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D LCO or T LCO (diffusing capacity or transfer factor of the lung for carbon monoxide (CO), [1]) is the extent to which oxygen passes from the air sacs of the lungs into the blood. Commonly, it refers to the test used to determine this parameter. It was introduced in 1909. [2]
The person then inhales a test gas mixture rapidly and completely, reaching the total lung capacity as nearly as possible. This test gas mixture contains a small amount of carbon monoxide (usually 0.3%) and a tracer gas that is freely distributed throughout the alveolar space but which doesn't cross the alveolar-capillary membrane.
People with COPD also exhibit a decrease in diffusing capacity of the lung for carbon monoxide due to decreased surface area in the alveoli, as well as damage to the capillary bed. [112] Testing the peak expiratory flow (the maximum speed of expiration), commonly used in asthma diagnosis, is not sufficient for the diagnosis of COPD. [111]
The diffusing capacity for carbon monoxide (DLCO) is invariably reduced in IPF and may be the only abnormality in mild or early disease. Its impairment underlies the propensity of patients with IPF to exhibit oxygen desaturation with exercise which can also be evaluated using the 6-minute walk test (6MWT).
Diffusing capacity (or DLCO) is the carbon monoxide uptake from a single inspiration in a standard time (usually 10 seconds). During the test the person inhales a test gas mixture that consisting of regular air that includes an inert tracer gas and CO, less than one percent.
The process of breathing does not fill the alveoli with atmospheric air during each inhalation (about 350 ml per breath), but the inhaled air is carefully diluted and thoroughly mixed with a large volume of gas (about 2.5 liters in adult humans) known as the functional residual capacity which remains in the lungs after each exhalation, and ...
Capillary transit time (tc), at rest is around 0.8s, allowing plenty of time for the diffusion of oxygen into the circulation and the diffusion of CO 2 out of the circulation. After training, the capillary volume is still the same however cardiac output is increased, resulting in a decreased capillary transit time, reducing to around 0.16s in ...
Pulmonary function testing in people with organizing pneumonia, either cryptogenic or due to secondary causes, shows a restrictive defect with a decrease in the gas absorptive capacity of the lungs (seen as a decrease in the diffusion capacity of carbon monoxide). [9] Airflow obstruction is usually not seen on pulmonary function testing. [9]