Office spirometry

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]. Spirometry is not recommended as a screening test for asymptomatic adults [4,11], but rather facilitates diagnosis of respiratory diseases.

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".)

EQUIPMENT AND HYGIENE — Office spirometers should meet equipment specifications as described in international guidelines [5,10,12,13]. The majority of spirometers manufactured since 1990 are accurate, although some flow-sensing office spirometers can produce falsely high results [14-16]. 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 and disposable in-line bacterial and viral filters. Together, these measures dramatically reduce the risk of inhalational cross contamination. Disposable one-way mouthpieces may also be used.

Volume sensing spirometers maintain accuracy over many years but are more difficult to clean and are rarely used for office spirometry.

Spirometry and other pulmonary function test (PFT) maneuvers can promote coughing and aerosol generation. During times of high respiratory virus community prevalence, allowing time between patients for air exchange is prudent for prevention of patient-to-patient transmission. Transmission risk can also be diminished by using adequately ventilated spaces (eg, rooms with at least six air exchanges per hour). Use of face masks by laboratory staff should be encouraged.

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 [17].

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 [18].

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 [19]. 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) [12,20].

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) [10,21].

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 an obstructive, a possible restrictive, or a possible mixed pattern. Lung volumes are necessary to confirm whether or not the patient has a restrictive deficit. The severity of the ventilatory impairment is then assessed, according to the algorithm (algorithm 1). (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 (algorithm 1). In general, a low FVC needs further evaluation with full pulmonary function tests to determine whether lung restriction is present [22]. Patients with obstruction and low FVC frequently demonstrate air trapping or failure to complete a full exhalation rather than an additional restrictive process. (See "Overview of pulmonary function testing in adults".)

When FVC is low, restriction is not confirmed by lung volumes, and there is not obstruction (based on FEV₁/FVC), this represents a "nonspecific" pattern. Nonspecific patterns are not clearly indicative of any lung disease subtype but may be associated with either ongoing or future obstructive or restrictive diseases [23]. Repeat testing to reassess lung function after several months to a year may be useful.

Due to these potential problems with air trapping and incomplete exhalation, FVC is not used to grade restriction severity. We prefer to assess the severity of restrictive deficits by applying the z-score approach to total lung capacity measurements, when available. If lung volumes are not available, FEV₁ may be used to assess the severity of previously established restriction, as was recommended in prior guidelines [21]. (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 [19,24]. 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 [19]. 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 (algorithm 1). 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).

FEV₁ may also be used to grade the severity of restrictive or mixed obstructive/restrictive disorders once restriction has been confirmed by lung volumes; however, we prefer to grade pure restriction using total lung capacity when this measurement is available (algorithm 1) [21]. (See "Overview of pulmonary function testing in adults".)

The measured FEV₁ should be reported based on z-score, instead of percent predicted. This measurement strategy helps to avoid age, sex, and height bias and is associated with important clinical outcomes [25,26]. The lower limit of normal (LLN) for FEV₁ and other spirometry measures is defined by z-score <-1.645, which is equivalent to the fifth percentile in the distribution of healthy never-smokers. This replaces using a fixed percent of predicted value, which does not incorporate demographic features [25,27]. An FEV₁ within the normal range may still represent a mild ventilatory impairment if obstruction or restriction is confirmed using other measures.

Reference equations from the Global Lung Function Initiative (GLI), which assessed healthy individuals age 3 to 95 years across ethnic and geographic groups in 26 countries, are recommended for both pediatric and adult patients [25,28]. These reference equations are endorsed by multiple international expert groups and replace the older generation of equations, including those derived from the NHANES III study [21,29]. The GLI offers equations that account for race/ethnicity and an alternative "GLI-Global" composite equation that can be applied universally [30]. While accumulating evidence has demonstrated flaws in the use of the race/ethnicity-specific equations, the effects of shifting to universal equations are not yet fully understood. (See "Selecting reference values for pulmonary function tests" and "Selecting reference values for pulmonary function tests", section on 'Effect of race/ethnicity'.)

