Standardisation of spirometry

M. R. Miller, J. Hankinson, V. Brusasco, F. Burgos, R. Casaburi, A. Coates, R. Crapo, P. Enright, C. P. M. van der Grinten, P. Gustafsson, R. Jensen, D. C. Johnson, N. MacIntyre, R. McKay, D. Navajas, O. F. Pedersen, R. Pellegrino, G. Viegi, J. Wanger



Edited by V. Brusasco, R. Crapo and G. Viegi

Number 2 in this Series


Spirometry is a physiological test that measures how an individual inhales or exhales volumes of air as a function of time. The primary signal measured in spirometry may be volume or flow.

Spirometry is invaluable as a screening test of general respiratory health in the same way that blood pressure provides important information about general cardiovascular health. However, on its own, spirometry does not lead clinicians directly to an aetiological diagnosis. Some indications for spirometry are given in table 1.

In this document, the most important aspects of spirometry are the forced vital capacity (FVC), which is the volume delivered during an expiration made as forcefully and completely as possible starting from full inspiration, and the forced expiratory volume (FEV) in one second, which is the volume delivered in the first second of an FVC manoeuvre. Other spirometric variables derived from the FVC manoeuvre are also addressed.

Spirometry can be undertaken with many different types of equipment, and requires cooperation between the subject and the examiner, and the results obtained will depend on technical as well as personal factors (fig. 1). If the variability of the results can be diminished and the measurement accuracy can be improved, the range of normal values for populations can be narrowed and abnormalities more easily detected. The Snowbird workshop held in 1979 resulted in the first American Thoracic Society (ATS) statement on the standardisation of spirometry 1. This was updated in 1987 and again in 1994 2, 3. A similar initiative was undertaken by the European Community for Steel and Coal, resulting in the first European standardisation document in 1983 4. This was then updated in 1993 as the official statement of the European Respiratory Society (ERS) 5. There are generally only minor differences between the two most recent ATS and ERS statements, except that the ERS statement includes absolute lung volumes and the ATS does not.

This document brings the views of the ATS and ERS together in an attempt to publish standards that can be applied more widely. The statement is structured to cover definitions, equipment and patient-related procedures. All recording devices covered by this statement must meet the relevant requirements, regardless of whether they are for monitoring or diagnostic purposes. There is no separate category for “monitoring” devices.

Although manufacturers have the responsibility for producing pulmonary function testing systems that satisfy all the recommendations presented here, it is possible that, for some equipment, meeting all of them may not always be achievable. In these circumstances, manufacturers should clearly identify which equipment requirements have not been met. While manufacturers are responsible for demonstrating the accuracy and reliability of the systems that they sell, it is the user who is responsible for ensuring that the equipment's measurements remain accurate. The user is also responsible for following local law, which may have additional requirements. Finally, these guidelines are minimum guidelines, which may not be sufficient for all settings, such as when conducting research, epidemiological studies, longitudinal evaluations and occupational surveillance.



FVC is the maximal volume of air exhaled with maximally forced effort from a maximal inspiration, i.e. vital capacity performed with a maximally forced expiratory effort, expressed in litres at body temperature and ambient pressure saturated with water vapour (BTPS; see BTPS correction section).

FEV1 is the maximal volume of air exhaled in the first second of a forced expiration from a position of full inspiration, expressed in litres at BTPS.



The spirometer must be capable of accumulating volume for ≥15 s (longer times are recommended) and measuring volumes of ≥8 L (BTPS) with an accuracy of at least ±3% of reading or ±0.050 L, whichever is greater, with flows between 0 and 14 L·s−1. The total resistance to airflow at 14.0 L·s−1 must be <1.5 cmH2O·L−1·s−1 (0.15 kPa·L−1·s−1; see Minimal recommendations for spirometry systems section). The total resistance must be measured with any tubing, valves, pre-filter, etc. included that may be inserted between the subject and the spirometer. Some devices may exhibit changes in resistance due to water vapour condensation, and accuracy requirements must be met under BTPS conditions for up to eight successive FVC manoeuvres performed in a 10-min period without inspiration from the instrument.


For optimal quality control, both flow–volume and volume–time displays are useful, and test operators should visually inspect the performance of each manoeuvre for quality assurance before proceeding with another manoeuvre. This inspection requires tracings to meet the minimum size and resolution requirements set forth in this standard.

Displays of flow versus volume provide more detail for the initial portion (first 1 s) of the FVC manoeuvre. Since this portion of the manoeuvre, particularly the peak expiratory flow (PEF), is correlated with the pleural pressure during the manoeuvre, the flow–volume display is useful to assess the magnitude of effort during the initial portions of the manoeuvre. The ability to overlay a series of flow–volume curves registered at the point of maximal inhalation may be helpful in evaluating repeatability and detecting submaximal efforts. However, if the point of maximal inhalation varies between blows, then the interpretation of these results is difficult because the flows at identical measured volumes are being achieved at different absolute lung volumes. In contrast, display of the FVC manoeuvre as a volume–time graph provides more detail for the latter part of the manoeuvre. A volume–time tracing of sufficient size also allows independent measurement and calculation of parameters from the FVC manoeuvres. In a display of multiple trials, the sequencing of the blows should be apparent to the user.

For the start of test display, the volume–time display should include ≥0.25 s, and preferably 1 s, before exhalation starts (zero volume). This time period before there is any change in volume is needed to calculate the back extrapolated volume (EV; see Start of test criteria section) and to evaluate effort during the initial portion of the manoeuvre. Time zero, as defined by EV, must be presented as the zero point on the graphical output.

The last 2 s of the manoeuvre should be displayed to indicate a satisfactory end of test (see End of test criteria section).

When a volume–time curve is plotted as hardcopy, the volume scale must be ≥10 mm·L−1 (BTPS). For a screen display, 5 mm·L−1 is satisfactory (table 2).

The time scale should be ≥20 mm·s−1, and larger time scales are preferred (≥30 mm·s−1) when manual measurements are made 1, 6, 7. When the volume–time plot is used in conjunction with a flow–volume curve (i.e. both display methods are provided for interpretations and no hand measurements are performed), the time scale requirement is reduced to 10 mm·s−1 from the usually required minimum of 20 mm·s−1 (table 2). The rationale for this exception is that the flow–volume curve can provide the means for quality assessment during the initial portion of the FVC manoeuvre. The volume–time curve can be used to evaluate the latter part of the FVC manoeuvre, making the time scale less critical.


It is strongly recommended that spirometry systems should be evaluated using a computer-driven mechanical syringe or its equivalent, in order to test the range of exhalations that are likely to be encountered in the test population. Testing the performance of equipment is not part of the usual laboratory procedures (see Test signals for spirometer testing section).

Quality control

Attention to equipment quality control and calibration is an important part of good laboratory practice. At a minimum, the requirements are as follows: 1) a log of calibration results is maintained; 2) the documentation of repairs or other alterations which return the equipment to acceptable operation; 3) the dates of computer software and hardware updates or changes; and 4) if equipment is changed or relocated (e.g. industrial surveys), calibration checks and quality-control procedures must be repeated before further testing begins.

Key aspects of equipment quality control are summarised in table 3.

Calibration is the procedure for establishing the relationship between sensor-determined values of flow or volume and the actual flow or volume.

