What is a pulmonary function test?

A pulmonary function test is used to assess a patient’s ability to inhale, exhale, and transfer oxygen to the blood stream. Obstructive lung disorders, such as asthma, chronic bronchitis and emphysema, can cause the patient to have difficulty exhaling due to the narrowing of the airways. Other conditions, such as fibrosis, lung cancer and obesity, can cause the lungs to hold too little air and impair the lungs’ ability to transfer oxygen to the blood stream.
To determine lung volume, a pulmonary function test requires the patient to sit in a booth, similar to a phone booth, while breathing into a mouthpiece. The respiratory therapist will measure changes in pressure in the booth to calculate lung volume. To determine the lungs’ ability to transfer oxygen into the blood stream, the lung diffusion testing is used. For this test, the patient inhales a small amount of a trace gas, holds their breath, and then exhales. The respiratory therapist will measure how much of the trace gas was absorbed by the blood.
These tests are used to diagnose lung disorders and also performed in regular intervals for patients with chronic lung problems to help the physician determine whether treatments are working by tracking whether lung function is improving or weakening.