Spirometry tests evaluate pulmonary function and helps determine the severity of asthma, chronic obstructive pulmonary disease (COPD), and other lung diseases. These tests are very useful in detecting lung disease early on, before symptoms begin.

Tests can be performed at your GP practice or in hospital. It is usually carried out during a short visit and is a painless, non-invasive procedure. The test is conducted with a device called a spirometer, which is attached to a mouthpiece that you hold in your mouth.

The test involves breathing into the spirometer tube as deeply as you can while it is attached to your mouth, then blowing air out of the device as quickly and forcefully as possible until the tube is empty. The results of the test are compared with a normal spirometer result for someone your age, height, and sex to assess your lung health.

There are two types of spirometry tests: relaxed or slow vital capacity (SVC) and forced vital capacity (FVC). A lower than standard FVC reading is considered restrictive lung disease. A higher FVC reading is normal or healthy.

Spirometry testing also provides the physician with information about tidal volume, which is the normal amount of air displaced between normal breathing in and out when extra effort is not applied. A tidal volume of approximately 500 mL per inspiration or 7 mL/kg of body mass is considered to be healthy.

In general, spirometry testing is safe and generally does not result in any negative effects or complications. However, some people may feel dizzy, faint, shaky, or sick or tired for a short period after the test.

The test should only be performed while sitting as standing might slightly affect your results, causing some numbers to differ. It is a "effort-dependent" test, meaning it is important to give your best effort to obtain accurate results.

Before the test, you should not smoke cigarettes for at least 24 hours or be taking medication that might affect your spirometry results. This includes bronchodilators, which can slow down your breathing.

During the test, your doctor will place a marker on the Spirometer คือ sensor tube to measure how much effort you are using to breathe in and out. This will tell you what your breathing effort is, and will appear on a computer screen in the form of a graph and numerical values.

Your doctor will also ask you to keep a ball in the middle of the spirometer while you are inhaling and exhaling into the device. As you inhale, the piston in the spirometer will rise, which will show up on the computer screen. You will then need to try to maintain this effort while you are exhaling.

You may need to repeat the test several times before you get consistent results. This is because your lung size (FVC) and respiratory rate (FRR) vary when you breathe in and out.

Spirometry tests should be delayed or avoided if there are any other conditions that could make the forced exhalation pressure on your head, chest, stomach, and eyes dangerous, such as unstable angina, uncontrolled high blood pressure, recent surgery to these areas, or a history of syncope associated with forced expiration.