Chest x-ray is an imprecise method of diagnosis of COPD. It is only consistently abnormal in severe cases and should be performed in the initial evaluation to exclude other lung diseases. Findings characteristic of COPD in chest x-ray are hyperinflated lungs with flattened diaphragm, hyperlucent lungs (chest film shows greater than normal film blackening from increased transmission of x-rays), and central pulmonary artery enlargement. Bullae, areas of destroyed lung tissue that create large dilated air sacs, may be seen as well.
CT scan may be used to more accurately diagnose emphysema. This is usually not necessary, however, and abnormal lung anatomy is not always detected.
Pulmonary function tests are the primary diagnostic tools for COPD, after the medical history and physical examination. These tests demonstrate characteristic abnormalities in lung function that, in the proper clinical context (i.e., medical history, physical examination, chest x-ray) confirm or support the diagnosis of COPD and give some idea of the degree of impairment and prognosis. Lung biopsy is rarely used to diagnose emphysema.
There are four components to pulmonary function testing: spirometry, postbronchodilator spirometry, lung volumes, and diffusion capacity. In the initial evaluation, all four components are often performed. Periodically, an individual component, most commonly spirometry, is performed to assess progression of disease and to determine the effectiveness of medication.
* Spirometry
The most reliable way to determine reversible airway obstruction is with spirometry, a procedure that measures the amount of air entering and leaving the lungs. This simple test can be performed in most physicians' offices, with the patient sitting comfortably in front of the spirometry machine. The machine measures airflow that passes through the inhalation port attached to the machine. The inhalation device is usually a disposable cardboard tube or a reusable tube that can be sterilized after use.
The patient inhales as deeply as possible and forms a seal around the tube with their mouth. Then the patient exhales, as forcefully and rapidly as they can, until they can exhale no more. To be an adequate test, the patient must exhale all the air they possibly can continue exhaling for at least another 6 seconds. Usually, three separate attempts are made and the best result is used for evaluation.
Multiple measurements are obtained from this maneuver. Those most commonly used for interpretation are (1) forced expiratory volume after 1 second, (2) forced vital capacity and (3) forced expiratory flow at 25%-75% of maximal lung volume. They are expressed as percentages of what is predicted for normal lung function, depending on the variables of height, age, race, and sex.
COPD produces characteristic results in this test. The amount of air exhaled (forced vital capacity, or FVC) is reduced, compared to a person with normal lung function.
Perhaps his physician performed arterial blood gases which are measured using blood drawn from an artery, usually in the wrist. Blood is usually drawn from a vein, but venous blood is inaccurate for these measurements. Drawing blood from an artery, unfortunately, causes more discomfort.
Arterial blood gases are measured to determine the amount of oxygen dissolved in the blood (pO2), the percentage of hemoglobin saturated with oxygen (O2 sat), the amount of carbon dioxide dissolved in the blood (pCO2), and the amount of acid in the blood pH.
The oxygen measure may be used to determine whether a patient needs oxygen therapy. The carbon dioxide measure gives some idea of lung function and is especially important to know when starting oxygen therapy.
I would have your son make an appointment with a pulmonologist (Lung specialist) for an accurate diagnosis and treatment plan.