Chronic Obstructive Pulmonary Disease (COPD) describes lung conditions that hinder airflow and make breathing challenging. This progressive disease affects millions, often causing symptoms like chronic cough, shortness of breath, and wheezing. Pulmonary function tests are diagnostic tools used to monitor lung health in individuals with COPD, providing insights into lung function.
Understanding the DLCO Test
The Diffusing Capacity of the Lungs for Carbon Monoxide (DLCO) is a pulmonary function test measuring the lungs’ ability to transfer gas from inhaled air into the bloodstream. It evaluates how well oxygen moves from the tiny air sacs (alveoli) across their walls into surrounding capillaries to bind with red blood cells.
To perform the test, a patient breathes in a special gas mixture containing a small, harmless amount of carbon monoxide and a tracer gas. After inhaling this mixture and holding their breath for about 10 seconds, the patient exhales into a machine. The machine analyzes the exhaled air to determine how much carbon monoxide was absorbed into the blood.
Carbon monoxide is used because it binds strongly to hemoglobin, allowing precise measurement of gas transfer efficiency. The difference between inhaled and exhaled carbon monoxide indicates how effectively gases are exchanged in the lungs.
The Significance of DLCO Results in COPD
For individuals with COPD, DLCO values are typically reduced. This reflects damage to lung structures responsible for gas exchange. COPD often involves destruction of alveolar walls and surrounding capillary beds, where oxygen enters the bloodstream and carbon dioxide exits.
When alveoli are damaged or their surface area diminished, gas transfer efficiency decreases. A lower DLCO value indicates less oxygen moves from lungs into blood, impacting the body’s ability to receive adequate oxygen. This measurement assesses the lung’s primary function—gas exchange—and helps gauge structural damage. Impaired DLCO has also been linked to increased COPD symptoms, reduced exercise capacity, and a higher risk of severe exacerbations.
How DLCO Helps Classify COPD
COPD encompasses conditions like emphysema and chronic bronchitis, which affect the lungs distinctly. The DLCO test helps differentiate between these subtypes.
Emphysema involves significant destruction of alveolar walls, leading to enlarged air spaces and a substantial reduction in surface area for gas exchange. This damage results in a low DLCO.
In contrast, chronic bronchitis primarily affects airways, causing inflammation, narrowing, and excessive mucus production, with less direct damage to alveoli. Since the primary issue is airflow obstruction rather than extensive gas exchange surface destruction, DLCO in chronic bronchitis may be near normal or only slightly reduced. Observing DLCO alongside other pulmonary function tests provides a clearer picture of the dominant COPD form.
Factors Influencing DLCO and Management Strategies
DLCO results can be influenced by several factors beyond lung tissue damage. Conditions like anemia (fewer red blood cells), pulmonary hypertension, or a previous lung resection can lower DLCO values. Conversely, obesity, asthma, or exercising before the test can sometimes result in a higher DLCO.
While underlying lung damage from COPD is generally irreversible, managing the condition can support remaining lung function. Strategies include smoking cessation, medications (bronchodilators, inhaled corticosteroids), and pulmonary rehabilitation. Pulmonary rehabilitation, a supervised program combining exercise and education, can improve exercise tolerance, reduce dyspnea, and enhance quality of life. It may also improve DLCO values in some patients.