RP17

• Spirometer


  Device which measures breathing and respiration
• What a spirometer can measure

  • Breathing rate (number of breaths per minute)
  • Tidal volume (volume of gas of one normal breath)
  • Respiratory minute ventilation (volume of gas inhaled per minute)
  • Vital capacity (volume of gas of one forced deep breath)
• Spirometer


  • Chamber filled with air, connected by tubes and suspended in a tank of water
  • Lid of the chamber moves up and down as the volume of gas changes
  • Contains soda lime to absorb the exhaled carbon dioxide
• Using a spirometer


  1. Find the vertical scale by emptying the chamber, starting the kymograph and then forcing a known volume of air into the chamber

  2. Find the horizontal scale by setting it to 1 mm per second, using the switch (or as close to 1 mm per second as possible)

  3. A trained member of staff can fill the spirometer with medical grade oxygen

  4. Disinfect the mouthpiece and attach it to the tube

  5. Subject attaches the nose clip and breathes into the tube for a while to practice

  6. Start the datalogger/kymograph and turn the tap to attach the tube to the spirometer

  7. Subject takes one forced deep breath and then breathes normally into the spirometer for a duration of 5 minutes maximum
• The graph produced by a spirometer is called a spirograph or spirometer trace
• Equipment needed


  • Spirometer
  • Datalogger/computer/kymograph
  • Soda lime
  • Disinfectant
  • Nose clip
• If the experiment is repeated after exercise

  • Tidal volume increases
  • Vital capacity remains the same
  • Breathing rate increases
  • Respiratory minute ventilation increases
• Respiration increases during exercise because of increased muscle contraction, so more oxygen is required and more carbon dioxide is produced, so breathing rate, tidal volume and therefore respiratory minute ventilation increases to cope with this demand up to the maximum aerobic rate. After this point, minute ventilation will plateau to a maximum and further respiration will be anaerobic.
• Informed consent should be obtained before anyone uses the spirometer, as they are a participant in scientific research. Anyone should be allowed to refrain from participating or contributing their data, and can stop at any time during the practical.