Measuring Lung Volumes: Skills (DP IB Biology)

Measuring Lung Volumes

• It is possible to investigate the effect of exercise on ventilation using an apparatus called a spirometer

  • It contains a chamber filled with water which is covered by a hinged plastic lid

  • The person partaking in the experiment breathes through a mouthpiece which is connected to the spirometer chamber

  • The plastic lid moves up and down as breathing occurs

• The spirometer chamber could be filled with either air or oxygen

  • When filled with air, it can be used to determine lung capacity in different conditions

  • When filled with oxygen and soda lime (for absorbing carbon dioxide), it can measure oxygen consumption in different conditions

• Spirometer traces are created by:

  • Drawing a line on a revolving drum as the lid moves

  • A computer which draws a graph of the results

• Several measurements can be made using spirometer traces such as:

  • Ventilation rate

  • Tidal volume

  • Reserve volumes during inspiration and expiration

  • Vital capacity

A classic spirometer can be used to investigate ventilation

Using a spirometer to monitor ventilation can also be carried out with an electric spirometer

Analysis of spirometer trace

• The effect of exercise on ventilation can be seen in the spirometer trace below

Tidal volume

• The tidal volume is the volume of air inhaled and exhaled during normal breathing

  • Exercise will lead to an increase in the tidal volume as more air is moved in and out of the lungs 

  • We do have the potential to take extra deep breaths

    • The maximum volume of air that can enter the lungs during inspiration is known as the maximum inspiratory level

    • Similarly, the maximum volume of air that can be exhaled during expiration is known as the maximum expiratory level

Inspiratory and expiratory reserve volumes

• The reserve volumes of the lungs refer to the extra volume of air that can be inhaled or exhaled when taking an extra deep breath and are determined as follows:

  • The difference between the maximum inspiratory level and tidal volume is called the inspiratory reserve volume

  • The difference between the maximum expiratory level and tidal volume is called the expiratory reserve volume

Vital capacity

• The vital capacity (VC) refers to the total amount of air exhaled after taking a deep breath

  • This can be calculated by adding the tidal volume (TV), inspiratory reserve volume (IRV) and expiratory reserve volume (ERV) together

VC = TV + IRV + ERV

Ventilation rate

• The ventilation rate can be determined by counting the number of inhalations or exhalations per minute

  • Exercise will cause an increase in the ventilation rate as you will be taking more breaths per minute