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?

25
Equation for calculating Volume flow
Q= V x A ``` Q= Volume flow V= Velocity A= Area ```
26
Blood flow direction
Aorta -> Arteries -> Arterioles -> Capillaries -> Venules -> Veins -> Vena cava
27
Which blood vessels have laminar blood flow?
- Most arteries - Arterioles - Venules - Veins
28
Describe laminar blood flow
- 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
Which blood vessels have turbulent blood flow?
- Ventricles (mixing) - Aorta (peak flow) - Atheroma (bruits)
30
Describe turbulent blood flow
Blood does not flow linearly and smoothly in adjacent layers (whirlpools, eddies, vortices) due to increased pressure and velocity
31
Which blood vessels have bolus blood flow?
Capillaries
32
Describe bolus blood flow
- 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
What is Reynold's number?
It describes what determines change from laminar to turbulent flow
34
What is the equation for calculating Reynold's number?
Re= (p x V x D)/u ``` p= Density V= Velocity D= Diameter u= viscosity ```
35
When does turbulence occur specifically?
When Reynold's number exceeds a critical value (>2000) | e.g. bruits, ejection number, increased blood velocity
36
Factors that affect arterial blood pressure
- Cardiac output (SV, HR) - Properties of arteries - Peripheral resistance - Blood viscosity
37
Flow equation
Flow= Pa/TPR
38
What are the four relationships influencing arterial blood pressure?
1. Systolic pressure 2. Diastolic pressure 3. Pulse pressure 4. Mean blood pressure
39
What is systolic pressure?
Pressure when ejecting
40
What is diastolic pressure?
Pressure when relaxing
41
What is pulse pressure?
Difference between diastolic and systolic pressure
42
What is mean blood pressure?
Average pressure
43
What is the role of the aorta?
Recoil of elastic fibers of the aorta and large arteries helps to propel the blood into the circulation
44
What occurs during LV ejection?
- 60-80% of stroke volume is stored in the aorta and arteries as these structures are opened - Energy is stored in stretched elastin
45
What occurs in LV diastole?
- 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
What is pulse pressure?
What the finger senses, e.g. at the wrist (radial artery)
47
What is the equation for calculating pulse pressure?
Pulse pressure = Stroke volume / Compliance
48
Describe difference in pulse pressure during rest and exercise
- Greater stroke volume - Greater stretch of arteries - Less compliant - Relatively greater systolic pressure
49
Effect of raising stroke volume
Bigger pulse pressure
50
Describe the effects of exercise on the compliance curve
- 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
Compliance equation
Compliance = changes in volume/change in pressure
52
Pulse pressure equation
Pulse pressure = Stroke volume/compliance
53
Explain relationship between pulse pressure and arterial tree
- 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
Explain relationship between pulse pressure and age
- Age increases the stiffness of the vessels: particularly the aorta - This means that large pulse pressure is present throughout the arterial tree
55
How is mean BP calculated?
could integrate the area under curve but this is too complicated. Mean BP= diastolic pressure + 1/3 (pulse pressure)
56
What factors control mean blood pressure?
- 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