Spirometry: what it is, what it’s for and how it’s done

Spirometry is one of the most widely used tests to assess pulmonary function, and it plays a key role in diagnosing and monitoring various lung disorders. Simple, fast and non-invasive, this test measures the volume and speed of air a person is able to inhale and exhale.

Although this test is often associated with diagnosing asthma or Chronic Obstructive Pulmonary Disease (COPD), spirometry can be helpful in many other clinical scenarios.

Find out what it is, what it’s for, how it’s done and how to interpret the results.

Spirometry: what is it?

Spirometry is a diagnostic test that assesses lung capacity by measuring the volume and flow of air that is inhaled and exhaled. To perform this exam, the patient blows into a device called a spirometer, which records various parameters relating to pulmonary function. These data can detect respiratory changes that may not be apparent from symptoms or clinical examination alone.

Spirometry is considered the primary pulmonary function test to identify obstructive and restrictive patterns, two different forms of impaired lung function.
Simply put, an obstructive pattern occurs when patients experience difficulty exhaling air from the lungs, as is the case with asthma or COPD (Chronic Obstructive Pulmonary Disease). In the specific case of COPD, the diagnosis is confirmed using post-bronchodilator spirometry. In the case of a restrictive pattern, the lungs have less expansion capacity, reducing the total volume of air that a person is able to inhale. However, although spirometry helps identify or suggest changes compatible with a restrictive pattern, the restriction should be confirmed by measuring the total lung capacity.

Spirometry: what is it for?

Spirometry is used to assess lung function and help diagnose, monitor and manage various respiratory conditions.
The principal indications include:

•    Diagnosing asthma;
•    Diagnosing and monitoring COPD (Chronic Obstructive Pulmonary Disease);
•    Assessing restrictive pulmonary diseases;
•    Analysing persistent respiratory symptoms;
•    Pre-operative assessment for certain surgeries;
•    Monitoring the effectiveness of respiratory treatments;
•    Monitoring lung function in people exposed to occupational risk factors.

Furthermore, spirometry can help detect respiratory changes at an early stage, before the onset of serious symptoms.

Simple spirometry vs. bronchodilator spirometry: what’s the difference?

There are two primary types of spirometry: simple spirometry and bronchodilator spirometry. Both tests assess pulmonary function, but they are performed differently.

Simple spirometry

Simple spirometry involves measuring lung parameters without administering any medication during the test.
This test is often the first approach used to assess symptoms such as persistent cough, shortness of breath, wheezing or chest tightness. The results help identify changes in pulmonary function and determine the need for additional studies.

Bronchodilator spirometry

In the case of bronchodilator spirometry, the test is performed in two stages. First, a simple spirometry is carried out. Next, an inhaled bronchodilator is administered — a drug that relaxes the muscles around the airways — and, following a waiting period, the test is repeated.
A comparison of these two results indicates whether there is a substantial improvement in lung function after the medication was taken. This information is particularly useful to assess asthma and distinguish between different respiratory conditions.

Spirometry test: how is it done?

A spirometry test is simple, but requires the patient’s active cooperation for the results to be reliable. The test usually takes a few minutes and involves the following steps:

1. Preparation

Before the test, the healthcare professional explains the entire procedure and confirms all important information, such as symptoms, regular medication and respiratory history. In some cases, the patient may need to temporarily withhold certain inhaled medications, as instructed by the physician.

2. Placing the nose clip

A small clip is placed on the nose to prevent air from passing through the nasal passages during the test. Like this, all breathing takes place through the mouth.

3. Taking the deepest breath possible

At this stage, the patient takes a deep breath until the lungs are completely full. This is essential to ensure an accurate assessment of lung capacity.

4. Forced exhalation

Next, the patient blows into the spirometer’s mouthpiece as hard and as fast as possible. The exhalation should be maintained until instructed otherwise by the healthcare professional, even when it feels like there is no more air to exhale.

5. Repeat the manoeuvres

To ensure reliable results, the procedure is usually repeated several times. This way, the best readings are considered.

6. Bronchodilator test (when applicable)

If a bronchodilator spirometry test has been prescribed, an inhaled medication is administered and the test is repeated after a few minutes. This comparison provides an assessment of the airway’s response to treatment.

Spirometry: preparation for the test

While spirometry is a simple and non-invasive test, some prior precautions can help ensure more accurate results. As the goal is to assess pulmonary function in the best possible conditions, it’s important to follow the guidelines provided by the medical team before undergoing the test.

It is usually recommended to:

•    Avoid smoking in the hours before the test; 
•    Avoid caffeinated drinks such as coffee, black tea or energy drinks, unless advised otherwise; 
•    Avoid heavy meals immediately before a spirometry test, as abdominal discomfort can impair respiratory movements; 
•    Wear comfortable clothing that does not constrict the chest or abdomen; 
•    Avoid strenuous physical exercise in the hours before the test.

In some cases, it may also be necessary to temporarily withhold certain inhaled medication, such as short- or long-acting bronchodilators. However, this decision should always be made as directed by your physician, as it depends on the purpose of the spirometry test.

If you have an acute respiratory infection, such as a cold or flu, you should inform the medical team before the test, as certain situations may justify postponing the procedure to prevent the results from being influenced by a temporary condition.

Following these recommendations will help the spirometry test reflect your normal pulmonary function more precisely, enabling a more accurate interpretation of the results.

Spirometry: take care of your airways with Joaquim Chaves Saúde

A spirometry test is a key tool to assess pulmonary function, as it helps identify respiratory changes, aid the diagnosis of conditions such as asthma and COPD (Chronic Obstructive Pulmonary Disease), and monitor the effectiveness of treatments over time. 

If you are experiencing persistent respiratory symptoms, such as shortness of breath, chronic coughing or wheezing, or if you need to monitor a respiratory disorder that has already been diagnosed, schedule your consultation or test at a Joaquim Chaves Saúde clinic and receive outstanding medical care. A proper assessment can make all the difference when it comes to protecting your respiratory health.