This noninvasive method determines the oxygenation of the blood (O2 sat; normal is greater than 90 percent) by measuring the amount of light transmitted through an area of skin. The device must be able to read pulsatile flow, so it must pick up a pulse to be accurate.
Oximetry is not as accurate as the measurement of arterial blood gases. It is commonly used during exercise and sleep. Exercise oximetry can determine if a patient's oxygen decreases during activity. If so, oxygen therapy with activity may be beneficial. Overnight oximetry is done to see if oxygen concentrations decrease during sleep.
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.