A calibration check is different from calibration and is the procedure used to validate that the device is within calibration limits, e.g. ±3% of true. If a device fails its calibration check, then a new calibration procedure or equipment maintenance is required. Calibration checks must be undertaken daily, or more frequently, if specified by the manufacturer.

The syringe used to check the volume calibration of spirometers must have an accuracy of ±15 mL or ±0.5% of the full scale (15 mL for a 3-L syringe), and the manufacturer must provide recommendations concerning appropriate intervals between syringe calibration checks. Users should be aware that a syringe with an adjustable or variable stop may be out of calibration if the stop is reset or accidentally moved. Calibration syringes should be periodically (e.g. monthly) leak tested at more than one volume up to their maximum; this can be done by attempting to empty them with the outlet corked. A dropped or damaged syringe should be considered out of calibration until it is checked.

With regard to time, assessing mechanical recorder time scale accuracy with a stopwatch must be performed at least quarterly. An accuracy of within 2% must be achieved.

Quality control for volume-measuring devices

The volume accuracy of the spirometer must be checked at least daily, with a single discharge of a 3-L calibrated syringe. Daily calibration checking is highly recommended so that the onset of a problem can be determined within 1 day, and also to help define day-to-day laboratory variability. More frequent checks may be required in special circumstances, such as: 1) during industrial surveys or other studies in which a large number of subject manoeuvres are carried out, the equipment's calibration should be checked more frequently than daily 8; and 2) when the ambient temperature is changing (e.g. field studies), volume accuracy must be checked more frequently than daily and the BTPS correction factor appropriately updated.

The accuracy of the syringe volume must be considered in determining whether the measured volume is within acceptable limits. For example, if the syringe has an accuracy of 0.5%, a reading of ±3.5% is appropriate.

The calibration syringe should be stored and used in such a way as to maintain the same temperature and humidity of the testing site. This is best accomplished by keeping the syringe in close proximity to the spirometer, but out of direct sunlight and away from heat sources.

Volume-type spirometer systems must be evaluated for leaks every day 9, 10. The importance of undertaking this daily test cannot be overstressed. Leaks can be detected by applying a constant positive pressure of ≥3.0 cmH2O (0.3 kPa) with the spirometer outlet occluded (preferably at or including the mouthpiece). Any observed volume loss >30 mL after 1 min indicates a leak 9, 10 and needs to be corrected.

At least quarterly, volume spirometers must have their calibration checked over their entire volume range using a calibrated syringe 11 or an equivalent volume standard. The measured volume should be within ±3.5% of the reading or 65 mL, whichever is greater. This limit includes the 0.5% accuracy limit for a 3-L syringe. The linearity check procedure provided by the manufacturer can be used if it is equivalent to one of the following procedures: 1) consecutive injections of 1-L volume increments while comparing observed volume with the corresponding cumulative measured volume, e.g. 0–1, 1–2, 2–3,…6–7 and 7–8 L, for an 8-L spirometer; and 2) injection of a 3-L volume starting at a minimal spirometer volume, then repeating this with a 1-L increment in the start position, e.g. 0–3, 1–4, 2–5, 3–6, 4–7 and 5–8 L, for an 8-L spirometer.

The linearity check is considered acceptable if the spirometer meets the volume accuracy requirements for all volumes tested.

Quality control for flow-measuring devices

With regards to volume accuracy, calibration checks must be undertaken at least daily, using a 3-L syringe discharged at least three times to give a range of flows varying between 0.5 and 12 L·s−1 (with 3-L injection times of ∼6 s and <0.5 s). The volume at each flow should meet the accuracy requirement of ±3.5%. For devices using disposable flow sensors, a new sensor from the supply used for patient tests should be tested each day.

For linearity, a volume calibration check should be performed weekly with a 3-L syringe to deliver three relatively constant flows at a low flow, then three at a mid-range flow and finally three at a high flow. The volumes achieved at each of these flows should each meet the accuracy requirement of ±3.5%.

Test procedure

There are three distinct phases to the FVC manoeuvre, as follows: 1) maximal inspiration; 2) a “blast” of exhalation; and 3) continued complete exhalation to the end of test (EOT).

The technician should demonstrate the appropriate technique and follow the procedure described in table 4. The subject should inhale rapidly and completely from functional residual capacity (FRC), the breathing tube should be inserted into the subject's mouth (if this has not already been done), making sure the lips are sealed around the mouthpiece and that the tongue does not occlude it, and then the FVC manoeuvre should be begun with minimal hesitation. Reductions in PEF and FEV1 have been shown when inspiration is slow and/or there is a 4–6 s pause at total lung capacity (TLC) before beginning exhalation 12. It is, therefore, important that the preceding inspiration is fast and any pause at full inspiration be minimal (i.e. only for 1–2 s). The test assumes a full inhalation before beginning the forced exhalation, and it is imperative that the subject takes a complete inhalation before beginning the manoeuvre. The subject should be prompted to “blast,” not just “blow,” the air from their lungs, and then he/she should be encouraged to fully exhale. Throughout the manoeuvre, enthusiastic coaching of the subject using appropriate body language and phrases, such as “keep going”, is required. It is particularly helpful to observe the subject with occasional glances to check for distress, and to observe the tracing or computer display during the test to help ensure maximal effort. If the patient feels “dizzy”, the manoeuvre should be stopped, since syncope could follow due to prolonged interruption of venous return to the thorax. This is more likely to occur in older subjects and those with airflow limitation. Performing a vital capacity (VC) manoeuvre (see VC and IC manoeuvre section), instead of obtaining FVC, may help to avoid syncope in some subjects. Reducing the effort part-way through the manoeuvre 13 may give a higher expiratory volume in some subjects, but then is no longer a maximally forced expiration. Well-fitting false teeth should not be routinely removed, since they preserve oropharyngeal geometry and spirometry results are generally better with them in place 14.

With appropriate coaching, children as young as 5 yrs of age are often able to perform acceptable spirometry 15. The technicians who are involved in the pulmonary function testing of children should be specifically trained to deal with such a situation. A bright, pleasant atmosphere, including age-appropriate toys, reading material and art, is important in making children feel at ease. Encouragement, detailed but simple instructions, lack of intimidation and visual feedback in the teaching are important in helping children to perform the manoeuvre. Even if unsuccessful at the first session, children will learn to be less intimidated and may perform far better in a subsequent session. Testing children in “adult” laboratories, where no effort is made to cater for the specific needs of the younger subjects, is to be discouraged.

The use of a nose clip or manual occlusion of the nares is recommended, and, for safety reasons, testing should be preferably done in the sitting position, using a chair with arms and without wheels. If testing is undertaken with the patient standing or in another position, this must be documented on the report.

Within-manoeuvre evaluation

Start of test criteria

The start of test, for the purpose of timing, is determined by the back extrapolation method (fig. 2) 1, 3, 9, 16. The new “time zero” from back extrapolation defines the start for all timed measurements. For manual measurements, the back extrapolation method traces back from the steepest slope on the volume–time curve 17. For computerised back extrapolation, it is recommended that the largest slope averaged over an 80-ms period is used 18. Figure 2 provides an example and explanation of back extrapolation and the derivation of EV. To achieve an accurate time zero and assure the FEV1 comes from a maximal effort curve, the EV must be <5% of the FVC or 0.150 L, whichever is greater. If a manoeuvre has an obviously hesitant start, the technician may terminate the trial early to avoid an unnecessary prolonged effort.

