Spirometry in Pc

primary health care | Vol 18 No 10 | December 2008 37

Spirometry in primary carePHC180 Booker R (2008) Spirometry in primary care. Primary Health Care. 18, 10, 37-47. Date of acceptance: August 7 2008.

continuing professional development

SummaryAn evaluation of lung function is an essential part of the diagnosis and management of respiratory disease but spirometry was, until recently, rarely available in primary care. The emphasis in national chronic obstructive pulmonary disease (COPD) and asthma guidelines on spirometry for diagnosis and monitoring, together with its inclusion in the quality and outcomes framework (QOF) for COPD in the General Medical Services contract, has led to its wider availability in this setting. Spirometry is a relatively easy test, but is unreliable and confusing if not performed and interpreted correctly.

AuthorsRachel Booker RGN, DN (Cert), HV is an independent specialist respiratory nurse and freelance medical writer

KeywordsRespiratory system and disorders; Spirometry; Primary care

These keywords are based on the subject headings from the British Nursing Index. This article has been subject to double-blind review. For related articles and author guidelines visit our online archive at www.primaryhealthcare.net and search using the keywords.

Aims and learning outcomes

This article aims to describe the types of spirometry equipment suitable for use in primary care, their correct maintenance and use, and how to obtain reliable, technically acceptable recordings from patients. The essential parameters of lung function are defined and the effect of various types of ventilatory defect on these parameters explained.

After studying this article you will be able to:Review the types of spirometer }}available and discuss their usefulness in various healthcare settings.Describe spirometer maintenance and }}infection prevention procedures.Summarise the indications and }}contraindications for spirometry.Identify the main parameters of lung }}function measured with a spirometer and discuss the determination of

reference values for these parameters in various patient groups.Describe spirometry procedures and }}evaluate the technical acceptability of a patient’s spirometry reading.Identify the typical spirometry }}readings associated with the more common respiratory conditions.

The first spirometer, invented by John Hutchinson, a 19th century surgeon, consisted of a calibrated bell inverted in water. Air, exhaled from fully inflated lungs, was captured in the bell, and Hutchinson termed this volume the ‘vital capacity’, theorising that its reduction was associated with reduced life expectancy. It was 150 years before his ideas gained credence. A large epidemiological study (Kannel et al 1980) demonstrated that reduced vital capacity is a powerful predictor of premature death from respiratory and cardiac disease and a further study found that abnormal spirometry is associated with an increase in ‘all cause’ mortality (Hole et al 1996).

Despite evidence of its value, spirometry was, until recently, rarely used in primary care settings. National, evidence-based guidelines for the management of asthma (British Thoracic Society (BTS) and Scottish Intercollegiate Guidelines Network 2007) and chronic obstructive pulmonary disease (COPD) (BTS 1997, National Collaborating Centre for Chronic Conditions (NCCCC) 2004), recommend spirometry for diagnosis and disease monitoring, and the inclusion of spirometry in the Quality and Outcomes Framework (QOF) of the General Medical Services Contract (British Medical Association 2003) have led to an increase in its availability in this setting.

In the 21st century health care is driven by objective measurements and clinical evidence. We would not diagnose and manage hypertension without measuring the blood pressure, and it is equally inappropriate to diagnose and manage respiratory disease without measurements

respiratory diseaserespiratory disease

38 primary health care | Vol 18 No 10 | December 2008

of lung function. Spirometers should be as available as sphygmomanometers.

Types of spirometer

There are two basic types of spirometer:Volumetric – measuring the volume }}of exhaled air directly.Flow measuring – measuring airflow }}and extrapolating volume from flow.

Volumetric spirometersThe volumetric spirometer that is occasionally used in general practice is the bellows spirometer (Figure 1). Other types are almost exclusively confined to the pulmonary function laboratory.

Air exhaled into the bellows spirometer causes the bellows to inflate. The stylus, attached to the bellows, moves downwards as the bellows inflates, pressing on the pressure-sensitive recording paper on the front of the spirometer. At the same time a motor moves the recording paper horizontally,

taking six to 12 seconds to move its full distance of travel, depending on the model of spirometer. Thus, the stylus moves vertically while the recording paper moves horizontally, producing a trace of volume exhaled against time – the volume time trace.

Bellows spirometers are very accurate, but are quite large. They can be fitted on to a stand and moved from room to room, but are not suitable for taking out to a patient’s home or transporting from site to site. A wide range of flow measuring spirometers are now available and these smaller, more portable devices have largely superseded the bellows spirometer in primary care settings.

