spirometry lung function tests

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

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