Rapid computerised feedback to the technician when the start criteria are not met is strongly encouraged. In addition to the expiratory manoeuvre, the volume-time curve display (graph) should ideally include the whole preceding inspiratory manoeuvre, but must include ≥0.25 s and preferably ≥1 s prior to the start of exhalation (time zero). The equipment should display the EV value. Inspection of the flow–volume curve may be added as a measure of the satisfactory start of test. PEF should be achieved with a sharp rise and occur close to the point of maximal inflation, i.e. the start of exhalation (see Equipment section).

End of test criteria

It is important for subjects to be verbally encouraged to continue to exhale the air at the end of the manoeuvre to obtain optimal effort, e.g. by saying “keep going”. EOT criteria are used to identify a reasonable FVC effort, and there are two recommended EOT criteria, as follows. 1) The subject cannot or should not continue further exhalation. Although subjects should be encouraged to achieve their maximal effort, they should be allowed to terminate the manoeuvre on their own at any time, especially if they are experiencing discomfort. The technician should also be alert to any indication that the patient is experiencing discomfort, and should terminate the test if a patient is becoming uncomfortable or is approaching syncope. 2) The volume–time curve shows no change in volume (<0.025 L) for ≥1 s, and the subject has tried to exhale for ≥3 s in children aged <10 yrs and for ≥6 s in subjects aged >10 yrs.

The equipment should signal to the technician if the plateau criteria were not met. A satisfactory EOT may still have been achieved, but an equipment alert will help the technician to pinpoint where the subject may need more encouragement. It is of note that a closure of the glottis may prematurely terminate a manoeuvre at <6 s, even when the apparent duration of the blow exceeds 6 s.

For patients with airways obstruction or older subjects, exhalation times of >6 s are frequently needed. However, exhalation times of >15 s will rarely change clinical decisions. Multiple prolonged exhalations are seldom justified and may cause light headedness, syncope, undue fatigue and unnecessary discomfort.

Achieving EOT criteria is one measure of manoeuvre acceptability. Manoeuvres that do not meet EOT criteria should not be used to satisfy the requirement of three acceptable manoeuvres. However, early termination, by itself, is not a reason to eliminate all the results from such a manoeuvre from further consideration. Information such as the FEV1 may be useful (depending on the length of exhalation) and can be reported from these early terminated manoeuvres.

Some young children may have difficulty meeting the ATS EOT criteria 3, although they may meet other repeatability criteria 19. Curve-fitting techniques 20 may prove useful in developing new EOT criteria specific for young children.

Additional criteria

A cough during the first second of the manoeuvre can affect the measured FEV1 value. Coughing in the first second or any other cough that, in the technician's judgment, interferes with the measurement of accurate results 3 will render a test unacceptable.

A Valsalva manoeuvre (glottis closure) or hesitation during the manoeuvre that causes a cessation of airflow in a manner that precludes an accurate estimate of either FEV1 or FVC 3 will render a test unacceptable.

There must be no leak at the mouth 3. Patients with neuromuscular disease may require manual or other assistance from the technician to guarantee an adequate seal.

Obstruction of the mouthpiece, e.g. by the tongue being placed in front of the mouthpiece or by teeth in front of the mouthpiece, or by distortion from biting, may affect the performance of either the device or the subject.

Summary of acceptable blow criteria

The acceptability criteria are a satisfactory start of test and a satisfactory EOT, i.e. a plateau in the volume–time curve. In addition, the technician should observe that the subject understood the instructions and performed the manoeuvre with a maximum inspiration, a good start, a smooth continuous exhalation and maximal effort. The following conditions must also be met: 1) without an unsatisfactory start of expiration, characterised by excessive hesitation or false start extrapolated volume or EV >5% of FVC or 0.150 L, whichever is greater (fig. 2); 2) without coughing during the first second of the manoeuvre, thereby affecting the measured FEV1 value, or any other cough that, in the technician's judgment, interferes with the measurement of accurate results 3; 3) without early termination of expiration (see End of test criteria section); 4) without a Valsalva manoeuvre (glottis closure) or hesitation during the manoeuvre that causes a cessation of airflow, which precludes accurate measurement of FEV1 or FVC 3; 5) without a leak 3; 6) without an obstructed mouthpiece (e.g. obstruction due to the tongue being placed in front of the mouthpiece, or teeth in front of the mouthpiece, or mouthpiece deformation due to biting); and 7) without evidence of an extra breath being taken during the manoeuvre.

It should be noted that a usable curve must only meet conditions 1 and 2 above, while an acceptable curve must meet all of the above seven conditions.

It is desirable to use a computer-based system that provides feedback to the technician when the above conditions are not met. The reporting format should include qualifiers indicating the acceptability of each manoeuvre. However, failure to meet these goals should not necessarily prevent reporting of results, since, for some subjects, this is their best performance. Records of such manoeuvres should be retained since they may contain useful information.

Between-manoeuvre evaluation

Using the previously described criteria, an adequate test requires a minimum of three acceptable FVC manoeuvres. Acceptable repeatability is achieved when the difference between the largest and the next largest FVC is ≤0.150 L and the difference between the largest and next largest FEV1 is ≤0.150 L 21. For those with an FVC of ≤1.0 L, both these values are 0.100 L. If these criteria are not met in three manoeuvres, additional trials should be attempted, up to, but usually no more than, eight manoeuvres. Large variability among tests is often due to incomplete inhalations. Some patients may require a brief rest period between manoeuvres. Volume–time or flow–volume curves from at least the best three FVC manoeuvres must be retained. Table 5 gives a summary of the within- and between-manoeuvre evaluation.

Manoeuvre repeatability

For FVC measurements, acceptability must be determined by ascertaining that the recommendations outlined previously on performing the FVC test are met. The guidelines of the ATS 3 contain examples of unacceptable volume–time and corresponding flow–volume curves. Figure 3 shows a flow chart outlining how the criteria for blow acceptability are applied before those for repeatability.

The repeatability criteria are used to determine when more than three acceptable FVC manoeuvres are needed; these criteria are not to be used to exclude results from reports or to exclude subjects from a study. Labelling results as being derived from data that do not conform to the repeatability criteria described previously is recommended. In addition, the repeatability criteria are minimum requirements. Many subjects are able to achieve FVC and FEV1 repeatability to within 0.150 L. Manoeuvres with an unacceptable start of test or a cough (unusable curve) must be discarded before applying the repeatability criteria and cannot be used in determining the best values. Manoeuvres with early termination or a Valsalva manoeuvre may be used for selecting the largest FVC and FEV1.

No spirogram or test result should be rejected solely on the basis of its poor repeatability. The repeatability of results should be considered at the time of interpretation. The use of data from manoeuvres with poor repeatability or failure to meet the EOT requirements is left to the discretion of the interpreter.

Maximum number of manoeuvres

Although there may be some circumstances in which more than eight consecutive FVC manoeuvres may be needed, eight is generally a practical upper limit for most subjects 22, 23. After several forced expiratory manoeuvres, fatigue can begin to take its toll on subjects and additional manoeuvres would be of little added value. In extremely rare circumstances, subjects may show a progressive reduction in FEV1 or FVC with each subsequent blow. If the cumulative drop exceeds 20% of start value, the test procedure should be terminated in the interest of patient safety. The sequence of the manoeuvres should be recorded.

