Sufficient space is required to be able to position the patient comfortably, taking into account that it may be necessary to handle a wheelchair. Therefore, the minimum recommended space is 2.5×3m, with 120cm wide doors. In laboratories where spirometry can be performed in decubitus, the size of the area should allow positioning of a hospital bed.19 The spirometer should be placed on a table or countertop which allows the technician to work in various positions with respect to the patient. The space should have sufficient storage for all the material.

A certified stadiometer and scales are essential. A thermometer, barometer and hygrometer, which must pass regular accuracy or calibration checks, are required in equipment that does not incorporate these devices.

There are 2 broad classes of spirometers: closed circuit and open circuit. Within the closed spirometers are wet and dry spirometers, consisting of an air collection system which may be either a piston (chamber containing a moveable plunger) or bellows (more manageable) and a recording system mounted on a support that moves at the desired rate. Most modern spirometers can also derive the flow value from the volume measured.

The most widely used spirometers at present are those known as open systems, as they do not have a hood or similar recipient to collect the air.9,20 These measure the air flow directly and, integrating the signal, calculate the volume. There are different systems, but the best known are pneumotachographs, which measure the difference in pressure generated on passing a laminar flow through a known resistance. Most equipment currently uses a resistance, either metallic and heated to prevent condensation, or made of synthetic tissues. Since the head transforms the turbulent flow that passes through into a laminar flow, the pressure difference between the ends of the pneumotachograph is directly proportional to the flow. A pressure transducer transforms the differential pressure signal into an electrical signal, which is then amplified and processed. The electronic integration of the flow value provides the volume moved.6

There are other open systems that use other principles.2,20 The most widely used at present is the turbine flow metre, which is based on the fact that the rate at which the blades turn, recorded by optical sensors, is proportional to the flow that passes through the device.20 Hot wire spirometers, or thermistors, have a metal wire in their head (generally platinum) heated to a constant temperature by an electric current. As the air flow passes, the wire cools and the flow is calculated. Ultrasound spirometers are based on one of these properties, so that when they form a certain angle with the direction of the flow, the ultrasounds that go in the same direction as the flow take less time to reach the receptor than those that go in the opposite direction. The greater the time difference the higher is the flow.20 The choice of equipment depends on the type of use, but can also vary depending on other circumstances, such as technological development or the cost. Closed systems can generally be considered more reliable, as they are precise and accurate over a range of volumes, but they also have the disadvantage of being larger, have more inertia and are more expensive. One of their major problems is difficulty in cleaning and sterilisation.21

The open systems, however, are easy to clean and have a very low risk of contamination.21 They are precise and accurate, once the necessary adjustments have been made, but require verification of satisfactory calibration and measurement conditions. Although turbine spirometers were initially blamed for non-linearity problems in the response and a certain degree of inertia, extremely reliable turbine spirometers are available today.20 To these characteristics we can add their stability, little or no need for calibration (although this should be checked regularly), ease of cleaning and low price. Furthermore, disposable turbines have recently been marketed.

On presenting in the laboratory, patients should bring (or it should be listed in the electronic diary) a referral slip with the required tests. When the appointment is made, they should be given written instructions which state the guidelines for withdrawal of bronchodilators (Table 4), as well as the importance of abstaining from smoking or doing any physical exercise in the hours prior to the test.

Before beginning the examination, the test should be explained to the patient, stressing the importance of their collaboration. They should also be asked about the withdrawal of drugs, possible contraindications or infectious diseases that require special measures (in which case it is recommended that the spirometry be postponed until the end of the day, just before cleaning the equipment, and that antimicrobial filters are used).

The patient should be measured barefoot with their back placed firmly against the stadiometer, weighed wearing light clothing and asked their date of birth to calculate their age on the day on which the test is performed. In the case of chest deformities, the span should be measured (crossed arms from middle finger to middle finger), estimating the height from the following ratio: height=span/1.06.25 Another possibility is to use the equations proposed by Parker et al.,25 which are valid for different ethnic groups.

The test should be performed with the individual sitting upright, without crossing their legs or wearing tight-fitting clothing. In the case of children, it can be performed either sitting or standing, noting the way in which it is carried out and always using the same procedure for the same individual. During the manoeuvre, the back must be supported on the backrest, ensuring that the patient does not lean forward while performing the test. Dentures do not need to be removed, unless they make it difficult to perform the manoeuvres.

