Respiratory & Sleep Medicine

Question 1

During which stage of lung development is surfactant first produced?

Answer 1

The canalicular stage (16-24 weeks) - cells start differentiating into type I pneumocytes and type II pneumocytes, and surfactant is produced during this late phase.

Question 2

Name the classes of mutations in cystic fibrosis

Answer 2

Class I - defective production (nonsense, frameshift, or splice-site mutations). Results in premature MRNA termination and complete absence of CFTR protein.

Class II - defective processing (abnormal post-translational trafficking). Examples include F508del, N1303Lys (N1303K) and A455E.

Class III - defective regulation (aka gating mutations). Occur when there is decreased channel activity in response to ATP. Most common is G551D. Ivacftor is a modulator (aka potentiator) that allows constitutive opening.

Class IV - defective conduction. Occur when normal protein production and localisation within cell, but impaired pump/cAMP signalling.

Question 3

What is vital capacity (VC)?

Answer 3

Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume

VC = IRV + TV + ERV

Question 4

What is functional residual capacity (FRC)?

Answer 4

Functional residual capacity = expiratory reserve volume + residual volume

FRC = ERV + RV

Question 5

What is inspiratory capacity (IC)?

Answer 5

Inspiratory capacity = inspiratory reserve volume + tidal volume

IC = IRV + TV

Question 6

What is total lung capacity (TLC)?

Answer 6

Total lung capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume + residual volume

TLC = IRV + TV + ERV + RV

Question 7

What is inspiratory reserve volume (IRV)?

Answer 7

Inspiratory reserve volume = the extra volume that can be breathed IN with maximal effort after reaching the end of a normal, quiet inspiration

Question 8

What is tidal volume (TV)?

Answer 8

Tidal volume = the amount of air that moves IN or OUT of the lungs with each respiratory cycle

Neonates: 3–5 mL/kg (poorer compliance)
Older children: 6–8 mL/kg (better compliance)

Question 9

What is expiratory reserve volume (ERV)?

Answer 9

Expiratory reserve volume = the extra volume that can be breathed OUT with maximal effort after reaching the end of a normal, quiet expiration

Question 10

What is residual volume (RV)?

Answer 10

Residual volume = the amount of air that remains in the lungs after fully breathing OUT

NB: this is NOT the same as “dead space”. RV air can still participate in gas exchange, whereas anatomical dead space volume cannot

Question 11

Define compliance

Answer 11

Compliance = change in volume / change in pressure

E.g. - higher compliance if larger increase in volume with smaller increase in pressure