Spirometry is an important investigation used to assist clinicians in the diagnosis and assessment of severity in people who have respiratory conditions.
However it is imperative that spirometry is quality assured, and it should be performed and interpreted to an Association for Respiratory Technology & Physiology (ARTP) or equivalent-approved standard.1
Two documents have been published which outline the recommended quality assured standards for diagnostic spirometry.1,2
- Understand the key indications for spirometry
- Outline what is required to prepare a patient for the test to achieve the optimal quality result
- Identify the relative and absolute contraindications for spirometry
- Describe the procedure to achieve a quality-assured spirometry report and how to review a report and ascertain if it meets the recommended standards
- Outline the different lung function measurements and how they can be used in clinical practice when managing respiratory symptoms
- Understand the key spirometric measurements used to identify an obstructive or restrictive lung disorder
- Be aware of the key documents used to support spirometry in primary care
This module was developed by Judith Lawrence, a nurse practitioner based at Jubilee Park and Collingwood Surgery.
Spirometry is the measurement of lung volumes and airflow. The patient blows a series of relaxed and forced blows into a spirometer. The machine, procedure and interpretation should all meet the recommended standard for quality assured spirometry.1-4
Spirometry is an objective test and is one of the few effort-dependent tests undertaken in primary care.
To achieve the best possible result, the operator must give clear instructions and ‘encouragement’ to the patient. Suboptimal effort will give a technically unacceptable result. The clarity of instruction is vital. The operator must be sensitive to the person’s ability to comprehend and execute instructions.
The spirometry will measure the patient’s volumes and flow rate, allowing identification of the following patterns:
- Combined obstructive and restrictive
The spirometry result must be used in conjunction with the clinical history/examination and other appropriate tests (blood tests, including full blood count, and chest x-ray and/or CT scan).5
Currently there is an increasing focus on the need to ensure that all diagnostic spirometry is undertaken and interpreted by a clinician or practitioner who is trained to Association for Respiratory Technology & Physiology (ARTP) or equivalent standards. It must be performed and interpreted to an approved quality standard.2
The two main measurements are airflow and volume. Volume is the relaxed vital capacity (RVC, referred to as VC, see below) and forced vital capacity (FVC). Airflow is the forced expiratory volume in 1 second (FEV1). The VC and the FVC provide the necessary indices to allow the interpreter to calculate if lung function is normal, obstructive, restrictive or a combination of obstruction and restriction.
Vital Capacity (VC)
There can be confusion around some of the terminology as some terms are used interchangeably. Strictly, the term VC means the larger of the RVC or FVC. However, VC is frequently used to mean the RVC, and this is the terminology that will be used here. This is in line with the guidance produced by Primary Care Commissioning.2
Relaxed vital capacity (RVC)
The RVC is the maximum volume of air that can be expired from the lungs by a gradual exhalation from a point of maximum inhalation. You may sometimes see it referred to as expired relaxed capacity (EVC), slow vital capacity (SVC) and, as discussed above, vital capacity (VC).
Forced vital capacity (FVC or dynamic VC)
The FVC, or dynamic VC, is the maximum volume of air that can be expired from the lungs from a position of full inspiration to full expiration during a forced blow.
Forced expiratory volume in 1 second (FEV1)
FEV1 is the maximum expired volume of air expelled from the lungs in the 1st second of the FVC. The readings are taken from the FVC blow. It is one of the most widely-used measurements as it is affected in all patterns of lung disease. It is used from diagnosis through to assessing severity of lung disease. It is seen as a good predictor of all-cause mortality.
The FEV1/VC is the amount of air expired during the first second of a forced blow as a percentage of the VC.
The FEV1/FVC is the amount of air expired during the first second of the forced blow as a percentage of the FVC.
In some patients with obstructive lung disease there may be air trapping and the VC will be higher than the FVC. Therefore for diagnostic spirometry it is vital to measure both relaxed vital capacity and forced vital capacity.
Whichever of VC or FVC is the higher volume should be used to determine if there is an obstructive deficit i.e. if the VC is higher than the FVC the FEV1/VC ratio would be used, and if the FVC is higher than the VC the FEV1/FVC would be used.
Performance and interpretation are key but if the machine does not meet the quality assured standard the result cannot be relied on.
- A spirometer that meets the ISO standard 26782
- A calibration protocol – incorporating the standard documented in Miller et al (2005)4
- A cleaning protocol
- One-way mouthpieces and nose clips
- A validated height measure and weighing scales
- A nebuliser or spacer for post-bronchodilator/reversibility testing
- Short-acting bronchodilators as per guideline recommendations (see page 6 of the PCC guide)2
Lung volume is dependent on:
- Sex – males have larger lung volumes than females
- Age – lung volumes decline with age after 21 years old
- Height – taller individuals have larger lung volumes compared with smaller individuals
- Ethnic group – the anthropometric characteristics of different ethnic groups affect lung volumes. Correction factors that adjust for ethnicity can be applied to reference values for European populations. The European reference value can be multiplied by 0.9 for those of Japanese, Indian, Pakistani, Polynesian and African descent. However this must then also be applied to subsequent tests. In practice it can be difficult to apply a correction factor when an individual has a mixed ethnic background and the exact ethnic group cannot be determined. It is always important to interpret with a clinical understanding of the background of the patient and to use clinical judgement.
