Pulmonary function test at Guildford Hospital

What is a pulmonary function test?

A pulmonary function test, also called a lung function test, is a group of breathing tests that check how well your lungs are working. It measures things like how much air you can breathe in and out, and how well oxygen moves from your lungs into your blood.

Why might I need one?

Your doctor might recommend a pulmonary function test if you have symptoms such as breathlessness, a persistent cough, or wheezing that isn't explained by a cold or other short-term illness.

It's also used to:

• monitor a lung condition you already have, such as asthma or COPD, and see how well your treatment is working
• check your general health before surgery
• look into how work or environmental exposures might have affected your lungs.

What are the benefits of having it?

A pulmonary function test can confirm what's causing your symptoms and rule out other causes, so you and your doctor can agree on the right treatment sooner. If you already have a lung condition, repeating the test over time is one of the most useful ways to track whether it's getting better or worse, and whether your treatment is working.

Are there different types of test?

Yes. A pulmonary function test can include one or more of the following:

• spirometry, the most common test, which measures how much air you can breathe out and how quickly
• a lung volume test, sometimes done using a sealed booth called a body plethysmograph, which measures the total amount of air your lungs can hold
• a gas transfer test, which measures how well oxygen moves from your lungs into your blood
• a cardiopulmonary exercise test, such as a six-minute walk test, which checks how your lungs perform when you're active
• oscillometry, a quick test that uses gentle sound waves to check how open your airways are.

A 'full' lung function test usually means having spirometry, a gas transfer test and body plethysmography together.

How do I prepare for the test?

Your clinic will give you specific instructions, since these can vary depending on why you're having the test, but common advice includes:

• avoiding short-acting reliever inhalers, such as salbutamol (Ventolin, Salamol) or ipratropium (Atrovent), for 6 hours beforehand
• avoiding longer-acting inhalers, such as Seretide, Symbicort or Fostair, for 12 hours beforehand, and inhalers such as Anoro or Relvar for 24 hours beforehand
• not smoking for 24 hours before the test
• avoiding a heavy meal for 2 to 4 hours beforehand, and alcohol on the day
• avoiding vigorous exercise shortly before the test
• wearing loose, comfortable clothing.

Always take your other regular medication as normal unless you're told otherwise and let the department know if you're unable to stop an inhaler because you're too short of breath.

What happens during the test?

For spirometry, the most common test, you'll usually be asked to:

1. sit beside the spirometer, with a soft clip fitted over your nose
2. breathe in as deeply as you can, filling your lungs completely
3. seal your lips firmly around the mouthpiece
4. blow out as hard and as fast as possible, until your lungs feel completely empty
5. do this twice more, to help make sure the reading is accurate.

You may also be asked to use an inhaler and repeat the test after a short break, to see whether it changes your results.

If you're having a full lung function test, you may also have:

• a gas transfer test, where you breathe in a harmless gas mixture, hold your breath for up to 10 seconds, then breathe out fully
• body plethysmography, where you sit inside a small, clear booth and breathe normally through a mouthpiece while measurements are taken.

The whole appointment usually takes between 30 minutes and an hour, or longer if an inhaler is also being tested.

What happens after the test?

You can return to your normal activities straight after the test, though you might feel a little dizzy or lightheaded for a short time from breathing so hard.

The physiologist carrying out the test usually can't give you your results on the day. Instead, they're reported to the doctor who referred you, who will then arrange to discuss them with you, either in a letter, a follow-up appointment, or a call with a specialist nurse.

You should hear something within a few weeks. Contact your GP surgery if you haven't heard anything after that time.

What are the risks?

These tests are generally very safe, and serious problems are rare. You might feel dizzy, lightheaded, or need to cough during or shortly after the test, from breathing so hard, but this should pass quickly.

Rarely, more serious problems can occur, including airway narrowing, a sudden change in blood pressure, or, in people with existing heart or eye conditions, a heart attack, stroke or retinal detachment. This is why you'll be asked about your health beforehand.

Let the department know before your appointment if, in the last three months, you've had any of the following, since it may need to be rescheduled:

• a chest infection you're still being treated for
• an uncontrolled heart condition or high blood pressure
• a heart attack or stroke
• recent eye surgery, or chest or abdominal surgery
• coughing up blood.