The first steps in evaluating respiratory problems involve a review of your medical history and a physical examination. These will help your doctor, who may be a pulmonologist (a lung specialist), to determine which laboratory tests and chest-imaging techniques are required.
Your doctor will ask a number of questions about current symptoms, past behaviors, occupation, toxic exposures (for example, to cigarette smoke, silica [fine dust from quartz] or asbestos), and family medical history. The doctor will also take into account the presence of infections, such as the flu, in the family or community.
You will need to give information about any respiratory illnesses that you or your family members may have. You will also discuss any allergies and any medications you take. Some medications, such as diet pills and amiodarone (Cordarone, used to treat an irregular heart rhythm), can contribute to lung disease.
In some people, problems that seem unrelated to the lungs—for instance, skin rash, joint pain, and visual changes—are symptoms of a more generalized inflammatory disease that has respiratory difficulty as one of its symptoms. In addition, a disease such as lung cancer can cause symptoms elsewhere in the body if it spreads.
The physical examination for a possible lung disease includes a check of breathing rate and pattern and an assessment of how the torso moves during breathing. The way the torso moves is important because some people with lung disease use extra muscles in their abdomen, neck and rib cage to aid in breathing. Also, reduced movement in one side of the chest might suggest disease in the lung on that side. Finally, abnormalities in the structure of the chest could be the cause of breathing difficulty.
In addition, your doctor will use his or her senses of touch and hearing to evaluate the condition. Touching the chest wall may reveal rib fractures or other sources of chest pain. Tapping the chest to generate sound helps the doctor determine how far the diaphragm moves and how much the lungs inflate during breathing. The doctor will also listen to your breath sounds using a stethoscope.
Finally, your doctor can find numerous clues to lung disease simply by looking at you carefully. Examining the hands may reveal discoloration of the nail beds or clubbing of the fingers (a thickening of the fingertips and increased curvature of the fingernails). Blue nail beds suggest low oxygen levels in the blood. Clubbing suggests lung cancer, interstitial lung disease, bronchiectasis, or other problems.
Heart failure can cause difficulty breathing, as can a heart condition known as cor pulmonale, which is caused by high blood pressure in the lungs. Swelling of the legs and feet suggests that a heart problem may be the cause of symptoms. Swelling in one leg suggests a blood clot, which could lead to a pulmonary embolism if it detaches from a vein and travels through the bloodstream to cause a blockage in or around the lungs.
Your doctor may order a blood test to look for clues such as anemia (low red blood cell count), a finding that might explain shortness of breath or suggest a chronic condition such as lung cancer. Or, a blood test might reveal an elevated white blood cell count, perhaps indicating a lung infection.
The 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.
Doctors often turn to exercise testing, using a treadmill or a stationary bicycle, to help evaluate shortness of breath and to determine whether it is caused by a lung problem, heart disease, or simply being out of shape.
When the lungs are not functioning properly, the blood gases (amount of oxygen and carbon dioxide in the blood) may be affected. One way to measure blood gases is to take a blood sample from an artery. A noninvasive alternative is pulse oximetry, which measures the level of oxygen in the blood.
In this test, a sensor placed on the fingertip or earlobe directs a beam of light through the tissues and then measures the amount of light absorbed by hemoglobin, a pigment in the blood that carries oxygen. This gives an estimation of the blood oxygen level.
Usually, the general evaluation just described provides enough information for the doctor to diagnose a lung disorder and devise a management plan. Sometimes, however, the initial evaluation does not provide a definitive diagnosis. If this is the case, invasive procedures, such as bronchoscopy, may be necessary to obtain biopsy samples of cells and tissues.