What are the parts of a spirometer?

Written by misty barton
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What are the parts of a spirometer?
Spirometers are used both at home and in hospitals. (Comstock/Comstock/Getty Images)

A spirometer is a medical tool used to measure the amount of air a person pushes out of their lungs while exhaling. It can be used both as a diagnostic tool and as a mode of treatment to improve the lungs' overall function. A spirometer has six basic parts: the nose plug, the mouthpiece, the breathing coach indicator, the barrel, the piston and an adjustable indicator.

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Nose Plug

Most spirometers have a nose plug with a clip on top. The clip allows the nose plug to be attached to the main body of the spirometer for storage. The nose clip is worn by the person breathing through the spirometer to make sure that all the air they express through their lungs comes out through their mouth. Exhaling through the nose would make the test results inaccurate.


The mouthpiece on a spirometer is contoured to sit comfortably inside the lips and in front of the teeth. The person using the spirometer breaths naturally into the mouthpiece, which is attached to the spirometer by a wide plastic tube. The end of the tube is connected to the breathing coach and barrel.

Breathing Coach Indicator

The breathing coach indicator is a small plastic bead set inside a vacuum chamber. The bead rises in the chamber as the patient inhales. The bead rises as a visual aid to show the depth of the breath taken. When the bead reaches the target range for the user, it is at the top of the vacuum chamber.

Adjustable Indicator

The adjustable indicator is a small plastic arrow that attaches to a slide on the outside of the barrel. The slide can be moved up or down to mark breathing goals or best results.


The barrel is the main chamber of the spirometer. The outside of the barrel is marked with a breath volume indicator. It has marked lines from 500 to 5000ml, with hash marks in increments of 500. The piston is inside the barrel.


The piston is a large flat weight that rises in the barrel as the user blows his breath out into through the mouthpiece and into the spirometer. The higher the piston raises in the barrel, the greater the volume of the exhalation.

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