INTRODUCTION — Spirometry is used to measure forced expiratory flow rates and volumes. It is the most commonly used pulmonary function test and is useful in the evaluation of patients with respiratory symptoms (eg, dyspnea, cough, wheeze), and the monitoring of lung function in patients with lung disease, being treated with drugs that can affect lung function, or at risk of lung disease (eg, smoking, occupational exposures, family history).
In the office setting, spirometry is typically used to detect, confirm, and monitor obstructive airway diseases (eg, asthma, chronic obstructive pulmonary disease [COPD]) and monitor known restrictive lung disease [1-5]. In this setting, the clinician must be knowledgeable about issues related to equipment, performance of the forced expiratory maneuver, and interpretation of the data to obtain reliable and clinically useful information [6-8]. International guidelines for performance of office spirometry have been published [9,10].
The performance of spirometry in the office setting will be reviewed here. More general issues related to pulmonary function tests, the interpretation of flow volume loops, and the technique of bronchoprovocation testing are discussed separately. (See "Overview of pulmonary function testing in adults" and "Flow-volume loops" and "Bronchoprovocation testing".)
ADVICE RELATED TO COVID-19 PANDEMIC — Spirometry and other pulmonary function test (PFT) maneuvers can promote coughing and aerosol generation and could lead to spread of coronavirus disease 2019 (COVID-19; SARS-CoV-2) by infected patients. It is difficult to screen patients for active COVID-19 infection, particularly those with underlying respiratory symptoms, and infected but asymptomatic patients can shed the virus. Thus, we agree with expert recommendations that spirometry and other PFTs be limited to patients in whom results are essential to immediate management decisions [11,12]. Use of nebulizers to administer bronchodilators or methacholine should be avoided.
Measures to prevent spread of COVID-19 should include hand hygiene and personal protective equipment (PPE; glove, gown, face mask and shield) for staff and anyone else in the testing space (eg, interpreters). N95 masks or powered air purifying respirators (PAPR) are preferred over surgical masks. Patients should be brought to a testing room using an approach that avoids queuing or grouping individuals in a waiting area and that allows adequate time between patients for sufficient air exchange. Enhanced cleaning of the testing area should be performed between patients.
EQUIPMENT — Office spirometers should meet equipment specifications as described in international guidelines [5,10,13,14]. The majority of spirometers manufactured since 1990 are accurate, although some flow-sensing office spirometers can produce falsely high results [15-17]. Reference standards are discussed separately. (See "Selecting reference values for pulmonary function tests".)
To avoid cross-contamination between patients when using permanent flow sensors, it is preferable to employ single use disposable flow sensors that practically eliminate the risk of inhalational cross contamination. Disposable one-way mouthpieces may also be used; otherwise, patients should be instructed not to inhale from the spirometer when only forced exhalation maneuvers are being obtained.
Volume sensing spirometers maintain accuracy over many years, but are more difficult to clean and are rarely used for office spirometry.
QUALITY CONTROL — Office spirometers should accurately measure the forced expiratory volume in one second (FEV1), forced expiratory volume in six seconds (FEV6), and forced vital capacity (FVC) and also provide quality checks and error messages. A survey of 17 spirometers used in primary care offices found only 1 of 17 met accuracy criteria; clearly manufacturers and practitioners need to be aware of potentially significant quality issues related to office spirometry [18].
In addition to internal calibration performed by the device, daily calibration checks with a three liter syringe are recommended [10]. When performing a calibration check, the three liter syringe should be discharged into the spirometer three times. The volumes read by the machine should be within 3 percent of three liters. If the spirometer reading remains outside these limits after replacing the flow sensor, the device should be removed from use until checked by the manufacturer.
It is also essential that the nurse or technician enter correct values for age, height, and sex at birth, as these values are used to generate the appropriate predicted values for the individual patient. Height should be measured with shoes off, preferably using a stadiometer, rather than relying on the patient's stated height. Percent predicted values that are unexpectedly higher or lower than expected are a clue that an incorrect age or height value may have been entered. Waist circumference, while not used to calculate predicted normal values, can also be measured because abdominal obesity is a common cause of mildly low values for FEV1 and FVC [19].
