1107.pdf

An Approach to Interpreting Spirometry
TIMOTHY J. BARREIRO, D.O., and IRENE PERILLO, M.D.
University of Rochester School of Medicine and Dentistry, Rochester, New York
Spirometry is a powerful tool that can be used to detect, follow, and manage patients with lung dis-
orders. Technology advancements have made spirometry much more reliable and relatively simple
to incorporate into a routine office visit. However, interpreting spirometry results can be challeng-
ing because the quality of the test is largely dependent on patient effort and cooperation, and the
interpreter’s knowledge of appropriate reference values. A simplified and stepwise method is key to
interpreting spirometry. The first step is determining the validity of the test. Next, the determination
of an obstructive or restrictive ventilatory patten is made. If a ventilatory pattern is identified, its
severity is graded. In some patients, additional tests such as static lung volumes, diffusing capacity
of the lung for carbon monoxide, and bronchodilator challenge testing are needed. These tests can
further define lung processes but require more sophisticated equipment and expertise available only
in a pulmonary function laboratory. (Am Fam Physician 2004;69:1107-14. Copyright 2004 American
Academy of Family Physicians.)
to 1994 found high rates of undiagnosed and untreated COPD in current and for- nary disease (COPD) is the most common respiratory disease and the fourth lead- mer smokers.5 Population-based studies have identified vital capacity (VC) as a powerful United States.1 Despite preventive efforts, prognostic indicator in patients with COPD. has doubled in the past decade, and this forced vital capacity (FVC) as a risk factor trend is likely to continue.2,3 Evidence indi- for premature death.6 The Third National cates that a patient’s history and physical Health and Nutritional Examination Survey examination are inadequate for diagnosing showed potential benefits for patients with early identification, intervention, and treat- pulmonary function test provides the most was the first study to show that early iden- impairment, spirometry is the preferred test tification and intervention in smokers could for the diagnosis of COPD because it can affect the natural history of COPD.7 These surveys also showed that simple spirometry could detect mild airflow obstruction, even ever, the results must be correlated care- fully with clinical and roentgenographic data for optimal clinical application. This article reviews the indications for use of spirometry, provides a stepwise approach Organization and the U.S. National Heart, to its interpretation, and indicates when lished the Global Initiative for Chronic Obstructive Lung Disease to increase Background
Downloaded from the American Family Physician Web site at www.aafp.org/afp. Copyright 2004 American Academy of Family Physicians. For the pri- vate, noncommercial use of one individual user of the Web site. All other rights reserved. Contact copyrights@aafp.org for copyright questions and/or tion, followed by a forced expiration that rapidly Normal lungs can empty more than 80 percent of their empties the lungs. Expiration is continued for as long as possible or until a plateau in exhaled volume is reached. These efforts are recorded and graphed. (A glossary of terms used in this article can be found in Table 1.) Lung function is physiologically divided into and to provide comprehensive treatment guide- four volumes: expiratory reserve volume, inspira- lines aimed at decreasing COPD-related morbid- tory reserve volume, residual volume, and tidal volume. Together, the four lung volumes equal the total lung capacity (TLC). Lung volumes Spirometry Measurements
and their combinations measure various lung and Terminology
capacities such as functional residual capacity Spirometry measures the rate at which the (FRC), inspiratory capacity, and VC. Figure 111 lung changes volume during forced breathing shows the different volumes and capacities of maneuvers. Spirometry begins with a full inhala- The most important spirometric maneuver is the FVC. To measure FVC, the patient inhales maxi- Glossary
mally, then exhales as rapidly and as completely as possible. Normal lungs generally can empty Spirometric values
more than 80 percent of their volume in six sec- FVC—Forced vital capacity; the total volume of air that can be exhaled during a onds or less. The forced expiratory volume in one second (FEV1) is the volume of air exhaled in the FEV1—Forced expiratory volume in one second; the volume of air exhaled in the first second of the FVC maneuver. The FEV1/FVC first second under force after a maximal inhalation.
ratio is expressed as a percentage (e.g., FEV1 of 0.5 FEV1/FVC ratio—The percentage of the FVC expired in one second. L divided by FVC of 2.0 L gives an FEV1/FVC ratio FEV6—Forced expiratory volume in six seconds.
FEF25-75%—Forced expiratory flow over the middle one half of the FVC; the aver- age flow from the point at which 25 percent of the FVC has been exhaled to the Lung Volumes and Capacities
point at which 75 percent of the FVC has been exhaled.
MVV—Maximal voluntary ventilation.
