The Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) measures how efficiently lungs transfer gases from the air into the bloodstream. A “low DLCO” indicates this transfer is ineffective, meaning less oxygen moves into the blood. This article clarifies what a low DLCO signifies and the symptoms that might suggest its presence.
Understanding Reduced Gas Exchange
DLCO specifically measures the ability of carbon monoxide to move from the air sacs, called alveoli, into the red blood cells within the pulmonary capillaries. This process mirrors how oxygen moves from the lungs into the bloodstream. The test uses a very small, safe amount of carbon monoxide because it binds readily to hemoglobin in red blood cells, which allows for a clear measurement of gas uptake.
A reduced DLCO indicates an impairment in this gas exchange, suggesting that oxygen is not efficiently entering the bloodstream. This can happen if the alveolar-capillary membrane, the thin barrier between the air sacs and blood vessels, becomes thickened or damaged, or if the amount of blood in the pulmonary capillaries is reduced. Think of it like a filter that has become clogged or has lost some of its functional area, making it harder for air to pass through and reach the blood effectively.
Recognizing the Signs
When oxygen transfer is impaired, the body’s tissues and organs may not receive enough oxygen. This can lead to several symptoms:
Shortness of breath (dyspnea), particularly during physical activity or exertion.
Persistent fatigue and general weakness, leading to reduced exercise tolerance.
Lightheadedness or dizziness, especially when standing up quickly.
Bluish discoloration of the lips or nail beds (cyanosis) in more severe cases.
A chronic cough, if related to an underlying lung condition.
Common Causes of Reduced Gas Exchange
Several conditions can lead to a reduced DLCO by affecting the lung’s ability to transfer gases.
Interstitial Lung Diseases (ILDs)
Interstitial lung diseases (ILDs), such as pulmonary fibrosis and sarcoidosis, are frequent causes. In these conditions, the lung tissue becomes scarred and thickened, which directly impedes the movement of oxygen across the alveolar-capillary membrane. This scarring reduces the surface area available for gas exchange and increases the distance gases must travel.
Vascular Lung Diseases
Vascular lung diseases, including pulmonary hypertension and pulmonary embolism, also contribute to low DLCO. Pulmonary hypertension involves high blood pressure in the lung arteries, which can reduce the volume of blood available for gas exchange in the capillaries. A pulmonary embolism, a blockage in a lung artery, directly limits blood flow to parts of the lung, thereby decreasing the effective surface area for gas transfer.
Emphysema
Emphysema, a form of chronic obstructive pulmonary disease (COPD), is another common cause. Emphysema damages the alveoli, leading to a loss of the tiny air sacs and a reduction in the total surface area available for gas exchange. This destruction of alveolar walls and associated capillaries significantly impairs the lung’s diffusing capacity.
Anemia and Heart Failure
Anemia, characterized by a reduced number of red blood cells or low hemoglobin, can result in a lower DLCO. Hemoglobin is the protein in red blood cells that transports oxygen, and a decreased amount means less capacity to pick up oxygen, even if the lungs are otherwise healthy. Heart failure, particularly left-sided heart failure, can lead to fluid accumulation in the lungs. This fluid can thicken the alveolar-capillary membrane and reduce the lung’s ability to transfer gases, contributing to a lower DLCO.
Guidance for Seeking Medical Help
If you experience persistent shortness of breath, unexplained fatigue, or any of the other symptoms discussed in this article, it is advisable to consult a healthcare professional. These symptoms can indicate a variety of underlying health conditions, and early evaluation can lead to a more timely diagnosis and management plan. A doctor can perform a thorough physical examination and may recommend various tests, including lung function tests such as the DLCO.
The DLCO test, along with other pulmonary function tests, helps clinicians assess how well your lungs are working and can provide insights into the cause of your symptoms. While a low DLCO result alone does not provide a specific diagnosis, it serves as an important indicator that further investigation is needed. Seeking professional medical advice allows for an accurate diagnosis of the underlying issue and the development of an appropriate treatment strategy tailored to your specific condition.