PROCEDURE — Patients are usually seated during spirometry, unless otherwise noted. Nose clips or manual occlusion of the nares help to prevent air leakage through the nasal passages, although spirometry can be performed without nasal occlusion [20]. The deep inhalation should occur before the mouthpiece is placed in the mouth. Immediately after the deep inhalation, the mouthpiece is placed just inside the mouth between the teeth. The lips should be sealed tightly around the mouthpiece to prevent air leakage during maximal forced exhalation. The patient should then be instructed to blast out the air without hesitation (within two seconds of reaching full inflation). Exhalation should last until a plateau in exhaled volume is reached, or a maximum of 15 seconds. However, if measuring FEV6 as a surrogate for FVC, then exhalation need only last at least six seconds. To fully evaluate flow volume loops, it is necessary to perform a complete inspiratory maneuver at the end of the test. The maximal inspiration at the end of test requires vigorous coaching to achieve good quality results and patients should be informed that this aspect of the maneuver feels somewhat uncomfortable. (See "Flow-volume loops".)
The patient is allowed to rest for several seconds and the procedure is repeated. Usually, three maneuvers are performed, although additional tests may be needed if one or more of the curves are unacceptable.
COACHING THE PATIENT — The most important task of the technician or person performing the test is to obtain maximal, reproducible efforts from the patient.
Even with the use of accurate instruments, office spirometry results may be misleading if the patient's efforts are submaximal. Unlike most other medical tests in which the patient remains passive, accurate spirometry results require significant exertion on the part of the patient.
The technician must instruct and encourage the patient to perform the breathing maneuvers in three phases (figure 1):
●Phase 1: Coach the patient to take as deep a breath as possible
●Phase 2: Strongly prompt the patient to blast out the air into the spirometer without hesitation after reaching a full inspiration
●Phase 3: Encourage the patient to continue exhaling until a plateau in exhaled volume or 15 seconds is reached, unless just measuring FEV6 in which case the exhalation should last at least six seconds (three seconds for children)
Patients in whom a flow volume loop is needed will need to perform an additional phase of deep and forceful inspiration to total lung capacity immediately after phase 3.
ADEQUACY OF TEST — An adequate test usually requires three acceptable and repeatable forced vital capacity (FVC) maneuvers [10]. The clinician and technician must learn to recognize the patterns of acceptable and unacceptable efforts, since poorly performed maneuvers often mimic disease patterns. Detection of poorly performed maneuvers requires direct inspection of both flow-volume curves and volume-time spirograms (figure 2) [13,21].
An acceptable maneuver requires a sharp peak in the flow curve and an expiratory duration that reaches a plateau of exhaled volume or 15 seconds, or greater than six seconds if measuring FEV6 instead of FVC (figure 3). At least three acceptable maneuvers should be available for analysis.
Repeatability is determined by comparing the FVC and FEV1 values of the maneuvers. The two highest values for FVC and for FEV1 should be within 0.15 L of each other (for adults; the limit is 0.10 L for children) [10,22].
The grading system for the quality of spirometry factors in the number of acceptable maneuvers and the degree of repeatability for FEV1 and FVC separately (table 1) [10].
INTERPRETATION — All tracings from the forced expiratory maneuvers should be examined for acceptability and repeatability, according to the criteria mentioned above. The study should then be classified as normal or abnormal, the latter showing either an obstructive or a restrictive pattern (figure 3). The severity of any obstructive impairment is then assessed (figure 4). (See 'Forced expiratory volume in one second' below and "Overview of pulmonary function testing in adults".)
Forced vital capacity — The forced vital capacity (FVC) (also known as the forced expiratory volume) is the maximal volume of air exhaled with a maximally forced effort from a position of full inspiration and is expressed in liters [10]. The highest FVC from the three acceptable forced expiratory maneuvers is used for interpretation [10].
The FVC may be reduced by suboptimal patient effort, airflow limitation, restriction (eg, from lung parenchymal, pleural, or thoracic cage disease), or a combination of these. An approach to the interpretation of abnormal values is provided in the figures (figure 4) [13]. The specific values assigned to mild, moderate, and severe disease vary among the different guidelines; we have included in the figure the ones that we find most consistent for predicting the degree of impairment [15,22]. In general, a low FVC needs further evaluation with full pulmonary function tests [23]. (See "Overview of pulmonary function testing in adults".)
The slow vital capacity (SVC) is the maximal volume of air exhaled after a maximal inspiration, but without a forced effort. The SVC is rarely measured outside of hospital-based pulmonary function labs. For normal subjects, the slow and forced vital capacities are very close, whereas patients with airflow limitation tend to have a lower FVC than SVC. (See "Overview of pulmonary function testing in adults", section on 'Spirometry'.)
Forced expiratory volume in six seconds — The forced expiratory volume in six seconds (FEV6) is sometimes used as a surrogate for FVC [20,24]. The FEV6 has the advantage of being more reproducible than the FVC and less physically demanding for the patient.