Flow measuring spirometersThree types of flow measuring spirometer are in common use in primary care settings:

Differential pressure pneumotachographs.}}Turbine/rotary vane.}}Ultrasonic. }}

They range in size from ‘hand held’ to desk-top models.

When air is blown down a partially obstructed tube there is a pressure drop beyond the obstruction. The extent of the drop is dependent on the airflow rate. A differential pressure pneumotachograph instantaneously measures air pressure before and after a partial obstruction and calculates airflow rate and volume from the pressure drop. The two most commonly used differential pressure pneumotachographs are the Lilly and the Fleisch (Figure 2).

In a turbine/rotary vane spirometer (Figure 3) air blown into the spirometer spins a low inertia vane. Each rotation of the vane interrupts a light signal emitted from two diodes, producing a digital pulse. The volume

Figure 1

The bellows spirometer

Figure 2

Differential pressure pneumotachographs

Figure 3

Turbine/rotary vane spirometer

Bellows (expanded)

Wire mesh

Lilly Fleisch

Differential pressure transducer

Differential pressure transducer

Capillary tubes

Recording stylus

Chart paper

Paper motor device

Bellows (collapsed) Expired air from subject

Mouthpiece

Swirl plate

Light source

Optical sensorMoving vane



of air is calculated from the number of pulses and the flow rate from their frequency.

Ultrasonic spirometers use a piezoelectric crystal to generate an ultrasonic beam. In one type of ultrasonic spirometer partial obstructions in the air tube break the airflow into waves. Each wave passing through the beam produces a pulse proportional to its volume. The second type sends ultrasonic signals between two piezoelectric crystals within the airflow through the spirometer. The speed of the signal passing from one crystal to another is reduced or increased depending on the speed of the airflow.

Choosing a spirometer

The purchase of a spirometer entails capital and continuing costs. There are several ‘essential’ and ‘desirable’ features of a spirometer (Table 1) and many practical points to be thought through. It is a good idea to obtain your preferred model for a trial, to ensure it fulfils all your requirements.

Where will the spirometer be used? If it does not need to be moved or taken out into the community, then a bellows spirometer may be suitable. A small hand-held spirometer may be an attractive option for monitoring patients in their home, but some have serious limitations. Lack of a real-time graphic display makes it impossible to verify the adequacy of the patient’s technique and correct errors as they are performing the test. Some need to be downloaded onto a computer at the end of the test to view graphs and lung function data. Spirometers that only give a digital display of the lung function parameters are unsuitable for diagnostic spirometry and the inability to ensure adequate technique limits their usefulness. A small, desk-top spirometer, or hand-held spirometer and laptop computer may overcome difficulties and be suitable for use in the community.

Most desk-top spirometers produce ‘real time’ digital graphics and hard copy printouts. However, some use heat sensitive paper and the graphs will need to be photocopied for long-term storage. The pressure sensitive recording paper of a bellows spirometer is similarly difficult to store. A facility to download results, including graphs, to the practice computer system can be particularly useful. It will allow you to email spirometry results for quality control or a second option.

Training, practice and continual use makes perfect. A spirometer that is used infrequently

may not be a good investment in terms of capital outlay and staff training. Spirometry also requires co-operation and effort from patients. Poorly trained or untrained staff are unlikely to obtain high quality, meaningful spirometry recordings from them (Eaton et al 1999, Ponsioen et al 2002). This can lead to confusion and potentially dangerous misdiagnosis. All healthcare personnel using a spirometer must be trained in the safe use of the equipment, and must be able to recognise and correct poor technique. Those responsible for interpreting results and supervising others should be trained to at least diploma level and preferably certified as competent.

Spirometers are precision instruments that need regular maintenance. Technical support is also sometimes necessary. Cheap, imported models may not come with access to a free ‘helpline’ and servicing may be difficult and costly. The cost and availability of disposables, such as recording paper and mouthpieces, can also vary considerably.Now do Time out 1

infection prevention

It is vital that you are conversant with and follow infection prevention policies for your place of work. Cross infection from spirometry equipment is rare (Rutula et al 1991, Leeming et al 1993), but the rising incidence of multidrug-resistant bacterial infection makes this an important issue. One of the most effective methods of preventing infection is to make sure that you wash your hands between patients and before and after handling spirometry equipment.

