Spirometry test: Who it’s for and why it’s needed

The lungs play an essential role in supplying the body with the oxygen needed for cells to produce energy. There is no source of oxygen other than what the lungs provide, and holding your breath for only a few seconds is all it takes to quickly feel the signs of oxygen deprivation. In addition, the lungs eliminate a large proportion of the carbon dioxide (CO2) resulting from metabolism, helping maintain pH balance in the blood and preventing it from dropping (acidosis). Finally, the lungs can react almost instantaneously to the body’s need to take in oxygen or eliminate CO2, depending on our physical needs and the quality of the air we breathe.

The respiratory system begins with the nose and mouth, then continues through the pharynx and larynx to the trachea. The trachea then splits into two primary bronchi, which feed the three lobes of the right lung and the two lobes of the left lung. These main bronchi then branch out like a tree, subdividing into ever more tubes with ever smaller diameters, known as bronchioles. The bronchioles end in tiny alveolar sacs that are in contact with blood vessels, where exchanges of gases (oxygen and CO2) take place. The lungs contain around 300 million of these alveoli, corresponding to a surface area of nearly 80 square metres (800 square feet) in contact with the bloodstream, or about half the size of a tennis court![4]

The lungs are surrounded by the pleurae, which consist of two layers. One is in contact with the lung (visceral pleura) and the other is in contact with the rest of the chest (parietal pleura). The two layers are separated by the pleural cavity, which contains a liquid that enables the lungs to move more easily under pressure from the diaphragm, the muscle responsible for breathing.

In a resting state, we inhale about 500 mL of air, 350 mL of which eventually reach the alveoli, leaving a dead volume of 150 mL. Normal respiratory flow is between six and eight litres per minute.

A number of diseases and other conditions can lead to impaired breathing, either by obstructing and/or causing inflammation of the bronchi and bronchioles, or by interfering with the exchange of gases in the alveoli.

Respiratory problems are often the result of a combination of causes. However, one of the most common remains smoking, whether current or past, via direct exposure to smoke or second-hand smoke. We must also not overlook the impact of poor air quality and occupational exposure on respiratory health.

According to the Canadian Lung Association, spirometry is recommended for people with any of the following symptoms, especially smokers over the age of 40:[6]

• Tightness, pain or pressure in the chest
• Cough, especially if accompanied by mucus
• Difficulty breathing deeply
• Shortness of breath (dyspnea) even after a simple task
• Wheezing during exertion or at night
• Colds that last longer than those of people around you

Spirometry is also recommended for anyone diagnosed with chronic obstructive pulmonary disease (COPD) or with asthma that is worsening:[7]

• More than two asthma attacks per week
• At least one nocturnal asthma attack per week
• More than two doses of rescue medication per week
• Any limitation of activity (school, work, leisure) due to asthma

Spirometry is a technique used to assess lung function by measuring the quantity of air inhaled and exhaled, along with the speed of these respiratory movements. This technique helps identify the nature of a lung problem, whether it is obstructive or restrictive. Spirometry is also used to assess the quality of breathing when establishing a diagnosis, as well as to track a disease’s progression and the efficacy of treatments over time.

Three basic techniques are used in spirometry:[8]

1. The simple spirometry test objectively assesses an individual’s lung function, and in a patient undergoing treatment, verifies the treatment’s efficacy.
2. The pre- and post-bronchodilator spirometry test measures breathing response to a fast-acting bronchodilator similar to the one used in treatment at home.
3. The methacholine bronchial challenge test is used to diagnose bronchial hyperreactivity (asthma), especially when clinical pulmonary and spirometry tests reveal no abnormalities.

These three procedures are performed under the supervision of a qualified respiratory therapist, and the results are interpreted by respirologists.

Each test requires little preparation (no food in the past hour, restriction on certain medications, etc.). You will be asked to take a seat, then empty your lungs without forcing, inhale as deeply as possible, and then exhale as quickly and for as long as possible. These steps can be repeated several times until satisfactory results are obtained. The test is conducted in complete safety, and the respiratory therapist will make sure you breathe as comfortably after the test as you did before.