L1 - Respiration - Airflow

Question 1

Which 4 factors have a role in determining air flow?

Answer 1

Type of air flow
Resistance of the pathway
Pressure gradients
Links between lung volume, resistance and airflow

Question 2

What is laminar flow?

Answer 2

Steady flow down a tube in a uniform direction and speed

Flow rate is maximal in the centre but reduces towards the edge

Question 3

During laminar flow movement of air into and out of the lungs is?

Answer 3

Proportional to the pressure gradient

Inversely proportional to the resistance

Question 4

What is turbulent flow?

Answer 4

If flow rate moves beyond a critical value, irregular currents – vortices develop
Greater pressure gradient needed to obtain the same flow seen under laminar conditions – more effort

Question 5

During turbulent flow the rate of gas movement is?

Answer 5

Proportional to square root of the pressure difference

Question 6

What is transitional flow?

Answer 6

High numbers of bifurcations in the airways disrupt flow - creating eddies

Question 7

What is determination of flow type governed by?

Answer 7

Reynolds number 
o	r - radius
o	v - velocity
o	ρ - density of the gas
o	η - viscosity

Question 8

Reynolds number equation

Answer 8

Re = 2rvp/n

Question 9

If Re < 1000 what flow is seen?

Answer 9

Laminar flow

Question 10

If Re is between 1000 and 1500 what flow is seen?

Answer 10

Flow switching between laminar and turbulent

Question 11

If Re is > 1500 what flow is seen?

Answer 11

Turbulent flow

Question 12

What is Poiseuilles law?

Answer 12

Airway resistance is proportional to gas viscosity
Length of the tube but is inversely proportional to the fourth power of the radius
Small changes in airway diameter have a big impact on the resistance and therefore flow rate

Question 13

In a normal individual what is the airway resistance throughout the lung?

Answer 13

Total airway resistance is 1.5cm H2O .s.litres-1

• Pharynx-Larynx - 40%
• Airways >2mm diameter – 40%
• Airways <2mm diameter – 20%

Question 14

In a COPD patient what is the airway resistance throughout the lung?

Answer 14

Total airway resistance is 5.0 H2O .s.litres-1

• Pharynx-Larynx - 12%
• Airways >2mm diameter – 18%
• Airways <2mm diameter – 70% (huge difference from normal patients)

Question 15

What are the 2 factors impacting airway resistance?

Answer 15

Airway diameter

Lung volume

Question 16

How does airway diameter impact airway resistance?

Answer 16

Increased mucus secretion reduces airway diameter – increased resistance
Oedema – increased fluid retention in lung tissue – increased resistance

Question 17

How does lung volume impact airway resistance?

Answer 17

At a given lung volume, airway resistance is higher in COPD

At smaller volumes you have higher resistance

Question 18

What is the effect of dynamic pressures on airflow during inspiration?

Answer 18

During inspiration - forced expansion of higher airways

Dilation of airways – decrease in resistance

Question 19

What is the effect of dynamic pressures on airflow during expiration?

Answer 19

During expiration – forced collapse of higher airways

Constriction of airways – increase in resistance

Question 20

What impact does emphysema have on airway compression?

Answer 20

Airway compression is exaggerated

• Loss of elastic tissue and break down of alveolar walls
• Tethering between the walls of airspaces reduced
• Airways less able to resist the collapse

Question 21

How are the issues of emphysema overcome?

Answer 21

Slow exhalation
Breathing takes place at a higher lung volume
Exhale through pursed lips

Question 22

When resistance is increased what is impaired about the lungs?

Answer 22

Inflation
In normal patient, after 1s of inspiration, lungs have reached tidal volume (500ml)
In COPD patients, after 1s of inspiration, lungs have only reached 60% of tidal volume

Question 23

How do you calculate interpleural pressure?

Answer 23

Alveolar pressure - transpulmonary pressure

Question 24

How do you calculate transmural pressure?

Answer 24

Airway pressure - intrapleural pressure