Physiology

Question 1

A-a gradient definition

Answer 1

Difference in partial pressure of oxygen between alveoli and arteries

Question 2

Causes of raised A-a gradient

Answer 2

○ Diffusion defect (rare)
○ V/Q mismatch (think pneumonia)
○ Right-Left shunt (intrapulmonary or cardiac)
If intrapulmonary, think “complete V/Q mismatch”

Question 3

How to calculate PAO2 (oxygen in alveoli)

Answer 3

At room air (FiO2 0.21), PAO2 = 150 - (5/4) x PaCO2

Question 4

What causes a RIGHT shift in the Hb-Disassociation curve?

Answer 4

1. Increased temperature
2. Increased CO2
3. Decrease in pH

Question 5

What causes a LEFT shift in the Hb-Disassociation curve?

Answer 5

1. Decreased temp
2. Reduced CO2
3. Increase in pH
4. Carbon monoxide

Question 6

Three-test combination

Answer 6

1. Pleural fluid protein >30g/L
2. Pleural fluid cholesterol >55mg/dl
3. Pleural fluid LDH >2/3 serum LDH upper limit of normal

Question 7

Causes of exudative pleural effusions

Answer 7

• Malignancy
• Infection
• Autoimmune
• Chylothorax
• Cholesterol effusion
• Pancreatitis

Question 8

Causes of transudative pleural effusions

Answer 8

• Atelectasis
• CSF leak
• HF
• Hepatic disease
• Hypoalbuminaemia

Question 9

Causes of V/Q mismatch

Answer 9

1- Dead space
2- Shunt

Question 10

Causes of dead space

Answer 10

• Erect posture
• Decreased pulmonary artery pressure/impaired pulmonary blood flow
• Hypovolaemia
• RV failure/Increased RV afterload:
  – HPV
  – MI
  – PE
• Increased alveolar pressure
• COAD

Question 11

Causes of shunt

Answer 11

Intra-cardiac e.g. VSD
Extra-cardiac
e.g. Pulmonary AVM, PDA