🎯 What are lung function tests?

• lung function tests are used to identify if a restrictive condition is obstructive or restrictive

• examples:

  • spirometry

  • peak expiratory flow (PEF)

  • diffusing capacity of the lungs for carbon monoxide (DLCO)

​

⚡️ Spirometry

• measures how much air can be breathed in and out of the lungs

• it can help diagnose obstructive lung disease and restrictive lung disease by taking into account two important measurements:

  • forced expiratory volume in 1 second (FEV1): how much air that can be forcefully exhaled in 1 second from maximal inhalation

  • forced vital capacity (FVC): the total amount of air that can be exhaled from maximal inhalation

  • the ratio of the FEV1 to the FVC can then be calculated (see below)

​

⚡️ Peak expiratory flow

• measured using a peak flow meter to help with the diagnosis of asthma

• measures the diurnal variability

​

⚡️ Diffusing capacity of the lungs for carbon monoxide (DLCO)

• assesses the efficiency of gas transfer from the alveoli into the surrounding capillaries

• it measures the quantity of carbon monoxide that is transferred from alveolar gas to red blood cells per minute

• carbon monoxide is used because it has a greater affinity to haemoglobin than oxygen (200-250X more)

​

💡 Obstructive lung disease​

• FEV1: significantly reduced

• FVC: reduced

• FEV1/FVC ratio < 70%

​

• Causes of obstructive lung disease ('ABCO')

  • Asthma

  • Bronchiectasis

  • COPD / Cystic fibrosis

  • Obstruction

​

💡 Restrictive lung disease

• FEV1: normal or reduced

• FVC: significantly reduced

• FEV1/FVC ratio > 70%

​

• Causes ('PAINT')

  • Pleural disease (e.g. asbestosis)

  • Alveolar (e.g. pus, oedema)

  • Interstitial lung disease (e.g. idiopathic pulmonary fibrosis)

  • Neuromuscular (e.g. myasthenia gravis)

  • Thoracic (e.g. kyphoscoliosis, obesity, ankylosing spondylitis)