Disposable mouthpieces and nose clips should be used. One-way, ‘valved’ disposable mouthpieces can prevent cross infection from accidental inhalation through the spirometer. Use of disposable gloves for handling mouthpieces will further reduce the cross infection risk. In primary care settings inspiratory manoeuvres are rarely needed, but

TAble 1

Spirometer features to consider

Essential Real-time graphic display of patient’s effort}}Hard copy of results, including volume/time and flow/volume graphics}}Memory facility that will save all the patient’s efforts }}Proven reliability and accuracy}}

Desirable Easy-to-use software}}Facility to download to the practice computer/patient database}}Free ‘helpline’ and good technical support services}}Calibration syringe sold with the spirometer}}Training provided}}

Time out 1What type of spirometer do you use in your place of work?Compile a list of the advantages and disadvantages of this spirometer. Are there any additional features that would be useful?

If you do not use a spirometer compile a list of the desirable features of a spirometer for your particular place of work and construct a business case for the purchase of a spirometer, bearing in mind all the issues that have been discussed.



disposable viral and bacterial filter mouthpieces are available to prevent contamination of equipment if these are required (Kendrick et al 2003). Spirometer parts in direct contact with the patient must be washed in hot, soapy water to remove saliva and mucus prior to disinfection and sterilisation.

Unless spirometry measurements are urgently needed for medical reasons, patients with known, active respiratory infection should not be tested. If spirometry is necessary, tests should be carried out at the end of the day and the equipment dismantled and sterilised after use. Immunocompromised individuals, such as chemotherapy patients or those with HIV, AIDS or post transplant, should be tested at the start of the day on newly sterilised equipment.

It is extremely important to adhere to the manufacturer’s instructions for methods of disinfection and sterilisation. Inappropriate methods can destroy expensive equipment. Cleaning and disinfection of spirometry equipment should be routine and a log kept. It is also helpful to keep a log of the date, time and details of the patients tested on the equipment to assist in risk assessment and contact tracing, should it become necessary.Now do Time out 2

Calibration and verification

Modern spirometers are generally robust and reliable, but it is still important to check that they are recording accurately. Calibration checks must be done as a daily routine, using a calibration syringe, and a log kept. This is the only method of demonstrating that the equipment is reliable.

A calibration syringe injects an exact volume of air (one or three litres) into the spirometer. It must be accurate to within 0.5 per cent; 15ml for a three litre syringe and 5ml for a one litre syringe. It must be serviced at the recommended intervals and kept next to the spirometer, so that it is at the same temperature and humidity. Calibration syringes are delicate; if one is dropped you should assume it is inaccurate until it has been serviced.

The spirometer must record within 3 per cent of the syringe volume. The calibration of some spirometers, for example, ultrasonic, turbine and bellows spirometers, can only be adjusted by an engineer. Others, for example, some models of Fleisch pneumotachograph, can be updated on a daily or sessional basis if necessary. Spirometers using disposable, single-patient-use flow sensors will need checks

to be performed on each new batch of sensors, in addition to the routine daily checks.

If there is a significant change in temperature during a spirometry session calibration should be rechecked. A spirometer that is transported to a patient’s home must be allowed to ‘settle’ for at least ten minutes. It needs to be left to reach room temperature and humidity, and its calibration checked before it is used. A spirometer carried in the boot of a car on a cold day and used straight away will be inaccurate.

The spirometer and the calibration syringe must be routinely serviced and maintained according to the manufacturer’s instructions. For most models this is required annually and may necessitate the spirometer being sent away.

The accuracy of the spirometer should also be verified on a regular basis, using a ‘biological control’, for example, an individual with no respiratory disease and known lung function values. Once the normal range of the biological control is known a spirometry recording from that individual can be used to verify the spirometer’s accuracy.Now do Time out 3

indications and contraindications

Spirometry should be a routine for any patient presenting with cardio-respiratory symptoms; cough, wheeze or breathlessness. Spirometry is also used for routine occupational surveillance of people exposed to hazardous substances at work. It is also being increasingly requested during routine medical checks for insurance or diving. Spirometry is vital for any patient suspected of having COPD. Early COPD is asymptomatic and airflow obstruction can only be detected with spirometry.

Another important role for spirometry testing is to monitor patients with chronic respiratory conditions, such as asthma and COPD. Spirometry can be used to assess response to therapy and to monitor for any rapid, or unexpected deterioration. Now do Time out 4

Spirometry is generally safe and there are no absolute contraindications. There are, however a few relative contraindications (Table 2). It is important to assess each patient and, in cases of doubt, to seek advice from your local pulmonary function laboratory.

Spirometry measurements

A spirometer will give you some essential information:

Time out 2Find out what infection prevention policies are applicable to spirometry in your place of work.If you do not already have a log of cleaning procedures construct a template for recording:} Cleaning procedures.} Which patients are tested on

the spirometer.

Time out 3Determine the normal range for a ‘biological control’.} Record your own spirometry

every day (or that of a colleague if you have a respiratory condition) at the same time of day, on the same spirometer for 14 days. You will need a minimum of ten recordings.

