Volume of substance over time (cm3/s)

Resistance of a fluid to deformation

6.1 Haemodynamics Flashcards by sanaya k

define flow

Volume of substance over time (cm3/s)

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define velocity

Distance substance is displaced over time
(cm/s)

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define vascular resistance

Force within the circulatory system opposing
the flow of blood

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define laminar flow

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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define turbulent flow

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

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define critical velocity

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

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define viscosity

Resistance of a fluid to deformation

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Most important takeaway of poiselle-hagan formuala ?

small changes to radius have a big impact on flow

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Poiselle-Hagan formuala expresses relationship between ?

flow, viscosity and tube (blood vessel) radius

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

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

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most important implication of law of laplace ?

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

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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what is the flow of blood flow through vessels ?

laminar

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Explain blood flow through vessels:

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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until when will blood flow remain laminar?

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

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

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

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why does aorta have highest velocity ? [check!]

high pressure
low surface area

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Why is the lowest velocity within the capillaries ?

largest total area is at the level of capillaries

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

total area of all tubes running in parallel within the system

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turbulent flow…

Viscosity is degree to which …?

a fluid resists deformation
INC Viscosity = DEC flow

What is viscosity in blood produced by ?

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

what is hereditary spherocytosis (change!)?

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

what is shear stress ?
proportional to ?

force exerted onto the endothelium parallel to blood flow
viscosity

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

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

What's problem with turbulent flow ?

* 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)

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

orientation change ?

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

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

Poiseuille-Hagen is a formula that shows what ?

radius has a HUGE impact on Flow and Resistance

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

1. 16x flow 2. 16x resistance

Effects of small increase and decrease in diameter?

INCREASE = massively INC flow DECREASE = massicely INC resistance

What cannulae are used for IV drug administration ?

peripheral

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

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

french catheter scale ?

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

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

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

What is critical closing pressure ? = ALTER Q + 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

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

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 ! **

law of laplace tension ?

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

law of laplace transmural pressure ?

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

law of laplace wall thickness ?

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

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

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

what type of vessels are veins considered to be ?

capacitance vessels

Why are veins referred to as capacitance vessels ?

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

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

50%

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

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.

How does the distensibility of veins benefit the circulatory system?

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.

What would likely happen if veins were not as distensible?

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