L12 Laminar and Turbulent flow

Question 1

How to work out Flow

Answer 1

Flow = pressure / resistance

Question 2

from what pressures does the air or the blood flow to

Answer 2

from high pressure to low pressure

Question 3

How to work out BP

Answer 3

Arterial blood pressure - cardiac venous pressure

Question 4

how to work out CO

Answer 4

BP/ resistance (TPR)

Question 5

what is the resistance in the CVRS

Answer 5

It’s the vascular resistance in the vascular beds (vessels)

Question 6

work out Air flow ?

Answer 6

pressure gradient (batometric pressure - alveolar pressure)/ airway resistance 
- the pressure gradient needs to be bigger than the resistance so the air can flow during inspiration

Question 7

During inspiration, what is the pressure gradient like so is it PB > PA or PA

Answer 7

PB > PA

-this allows the air to flow inside

Question 8

during Expiration, what is the pressure gradient like so is it PB > PA or PA

Answer 8

PA>PB

Question 9

what is the resistance in the RS

Answer 9

in the airways of the lungs

Question 10

is the resistance greater in CVS or RS?

Answer 10

• the resistance is greater in the CVS because there is a greater driving force generated in the CVS.

Question 11

What is the formula for Poiseuille’s law

Answer 11

V dot = change in P x ((pi x r^4)/8nl)

- this formula only applies to laminar flow

Question 12

what is flow proportional to

Answer 12

driving pressure so

• for RS, it’s PB-PA depending on the chest wall muscles
• for CVS, it’s ABP-CVP, depending on cardiac work

Question 13

What is flow inversely proportional to

Answer 13

-resistance
so R = 8nl/pi x r^4
- viscosity(n) is constant, can be changed by heliox or haematocrit
- the length of the blood vessels set up by the anatomy so cant change it
- radius (r) is dependent on the smooth muscle so we have physiological control over it so like (bronchodilation/constriction for RS and vasodilation/constriction for CVS)

Question 14

what is resistance inversely proportional to?

Answer 14

• R = 1/ r^4
• as the radius increases, the R will decrease
• • radius (r) is dependent on the smooth muscle so we have physiological control over it so like (bronchodilation/constriction for RS and vasodilation/constriction for CVS)

Question 15

what is laminar flow and describe the velocities of the flow

Answer 15

• It’s a flow where the centre of the flow has the max velocity
• the outermost layer of the flow nearest to the vessel wall is the fluid that is immobile
• after that, each successive layers from fluid layer to the centre, it increases in speed
• it has a parabolic flow pattern

Question 16

What is LF inversely proportional to ?

Answer 16

• to R

- so it’s energy efficient and in order so it’s silent flow

Question 17

What is turbulent flow (TF)

Answer 17

• it’s a random flow where tje parabolic pattern is lost
  -the fluid and blood mixes so it’s noisy
  -less energy effecient because we lose KE
  so the energy is lost of sound

Question 18

What is TF inervsely proportional to

Answer 18

square root of chnage in pressure

Question 19

What factor can determine whether it’s TF or LF

Answer 19

Reynolds number (NR)
- NR =( density x diameter x velocity ) / viscosity

Question 20

What factors can increase occurrence of TF

Answer 20

• density
• diameter of the tube
• velocity of the flow

Question 21

What factor can decrease the TF

Answer 21

• viscosity

- so if the viscosity is higher, the TF occurs less often

Question 22

• Where does TF occur in the RS and why?

Answer 22

• in the trachea
• because there is a higher velocity and large radius, contributing to an increase of NR
• Energy is lost so the flow is no longer proportional to change in Pressure
• but the flow is now proportional to square root of change in Pressure

Question 23

what flow occurs in the bronchial tree

Answer 23

• both TF and LF

Question 24

What flow occurs in small airways

Answer 24

LF

Question 25

Where does LF occur in the CVRS

Answer 25

- most blood vessels where the RBCs would be at the centre of the vessel at the max velocity

Question 26

Where does TF occur in CVS

Answer 26

in the vessels where there is an irregularity so like valves, clots, blood vessel branches

Question 27

Why does narrowing of blood vessels lead to increases flow velocity

Answer 27

Velocity = Flow/ CSA | so if the CSA decreases, the velocity increases

Question 28

normal Indicators for TF

Answer 28

- herat sounds caused by closing of the AV and SLV | -

Question 29

What is a murmur caused by the TF

Answer 29

- it's when the area of the vessel is smaller than usual like the valves are fused together - this leads to higher velocity because it needs to compensate for the same flow - causing more TF than usual

Question 30

How can a cuff measures the systolic and diastolic pressure ?

Answer 30

- when the cuff is first used, it stops the flow because it is tight - but as the cuff is gradually released, it produces sounds as the flow becomes turbulent due to the tightening of the cuff - so the systolic pressure is when the korotkoff sounds start happening and diastolic pressure is when it stops - after wards, the cuff becomes loose and the flow becomes laminar soon after