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

Vo

lum

e in

dm3

maximum inspiration

Inspiratory capacity

Inspiratory reserve volume

Inspiratory reserve volume

Vital capacityVital capacity

Tidal volumeTidal volume

Expiratory capacityExpiratory capacity

Residual volumeResidual volume

Total lungcapacity

Total lungcapacity

Expiratory reserve volume

Expiratory reserve volume

inspiration at restinspiration at rest

expiration at restexpiration at rest

maximum expirationmaximum expiration