Measuring lung volumes

• Using a spirometer

  • a device that can measure the movement of air into and out of lungs
  • a float-chamber apirometer consists of a chamber of air or medical-grade oxygen floating on a tank of water
  • Inspiration, air is drawn from chamber so the lid moves down
  • Expiration, air returns to chamber, raising lid
  • movements are recorder on a datalogger
  • the carbon dioxide-rich air exhaled is passed through a chamber of soda lime, which absorbs the carbon dioxide. This allows the measurements of oxygen consumptions.
• precautions

  • the subject should be healthy and in particular free from asthma
  • the soda lime should be fresh and functioning
  • there shjould be no air leaks in the apparatus, as this would give an invalid or inaccurate results
  • the mouthpiece should be sterilised
  • the water chamber must not be overfilled
• lung volumes

  • total lung volume consists of vital capacity, which can be measured, and residual volume, which cannot be measured with spirometer
  • Vital capacity - maximum volume of air that can be moved by the lungs in one breath

  this is measured by taking a deep breath and expiring all the air possible from the lungs

  factors : size of person (particularly their height) , age and gender, level of regular exercise

  vital capacity is usually 2-5-5.0 dm 3 , but may rise above this in trained athletes
• lung volumes 2

  • Residual volume - volume of air remaining in the lungs after maximum expiration
  • this air remains in the airways and alveoli ; apprximately 1.5dm 3
  • Tidal volume - volume of air inhaled and exhaled during normal breathing
  • normally measured at rest ; typical tidal volume at rest might be 0.5dm 3 and usually insufficent to supply oxygen required at rest
• Oxygen uptake

  • As a person breathes from spirometer , oygen is absorbed by blood and replaced by carbon dioxide; when carbon dioxide is absorbed by soda lime, the volume of air in chamber decreases
  • this decrease can be observed and measured on spirometer trace
  • assume that volume of carbon dioxide relased and absorbed by soda lime = the volume of oxygen absorbed by the blood →that’s why measuring the gradient of the decrase in volume enables us to calculate rate of oxygen uptake

  oxygen uptake depends on :

  • increased breathing rate
  • deeper breaths
• THE AIR YOU BREATHE IN IS OXYGEN-RICH, OUT IS CARBON DIOXIDE-RICH