} Calculate the mean (average) for each spirometry parameter.

} Add up all the readings for that parameter and divide by the number of recordings.

} Now calculate 5 per cent of each of these values.

} Finally, calculate the normal range for each of these values by adding and subtracting this 5 per cent.

You can now use yourself (or your colleague) to verify the accuracy of your spirometer on a weekly basis, in addition to the daily calibration check.



Measurements of volume – vital capacity }}(relaxed and forced) and forced expired volume in one second (FEV1).Measurements of airflow – ratio of }}FEV1 to forced and relaxed vital capacity, peak expiratory flow.

These measurements are defined in Box 1.

Volume measurementsVital capacity represents the total amount of air an individual can breathe in and out of their lungs in a single maximum breath and, in primary care, is most commonly measured as an expired volume. Expired vital capacity is measured as a relaxed and a forced expiration. FVC is reached after a maximum of 15 seconds forced expiration, or when the expiratory flow rate has fallen below 0.05 L/sec.

The abbreviation VC conventionally refers to the expired relaxed vital capacity. It is important to record this. In patients with obstructive airways disease the narrowed airways can collapse, trapping air in the lungs, during forced expiration. This reduces the volume of the FVC and, in patients with severe airflow obstruction, the VC will be greater and a more accurate measure of vital capacity.

Measurement of FEV1 is simple to do and there are clearly defined reference (predicted) values. It is affected in all patterns of lung disease.

Measurement of airflowAirflow is only measured directly with a flow measuring spirometer. Volumetric spirometers calculate flow from volume.

Peak expiratory flow (PEF) can be measured with a flow measuring spirometer, but is most commonly measured with a peak

flow meter. The PEF recorded with a flow measuring spirometer will be different from that recorded with a PEF meter because the blowing technique is different. The reference values for PEF recorded with a spirometer (Quanjer et al 1993) are also different from those for PEF recorded with a peak flow meter (Nunn and Gregg 1989) and it is important to compare the patient’s readings with the appropriate reference value.

The ratio of FEV1 to VC (FEV1/VC) should be used if the VC is greater than the FVC. The FEV1/FVC is also referred to as the FEV1% or FER, depending on the model of

Time out 4Discuss with your colleagues the clinical situations where spirometry may be useful. How could you incorporate spirometry into your normal, daily clinical practice and use it to best advantage for early diagnosis of respiratory disease? Spirometry is vital for the early detection of COPD. ‘The primary care face of COPD’ (Booker 2008) discusses which people are at particular risk and may help you develop strategies for identifying and monitoring these individuals.

TAble 2

relative contraindications to spirometry

Relative contraindication Rationale

Haemoptysis of unknown origin Exacerbation of the problem and possible major haemorrhage.Possible active pulmonary tuberculosis leading to contamination of equipment and cross infection risk.

Pneumothorax Aggravation of the condition.

Unstable cardiovascular status: recent (within one month) myocardial infarction, uncontrolled hypertension or pulmonary embolism

Forced expiration can worsen angina or cause potentially dangerous blood pressure changes.

Uncontrolled hypertension or history of haemorrhagic cerebrovascular event

Precipitation of cerebral bleed.

Recent thoracic, abdominal or eye surgery Pain or incisional hernias. Raised intraocular pressure post ophthalmic surgery undesirable.

Nausea, vomiting or pain Effect on patient’s ability to co-operate and perform the test.

box 1

Definitions of essential spirometry parameters (Miller et al 2005)

Vital capacityThe volume, measured at the mouth, between the positions of full inspiration and full expiration.

Expired relaxed vital capacity (VC)The maximum volume of air that can be expired from the lungs during a relaxed, but complete expiration from a position of full inspiration.

Forced expired vital capacity (FVC)The maximum volume of air that can be expired from the lungs during a forced and complete expiration from a position of full inspiration.

Forced expired volume in one second (FEV1)The maximum volume of air that can be expelled from the lungs in the first second of a forced expiration from a position of full inspiration.

Peak expiratory flow (PEF)The highest flow achieved from a maximal forced expiratory manoeuvre started without hesitation from a position of maximal lung inflation.

The ratio of FEV1 to VC (FEV1/VC)The amount of air expired during the first second of a forced expiration from a position of maximal inspiration expressed as a percentage of the total amount expired during a relaxed vital capacity manoeuvre.

