Diffusion capacity

Diffusion capacity or DLCO (Diffusing capacity or Transfer factor of the Lung for Carbon Monoxide) is a medical test that determines how well oxygen passes from the air sacs of the lungs into the blood. It is a part of Pulmonary function testing and is used to diagnose certain types of lung disease such as pulmonary fibrosis and emphysema, and to evaluate lung function before surgery.

Overview

The diffusion capacity of the lungs for carbon monoxide (DLCO) is a measure of the lung's ability to transfer gases from the inhaled air to the red blood cells in pulmonary capillaries. This process is essential for the delivery of oxygen to the tissues and the removal of carbon dioxide from the body.

Measurement

The DLCO test is performed by having the patient inhale a test gas mixture that contains a small amount of carbon monoxide, usually less than 1%. The patient then holds their breath for about 10 seconds, allowing the gas to mix with the air in the lungs. The patient then exhales, and the amount of carbon monoxide in the exhaled air is measured. The difference between the inhaled and exhaled concentrations of carbon monoxide is used to calculate the DLCO.

Interpretation

A decreased DLCO can be seen in conditions that affect the alveolar-capillary interface, such as pulmonary fibrosis, emphysema, and pulmonary hypertension. An increased DLCO can be seen in conditions that result in increased pulmonary blood volume, such as polycythemia and left-to-right shunt.

See also

• Pulmonary function testing
• Spirometry
• Lung volumes
• Pulmonary fibrosis
• Emphysema