Lung Function Tests

• Lung function tests (spirometry) help diagnose various lung conditions such as asthma, chronic obstructive pulmonary disease (COPD), and restrictive lung diseases
• Spirometry


  Test used to establish objective measures of lung function by measuring volumes of air and flow rates
• Reversibility testing


  Involves giving a bronchodilator before repeating spirometry to see if it impacts the results
• Forced expiratory volume in 1 second (FEV1)


  The air a person can forcefully exhale in 1 second, measuring how easily air can flow out of the lungs, reduced with airflow obstruction
• Forced vital capacity (FVC)

  The total air a person can exhale after a full inhalation, measuring the total volume of air that can be taken into the lungs, reduced with restricted lung capacity
• Obstructive lung disease is diagnosed when

  FEV1 is less than 70% of FVC, indicating an FEV1:FVC ratio of less than 70%, suggesting obstruction slowing air passage out of the lungs
• In asthma


  The obstruction is a narrowed airway due to bronchoconstriction
• In COPD


  There is chronic airway and lung damage causing obstruction
• Obstructive picture is typically reversible in asthma but less so in COPD


  Reversibility can be tested by giving a bronchodilator like salbutamol
• In restrictive lung disease

  FEV1 and FVC are
• Reversibility of obstruction


  Test by giving a bronchodilator (e.g., salbutamol)
• Obstructive picture is typically reversible in asthma but less so in COPD
• Restrictive lung disease includes conditions such as

  • Interstitial lung disease, such as idiopathic pulmonary fibrosis
  • Sarcoidosis
  • Obesity
  • Motor neurone disease
  • Scoliosis
• Restrictive lung disease


  Limits the ability of the lungs to expand and fill with air. The lungs are restricted from effectively expanding. This is different from obstructive lung disease, where there is obstructed airflow
• Restriction of lung expansion

  Leads to inadequate ventilation of the alveoli and insufficient blood oxygenation
• FEV1:FVC ratio


  Greater than 70% in restrictive lung disease
• FEV1:FVC ratio


  Normal or raised in restrictive lung disease without obstructive pathology affecting airflow through the airways
• FVC


  Reduced due to the restriction of lung expansion and capacity
• A low FVC indicates restrictive lung disease, and a low FEV1:FVC ratio (under 70%) indicates obstructive lung disease
• A low FVC and a low FEV1:FVC ratio indicate a combination of obstructive and restrictive lung disease
• Peak Flow


  Measures the “peak”, or fastest point, of the expiratory flow of air. Also called peak expiratory flow rate (PEFR) and measured using a peak flow meter
• Technique for measuring Peak Flow

  Stand tall, take a deep breath in, make a good seal around the device with the lips and blow as fast and hard as possible into the device. Take three attempts and record the best result
• An average peak flow varies dramatically between individuals
• Predicted peak flow


  Based on sex, height, and age using a reference chart or calculator. The result can be recorded as a percentage of the predicted
• For example, an asthmatic patient with a predicted peak flow of 400 that manages a score of 200 on their best attempt has a peak flow of 50% of the predicted result (actual / predicted x 100)