Flow-Volume Curves

Question 1

Describe the appearance of a normal flow-volume curve

Answer 1

• Expiratory - steep rise, well-defined peak, steady fall
• Inspiratory - almost semi-circular

Question 2

How might obstructive lung disease change the appearance of a flow-volume curve?

Answer 2

• Obstructive airways disease will cause the FV loop to be squashed on the flow axis (COPD)
  
  • Often smaller VC due to RV increase (gas trapping)

Question 3

How might restrictive lung disease change the appearance of a flow-volume curve?

Answer 3

• Restrictive airways disease will cause the FV loop to be squashed on the volume axis (pulmonary fibrosis)
  
  • All lung volumes decreased (low VC doesn’t necessarily mean restriction!)

Question 4

How might a fixed stenosis present on a flow-volume curve?

Answer 4

• Fixed stenosis will cause a decreased inspiratory and expiratory flow rate (and flattened curve) as the obstruction is fixed (structures, tracheal obstruction)

Question 5

How might a variable stenosis present on a flow-volume curve?

Answer 5

• Variable stenosis may cause a decrease in/expiratory flow rate (e.g. tracheomalacia causing collapse)
  
  • Extrathoracic obstruction will cause inspiratory collapse
  • Intrathoracic obstruction will cause expiratory collapse (sometimes with a little peak beforehand where a patient can blow hard before collapse) - intrathoracic pressure greater than intraluminal