What kind of lung function tests are there and what do they involve?

Your doctor may suggest that you have your lung function checked in the following situations:

• if you have symptoms like shortness of breath, a persistent cough, abnormal breathing sounds, or if you cough up phlegm,
• if an x-ray of your lungs shows something unusual, or
• in order to prepare for surgery.

Lung function tests are typically done if it's thought that you could have one of the following diseases:

• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Pulmonary fibrosis (scarring of lung tissue)
• Pulmonary emphysema

These tests are also used to monitor treatment outcomes and the course of chronic lung diseases like asthma or COPD. They are sometimes part of employee health check-ups too, or used in sports medicine.

There is no need to prepare for a lung function test. It doesn't hurt or have any side effects. But you shouldn't smoke right before the test, and you shouldn't eat or drink too much. If you need medication, such as an asthma spray, it is best to first ask the doctor whether you can still use it as you would otherwise.

Spirometry is the basic test used to measure lung function. It can either be carried out by your family doctor or in a specialist practice.

The test measures the amount of air you inhale and exhale, and how fast the air is breathed in and out. You do this test while in a seated position. After taking a few normal breaths, you exhale into a mouthpiece as forcefully or as long as possible, depending on what the examiner asks you to do. For accurate results, it's important to follow their instructions carefully. Your nose will be pinched with a nose clip to prevent you from breathing through your nose. The mouthpiece is connected to a device called a spirometer. This device measures the amount of air you inhale and exhale when you breathe. The measurements are then displayed as a graph on the device's monitor.

The test takes just a few minutes to complete. If other tests are done too (see below), the appointment could take between 30 and 90 minutes in total.

Spirometry can help find out things like how narrow your airways are if you have asthma, or how severe lung hyperinflation is in pulmonary emphysema.

Whole-body plethysmography (also called body plethysmography) can deliver more exact results and additional information. This test is usually done in a pulmonology (lung specialist) practice.

It involves sitting in an airtight chamber and breathing in and out of a mouthpiece, like in the spirometry test. When you breathe in and out, your chest moves up and down, causing the pressure inside of the chamber to change. The changes in pressure are used to determine the amount of air you inhale and exhale, and also the amount of air that stays in your lungs once you have breathed out completely (residual volume). Even when you exhale as hard as you can, there's always still a small amount of air in your lungs. Airway resistance is also measured. This is higher if the path through the bronchi is narrowed – for instance, by asthma or COPD.

You don't need to breathe as hard as you can for this measurement. Normal, calm breathing is enough. This procedure takes a few minutes and is slightly more elaborate than spirometry. Because the measurements rely less on the active participation of the person being examined, it is suitable for young children too.

The following tests may be done too:

• Ergospirometry: Your lung function may also be tested during strenuous physical activity – usually while on an exercise bike. This shows whether, for example, coughing or shortness of breath are caused by physical activity or become worse because of it.
• Bronchial challenge test: In this test you inhale small amounts of allergy-triggering substances. If your lung function worsens as a result, it is a sign that you have an allergy.
• Reversibility test: Here you inhale medication to open your airways (a bronchodilator). If lung function improves as a result, it is likely to be asthma rather than COPD or chronic bronchitis.
• Lung diffusion capacity test: This test is used to check the exchange of oxygen and carbon dioxide between the lungs and the bloodstream. During the test, you inhale specially prepared air that contains a safe amount of carbon monoxide (CO). It is possible to tell how well oxygen and carbon dioxide are exchanged based on the amount of CO you exhale. Pulmonary fibrosis, for example, makes this exchange less effective.

This test allows people with a diagnosed lung disease to monitor it on their own. To perform the test, you hold a portable measuring device called a peak flow meter horizontally in front of your mouth. You inhale, hold your breath, and then exhale as forcefully as you can while keeping your lips tightly sealed around the mouthpiece. The maximum speed reached while exhaling (known as the "peak flow") is recorded by the device. This test is supposed to be done once or twice a day, taking up to three measurements each time. The highest of these repeated measurements is recorded in a diary each time.

You can talk to your doctor about when to adjust your medication if the peak flow readings change a lot. You can also learn about this in patient education classes. The peak flow meter must be completely dry when it is used, and it needs to be cleaned regularly.

Blood gas analysis is used to measure the amount of oxygen and carbon dioxide in your blood, among other things. This makes it easier to judge how severe COPD or an acute COPD attack (exacerbation) are, for example.

Because oxygen-rich blood is needed for blood gas analysis, it is not taken from one of the usual places like a vein in your arm or hand, but from your earlobe (using a lancet). This blood, called capillary blood, has oxygen levels similar to those of blood from the arteries, but it is easier to sample.

In specific situations, such as when monitoring artificial ventilation or in circulatory shock, the blood is taken directly from an artery in the wrist or thigh. A pressure bandage is then applied to the wound to prevent bleeding.