Mechanics of Breathing

Question 1

What is the pleura and the Pleural cavity

Answer 1

Visceral pleura - covers lungs
Parietal pleura - lines chest wall
pleural cavity - thin fluid filled space between them (prevents lungs from collapsing or chest from expanding outwards freely)

Question 2

Key pressures in breathing

Answer 2

Alveolar pressure, intrapleural pressure (usually negative), transmural (distending) pressure (the difference across the lung or chest wall), barometric pressure (outside chest)

Question 3

Resting pressures

Answer 3

Pressure in alveoli - 0
Pressure in interpleural cavity - - 0.5 (negative pressure helps keep lungs expanded and prevents collapse, during inspiration it becomes more negative)

Lung wanting to collapse inward and chest wall wanting to spring outwards balance

Question 4

Muscles involved in breathing

Answer 4

Inspiration
- Diaphragm contracts, throacic volume increases, air is drawn in
- External intercostal muscles contract to help deeper breaths

Expiration
- Diagphragm relaxes
- Natural recoil of lungs
- Abdominal and internal intercostal muscles contract during forced expiration

ALWAYS REFERENCE BOYLES LAW

Question 5

Distending pressure def

Answer 5

Pressure in alveoli - pressure in pleural space

So a positive distending pressure keeps lungs expanded, zero or negative causes it to collapse