Spirometry Measurements Spirometry is one of the basic tests of breathing function in health and disease. It is recognized as a measure of global health, predicting all causes of death and illness in adults. Simplified, this means that when your lungs run out of function - so does your body! Not surprising really - but it shows how important it is to get the measurement right if we are to predict your future health Some health professionals think that spirometry is a simple test. Don't be fooled - there's a lot more to the technique to get quality results than many doctors and nurses think!
Spirometry is measured on a spirometer or “breathing measurer” and these were developed from simple water displacement devices in the 1800s, to the compact hand-held devices used today. They simply measure flow or volume, and once one is measured the other can be calculated. The availability of spirometers at your GP surgery has increased dramatically in the last decade or so because of the development of guidelines for diagnosing chronic obstructive pulmonary disease (COPD). The role of spirometry has become a central mainstay of screening for lung disease and its effective measurement and interpretation is now extremely important for delivering respiratory healthcare.
The majority of spirometers are of the flow measuring type due to their small size and relatively low cost. Caution should be taken when interpreting spirometry results from different centres where staff have different degrees of training and competence. A good place to have your spirometry performed is where the staff have attained the ARTP/BTS Spirometry Certificate of Competence. (see ARTP website link)
Peakflow is a simple respiratory measurement that is useful for assessing the airways in either in an emergency or can be used for long term monitoring and diagnosing if you have asthma. However it is rarely a useful diagnostic test and should only really be used in asthma since it doesn’t tell you which type of respiratory disease you have.
Spirometry however, requires a more complex series of efforts by getting you to fully breathe in and blow out under the supervision of an appropriately trained and competent person. The steps for the test can be summarised as;> (i) Sit down and listen to the explanation of the test. (ii) Take full breath in as full as you can then immediately- (iii) Blow out hard and fast in one until you are as empty as you can get. (iv) Sometimes you may be asked to breathe back up to being full again straight away. This test may require you to wear a noseclip, and you will need to repeat the test for at least 2 more times (or maybe more) until a stable best value is obtained.
How to measure spirometry The spirometer should be prepared so that there is no risk of cross-infection between patients and the device is calibrated so that it measures accurately Before you perform your spirometry you may need to be prepare in advance in terms of a number of well-recognised factors that can affect results: 1. Do not wear tight clothing or have a large meal as these could restrict your efforts. 2. For safety you should also be seated in case the forced effort makes you dizzy and cause you to fall and hurt yourself. 3. If you have had a recent heart attack, chest, abdomen or eye surgery, 4. Or have an unstable cardiovascular conditions, (e.g. aneurism, black-outs) then you tell the person going to test you and make sure it is safe to proceed with your test.
What will be measured? The common indices of spirometry are usually taken from the volume-time graph, with the most useful indices being the FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity). The FEV1 is the amount of air you can blow out fast from being full in 1 second and is usually three quarters of all the air you can blow out in healthy lungs. The FVC is the amount of air you can blow out fast from being full to as empty as you can get in up to 12 seconds.
Expressing the FEV1 / FVC as a percentage is a very good indicator of the presence of any airways obstruction (when a ratio <60% is observed). The absolute values mean little in isolation so referring values to a reference range expresses the values in a meaningful context. (in other words - just saying that your lungs are "big" doesn't meean very much, but saying they are at the "top end" of the expected range for someone of your height is more helpful) The use of percent of predicted is commonly may used but can leads to errors of over-diagnosis of COPD when a 70% cut off is used. A more appropriate way to interpret spirometry values is to see whether a value is below the lower limit of normal (LLN). Ask the person making the measurment what this means. They should know!
However, much more information about the airways can be gained by observing the flow-volume loop which can give characteristic patterns which can identify small airways obstruction, emphysema or large airways obstruction. Figure 1 shows typical patterns of flow volumes loops when compared with the normal shape in healthy airways.
Many spirometers try to describe the shape of the expiratory curve of the flow-volume loop by quoting “mid flow measurements” (such as MEF25-75, MEF50 yuk! medi-jargon!!!) but the reference ranges are often too great for these numbers to be helpful. “Shape recognition” is a more powerful tool to describe the presence of the obstruction.10 things patients should ask about their spirometry test
1. Does the person measuring the test have the ARTP/BTS Certificate of Competence in Spirometry? This is a national quality standard in the level of training in spirometry in the UK. Staff who have completed this course have achieved a recognised standard of expertise and will get the best results from you to help in your diagnoisis
2. Are they using a one way mouthpiece or filter to protect you? There is a risk of spreading infection by using just a straight cardboard tube without a one-way valve or a filter. Insist that you have one
3. Has the spirometer been calibrated/checked with volume syringe before the test? Many spirometer manufacturers claim that their spirometers do not need checking before use. Experience of many lung function departments worldwide shows that such checks are essential. Insist that they have done this for your testing session!
