Measuring lung capacity

• What is a spirometer?

  The instrument used to measure vital capacity, tidal volume, breathing rate and oxygen uptake
• What are the mechanics of ventilation? (inspiration)

  The inspiratory control centre in the medulla oblongata sends out nerve impulses to cause the inspiratory muscles to contract
• What are the mechanics of ventilation? (expiration)

  The inspiratory control centre in the medulla oblongata stops sending out impulses to inspiratory muscles so they relax
• How does a spirometer work?

  1. There is a static, lower half of the tank which has water
  2. There is a mobile, upper half of the tank which has air
  3. A person breathes out of the tank which causes the upper half to rise
  4. A person breathes into the tank which causes the upper half to fall
  5. There is a trace marker attached to the upper half shows how much air has been inspired and expired
• What does a peak flow meter do?

  Measures the rate that air is expelled (expired) at
• What happens to the trace when inspiration happens

  Trace goes down
• What happens to the trace when expiration happens?

  Trace goes up
• What is the inspiratory reserve volume?

  The maximum volume of air you can inspire over and above normal inhalation
• What is the Tidal volume?

  The volume of air that moves in and out of the lungs per breath (average adult = 500 ml)
• What is the expiratory reserve volume?

  The maximum volume of air you can expire over and above normal expiration
• What is the residual volume?

  The volume of air left in your lungs after maximum exhalation
• What is the vital capacity?

  The maximum volume of air that can be expired after maximum inspiration
• What is the total lung capacity?

  The potential volume of air in the lungs

  (vital capacity + residual volume)
• What happens to the gas tank of the spirometer over time?

  1. When breathing, the oxygen from the tank is is used up
  2. When breathing, the carbon dioxide expired is dissolved in soda lime
  3. This causes the total volume of the tank to decrease over time