Haemodynamics Flashcards

1
Q

What is haemodynamics?

A

physical laws governing pressure/flow relationships in blood vessels

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2
Q

fluid mechanics principles can apply to the CVS, but what is different?

A

blood is not simple ‘Newtonian fluid’ - contains red and whtie blood cells, platelets, lipds
blood vessels are not uniform, straight, rigid tubes

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3
Q

Equation for flow

A

flow = change in p / resistance

p = pressure gradient between arteries and veins created by pumping heart action

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4
Q

General structure if blood vessel

A

adventitia
media (smooth muscle, elastin, collagen)
intima (endothelium)
lumen

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5
Q

How is there active control over the blood vessels?

A

smooth muscle contracts and relaxes, expanding and narrowing the lumen

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6
Q

What is normally found between the media and adventitia?

A

sympathetic nerves which innervate the smooth muscle

causes vasoconstriction

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7
Q

How does internal diameter and wall thickness change between blood vessels?

A

aorta - arteries - arterioles - capillaries - venules - veins - vena cava

decreases to capillaries then increases to VC

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8
Q

How does elasticity and smooth muscle of arteries differ?

A

elasticity decreases with size

smooth muscle in areries and arterioles more

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9
Q

Which blood vessels have no smooth muscle and is not elastic?

A

capillaries and venules

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10
Q

Compare the total cross sectional areas with all the blood vessels

A

aorta < arteries < arterioles < capillaries

capillaries > venules > veins

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11
Q

What can be used to see CSA?

A

change in velocity of the blood

increased velocity = decreased CSA

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12
Q

What are the determinants of flow?

Darcy’s

A

Flow – directly related to the pressure difference (Pi-Po)

Flow – inversely related to the resistance (R)

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13
Q

What are the determinants of flow?

Poiseuille’s

A

Flow – directly related to pressure difference (Pi-Po)
Flow – inversely related to length of tube (l)
Flow – inversely related to viscosity of fluid ()
Flow – directly related to radius of tube (r)4

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14
Q

Key point for flow being directly related to pressure difference

A

greater the pressure gradient, greater the flow

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15
Q

Key point for flow being inversely related to length of tube

A

longer the vessel, lower the flow

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16
Q

Key point for flow being inversely related to the viscosity

A

increased viscosity, lower flow

17
Q

Key point for flow being directly related to the radius of the tube

A

greater radius of vessel, greater flow

18
Q

In real body, what is resistance (flow) actually determined by?

A

radius of the blood vessels

and pumping of the heart

19
Q

What is the exact relationship between relative radius and relative flow?

A

F ∝ r^4

slight increase in radius means large increase in flow

20
Q

Which vessels have the greatest capacity to change radius?

A

small arteries and arterioles

‘resistance vessels’

21
Q

Which vessels have the largest drop in pressure? why? and why is this important?

A

small arteries and arterioles
increased resistance due to change in radius
to decrease pressure before entering capillaries

22
Q

Equation for total peripheral resistance

A

arterial - venous P / cardiac output

23
Q

What also occurs in blood when flow changes?

A

smoothing of pulsatile blood to steady

24
Q

Equation for resistance

not necessary to remember

A

pressure difference / flow

25
Why will individual blood flows be less than the total flow?
cardiac output is distributed to vascular beds (usually arranged in parallel)
26
How is total peripheral resistance affected by parallel vascular beds?
less than individual resistance
27
What is laminar blood flow?
velocity is max in the centre | straight flow
28
What is turbulent flow?
lack of laminar movement | need higher dirving pressure to achieve same flow
29
Why does turbulent flow occur?
when there is branches in the blood vessels | atherosclerosis - artificially narrows the vessels
30
How do the vessels make blood flow as laminar as possible?
Vessels are not rigid tubes Elasticity conferred by elastin + collagen Elastic conduits (arteries) and high resistance arterioles have a smoothing effect on blood flow
31
What is compliance in relation to blood vessels?
change in volume for a given change in pressure
32
Arterial role in relation to compliance
provides filtering and smoothing
33
Venous role in relation to compliance
provides capacity for storage
34
If a blood vessel is compliant, what does this mean?
it is less distensible
35
What is venous return affected by?
venomotor tone (constriction) venous valve competence skeletal muscle pump - muscle contraction in legs respiration - increased inspiration, decreases intra-thoracic pressure, increases intra-abdominal pressure, provides pressure gradient