Forced expiratory volume in one second — The forced expiratory volume in one second (FEV1) is the maximal volume of air exhaled in the first second of a forced exhalation that follows a full inspiration, expressed in liters [20]. The FEV1 reflects the average flow rate during the first second of the FVC maneuver. The FEV1 is the most important spirometric variable for assessment of the severity of airflow obstruction (figure 4). The highest FEV1 from the three acceptable forced expiratory maneuvers is used for interpretation, even if it does not come from the maneuver with the highest FVC [10].
In patients with asthma, the FEV1 typically declines with clinical worsening of airways obstruction, and increases with successful treatment of airways obstruction. The FEV1 should be used for determining the degree of obstruction (mild, moderate, or severe) and for serial comparisons when following patients with asthma or chronic obstructive pulmonary disease (COPD).
The measured FEV1 is usually expressed as a percent of the predicted value for determination of normality (figure 4). The lower limit of normal (LLN) FEV1 is more accurately defined by the fifth percentile of healthy never-smokers, instead of 80 percent of predicted [25]. The reference equations used by most spirometry software for determining predicted values in North America are derived from the NHANES III study [22,26]. Reference equations from the Global Lung Function Initiative, which assessed healthy individuals age 3 to 95 years across ethnic and geographic groups in 26 countries, may also be used and can be applied to both pediatric and adult patients [27]. These reference equations are endorsed by the American Thoracic Society, the American College of Chest Physicians, the European Respiratory Society, the Australian and New Zealand Society of Respiratory Science, the Thoracic Society of Australia and New Zealand, and the Asian Pacific Society for Respirology. (See "Selecting reference values for pulmonary function tests".)
As a rough guideline, the predicted FEV1 for a 50 year-old of average height is about 4 L for a man and 3 L for a woman. When predicted values have not been calculated, patients with severe COPD generally have an FEV1 less than one liter, while those with moderate COPD have an FEV1 between 1 and 1.5 liters. Individuals with an FEV1 ≤75 percent of predicted are more likely to report dyspnea, wheezing, or cough, than those with an FEV1 >75 percent predicted [28]. (See "Selecting reference values for pulmonary function tests".)
Ratio of FEV1/FVC — The FEV1/FVC ratio is the fraction of the forced vital capacity that can be exhaled in the first second. It is the most important parameter for detecting airflow limitation in diseases like asthma and COPD (figure 4). However, once it has been determined that a patient has airways obstruction, the FEV1/FVC ratio is not useful for gauging severity of disease, since the FVC also tends to decrease with increasing obstruction. The FEV1, not the FEV1/FVC ratio, should be used to monitor patients with asthma or COPD. (See "Pulmonary function testing in asthma" and "Chronic obstructive pulmonary disease: Definition, clinical manifestations, diagnosis, and staging".)
The use of the fifth percentile LLN for FEV1/FVC to detect airway obstruction reduces the misclassification associated with using a fixed threshold of 0.7 [25,29-32].
When FVC maneuvers are routinely stopped after six seconds, the FEV1/FEV6 should replace the FEV1/FVC [33]. The advantages of the FEV1/FEV6 include less frustration for the patient and technician trying to achieve an end-of-test plateau, less chance of syncope, shorter testing time, and better repeatability, without loss of sensitivity or specificity [24,34-36]. The appropriate lower limit of normal for FEV1/FEV6 from NHANES III should be used [26,37].
Other flow measures — The transition from normal function to moderate airflow obstruction is generally gradual. Physiologists have searched for a test that is more sensitive than the FEV1 for detection of airflow obstruction in its early stages. None has proven to be as reliable as the index obtained by dividing the FEV1 by the FVC. The forced expiratory flow between 25 and 75 percent of the FVC (also known as FEF25-75 or maximal mid-expiratory flow rate) should not be used to detect "small airways disease" in adults, due to poor specificity and reproducibility [20].
Choosing the best values — Report the highest FVC and the highest FEV1 from three spirometric maneuvers, even if they are derived from different maneuvers [10].
Flow-volume loops — The flow-volume loop is a plot of inspiratory and expiratory flow (on the Y-axis) against volume (on the X-axis) during the performance of maximally forced inspiratory and expiratory maneuvers. Changes in the contour of the loop can detect upper airway obstruction. The analysis of flow-volume loops is discussed separately. (See "Flow-volume loops".)
Post-bronchodilator spirometry — In patients who have evidence of airflow limitation on baseline spirometry, and no prior diagnosis of asthma or COPD, post-bronchodilator spirometry may be useful. If post-bronchodilator spirometry is normal, COPD is less likely. The assessment of bronchodilator responses in patients with asthma-like symptoms is described separately. If the change in spirometry post-bronchodilator does not support a diagnosis of obstructive lung disease, referral for bronchial challenge testing (eg, with methacholine or exercise) may be helpful [38]. (See "Pulmonary function testing in asthma", section on 'Bronchodilator responses'.)