4. Have you been made to produce 3 repeatable values of your test? Even though it may be hard work, you should be made to perform 3 efforts of the test to within 100ml for FEV1 and FVC (see above) so that your best value can be taken. Sub-maximal results can result in you receiving unecessary medication or further exhaustive tests for no reason!
5. Can performing this test do me any harm? Usually performing this test should not present you with any problems. Yes, it is a test which requires your maximum effort and coordination, but in most cases this shouldn’t produce any concerns. However there are a series of situations which should be considered carefully before performing the test. These are known clinically as “contraindications”
6. Will recent surgery affect my test results/performance or harm me? Yes, any recent surgery including head, chest, abdominal surgery may cause a problem. This includes;1. Any recent acute heart/major blood vessel condition (heart attack, aneurysm, etc.) or related surgery (heart surgery, aortic surgery, etc.) 2. Eye, ear or nasal surgery or conditions 3. Any recent episodes of coughing up blood 4. Any chest trauma (pneumothorax, broken ribs, etc.)Whilst these situations are not the best for spirometry, it may be necessary to predict from your results whether you will get any post-operative symptoms and so the risk from the test will be out-weighed by the benefit from knowing your outcome from a more dangerous surgical procedure. The person performing your testing should be knowledgeable about these issues. If not, ask to speak to a chest doctor, respiratory nurse on registered lung function scientist.
7. Will I know the results today? Often the doctor asking for the test will be using the spirometry along with other tests, signs and symptoms to build up a picture of your breathing problems and so the result in isolation may not mean very much. Clinical staff are trained not to give patients information out of context. This is not to be deliberately secretive or under-hand, but if you had a serious condition that needed a lot of questions answering, then those answers should be correct and explained appropriately to you by the person who knows most about your case. Generally, clinical staff will tell you if a test confirms a condition that you already had or shows an improvement to a drug (e.g. inhaler). However, rushing off to the internet may actually produce more questions than it solves. We know this website gives you honest and reliable answers, but not all do – but feel free to contact us with any questions on clarification if you wish. (See Contact Us at the top of the page
8. What are the essentials of the spirometry report? The lung function report should contain the following essential information;• Your name, date of birth, gender, height and weight. • Numerical values for your FEV1, FVC, VC and possibly PEF (see patient Info on Spirometry) • Reference (or “predicted”) values for someone of your, gender, age and height • A “Flow-volume” graph of your best 3 spirometry efforts • A comment or grade on the quality of your testing • A comment on the last time you took or were given medicationA written summary of the result may be provided for you or may be written by the requesting doctor when they receive the results. The test MUST be dated and signed by the person reporting the test.
9. Can I take my inhalers/medication before the test? This is a question you should have answered before you attend for your breathing test. Sometimes the appointment letter will tell you what to avoid before your tests. If this is unclear you should contact the centre who sent you the appointment and find out what you should do. If you are having an annual test (e.g. if you’ve been diagnosed with a breathing condition) you may be asked to have your medication prior to the test or you may be asked to take it at the breathing test centre. If in doubt - ask.
10. Is there anything else I need to know before my spirometry test? Finally, you should make sure that you prepare yourself for the tests. Make sure to avoid the following;Ask all or any of these questions and you should receive the correct answers from appropriately qualified and competent staff. If you feel they don’t know what they’re doing, ask for a more senior person or decline the test. Unless we stop the well-meaning amateurs, your time and efforts could well be wasted and at worse your health could be a risk. The wrong result could miss finding something serious or could mean unnecessary further tests and medication. Always look for the “ARTP” seal of approval in staff qualifications and training.• Tight clothing that would restrict you breathing in. • Eating a large meal just prior to the test (a snack within an hour should be OK) • If you need to go to the loo (bladder or bowel) before the test, make sure you do because the maximum manouvres can cause a little urinary incontinence or at the very least be uncomfortable. • If you have either diarrhoea or vomiting you should refrain from the test. • If you have a heavy cold or chest infection you should in most cases inform the centre and postpone the test until you are better.