Test result selection

FVC and FEV1 should be measured from a series of at least three forced expiratory curves that have an acceptable start of test and are free from artefact, such as a cough (i.e. “usable curves”). The largest FVC and the largest FEV1 (BTPS) should be recorded after examining the data from all of the usable curves, even if they do not come from the same curve.

Other derived indices


FEVt is the maximal volume exhaled by time t seconds (timed from the time zero defined by back extrapolation) of a forced expiration from a position of full inspiration, expressed in litres at BTPS. Very young children may not be able to produce prolonged expirations, but there is increasing evidence that indices derived from blows with forced expiratory times of <1 s may have clinical usefulness 19. At present, there are insufficient data to recommend the use of FEV0.5 or FEV0.75.

When the subject does not exhale completely, the volume accumulated over a shorter period of time (e.g. 6 s) may be used as an approximate surrogate for FVC. When such surrogates are used, the volume label should reflect the shorter exhalation time (e.g. FEV6 for a 6-s exhalation). FEV6 has been increasingly considered a reasonably reliable surrogate for FVC 24 and can be used for normalising FEV1 (e.g. FEV1/FEV6). Recording FEV6 seems to have the advantage of being more reproducible than FVC, being less physically demanding for patients and providing a more explicit EOT. Confirmation from other studies is required.

Standardisation of FEV1 for expired volume, FEV1/FVC and FEV1/VC

In some patients, a slow or unforced VC or inspiratory vital capacity (IVC) manoeuvre (see VC and IC manoeuvre section) may provide a larger and more appropriate denominator for calculation of the FEV1/VC%. Some investigators have reported that the VC is slightly higher than the FVC in normal subjects 25.


The mean forced expiratory flow between 25% and 75% of the FVC (FEF25–75%) has also been known as the maximum mid-expiratory flow. This index is taken from the blow with the largest sum of FEV1 and FVC. The FEF25–75% must be measured with an accuracy of at least ±5% of reading or ±0.200 L·s−1 whichever is greater, over a range of up to 7 L·s−1. It should be noted that it is highly dependent on the validity of the FVC measurement and the level of expiratory effort.


PEF is usually obtained from flow–volume curve data. It is the maximum expiratory flow achieved from a maximum forced expiration, starting without hesitation from the point of maximal lung inflation, expressed in L·s−1. When PEF is recorded using a patient-administered portable PEF meter, it is often expressed in L·min−1. PEF is covered in more detail later.

Maximal expiratory flow–volume loops

The shape of a maximum flow–volume loop (MFVL), which includes forced inspiratory manoeuvres, can be helpful in quality control and in detecting the presence of upper airway obstruction. None of the numerical indices from a MFVL has clinical utility superior to FEV1, FVC, FEF25–75% and PEF, and are not considered in detail here.


With regard to instantaneous flows, the recommended measure is the instantaneous forced expiratory flow when X% of the FVC has been expired (FEFX%). The maximal instantaneous forced expiratory flow when X% of the FVC remains to be expired (MEFX%) was the term previously recommended in Europe.

Instantaneous forced inspiratory flow when X% of the FVC has been expired (FIFX%) and mid-inspiratory flow when X% of the FVC has been expired refer to the flows measured on the inspiratory limb of a flow–volume loop. FIF25–75%, also referred to as maximal mid-inspiratory flow, is analogous to FEF25–75% (see Other derived indices section).


Instantaneous flows must be measured with an accuracy of ±5% of reading or ±0.200 L·s−1, whichever is greater, over a range of -14–14 L·s−1. The level of minimum detectable flow should be 0.025 L·s−1. When a maximum flow–volume loop is plotted or displayed, exhaled flow must be plotted upwards, and exhaled volume towards the right. A 2:1 ratio must be maintained between the flow and volume scales, e.g. 2 L·s−1 of flow and 1 L of exhaled volume must be the same distance on their respective axes. The flow and volume scales, used in reviewing test performance, must be equivalent to that shown in table 2.

Test procedure

The subject has to make a full expiratory and inspiratory loop as a single manoeuvre. In many laboratories, this is the primary manoeuvre for spirometry. The subject is asked to take a rapid full inspiration to TLC from room air through the mouth, then insert the mouthpiece and, without hesitation, perform an expiration with maximum force until no more gas can be expelled, followed by a quick maximum inspiration. At this point, the manoeuvre is finished.

An alternative procedure is for the subject to insert the mouthpiece while undertaking tidal breathing at FRC, and then, in one continuous sequence, do the following: make a slow expiration to residual volume (RV); followed directly by a slow inspiration to TLC; follow this by a rapid full expiration with maximal effort to RV; and followed by a rapid full inspiration with maximal effort back to TLC.

This procedure is slightly more complicated and may not be suitable for all equipment, but it obtains a measurement of VC as well as FVC.

Within- and between-manoeuvre evaluation

These evaluations are the same as for FVC (see Within-manoeuvre evaluation and Between-manoeuvre evaluation sections). Occasionally, a subject is unable to perform a satisfactory inspiratory limb immediately following a maximal forced expiratory manoeuvre. This is particularly common in the elderly and the infirm. In these circumstances, it may be necessary for the subject to record an inspiratory manoeuvre separately from the expiratory manoeuvre. Equipment should be able to perform these separately and then present three or more loops together on a graphical display or output.

Flow–volume loop examples

The following figures (figures 410) give typical examples of commonly encountered flow–volume loop configurations. The advantages of visual pattern recognition from the MFVL can readily be appreciated. The shapes of the manoeuvres must be repeatable (fig. 10) for any interpretation to be made. This is especially true for the plateau effect on expiratory and inspiratory limbs of the manoeuvre found in upper airway obstruction, as this can be mimicked by poor effort, which is usually variable from blow to blow. A further explanation is given in the ATS/ERS statement on lung function interpretation 26.

Reversibility testing

A determination of airflow-limitation reversibility with drug administration is commonly undertaken as part of lung function testing. The choice of drug, dose and mode of delivery is a clinical decision depending on what the clinician wishes to learn from the test.

If the aim of the test is to determine whether the patient's lung function can be improved with therapy in addition to their regular treatment, then the subject can continue with his/her regular medication prior to the test.

If the clinician wants to determine whether there is any evidence of reversible airflow limitation, then the subject should undergo baseline function testing when not taking any drugs prior to the test. Short-acting inhaled drugs (e.g. the β-agonist albuterol/salbutamol or the anticholinergic agent ipratropium bromide) should not be used within 4 h of testing. Long-acting β-agonist bronchodilators (e.g. salmeterol or formoterol) and oral therapy with aminophylline or slow-release β-agonists should be stopped for 12 h prior to the test. Smoking should be avoided for ≥1 h prior to testing and throughout the duration of the test procedure.


The following steps are undertaken. 1) The subject has three acceptable tests of FEV1, FVC and PEF recorded as described previously. 2) The drug is administered in the dose and by the method indicated for the test. For example, after a gentle and incomplete expiration, a dose of 100 μg of albuterol/salbutamol is inhaled in one breath to TLC from a valved spacer device. The breath is then held for 5–10 s before the subject exhales. Four separate doses (total dose 400 μg) are delivered at ∼30-s intervals. This dose ensures that the response is high on the albuterol dose–response curve. A lower dose can be used if there is concern about any effect on the patient's heart rate or tremor. Other drugs can also be used. For the anticholinergic agent ipratropium bromide, the total dose is 160 μg (4×40 μg).

