spirometry lung function tests

see also:

• respiratory medicine
• Aust. asthma Foundation QRG to spirometry for GPs
• Aust. Asthma Foundation's buying guide for spirometers for GPs
  • eg. amongst the least expensive are the very light, compact PC-based spirometers such as:
    • MIR MiniSpir 2 at $AU999 excl. gst but includes 60 free turbine mouthpieces

• spirometry provides an assessment of lung function by measuring:
  • FEV₁ = Forced Expiratory volume in 1 sec
  • FVC = Forced vital capacity
  • lung volume vs time curve
  • lung flow vs volume curve

• assess shape of flow-volume curve to fit with a clinical pattern:
  • normal
  • obstructive - unable to blow out quickly
    • asthma
    • COPD
  • restrictive - small lung capacity
    • pulmonary fibrosis
    • interstitial lung disease
    • pleural or chest wall disease
    • weak inspiratory muscles
    • rib deformity
    • obesity
  • mixed pattern
    • eg. cystic fibrosis
• FEV₁/FVC
  • is this above lower limit of normal (LLN)?
    • is the FVC below LLN?
      • possible restriction
    • is the FVC above LLN?
      • normal spirometry
  • is this below lower limit of normal (LLN)?
    • this suggests an obstructive issue
    • severity grading of obstructive disease as determined by % of predicted FEV₁:
      • > 70% = mild
      • 60-69% = moderate
      • 50-59% = moderately severe
      • 35-49% = severe
      • < 35% = very severe
    • is FVC < LLN?
      • could be a mixed pattern
    • assess response to bronchodilator:
      • positive response indicated by:
        • FEV₁ increasing by > 12%
        • FVC increasing by > 12% and, in adults, by more than 200mL