Key learning points
- Spirometry is recommended in both asthma and chronic obstructive pulmonary disease (COPD) guidelines
- Variability in the performance and understanding of spirometry interpretation has resulted in an estimated 50% of people having an incorrect diagnosis
- Spirometry consists of two measurements, the relaxed vital capacity (VC) and the forced vital capacity (FVC)
- There should be three attempts at all blows as a check of repeatability/reproducibility
- Novel therapies have shown improvements in lung function and a reduced frequency of pulmonary exacerbations
The use of spirometry as an objective measurement in the diagnosis of respiratory disease is widely acknowledged. It is recommended in both asthma and chronic obstructive pulmonary disease (COPD) guidelines, as well as those specific to spirometry.1-5
It is a relatively straightforward test to undertake and is essentially a practical skill. It has been available and performed in primary care for several years now, but with varying degrees of expertise and understanding.6
The variability in performance and poor understanding of spirometry interpretation has resulted in an estimated 50% of people receiving an incorrect diagnosis.7 Consequently, people are prevented from receiving appropriate treatment for their condition, or conversely receive medication they do not need.
Key areas: Preparing the equipment
The European Respiratory Society, the Irish Thoracic Society and the Faculty of Respiratory Physiology IICMS all include outline standards and requirements for spirometry equipment and its maintenance in their guidance documents.3–5
In general, all equipment should be:
- Calibrated annually
- Verified with a 3-litre syringe daily
- Cleaned between according to manufacturer’s instructions
- Operated with a one-way single-patient-use mouthpiece
Preparing the patients
Patients should be well enough to undertake the test, and contraindications should be considered and recorded. These are defined as relative or absolute and are listed below.
|Table 1. Relative contraindications3|
|Due to increases in myocardial demand or changes in blood pressure
Acute myocardial infarction within one week
Systemic hypotension or severe hypertension
Significant atrial/ventricular arrhythmia
Non compensated heart failure
Uncontrolled pulmonary hypertension
Acute cor pulmonale
Clinically unstable pulmonary embolism
History of syncope related to forced expiration/cough
|Due to increases in intracranial/intraocular pressure
Brain surgery within four weeks
Recent concussion with continuing symptoms
Eye surgery within one week
|Due to increases in sinus and middle ear pressures
Sinus surgery or middle ear surgery or infection within one week
|Due to increases in intrathoracic and intra-abdominal pressure
Presence of pneumothorax
Thoracic surgery within four weeks
Abdominal surgery within four weeks
|Infection control issues
Active or suspected transmissible respiratory or systemic infection, including tuberculosis
Physical conditions predisposing to transmission of infections, such as haemoptysis, significant secretions, or oral lesions or oral bleeding
Patient comfort should also be considered and they should be asked in preparation for the test to avoid:4
- Smoking within one hour
- Consuming alcohol within four hours
- Performing vigorous exercise within 30 minutes
- Wearing tight fitting clothing
- Eating a large meal within two hours
Performing the test
Spirometry consists of two measurements, the first is the relaxed vital capacity (VC), and the second is the forced vital capacity (FVC).
Relaxed vital capacity or VC
For this test, the patient must wear a nose clip or hold their nose. They are encouraged to take a maximum breath in, and then slowly and steadily exhale until all of the air is expelled and they cannot blow any more.
During the test, the mouthpiece should be completely within the mouth enclosed tightly by the teeth and not blocked by the tongue. Disposable, one-way filter mouthpieces should be used.
This should be repeated at least two more times and the values recorded manually to enable a check of repeatability/reproducibility. Guidelines state that three good blows should be performed, and the best two blows should be within 100 ml of each other.3–5
Forced vital capacity or FVC
The forced expiratory volume (FEV1) is taken from this test. FEV1 is the amount of air that is blown out in the first second of the FVC. A nose clip is not required for this test. Patients are encouraged to take a maximum breath in, and then exhale hard and fast until all of the air is expelled and they cannot blow any more.
As with the VC, the mouthpiece should be completely within the mouth enclosed tightly by the teeth and not blocked by the tongue. Disposable, one-way filter mouthpieces should be used.
This test should be repeated at least two more times and the values recorded manually to enable a check of repeatability/reproducibility. Guidelines state that three good blows should be performed and the best two blows should be within 100 ml of each other.3–5 This applies to both the FEV1 and the FVC values. For example:
- FVC | 4.26 | 4.28 | 4.32
- FEV1 | 3.99 | 3.97 | 3.99
The best two FVC values are highlighted and are within 40 ml of each other. All three are within 100 ml of each other. The best two FEV1 are the same, but are also only 20 ml different from the third blow. These results suggest this is a highly reproducible/repeatable test.
Finally, before the test can be interpreted, all readings and graphs need to be checked to see if they are also technically acceptable.
Some common technical errors in spirometry4,5
Further information about accredited spirometry training can be found at https://www.iars.ie/index or https://rotherhamrespiratory.com/course-portfolio/
Chris Loveridge, primary care respiratory nurse and Director of Inspirometry Training and Consultancy Limited
This project was initiated and funded by Teva Respiratory. Teva have had no influence over content. Topics and content have been selected and written by independent experts.