Pressure & Flow

Question 1

What are the X2 formulas for calculating MAP?

Answer 1

MAP = diastolic + (1/3 pulse pressure)

MAP = C.O. x T.P.R.

Question 2

What law is linked to the rate of diffusion?

Answer 2

Fick’s law

Question 3

What X3 things influence fick’s law?

Which of these is the main limiting factor?

Answer 3

Area (over which diffusion is occurring)

Concentration (of the substance across the membrane)

Distance (over which it is diffusing)

DISTANCE IS THE LIMITING FACTOR!

Question 4

Diffusion over large distances becomes too slow. What does the body employ to combat this?

Answer 4

Flow!

Question 5

State and describe darcy’s law?

Answer 5

Flow ∝ change in pressure (p1-p2)

Flow ∝ 1 / resistance

Question 6

What it is important to note about the resistance variable in darcy’s law?

Answer 6

Changes in flow or pressure will NOT alter resistance, however changes to resistance WILL change both pressure and flow.

Question 7

What is poiseulles’s law and what is the formula for resistance that this law uses?

Answer 7

Poiseulle’s law describes the flow through a tube

Resistanceq = [8 x viscosity (V) x length of tube (L)] / [π x radius of tube (r)^4]

When the above equation is combined with:

Flow = ΔP / resistance

Gives:

Flow = ΔP πr^4 / 8VL

Question 8

What can we infer from poiseulle’s law about flow and tube radius?

What happens to the flow if the radius is doubled?

What happens to the flow if the radius is reduced by 20%?

Answer 8

That flow is proportional to the radius^4.

This means that the radius/diameter of a tube is the biggest controlling factor in determining the flow of a liquid through it.

Therefore by doubling the radius, a X16 fold increase in flow can be seen.

If r=0.80 (a 20% reduction) then flow = 0.80^4 = 0.40 (a 60% reduction in flow!).

Question 9

What is laminar flow?

Answer 9

An effect whereby the fluid flows in parallel layers/lines.

Question 10

Where is the fastest flow of fluid within a vessel found and why?

Answer 10

In the centre, as viscous drag occurs at the walls.

Question 11

What is the name of the effect whereby the RBC’s align themselves centrally within the vessel to be in the fastest stream of flow?

What does this help to do?

Answer 11

The Fahraeus-Lindquist effect.

This helps to reduce the viscosity of the blood.