As a rough guideline, the predicted FEV₁ for a 50-year-old of average height is about 4 L for a male and 3 L for a female. 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 [31]. (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 obstruction in diseases like asthma and COPD (algorithm 1). 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 often decreases with increasing obstruction due to air trapping or premature termination of exhalation. 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: Diagnosis and staging".)

The use of z-score <-1.645 or the fifth percentile LLN for FEV₁/FVC to detect airway obstruction reduces the misclassification associated with using a fixed threshold of 0.7 [27,32-35].

If FEV₁/FVC is low, but FEV₁ is normal, this is still considered indicative of mild airflow obstruction. In some cases, a low FEV₁/FVC in the presence of a low FEV₁ is classified as reflecting dysanapsis, or airways size being too small relative to lung volume size. While dysanapsis may be a physiologically normal variant, it has also been associated with COPD [36], bronchodilator responsiveness, and [37] severe asthma in children with obesity [38].

If FEV₁/FVC is normal, but FEV₁ is low, this may represent restriction, which should be evaluated by lung volumes. When lung volumes are not available, this pattern has also been labeled "Preserved Ratio Impaired Spirometry", or PRISm. It is unclear if PRISm is a distinct phenotype of lung disease, but multiple studies have demonstrated that PRISm is associated with increased cardiopulmonary disease and mortality [39-41].

When FVC maneuvers are routinely stopped after six seconds, the FEV₁/FEV₆ may replace the FEV₁/FVC [42]. 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 [24,43-45]. The appropriate lower limit of normal for FEV₁/FEV₆ from NHANES III should be used [29,46]; unfortunately, the GLI equations do not include prediction equations for FEV₆.

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 [19].

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. Note, however, that a bronchodilator response alone does not distinguish asthma from COPD [47,48]. 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 [49]. (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 [50-54]. 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 [55].

●Misclassification rates due to suboptimal spirometry performance or interpretation are relatively high in the office setting [7,17,56]. 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 [17]. 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 [57,58].

●There are multiple barriers to performing in-office spirometry. One comprehensive survey identified multiple barriers including lack of knowledge about how to interpret spirometry, lack of resources (equipment, personnel, skills, time), and lack of belief in importance of results [59]. Most of the barriers identified were also true for out-of-office (ie, hospital) spirometry, indicating that implementing spirometry in general faces many challenges.

RISKS — Spirometry is a low-risk procedure and has few side effects [12]. 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 [60]:

●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 [4,61,62].

Office spirometry is also useful for monitoring disease progression in patients with idiopathic pulmonary fibrosis [63].

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 fixed threshold of 0.7 because 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 (algorithm 1) (see 'Interpretation' above). If FEV₁/FVC is low but FEV₁ is normal, this is still considered obstruction but may also represent dysanapsis, which can be a normal variant.

●A normal FEV₁/FVC but reduced FVC suggests restriction, which must be confirmed by lung volume measurement. If restriction is not confirmed, this pattern has been termed "nonspecific". If lung volumes are not available, a low FEV₁ and normal FEV₁/FVC has also been referred to as Preserved Ratio Impaired Spirometry, or PRISm.

●The FEV₁/FEV₆ can be helpful instead of 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 in obstructive and mixed obstructive-restrictive disorders. It may also be used in the absence of lung volumes for grading previously confirmed restriction. FEV₁/FVC ratio is not useful for gauging severity of ventilatory impairment, since the FVC often decreases with increasing obstruction due to air trapping or premature termination of exhalation (algorithm 1). (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.)

●Despite the potential benefits, ongoing barriers to office spirometry implementation include primary care provider uncertainty regarding the benefits of testing, lack of resources, and lack of confidence in spirometric interpretation.

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Paul Enright, MD, who contributed to earlier versions of this topic review.