A breathing test, also called spirometry, or a pulmonary function test/study, is one of the easiest, non-invasive methods of measuring lung function. Doctors find these tests to be extremely useful for diagnosing respiratory disease and monitoring the effectiveness of treatment. However, doctors also use other tests to rule out possible cause of breathing difficulties such as a bronchoscopy, lung scan, sputum samples and arterial blood gases to pinpoint the cause.
Measurements
Total lung capacity measures the volume of air in a person's lungs after they take a deep breath. Normal lung capacity is 5.8 liters. Tidal volume is the amount of air that moves into and out of the lungs; normal tidal volume is 0.5 liters. Forced expiratory volume, or FEV1, is the volume of air exhaled in the first second. Residual volume is the amount of air left in the lungs after a person exhales as much and as long as possible; a normal value is 1 liter. Vital capacity is the difference between the amount of air left in the lungs after a maximum exhalation and the total lung capacity.
Spirometry
Doctors use a device called a spirometer to measure the amount of air a person inhales and exhales over time. For a spirometry test, the patient places a tight seal with their lips over the spirometer mouthpiece. The patient breathes normally for two breathes, then to take a deep breath in and quickly blow out all the air as quickly as possible, completely emptying the lungs.
According to the U.S. National Library of Medicine, spirometry provides valuable information about how well the person's lungs are functioning. Spirometry can detect reduce airflow, which is often the result of airway narrowing as seen in chronic bronchitis and asthma.
Peak Flow Measurement
The peak flow is the highest rate at which air can be exhaled and is measured with a peak flow meter. A person exhales as forcefully as possible as the device measures their peak expiratory flow, or how fast they exhale through the device. It will register in the green, yellow or red peak flow zone indicating their level of acuity. Asthmatics generally have a lower than normal peak flow value. People with asthma can monitor their condition at home using a peak flow meter. Daily peak flow measurements are useful in monitoring asthma symptoms and in recognizing and avoiding asthma flare-ups.
Diffusion Capacity Test
A diffusion capacity test, called a DLCO, measures how easily gases such as oxygen and carbon dioxide can diffuse between the bloodstream and the air sacs of the lungs. Disease decreases the surface area of the lung's air sacs or alveoli, thereby reducing the diffusion capacity. The loss of surrounding capillaries, thickening of the tissue between the air sacs and capillaries or anemia will also cause a low DLCO result. To perform the DLCO test, the person breathes through a mouthpiece attached to a computer that evaluates the diffusing capacity. The patient exhales completely, then takes as deep a breath as possible, holds it, then blows it out. An analysis of the gases in the exhaled breath determines the lung diffusion capacity.
