5: Respiratory pathophysiology 2

Question 1

What are the characteristic features of COPD?

Answer 1

• Airflow limitation that is not fully reversible

- Airflow limitation usually progressive and associated with abnormal inflammatory response

Question 2

How does stopping smoking affect decline of lung function?

Answer 2

Declines at a slower rate (reduced to that of non smoker)

Question 3

What is the most important cause of hypoxaemia?

Answer 3

V/Q mismatch

Question 4

Why are smokers dependent on hypoxic drive for ventilation?

Answer 4

• Chronically high CO2 levels resets chemoreceptors

- pH normalised by renal compensation

Question 5

Why does hyperventilation normalise CO2 but not O2 levels in smokers?

Answer 5

Difference in dissociation curves - elevated PaO2 does not result in increased haemoglobin saturation

Question 6

Why might a hypoxaemic patient have a “high colour”?

Answer 6

• Polycythaemia

- Due to inc EPO production from kidney stimulated by hypoxaemia (inc RBCs)

Question 7

How do you differentiate hypoxaemia due to V/Q mismatch and that due to an anatomical shunt?

Answer 7

• Administer 100% O2 to patient

- VQ mismatch will eventually reach normal arterial PO2