Session 2-Ventilation and Lung Mechanics

Question 1

Which two forces is the lung subjected to at rest?

Answer 1

• lung’s elasticity and surface tension favouring small lung volume
• muscles of rib cage have elasticity and these favour outward movement of chest wall

Question 2

What is the net effect of the two forces acting on the lung?

Answer 2

Balance each other and create negative pressure within the intrapleural space relative to atmosphere

Question 3

Describe the mechanism of quiet inspiration

Answer 3

• diaphragm contracts and moves down
• external intercostals contract and elevate ribs
• thoracic cavity expands so pressure inside lungs falls below atmospheric pressure
• air flows in

Question 4

Describe the mechanism of quiet expiration

Answer 4

• muscles relax
• elastic recoil of lungs -> thoracic cavity and lung return to original equilibrium position and resting end-expiratory level

Question 5

Describe the mechanism of forced inspiration and the accessory muscles involved

Answer 5

• maximum increase in capacity of thoracic cavity and every muscle that can raise ribs is bought into action
• SCM, scalene, pectoralis minor and major and trapezius

Question 6

Describe the mechanism of forced expiration and the accessory muscles involved

Answer 6

-active process bought on by forced contraction of muscles of anterior abdominal wall and internal intercostals

Question 7

What happens if the pleural seal is broken?

Answer 7

Ipsilateral lung shrinks down

Question 8

Describe the pleural pressure at rest

Answer 8

Negative because of opposing forces of lungs and chest wall

Question 9

Describe the pleural pressure during inspiration

Answer 9

More negative than at rest due to expansion of thorax and returns to resting at the end of quiet expiration

Question 10

How does pneumothorax occur?

Answer 10

When air or gas is present within the pleural cavity -> removal of surface tension -> reduction of lung expansion

Question 11

How does pneumothorax result in lung collapse?

Answer 11

Loss of pleural cavity means that lungs and chest wall are no longer attached so the lung’s natural elastic recoil leads to a collapsed lung

Question 12

What is compliance?

Answer 12

Stretchiness of the lungs; relationship between pressure and volume

Question 13

What is the equation for compliance?

Answer 13

compliance = change in volume / change in pressure

Question 14

What are the factors affecting compliance?

Answer 14

• elastin, reduced in ageing so lungs become slacker, also in emphysema
• fibrosis (disease) - lungs become stiffer
• surface tension

Question 15

True or false: surface tension makes inflation of alveoli easier

Answer 15

FALSE - makes it harder

Question 16

What is surfactant?

Answer 16

Surface active agent - mixture of lipids and proteins secreted by alveolar cells

Question 17

What does surfactant do?

Answer 17

• Reduces surface tension and therefore increases lung compliance
• stabilises lung by preventing small alveoli collapsing into larger ones

Question 18

How does surfactant work?

Answer 18

Hydrophilic ends lie in alveolar fluid and hydrophobic end projects into alveolar gas so they float on the surface between molecules, disrupting the interaction between surface molecules and therefore reducing surface tension

Question 19

Where is the main site of resistance in the respiratory tract and why?

Answer 19

Upper respiratory tract because total cross-sectional area of bronchioles > trachea

Question 20

What are the factors affecting airway resistance?

Answer 20

• increased mucus
• hypertrophy of smooth muscle
• oedema
• loss of radial traction

Question 21

True or false: airway resistance increases as lung volume decreases

Answer 21

TRUE

Question 22

Define tidal volume

Answer 22

volume of air which enters and leaves the lungs with each breath

Question 23

Define inspiratory reserve volume

Answer 23

maximal amount of additional air that can be drawn into lungs

Question 24

Define expiratory reserve volume

Answer 24

additional amount of air that can be expired from the lungs

Question 25

Define residual volume

Answer 25

volume of air still remaining in the lungs after the most forcible expiration

Question 26

Define inspiratory capacity

Answer 26

From end of quiet expiration to maximum inspiration (inspiratory reserve + tidal volume)

Question 27

Define functional residual capacity

Answer 27

Volume of air in lungs at the end of quiet expiration

Question 28

Define vital capacity

Answer 28

Inspiratory capacity + expiratory reserve OR

inspiratory reserve volume + tidal volume + expiratory reserve volume

Question 29

Define total lung volume

Answer 29

Vital capacity + reserve volume

Question 30

Define anatomical dead space

Answer 30

Upper resp tract between mouth and resp bronchioles

Question 31

Define alveolar dead space

Answer 31

Where alveoli are ventilated but not perfused, or very poorly perfused

Question 32

Define physiological dead space

Answer 32

Anatomical and alveolar dead space

Question 33

How is pulmonary ventilation calculated?

Answer 33

Tidal volume x resp rate

Question 34

How is alveolar ventilation calculated?

Answer 34

(Tidal volume - dead space) x resp rate

Question 35

What is respiratory distress syndrome in newborns?

Answer 35

Surfactant is absent from alveoli and without it, surface tension of the alveolar sacs is high -> increased tendency of alveoli to collapse

Question 36

What are the signs of respiratory distress syndrome in newborns?

Answer 36

Cyanosis, grunting, intercostal and subcostal recession

Question 37

How is respiratory distress syndrome in newborns treated?

Answer 37

Surfactant replacement and supportive (O2 and assisted ventilation)

Question 38

Why do newborn’s with respiratory distress syndrome get intercostal recession?

Answer 38

Baby’s chest wall is more pliable and less compliant so doesn’t have strength to resist the recoil of the lung

Question 39

Describe the lung compliance in fibrosis

Answer 39

Low (stiffer)

Question 40

Describe the lung compliance in emphysema

Answer 40

High (slacker)