Question

For each description of respiratory pressures A–E, select the most appropriate option from the following list. 

1. Intrapleural pressure. 

2. Intra-abdominal pressure. 

3. Intra-alveolar pressure. 

4. Intra-oesophageal pressure. 

5. Atmospheric pressure. 

A. Intra-alveolar pressure at end-inspiration and end-expiration. 

B. Shows transient rises and falls during the respiratory cycle peaking at mid-expiration and mid-inspiration respectively. 

C. Approximates to intrapleural pressure. 

D. Rises markedly during the vomiting reflex. 

E. Determines the pressure gradient for inspiration and expiration.

Answer 1

A. Option 5 Atmospheric pressure. Intra-alveolar pressure returns to atmospheric pressure at the end of each inspiratory and expiratory phase. 

B. Option 3 Intra-alveolar pressure. This dips transiently during inspiration and rises to a similar extent during expiration. 

C. Option 4 Intra-oesophageal pressure. Since the oesophagus and the intrapleural spaces are normally closed cavities within the chest, intra-oesophageal pressure normally approximates to intrapleural pressure. 

D. Option 2 Intra-abdominal pressure. During vomiting this rises markedly to compress the gut while the way out through the lower oesophageal (cardiac) sphincter is open due to relaxation of oesophageal smooth muscle. 

E. Option 3 Intra-alveolar pressure. The difference between this and atmospheric pressure constitutes the pressure gradient which determines the flow of air into or out of the lungs.