A series of examinations known as pulmonary function tests are used to evaluate one's ability to breathe and how well their lungs are functioning.

Airflow is measured via spirometry. Spirometry can assess a wide variety of lung illnesses by monitoring the quantity and rate of air you exhale. During a spirometry test, you sit and breathe through a mouthpiece attached to a device known as a spirometer. The spirometer keeps track of the volume and rate of air you breathe in and out over time. Some numbers may alter somewhat when standing.

You can breathe regularly and quietly throughout part of the test measurements. Some tests demand a forced breath in or a forceful breath out. On occasion, you can be asked to breathe in a different gas or a medicine to check if the results of the test change.

There are two ways to measure the capacity of the lungs:

• Body plethysmography is the most precise method. You are seated in what appears to be a phone booth-like clear sealed enclosure. You are asked to breathe in and out through a mouthpiece by the technician. The lung volume is determined by changes in internal pressure.
• When you inhale nitrogen or helium gas through a tube for a predetermined amount of time, your lung volume can also be assessed. To calculate the lung volume, the gas concentration in a chamber connected to the tube is monitored.

You breathe a harmless gas, known as a tracer gas, for a brief period of time—often only one breath—to evaluate diffusion capacity. It is measured how much gas is present in the air you exhale. How efficiently gas moves from the lungs into the blood is determined by the difference between the amounts of gas exhaled and inhaled. With the use of this test, a medical professional can measure how efficiently the lungs transfer oxygen from the air to the blood.

Watch this video to learn how to perform a simple lung test that medical professionals use to identify respiratory illnesses.

Reference: “Pulmonary Function Tests: MedlinePlus Medical Encyclopedia.” Pulmonary Function Tests: MedlinePlus Medical Encyclopedia, medlineplus.gov/ency/article/003853.htm.