Spirometers

What can be used to measure and analyse an individual’s breathing?

A piece of equipment called a spirometer

How does a spirometer function?

• The individual breathes via a tube that is connected to a floating box of air

  • The tube is also connected to a canister of a chemical called soda-lime which absorbs exhaled carbon dioxide; this allows the spirometer to record only the changing volumes of oxygen

• An inward breath removes air from the box, causing it to sink lower into the water

• Breathing outputs air into the box and causes it to rise up in the water

• A metal arm with a pen is attached to the side of the box, and this arm draws a trace on a rotating drum as the individual breathes, producing a spirometer trace

When can a spirometer be used?

By an individual at rest or during exercise

What can spirometer traces be used to determine?

• Tidal volume

  • The volume of air breathed in and out with each normal breath

  • At rest, tidal volume is approximately 500ml

• Inspiratory reserve volume

  • The difference between the tidal volume and the total volume of air breathed in during a deep inhalation

• Expiratory reserve volume

  • The difference between the tidal volume and the total volume of air breathed out during an active exhalation

• Residual volume

  • The volume of air that remains in the lungs even after a maximal exhalation

Analysis of a spirometer allows differences between what to be determined?

between breathing rate and breathing during exercise to be determined