Spirometer: what it measures and what to expect

A spirometer is a device that measures how much air you move and how quickly you breathe it out.

It records a breathing manoeuvre through a mouthpiece, usually while you wear a nose clip. The recording can show the amount of air exhaled and the flow of air at different points in the breath. A clinician considers these measurements alongside your symptoms, examination, health history and test quality.

For spirometry, staff explain the technique before asking you to seal your lips around the mouthpiece, take a full breath in, and blow out forcefully until told to stop. More than one attempt may be needed so the clinician can assess whether the efforts are consistent. You may be asked to repeat the manoeuvre after using an inhaled medicine.

The device is used in a structured breathing assessment rather than as a diagnosis by itself. It can help a clinician investigate breathlessness, cough, wheeze or a known lung condition, and monitor changes over time.

A trace can be affected by technique, tiredness, coughing, pain or difficulty creating a tight seal around the mouthpiece. Results also need context: similar patterns can occur for different reasons, and a normal result does not explain every breathing symptom. Other assessment may be needed when symptoms and measurements do not match.

Depending on the question, a clinician may use an examination, oxygen measurement, peak-flow monitoring, imaging, blood tests or other lung-function testing. The choice depends on your symptoms, current health and the information needed. A spirometer complements these approaches; it does not replace a full assessment when one is indicated.

Ask what the recording showed, whether the attempts were technically reliable, and what the result means for your particular symptoms. Bring a current list of inhalers and other medicines. Follow any preparation instructions from the testing service, including whether a medicine should be taken as usual before the appointment.

Forceful breathing can briefly make some people cough, feel light-headed or uncomfortable. Tell staff before starting if you feel unwell, have chest pain, recently had an operation, or have been given instructions to avoid strenuous breathing efforts. Stop and alert staff if you develop concerning symptoms during the test.