The use of a nose clip in forced spirometry is controversial, although it is essential for measuring the VC, to prevent possible leakage due to nasal respiration. Although some authors have not identified differences between manoeuvres carried out with or without a nose clip,26,27 their use is recommended in adults.9

Before beginning the examination, check that the calibration has been verified on the day of the test. If a meteorological station incorporated in the equipment is used, the atmospheric pressure, humidity and ambient temperature should be entered or verified.

Before beginning, the subject must be given precise, clear and concise instructions. After placing the mouthpiece in the mouth, checking that there are no leaks and that the patient is not obstructing or bending it, ask him/her to: a) breathe in as much air as he/she can with a pause at the total lung capacity (TLC) for less than 1s28; b) blow hard and fast and c) prolong the following expiration without stopping until told to do so. In cases in which only the forced expiration is to be measured or there are no antibacterial filters, the patient should insert the mouthpiece after step (a) and try not to breathe from the tube. The technician must monitor the patient and watch the manoeuvre being performed. If defects are noted that could alter it, stop the manoeuvre so as not to tire the patient and correct them. If inspirometry is also to be performed, ask the patient to breathe in deeply until TLC without removing the mouthpiece from the mouth. In the case of children, using graphic incentives is useful for achieving better cooperation, especially in the time and volume of the manoeuvre, in addition to performing a test manoeuvre beforehand.29

To perform slow spirometry, tell the patient that they must: a) breathe calmly through the mouthpiece, at least 3 breaths to verify that the baseline (functional residual capacity [FRC]) is stable; b) breathe in until TLC, and c) blow slowly until the residual volume (RV). Alternatively, a slow expiration may be performed until RV, before the inspiration until TLC, which usually facilitates the manoeuvre in the case of air trapping. A nose clip should always be used in slow spirometry, to prevent possible air leaks on breathing through the nose. A minimum of 3 manoeuvres should be performed, separated by 1min.7

The decision on whether a forced spirometry manoeuvre can be considered acceptable must take into account its start, course and completion.

• 1.

  The start must be rapid, without hesitation. The main criterion for a proper start requires a back extrapolated volume (BEV) less than 0.15l or 5% of the FVC (0.08l or 12.5% FVC in pre-school children).29,30 As an additional criterion to assess the start of the manoeuvre, the time to reach the peak expiratory flow (PET) can be used; this must be less than 120ms2. If it is greater, tell the patient to blow faster at the start.

• 2.

  The course of the expiratory manoeuvre should be continuous, without any artefacts or evidence of coughing in the first second that could affect the FEV1. To verify this, both the volume-time and the flow-volume graph should be monitored. If the course of the manoeuvre is not incorrect, generally due to coughing or excessive pressure and closure of the glottis, ask the patient to repeat it in a more relaxed manner (while continuing to blow hard) and not to reduce the force generated until the end of the expiration.

• 3.

  The end of the manoeuvre must not show early or abrupt interruption of the expiration, so volume changes must be less than 0.025l for ≥1s. The final “plane” of the manoeuvre is only seen in the volume-time curve. The manoeuvre should last at least 6s. Young adults may have difficulty in maintaining the expiration for more than 4s, sometimes less. In these cases, verify that the end has not been abrupt. In children under 6 years of age, a duration of at least 1s should be attempted; between 6 and 8 years, it should be equal to or greater than 2s,30 and between 8 and 10 years, to 3s.29 In the case of a poor ending, ask the patient not to stop until told to do so, even though it seems that there is no output of air.

The equipment usually indicates if any of the errors detailed occurs. A manoeuvre will be considered useful (the spirometric parameters can be derived from it) when it has a good start and there are no artefacts in the first second. It will be considered acceptable (the errors must be taken into account to determine whether the spirometric parameters obtained can be used) when there are no errors at the start, during or at the end of the test.

The circumstances that most often cause incorrect manoeuvres are:

• -

  Lack of or incorrect calibration/verification, or environmental data.

• -

  Poor patient preparation, with non-compliance with pharmacological and non-pharmacological recommendations.

• -

  Poor instructions by the technician, before and during the manoeuvre.

• -

  Early completion of the expiration (expiration time less than required, excessive final flow or abrupt end-of-test morphology); slow, hesitant start; presence of coughing or glottic closure during the manoeuvre; or air leakage during the forced expiration.

• -

  Poor patient collaboration. If the patient does not improve, after advising them that good manoeuvres cannot be obtained without their cooperation, this should be indicated along with the results.