Three additional acceptable tests are recorded ≥10 min and up to 15 min later for short-acting β2-agonists, and 30 min later for short-acting anticholinergic agents.

Comment on dose and delivery method

Standardising the bronchodilator dose administered is necessary in order to standardise the definition of a significant bronchodilator response. The rate of pulmonary deposition of a drug with tidal breathing from an unvented nebuliser will depend on drug concentration, rate of nebuliser output, particle-size distribution, and the ratio of the time spent in inspiration over the total respiratory time (ti/ttot) 27. The fraction of the aerosol carried in particles with a diameter of ≤5 μm that is expected to deposit in adult lungs if inhaled through a mouthpiece 28 is defined as the respirable fraction (RF). For example, 2.5 mg of salbutamol (albuterol) in 2.5 mL of solution, placed in a Hudson Updraft II (Hudson RCI, Temecula, CA, USA) driven by a PulmoAide compressor (De Vilbiss, Somerset, PA, USA), would produce ∼0.1 mg·min−1 in the RF. For a respiratory rate of 15 breaths·min−1 and a ti/ttot of 0.45, this would give ∼3 μg deposited in the lungs per breath, or 45 μg·min−1. For adults using a metered dose inhaler (MDI) with a valve-holding chamber (spacer), between 10 and 20% 29, 30 of a 100-μg “puff” (or ∼15 μg per activation) would be expected to be deposited in the lung of an adult. Without a spacer, the deposition will be less, and heavily technique dependent 31. Pulmonary deposition from dry-powder inhalers is device specific, and breath-enhanced nebulisers deposit much more than unvented ones 32, 33. CFC-free MDIs produce a smaller particle-size distribution and improved (up to 50% of dose) lung deposition compared with those with CFC propellant 34. For children, pulmonary deposition is less than that in adults 35, possibly relating to the size of the upper airway. Each laboratory should be familiar with the pulmonary-deposition characteristics of the devices they use.

Determination of reversibility

This aspect is covered in detail in the interpretative strategy document of the ATS and ERS 26.



VC and IVC

The VC is the volume change at the mouth between the position of full inspiration and complete expiration, expressed in litres at BTPS. The slow VC can be derived in two ways. The expiratory vital capacity (EVC) is the maximal volume of air exhaled from the point of maximal inhalation. The IVC is the maximal volume of air inhaled from the point of maximal exhalation, achieved by a slow expiration from end-tidal inspiration. These manoeuvres are unforced, except at the point of reaching RV or TLC, respectively, where extra effort is required 36.


Inspiratory capacity (IC) is volume change recorded at the mouth when taking a slow full inspiration with no hesitation, from a position of passive end-tidal expiration, i.e. FRC, to a position of maximum inspiration, expressed in litres at BTPS. IC is an indirect estimate of the degree of lung hyperinflation at rest, and is useful to assess changes in FRC with pharmacological interventions and physical exercise 3741.


For measurements of VC and IC, the spirometer or flow meter must comply with the requirements for FVC (as described previously) and be capable of accumulating volume for ≥30 s.

Expiratory manoeuvres or, ideally, both inspiratory and expiratory manoeuvres should be included in the display of VC manoeuvre. Regardless of whether the inspiratory or expiratory manoeuvre is used for deriving measurements, a display of the entire recorded VC manoeuvre must be provided. The maximal expiratory volume must be assessed to determine whether the subject has obtained a plateau in the expiratory effort. For display of the slow VC, the time scale may be reduced to 5 mm·s−1.

Test procedure


VC can be measured using conventional spirometers. It may also be recorded from equipment used to measure static lung volumes and their subdivisions 42. For slow VC, a maximum of four manoeuvres is a practical upper limit. It is preferable that VC manoeuvres be performed before FVC manoeuvres because of the potential for muscular fatigue and volume history effects, where, after maximal inspiratory efforts, some patients with severe airways obstruction return to a falsely high level of FRC or RV, due to gas trapping or stress relaxation 3. The VC manoeuvre may be considered either as an IVC, where the subject inhales completely from a position of full expiration, or as an EVC, where the subject exhales completely from a position of full inspiration. Figure 11 shows the recording of IVC and figure 12 shows an EVC recording. Important differences between inspiratory (i.e. IVC) and expiratory (i.e. EVC) manoeuvres may be observed in patients with airways obstruction 43, 44.

The test is begun by instructing the subject in the VC manoeuvre and demonstrating the appropriate technique. It is important that subjects understand they must completely fill and empty their lungs. The VC manoeuvre is performed with the subject using a mouthpiece and wearing a nose clip. The manoeuvre is not forced; it is performed in a relaxed manner, except near end-inspiration and end-expiration. The subject exhales completely to RV, then inhales to TLC, and finally exhales to RV again. The technician should encourage the subject to reach maximal inhaled and exhaled volumes with a relatively constant flow. The exhalation should not be unduly slow, as this can lead to underestimation of VC. Technicians should observe the subject carefully to ensure that his/her lips are sealed, nothing obstructs the mouthpiece, no leaks occur, and that TLC and RV are reached.

Alternatively, the subject inhales maximally, inserts the mouthpiece just past his/her front teeth, seals his/her lips around the mouthpiece, and blows slowly and evenly until there is no volume change (<0.025 L) for a 1-s period (see End of test criteria section). Patients with neuromuscular disease may need assistance in maintaining a tight seal at the mouth. The technician must observe the subject's inhalation to ensure that it is complete, and that air is not exhaled while the mouthpiece is being inserted. The technician should assure that the expiratory manoeuvre is not forced. In healthy subjects, adequate maximal inspiratory and expiratory levels are achieved within 5–6 s.


Subjects should be tested in the seated position wearing a nose clip with no air leaks between the mouth and the mouthpiece. Subjects should be relaxed (shoulders down and relaxed) and asked to breathe regularly for several breaths until the end-expiratory lung volume is stable (this usually requires at least three tidal manoeuvres). They are then urged to take a deep breath to TLC with no hesitation. Figure 12 shows a tracing from the recording of IC.

Use of a nose clip

The use of a nose clip is encouraged in VC measurements, since some people breathe through the nose when performing a slow VC manoeuvre. A nose clip must be used when performing inspiratory manoeuvres such as the IVC or IC.

Within-manoeuvre evaluation

These are the same as for FVC EOT criteria as described previously. There must be no leak at the mouth, no hesitation during the manoeuvre, and no obstruction of the mouthpiece (see Additional criteria section). The IC may be underestimated if the inspiratory manoeuvre is too slow due to poor effort or hesitation, or if there is premature closure of the glottis.

Between-manoeuvre evaluation

As with spirometry, a minimum of three acceptable VC manoeuvres must be obtained. If the difference in VC between the largest and next largest manoeuvre is >0.150 L, additional trials should be undertaken. Meeting repeatability criteria may require that up to, but usually no more than, four manoeuvres are performed, with a rest period of ≥1 min between the manoeuvres. Large variability in this test is often due to incomplete inhalations. Volume–time curves from the best two VC manoeuvres must be retained. For the IC, at least three acceptable manoeuvres should be performed. The mean coefficient of variation for IC in chronic airflow obstruction has been found to be 5 ±3% 39.

Test result selection

For VC, the largest value from at least three acceptable manoeuvres should be reported. For IC, the average of at least three manoeuvres should be reported.


