Pulmonary Function Testing

The following articles on Pulmonary Function Testing (PFT) are contributed by Richard Johnston. Click on their titles to access their content. 

Pulmonary Function Lab

A Pulmonary Function Lab is the location in a hospital where breathing tests are performed. This is where your spirometry, diffusing capacity (DLCO) and total lung capacity (TLC) tests will probably be performed.


An oximeter is a device that measures the amount of oxygen, or oxygen saturation, in your arterial blood. Most often an oximeter is a hand-held device with a probe that clips onto one of your fingers or possibly onto an earlobe. Arterial blood in the measuring site pulses and fades with your heartbeat and this allows a pulse oximeter to measure both your pulse rate and your oxygen saturation level.

Spirometry: Dynamic Lung Volumes

A spirometry test measures the amount of air you are capable of exhaling during a forced breathing maneuver and the speed at which you can exhale it. The results from this test give an idea about the capacity of your lungs and the condition of your airways.

Diffusing Capacity of the Lungs

This test is used to estimate the transfer of oxygen from the alveoli in your lungs to your bloodstream. The diffusing capacity of the lungs (DL) of oxygen is technically very difficult to measure, and the test actually measures the diffusing capacity of carbon monoxide (DLCO) which provides a valid estimate of the oxygen diffusion.

Static Lung Volumes

This test measures the static or absolute lung volumes. The most important are the total lung capacity (TLC) and residual volume (RV). The RV is the volume of air remaining in the lungs at the end of a maximal exhalation. The TLC is the volume of air in the lungs at the end of a maximal inhalation.

6-Minute Walk Test

This is a simple walking test that will provide your physician with an indication of your exercise capacity and general health status. It is measured by the distance you are able to walk in six minutes.

Hypoxia Altitude Simulation Test

HAST is a special breathing test to determine whether you need supplemental oxygen when flying on an airplane. This test has not been standardized so there may be differences in the way this test is performed by different pulmonary function labs.

Cardiopulmonary Exercise Testing

This is an exercise test where an individual's heart function (cardio) and lung function (pulmonary) are carefully monitored during a steadily increasing workload. The reasons why an individual has a limited exercise capacity or is short of breath can be complicated and can involve multiple body systems. A cardiopulmonary exercise test may be recommended for you when your shortness of breath or exercise limitation cannot be fully explained by simpler tests.

Arterial Blood Gases

An arterial blood gas is a special blood test to measure how much oxygen and carbon dioxide are in your blood.

A Physiology of ILD article is in preparation to further inform the understanding of Pulmonary Function Testing. It will include a discussion of the functional-morphologic correlation in the estimation of disease extent/activity, how spirometry and DLCO are used to stage and quantify ILD severity at initial diagnosis, and how DLCO best detects changes in severity over time. It will compare the diagnostic and prognostic value of PFT in ILD with those of other methods used in the clinical evaluation of the disease. For example, while PFT reflects histologic changes better than symptoms or chest radiography, it cannot distinguish fibrosis from inflammation. Some subtle aspects of the disease will be addressed, for example, how the lack of physiologic deterioration, particularly in early stages of the disease, does not indicate absence of disease progression. In addition, the article will offer explanations of some physiological phenomena that patients self-observe and report like a shallow breathing pattern and exertional dyspnea.