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spirometry

spirometry lung function tests

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Introduction

  • 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

Interpretation

  • 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
    • 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
spirometry.txt · Last modified: 2021/09/12 12:48 by gary1