Studies on the measurement of PEF are ongoing. Recent evidence has suggested that the previously applied standards may allow incorrect measurements to be made 45, and it is possible that more stringent requirements may be required. A further statement will be made when the position on the clinical significance of this is clear. However, since PEF measurements are part of asthma-management programmes, the previous recommendations 3, 46 are reiterated here.

Other instantaneous flow measurements (e.g. FEF50%, FEF75%) are not proven to be superior to conventional spirometric indices in a clinical setting, and, therefore, are not considered further.


PEF is the highest flow achieved from a maximum forced expiratory manoeuvre started without hesitation from a position of maximal lung inflation 46. When it is obtained from flow–volume curve data, it is expressed at BTPS in L·s−1. The defining characteristics of the flow–time curve, in relation to PEF, are the time taken for flow to rise from 10% of PEF to 90% of PEF, i.e. the rise time (RT), and the duration that flow is >90% of PEF, called the dwell time (DT). When PEF is obtained with portable monitoring instruments, it is expressed in L·min−1.


Ideally, PEF should be recorded by an instrument that primarily records flow. Measuring PEF requires an instrument that has a flat frequency response (±5%) up to 15 Hz 46. Although there is evidence of significant frequency content in PEF up to 20 Hz 47, it is recommended, at this stage, that manufacturers achieve a goal of recording fidelity up to 15 Hz. The PEF must be measured with an accuracy of ±10% or ±0.3 L·s−1 (20 L·min−1), whichever is the greater. Mean instrument resistance measured across the range of the instrument should be <2.5 cmH2O·L−1·s−1 (0.25 kPa·L−1·s−1; table 6). PEF is sensitive to the resistance of the meter; for example, a resistance of 0.25 kPa·L−1·s−1 decreases PEF by ∼8% compared with PEF measured with a low-resistance pneumotachograph 48.

Intra-instrument repeatability must be <5% or 0.150 L·s−1 (10 L·min−1), whichever is the greater. Inter-device reproducibility must be <10% or 0.300 L·s−1 (20 L·min−1), whichever is the greater. Calculating PEF by differentiating volume–time data may introduce noise; hence, a parabolic-fitting algorithm may be used 2 as a smoothing procedure.

Equipment validation is covered in the Test signals for PEF meter testing section.

Test procedure

PEF is dependent on effort and lung volume, with subject cooperation being essential. PEF must be achieved as rapidly as possible and at as high a lung volume as possible, in order to obtain the maximum value 49. The subject must be encouraged to blow as vigorously as possible. The neck should be in a neutral position, not flexed or extended, and the subject must not cough. A nose clip is not necessary.

After the point of full lung inflation, the subject must deliver the blow without any delay. Hesitating for as little as 2 s or flexing the neck allows the tracheal visco-elastic properties to relax and PEF to drop by as much as 10% 50. Tonguing, spitting or coughing at the start of the blow may falsely raise the recorded PEF in some devices.

In the laboratory, the subject must perform a minimum of three PEF manoeuvres. When PEF is a self-administered recording, it is important that the subject has been adequately taught how to perform the test, when to perform it and what action to take depending on the resulting value obtained. Regular checks of the patient's PEF technique and meter are an important part of the follow-up.

Within-manoeuvre evaluation

The subject must be observed to ensure a good seal at the mouth, no hesitation occurred, and there was no abnormal start to the manoeuvre.

Between-manoeuvre evaluation

The PEF values and their order must be recorded so that manoeuvre-induced bronchospasm can be detected. If the largest two out of three acceptable blows are not reproducible within 0.67 L·s−1 (40 L·min−1), up to two additional blows can be performed. Ninety-five per cent of untrained healthy subjects and patients can reproduce PEF to within 0.67 L·s−1 (40 L·min−1), and 90% to within 0.5 L·s−1 (30 L·min−1) 48. If satisfactory repeatability has not been in achieved in five attempts, more are not likely to be helpful 51.

Test result selection

The largest value from at least three acceptable blows is recorded.


This test has been largely superseded by FEV1, which was defined as the index from a single maximum forced expiratory manoeuvre that best correlated with maximum voluntary ventilation (MVV). If FEV1 is available, then MVV has little additional contribution to make in a clinical setting. However, it may be useful in those conditions where ventilatory capacity may be impaired by mechanisms that are different from those affecting FEV1 26.


The MVV is the maximum volume of air a subject can breathe over a specified period of time (12 s for normal subjects). It is expressed in L·min−1 at BTPS.


A spirometer used for measuring MVV must have an amplitude–frequency response that is flat (±10%) from zero to ≥4 Hz, at flows of up to 12 L·s−1, over the volume range. The time for exhaled volume integration or recording must be no less than 12 s and no more than 15 s 52. The indicated time must be accurate to within ±3%. The MVV must be measured with an accuracy of ±10% of reading or ±15 L·min−1, whichever is greater.

The evaluation of equipment is covered in the Test signals for MVV testing section.

Test procedure

The technician should provide proper instructions and demonstrate the manoeuvre prior to the start of testing. The subject should be tested in the sitting position wearing a nose clip. After the subject makes an airtight seal around the mouthpiece, at least three resting tidal breaths should be obtained, followed by breathing as rapidly and deeply as possible. The tongue and teeth must be positioned so as to not obstruct airflow. The technician should enthusiastically coach the subject throughout the manoeuvre, and may need to suggest faster or slower breathing to achieve an ideal rate of 90–110 breaths·min−1 53, 54, although subjects with disease may not always achieve this rate. The technician will need to carefully observe the subject with occasional glances at the tracing to help the subject to obtain an acceptable manoeuvre. An acceptable manoeuvre should be performed with maximal effort without evidence of leakage, hesitation or measurement artefact. The subject is instructed to breathe as deeply and rapidly as possible and the tidal volume (VT) during the manoeuvre should be greater than the subject's resting VT.

The test interval (e.g. 12 s) should be reported. A rest between manoeuvres will improve subsequent efforts.

The MVV should be calculated from the sum of all individual exhalations, multiplied by the appropriate BTPS correction factor during the best 12 s of the manoeuvre. From a technical standpoint, changes in respiratory rate or VT during the manoeuvre will influence test results.

Within-manoeuvre evaluation

In normal subjects, the goal for an acceptable MVV should be a VT that is ∼50% of the VC, with a breathing frequency that is ∼90 breaths·min−1 54. It is unlikely that an acceptable manoeuvre will be obtained when the breathing frequency is <65 breaths·min−1 54. However, since there are little data on MVV acceptability criteria, no specific breathing frequency or volume is required. The emphasis should be on maximal effort with a goal of 90 breaths·min−1 and a volume representing ∼50% of the VC. VT during the manoeuvre is probably not as important as breathing frequency, since patients tend to breathe on the portion of the expiratory curve where air is best moved at a given frequency.

Between-manoeuvre evaluation

The subject should perform a minimum of two acceptable manoeuvres. There are no clinical studies addressing repeatability; however, additional trials should be considered when the variability between acceptable manoeuvres exceeds 20%.

Test result selection

The highest acceptable MVV (L·min−1 BTPS) and MVV rate (breaths·min−1) should be reported. An MVV/(40×FEV1) <0.80 indicates that the MVV is low relative to the FEV1, and suggests disease or poor effort. Volume versus time tracings from at least two acceptable manoeuvres should be retained and available for inspection.


