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Lung function

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:

Lung function tests are performed using anti-bacterial or antiviral filters, which prevent risk of cross-contamination. 

Why you might need a lung function test

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

  • Detect if the breathing problem you may have is due to a lung condition. 
  • Assess if you are fit for surgery, and to help an anaesthetist decide if your lungs can cope with any anaesthesia you may be given. 
  • Monitor the progression of any existing lung conditions. 
  • Monitor the effects of any medicine or treatments on your lungs. This means you may be asked to have a lung function test before and after starting treatment.

Risks of lung function tests 

All procedures have some risks, but lung function tests are safe for most people. 

The risks of this procedure may include:

  • dizziness
  • breathlessness
  • coughing
  • fainting
  • palpitations or fast heart rate (when taking salbutamol for bronchodilator reversibility testing)

Your risks may vary depending on your general health and other factors. You will be asked a series of questions about your current health and risk factors before performing the tests. If you are thought to be at high risk, then your tests may be postponed or the procedure modified.

Preparing for a lung function test

  • Do not smoke or vape for one hour before your test.
  • Do not drink alcohol for at least 8 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 2 hours. 
  • Wear comfortable clothing which does not restrict full chest and abdominal expansion.
  • If you currently take a short-acting bronchodilator inhaler. For example, Ventolin (salbutamol), Bricanyl (Atrovent). Please avoid taking this for at least 4 hours before 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 before 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 them for at least 24 hours before 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.

Types of lung function tests

Spirometry test

A spirometry 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.

First, we will ask you to breathe normally into a mouthpiece. Then we will ask you to take a deep breath in and gradually blow out as much as possible until your lungs are completely empty.

You will need to do this a minimum of 3 times. You will have time to rest between each breath in and blow out. 

You will then need to repeat the test again. This time blowing out as fast and hard as possible until your lungs are completely empty, again for a minimum of 3 times.

Bronchodilator reversibility test

We may ask you to repeat a spirometry test after taking a type of medicine called a bronchodilator. Bronchodilators are medicines that open the airways. 

We ask you to take the bronchodilator medicine using an inhaler. Then we ask you to do the spirometry test.

The aim of test is to see if there is any improvement in your airways as a result of taking the medicine.

The bronchodilator reversibility test is also known as bronchodilator responsiveness testing.

Body plethysmography test

A body plethysmography test measures the total amount of air within your lungs and gives us more detailed information about the size of your lungs. This test is also called a lung volumes test.

For this test, you need to sit in a transparent chamber with the door closed. The door is closed but not locked. There is a button that you can press to open the door from the inside, if needed. 

We will ask you to start by breathing normally and then take some rapid shallow breaths against a shutter blocking the mouthpiece for about 2 seconds. 

Once the shutter is open you will be asked to blow out gently until your lungs are empty. 

Then we will ask you to take a breath in until your lungs are full up and then go back to normal breathing. 

This test will be repeated a minimum of 3 times.

Gas transfer measurement test

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 if you have conditions such as emphysema and pulmonary fibrosis. 

First, we will ask you to breathe normally on the mouthpiece. Then we will ask you to blow out until your lungs are completely empty. You then need to take a deep breath in and hold your breath for around 10 seconds before blowing all the way out. 

This test will be performed a maximum of 5 times. We will give you a 4-minute break between each of the 5.

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.

Exhaled nitric oxide measurement (FeNO) test

A fractional exhaled nitric oxide (FeNO)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.

You will be asked to breathe in through a mouthpiece until your lungs are full up. 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 once (one time).

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 inspiratory pressure (MIP) and mouth expiratory pressure (MEP)
  • sniff nasal inspiratory pressure (SNIP)

MIP test

A MIP test checks the strength of the muscles that help you breathe in.

You will be asked to breathe out for as long as you can, and then suck hard on a mouthpiece for at least one second. It will feel like sucking a very thick milkshake through a straw. This may be repeated up to 5 times. 

MEP test

An MEP test checks the strength of the muscles that help you breathe out.

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 5 times.

SNIP 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 5 times for both nostrils. The sniff pressure test also looks at the strength of the muscles that help you breathe in.

Hyperventilation screening test

A hyperventilation screening test assesses your breathing pattern by measuring the amount of carbon dioxide in your breath.

Your breathing will be monitored by small mouthpiece. You may then be asked to increase your breathing rate (hyperventilate) by breathing quickly and deeply for 3 minutes. Your breathing pattern will then be monitored again. This test may take up to 25 minutes.

6-minute walk test

The 6-minute walk test is used to measure the distance a person can walk. You walk on a flat, hard surface for a period of 6 minutes while your oxygen levels and heart rate are measured.

Contact

1st floor, Anzac Centre, Harefield Hospital, Hill End Road, Harefield, UB9 6JH

Sleep Services

Lead: Amna Hoda, chief clinical physiologist
Phone: 01895 828 589
Sleep Services email: SleepTechHH@rbht.nhs.uk

Lung function

Lead: Peter Dickel, chief clinical physiologist
Phone: 01895 828 589
Lung function email: P.Respiratory@rbht.nhs.uk

Opening hours: Monday to Friday, 9am to 5pm (excluding bank holidays)

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