Pulmonary Function Tests


Lt Col Reynolds
Pulmonary function tests, sometimes called lung function tests, measure how well the lungs work. For patients with asthma, pulmonary function tests are an important part of monitoring their disease and how well their treatment is working. Dr. Green, can you tell us about pulmonary function tests?

Dr. Green
Absolutely, Dr. Reynolds. Some pulmonary function tests, such as spirometry and lung volume tests, measure lung size and airflow. Spirometry uses a tube, called a spirometer, connected to a computer to measure the rate of airflow during regular and heavy breathing. It can also estimate lung size.

Lung volume tests are similar to spirometry, except that instead of breathing into a spirometer, the patient is placed in a small room with clear walls. Lung volume tests are the most accurate way to measure how much air a person’s lungs can hold. Spirometry and lung volume tests may make some people lightheaded or tired from the required breathing effort.

Other tests measure how well oxygen and carbon dioxide get in and out of the blood. These tests include lung diffusion capacity, pulse oximetry, and arterial blood gas tests. Lung diffusion capacity assesses how well oxygen gets into the blood from the air you breathe. This test involves breathing in and out through a tube for several minutes without having to breathe intensely. Blood may also be drawn to measure hemoglobin levels.

Pulse oximetry uses a probe that is placed on the finger or another skin surface, such as the ear, to measure oxygen levels in the blood.

Arterial blood gas tests directly measure the levels of oxygen and carbon dioxide in the blood. This test is usually performed in a hospital, but it may be done in a primary care clinic. Blood is drawn from an artery, usually in the wrist where the pulse is measured, and analyzed for oxygen and carbon dioxide levels.

Another type of pulmonary function test, called fractional exhaled nitric oxide, measures nitric oxide, which is a marker for inflammation in the lungs. This test involves breathing into a tube connected to a portable device. It requires steady but not intense breathing.

Other tests may be necessary for infants, children, and other patients who are not able to perform spirometry and lung volume tests. Your provider will help you determine which pulmonary function tests are best for monitoring your asthma and treatment plan.