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T3 CVS > 6.1 Haemodynamics > Flashcards

6.1 Haemodynamics Flashcards

1
Q

define flow

A
  • Volume of substance over time (cm3/s)
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2
Q

define velocity

A

Distance substance is displaced over time
(cm/s)

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3
Q

define vascular resistance

A

Force within the circulatory system opposing
the flow of blood

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4
Q

define laminar flow

A

Flow of a substance (blood) through a tube (blood vessel) parallel to the tube’s edges (vessel walls) whereby velocity increases towards the centre of the lumen

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5
Q

define turbulent flow

A

Disorganised flow of substance (blood) through a tube
(blood vessel) in a wide variety of antegrade and retrograde velocities simultaneously

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6
Q

define critical velocity

A

The velocity at which a fluid will switch from a laminar
flow to a turbulent flow

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7
Q

define viscosity

A
  • Resistance of a fluid to deformation
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8
Q

Most important takeaway of poiselle-hagan formuala ?

A

small changes to radius have a big impact on flow

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9
Q

Poiselle-Hagan formuala expresses relationship between ?

A

flow, viscosity and tube (blood vessel) radius

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10
Q

What is tension on wall of a (blood vessel) cylinder equal to ?

A

the product of transmural pressure and radius divided by wall thickness (P x r)/ w

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11
Q

most important implication of law of laplace ?

A

explains why capillaries don’t rupture despite having very thin walls

  • Since the smaller the radius of a vessel, the less tension is required to withstand the internal pressure
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12
Q

What is flow (volume of fluid moved per unit time) affected by ?

A
  • Pressure – fluids flow from high to low pressure
    -> therefore ∆P as pressure difference between one end of the tube and the other is taken
  • Resistance – High resistance reduces flow
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13
Q

what is the flow of blood flow through vessels ?

A

laminar

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14
Q

Explain blood flow through vessels:

A
  • Flow is organised and parallel to the cylinder (blood vessel) walls
  • Velocity is highest in the centre of the lumen and lowest where blood is in contact with the cylinder (blood vessel) walls
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15
Q

until when will blood flow remain laminar?

A

Until it reaches a critical velocity, at which point flow will become turbulent

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16
Q

Velocity = distance over time , what is this affected by ?
[Assuming that ∆P is constant]

A

the flow rate through a vessel and the cross-sectional area of that vessel

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17
Q

why does aorta have highest velocity ? [check!]

A
  • high pressure
  • low surface area
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18
Q

Why is the lowest velocity within the capillaries ?

A

largest total area is at the level of capillaries

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19
Q

what does area refer to in average velocity ? [alter and change!]

A

total area of all tubes running in parallel within the system

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20
Q

turbulent flow…

A
21
Q

Viscosity is degree to which …?

A

a fluid resists deformation
INC Viscosity = DEC flow

22
Q

What is viscosity in blood produced by ?

A
  • friction between molecule and cells (INC molecuels = INC V and INC haematocrit = INC V)
  • compressibility of cells (ING rigidity = INC V e.g. hereditary spherocytosis)
  • composition of plasma e.g. conditions leading to INC immunoglobulin concentration
23
Q

what is hereditary spherocytosis (change!)?

A

red blood cells have deficiency gene mutation expression of protein messes up cytoskeleton of red blood cell

24
Q
  1. what is shear stress ?
  2. proportional to ?
A
  1. force exerted onto the endothelium parallel to blood flow
  2. viscosity
25
Q

….1… flow produces regular ..2.. this impacts ..3… cells and …4… of athero-protective factors

A
  1. pulsatile laminar
  2. shear stress
  3. smooth muscle
  4. increased expression
26
Q

What’s problem with turbulent flow ?

A
  • can damage endothelium and INC risk of atherogenesis
  • often occurs at arterial bifurcations and curvature => INC plaque formation
  • more likely to occur after a constriction (stenosis)
27
Q

why bifurcation -> plaque ? [what did he mention !!!]

A

orientation change ?

28
Q

One problem of turbulent flow is it’s more likely to occur after a constriction (stenosis), why ?

A
  • Increased velocity through stenosis due to decreased cross sectional area of lumen
  • Further damage directly after plaque/stenosis
  • Further increases risk of atheroma proliferation
29
Q

Poiseuille-Hagen is a formula that shows what ?

A

radius has a HUGE impact on Flow and Resistance

30
Q

Poiseuille-Hagen, what happens when:
1. double diameter
2. half diameter

A
  1. 16x flow
  2. 16x resistance
31
Q
A
32
Q

Effects of small increase and decrease in diameter?

A

INCREASE = massively INC flow
DECREASE = massicely INC resistance

33
Q

What cannulae are used for IV drug administration ?

A

peripheral

34
Q

Poiseuille-Hagen relationship to peripheral cannulla sizes ? [he mentioned in lecture ]

A

measured in gauge
higher the guage = smaller diameter / the less fluid you can give in given time

35
Q

french catheter scale ?

A

one french unit = 0.33 mm therefore as they INC diameter gets bigger
urinary catheter
give 12 - 16 inch catheters

36
Q

Arterioles have:
..1… in their walls so a …2.. area this makes them …3. at INC flow or ….4… which is very effective at controlling ..5.. to organs

A
  1. smooth muscle
  2. very large total
  3. very effective
  4. resistance
  5. blood supply
37
Q

What is critical closing pressure ? = ALTER Q + A

A

In small vessels when luminal P < tissue pressure the vessel will collapse
- due to surrounding tissues exerting a small amount of pressure
- there is a point where flow = 0 , even though pressure > 0

38
Q

Although capillary walls are 1 cell thick they don’t burst, why don’t they rupture ?

A

law of laplace [T = Pxr/w]
T = tension
P = transmural pressure
r = radius
w = wall thickness

**they don’t burst because of their small radius ! **

39
Q

law of laplace tension ?

A

required to withstand pressure INC in T = INC in chance of rupture

40
Q

law of laplace transmural pressure ?

A

Transmural pressure = inside pressure – outside pressure
* Outside pressure is so small it can be ignored
* Therefore, Transmural pressure = inside pressure

41
Q

law of laplace wall thickness ?

A

Capillary wall so thin that this can be ignored so law of laplace equation becomes T = Pxr

42
Q

Law of laplace when pressure in an individual capillary stays very low ?

A

P = T/r (smaller value of r = DEC tension requirement)

43
Q

what type of vessels are veins considered to be ?

A

capacitance vessels

44
Q

Why are veins referred to as capacitance vessels ?

A

they can hold a large volume of blood without a significant INC in venous pressure due to their distensibility

45
Q

% of body’s circulating blood volume is contained within veins ?

A

50%

46
Q

How do veins differ from arteries in terms of their ability to store blood?

A

Veins have a greater capacity to store blood than arteries due to their high distensibility, which allows them to expand and accommodate more blood without raising pressure significantly.

47
Q

How does the distensibility of veins benefit the circulatory system?

A

The distensibility of veins allows them to act as reservoirs that can accommodate excess blood, helping to regulate blood volume and pressure throughout the circulatory system.

48
Q

What would likely happen if veins were not as distensible?

A

If veins were not as distensible, even a small increase in blood volume could cause a significant rise in venous pressure, potentially leading to problems like venous hypertension or impaired blood return to the heart

T3 CVS (11 decks)

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