVS II > Haemodynamics > Flashcards

Haemodynamics Flashcards

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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
Factors that affect arterial BP?
CO : Starling’s/Laplaces’s laws, contractility, HR Properties of arteries : aorta Peripheral resistance : arterioles, Haem-arterioles+veins Blood viscosity : haemocrit, Haem-arterioles+veins
26
What does arterial BP involve?
Systolic, diastolic, pulse + mean blood pressure
27
Why have elastic fibres in aorta?
makes aorta compliant - can stretch under p to propel blood into circulation
28
How much SV is stored in aorta during LV ejection?
60-80% as these structures expand | Energy stored in stretched elastin
29
What sustains diastolic BP + blood flow when heart's relaxed?
in LV diastole energy returned to blood as aorta walls contract
30
Equations for pulse p
Systolic pressure-Diastolic pressure = Pulse pressure 120 - 80 = 40 Pulse pressure = SV/compliance
31
Describe pressure profile
``` 1 – Ejection 2 – Peak Systolic 3 – Systolic decline (aorta compliance) 4 – Incisura/dicrotic notch (aortic valve closes) 5 – Diastolic run off, 6 – Peak Diastolic ```
32
What is pulse p + what does it tell you?
finger senses radial artery which tells you about SV + arterial compliance (stretchiness)
33
Describe relationship between volume of blood in elastic arteries vs arterial p
exponential | when SV raised bigger pulse p
34
Why's there a greater systolic p when there's a greater SV?
as eject more blood it stretches aortic wall more, finite amount can stretch, aorta loses compliance creating more pressure
35
Describe elderly graph of volume of blood in elastic arteries vs arterial p
steeper exponential because, decreased compliance, increase in afterload, to increase SV
36
Equation for compliance?
compliance = change in v/change in p
37
Why decreased compliance with age?
stiffer arteries (arteriosclerosis)
38
Why does pulse p increase down arterial tree?
Tapering of vessels + increased stiffness of distal arteries
39
What happens to pulse p at arterioles?
At arterioles pulse pressure disappears – drop of pressure means flow more continuous
40
What's aortic stenosis?
narrowing of aortic valve which narrows exit from heart so slower upstroke, smaller peak indicating poorer ejection
41
What's aortic regurgitation?
Leaky aortic valve | fast upstroke, larger peak, poor diastolic run off indicating blood entering aorta/ventricles during diastolic
42
How to calculate mean BP?
diastolic pressure + 1/3 [pulse pressure]
43
What controls mean BP?
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
Equation of blood flow?
``` 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
Equation of blood pressure (Pa)?
Pa = CO x TPR
46
What's used in Darcy's law of flow states?
Arterial p (Pa – mean BP 90 mmHg) TPR (Total Peripheral Resistance of vasculature) CVP (Central Venous Pressure)
47
Role of TPR?
controls blood flow + BP so when increased resistance, increase in pressure to keep constant flow
48
What controls TPR?
Poiseuille’s law Myogenic response Blood viscosity
49
How does vasodilation affect blood flow?
lower BP in artery, lower TPR in arterioles so increased blood flow
50
How does constriction affect blood flow?
higher BP in artery, higher TPR in arterioles so decreased blood flow
51
How does hypertension happen?
over constriction of arterioles --> reduction in blood flow – harmful --> end organ damage
52
Why does pressure drop from arteries to capillaries?
increased resistance
53
Define Poiseuille’s law
describes parameters that govern TPR
54
Equation of resistance?
``` resistance = 8ηL / πr⁴ r = Radius of vessel η = Blood viscosity L = Vessel length ```
55
Equation of conductance?
``` conductance = πr⁴ / 8ηL r = Radius of vessel η = Blood viscosity L = Vessel length ```
56
What's the equation of Darcy's + Poiseullie's law?
blood flow = Pa - CVP x (πr⁴ / 8ηL) r = Radius of vessel η = Blood viscosity L = Vessel length
57
eg of r⁴ effect?
radius 1 vs radius 2 | 2 has increased flow by 16x + exerts 1/16th of the resistance of radius 1
58
What's TPR in arterioles controlled by?
r⁴ pressure diff across vessels P1 - P2 length L
59
What's arteriole radius controlled by?
ANS release NA - vascular tone
60
Why do arterioles control TPR and not capillaries?
-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
Why's there less resistance in capillaries?
-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
What's local blood flow mainly controlled by?
changes in radius of arterioles supplying a given organ/tissue
63
eg of intrinsic control of arteriole radius?
Factors entirely within an organ or tissue: | neural, humoral
64
eg of extrinsic control of arteriole radius?
Factors outside the organ or tissue: | bayliss myogenic response, tissue metabolites, local hormones, endothelial factors
65
What's bayliss myogenic response?
- Increase pressure - distended vessel - feedbacks to constrict - controls flow - Decrease pressure - dilate vessel - maintain blood flow in presence of low BP
66
When does the bayliss myogenic response not work?
critical point below 60mmHg
67
Importance of bayliss myogenic response?
- 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
Define viscosity
measure of internal friction opposing the separation of the lamina
69
What does blood viscosity depend on?
Velocity of blood Vessel diameter Haematocrit
70
What's normal haematocrit?
45%
71
What's typical blood η relative to water?
4-5
72
Clinical implications of polycythaemia?
- high η - high TPR/BP - low BF
73
Clinical implications of anaemia?
- low η - low TPR/BP - high HR (baroreceptor reflex)
74
Clinical implications of tube diameter (Fahraeus-Lindqvist effect)?
- η falls in small vessels (< 100 µm) due to bolus flow - low resistance - high BF in microvessels
75
Clinical implications of 🔴deformability?
- high η - low BF - sickle cell crises (pain)
76
Clinical implications of blood velocity?
slow venous flow in immobile legs – increased η
77
How much blood volume is in systemic veins + venules?
60%
78
Describe veins
Thin-walled, collapsible, voluminous vessels Contain 2/3ths of blood volume Contractile – has smooth muscle, innervated by sympathetic nerves Control radius
79
What does the contraction of veins do?
Expels blood into central veins Increases venous return/CVP/end-diastolic volume Increases stroke volume (Starling’s law)
80
What's the typical venous pressure of limb vein, heart level?
5-10 mmHg
81
What's the typical CVP?
0-5 mmHg
82
What's the typical venous pressure of foot vein, standing?
90 mmHg
83
Why do veins collapse when hand above heart?
gravity
84
What happens when you stimulate sympathetic nerves of veins?
``` Venoconstriction Shifts blood centrally Increases venous return/CVP/end-diastolic pressure Increased SV (Starling’s law) ```
85
How do veins return blood back to heart?
pressure gradient thoracic pump skeletal muscle pump
86
How does pressure gradient cause venous return?
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
How does thoracic pump cause venous return?
- 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
How does skeletal muscle pump cause venous return?
- 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
Why can standing for a long time cause you to faint?
-pooling blood -decrease starlings low -decrease SV -decrease CO -poor perfusion of brain gravity, heat-induced vasodilatation, lack of muscle use
90
How does blood flow with very little pressure difference?
- 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
What's Bernoulli theory?
mechanical energy of flow is determined by pressure, kinetic, potential energies Pressure (PV) + Kinetic (ρV2/2) + potential (ρgh) ρ: fluid mass
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