Spirometry is a pulmonary function test that measures how quickly a person breathes and how quickly they breathe. Pulmonary function tests measure how well the lungs work. A short, simple and frequently used office-based diagnostic test.
Experts use spirometry to diagnose a variety of lung disorders, including:
• Asthma: Long-term inflammation, swelling and constriction of the airways.
• Chronic obstructive pulmonary disease (COPD): A group of lung diseases that narrow the airways and have difficulty in evacuating the lungs.
• Cystic fibrosis: An inherited condition in which the lungs and digestive organs are obstructed by dense, sticky mucus.
• Pulmonary fibrosis: Accumulation of scar tissue in lung air sacs leads to poor oxygenation of blood.
A doctor will use the spirometer to monitor a person’s progress as part of a chronic lung disease treatment. It can help determine the effect of any drug, including how they control the condition. Previous or existing smokers should be tested as in people older than 40 years. Those exposed to substances that harm the lungs, such as smoke, should also consider controlling lung health in this way.
The spirometry test is a simple diagnostic test performed using a spirometer. A person who records the results into the tube attached to the spirometer will breathe. The doctor will ask a person questions about any respiratory medications he may take, including bronchodilators. Bronchodilators help to relax, widen the airways and facilitate breathing. A person may be asked to stop taking them before testing so that their effects on respiration can be tested.
The doctor may recommend that the person is wearing loose clothing and not eating a large meal before the test to help him breathe. Testers will also need to observe the following rules:
• Smoking within 24 hours
• Strenuous exercise
• Drinking alcohol
The following steps are taken during the procedure:
1. Place a clip on the nose to close the nostrils.
2. The person breathes as much air as possible to fill his lungs.
3. A person closes his lips tightly in the mouth of the tube.
4. Breathe in the tube as quickly and vigorously as possible for a few seconds.
The test is usually repeated at least three times to ensure a consistent and accurate result. The highest value obtained from the three tests is normally used as the final result. The appointment can take 30-90 minutes. The doctor may administer an inhaled bronchodilator and then run the test again. This will measure the effect of a bronchodilator on a person’s ability to breathe. It may not be possible for the doctor to give immediate feedback as a lung specialist, or a lung doctor should ensure the interpretation of the results.
The results of the spirometry test will help the doctor determine the next steps of treatment. Spirometry measures air flow over time. The results produce two values that are useful when evaluating and monitoring people with lung dysfunction:
• Mandatory Vital Capacity (FVC) is the total amount of air that can be discharged at full capacity.
• Forced Expiratory Volume (FEV1), measured for more than 1 second, refers to air flow in the first second of the FVC.
FEV1 is then divided by FVC to give the rate of air that can be excreted in a person’s lungs in one second. A FVC reading lower than normal is indicative of limited respiration. FEV1 reading helps doctors determine the severity of the respiratory problem. Low FEV1 values indicate more pronounced respiratory obstruction.
This information can help a doctor determine the next steps of treatment. Normal spirometry test results vary from person to person. Average results depend on various factors such as age, height, gender and race. The test results are generally compared with the means within the various groups based on data from the Third National Health and Nutrition Questionnaire (NHANES III).
Obstructive airway disease is a disease where narrowing of the airways affects a person’s ability to breathe quickly, but still holds a normal amount of air in his lungs. This is common in people with asthma and COPD. In a restrictive lung disease, air intake is reduced because the lungs cannot fully expand as in pulmonary fibrosis. According to data from NHANES III, if a person’s FEV1 / FVC ratio is less than 70 percent in adults and less than 85 percent in children aged 5-18, it is said to be a preventive defect. This places one’s results below the fifth percentile.
A physician can check whether a condition is reversible by changes in FVC / FEV1 results after administration of a bronchodilator. A 12 percent increase in results indicates the effectiveness of a bronchodilator in reversing a condition such as asthma. As with COPD, some symptoms cannot be reversed. An restrictive pattern in adults is shown by the FVC result below the fifth percentile, based on NHANES III data. In young people aged 5-18 years, a result of less than 80 percent indicates a restrictive condition in the lungs.
If a person is found to have a restrictive pattern, a wide range of pulmonary function tests should be performed. They occur to confirm a restrictive lung disease and how it forms.
Other Test Methods
Spirometry is the simplest and most commonly used pulmonary function test, but other tests may be required to make a definitive diagnosis. Lung volume tests are the most accurate measure of lung capacity. They measure the total lung volume and are performed in a small, sheltered room with people with clean walls that can detect changes in volume within the lung. Blood oxygen levels can be tested using a pulse oximeter test. Lung diffusion capacity determines how well oxygen enters into the blood from the inhaled air using a gas mixture containing 0.3 percent carbon monoxide (CO). The amount of CO remaining in the breathing air indicates how well the person is able to absorb the gas.
Breathing in this test is less intense than spirometry, but may take longer. Blood can be tested to find the hemoglobin level it contains. Hemoglobin affects oxygen absorption. The pulse oximeter provides a prediction of oxygen levels in the blood by placing a probe on the surface of the skin. Arterial blood gas tests measure the level of a range of gases in the blood, such as oxygen and carbon dioxide. Fractional exhaled nitric oxide tests measure how much nitric oxide is in a person’s exhaled air.
In addition to those who cannot perform spirometry and lung tests, additional test methods can be used to assess lung function in infants and children. Chest X-rays and chest CT scans can also be used to see inside the lungs and diagnose specific conditions.