The residual volume can not be measured directly.
Residual volume is known to be measured by what we call a gas dilution test.
Note that this test often measures how the concentration of the gases in the container changes.
This is known to be the Volume of air that is left over after a FORCED EXPIRATION. Note that it is one that cannot be measured by a spirometer.
Hence, The residual volume can not be measured directly.
Learn more about residual volume from
https://brainly.com/question/12897209
#SPJ1