1.2 Ventilation and lung mechanics

Question 1

COPD

Answer 1

• Characterised by chronic respiratory symptoms e.g. impaired airflow
• Not fully reversible
• Chronic bronchitis
• Emphysema

Question 2

How does chronic bronchitis affect airways?

Answer 2

• Disease of the smaller airways causing inflammation
• Hyperplasia of epithelia - mucus hypersecretion
• Reduced cilia - mucus is not cleared - narrowed airways
• Loss of small airways
• Epithelial remodelling - narrows airways
• Reduced clara cells - less surfactant - increased airway surface tension + resistance

Question 3

Radial traction

Answer 3

• Outward tugging action of the surrounding alveolar walls on bronchioles
• Help bronchioles to stay open during expiration - prevent collapse

Question 4

Emphysema pathophysiology

Answer 4

• Permanent enlargement of air spaces due to destruction of alveolar walls
• Causes by inflammatory cells (elastases and oxidants) destroying walls and elastin
• Reduces elastic recoil - increased compliance
• Harder to exhale - takes longer to recoil back and let air out (air trapping)
• Reduced surface area due to destroyed alveolar walls - less gas exchange
• Small airways collapse on expiration - less radial traction from alveoli (reduced elastic recoil)

Question 5

What can air trapping lead to?

Answer 5

• When elastic recoil of alveoli is reduced so on expiration - harder to let air out
• Increased air flattens diaphragm - can’t contract properly so impairs inspiration
• Can cause barrel chest
• Less room for new air upon inhaling

Question 6

Why is obstruction worse in expiration with COPD?

Answer 6

• Negative pressure in pleural space relative to alveoli helps keep lower airways open in inspiration
• On expiration, pulmonary pressure increases (more air in alveoli) so this narrows airways - less radial traction

Question 7

Atelectasis causes

Answer 7

• Impaired surfactant production

• increased surface tension means lower compliance
• alveoli unable to stretch as much

• Compression atelectasis

• air/fluid in pleural cavity/obesity/post-op
• cause compression of alveoli

• Resorption collapse

• due to obstruction of a large airway causing alveolar collapse
• e.g. lung cancer / mucus plugs