LIMITATIONS — Office spirometry has some important limitations, even when all of the above described quality measures are employed. As examples:
●Abnormal spirometry results have little if any value in prompting smokers to quit [39-43]. All patients who smoke should be advised to stop smoking and provided smoking cessation assistance.
●In a patient with asthma, which is characterized by variability in clinical symptoms and airflow obstruction, normal airflow at the time of office visits does not exclude airflow obstruction at other times.
●Patients with early interstitial lung disease may have normal spirometry and need further testing of gas transfer with a diffusing capacity of the lungs for carbon monoxide (DLCO) and/or exercise oximetry to identify the cause of dyspnea [44].
●Misclassification rates due to suboptimal spirometry performance or interpretation are relatively high in the office setting [7,18,45]. Among eight general practices, rates for successfully meeting American Thoracic Society (ATS) quality standards were below 80 percent [7]. In 16 primary care offices involving 17 different spirometers, only 60 percent of patients had spirometry that met acceptability criteria [18]. Therefore, continuous quality review and feedback to nurses and technologists performing office spirometry are necessary and results should be verified by repeat testing in a Pulmonary Function Test (PFT) laboratory when important clinical decisions will be made based on the results [46,47].
RISKS — Spirometry is a low risk procedure and has few side effects [13]. During the test, some patients may experience dizziness. The forced expiratory maneuver causes an increase in the pressure in the chest, abdomen, head, and eyes. In general, patients who have recently (eg, less than six weeks) had abdominal, intracranial, or eye surgery or a pneumothorax should not perform spirometry, although data are limited.
Spirometry requires exertion and should be avoided in patients with unstable angina or a recent myocardial infarction.
Rarely, performance of a forced expiratory maneuver will precipitate acute bronchoconstriction. This seems more likely to occur when a patient's asthma or COPD is poorly controlled. Treatment includes administering inhaled albuterol and supplemental oxygen.
MONITORING — Office spirometry is also useful for monitoring control of asthma The National Asthma Education and Prevention Program advises the following frequencies for spirometry testing when caring for patients with asthma [48]:
●At the time of initial assessment
●After treatment is initiated and symptoms and peak flow have stabilized
●During periods of progressive or prolonged loss of asthma control
●At least every one to two years
For patients with chronic obstructive pulmonary disease (COPD), repeat spirometry is advised whenever there is a substantial increase in symptoms or decrease in exercise tolerance [4,49,50].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Pulmonary function testing".)
SUMMARY AND RECOMMENDATIONS
●Spirometry is used to detect and monitor obstructive airway disease in patients with respiratory symptoms and risk factors. (See 'Introduction' above.)
●Office spirometers should accurately measure the forced expiratory volume in one second (FEV1) and either the forced vital capacity (FVC) or the forced expiratory volume in six seconds (FEV6). Calibration checks should be performed daily with a three liter syringe. (See 'Quality control' above.)
●Since poorly performed maneuvers often mimic disease patterns, the clinician and technician must learn to recognize the patterns of unacceptable efforts (figure 2). (See 'Quality control' above.)
●An acceptable maneuver requires a sharp rise in the flow volume curve to the peak flow and an expiratory duration that reaches a plateau in expired volume or a duration of 15 seconds; however, if FEV6 is being measured instead of FVC, then only a duration of at least six seconds is required. At least three good quality maneuvers should be performed. (See 'Quality control' above.)
●Report the highest FVC and the highest FEV1 from three spirometric maneuvers, even if they are derived from different maneuvers. The fifth percentile lower limit of normal (LLN) for FEV1/FVC is preferred over the commonly accepted fixed threshold of 0.7, as it reduces the misclassification rate for detecting airway obstruction. (See 'Choosing the best values' above and 'Ratio of FEV1/FVC' above.)
●Reduction of the FEV1/FVC suggests airway obstruction (figure 4). (See 'Interpretation' above.)
●The FEV1/FEV6 is preferred over the FEV1/FVC when the FVC maneuvers are routinely stopped after six seconds. (See 'Ratio of FEV1/FVC' above.)
●The FEV1 should be used for determination of the degree of impairment and for serial comparisons. FEV1/FVC ratio is not useful for gauging severity of disease, since the FVC also tends to decrease with increasing obstruction. (See 'Interpretation' above.)
●Office spirometry results should be verified by formal testing in a pulmonary function test (PFT) laboratory when important clinical decisions will be made based on the results. (See 'Interpretation' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Paul Enright, MD, who contributed to an earlier version of this topic review.
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