Minimal recommendations for spirometry systems

Accurate results require accurate equipment. Spirometer equipment recommendations apply to all spirometers and are minimal requirements. In some circumstances, it may be appropriate to exceed these requirements (i.e. in some research/surveillance applications). Instrumentation recommendations should be followed to provide accurate spirometric data and information that is comparable from laboratory to laboratory and from one time period to another 1. The accuracy of a spirometry system depends on characteristics of the entire system, from the volume or flow transducer and the use of an in-line filter, to the recorder, display or processor. Changes in any aspect of the equipment or errors at any step in the process can affect the accuracy of the results. For example, if the BTPS correction factor is wrong, an accurately measured FVC will be incorrectly reported.

Spirometers and PEF meters are not required to measure all of the indices in table 6, but must meet the recommendations for those that are measured. Accuracy and repeatability recommendations apply over the entire volume range of the instrument.

BTPS correction

All spirometry values should be reported at BTPS by any method (measuring temperature and barometric pressure) proven effective by the manufacturer. For volume-type spirometers, the temperature inside the spirometer should be measured for each breathing manoeuvre. Regardless of the BTPS correction technique used, the ambient temperature must always be recorded with an accuracy of ±1°C. In situations where the ambient air temperature is changing rapidly (>3°C in <30 min), continuous temperature corrections may be necessary. Spirometer users should be aware of potential problems with testing performed at lower ambient temperatures: 17°C is the lower limit 5563 for ambient temperature, unless a manufacturer states that their spirometer will operate accurately at lower ambient temperatures. If barometric pressure is not used in calculating the BTPS correction factor, the range of barometric pressures over which the BTPS correction factor is valid must be published by the manufacturer.


The rationale for this recommendation is based, in part, on the problems with finite cooling times of gases in volume-type spirometers 5557 and the problems of estimating BTPS correction factors for flow devices 5860. When a subject performs an FVC manoeuvre, the air leaving the lungs is ∼33–35°C 61, 62 and saturated with water vapour. If the expired gas is assumed to be at BTPS, an error of ∼1% will result. Most volume-type spirometers assume instantaneous cooling of the air as it enters the spirometer. This is not always the case, and FEVt can be incorrectly reported because of it. For capillary and screen pneumotachometers, the signal depends on gas viscosity, which increases with increasing temperature. Therefore, for pneumotachometers, a different correction factor is needed for recording patients as compared with recording from the calibrating syringe. Also, correction factors will be different for inspiratory and expiratory manoeuvres. It is usually assumed that expired gas does not cool as it passes through the flow sensor. This may not be the case, particularly with unheated flow sensors 58, 59. The error will increase if the flow sensor is located further from the mouth and more cooling occurs, as is the case when a filter is placed in front of the flow sensor. Water condensation within or on the surfaces of a flow sensor may alter its calibration.

Depending on environmental temperature, the BTPS correction factor may be as large as 10%. The method used to calculate or estimate the BTPS factor can potentially introduce significant errors; examples and a fuller explanation can be found elsewhere 3, 4.

Changes in spirometer temperature can be a source of variability. Spirometer temperature should be measured and not assumed to be constant, even over the course of one testing session. For volume spirometers, errors up to 6% in FEV1 and FVC can occur if ambient temperature is used instead of internal spirometer temperature 64. For volume spirometers, the temperature inside the spirometer should be measured for each breathing manoeuvre.

Test signals for spirometer testing

The diversity of FVC manoeuvres encountered in clinical practice is currently best simulated by the 24 standard volume–time waveforms developed by the ATS 3 and Hankinson and Gardner 65. These waveforms can be used to drive a computer-controlled mechanical syringe, or its equivalent, for testing actual hardware and software 66, 67, or, when put in a digital form, they can evaluate only the software. Computer-controlled mechanical syringes (i.e. pump systems) used for validation should be accurate within ±50 mL, which is 0.5% of their full range up to 10 L for FVC and FEV1. Pump systems may have accuracy values better than this for many profiles, but reproduce less accurately those test profiles with short DTs and RTs to peak flow 68, 69. The ATS spirometry statement 3 shows the measured values for each of the 24 standard waveforms. On request, the ATS can provide these waveforms in an electronic format. Appropriate corrections for using gas at the ambient temperature and humidity instead of BTPS may need to be made for some mechanical syringe–spirometer combinations.


A production spirometer is connected to the pump system for testing, orientated as it would be to test human subjects. Connecting tubing must be kept to the minimum (<0.300 L) and must not be distensible. If an in-line filter is required for testing human subjects, one must be included when the instrument is tested. Each of the 24 ATS waveforms is discharged into the spirometer five times under ambient conditions, and all of the readings are recorded.

BTPS conditions are simulated by discharging waveforms 1–4 to the spirometer three times, using air heated to 37±1°C and at >98% relative humidity. The time between each of the three tests should be <2 min.

Accuracy test

The average of the five tests under ambient conditions is compared with the standard value in the following way: FormulaFormulaThe accuracy validation limits for volumes, which include the waveform-generator inaccuracy, are ±3.5% of reading or ±0.100 L, whichever is greater. An accuracy error occurs if the deviation (for volumes <2.857 L) or percentage deviation (for volumes >2.857 L) exceed these limits. These limits include the allowable inaccuracy of the pump system.

Acceptable spirometer performance is defined as fewer than three accuracy errors for either FVC or FEV1 across the 24 waveforms (<5% error rate).

The average FVC and FEV1 values of the three tests simulating BTPS conditions are compared with the standard values. The validation limits for these tests under BTPS conditions are ±4.5% or 0.200 L, whichever is the greater, and these limits include the allowable inaccuracy for the pump system.

Acceptable spirometer performance under BTPS conditions is defined as the accuracy requirement being met for all of the four profiles used.

Repeatability test

The FEV1 and FVC data from the accuracy test are used to derive the span of the five recordings: FormulaFormulaThe repeatability validation limits for the volume measured at ambient conditions are ±3.5% or ±0.100 L, whichever is the greater, and, for BTPS conditions, ±4.5% or ±0.200 L, whichever is the greater. A repeatability error occurs if the span (for volumes <2.857 L at ambient or 4.444 L at BTPS) or percentage span (for volumes above this) exceeds these limits.

Acceptable spirometer performance for repeatability under ambient conditions is defined as fewer than three accuracy errors for either FVC or FEV1 across the 24 profiles (<5% error rate). For BTPS conditions, the acceptable spirometer performance for repeatability is defined as the accuracy requirement being met for all of the four profiles.

Test signals for PEF meter testing

The 26 flow–time ATS waveforms were chosen to represent a range of PEF profiles suitable for delivery by mechanical syringe or pump systems to test PEF meters 3. The range of profiles and method of delivery may need to be revised, as research on PEF measurement continues 45. The mechanical syringe or suitable pump system used to validate PEF measuring equipment must have an accuracy of ±2% in delivering PEF. Pump systems may have difficulty meeting this accuracy standard for profiles more demanding than the set of 26 68, 69. Recent evidence suggests that the frequency content in the first second of the blow that contributes to PEF is higher 47 than previously determined 70, 71. The 26 waveforms may not cover the range of RT and DT found in ∼25% of the client population 72, and, hence, more demanding test profiles may be required in future 45.


Two randomly chosen production models of the flow meters should each have the 26 waveforms delivered to them five times under ambient conditions and the readings recorded. Any waveforms with a PEF outside the meter's stated operational range would not be included in the testing sequence. Appropriate correction factors for testing under ambient conditions should be applied as recommended by the manufacturer.