The difference between the best two acceptable VC, IC, FVC and FEV1 should be less than 0.15l. In patients with FVC less than 1l, a repeatability criterion <0.10l is recommended.9 In children, 2 manoeuvres will be considered repeatable when the difference in the FVC and FEV1 is <0.10l or <10%. A minimum of 3 acceptable manoeuvres should be carried out, with a maximum of 8, leaving sufficient time between them for the patient to recover their strength. In children, a minimum of 2 acceptable manoeuvres is considered sufficient, with no recommended maximum.

The largest VC, IC, FVC and best FEV1 should be selected from all the acceptable manoeuvres with no artefacts, even if their values do not come from the same manoeuvre. The rest of the parameters should be obtained from an acceptable curve where the sum of the FVC and FEV1 values reach their maximum value (Fig. 1).

Fig. 1.

Flow diagram for the application of acceptability and repeatability criteria. Adapted from Miller et al.9

(0.17MB).

At present, almost all spirometers incorporate mathematical algorithms that allow the quality of the manoeuvre to be evaluated automatically, selecting the best manoeuvre performed. Despite their usefulness, it is recommended that the technician is the one who verifies that the selection is correct or selects the best results manually.

The use of a grading system has been proposed to assess the quality of the spirometry depending on the number of acceptable manoeuvres and the repeatability of the FEV1 and FVC (Table 5).9,31,32 Spirometries with grade A and B are considered good quality, and grade C of sufficient quality. Grade D spirometries and higher are not valid for interpretation. This quality classification has been shown to be useful in both epidemiological studies and in clinical practice, having been implemented automatically in some spirometers and referenced in many publications.2,23,31,33

Nevertheless, it should be taken into account that in around 10%–20% of cases, it is not possible to achieve good quality manoeuvres despite the technician's best efforts and good patient cooperation.31,33

The parameters for lung function tests have large interindividual variability, and depend on the patients’ anthropometric characteristics (sex, age, height, weight and race). Spirometry interpretation is based on comparing the values produced by the patient with those that would theoretically correspond to a healthy individual with the same anthropometric characteristics. This theoretical or reference value is obtained from prediction equations.34

In general, it is advisable to use the set of prediction equations that best fits the particular area. Nevertheless, the most usual procedure is to select equations closest to the patient population (in our case the Spanish population); in this respect, the previous SEPAR guidelines recommended those of Roca et al.1,35,36 However these equations do not have sufficient subjects over 70 years of age and, therefore, introduce bias in their interpretation. Moreover, there is a large and growing population of patients eligible for spirometry over this age, or of non-European ancestry. García-Río et al.37 recently published equations for the 65–85 year range, which allow this age group to be properly covered.

These guidelines recommend using the reference values of Casan et al.35 for children (range 6–20 years), those of Roca et al.36 for adults (range 20–65 years) and those of García-Río et al.37 for elderly patients (range 65–85 years) (Table 7). These reference equations should only be used in Caucasian subjects.

In 2012, new multiethnic reference equations were published for the 3 to 95 year age range, using 97 759 spirometries from 72 centres in 33 countries.38 This could have great future impact, both due to the number of subjects included in the equations and the wide age range, as well as the fact that they can be applied to different ethnicities. However, comparisons have not been made with the values traditionally used in Spain, although they undoubtedly raise great expectations for reaching international harmonisation.

The type of bronchodilator, dose and time of measuring the effect influence the response obtained. The use of short-acting β2-adrenergic agonists (SABA) or ipratropium bromide9 is recommended, although the onset of action of formoterol is also sufficiently rapid to be used.68 Although there is a small group of asthmatic patients who respond better to ipratropium,69,70 the bronchodilator effect of SABA is usually greater than the effect of ipratropium in these patients.69-71 However, in many patients diagnosed with COPD, ipratropium bromide is more effective,69,72 and the combination of a SABA and ipratropium bromide is even more so.73,74

Except in some circumstances, such as known arrhythmias, tremor or previous adverse reaction, where it is preferable to administer lower doses, the administration of 400μg of salbutamol in 4 puffs (100μg per puff) separated by 30s intervals is recommended. If ipratropium bromide is used, a total dose of 160μg (8×20μg) should be given. In both cases, it is preferable to use pressurised cartridges with a spacer device, following the correct technique. The administration of terbutaline, both in a pressurised cartridge and as a dry power, may be an alternative to salbutamol. The use of high doses, such as those mentioned, almost always ensures that the bronchodilator effect is close to the maximum area of the dose-response curve, thus minimising the variability due to the distribution of aerosol and the patient's technique.9,75,76

