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 and others.
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 disability 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:
The results of spirometry depend a lot upon patient effort and technician training. So, if any of these two factors are lacking proper results will not be there. A lot of spirometry labs do not do proper diligence to these two factors and as a result wrong diagnosis can be made. Also, it is very important not to depend on the diagnosis provided by the spirometry machine.
It is the doctor’s interpretation which is valid and which should be focused upon. Spirometric parameters vary widely in normal situations according to age, sex, height and weight in different ethnicities. These are therefore better expressed as “% of predicted” rather than in absolute terms.
With spirometry, we can diagnose an ‘obstructive’, ‘restrictive’ or ‘mixed’ pattern suggestive of one or the other disease group.