Accuracy test

The average reading for each of the two meters is compared with the standard, as for volumes.

The accuracy validation limits are ±12% or ±25 L·min−1, whichever is the larger, and these limits include the 2% inaccuracy limit for the waveform generator. An accuracy error for a given meter and given waveform occurs if the deviation and percentage deviation exceed these limits.

Acceptable performance is defined as fewer than three accuracy errors out of the total of 52 tests (26 waveforms, two meters).

Repeatability test

Flow waveforms 1, 4, 8 and 25 are discharged three times to each of 10 production meters. The repeatability validation limits are ±6% or ±15 L·min−1, whichever is the greater, and these limits include 1% for waveform-generator variability. A repeatability error occurs if the span and percentage span exceed these limits.

Acceptable performance is defined as six or fewer errors in the 120 tests (i.e. maximum error rate of 5%).

Test signals for MVV testing

A spirometry system used to measure MVV should be tested under ambient conditions with a pump producing a sinusoidal waveform, with stroke volumes up to 2 L using the four patterns of delivery previously specified 3. Testing at BTPS is not required, and each pattern is tested twice. The accuracy validation limits of the spirometer used for measuring MVV with flows up to 250 L·min−1 are ±10.5% of reading or ±20 L·min−1, whichever is greater. The pressure at the mouthpiece must not exceed ±10 cmH2O (1 kPa) at any point during MVV testing. These requirements apply to volume spirometers throughout their volume range.

Acceptable performance is defined as no errors in the eight tests (four patterns, twice).


Table 7 contains a list of abbreviations and their meanings, which will be used in this series of Task Force reports.

Fig. 1—

Spirometry standardisation steps.

Fig. 2—

Expanded version of the early part of a subject's volume–time spirogram, illustrating back extrapolation through the steepest part of the curve, where flow is peak expiratory flow (PEF), to determine the new “time zero”. Forced vital capacity (FVC) = 4.291 L; back extrapolated volume (EV) = 0.123 L (2.9% FVC). -----: back extrapolation line through PEF.

Fig. 3—

Flow chart outlining how acceptability and reapeatability criteria are to be applied. FVC: forced vital capacity; FEV1: forced expiratory volume in one second.

Fig. 4—

Flow–volume loop of a normal subject.

Fig. 5—

Flow–volume loop of a normal subject with end expiratory curvilinearity, which can be seen with ageing.

Fig. 6—

Moderate airflow limitation in a subject with asthma.

Fig. 7—

Severe airflow limitation in a subject with chronic obstructive pulmonary disease.

Fig. 8—

Variable intra-thoracic upper airway obstruction.

Fig. 9—

Variable extra-thoracic upper airway obstruction.

Fig. 10—

Fixed upper airway obstruction shown by three manoeuvres.

Fig. 11—

Tracing of tidal breathing followed by an expiratory manoeuvre to residual volume (RV), followed by a full inspiration to total lung capacity (TLC) to record inspiratory vital capacity (IVC) and inspiratory capacity (IC). FRC: functional residual capacity; ERV: expiratory reserve volume.

Fig. 12—

Tracing of tidal breathing followed by an inspiratory manoeuvre to total lung capacity (TLC) to record inspiratory capacity (IC), followed by a full expiration to residual volume (RV) to record expiratory reserve volume (EVC). FRC: functional residual capacity.

View this table:
Table. 1—

Indications for spirometry

View this table:
Table. 2—

Recommended minimum scale factors for time, volume and flow on graphical output

View this table:
Table. 3—

Summary of equipment quality control

View this table:
Table. 4—

Procedures for recording forced vital capacity

View this table:
Table. 5—

Summary of within- and between-manoeuvre acceptability criteria

View this table:
Table. 6—

Range and accuracy recommendations specified for forced expiratory manoeuvres

View this table:
Table. 7—

List of abbreviations and meanings

View this table:
Table. 8—

List of parameters#


Rationale for proposing a standard data format for spirometry

This proposal would not preclude the use of other data formats, but would require that a spirometer should at least be able to output data in the required format. The advantage of a standard format is the ease of moving data into data repositories, such as quality control, healthcare and research databases. It should simplify and reduce the cost of data transfer when users change instrument models and manufacturers. Easier transfer of data into healthcare databases has the potential for improving the utility of lung function by making more complete data readily available to clinicians and healthcare researchers. In research and clinical settings, a standard data format should simplify and reduce the cost of transferring data into quality control software and could contribute to improved overall test quality. Finally, it is time for this change; pulmonary function is one of the last medical arenas without a standard data format.

Proposed format

The spirometry data file will consist of an American Standard Code for Information Interchange, comma-delineated file with variable length records. Comma-delineated text files are easily generated and are standard import formats for several database programs. Although some redundancies will exist, each record shall represent one curve and will be terminated with a carriage return and line feed.

Table 8 shows a list of parameters that must be included in every record. If a parameter is unavailable, the space must remain blank ( “,,”). The flow–time data points must be provided with a sampling interval of 0.01 s (100 samples·s−1) in mL·s−1. If necessary, interpolation or other techniques must be used to provide the 0.01-s sampling interval. The record length will vary, depending on the number of data points present in the flow–time portions of the record. The curve data must include ≥0.25 s of data points prior to the onset of the inspiratory or expiratory manoeuvre.

Volume–time curves may be calculated by adding the flow–time values (mL·s−1) and multiplying the sum by 0.01 s. To obtain the highest precision, the sum of the flow values should be calculated for each volume data point before multiplying by 0.01 s.

#: All text type variables should be enclosed with double quotes (“) to prevent confusion with control or data separator type characteristics.


M.R. Miller: University Hospital Birmingham NHS Trust, Birmingham, UK; J. Hankinson: Hankinson Consulting, Inc., Valdosta, GA, USA; V. Brusasco: Università degli Studi di Genova, Genova, Italy; F. Burgos: Hospital Clinic Villarroel, Barcelona, Spain; R. Casaburi: Harbor UCLA Medical Center, Torrance, CA, USA; A. Coates: Hospital for Sick Children, Toronto, ON, Canada; R. Crapo and R. Jensen: LDS Hospital, Salt Lake City, UT, USA; P. Enright: 4460 E Ina Rd, Tucson, AZ, USA; C.P.M. van der Grinten: University Hospital of Maastrict, Maastricht, the Netherlands; P. Gustafsson: Queen Silvias Children's Hospital, Goteborg, Sweden; D.C. Johnson: Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA; N. MacIntyre: Duke University Medical Center, Durham, NC, USA; R. McKay: Occupational Medicine, Cincinnati, OH, USA: D. Navajas: Universitat de Barcelona - IDIBAPS, Barcelona, Spain; O.F. Pedersen: University of Aarhus, Aarhus, Denmark; R. Pellegrino: Azienda Ospedaliera S. Croce e Carle, Cuneo, Italy; G. Viegi: CNR Institute of Clinical Physiology, Pisa, Italy; J. Wagner: Pharmaceutical Research Associates, Inc., Lenexa, KS, USA.


  • Previous articles in this series: No. 1: Miller MR, Crapo R, Hankinson J, et al. General considerations for lung function testing. Eur Respir J 2005; 26: 153–161.

  • Received March 23, 2005.
  • Accepted April 5, 2005.


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