Lung volumes and their combinations measure various lung capacities such as functional residual capacity FRC , inspiratory capacity, and VC. Figure 1 11 shows the different volumes and capacities of the lung. Reprinted with permission from Gold WM.
Pulmonary function testing. Textbook of respiratory medicine. Philadelphia: Saunders, The most important spirometric maneuver is the FVC.
To measure FVC, the patient inhales maximally, then exhales as rapidly and as completely as possible. Normal lungs generally can empty more than 80 percent of their volume in six seconds or less. The forced expiratory volume in one second FEV 1 is the volume of air exhaled in the first second of the FVC maneuver. The absolute ratio is the value used in interpretation, not the percent predicted. Adapted with permission from Salzman SH.
Pulmonary function testing: tips on how to interpret the results. J Resp Dis ; The parameter is based on a six-second maneuver, which incorporates a standard time frame to decrease patient variability and the risk of complications. One of the pitfalls of using this type of spirometer is that it must be calibrated for temperature and water vapor.
It should be used with caution in patients with advanced COPD because of its inability to detect very low volumes or flows. Spirograms and flow volume curves. A Restrictive ventilatory defect. B Normal spirogram. C Obstructive ventilatory defect. Different spirographic and flow volume curves are shown in Figure 2.
It quickly identifies patients with airway obstruction in whom the FVC is reduced, and it identifies the cause of a low FEV 1. Normal spirometric parameters are shown in Table 2. Spirometry is designed to identify and quantify functional abnormalities of the respiratory system. The NLHEP recommends that primary care physicians perform spirometry in patients 45 years of age or older who are current or former smokers; in patients who have a prolonged or progressive cough or sputum production; or in patients who have a history of exposure to lung irritants.
Chest pain or orthopnea. Cough or phlegm production. Dyspnea or wheezing. Chest wall abnormalities. Decreased breath sounds. Finger clubbing. Blood gases. Chest radiograph. Chronic obstructive pulmonary disease. Cystic fibrosis. Interstitial lung diseases. Congestive heart failure. Congenital heart disease. Pulmonary hypertension. Amyotrophic lateral sclerosis.
Multiple sclerosis. Myasthenia gravis. Coronary bypass. Correction of congenital abnormalities. Valvular surgery. Gastric bypass. Spirometry requires considerable patient effort and cooperation. Therefore, results must be assessed for validity before they can be interpreted. An algorithm for interpreting spirometry results is given in Figure 3. Hemoptysis of unknown origin FVC maneuver may aggravate underlying condition. The clinical context of the test is important because parameters in patients with mild disease can overlap with values in healthy persons.
The normal ranges for spirometry values vary depending on the patient's height, weight, age, sex, and racial or ethnic background. FVC and VC values vary with the position of the patient. These variables can be 7 to 8 percent greater in patients who are sitting during the test compared with patients who are supine. FVC is about 2 percent greater in patients who are standing compared with patients who are supine.
Algorithm for interpreting results of spirometry. To determine the validity of spirometric results, at least three acceptable spirograms must be obtained. In each test, patients should exhale for at least six seconds and stop when there is no volume change for one second.
The test session is finished when the difference between the two largest FVC measurements and between the two largest FEV 1 measurements is within 0. If both criteria are not met after three maneuvers, the test should not be interpreted. Repeat testing should continue until the criteria are met or until eight tests have been performed.
Figure 4 25 shows normal flow-volume and time-volume curves. Notice that the lines of the flow-volume curve are free of glitches and irregularities. The volume-time curve extends longer than six seconds, and there are no signs of early termination or cutoff.
If the test is valid, the second step is to determine whether an obstructive or restrictive ventilatory pattern is present.
However, to make a definitive diagnosis of restrictive lung disease, the patient should be referred to a pulmonary laboratory for static lung volumes.
If the TLC is less than 80 percent, the pattern is restrictive, and diseases such as pleural effusion, pneumonia, pulmonary fibrosis, and congestive heart failure should be considered. A bronchodilator is given, and spirometry is repeated after several minutes. The patient should not use any bronchodilator for at least 48 hours before the test. A negative bronchodilator response does not completely exclude the diagnosis of asthma.
It can help in the diagnosis of an obstructive ventilatory pattern. The maximal voluntary ventilation MVV maneuver is another test that can be used to confirm obstructive and restrictive conditions. The patient is instructed to breathe as hard and fast as possible for 12 seconds. The result is extrapolated to 60 seconds and reported in liters per minute. A low MVV can occur in obstructive disease but is more common in restrictive conditions.
COPD is a progressive condition, meaning that it worsens over time. Follow-up pulmonary function tests are carried out in people with COPD to track how the condition progresses, which varies from person to person.
The results of these tests will help the individual and the doctor understand how COPD is progressing over time. Individuals who smoke may require more testing, as their symptoms are more likely to progress when compared with people who do not smoke. People with COPD should regularly attend medical appointments and complete recommended pulmonary function tests. There are other steps an individual with COPD can take to relieve symptoms and slow disease progression.
These include:. It is also vital to inform a doctor if a person notices any changes in symptoms. Symptoms of COPD flare-ups include worsening:. FEV1 is a useful measurement that is taken during a pulmonary function test. People who smoke may require more frequent testing. It can be used at night or when symptoms flare…. Emphysema is a lung condition. There is no cure, but certain treatments can ease the symptoms and prevent the condition from worsening.
Learn more…. Spirometry is performed by deeply inhaling and forcefully exhaling into a spirometer the device that records the various measurements of lung function. There are two measurements that are crucial in the interpretation of spirometry results.
The first is called the forced vital capacity FVC. This is a measurement of lung size in liters and represents the volume of air in the lungs that can be exhaled following a deep inhalation.
The second is the forced expiratory volume-one second FEV1. This is a measure of how much air can be exhaled in one second following a deep inhalation.
This number represents the percent of the lung size FVC that can be exhaled in one second. The reference value is based on healthy individuals with normal lung function and it tells the doctor the values that would be expected for someone of the same sex, age and height. When compared to the reference value, a lower measured value corresponds to a more severe lung abnormality. See table below.
Restrictive lung diseases can cause the FVC to be abnormal.
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