The ratio of FEV1 to FVC (FEV1/FVC)The amount of air blown out in the first second of a forced expiration from a position of maximal inspiration expressed as a percentage of the total amount expired (regardless of time) during that forced manoeuvre.



spirometer. These abbreviations all refer to the same measurement. Box 2 gives examples of how to calculate FEV1/VC and FEV1/FVC.

reference values

The normal lung function value (reference value) for any individual depends on their age, height, gender and ethnic group. Lung volumes increase during childhood and adolescence, reach a peak at around 25 years and decline into old age. Tall individuals have larger thoraces and hence greater lung volumes than short people. Males have larger lung volumes in relation to their height than females and anthropometric differences between different racial groups also influence lung function. For example, negro racial groups tend to have longer legs and shorter torsos than white Europeans, and hence smaller lung volumes in relation to their overall height. Large population surveys in different populations have been conducted to determine the reference values for spirometry and tables of the results, showing the mean reference value for individuals within a range of age and height, and either gender, are available.

The reference values recommended for use in European populations are those developed for the European Community for Coal and Steel (Quanjer et al 1993). Charts of these reference values are widely available and they are incorporated in the software of all electronic spirometers sold for use in the UK. Correction factors can be applied to these to adjust for ethnicity. However, it can be difficult to determine whether to apply a correction factor if the individual is of mixed ethnic background. If correction is applied it must be recorded and applied consistently in subsequent tests and in cases of doubt the advice of your local pulmonary function laboratory should be sought.

Actual data from population surveys are limited for adolescents and the elderly. Data from the 18-70 year old age group are extrapolated to cover these groups and the resulting reference values are therefore less robust. This needs to be borne in mind when interpreting spirometry from these individuals.

Patient preparation

Spirometry can be performed opportunistically, but it is helpful to do this as a planned procedure and give patients instructions to enable them to prepare (Box 3). Any bronchodilators the patient is taking will need to be withheld for diagnostic spirometry (Table 3) but this is not necessary for routine, monitoring of patients with known respiratory disease. Now do Time out 5

Height, without shoes, must be accurately measured. A proxy height measurement can be used for individuals unable to stand or with a kyphoscoliosis that prevents them from standing upright. Measure across the back from middle finger tip to middle finger tip with the arms outstretched at 90o. The patient should also be weighed and body mass index calculated since this can help in later interpretation of the spirometry.

Time out 5Devise an information and instruction sheet to give to patients when they make an appointment for spirometry, using the information in Box 3 and Table 4.This can help patients to prepare for the test, will reinforce the verbal instructions you give, and can save you time.

TAble 3

Withholding bronchodilators prior to diagnostic spirometry

Drug Class Example Withhold prior to spirometry

Short acting beta2 agonists salbutamol, terbutaline Two to four hours

Short acting anticholinergics ipratropium bromide Four to six hours

Long acting beta2 agonists salmeterol, formoterol 12 to 24 hours

Long acting anticholinergics tiotropium bromide 24 to 36 hours

Sustained release theophyllines Slo-phyllin, Neulin SA, Uniphyllin continuus

24 to 36 hours

box 2

Calculation of ratio of FeV1 to VC and FVC

The FEV1/VC is calculated:

Measured FEV1 X 100

Measured VC

The FEV1/FVC is calculated:

Measured FEV1 X 100

Measured FVC

box 3

Preparation for spirometry

DO:

Wear loose and comfortable clothing }}that does not restrict breathing.

Arrive for your appointment in time to empty }}your bladder and relax before testing.

DO NOT:

Eat a substantial meal within two hours of the test. }}

Smoke within one hour of the test or consume }}alcohol within four hours of the test.

Take vigorous exercise within }}30 minutes of the test.



Performing the test

Spirometry must be performed with the patient sitting down. Forced expiratory manoeuvres can cause dizziness or syncope and patients are unsafe standing up. They should be comfortably seated with both feet on the floor, in a chair that gives them good support. False teeth should be left in.

relaxed expiratory manoeuvresThese should be performed first and a nose clip used to prevent air leak. Instruct the patient to take a rapid, but unforced, maximum breath in, and to place the mouthpiece in their mouth, so that their teeth and tongue do not obstruct it, making a good seal with their lips. With the minimum of delay between inhalation and the start of exhalation, they should exhale gently and steadily into the mouthpiece, until they have completely emptied their lungs. You will need to encourage them to ‘squeeze’ out every last drop of air, but exhalation should not be forced and there is no need for them to empty their lungs within any particular timeframe. Some electronic spirometers will give an audible signal when airflow through them has ceased. Allow the patient to rest for at least one minute between efforts.

Forced expiratory manoeuvresNose clips are not essential, but can be used if there are difficulties obtaining reproducible tests. You will need to stress the need for absolutely maximum effort.

