Spirometer: What is it? What is it for? Preparation, Procedure, Side Effects and Values ​​of the Spirometry Test

It is a small breathing machine that is used to perform a spirometry test.

Spirometry is a standard test that doctors use to measure how well your lungs are working . The test works by measuring the flow of air in and out of the lungs.

The spirometer medical device records the amount of air you breathe in and out and the speed of your breathing .

Spirometry tests are used to diagnose the following conditions:

  • Chronic obstructive pulmonary disease or COPD.
  • Asthma .
  • Restrictive lung disease (such as interstitial lung fibrosis).
  • Other disorders that affect lung function.

They also allow your doctor to monitor chronic lung conditions to verify that your current treatment is improving your breathing.

Spirometry is often done as part of a group of tests known as pulmonary function tests.

How to Prepare for a Spirometry Test

You should not smoke an hour before a spirometry test. You will also have to avoid alcohol that day as well. Eating too much food could also affect your ability to breathe.

Do not wear clothing so tight that it can restrict your breathing. Your doctor may also have instructions on whether to avoid using inhaled breathing medications or other medications before your test.

Spirometry procedure

A spirometry test usually takes about 15 minutes and usually occurs in your doctor’s office. This is what happens during a spirometry procedure:

  1. You will be sitting in a chair in an exam room at your doctor’s office. Your doctor or a nurse places a clip on your nose to keep both nostrils closed. They also put a cup-like breathing mask around their mouth.
  2. Your doctor or nurse then instructs you to take a deep breath, hold your breath for a few seconds, and then exhale as hard as possible into the breathing mask.
  3. Repeat this test at least three times to make sure your results are consistent. Your doctor or nurse may ask you to repeat the test more times if there is a large variation between the test results. They will take the highest value from three close test readings and use it as the final result.

If you have evidence of a breathing disorder, your doctor may give you an inhaled medicine known as a bronchodilator to open your lungs after the first round of tests. They will then ask you to wait 15 minutes before taking another set of measurements.

Your doctor will then compare the results of the two measurements to see if the bronchodilator helped increase your airflow.

When used to monitor respiratory disorders, a spirometry test is usually performed once a year to once every two years to monitor changes in breathing in people with COPD or well-controlled asthma.

Those with more severe breathing problems or breathing problems that are not well controlled are recommended to perform more frequent spirometric tests.

Spirometry side effects

Few complications can occur during or after a spirometry test. You may feel dizzy or have trouble breathing immediately after taking the test. In very rare cases, the test can trigger serious breathing problems.

The test requires some effort, so it is not recommended if you recently had heart disease or have other heart problems.

Spirometry Normal Values ​​and How to Read Test Results

Normal results for a spirometry test vary from person to person. They are based on your age, height, race, and gender. Your doctor calculates the normal value expected for you before performing the test.

After you’ve run the test, they look at the test score and compare that value to the predicted value. Your result is considered normal if your score is 80 percent or more of the predicted value.

You can get a general idea of ​​your predicted normal value with a spirometry calculator. The Centers for Disease Control and Prevention provides a calculator that allows you to enter your specific details.

If you already know your spirometry results, you can enter those as well, and the calculator will tell you what percentage of the predicted values ​​your results have.

Spirometry measures two key factors: forced expiratory vital capacity (FVC) and forced expiratory volume in one second (FEV1). Your doctor also considers them as a combined number known as the FEV1 / FVC ratio.

If you’ve blocked your airway, the amount of air you can quickly push out of your lungs will be reduced. This results in a lower FEV1 and FEV1 / FVC ratio.

FVC measurement

One of the main spirometry measurements is FVC, which is the highest total amount of air that you can forcefully exhale after taking as deep a breath as possible. If your FVC is lower than normal, something is restricting your breathing.

Normal or abnormal results are evaluated differently between adults and children:

For children from 5 to 18 years old:

  • 80% or more: normal.
  • Less than 80%: abnormal.

For adults:

  • Greater than or equal to the limit: normal.
  • Less than limit: abnormal.

An abnormal FVC could be due to restrictive or obstructive lung disease, and other types of spirometry measurements are required to determine what type of lung disease is present.

An obstructive or restrictive lung disease may be present on its own, but it is possible to have a mixture of these two types at the same time.

FEV1 measurement

The second key spirometric measurement is forced expiratory volume (FEV1). This is the amount of air that you can expel from your lungs in one second. It can help your doctor assess the severity of your breathing problems.

A lower than normal FEV1 reading shows that you may have significant respiratory obstruction.

Your doctor will use your FEV1 measurement to assess how severe the abnormalities are. Here’s what is considered normal and abnormal when it comes to FEV1 spirometry test results, based on the American Thoracic Society guidelines:

  • 80% or more: normal.
  • 79%-70%: slightly abnormal.
  • 69% -60: moderately abnormal.
  • 59% -50%: moderate to severely abnormal.
  • 49%-35%: severely abnormal.
  • Less than 35%: very severely abnormal.

FEV1 / FVC ratio

Doctors often analyze FVC and FEV1 separately, and then calculate their FEV1 / FVC ratio. The FEV1 / FVC ratio is a number that represents the percentage of lung capacity that you can exhale in one second.

The higher the percentage derived from your FEV1 / FVC ratio, in the absence of restrictive lung disease causing a normal or elevated FEV1 / FVC ratio, the healthier your lungs will be. A low proportion suggests that something is blocking your airway:

  • Low FEV1 / FVC ratio from 5 to 18 years: less than 85%.
  • Low FEV1 / FVC ratio in adults: less than 70%.

Next steps

If your doctor finds that your results are abnormal, they will likely perform other tests to determine if your breathing disturbance is caused by a breathing disorder. These could include chest and breast x-rays or blood tests.

Primary lung conditions that will cause abnormal spirometric results include obstructive diseases such as asthma and COPD and restrictive diseases such as interstitial pulmonary fibrosis.

Your doctor can also detect conditions that commonly occur along with breathing disorders that can make your symptoms worse. These include heartburn, hay fever, and sinusitis.