Haemodynamics- Vascular Function Flashcards

1
Q

CO = sum of…?

A

Sum of all local tissue blood flows

*tissue blood flow precisely controlled depending of tissue needs

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2
Q

What is the most important artery in terms of regulating blood flow/ where does biggest pressure drop occur

A

Small arteries and arteriole: these have muscular walls, can control lumen size and therefore resistance

High resistance > big pressure drop

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3
Q

Velocity is inversely proportional to cross-sectional area.

A
Q = (mean velocity) x (cross-sectional area)
Q= v x A

v propor. 1/A

This is why flow DROPS in capillaries.

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4
Q

DRAW MAP flow diagram

A

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5
Q

Q = change P / R

A

P is the pressure gradient, normally this is 0

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6
Q

Blood flow (Q) equals

A

Cardiac Output (CO) which is ~5L/min at rest

*** so BF is directly proportional to the pressure gradient and to TPR

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7
Q

CO should equal (PA - PV)/TPR

Why is only MAP used?

A

Because USUALLY PV = 0mmHg

But in some situations (heart failure) it can be significant

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8
Q

Resistance in series

A

R(total) = R1 + R2 + R3

very uncommon in the body.

Increasing the R anywhere will increase the total R significantly.

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9
Q

Resistance in parallel

A

1/R(total) = 1/R1 + 1/R2 + 1/R3

Increasing the R at one point means other organ/tissue areas have little to no effect on TPR, but a big effect on local flow.

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10
Q

Draw the Jean Pouiseuille equation of flow

A

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11
Q

Draw Resistance equation

A

R is proportional to

1) tube length L
2) the viscosity of fluid (n)

incersely proportional to
3) radius

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12
Q

the r^4 factor

A

r=1 Q=1
r=2 Q=16
r=4 Q=256

So anything that alters vessel diameter has a huge effect!

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13
Q

Viscosity.

Determinants of?

A

A measure of d=friction between adjacent layers of fluid.

1) Temperature : more viscous with cold
2) Haematocrit
3) Shear rate (velocity)
4) Vessel diameter

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14
Q

Anaemia

A

low blood cells, lower viscosity, higher blood flow

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15
Q

What happens at slow shear rates (velocities)

A
  • Viscosity no longer independent of shear rate

- viscosity increases as cells aggregate

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16
Q

Haematocrit

A

Red cell vol: total volume

in a sample of peripheral blood

17
Q

How does vessel diameter affect viscosity

A

in very small blood vessels (less haematocrit> axial streaming/plasma skimming)

18
Q

Poiseuilles equation assumes

A

1) steady laminar flow
2) Newtonian fluid
3) Rigid straight tube

these criteria don’t really fit!

19
Q

How is the contractile state of vascular SM controlled?

A

1) Vascular endothelial cells (NO)
2) Mediators release locally from sympathetic nerve terminals
3) Circulating hormones (angio tensin II)

20
Q

Shear Stress

A

as flow increases, shear stress on endothelial cells increase
-NO release: leads to vasodilation.

21
Q

What factors result in turbulent Flow

A
  • High fluid densities
  • large tube diameters
  • high flow velocities
  • Low fluid viscosities
  • abrupt variation in tubes
  • Tube wall irregularities
22
Q

How to predict turbulent flow with Re

A

if Re >2000 = turbulent

Re = pvD/ n

as we rarely know velocity we use

Re 4pQ/piDn

23
Q

Stenosis

A

Turbulent flow in the area post the stenosis.

Turbulence generates sound waves (murmurs) that can be heard, these intensify with flow

24
Q

Conservation of Energy: Bernoulli’s principle

A

Principle states: total energy of laminar flow without resistanct is constant and equals the sum of
Pressure energy (PxV)
Potential/gravitational energy (pgh)
Inertia/kinetic energy (1/2pv^2)

Total Energy:
E= PV + pgh + 1/2pv^2

25
In terms of Bernoulli's Principle, what happens when there's a narrowing in a vessel
- v increase - KE increases - and Total energy remains the same so Pressure must decrease! (why P drops in the narrowest part)
26
Transmural Pressure
change P = Pinside - Poutside Pressure difference across the wall of the vessel tht tension is very much dependent on the radius.
27
Laplace Law
The larger the vessel radius the larger the wall tension required to withstand an internal pressure proportional to radius pressure 1/wall thickness eg) giraffe
28
Giraffe
high pressure at top of neck = very very thick wall thickness.