Mechanics of breathing

Question 1

What does Boyle’s Law state?

Answer 1

At a given temperature, the pressure and volume of an ideal gas are inversely proportional

Question 2

Name the 4 accessory muscles of forced inspiration.

Answer 2

Sternocleidomastoid
Scalene muscles
Pectoralis major
Latissimus dorsi

Question 3

Name the 3 muscles of forced expiration.

Answer 3

Abdominal muscles
Internal intercostal muscles
Innermost intercostal muscles

Question 4

Is the pleural space a higher or negative pressure compared to atmospheric pressure?

Answer 4

Negative

Question 5

What prevents our lungs from collapsing?

Answer 5

The negative pressure in the pleural cavity (negative intrapleural pressure)

Question 6

Which 3 factors create a negative intrapleural pressure?

Answer 6

Elastic recoil of the lungs
Surface tension
Outward recoil of the chest wall

Question 7

What is transpulmonary pressure?

Answer 7

The pressure difference between intrapulmonary pressure and intrapleural pressure

Question 8

What is the usual value of transpulmonary pressure?

Answer 8

Transpulmonary pressure = intrapulmonary pressure – intrapleural pressure

0 – (-4) = 4mmHg

Question 9

How is lung compliance calculated?

Answer 9

Compliance = change in volume / change in transpulmonary pressure

Question 10

The elastic properties of the lung are due to which 2 components?

Answer 10

Elastin + collagen fibres
Surface tension

Question 11

Where in the lungs is intrapleural pressure more negative, the apex or base?

What causes this?

Answer 11

Apex

The effect of gravity pulling the lung downwards, causing higher volume at the apex of the lung and therefore less pressure than at the base

Question 12

Where in the lungs is there a greater transmural pressure gradient, the apex or base?

Answer 12

Apex

Question 13

Describe the apex and base alveoli in terms of size and compliance.

Answer 13

Apex – larger alveoli, less compliant

Base – smaller alveoli, more compliant

Question 14

Where in the lungs is ventilation greatest, apex or base?

Answer 14

Base

Question 15

Surface tension at the air-fluid interface in the alveoli creates what kind of pressure?

Answer 15

An inward collapsing pressure

Question 16

Describe the equation of Laplace’s Law.

Answer 16

Pressure in a bubble = 2 x surface tension / radius

Question 17

Which size alveoli require a higher pressure to stay inflated, big or small?

Answer 17

Small alveoli

Question 18

Which 2 factors help to stabilise alveoli?

Answer 18

Alveolar interdependence – Pores of Kohn + canals of Lambert

Surfactant

Question 19

How and where is surfactant secreted from?

Answer 19

Exocytosis

Type II pneumocytes

Question 20

By what mechanism does surfactant decrease surface tension?

Answer 20

Disrupts hydrogen bonds between surface water molecules

Question 21

Define the work of breathing.

Answer 21

The energy consumed by the respiratory muscles during the respiratory cycle

Question 22

The work of breathing consists of which 2 components?

Answer 22

Elastic work
Resistive work

Question 23

What is elastic work in breathing?

Answer 23

The energy required to overcome the elastic recoil of the lungs and chest wall during inspiration

Question 24

What happens to some of the energy used in elastic work of breathing?

Answer 24

Stored as potential energy and used in expiration

Question 25

What is resistive work in breathing?

Answer 25

The energy needed to overcome airway resistance during ventilation

Question 26

What happens to the energy used in resistive work?

Answer 26

Energy is ‘wasted’ as heat and sound

Question 27

What element(s) of work of breathing is affected in obesity and how?

Answer 27

Increases elastic work of breathing – opposes the outward elastic recoil of the chest wall

Question 28

What element(s) of work of breathing is affected in pulmonary fibrosis and how?

Answer 28

Increases elastic work of breathing – lung tissue is replaced by scar tissue which means the lungs are stiffer and reduces lung compliance Increases resistive work of breathing – increased amount of lung tissue increases tissue resistance

Question 29

What element(s) of work of breathing is affected in asthma and how?

Answer 29

Increases resistive work of breathing – airway narrowing due to bronchoconstriction and mucosal oedema increases airway resistance

Question 30

What are the 2 main factors affecting airway resistance?

Answer 30

Turbulent air flow Change in airway radius

Question 31

Describe dynamic airway compression.

Answer 31

During forced expiration, intrapleural pressure can become positive, causing collapse of airways without cartilage in their walls e.g. bronchioles. This can be worsened in disease which cause airway narrowing or loss of elastic tissue

Question 32

Which 2 muscles are involved in quiet (tidal) breathing?

Answer 32

Diaphragm External intercostals

Question 33

How does intrapleural pressure change during inspiration?

Answer 33

Becomes more negative

Question 34

How does intrapleural pressure change during expiration?

Answer 34

Becomes less negative

Question 35

During inspiration, what changes occur in intrapleural and transpulmonary pressure?

Answer 35

Decreased intrapleural pressure Increased transpulmonary pressure

Question 36

During expiration, what changes occur in intrapleural and transpulmonary pressure?

Answer 36

Increased intrapleural pressure Decreased transpulmonary pressure

Question 37

How does elasticity and compliance change in emphysema?

Answer 37

Decreased elasticity Increased compliance

Question 38

How does elasticity and compliance change in pulmonary fibrosis?

Answer 38

Increased elasticity Decreased compliance

Question 39

When is compliance highest in terms of lung volume?

Answer 39

Low long volumes

Question 40

When is compliance lowest in terms of lung volume?

Answer 40

High lung volumes

Question 41

Which type of epithelium are type II pneumocytes?

Answer 41

Cuboidal

Question 42

Dynamic airway compression occurs during which type of breathing?

Answer 42

Forced expiration