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Know what a spirometer is?

A spirometer is a device used to measure the volume of air inhaled and exhaled by an individual. Spirometry, derived from the Latin words SPIRO (to breathe) and METER (to measure), is a medical test that provides diagnostic information to assess a patient's lung function.

Normal inhalation involves the unrestricted passage of air down the trachea or windpipe, then through the bronchi, which are large tubes, the bronchioles, which are smaller tubes, and ultimately into the alveoli, which are tiny sacs. Your alveoli are surrounded by tiny blood arteries called capillaries. Your capillaries receive oxygen from the air you inhale. Afterward, carbon dioxide from your body exits your capillaries and enters an alveolus. When you exhale or breathe out, you get rid of the carbon dioxide.

Asthma, bronchitis, and pulmonary fibrosis are a few illnesses that can cause your bronchioles to get narrower and less air can enter your lungs. Additionally, illnesses like emphysema and lung cancer harm your alveoli, lowering the amount of oxygen in your blood. You may have trouble breathing as a result of certain illnesses. To diagnose a lung condition, assess the severity of an existing lung condition, or ascertain if the treatments you are taking are effective, a doctor may advise a spirometry test. The caregiver will use a tool called a spirometer during the test.

As a result, a spirometer's main use is to aid medical practitioners in the diagnosis and monitoring of respiratory disorders such as cystic fibrosis, chronic obstructive pulmonary disease (COPD), and asthma.

Basics of Spirometer

A mouthpiece for the user to breathe through, a measuring chamber, and a recording device make up a simple spirometer. Spirometers are available in both handheld and desktop varieties, and the most advanced ones are digital and include software to plot and analyze data.

The measurement chamber is linked to the mouthpiece, which is then linked to the recording tool, which might be a pen and paper, a digital display, or even a computer. The spirometer monitors the amount of air that is inhaled and exhaled over time when the user inhales and exhales through the mouthpiece.

Units measured in a Spirometer

The spirometer measures several different respiratory parameters that are used to diagnose and monitor respiratory diseases. The most common measurements are:

  • Forced Vital Capacity (FVC): The total volume of air that an individual can exhale forcefully after taking the deepest breath possible.

  • Forced Expiratory Volume in 1 Second (FEV1): The volume of air that an individual can exhale forcefully in one second.

  • Forced Expiratory Flow 25%-75% (FEF 25%-75%): The average flow rate of air that an individual can exhale during the middle half of the FVC maneuver.

These spirometry measurements are expressed as numbers and are often compared to normal values for age, height, sex, and race. Because lung function declines with age, the normal values for each measurement also decrease with age.

Interpretation of Spirometry

Once the spirometry measurements have been obtained, they are interpreted to determine if an individual has a respiratory condition. Depending on the particular respiratory condition being evaluated, there are various ways to interpret spirometry results.

For example, in asthma, the FEV1 value is often used to assess the severity of the disease. A low FEV1 value indicates that there is reduced airflow in the lungs, which can indicate asthma. In COPD, the FEV1/FVC ratio is used to determine the severity of the disease. A low FEV1/FVC ratio indicates that an individual has COPD and that their airways are significantly narrowed.

Limitations of Spirometry

Spirometry has various limitations that must be considered even though it is a crucial tool in the diagnosis and treatment of respiratory diseases. Spirometry measures can be affected by elements including age, sex, and ethnicity, which is one drawback. Therefore, it is essential to compare spirometry results to normal values for the same age, sex, and race to get an accurate diagnosis.

In addition, spirometry measurements can also be affected by other factors such as smoking, obesity, and recent lung infections. These factors can often lead to false-negative or false-positive results and need to be taken into account when interpreting spirometry results.

The spirometer is also not suitable for young children, as they may not be able to perform the test correctly, and the results may not be accurate.

Finally, spirometry does not provide information about the structure of the lungs or airways. Other tests, such as a chest X-ray or CT scan, may be required to get a complete picture of an individual's respiratory health.


Spirometers are beneficial tools for the diagnosis and management of respiratory conditions. It provides lung volume and airflow measurements that are used to measure how severe respiratory disorders like asthma and COPD are. Spirometry is a useful tool for healthcare practitioners even if it has several drawbacks, such as its reliance on normal values and the possibility of false-positive and false-negative results. Therefore, spirometry testing should be done frequently, whether a person has respiratory symptoms or a family history of respiratory diseases.

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