Impulse oscillometry (IOS): how it works.

What the test measures.

Impulse oscillometry measures the resistance in your airways while you breathe quietly. It requires no blowing manoeuvre and is used as a supplement to spirometry, or where spirometry is difficult to perform.

How to prepare.

The preparation is the same as before spirometry.

• Important information about your medication: only pause if the clinic has asked you to. If the clinic has given you instructions, follow them, and call if you are in doubt.
• Medication pause (the clinic's standard): short-acting reliever (e.g. salbutamol): 6 hours · long-acting beta2 agonist (e.g. formoterol, salmeterol): 24–36 hours · ultra-long-acting beta2 agonist (e.g. vilanterol, indacaterol): 48 hours · ipratropium (e.g. Atrovent): 12 hours · long-acting anticholinergic (e.g. tiotropium): 36–48 hours.
• Continue as usual: inhaled corticosteroid (preventer).
• Avoid strenuous exercise and smoking/nicotine in the last hour, and a large meal in the last 2 hours.
• An airway infection within the last 2–4 weeks: please call, and we will assess whether to move the appointment.

Duration

A few minutes.

How it is done.

You sit upright with a nose clip and support your cheeks with your hands while you breathe normally and calmly into a mouthpiece for 30–60 seconds at a time, at least three times. Try not to swallow during the measurement. If you are also having spirometry on the same day, IOS is measured first.

Side effects

None known. You will feel small, rapid pressure pulses in the mouthpiece; they are harmless.

When the test cannot be done.

No particular restrictions beyond those that apply to spirometry.

Your result

The result is available straight after the test and is reviewed with you together with your spirometry.

What to bring

• Bring ID, for example your health insurance card or driving licence (app versions also count) or your passport. Your CPR number alone is no longer enough.
• Bring an up-to-date medication list and any earlier lung function measurements.
• Always bring your reliever inhaler.
• Arrive in good time, so you are not out of breath when we start.

Background and sources

• The clinic's own source for medication pauses and preparation (version 20-10-2026) and the clinic's test protocols.
• King GG et al. Technical standards for respiratory oscillometry. Eur Respir J 2020;55:1900753.

Lung function test