Spirometry is a simple instrumental test used to ascertain (diagnose) and follow (monitor) diseases of the respiratory tract over time and to evaluate the effectiveness of treatments. It measures the amount (volume) of air that enters (inhale) and exits (exhalation) from the lungs and the strength of the respiratory flow.
It is performed using an instrument called a spirometer, a small computerized machine connected via a cable to a mouthpiece inserted between the teeth of the person undergoing the examination.
Spirometry can be done by a nurse or doctor in an outpatient, hospital, or clinic. Usually, it is prescribed by the attending physician at the end of a visit if he detects respiratory problems such as, for example, a persistent cough; suspect the presence of bronchopulmonary disease or believe that the person examined is at risk of developing lung disease such as smokers do.
Diseases that can be identified and tracked with spirometry include:
- asthma, persistent (chronic) disease in which the airways periodically become inflamed causing respiratory crises, breathlessness and a sense of constriction
- pneumonia, inflammation of the lungs usually caused by viral, bacterial or fungal infections
- chronic obstructive pulmonary disease (COPD), a chronic disease characterized by partial narrowing of the airways and a decrease in the flow of air that enters and leaves the lungs (includes pulmonary emphysema and chronic bronchitis)
- cystic fibrosisa, genetic disease that affects the digestive system and lungs and leads to the formation of thick, viscous mucus that clogs the main ducts
- idiopathic pulmonary fibrosis, rare respiratory disease characterized by the formation of scar tissue in the lungs that causes respiratory failure
If any of these conditions have already been ascertained (diagnosed), spirometry may be done to check the severity or evaluate the response to treatment.
Spirometry is a test normally performed (routine test) in people who need to undergo surgery or in individuals with other diseases to check their general health.
It is often requested by the doctor to issue the certificate of suitability for the practice of sporting activities (in particular of competitive type), it is used to verify (screening) the presence of lung diseases in people at risk, both as a preventive and periodic evaluation, and in individuals assigned to particular jobs that require exposure to dust, irritating fumes, volatile chemicals.
Spirometry is a simple and quick test to perform that allows you to measure the amount of air that is inhaled and exhaled (ie you take a deep breath and then expel the air well). The success of the examination requires the active collaboration and maximum commitment on the part of the person who undergoes it.
For this reason, it is advisable for the person to be well informed about the examination and the behaviors to follow:
- avoid making intense efforts in the 30 minutes preceding the test
- avoid smoking at least 24 hours before the exam
- avoid having a large meal at least 2 hours before taking the test
- avoid drinking alcohol in the 4 hours prior to carrying out the test
- wear loose, comfortable clothing that does not hinder breathing
- avoid taking bronchodilator drugs
Typically, the test is performed while seated and in some cases a soft nose clip is applied to the nose to prevent air from escaping through the nostrils. When the exam begins, you are asked to perform the following maneuvers:
- inhale deeply, so that the lungs are completely filled with air
- squeeze the mouthpiece firmly between your lipsa to avoid air leaks
- exhale with full force and as quickly as possible into the mouthpiece connected to the spirometer, until the lungs are completely empty (to obtain a complete emptying of the lungs, the exhalation must last at least 6 seconds)
To guarantee a reliable result, it is usually asked to repeat the test three times. If you are unable to perform the test correctly with three tests, you can continue with the attempts up to a maximum of eight.
In some cases, if the doctor deems it appropriate, it may be necessary to repeat the test 15 minutes after taking an inhaled bronchodilator drug. This is to understand if it is possible to improve the disease found through the use of these medicines .
Spirometry is a safe and non-invasive test. Some people, however, at the end of the examination may feel a sense of dizziness, weakness, instability, fatigue due to excessive effort during exhalation. Others, particularly sensitive, may experience an increase in pressure in the head, a slight pain in the chest, stomach or eyes, due to forced exhalation.People who have high blood pressure that is not under medical (drug) supervision, who have recently been affected by unstable angina or a heart attack, who have had head, chest, stomach or eye surgery, should not undergo spirometry until they are cured or their condition is stable.
The duration of the test as a whole generally does not exceed 30-90 minutes. Soon after, you can go home and resume your normal activities.
Spirometry measures the amount of air inhaled in one second and the total volume of air exhaled at one time.
The spirometer, therefore, detects:
- the flow of exhaled air (expressed in liters / second)
- the total volume of exhaled aira (expressed in liters)
- the total time in which the exhalation takes place (expressed in seconds)
The results obtained are graphically represented through two curves (spirogram): the volume / time curve and the flow / volume curve which allow to evaluate different factors:
- CVF (Forced Vital Capacity): the maximum volume of air that can be expelled in a forced exhalation starting from a complete inspiration
- FEV1 (Maximum Expiratory Volume in the 1st second) or FEV1: the volume of air expelled in the first second of a forced exhalation, starting from a complete inspiration; it allows to measure the speed of emptying of the lungs. It is one of the most important values in a spirometry. The average values of FEV1 in healthy people depend mainly on age, sex, height, body mass and ethnicity.In general, in a healthy person (and also in the overwhelming majority of those who are sick with asthma) a percentage that is around 70-80% is considered normal compared to the theoretical value (calculated according to the CECA 1983 parameters); in subjects suffering from chronic obstructive pulmonary disease (COPD) and in those who have suffered a worsening of bronchial asthma, this percentage can be significantly reduced
- VEMS / CVF: the ratio between the maximum volume of air expelled in the 1st second of a forced expiration and the total volume of air expelled after a deep inspiration. It is used to assess whether an "obstructive" or "restrictive" disease is present, or a combination of the two. Obstructive airway disease occurs when the ability to breathe quickly is affected by the narrowing of the airways, but the amount of air that can be kept in the lungs is normal, such as in asthma or COPD. Restrictive lung disease occurs when the amount of air you breathe in is reduced because the lungs are unable to expand fully, such as in pulmonary fibrosis. The results are compared to normal values for a person of the same age, height, weight and gender. The FEV1 / FVC ratio in normal adult individuals fluctuates between 70% and 80%; a value below 70% indicates an obstructive deficit and a high probability of COPD
The results will then need to be analyzed by a specialist or discussed with the family doctor. However, they must never be judged in isolation, but contextualized and evaluated by the doctor together with the data obtained from the visit, the personal history of the person undergoing the examination and any other investigations.
NHS. Spirometry (English)
Mayo Clinic. Spirometry (English)
American Lung Association. Spirometry (English)
Pulmonary league. Spirometry (respiratory function test)
European Lung Foundation (English)