Spirometers (AQA GCSE Physical Education (PE)): Revision Note

Interpretation of a Spirometer Trace

• An individual's breathing can be measured and analysed using a piece of equipment called a spirometer

• Spirometers function as follows:

  • 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

• Spirometers can be used by an individual at rest or during exercise, e.g. running on a treadmill

Spirometer diagram

• Spirometer traces can be analysed to determine the following:

  • 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 trace allows differences between breathing at rest and breathing during exercise to be determined, e.g.

  • Changes in tidal volume

  • Changes in breathing rate

Spirometer trace diagram