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

Lung volumes residual volume

Lung volumes The maximum volume of the lungs is about 5dm 3 (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 dm 3 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 dm 3, rising to about 2.5 dm 3 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

Lung volumes; definitions Volume in dm 3 maximum inspiration Inspiratory capacity Inspiratory reserve volume Inspiratory reserve volume Vital capacity Vital capacity Tidal volume Expiratory capacity Expiratory capacity Residual volume Residual volume Total lung capacity Total lung capacity Expiratory reserve volume Expiratory reserve volume inspiration at rest expiration at rest maximum expiration