Table of Contents
Introduction:
A lung diffusion test (DLCO) is a way of pulmonary function testing that defines the functioning capacity of the lungs. It incorporates a gas that contains carbon monoxide to measure the amount of oxygen moving from the lungs to the blood while inhaling. The technique was initially described 100 years ago. It is feasible and easy for the patient as well. The breath-holding required for the DLCO for ten seconds is an easier process for many patients to perform than the forced exhalation method performed in spirometry.
What Is Lung Diffusion Testing?
Lung diffusion testing is performed to calculate the way the lungs exchange gases. This is a crucial part of lung testing as the majority of the function of the lungs is to allow oxygen to diffuse or pass into the blood from the lungs and allow carbon dioxide to diffuse from the blood into the lungs. Diffusion testing is performed to:
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See the signs of lung damage.
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Help diagnose the cause of breathing issues.
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Track the progress of an ongoing illness.
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Test how well the treatment is working on an individual.
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To check lung health before the surgery.
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To check if a person is at risk for lung disease due to smoking, heart problems, and more.
What Is the Diffusing Capacity of the Lungs for Carbon Monoxide?
Diffusing capacity of the lungs for carbon monoxide (DLCO) or transfer factor for carbon monoxide (TLCO) is one of the clinically valuable tests performed to test the proper functioning of the lung. This test can calculate the potential of the lungs to transfer gas from inhaled air to the red blood cells in pulmonary capillaries. It is a kind of pulmonary functioning test that determines the exact functioning of the lungs.
While performing this test, a person is supposed to breathe in a gas containing a small amount of carbon monoxide. This evaluates the amount of carbon monoxide passing down the blood from the lungs or the diffusing capacity for carbon monoxide (DLCO).
When Is DLCO Performed?
DLCO is performed in cases that require:
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They identify parenchymal and non-parenchymal lung problems occurring in conjunction with spirometry.
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The severity of obstructive and restrictive lung diseases, pulmonary vascular disease, and preoperative risk can also be evaluated with the help of DLCO.
How Does a DLCO Test Work?
A DLCO test works by using a mixture of gases to measure how well the oxygen and carbon dioxide circulate between the lungs and the blood. During the test, a person is asked to breathe in a gas, which is a mixture of nitrogen and oxygen (which naturally make up most of the air a person breathes), and in addition to that:
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A small amount of carbon monoxide (which is in very little amount) should move easily from the lungs to the blood.
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A small amount of tracer gas, such as methane. A tracer gas is not absorbed into the blood, and it helps evaluate the amount of carbon monoxide absorbed.
When a person breathes in, some or all of the carbon monoxide is absorbed by the blood from the gas present in the lungs. When a person breathes out into the machine, it measures the amount of carbon monoxide the blood absorbs on the basis of how much is left in the gas a person exhaled. This measurement can give the doctor an idea of how well the lungs are functioning.
What Are the Conditions that Affect DLCO?
Certain conditions can affect the outcome of the DLCO. Conditions in which DLCO gets decreased are:
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The conditions that primarily impact pulmonary vasculatures are primary pulmonary hypertension and pulmonary embolism.
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The conditions that affect the lung diffusely, like emphysema and pulmonary fibrosis, reduce both DLCO and alveolar ventilation (VA).
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It can also be noted in patients with previous lung resections as the total lung volume is smaller, but DLCO corrects to or even exceeds normal when adjusted for alveolar ventilation.
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Patients who have anemia have low value of DLCO, which are corrected when hemoglobin values are adjusted.
What Are the Complications of DLCO?
DLCO can have complications in certain conditions; therefore, it is contraindicated. The DLCO contraindications are:
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Measurements of pulmonary diffusing capacity are not done in cases where chest and abdominal pain persists, oral or facial pain, dementia, or stress incontinence is present.
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The recommendation is to postpone pulmonary function testing (PFT) by a month frequently in cases of acute coronary syndrome or myocardial infarction. PFT is also not advised for patients with pneumothorax, ascending aortic aneurysm, pulmonary embolism, severe hypertension, hemoptysis, and complicated surgeries like thoracic, abdominal, brain, eye, ear, and otolaryngological surgery.
Conditions in which DLCO increases are:
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Heart Failure- In this condition, heart failure is presumably because the increased pulmonary venous and arterial pressure recruits additional pulmonary microvessels.
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Erythrocythemia- In erythrocythemia, DLCO increases since hematocrit is high and because of the vascular recruitment that takes place with increased pulmonary pressures due to increased viscosity.
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Alveolar Hemorrhage- In alveolar hemorrhage, red blood cells in the alveolar space can also bind to carbon monoxide and increase DLCO.
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Asthma- The increase in DLCO is seen due to vascular recruitment which is presumed. However, a few studies suggest that it might also be caused due to the growth factor-stimulated neovascularization.
Conclusion:
The diffusing capacity of the lungs for carbon monoxide (DLCO) is a safe, noninvasive way for the healthcare provider to get important information about how well the functioning of the lungs is. It is more feasible than spirometry. It can be performed in conditions like lung parenchymal and non-parenchymal conditions, emphysema, asthma, etc. It works by using a mixture of gases to measure how well the oxygen and carbon dioxide circulate between the lungs and the blood. It is not advised in cases where chest and abdominal pain persists, oral or facial pain, dementia, or stress incontinence is present, and certain major surgeries like ear, eyes, etc.