Ask the patient to make a rapid, but unforced, maximum breath in and place the mouthpiece into their mouth, as before, making a tight seal around it. They should then immediately, using maximum effort, exhale as hard and as fast as possible until

they are unable to exhale any further. Once again, active, verbal encouragement to keep blowing as hard as they can is absolutely essential. Allow the patient to rest for at least one minute between efforts.

reproducibility and technical errors

To ensure reproducibility you need a minimum of three relaxed vital capacity measurements. There should be less than 150ml difference between the two best efforts. If necessary further efforts, up to a maximum of four, can be attempted. The highest reading is recorded.

A minimum of three forced manoeuvres with less than 5 per cent difference between the best two, technically acceptable FVC and FEV1 readings are required. If the first three attempts do not produce reproducible results further efforts, up to a maximum of eight, can be attempted, unless the patient is becoming distressed. The highest FVC and FEV1 are recorded and these can be taken from different efforts if necessary.

A technically acceptable effort is where the individual has:

Exhaled completely from maximum }}inhalation to maximum expiration.Exhaled immediately from the }}position of maximal inspiration. Used maximum effort for the }}forced manoeuvre.Used maximum effort from the }}start of the forced manoeuvre.Has not coughed.}}

The volume time trace needs to be smooth, upwardly curving, free from irregularity and should plateau for at least one second. The flow volume trace needs to rise almost vertically to a peak and should merge smoothly with the horizontal axis of the graph (Figure 4).

Figure 4

Technically acceptable, normal volume time and flow volume traces

Volume trace time Flow volume trace



There are a number of technical errors that render a test invalid. Coughing during the forced expiratory manoeuvre will invalidate the FVC recording. It is a common problem, and will be apparent from observing the patient during the test. The volume time trace will be irregular. Several minutes’ rest between efforts can help, but if necessary the relaxed manoeuvre can be used to assess the vital capacity. If the patient has managed to blow for one second without coughing and produced a reproducible, good quality FEV1, the ratio of FEV1 to VC can be used.

A slow or delayed start to the forced expiratory manoeuvre is another common problem. This can be detected in the graphic display and print out. The volume time trace will have an ‘S’ shape at the start and the flow volume trace will show a slower, more sloping rise (Figure 5). It can be overcome by further explanation to the patient, using phrases such as: ‘I need you to really blast the air out right from the start – almost like you were going to cough.’

At the start of the patient’s effort a loud, verbal instruction to ‘BLOW’ and a forceful gesture such as stamping the foot can also help.

A common cause of reduced VC and FVC is a failure to exhale completely. The volume time trace will fail to plateau and the flow volume trace will not merge smoothly with the horizontal axis (Figure 6). It is hard work to squeeze every last drop of air out the lungs and it is vital that you continually encourage the patient throughout the manoeuvre.

Spirometry technique needs to be learned and, while some individuals will grasp what is needed quickly, others will need several practice attempts before they get it right. A poor effort from the patient will result in failure to meet reproducibility criteria. The role of the health professional as the patient’s ‘coach’ cannot be stressed strongly enough. Spirometry requires a great deal of effort and co-operation from them, so it is vital that your instructions are clear and you give plenty of encouragement. If possible you should demonstrate what you want the patient to

Figure 5

Slow start

Figure 6

Failure to exhale to FVC



do, as well as giving a verbal explanation. Now do Time out 6

interpretation

Normal ventilatory functionThe VC, FVC and FEV1 are expressed in terms of the volume, in litres, and as a percentage of the reference value (Box 4). A healthy individual will have lung volumes over 80 per cent of the reference value. The FEV1/VC and FEV1/FVC are expressed as a ratio, or as a percentage, for example, 0.75 or 75 per cent (Box 2). An individual with unobstructed airways will be able to exhale three quarters of their vital capacity in the first second of a forced expiration. In other words, the FEV1 should be around 75 per cent of the vital capacity, giving a ratio of FEV1 to VC or FVC of around 0.75. The time taken to exhale to FVC is normally four to six seconds. Figure 4 shows normal volume time and flow volume traces.

obstructive ventilatory defectsObstructive airways diseases are common. There are more than five million people with asthma and around one million diagnosed cases of COPD in the UK (BTS 2006). The feature of these conditions is difficulty with expiration. Inhalation is unaffected and vital capacity in mild to moderate airflow obstruction is usually normal; over 80 per cent of the reference value. However, airway obstruction reduces the speed of exhalation. Thus, the volume of FEV1 falls to less than 80 per cent of the reference value and the ratio of FEV1 to vital capacity drops.

