Two other diagnostic tools frequently used to evaluate people who are suspected of having a lung disorder are chest imaging and pulmonary function tests. These tests complement each other: Chest imaging provides information primarily about the structure of the lungs and chest, while pulmonary function tests measure how well the lungs are working.
A chest x-ray may reveal an abnormality that clearly explains a respiratory problem or may flag areas for further evaluation. Lung tumors, pneumonia, occupational lung diseases, emphysema, interstitial lung disease, and collection of fluid around the lungs can all be seen on a chest x-ray.
A chest computed tomography (CT) scan provides a more detailed assessment of abnormalities than a standard chest x-ray. Combination positron emission tomography (PET) and CT scans are now being used to determine the presence of lung cancer.
Comparing current chest images with previous images is extremely important; this can help distinguish a new disease from a pre-existing condition and also monitor the progression of a disease over time.
Pulmonary Function Tests
Pulmonary function tests measure lung capacity and reveal patterns characteristic of particular diseases. They allow a doctor to compare the lung function of someone who has a breathing disorder with that expected for a healthy person of the same age, height, and gender.
The tests can help characterize a lung abnormality as primarily obstructive (in which the airways are narrowed), primarily restrictive (in which the ability of the lungs to expand is impaired), or a combination of the two. The tests also determine whether the deficit in lung function is mild, moderate or severe.
The pulmonary function tests that are customarily used for diagnosis include spirometry, lung volume tests and diffusing capacity tests. In spirometry, a person breathes out into a tube attached to a spirometer, which measures how much air is being exhaled and how quickly. The two most important values are the forced expiratory volume in one second (FEV1) and the forced vital capacity (FVC).
FEV1 measures the amount of air expelled from the lungs in the first second of a forced exhalation, while FVC is a measure of the total volume of air exhaled. The spirometer calculates these values automatically, along with the ratio between them, FEV1/FVC.