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  1. Wash hands, introduce yourself, confirm patient details, explain the procedure, obtain consent
  1. Obtain patient details: sex, age, height, ethnic origin (to work out predicted value)
  2. Check that their current condition is stable
  3. Attach a clean mouthpiece
  4. Ensure patient is seated and upright, and apply nose clip
  5. Measure FEV1 and FVC
  6. Tell them to take a deep breath in fully, place their lips around the mouthpiece forming a tight seal, and exhale as hard and fast as they can
  7. Repeat at least 2 more times
  8. Calculate FEV1/FVC ratio
Range Reference
  • FEV1: >80% predicted
  • FVC: >80% predicted
  • FEV1/FVC ratio: >0.7
Assess Quality of the Results
  • Three consistent volume-time curves are required, of which the best two curves should be within 5% of each other.
  • The best of the three consistent readings of FEV1 and FVC should be used in your interpretation.
  • Abnormalities can be caused by coughing during expiration, an extra breath during expiration, slow start to forced expiration or a sub-maximal effort
Obstructive Pattern
  • FEV1 reduced (<80% of the predicted)
  • FVC reduced, but to a lesser extent than FEV1
  • FEV1/FVC ratio reduced (<0.7)
  • Causes: COPD, Asthma, Emphysema, CF
Spirometry Trace showning Obstructive causes

Restrictive Pattern
  • FEV1 reduced (<80% of the predicted)
  • FVC reduced (<80% of the predicted)
  • FEV1/FVC ratio normal (>0.7)
  • Causes: Pulmonary fibrosis, pulmonary oedema, lobectomy, lung tumours, skeletal abnormalities, pregnancy, obesity
Spirometry Trace showning Restrictive causes

  • It can be useful to assess reversibility with a bronchodilator if considering asthma as a cause of obstructive airway disease. Patients should be asked to stop bronchodilator therapy prior to spirometry, to ensure previous treatments do not affect the results.
  • To assess reversibility, administer 400 micrograms of salbutamol and repeat spirometry after 15 minutes:
    • The presence of reversibility is suggestive of asthma
    • The absence of reversibility suggests fixed obstructive respiratory pathology such as COPD Partial reversibility may suggest a coexisting diagnosis of asthma and another obstructive airway disease (e.g. COPD

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