A spirometer measures the breathing capacity of your lungs. It correlates the amount of air you can breathe out in 1 second and the total volume of air you can exhale in one forced breath. It is used to diagnose chronic lung condition such as:
- Asthma (especially exercise-induced asthma)
- Occupational-related lung disorders
- Chronic bronchitis
- Bronchiectasis (a condition where the bronchial tubes of your lungs are permanently damaged, widened, and thickened)
- Pulmonary fibrosis
Cystic fibrosis (a life-threatening disorder that damages the lungs and digestive system) physician may use a spirometer to evaluate if your asthma or chronic obstructive pulmonary disease (COPD) treatment is working.
Surgeons may use a spirometer before a planned surgery to assess your lung function.
What is a spirometer?
A spirometer is used to evaluate the functioning of the lungs. It measures the amount of air you inhale and exhale. It also assesses how quickly you exhale. It has a vacuum tube-like mouthpiece. The setup is connected to a computer with spirometer software. This will correlate and convert your breathing effort into a graph and numerical values. You'll have to take deep breaths and exhale at least thrice to get relatively consistent results. If there is too much variation among the three outcomes, you may need to repeat the test. The highest value among three close test results is used as the result.
How to use a spirometer?
While using a spirometer, you should follow these steps:
- Sit straight and hold the device.
- Place the mouthpiece of the spirometer in your mouth and secure it with the lips.
- Exhale normally.
- Inhale slowly.
- The piston in the spirometer will rise as you breathe in. The same effort will also be seen on the computer screen as an upward stroke on the graph.
- Try to raise the piston as high as you can.
- Usually, the doctor places a marker that tells you the amount of breath to be taken in.
- Aim to keep this ball in the middle of the chamber while you breathe in.
- If you inhale rapidly, the ball will shoot to the top.
- If you inhale slowly, the ball will stay at the bottom.
- Hold your breath for 3-5 seconds. Then slowly exhale. This will make a downward stroke on the graph.
The tests require you to take a deep breath followed by forceful expiration. Other test is normal breathing in and out.
Sometimes, your doctor may give you an inhaled medication (bronchodilator) to open your lungs after the initial round of tests. You'll need to wait 15 minutes and then perform another set of measurements. Your doctor then can compare the results of the two measurements to see whether the bronchodilator improved your airflow.
How to interpret the results of a spirometer?
The physician interprets the results of a spirometer with three key measurements:
- Forced vital capacity (FVC): This is the maximum amount of air that you can forcefully exhale after breathing in as deeply as you can. A lower than standard FVC reading signifies restricted breathing.
- Forced expiratory volume (FEV): It is the amount of air you can expel from your lungs in the first second of expiration. This reading helps your physician evaluate the severity of your breathing problems. Lower FEV-1 readings signify significant obstruction.
- Tidal volume: It is the lung volume representing the normal amount of air displaced between normal breathing in and out when extra effort is not applied. In a healthy young human adult, the tidal volume is approximately 500 mL per inspiration or 7 mL/kg of body mass.