Library · Physiology
Lung volumes
Make it clearer
Total lung capacity is the air inside the lungs when someone has inhaled with the greatest possible effort. In healthy adults it runs about 6 liters.
That total is not one single bag: it is divided into four volumes. Tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume.
The last one is the one that usually surprises people. Residual volume is the air that is still there after a maximal forced exhalation, that is, after blowing out everything you possibly can: it cannot be expelled, and it helps hold open the alveoli, the tiny sacs where the lung exchanges gases. It is a glass that never empties all the way.
That also shapes how each one is measured. Three of the four volumes are measured with a spirometer, the device you blow into, and residual volume is not: that one takes more advanced techniques.
In brief
Total lung capacity is the air in the lungs after a maximal inhalation, about 6 liters in healthy adults.
It is divided into four volumes: tidal, inspiratory reserve, expiratory reserve, and residual.
Residual volume is what remains after a maximal forced exhalation; it cannot be expelled and helps keep the alveoli expanded.
A glass that never empties all the way.
Three of these volumes are measured with a spirometer; residual volume is not, and requires more advanced techniques.
Sources (2)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Lung Capacity, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Residual Volume, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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