A ratio of less than 0.7 (70 per cent) is generally considered diagnostic of airflow

obstruction. Caution does however need to be exercised when applying this rule to adolescents and the elderly. Lungs lose elasticity as part of the normal ageing process. In a young person with elastic, compliant lungs exhalation will be rapid and the FEV1 and ratio of FEV1 to VC are likely to be high. In an older person natural loss of lung elasticity will slow exhalation and produce a relative reduction in FEV1 and ratio of FEV1 to VC. Thus, an FEV1/FVC of 0.73 may be abnormal in a symptomatic adolescent and an FEV1/FVC of 0.69 may be normal in an asymptomatic older person. It is therefore vital to consider the clinical presentation and other diagnostic tests, as well as the lung function, in all cases.

The volume time trace will be ‘flattened’ and the time taken to reach FVC and for the trace to plateau extended. The flow volume trace will still rise rapidly to a peak, but obstruction of airflow will produce a typical ‘scooped out’ concave shape to the trace (Figure 7). The flow volume trace can be particularly useful in identifying early airflow obstruction.

Severe obstructionSevere obstructive airways disease can cause air trapping. Small airways are normally ‘squeezed’ during forced expiration and will narrow slightly. When airways are already narrowed, or where they are unsupported, such as occurs in emphysema, forced expiration can cause collapse of the airways; so-called

Time out 6Consistent, verbal encouragement to ‘keep blowing’ is vital to ensure technically acceptable spirometry.Record the VC from a colleague, or patient who is not familiar with spirometry. Explain what you want them to do, but do not continually encourage them to continue blowing. Then repeat the test with the same person while continually encouraging them to ‘…blow, blow … Keep blowing’.Is there a difference between the two recordings?

Figure 7

obstructive volume time and flow volume traces

box 4

Calculating lung volumes as a percentage of the reference value

Measured lung volume x 100 Reference value for that lung volume



dynamic airway collapse. This reduces the volume of the vital capacity. Thus, in severe obstructive airways disease the FVC, FEV1 and FEV1/FVC are all reduced. The VC may be well preserved since this does not involve forced expiratory effort. The volume time trace will be markedly flattened and the flow volume trace will show a dramatic drop in flow through the latter part of the expiration, producing a ‘church steeple’ silhouette to the trace (Figure 8).

restrictive ventilatory defectsThe cause of a restrictive defect can be respiratory or non-respiratory. Intra-pulmonary causes include diseases that cause fibrosis of lung tissue reducing the ability of the lung tissue to expand, such as fibrosing alveolitis or sarcoidosis. Pulmonary oedema ‘stiffens’ lung tissue producing a restrictive ventilatory defect. Any condition that prevents full expansion of the thoracic cavity can also cause restrictive spirometry, such as:

Thoracic spine deformity – }}scoliosis or kyphoscoliosis.Neuromuscular disease – muscular }}dystrophy, motor neurone disease, Guillan Barre syndrome, paralysis of the diaphragm and so on. Obesity – excess fat on the thorax }}restricts respiratory muscle movement and excess fat within the abdomen restricts movement of the diaphragm.

Respiratory causes for restrictive spirometry are comparatively rare. A common cause of apparent restrictive defects is poor spirometry technique; failure to exhale to FVC.

The feature of restrictive ventilatory defects is reduced lung volume; VC, FVC and FEV1 will all be less than 80 per cent of the reference value and the FEV1 and FVC will be reduced in proportion to each other. Airways are not obstructed and the ratio of FEV1 to VC will be normal. Indeed, when lung volumes are significantly reduced the FEV1/FVC may be abnormally high and the time taken to reach

Figure 8

Severely obstructed volume time and flow volume traces

Figure 9

restrictive volume time and flow volume traces



ReferencesBooker R (2008) The primary

care face of COPD. Primary Health Care. 18, 5, 37-48.

British Medical Association (2003) New GMS Contract: Investing in General Practice. BMA. London.

British Thoracic Society (1997) BTS guidelines for the management of chronic obstructive pulmonary disease. Thorax. 52, (Suppl 5), S1-S28.

British Thoracic Society (2006) Burden of Lung Disease. British Thoracic Society, London. www.brit-thoracic.org.uk/Library/BTSPublications/BurdenofLungDiseaseReports/tabid/164/Default.aspx (Last accessed: May 21 2008.)

British Thoracic Society, Scottish

Intercollegiate Guidelines Network (2007) British Guideline on the Management of Asthma. Revised edition 2007. www.brit-thoracic.org.uk (Last accessed: May 4 2008.)