Spirometry is an objective test that can assist the clinician in reaching a diagnosis of a respiratory condition. Normal spirometry does not exclude respiratory disease. For example, asthma is a variable disease and on the day of the test spirometry may be normal. Likewise, a person with emphysema may have preserved small airways and obstruction is not identified. Spirometry is a piece of the jigsaw. The quality of the spirometry is primarily dependent on the machine, operator and interpreter all meeting the recommended quality standard and the patient having the ability to undertake the test.
Spirometry may be helpful in:
- Detecting the presence or absence of disease, for example when a patient presents with undiagnosed respiratory symptoms
- Quantifying the extent of a known disease
- Confirming diagnosis of a disease, for example suspected COPD, where post-bronchodilator spirometry is required to demonstrate obstruction before diagnosis can be confirmed. The diagnosis must also be supported by a clinical history
- Demonstrating reversibility in asthma patients
- Monitoring response to treatment, for example when checking an asthma treatment
- Monitoring the progression of a disease such as COPD
If the test has been undertaken to a quality standard then false positives and negatives should be minimised.
Although machines can interpret readings it is strongly advised that the interpreter is able to extrapolate the best possible values and confirm the result.
Remember the machine will give you information to decide if there is an obstructive, restrictive, combined or normal pattern. History is vital along with appropriate clinical examinations.
- Base-line spirometry
Used to investigate lung function when the diagnosis has not been established.
- Post-bronchodilator spirometry
Used to diagnose obstructive conditions where baseline spirometry has shown obstruction. It can be used for the monitoring of clinical progress of COPD/asthma. It may be used to monitor response to treatment in asthma.
- Reversibility testing
Can be used to differentiate asthma from COPD. It is always worth considering reversibility even when spirometry is within normal parameters, as you still may be able to demonstrate reversibility.2 Remember that patients with asthma do not always fully reverse with a single treatment with salbutamol, but often improve considerably with longer-term inhaled corticosteroid therapy which reduces the inflammatory process – hence reversibility is not always complete and clinical judgement is required.
Guidelines refer to absolute and relative contraindications. Levy et al (2009) state no absolute contraindications, only relative; however a number of guides do cite absolutes and therefore a list has been included.2,3,6
Within primary care there are very few absolute contraindications, but they are:
- Active infection: AFB-positive TB until treated for 2 weeks
- Any condition that if aggravated by a forced expiration would have serious consequences. Examples include unstable aortic aneurysm, recent abdominal, thoracic, or ophthalmic surgery, neurosurgery, or significant haemoptysis.
Spirometry is generally a safe procedure and it is rarely required urgently in primary care. The following conditions may be aggravated by a forced expiration; in these cases, consider whether the test is essential at this time or if it could be delayed. If it is required, seek additional expert advice from the local lung function lab. Pause for thought with the following:
- Haemoptysis of unknown origin
- Respiratory infection in last 4-6 weeks
- Patient is too unwell to perform expired forced expiration (often with cough)
- Patient is unable to fully comprehend the instructions to achieve a good spirometry test, for example there is dementia, confusion or learning disability
- Any condition aggravated by a forced expiratory blow: recent eye or ear, thoracic or abdominal surgery, recent MI/PE or uncontrolled BP, recent CVA or cerebral/abdominal aneurysm, pneumothorax, severe neck/upper back pain, first and last trimester of pregnancy.
There is a fine line between absolute and relative and the clinician needs to assess the risk and seek advice if appropriate. If in doubt it is usually better to wait.
Proper prior preparation prevents poor performance.
Ensure that the patient has been assessed before the test and has had an explanation of what is required. This should be in a letter or information sheet supplied before the test.
Ideally the patient should:
- Avoid a big meal within 2 hours of the test
- Not smoke within 1 hour
- Not consume alcohol within 4 hours of the test
- Wear loose comfortable clothing that does not restrict breathing
- Avoid vigorous exercise 30 mins before the test
- Arrive in plenty of time for the appointment and visit the toilet prior to the test to ensure comfort. Women may avoid FVC effort for fear of stress incontinence
If spirometry is to monitor disease progression and response to treatment the patient should take their inhaler(s) as normal.
If spirometry is for diagnosis or reversibility testing then inhaled medication should be withheld for a period before the test, see Table 1.2
Table 1. Time to leave between last inhaled medication and spirometry test.2
Quality standards are in place to ensure that diagnostic spirometry meets defined criteria.