Fifteen minutes after the inhalation of salbutamol, or 30min after the inhalation of ipratropium bromide, a second series of spirometric manoeuvres should be performed, following the same quality and repeatability criteria as stated above.9 The administration of both drugs, measuring the response at 30min, increases the proportion of patients with COPD who have a positive bronchodilator test.77 There is no evidence that indicates the sequence in which both drugs should be administered, or if they should be given consecutively or separated by an interval.69

The bronchodilator can be administered by any of the usual means (nebuliser, pressurised cartridge, dry power inhaler). Each laboratory must standardise the procedure and know the system characteristics and drug deposition in the airways. These guidelines recommend performing the bronchodilator test with a short-acting β2-adrenergic agonist, at doses equivalent to 400μg of salbutamol in a pressurised cartridge with a spacer device.19 The administration of a short-acting β2-adrenergic agonist and ipratropium bromide could increase the sensitivity of the test, particularly in patients with COPD.73,73,77 If so, this must be noted in the report.

The 3 most common indices for evaluating the bronchodilator response are the percentage change over the baseline value,78–80 the percentage change over the predicted value30,74 and the absolute change.79,80 An improvement in the FEV1 or in the FVC ≥12% and ≥0.2l is recommended as a reversibility criterion,63,81 due to its greater sensitivity. The expression of the change as a percentage of the predicted value normalises the result for gender, initial FEV1 and age, and eliminates the mathematical bias (the lower the baseline FEV1, the greater the percentage response),23,58,82 but it is less sensitive,49,59,83 especially in patients with more impaired function.59 In patients with emphysema, the FVC has been shown to be more sensitive than the FEV1,84,85 and its response appears to be better correlated with the clinical changes and tolerance to effort in patients with hyperinflation.84–88

The use of the FEF25%-75% or instantaneous flows is not recommended for assessing reversibility. Although it has been reported than an increase of 20% in the PEF may be indicative of reversibility,89,90 its use is not recommended either for the assessment of reversibility in lung function laboratories, or when the reversibility test is performed for diagnostic purposes.

In many patients with airflow limitation, in whom the FEV1 or FVC does not improve significantly, a significant increase in the IC has been observed however,75,88,91,92 and shows a better relationship with the clinical improvement and the effort capacity than changes in the FEV1.86–88,93,94 Therefore, an increase in the IC of 10% with respect to the previous value has also been proposed as a reversibility criterion.75 Nevertheless, this significant response criterion is not sufficiently proven to be recommended for general use.

Reversibility is a characteristic of asthma, and therefore the reversibility test is useful and is indicated in all patients with suspected asthma.63,89,95,96 However, the absence of significant reversibility does not permit the diagnosis of asthma to be ruled out.63,89,95,96

The response to bronchodilators cannot differentiate between COPD and asthma,43,97 although improvements of more than 0.4 l suggest asthma,97 or at least a mixed phenotype.98 One concept that has changed in recent years, in the wake of large clinical trials, is that the presence or absence of bronchodilation does not appear to predict symptomatic relief, changes in exercise capacity or long-term response to corticosteroids or bronchodilators with sufficient accuracy,59,99 so the bronchodilator test does not have any value as a treatment guide. It has been found that the reversibility is associated with an accelerated decline in the FEV1,100 but not all studies confirm this association.

There are spirometers currently on the market that can be used in both the specialised care and “office” setting.2,101–104 Their main advantages lie in the lower cost and smaller size, although some of their characteristics can present limitations for their widespread use.105–107 The general requirements for this equipment are as follows2,108,109:

• 1.

  Office spirometers “may” only provide FEV1, FEV6and FEV1/FEV6ratio values. The use of FEV6 has several advantages16,110: a) it is easier for the patient and technician when the manoeuvres only last 6s; b) it avoids technical problems with flow sensors related with precision, as it has to measure very low flows; c) the FEV6 is more repeatable than the FVC in patients with airway obstruction, and d) using the FEV6 reduces the total time for performing the test. One limitation, however, is the existence of fewer reference values than for the FVC and the possibility of underestimating the patient's real capacity.45 The existence of obstruction is identified when the FEV1/FEV6 and FEV1 are below their LLN.

• 2.

