Spirometry is a straightforward, painless and non-invasive test that provides information about a person’s lung function. It is the basic test used to diagnose respiratory diseases.
What is it used for?
Spirometry measures the volume of air an individual can retain in their lungs (air capacity) and the inspiration and expiration rates during respiration (air flow rate).
It gives doctors information about lung function, so they can diagnose, determine the severity of and monitor any respiratory diseases. The test is often requested before a surgical intervention on the chest or abdomen whenever there is a suspicion of respiratory alterations. It is also carried out as a matter of routine during occupational health examinations.
How do I prepare for a spirometry test?
You should wear comfortable clothes and do not smoke for 2 hours before the test. Although you do not need to fast, it is a good idea not to eat or drink large amounts 2 hours prior to the test; nor should you make any strenuous efforts.
Before doing the test, tell the instructor if you use an inhaler, as you cannot use it to record the baseline value.
How is it performed?
Spirometry involves breathing through the mouth into a small tube. Your nose will be covered before starting to prevent air from escaping during the test. In a seated position, you will hold a small air flow meter (spirometer) with a disposable nozzle attached to the end. Place the nozzle in your mouth, bite with your teeth and close your lips around the nozzle, taking care not to block the hole with your tongue. Then complete the following steps:
- Breathe in normally.
- Breathe out gently until your lungs are completely empty.
- Take a long, deep breathe and fill your lungs.
- Breathe out forcefully and continue until the instructor tells you to stop, after approximately 6 seconds. Even though you may feel as if you cannot breathe out any more air, you must continue exhaling, so the test can measure every last breath of exhaled air.
- When you are instructed to stop, remove the mouthpiece and rest. These steps will be repeated at least 3 times, but it could be more.
The test is often performed in two stages. Firstly, a baseline measure is made without medication. Then, 15 minutes later, salbutamol is administered using an inhaler to determine if it produces any changes in lung function.
A spirometry test cannot be conducted in the following situations:
- A recent pulmonary thromboembolism or pneumothorax (2 weeks).
- Bleeding from the mouth.
- An active respiratory infection (tuberculosis or flu).
- Cardiovascular problems such as a recent heart attack (last 7 days), unstable angina or a growing or large (wider than 6 cm) thoracic aortic aneurysm.
Other factors that would postpone the test are:
- High intracranial pressure or very high systemic blood pressure.
- Acute retinal detachment.
- Confusional states or dementia.
- Recent abdominal, thoracic, brain, ocular or otorhinolaryngological (ENT) surgery.
- Diarrhoea or vomiting.
- Oral, dental or facial problems that could impede or hinder the placement of and grip on the nozzle.
Who performs the test?
The spirometry test is performed by nursing staff or lung function technicians.
Who interprets the results?
The pulmonologist is responsible for evaluating the test results and will write the corresponding report.
What can I expect to feel during the test?
Some patients mention a certain degree of tiredness due to the repeated effort. Therefore, the person responsible for conducting the test will include pauses, so the patient can rest between measurements. Some patients develop a headache when they finish and, very rarely, dizziness.
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