Eaton T, Withy S, Garrett JE et al (1999) Spirometry in primary care practice: the importance of quality assurance and the impact of spirometry workshops. Chest. 116, 2, 416-423.

Hole DJ, Watt GC, Davey-Smith G et al (1996) Impaired lung function and mortality risk in men and women: findings from the Renfrew and Paisley prospective population study. British Medical Journal. 313, 7059, 711-715.

Kannel WB, Lew EA, Hubert HB et al (1980) The value of measuring vital capacity for prognostic purposes. Transactions of the Association of Life Insurance Medical Directors of America. 64, 66-83.

Kendrick AH, Johns DP, Leeming JP (2003) Infection control of lung function equipment: a practical approach. Respiratory Medicine. 97, 11, 1163-1179.

Leeming JP, Kendrick AH, Pryce-Roberts D et al (1993) Use of filters for the control of cross-infection during pulmonary function testing. Journal of Hospital Infection. 23, 3, 245-246.

Miller MR, Hankinson J, Brusasco V

et al (2005) Standardisation of spirometry. European Respiratory Journal. 26, 2, 319-338.

National Collaborating Centre for Chronic Conditions (2004) Chronic obstructive pulmonary disease: National Clinical Guideline for management of chronic obstructive pulmonary disease in adults in primary and secondary care. Thorax. 59, (Suppl 1), 1-232.

Nunn AJ, Gregg I (1989) New regression equations for predicting peak expiratory flow in adults. British Medical Journal. 298, 6680, 1068-1070.

Ponsioen BP, Bohnen AM, Martha I et al (2002) Measurement of

FEV1 and FVC with a hand held spirometer by GPs: feasibility and validity. Primary Care Respiratory Journal. 11, 2, 68-69.

Quanjer PH Tammeling GJ, Cotes JE et al (1993) Lung volume and forced ventilatory flows: report working party standardization of lung function tests, European Community for Steel and Coal. Official statement of the European Respiratory Society. European Respiratory Journal. 6 (Suppl 16), 5-40.

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resources and further reading

One day short courses and a diploma level module }}in spirometry (accredited with the Open University) are available from Education for Health www.educationforhealth.org.uk Successful graduates of the diploma level module are also awarded the BTS/ARTP certificate of competence in spirometry.

Training in spirometry, culminating in the award }}of the BTS/ARTP certificate of competence, is available from The Association for Respiratory Technology and Physiology. http://fp.artpweb2.f9.co.uk/

One day short courses and academic modules in }}spirometry (accredited with Edge Hill University) available from Respiratory Education UK www.respiratoryeduk.com

Booker R (2008) }} Vital Lung Function. Class Health. London.

TAble 4

Normal spirometry parameters and how these are affected in various ventilatory defects

Normal Obstruction Severe Obstruction Restriction

FVC More than 80 per cent of reference value

More than 80 per cent of reference value

Often less than 80 per cent of reference value but less reduced than FEV1

Less than 80 per cent of reference value. Reduced in proportion to FEV1

VC Same as FVC May be higher than FVC Greater than FVC Same as FVC

FEV1 More than 80 per cent of reference value

Less than 80 per cent of reference value

Less than 30 per cent of reference value Less than 80 per cent of reference value

FEV1/FVC Around 75 per cent (0.75) and more than 80 per cent of reference value

Less than 70 per cent (0.7) and less than 80 per cent of reference value

Usually less than 70 per cent (0.7) and 80 per cent of reference value – but may be higher if there is significant air trapping

In excess of 75 per cent (0.75) and more than 80 per cent of reference value

FVC reduced to two to four seconds. A ratio of greater than 0.85 in an adult is highly suggestive of a restrictive defect, although it may be normal in a child or adolescent.

The volume time trace will be a normal shape, but will be small and, in a severe restrictive defect, will plateau early. The flow volume trace will appear narrow and ‘domed’. The ‘scooping’ typical of obstruction will not be present (Figure 9).

The spirometry parameters affected in the types of ventilatory defect discussed here are summarised in Table 4.

Conclusion

There are many indications for spirometry and a wide variety of different spirometers available, many of which are suitable for use in general practice and community settings. However, all spirometers require regular maintenance, disinfection and calibration checks. Most importantly, the healthcare staff responsible for obtaining recordings from patients and those interpreting the results need to be adequately and

appropriately trained for the task. Once taught they also need to continually practice their skills in order to maintain them.

When these requirements are met primary care spirometry can provide a reproducible and meaningful test that enables accurate diagnosis and rational treatment of respiratory disease nNow do Time out 7

Time out 7Now that you have completed the article you might like to write a practice profile. Guidelines to help you are on page 48.

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