Diagnosing Chronic Obstructive Lung Disease

(Page 3)

Carbon Monoxide Diffusing Capacity. The lung carbon monoxide diffusing capacity (DLCO) test determines how effectively gases are exchanged between the blood and airways in the lungs. Patients should not eat or exercise before the test, and they should not have smoked for 24 hours.

The patient inhales a mixture of carbon monoxide, helium, and oxygen and holds his or her breath for about 10 seconds. The gas levels are then analyzed from the exhaled breath. Results can help physicians differentiate emphysema from chronic bronchitis and asthma. Patients with emphysema have lower DLCO results (a reduced ability to take up oxygen). Such results are also important in helping to determine appropriate candidates for lung reduction surgery. Carbon monoxide levels that are 20% or less than predicted values pose a very high risk for poor survival.

Exhaled Breath. The measurement of nitric oxide (NO) in exhaled breath can be a simple method of diagnosing COPD and monitoring the effects of treatment. In most patients with COPD, no levels are below normal. Levels above normal in a patient with COPD indicate that the person also has asthma.

Click the icon to see an image of lung diffusion testing.

Imaging Tests

Chest X-Rays. Chest x-rays are often performed, but they are not very useful for detecting early COPD. By the time an x-ray reveals COPD, the patient is already well aware of the condition. X-rays can look for growths in the lungs to rule out other diseases, however.

Clear signs of COPD on x-ray include the following:

Abnormally large amounts of air spaces in the lung

A flattened diaphragm

A smaller heart (however, if the person has heart failure, the heart becomes enlarged and there may not be signs of overinflated lungs)

Exaggerated lung inflation in upper areas

Larger amounts of air in the lower lungs in patients with emphysema related to alpha-1 antitrypsin deficiency

Chest x-rays are rarely useful for diagnosing chronic bronchitis, although they sometimes show mild scarring and thickened airway walls.