Lung volume tests

Helium dilation

We'll ask you to sit down and breathe normally into a monitoring device for two to five minutes . We'll then ask you to wear a nose clip and breathe in a gas containing helium.

Body plethysmography

We'll ask you to sit in a special cubicle. Your consultant physiologist will give you instructions through an intercom. They'll ask you to breathe into a mouthpiece, with your palms on your cheeks. They'll then ask you to pant in and out. You'll be asked to perform this process three to four times.

For both tests, you'll be asked to breathe in deeply and blow out as much as possible to finish.

Whether you're having a helium dilation or body plethysmography, we'll explain how to prepare for the test and what's involved. They normally take 30 to 90 minutes and you should be able to go home straight after. Part of this time may involve waiting while any medication you are given takes effect.

After having your helium dilation or body plethysmography, your physiologist will explain the results of the test to you. The tests usually take less than 90 minutes and you should be able to go home straight away.