You may then breathe normally and your doctor will ask you to breathe in and out as deeply or as quickly as you can for several seconds or you may also be asked to breathe in a medication. This medication will enter your airways and you will then breathe into the machine again to see if the medication affected your lung function.
Plethysmography test as a part of Pulmonary function tests
A plethysmography test measures the volume of gas in your lungs. For this test, you will sit or stand in a small booth. You will breathe into a mouthpiece. Your doctor can learn about the volume of gas in your lungs, also called lung volume by measuring the pressure in the booth.
Diffusion capacity test as a part of Pulmonary function tests
This test evaluates how well the small air sacs inside the lungs, called alveoli, work. You will be asked to breathe in certain gases such as oxygen, helium, or carbon dioxide for the diffusion capacity test.
You may also be asked to breathe in a “tracer gas” for one breath and then the machine can detect when you breathe out this gas.
How to Prepare for Pulmonary Function Tests
You may need to follow the below instructions for pulmonary function tests:
- No bronchodilator medication for four hours
- No smoking for four hours before the test
- No heavy meals
- Do not wear any tight clothing, for exercise testing please wear a shirt that buttons up from the front and comfortable shoes
- The complete pulmonary function test takes around one and a half hours