Pulmonary Function Tests (Spirometry)

Spirometry is a specialised test of lung function. It is essential in the diagnosis and follow up of respiratory disorders such as asthma, chronic obstructive pulmonary disease, interstitial lung disease, etc. It is also needed before major surgery in patients with respiratory diseases to assess the preoperative fitness for surgery. Spirometry is also helpful to assess the degree of severity and ventilator capacity of lung in certain specific situations.

There are different types of spirometers available. The procedure essentially involves breathing through a mouthpiece into a pipe which is attached to the spirometer. The rate and flow of air being breathed is then measured and used to derive further values. Some of the common values which are measured are:

  • FEV1 (Forced expiratory volume in one second) – this is the maximum amount of air exhaled in one second
  • FVC (forced vital capacity) – the maximum volume of air exhaled after a maximum inspiratory effort
  • The ratio of FEV1/FVC – this is important for differentiating obstructive from respiratory disease i.e. lung volume increase vs lung shrinkage respectively.