Measuring lung volumes
Syllabus reference:
 outline the mechanism of breathing in mammals, with reference to
the function of the rib cage, intercostal muscles and diaphragm
 explain the meanings of the terms tidal volume and vital capacity
 describe how a spirometer can be used to measure vital capacity,
tidal volume, breathing rate and oxygen uptake
 analyse and interpret data from a spirometer
Inspiration &
expiration
Inspiration &
expiration
Lung volumes
residual volume
Lung volumes

The maximum volume of the lungs is about 5dm3 (5 litres)
although we never completely empty the lungs; even if we
breathe out as much as possible (expiratory capacity) there
will still be about 1.5 dm3 left in the lung (residual volume).

The amount of air breathed in and out at each breath is called
the tidal volume. At rest this will be around 0.5 dm3, rising to
about 2.5 dm3 when we are breathing very deeply.

The maximum volume that can be exchanged by breathing in
as much as possible and then forcing out as much as possible
is our vital capacity.
The spirometer
oxygen
Spirometer
Lung volumes
Note: compare to ‘inverted’ trace in textbook
Lung volumes
The spirometer
oxygen
Lung volumes; definitions
maximum inspiration
Volume in dm3
Inspiratory
capacity
Inspiratory
reserve
volume
Vital
capacity
inspiration at rest
Tidal volume
expiration at rest
maximum expiration
Expiratory
Expiratory
capacity
capacity
Expiratory
reserve
volume
Total
lung
capacity
Residual
Residual
volume
volume