Lung function tests: a guide

What is a lung function test?

A lung function test involves you breathing into different pieces of equipment to test how well your lungs are working. There are several different lung function tests that your doctor may refer you for, these include:

• Spirometry
• Bronchodilator reversibility test
• Gas transfer measurement
• Body plethysmography
• Fractional exhaled nitric oxide (feno) measurement
• Respiratory muscles tests

What is spirometry?

This test measures the volumes and speed of the air you can blow out from your lungs. It will give an indication of the capacity of your lungs and how clear your airways are. For example, the airways may be narrower in conditions such as COPD (chronic obstructive pulmonary disease) or asthma.

What is bronchodilator reversibility?

After you have performed spirometry, it may be repeated after you have been given an inhaler. This will see if there is any improvement in your airways because of taking this medication.

What is a gas transfer measurement?

The main job of the lungs is to bring oxygen into your bloodstream and to remove carbon dioxide. The gas transfer test estimates how well your lungs work to take oxygen from the air you breathe and put it into your bloodstream. Lung conditions can affect gas transfer. For example, gas transfer will be reduced in emphysema and pulmonary fibrosis.

What is body plethysmography?

Body plethysmography, or lung volumes, measures the total amount of air and gives us more detailed information about the size of your lungs.

What is a fractional exhaled nitric oxide measurement? A fractional exhaled nitric oxide test measures how much nitric oxide is in your breath. A higher level of nitric oxide measured may indicate inflammation which may be a sign of asthma.

What are respiratory muscle tests?

Respiratory muscle tests measure how much pressure your breathing muscles can generate when you breathe in or out to check for muscle weakness. There are two types of respiratory muscle tests: mouth pressure and sniff (SNIP) pressure tests.

Why do I need this test?

There are different reasons why your doctor may have referred you for a lung function test:

• Help determine if the breathing concern you may have is due to a lung condition • Help decide if you are fit for surgery and to help the anaesthetist decide if you can cope with any anaesthesia that you may be given • Monitor the progression of any existing lung conditions • Monitor the effects of any medication or treatments that may affect the lungs – you may be asked to have a lung function test before and after starting treatment, so that the health of your lungs can be monitored.

How do I prepare for my lung function test?

• Do not smoke or vape for one hour before your test.
• Do not consume alcohol for at least eight hours before your test.
• Avoid vigorous exercise for at least one hour before your test.
• You can eat and drink before your appointment, but please avoid eating a large meal within two hours and avoid foods high in nitrates such as green leafy vegetables and beetroot.
• Wear comfortable clothing which does not restrict full chest and abdominal expansion.
• Your height and weight will be measured, please wear shoes that are easily removed
• If you currently take a short-acting bronchodilator inhaler (for example, Ventolin (salbutamol), Bricanyl, Atrovent), please avoid taking this for at least 4 hours prior to your test.
• If you currently take a long-acting bronchodilator inhaler (for example, Fostair, Serertide, Serevent, Symbicort, DuaResp, Foradil, Oxis), please avoid taking this for at least 12 hours prior to your test.
• If you currently take any combination inhalers (for example, Spirvia Respimat, Dulkir Genuair, Flutiform, Onbrez, Relvlar Ellipta, Seebri, Trimbow, Trelegy), please avoid taking this for at least 24 hours prior to your test.

However, if you are feeling very breathless then please take your inhalers as normal and let the physiologist know when you last took them.

In addition, if you have any of the following, please contact us:

• You have a current chest infection
• You are coughing up blood or vomiting
• You have an aortic or cerebral aneurysm
• You have had a recent heart attack or collapsed lung within 6 weeks
• You have a blood clot in your lung
• You have had recent chest, abdominal or eye surgery within 6 weeks
• You have uncontrolled hypertension or intracranial pressure elevation risk
• You are pregnant

What happens during my lung function test?

Most of the tests are performed with you seated and your nose sealed with a nose peg. Each test is explained in more detail below.

How is spirometry performed?

You will be asked to breathe normally into a mouthpiece and then take a deep breathe in and then gradually blow out as much as possible until your lungs are completely empty. This will then be repeated with you blowing out as hard and as fast as possible until your lungs completely empty. Once they are empty, you will be asked to take a big breath back in again. Both slow and fast spirometry will be repeated a minimum of three times, but you will be given sufficient rest in between each blow.

How is bronchodilator reversibility performed?

After you have completed the spirometry, you may be given an inhaler (this is usually 400mcg of Salbutamol) via a spacer device. The physiologist will ask you to take a deep breathe in while they press the inhaler down to release a dose of the medication. This will be done 4 times in total. You will be given a 15-minute break to allow for the medication to have its full effect before the spirometry test is repeated.

How is gas transfer performed?

You will need to breathe normally on the mouthpiece and then you will be instructed to blow out until you are completely empty. You then need to take a deep breathe in and hold your breath for approximately nine seconds before blowing all the way out. This test will be performed a maximum of five times, but you will have a break in between each trial.

The special gas mix that you inhale contains oxygen, carbon monoxide, methane and nitrogen. The concentrations of all these gases are very low and safe but if you have any concerns please speak to your physiologist.

How is body plethysmography performed?

To measure your lung volume, you will be seated in a transparent chamber with the door closed. Please note that the door is closed but not locked and there is a button that you can press to open the door from the inside. You will start by breathing normally and then take some rapid shallow breathes against a shutter blocking the mouthpiece for about two seconds. Once the shutter is open you will be asked to take a full deep breath in and then blow all the way out again. This test be repeated a minimum of three times.

How is fractional exhaled nitric oxide (FeNO) performed?

You will be asked to breathe in through a mouthpiece until you are completely full. You will then need to breathe out at a steady and controlled rate for 10 seconds. There will be a visual aid on the screen to help guide you to breathe at the correct rate. You will need to complete this successfully a total of one time.

How are respiratory muscle tests performed?

For mouth pressures

You will be asked to breathe out for as long as you can, and then suck hard into a mouthpiece for at least one second. It will feel like you’re sucking a very thick milkshake through a straw. This may be repeated up to five times. You will then be asked to breathe in deeply first and then blow out as hard as you can into a closed off mouthpiece. This may be repeated up to five times.

For SNIP/SNIFF test

A small probe is placed to block one of your nostrils. It measures the pressure while you sniff in as hard as you can. This may be repeated up to five times for both nostrils.

What happens before my lung function test?

Before your test, the physiologist will measure your health and weight, as well as asking you to confirm your ethnicity. This is so that we can calculate the predicted values for your lung function test results. They will also ask you questions about your current health and medical conditions on ensure that it is safe to go ahead with testing.

What happens after my lung function test?

Your results will be sent to your referring doctor and will be discussed with you if necessary.

Are there any risks and side effects?

Due to the nature of the tests and the exertion required, some patients may feel dizzy or faint during testing. Coughing is also common. Serious complications are rare, and risks will be kept to a minimum by your physiologist.

The following risks below are serious but are rare.

• Heart attack in patients with previous heart issues
• Sudden changes in blood pressure
• Stroke
• Collapsed lung
• Airway narrowing in sensitive airways
• Retinal detachment
• Rupture of surgical stiches

Your physiologist will always ask you questions about contraindications prior to starting the test, to evaluate the risk of any of these from happening. If you have any concerns about the risks, please speak to your physiologist prior to starting the test.

Lung function test alternatives

Unfortunately, there are no alternatives to lung function tests. If you are really struggling to perform the test, your physiologist will be able to adapt the way in which you perform the test.