Some chemo drugs and radiotherapy to the chest can affect how well your lungs work, so you’ll have this test before and during your treatment. Your doctors will tell you if you'll be having chemo drugs that might affect your lungs.

what happens?

Different tests are done to check different things. You might only have to do one or two of them, or your doctors might want you to do all of them. It depends on your type of cancer, which treatment you’re having and how well you are.

This is what the lung function test will involve:

• You’ll wear a nose clip so that you can only breathe through a mouthpiece that’s connected to a machine. 
• While you're sitting down, you’ll be asked to breathe normally or to forcefully breathe in and out as fast as you can. This is to check how much air your lungs can take over a certain amount of time. 
• You might also have to breathe in a small amount of a gas called carbon monoxide (which is harmless), to check how well the gas moves from your lungs into your bloodstream. 
• You might be asked to sit in a see-through that which looks a bit like a phone booth. While you breathe in and out, the pressure in the booth is changed. This checks how much air your lungs can hold. 
  An exercise test on a treadmill (running machine) or bike will test how well your lungs work when you're exercising.

All this can take about 30 minutes. You may find the nose clip and mouthpiece uncomfortable. You might feel out of breath or a bit dizzy because of all the breathing in and out exercises, but you’ll be given time to rest in between. There’ll be someone with you all the time, so if you start to feel ill, just let them know.