Lung volumes
ERV—Expiratory reserve volume; the maximal volume of air exhaled from end- IRV—Inspiratory reserve volume; the maximal volume of air inhaled from end- RV—Residual volume; the volume of air remaining in the lungs after a maximal T—Tidal volume; the volume of air inhaled or exhaled during each respiratory Lung capacities
FRC—Functional residual capacity; the volume of air in the lungs at resting end- IC—Inspiratory capacity; the maximal volume of air that can be inhaled from the TLC—Total lung capacity; the volume of air in the lungs at maximal inflation.
Reprinted with permission from Gold WM. Pulmonary VC—Vital capacity; the largest volume measured on complete exhalation after full function testing. In: Murray JF, Nadel JA, eds. Textbook of respiratory medicine. 3d ed. Philadelphia: Saunders, 2000:783. Spirometry
of 25 percent). The absolute ratio is the value low FEV1. Normal spirometric parameters are used in interpretation, not the percent predicted.
Some portable office spirometers replace the Indications for Office Spirometry
technician ease. The parameter is based on a Spirometry is designed to identify and quan- six-second maneuver, which incorporates a stan- tify functional abnormalities of the respira- dard time frame to decrease patient variability tory system. The NLHEP recommends that pri- and the risk of complications. One of the pit- mary care physicians perform spirometry in falls of using this type of spirometer is that it patients 45 years of age or older who are must be calibrated for temperature and water vapor. It should be used with caution in patients Spirograms and Flow Volume Curves
with advanced COPD because of its inability to detect very low volumes or flows. However, the FEV 1/FEV6 ratio provides accurate surrogate FEV1 and FEV6 values should be rounded to the nearest 0.1 L and the percent predicted and the curves are shown in Figure 2.11 It is important to understand that the amount exhaled during the first second is a constant fraction of the FVC, regardless of lung size. The significance of the FEV1/FVC ratio is twofold. It quickly identifies patients with airway obstruction in whom the FVC is reduced, and it identifies the cause of a Normal Values of Pulmonary Function Tests
Absolute FEV1/FVC Within 5% of the predicted ratio DLCO = diffusing capacity of lung for carbon monoxide. FIGURE 2. Spirograms and flow volume curves. (A) Restrictive ventilatory defect. Adapted with permission from Salzman SH. Pulmo- (B) Normal spirogram. (C) Obstructive ventilatory defect.
nary function testing: tips on how to interpret the Reprinted with permission from Gold WM. Pulmonary function testing. In: Murray JF, Nadel JA, eds. Textbook of respiratory medicine. 3d ed. Philadelphia: Saunders, 2000:805. Indications for Spirometry
Contraindications to Use of Spirometry
Detecting pulmonary disease
Acute disorders affecting test performance (e.g., Hemoptysis of unknown origin (FVC maneuver may Recent eye surgery (increases in intraocular Recent myocardial infarction or unstable angina Thoracic aneurysms (risk of rupture because of Assessing severity or progression of disease
Pulmonary diseases
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.9 Other indications for spirometry are to determine the strength and function of the chest, follow dis- ease progression,15,16 assess response to treat- ment,17,18 and obtain baseline measurements before prescribing drugs that are potentially toxic to the lungs, such as amiodarone (Corda- rone) and bleomycin (Blenoxane).19 Spirometry also is helpful in preoperative risk assessment for many surgeries20-23 and often is used in Risk stratification of patients for surgery
workers’ compensation and disability claims to assess occupational exposure to inhalation hazards.24 Tables 3 and 4 list indications and Interpreting Spirometry Results
Spirometry requires considerable patient effort and cooperation. Therefore, results must be assessed for validity before they can be inter- preted.17,25 Inadequate patient effort can lead to misdiagnosis and inappropriate treatment. An algorithm for interpreting spirometry results is Evaluating disability or impairment
Social Security or other compensation programs The clinical context of the test is important because parameters in patients with mild disease can overlap with values in healthy persons.26 Normal spirometry values may vary, and interpre- Spirometry
tation of results relies on the parameters used. very tall patients or patients with missing lower The normal ranges for spirometry values vary extremities. FEV1 and FVC are greater in whites depending on the patient’s height, weight, age, sex, compared with blacks and Asians. FVC and VC and racial or ethnic background.27,28 Predicted values vary with the position of the patient. These values for lung volumes may be inaccurate in variables can be 7 to 8 percent greater in patients Interpreting Spirometry Results
Determine if the test is interpretable.
