What should you know about an asthma spirometer?

Spirometry can support an asthma diagnosis, provide a baseline for future comparison, and show whether airflow changes after an inhaled reliever medicine. Results are interpreted alongside symptoms, examination findings, medical history, and the quality of each breathing effort.

The test records the total amount of air forced out after a full breath and the amount expelled early in that breath. The relationship between these measurements helps identify an obstructive airflow pattern. Improvement after a bronchodilator can support asthma as an explanation, but a normal result at one appointment does not automatically exclude asthma because airflow can vary over time.

Reliable interpretation depends on a tight seal around the mouthpiece, a rapid start, and continued forceful exhalation. The clinician may ask for repeated attempts to check that the measurements are consistent. Home peak-flow meters are different devices: they track peak expiratory flow and do not provide the same full set of measurements as diagnostic spirometry.

Before the appointment, follow the clinic's instructions about inhalers and other medicines. Do not stop prescribed treatment unless the clinician specifically tells you when and how to do so. Tell the tester about recent chest infections, surgery, pregnancy, heart problems, dizziness with forceful breathing, or current severe symptoms, as these may affect timing or technique.

Wear clothing that does not restrict your chest or abdomen and avoid a heavy meal immediately beforehand. During the test, sit or stand as directed, use a nose clip if provided, seal your lips firmly around the mouthpiece, inhale fully, then blow out as hard, fast, and long as instructed. Mention pain, marked breathlessness, chest tightness, or light-headedness straight away so the tester can stop and assess you.

Seek urgent medical help if breathlessness is severe or rapidly worsening, you cannot speak comfortably in full sentences, your lips or face look blue or grey, you feel faint or confused, or your prescribed reliever is not helping as expected. These warning signs matter regardless of any previous spirometry result.

Do not attempt home spirometry during a severe asthma episode if it delays your written asthma action plan or emergency care. For milder symptoms that keep returning, disturb sleep, limit activity, or require reliever use more often than usual, arrange a clinical review so treatment and inhaler technique can be checked.

Ask whether you should take your usual inhalers before testing, whether your results showed an obstructive pattern, and whether airflow changed after bronchodilator medicine. You can also ask how the findings fit with your symptoms, whether another test is needed when spirometry is normal, and what changes should trigger a review of your asthma action plan.