Spirometry

FVC FEV1 FEV1/FVC
Obstructive Reduced (to a lesser extent than FEV1) < 80% of  predicted < 0.7
Restrictive Reduced (< 80% predicted) < 80% of predicted > 0.7
Image of Spirometry trace

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Causes of an Obstructive picture

Extrapulmonary
  • Anything that causes obstruction to air flow.  Examples are…
  • Enlarged thyroid
  • Vocal cord dysfunctions
  • Tumours

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Intrapulmonary
  • COPD
  • Asthma
  • Bronchiectasis
  • Cystic fibrosis

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Causes of a Restrictive picture

Extrapulmonary
  • Scoliosis
  • Kyphosis
  • Ankylosing spondylitis
  • Diaphragm paralysis/elevated hemi-diaphragm
  • Neuromuscular diseases, such as polio, Guillain-Barre syndrome and Myasthenia gravis
  • Obesity

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Intrapulmonary
  • Pulmonary fibrosis
  • Drug induced fibrosis, for example with amiodarone or methotrexate
  • Extrinsic allergic alveolitis
  • Sarcoidosis
  • Asbestosis

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COPD & Asthma

  • COPD and Asthma are both obstructive lung disease.
  • If there is doubt, consider reversibility spirometry.
  • If high suspicion of asthma, treat and review.  In intermediate suspicion, do reversibility spirometry.
Clinical features
COPD Asthma
Smoker Almost all Maybe
< 35y Rare Often
Chronic productive cough Common Rare
Breathless Persistent and progressive Variable
Night time breathlessness or wheeze Rare Common
Day to day variation Rare Common

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Reversibility spirometry

Administer 400mcg of salbutamol and repeat spirometry after 15 minutes

  • Asthma suggested if >=12% FEV1 response
  • COPD excluded if FEV1/FVC & FEV1 returns normal
  • In mixed picture, may only have partial response

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Grading COPD severity
FEV1
< 80% of  predicted

50 – 80%: Mild COPD

30 – 49%: Moderate COPD

<30%: Severe COPD

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PEFR logs for asthma
  • Look for daily or diurnal variations
  • > 20% variation is of significance

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