increase in FEV1 and 200 mL increase in FVC or FEV1, FIGURE 3. Algorithm for interpreting results of spirometry. (DLCO = diffusing capacity of lung for carbon monoxide; VA = alveolar vol- and FEV1 are decreased, the distinction between an obstructive and restrictive ventilatory pat- 1/FVC ratio distinguishes obstructive from tern depends on the absolute FEV1/FVC ratio. If the absolute FEV1/FVC ratio is normal or increased, a restrictive ventilatory impairment may be present. However, to make a definitive who are sitting during the test compared with diagnosis of restrictive lung disease, the patient patients who are supine. FVC is about 2 percent should be referred to a pulmonary laboratory greater in patients who are standing compared for static lung volumes. If the TLC is less than 80 percent, the pattern is restrictive, and dis- To determine the validity of spirometric results, eases such as pleural effusion, pneumonia, pul- at least three acceptable spirograms must be monary fibrosis, and congestive heart failure obtained. In each test, patients should exhale for at least six seconds and stop when there is A reduced FEV1 and absolute FEV1/FVC ratio no volume change for one second. The test ses- indicates an obstructive ventilatory pattern, sion is finished when the difference between the and bronchodilator challenge testing is recom- two largest FVC measurements and between the mended to detect patients with reversible airway two largest FEV1 measurements is within 0.2 L. If obstruction (e.g., asthma). A bronchodilator is both criteria are not met after three maneuvers, given, and spirometry is repeated after several the test should not be interpreted. Repeat test- minutes. The test is positive if the FEV1 increases ing should continue until the criteria are met or by at least 12 percent and the FVC increases by until eight tests have been performed.26 at least 200 mL. The patient should not use any Figure 425 shows normal flow-volume and bronchodilator for at least 48 hours before time-volume curves. Notice that the lines of the test. A negative bronchodilator response the flow-volume curve are free of glitches and does not completely exclude the diagnosis of irregularities. The volume-time curve extends longer than six seconds, and there are no signs The mid-expiratory flow rate (FEF25-75%) is the average forced expiratory flow rate over the If the test is valid, the second step is to middle 50 percent of the FVC. It can help in the determine whether an obstructive or restrictive diagnosis of an obstructive ventilatory pattern. ventilatory pattern is present. When the FVC Because it is dependent on FVC, the FEF25-75% is highly variable. In the correct clinical situation, a reduction in FEF25-75% of less than 60 percent of that predicted and an FEV1/FVC ratio in TIMOTHY J. BARREIRO, D.O., is a second-year pulmonary disease and critical care medi- the low to normal range may confirm airway cine fellow at the University of Rochester (N.Y.) School of Medicine and Dentistry, Strong Memorial Hospital. Dr. Barreiro earned his medical degree from Ohio University College of Osteopathic Medicine, Athens, and completed an internal medicine residency at Allegheny General Hospital in Pittsburgh, Pa.
maneuver is another test that can be used to IRENE PERILLO, M.D., is assistant professor of medicine and director of the outpatient confirm obstructive and restrictive conditions. pulmonary clinic at the University of Rochester School of Medicine and Dentistry, Strong The patient is instructed to breathe as hard Memorial Hospital. Dr. Perillo earned her medical degree from State University of New and fast as possible for 12 seconds. The result York Upstate Medical University, Syracuse, and completed an internal medicine resi-dency, and pulmonary and critical care fellowship at the University of Rochester School is extrapolated to 60 seconds and reported in liters per minute. MVV generally is approxi- Address correspondence to Timothy J. Barreiro, D.O., University of Rochester School of mately equal to the FEV1  40. A low MVV Medicine and Dentistry, 601 Elmwood Ave., Box 692, Rochester, NY 14642 (e-mail: Timo- can occur in obstructive disease but is more thy_Barreiro@urmc.rochester.edu). Reprints are not available from the authors. common in restrictive conditions. If the MVV is low but FEV1 and FVC are normal, poor patient Spirometry
Spirometric Flow Diagram
The final step in interpreting spirometry is to determine if additional testing is needed to further define the abnormality detected by spi-rometry. Measurement of static lung volumes, including FRC, is required to make a definitive diagnosis of restrictive lung disease.
Final Comment
Basic spirometry can be performed in the family physician’s office with relative ease and inexpensive equipment. In most cases, office spi- rometry provides an adequate assessment of pulmonary function. In addition, spirometry may be used to address major issues in clinical man- The authors indicate that they do not have any con-flicts of interest. Sources of funding: none reported. 1. Murray CJ, Lopez AD. Evidence-based health pol- icy—lessons from the Global Burden of Disease 2. Murray CJ, Lopez AD. Alternative projections of mortality and disability by cause 1990-2020: Global Burden of Disease Study. Lancet 1997;349: 1498- 3. Murray CJ, Lopez AD. Global mortality, disability, and the contribution of risk factors: Global Burden of Disease Study. Lancet 1997;349:1436-42.
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