The following highlight the key components of a spirometry test:
- Height, weight, date of birth and identification should be recorded. Check for relative or absolute contraindications.
- Explain the test to the patient – clarity is essential.
- A nose clip is required for the relaxed blow.
- Ensure a maximum inspiratory effort and a maximum expiratory effort.
- Ideally the patient should be sitting.
- Verbal encouragement is essential.
- Ensure the mouth piece is not obstructed and ask the patient to remove false teeth if they are loose.
- Quality assured spirometry requires a minimum of 3 relaxed blows and 3 forced blows. These should be from a position of maximum inspiration to maximum expiration. The two highest readings should ideally be within 100ml of each other, but in patients with more variable blows you can accept up to 150ml difference with an appropriate technical comment. Be aware of, and monitor for, any abrupt stops or failure to take a deep breath and expire fully. There should be at least a 1 minute wait between attempts, and some patients may require longer.
- Allow a maximum of 4 VC and 8 FVC attempts in any one session.
- If the patient is unable to achieve the quality criteria this should be documented along with reasons why.
4 x 100mcg salbutamol single puffs via a spacer, or 2.5mcg via a nebuliser.
Wait at least 15 minutes prior to undertaking the test.
- The key indices used to determine if there is an obstructive or restrictive pattern are FEV1, FVC and VC.
- Obstruction is identified when the FEV1/FVC or FEV1/VC is <0.7 or <lower limit of normal (LLN).
- 95% of the normal population will have a value greater than the lower level of normal (LLN), hence there is interest in using this figure for the FEV1/VC or FEV1/FVC ratio in preference to a fixed ratio of 0.7 (70%). This is because the efficiency of our lungs at expiring air changes as we get older, and is not always fixed.
- There has been much debate around the use of a fixed ratio of 0.7 as it may lead to over-diagnosis of COPD in the elderly, especially in mild disease. The ATS/ERS and primary care guidelines recommend the use of the LLN.4 As it stands, the NICE COPD guidance still recommends 0.7 as the cut-off for obstruction but this guideline is due for review.5 The GOLD COPD guideline (2016) currently uses 0.7 as the cut-off for obstruction.7
- Please note that whichever is the higher (VC or FVC) should be used in the ratio.
- The parameters are considered normal if the FEV1, FVC and SVC are within the normal range of 80%–120% of the reference value for someone of that age, sex and ethnic group.
As a practitioner or clinician how can you be assured that the spirometry test that has been reported meets the recommended standard?2
There are key points to check when reviewing or reporting a set of spirometry results.
Make sure the report contains the correct age, identification, sex, height and ethnicity. Although weight and BMI are not required to interpret the spirometry they are useful when reviewing the clinical picture that is emerging.
- Technically acceptable blows
The flow volume (FV) and volume/time (VT) graphs should be printed. The volume/time trace should show a rapid rise as 3/4 of the air is expired in the first second. The trace plateau should reach a minimum of 6 seconds (Figure 1). The flow/volume trace should rise almost vertically to the peak expiratory flow and then as the air is expired from the airways the flow rate will decrease steadily (Figure 2). The trace should then merge smoothly with the horizontal axis of the graph.
The graphs should be free from abrupt stops, slow starts, cough or air leaks.
Figure 1. Normal volume/time trace
Figure 2. Normal flow/volume trace
- There should be a minimum of three relaxed vital capacity blows and three forced blows.
- Reproducibility (repeatability)
The criteria state that ideally there should be no more than 100ml (or 5%, whichever is the larger) between each blow (grade A) but up to 150ml (grade B) is acceptable in highly variable patients2. The highest FEV1, FVC and VC from 3 efforts meet reproducibility criteria if they are within 5%. The highest FEV1, FVC and VC can come from any of the three blows as long as they meet the reproducibility criteria. These figures are not always possible to achieve – indeed, even experts can find it problematic in people having their first-ever test.8
Table 2. Examples of pre- and post-bronchodilator spirometry after 400mcg salbutamol via spacer
Table 2 shows an example of a spirometry test:
VC – two highest readings within 10ml of each other (2.12. and 2.11)
FVC – two highest readings within 140ml of each other (1.84 and 1.70)
FEV1 – two highest readings within 50ml of each other (1.32 and 1.27)
VC – two highest readings within 20ml of each other (2.27 and 2.25)
FVC – two highest readings within 100ml of each other (2.34 and 2.24)
FEV1 – two highest readings within 30ml of each other (1.81 and 1.78)
Readings to use for best spirometry result:
As the VC is higher than the FVC the FEV1/VC ratio should be used: 1.32/2.12 (0.62). Note that if the VC had been used the ratio would have been 1.32/1.84 (0.72).
