What is it about ?
Spirometry is a pulmonary function test that is recommended when certain lung conditions are suspected and to assess their treatment or progress.
Using a spirometer (a small device in which you breathe in and out), the doctor measures how much air the lungs can hold and which is displaced during inhalation and exhalation. This test can also estimate the amount of air that remains in the lungs after a full exhalation. By blowing into the device a curve is displayed on the screen of the spirometer.
To ensure that the test was performed correctly, several measurements are taken. The results are compared to values normally expected in a healthy person.
Drugs that affect breathing make the test unreliable. Therefore, in consultation with the doctor, the drug is discontinued before the examination.
Good cooperation is essential for the pulmonary function test to be carried out correctly. It is therefore difficult to perform the test in children under 6 years old. Errors frequently occur with coughing, incomplete inspiration, or incomplete or too slow expiration. Strictly follow the instructions given to you: place the forceps on your nose, sit up straight and place the mouthpiece in your mouth.
What are lung function tests used for?
Spirometry can distinguish between obstructive pulmonary disease and restrictive lung disease. To fully understand this, we will first explain the main parameters measured during lung function tests:
- Maximum expiratory volume per second (FEV1) is measured after breathing in deeply; this is the maximum amount of air you can breathe out quickly by forcing yourself for a second.
- Forced Vital Capacity (FVC) is the maximum amount of air you can breathe out after taking a deep breath.
- The Tiffeneau ratio is the FEV1 / FVC ratio. Normally, a person can exhale 70-80% of their vital capacity during the first second of a forced exhale.
- Peak expiratory flow (PEF) measures the maximum amount of air you can breathe out in one minute. This parameter can also be measured with a peak flow meter and is usually decreased (obstructed) or is temporarily normal in moderate or well controlled asthma.
Obstructive pulmonary disease
In obstructive pulmonary disease, the passage of air through the airways is limited; there is resistance to air flow.
The most common obstructive pulmonary diseases are asthma and COPD.
In COPD, the airways are permanently narrowed (irreversible), as in chronic bronchitis and emphysema. The cause is an abnormal inflammatory reaction to the inhalation of particles (dust, cigarette smoke, etc.).
In asthma, the narrowing is due to a contraction of the muscles around the airways. This process is usually still reversible.
In obstructive pulmonary disease, the Tiffeneau ratio is less than 70% of the normal value. The small airways have indeed narrowed, so you can breathe less air than expected in a second (comparable to exhaling while blowing through a straw). Expiration usually takes much longer than normal.
To distinguish asthma from COPD, a bronchodilation test will also be done. It allows the doctor to check whether the narrowing of the airways is reversible and therefore can improve with medication. In this test, the doctor will make you breathe a medicine that dilates the airways, and the test will then be repeated. If the airway narrowing is reversible, FEV1 should improve sufficiently.
Restrictive lung diseases
Restrictive means limited. These are lung diseases in which the amount of lung tissue responsible for breathing is reduced, resulting in a limitation in the amount of inhaled and exhaled air. The causes of restrictive lung disease may be damage to lung tissue (pulmonary fibrosis, partial lung removal, lung tumor, pneumothorax), damage to the respiratory muscles (paralysis in nervous disorders) or deformation of the chest wall (scoliosis, depression of the thorax during an accident). The total volume of the lungs therefore decreased, as did the FVC. Tiffeneau’s ratio is normal or even increased.
Mixed lung diseases
Mixed lung disease has features of both obstructive lung disease and restrictive lung disease.
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