What is a Pulmonary Function Test (PFT)?
Pulmonary function testing measures how well the lungs take in and release air and how well they move gases such as oxygen into circulation. It includes three components: spirometry, lung volume, and diffusion capacity.
• Spirometry – measures airflow
• Lung volume – measures the capacity of the lungs
• Diffusion capacity – measures how well the lungs move oxygen from the air into the bloodstream
How the Test Is Performed
During a spirometry test, the patient would be seated. The technician would instruct the patient to breathe into a mouthpiece, first with normal breathing, and then withforced inhalation or exhalation after a deep breath. Sometimes the patient will be given medicine to see how it changes the test results.
Lung volume measurement is done within a sealed, clear box called a body pleismograph, shown here. While breathing in and out into a mouthpiece, changes in pressure inside the box will help determine lung volume.
During the last part of the test, the patient is instructed to breathe a harmless gas for a short time. The concentration of the gas in the air exhaled is measured. The difference in the amount of gas the patient inhaled versus exhaled will measure how effectively gas travels from the lungs into the blood.
How to Prepare for a PFT
• Do not eat a heavy meal right before the test
• Do not smoke for 4-6 hours before the test
• Your doctor will give you specific instructions regarding your medication or inhaler use before the test