Haemodynamics- Vascular Function

Question 1

CO = sum of…?

Answer 1

Sum of all local tissue blood flows

*tissue blood flow precisely controlled depending of tissue needs

Question 2

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

Answer 2

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

High resistance > big pressure drop

Question 3

Velocity is inversely proportional to cross-sectional area.

Answer 3

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

v propor. 1/A

This is why flow DROPS in capillaries.

Question 4

DRAW MAP flow diagram

Answer 4

…

Question 5

Q = change P / R

Answer 5

P is the pressure gradient, normally this is 0

Question 6

Blood flow (Q) equals

Answer 6

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

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

Question 7

CO should equal (PA - PV)/TPR

Why is only MAP used?

Answer 7

Because USUALLY PV = 0mmHg

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

Question 8

Resistance in series

Answer 8

R(total) = R1 + R2 + R3

very uncommon in the body.

Increasing the R anywhere will increase the total R significantly.

Question 9

Resistance in parallel

Answer 9

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.

Question 10

Draw the Jean Pouiseuille equation of flow

Answer 10

…

Question 11

Draw Resistance equation

Answer 11

…

R is proportional to

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

incersely proportional to
3) radius

Question 12

the r^4 factor

Answer 12

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

So anything that alters vessel diameter has a huge effect!

Question 13

Viscosity.

Determinants of?

Answer 13

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

Question 14

Anaemia

Answer 14

low blood cells, lower viscosity, higher blood flow

Question 15

What happens at slow shear rates (velocities)

Answer 15

• Viscosity no longer independent of shear rate

- viscosity increases as cells aggregate

Question 16

Haematocrit

Answer 16

Red cell vol: total volume

in a sample of peripheral blood

Question 17

How does vessel diameter affect viscosity

Answer 17

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

Question 18

Poiseuilles equation assumes

Answer 18

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

these criteria don’t really fit!

Question 19

How is the contractile state of vascular SM controlled?

Answer 19

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

Question 20

Shear Stress

Answer 20

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

Question 21

What factors result in turbulent Flow

Answer 21

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

Question 22

How to predict turbulent flow with Re

Answer 22

if Re >2000 = turbulent

Re = pvD/ n

as we rarely know velocity we use

Re 4pQ/piDn

Question 23

Stenosis

Answer 23

Turbulent flow in the area post the stenosis.

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

Question 24

Conservation of Energy: Bernoulli’s principle

Answer 24

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

Question 25

In terms of Bernoulli’s Principle, what happens when there’s a narrowing in a vessel

Answer 25

• v increase
• KE increases
• and Total energy remains the same

so Pressure must decrease! (why P drops in the narrowest part)

Question 26

Transmural Pressure

Answer 26

change P = Pinside - Poutside
Pressure difference across the wall of the vessel

tht tension is very much dependent on the radius.

Question 27

Laplace Law

Answer 27

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

Question 28

Giraffe

Answer 28

high pressure at top of neck = very very thick wall thickness.