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Cardiovascular system > Principles of haemodynamics > Flashcards

Principles of haemodynamics Flashcards

1
Q

What are the three factors that are important when looking at Blood Flow?

A
  1. Cardiac output
  2. Pressure difference
  3. Resistance
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2
Q

What is haemodynamics?

A

The relationship between blood flow, blood pressure and resistance to flow.

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3
Q

How does force influence haemodynamics?

A

Cardiac contraction

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4
Q

How does work influence haemodynamics?

A

Isovolumetric contraction/ejection (when pressure gets to a certain level)

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5
Q

How does pressure influence haemodynamics?

A

Difference in pressure in the aorta and veins

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6
Q

How does compliance influence haemodynamics?

A

Arterial stretch (in certain circumstances)

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7
Q

How does resistance influence haemodynamics?

A

Arterioles are the resistance vessels (not capillaries)

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8
Q

How does flow velocity influence haemodynamics?

A

Slowing down of blood flow in the capillaries (speeds up on the way back to the heart)

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9
Q

What type of system is the CVS?

A

Closed

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10
Q

How can the majority of the blood in the venous system be classified?

A

Low pressure reservoir system

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11
Q

What can the reservoir of venous blood be used for?

A

Can be used to increase cardiac output

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12
Q

Why does the events in one part of the CVS have major impacts on other parts?

A

Reduced blood flow to one area increases pressure upstream and alters flow to other areas.

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13
Q

What is the only factor that Darcy’s law considers when determining blood flow?

A

Pressure

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14
Q

What is Darcy’s law?

A

Q= (P1-P2)/R

Q= Flow 
P1-P2= Pressure difference 
R= Resistance to flow

FLOW= (Pa-CVP)/TPR

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15
Q

What factors does Bernoulli’s law consider when determining blood flow?

A

Takes into consideration Kinetic and potential energy (not just pressure)
- explains why blood moves from vena cava to aorta even if there is no difference in pressure

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16
Q

What is Bernoulli’s law?

A

Flow = Pressure (PV) + Kinetic (pV^2/2) + Potential (pgh)

Kinetic energy: momentum of blood 
Potential energy: effect of gravity 
p: fluid mass, P: pressure 
V: velocity; h: height 
g: acceleration due to gravity
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17
Q

Blood flow definition

A

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

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18
Q

Perfusion definition

A

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

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19
Q

Velocity of blood flow definition

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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20
Q

What is the velocity of blood flow in the aorta?

A

High

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21
Q

What slows down velocity?

A

Branching of the arteries

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22
Q

What happens to blood flow as cross sectional area increases?

A

The flow slows down, it is the slowest in the capillaries

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23
Q

Where does velocity then increase (after decreasing as the arteries branch)?

A

Increases with veins coming together

24
Q

At what value does blood flow remain constant?

A

10 ml/s

25
Q

Equation for calculating Volume flow

A

Q= V x A

Q= Volume flow 
V= Velocity
A= Area
26
Q

Blood flow direction

A

Aorta -> Arteries -> Arterioles -> Capillaries -> Venules -> Veins -> Vena cava

27
Q

Which blood vessels have laminar blood flow?

A
  • Most arteries
  • Arterioles
  • Venules
  • Veins
28
Q

Describe laminar blood flow

A
  • Concentric shells
  • Zero velocity at walls (molecular interactions)
  • Maximum velocity at centre
  • Moves RBCs towards the centre, speeds up blood flow through narrow vessels
29
Q

Which blood vessels have turbulent blood flow?

A
  • Ventricles (mixing)
  • Aorta (peak flow)
  • Atheroma (bruits)
30
Q

Describe turbulent blood flow

A

Blood does not flow linearly and smoothly in adjacent layers (whirlpools, eddies, vortices) due to increased pressure and velocity

31
Q

Which blood vessels have bolus blood flow?

A

Capillaries

32
Q

Describe bolus blood flow

A
  • RBCs have a larger diameter than diameter of capillaries so move in a single file
  • Plasma columns are trapped between RBCs
  • Uniform velocity, little internal friction & very low resistance
33
Q

What is Reynold’s number?

A

It describes what determines change from laminar to turbulent flow

34
Q

What is the equation for calculating Reynold’s number?

A

Re= (p x V x D)/u

p= Density 
V= Velocity 
D= Diameter 
u= viscosity
35
Q

When does turbulence occur specifically?

A

When Reynold’s number exceeds a critical value (>2000)

e.g. bruits, ejection number, increased blood velocity

36
Q

Factors that affect arterial blood pressure

A
  • Cardiac output (SV, HR)
  • Properties of arteries
  • Peripheral resistance
  • Blood viscosity
37
Q

Flow equation

A

Flow= Pa/TPR

38
Q

What are the four relationships influencing arterial blood pressure?

A
  1. Systolic pressure
  2. Diastolic pressure
  3. Pulse pressure
  4. Mean blood pressure
39
Q

What is systolic pressure?

A

Pressure when ejecting

40
Q

What is diastolic pressure?

A

Pressure when relaxing

41
Q

What is pulse pressure?

A

Difference between diastolic and systolic pressure

42
Q

What is mean blood pressure?

A

Average pressure

43
Q

What is the role of the aorta?

A

Recoil of elastic fibers of the aorta and large arteries helps to propel the blood into the circulation

44
Q

What occurs during LV ejection?

A
  • 60-80% of stroke volume is stored in the aorta and arteries as these structures are opened
  • Energy is stored in stretched elastin
45
Q

What occurs in LV diastole?

A
  • Energy is returned to the blood as the walls of the aorta and arteries contract
  • This sustains diastolic blood pressure and blood flow when the heart is relaxed
46
Q

What is pulse pressure?

A

What the finger senses, e.g. at the wrist (radial artery)

47
Q

What is the equation for calculating pulse pressure?

A

Pulse pressure = Stroke volume / Compliance

48
Q

Describe difference in pulse pressure during rest and exercise

A
  • Greater stroke volume
  • Greater stretch of arteries
  • Less compliant
  • Relatively greater systolic pressure
49
Q

Effect of raising stroke volume

A

Bigger pulse pressure

50
Q

Describe the effects of exercise on the compliance curve

A
  • During exercise, as the stroke volume increases compliance curve gets very steep leading to a very high pulse pressure
  • Greater stretch of the arteries as more blood is ejected, which causes less compliance and less recoil
  • The difference between systole and diastole increases ie pulse pressure increases
51
Q

Compliance equation

A

Compliance = changes in volume/change in pressure

52
Q

Pulse pressure equation

A

Pulse pressure = Stroke volume/compliance

53
Q

Explain relationship between pulse pressure and arterial tree

A
  • Pulse pressure at the aorta is relatively small
  • Further down the arterial tree, pulse pressure increases because the vessels become less compliant
  • Aorta still has en effect so doesn’t increase that much
  • Why pulse is measured in the radial artery (quite far away from the heart)
54
Q

Explain relationship between pulse pressure and age

A
  • Age increases the stiffness of the vessels: particularly the aorta
  • This means that large pulse pressure is present throughout the arterial tree
55
Q

How is mean BP calculated?

A

could integrate the area under curve but this is too complicated.
Mean BP= diastolic pressure + 1/3 (pulse pressure)

56
Q

What factors control 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: decreases BP to 80/50 mmHg

Cardiovascular system (16 decks)

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