In this case the FEV1/FVC is higher: 1.81/2.34 (0.77). The FEV1/VC is 1.81/2.27 (0.79).
Note reversibility is 490ml (pre-bronchodilator 1.32 and post-bronchodilator 1.81) – this supports a diagnosis of asthma but would need to be confirmed alongside history.
- Interpreting airflow obstruction
A reduction in the maximum forced expiratory airflow in one second (FEV1) relative to the maximum expired volume (FVC or VC) suggests an obstructive defect. This will be demonstrated by a reduced FEV1/VC or FEV1/FVC depending on which is higher, the FVC or VC – always use the higher when working out the ratio. There has been much debate about the use of the arbitrary 0.70 fixed cut-off versus using the LLN.3 Using the FEV1/FVC or FEV1/VC 0.70 fixed cut-off ratio is dependent on age, height and sex. It can lead to over-diagnosis in the elderly and under-diagnosis in the young.
Spirometry patterns are shown in Table 3 and Figure 3.
Obstructive airways disease causes a reduction in the rate of air expired but does not affect the maximum volume of air expired. Hence the FEV1 is usually reduced to less than 80% but the FVC and VC will usually be >80%. In severe obstruction you may get a reduction in the FVC.
Restrictive airways disease causes lung volumes to be reduced but the rate of airflow is unaffected. Hence the FEV1, FVC and VC are reduced in proportion to each other but the ratio will be >70%.
Table 3. Spirometry Interpretation
Figure 3. Spirometry patterns
Severity of airflow obstruction – the FEV1 as a percentage of predicted is used to assess the severity of the obstruction. Table 4 shows the classification of severity in COPD.
Severity (FEV1 % of predicted) – degree of breathlessness (Medical Research Council Score), exacerbation rate and smoking status has prognostic implications for people with COPD, with the greater the severity of obstruction, more breathlessness, continued smoking and more exacerbations having a worse prognosis.
Table 4. Classification of severity of airflow obstruction
Reversibility – the timing, dose and methods of delivery of bronchodilator should be documented to confirm that reversibility testing was undertaken to the recognised standard. 200ml or 12% improvement in FEV1 would denote a sufficient improvement to support an asthma diagnosis. Remember that asthma is a variable disease and a lack of reversibility on a single test does not exclude the diagnosis. GOLD and ATS/ERS recommend COPD is diagnosed on post-bronchodilator spirometry.4,7 The NICE COPD guideline recommends that a 400ml increase in FEV1 should prompt a re-examination of the patient’s history, as such a large variation should make you question a purely COPD diagnosis and consider asthma instead.
There are two main patterns – obstructive and restrictive – and a combination of both. Examples of restrictive and obstructive patterns are given in Table 5. It should be noted that many people with the restrictive conditions mentioned below can have entirely normal spirometry, and spirometry should not be used as a screening tool to identify either these conditions or a tumour or foreign body.
Table 5. Examples of conditions with restrictive and obstructive spirometry patterns
1) Calculate the FEV1, FVC and VC as a percentage of the reference value:
= Measured volume / Reference value x 100.
2) The FEV1/FVC (and/or FEV1/ VC)
= Measured volume / Reference value x 100.
3) Diagnosing asthma using peak flow to demonstrate diurnal variation:
There needs to be diurnal variation of 20% for 3 days in a week over several weeks.
On a day take the higher reading – lower/higher x100 = diurnal variation.
- Association for Respiratory Technology and Physiology (ARTP), Association of Respiratory Nurse Specialists, Asthma UK, British Lung Foundation, British Thoracic Society, Education for Health and Primary Care Respiratory Society UK. Improving the quality of diagnostic spirometry in adults. 2016.
- Primary Care Commissioning. A guide to performing quality assured diagnostic spirometry. 2013. Available at: www.pcc-cic.org.uk/sites/default/files/articles/attachments/spirometry_e-guide_1-5-13_0.pdf.
- Levy ML, Quanjer PH, Booker R, et al. Diagnostic spirometry in primary care: proposed standards for general practice compliant with American Thoracic Society and European Respiratory Society recommendations. Prim Care Respir J 2009;18(3):130-47.
- Miller MR, Hankinson J, Brusasco V, et al. Standardisation of spirometry. Eur Respir J2005; 26(2):319-38.
- National Institute for Health and Clinical Excellence. Management of chronic obstructive pulmonary disease in adults in primary and secondary care (partial update). 2010. Available at: www.nice.org.uk/CG101.
- Booker R. Vital Lung Function: your essential reference for the management and assesment of lung function. Class Health, London. 2008.
- Global Initiative for Chronic Obstructive Lung Disease. Global strategy for diagnosis, management and prevention of COPD. 2016.
- Maio S, Sherrill DL, MacNee W, et al. The European Respiratory Society spirometry tent: a unique form of screening for airway obstruction. Eur Respir J. 2012;39(6):1458-67.
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