  Quality standards in the manoeuvre. Many of the basic standards for assessing the reliability of the signals2,111,112 are already included in these devices. It is important that additional checks can be made to evaluate the acceptability of the manoeuvres in spirometers that do not have curve printing or display. The spirometer should show the quality control criteria, which should be monitored electronically, together with messages when errors are detected. The devices must present the spirometry results in numerical values, and they should only be interpreted if all the manoeuvres meet the quality criteria.

• 3.

  The existence of screens and graphs of the flow-volume curve may be optional. Graphic expression of the spirometry implies the possibility that the technicians who perform the test, as well as the physicians who interpret the results, can recognise if there are problems with respect to the quality of the test.113 However, a graphics screen increases the size, cost and complexity of spirometers, reducing their acceptance in the primary care setting. Most office devices do not show the flow-volume curve or the volume-time curve during the manoeuvre.107

• 4.

  Materials explaining the operation of office spirometers should be easy to understand. These materials should include standard operating procedures, audiovisual training aids (such as a video tape or multimedia CD-ROM), documents describing the potential risks and benefits of the spirometry, as well as the interpretation of results and limitations of the test.

• 5.

  There should be economic solutions that can replace the daily use of 3 l calibration syringes.2,109 Biological controls are recommended and in this case, the range of repeated measurements of FEV1 and FEV6 every 10 days should not exceed 10% of the mean. Most manufacturers state that their portable devices do not have to be calibrated before performing the measurements. Although this is a potential advantage, it is reasonable to say that periodic calibration or checking of portable spirometers, daily if possible, is vitally important for demonstrating the stability of the measurements.

• 6.

  The parameters should be corrected to BTPS conditions. The device should detect the temperature automatically, making an automatic correction to BTPS units (Appendix 2).

• 7.

  Hygiene measures. Personnel performing spirometries should be instructed in correct hand-washing techniques before and after attending each patient. The use of disposable mouthpieces is sufficient to minimise the risk of transmission of infections. The use of filters fitted to the mouthpiece is not mandatory, provided that the patient only performs the forced manoeuvre and does not inhale from the apparatus.

In short, office spirometer manufacturers should focus particularly on improving the precision of FVC measurements, calibration problems and the ability to show flow-volume and volume-time curves, in order to evaluate the quality of the manoeuvres. Although the software in portable spirometers allows the expression of volumes and flow measured as a percentage of the predicted value, it is essential that the user has the possibility of using reference values that correspond to the characteristics of the patient population studied (Table 11).

In addition to maximal expiratory flow metres,114 the development of pocket spirometers provides systems that incorporate measurements such as the FEV1 and FEV6.115 Their use is recommended for home monitoring of various diseases, such as asthma, but not as a diagnostic method. The advantage of these spirometers lies in that these are simple, safe and portable devices that are normally cheap. However, compared with standard spirometry, they are relatively insensitive for detecting mild obstruction and measure parameters that are very dependent on the effort, with greater variability, which, in the case of an abnormal study, requires these findings to be confirmed using a conventional test.

In recent years, information and communication technologies applied to the healthcare setting have undergone major development. The new systems, usually installed in both primary care centres and in hospitals, store patient prescriptions in a single point and allow the exchange of information. According to Spanish law, it is illegal to have databases on equipment that do not comply with Spanish Organic Law 15/1999, of 13 December, on Protection of Personal Data. This issue must be raised with managers and manufacturers before acquiring new equipment. In the healthcare setting, in order to facilitate the integration of the applications, various standards have been developed, such as XML, DICOM or HL7.116 These standards were born from the need to link the various peripheral healthcare systems, which are increasingly computerised, with a single central system that allows a patient's common record to be held, thus obtaining better flow of information and more security throughout the process.

There is a growing demand for integrating the information obtained in the spirometry in documents that use intraoperative formats (such as HL7 or CDA R2) to have access to the patient's spirometry history through the electronic medical record. The definition of these standards is essential for ensuring that they are adopted by spirometer manufacturers.117 Using this process, bases are set up to facilitate access to the spirometry from all the care settings, and in turn it is a fundamental technical element for designing quality control programmes for the examinations.118

The use of these technologies enables the reports to be shared via information systems, and also allows the physician to see the spirometry digitally from his or her work station, and to access the test history for each patient. To complete this process, office spirometers must also have the ability to send the data obtained, to operate not as an isolated element, but integrated in a common operating system. Once a spirometer has a digital information output, its form of integration can vary, with different studies carried out in recent years (web-based system, TechEd's network, telephone support or discs).119-122