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 lungsĀ
- 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