Static mechanics of breathing

Question 1

What is the physical force that influences breathing with the mechanical properties of the lung that influence gas flow but are dependent of volume change?

Answer 1

Static

1) Elasticity
2) Compliance
3) Surface tension

Question 2

What is the physical force that influences breathing with the mechanical properties affecting flow of air into and out of lung as volume chnages with time?

Answer 2

Dynamic

1) Flow
2) Resistance
3) Turbulence

Question 3

What links elastic forces in the chest wall and lung?

Answer 3

Pleural sac

Question 4

Describe how elastic forces link pleural pressure to alveolar pressure

Answer 4

• Elastin in alveoli acts as an inward ‘collapsing” force
• Opposing elastic recoil of ribs acts as an outward expanding force
• This results in a balance of forces in a sub-atmospheric intrapleural pressure

Question 5

Explain how pressure and volume changes during quiet breathing

Answer 5

• Intrapleural pressure is also sub-atmospheric

- Elastic retraction enables alveolar pressure go above atmospheric

Question 6

Whats the equation for compliance?

Answer 6

Change in volume/pressure

Question 7

What does it mean if a lung is easily distended?

Answer 7

It has high compliance

Question 8

What does it mean if a lung is difficult to distend?

Answer 8

It has low compliance

Question 9

Describe the components of emphysema

Answer 9

Mucus in bronchiole
Enlarged alveoli
Fewer capillaries

Question 10

What is pulmonary compliance/elastic recoil produced by?

Answer 10

Elastin connective fibres (elastic mesh around alveoli|)

Alveolar surface tension

Question 11

Describe surface tension and why molecules such as rain fall as drops

Answer 11

Molecules at the surface experience fewer interactions as they arent surrounded in 3-d like those within the molecule. This causes an energy cost

Question 12

Describe surface tension in the alveolus

Answer 12

• Resists stretch (greater surface tension-less compliance)
• Tends to become smaller
• Tends to recoil after stretch-contributes to elastic recoil pressure

Question 13

Describe the effect of inflating the lung with air-liquid

Answer 13

Overcomes recoil affect by dissipating surface tension

Question 14

Where does the input of energy come from to overcome surface tension?

Answer 14

Intercostals/diaphragm

Question 15

What is hysteresis?

Answer 15

When surface tension is overcome, there is a lag phase which requires less energy than the rest of inhalation

Question 16

Describe law of Laplace

Answer 16

Small diameter bubbles have higher surface tension than larger diameter ones

Question 17

How does pulmonary surfactant stabilise alveolar structure?

Answer 17

Reduces surface tension by;

• Preventing collapse of alveoli during lung expansion and contraction
• Reduces pressure required to inflate lungs

Question 18

What is pulmonary surfactant composed of and where is it secreted from?

Answer 18

Dipalmitoyl phosphatidyl choline (DPPC) packaged around surfacant proteins
Secreted by type II alveolar epithelial cells

Question 19

How does loss of surfactant cause alveolar collapse?

Answer 19

More work is required to inflate lung is saline is rinsed. Working against elasticity + surface tension
Saline rinsing raises surface tension which means hysteresis is lost