Expired volume is greater than inspired volume under most
atmospheric conditions. The increase, due to warming and humidification,
is typically 5-10%. For this reason there will be “breath-dependent
drift” of the volume trace, even when the Spirometer is correctly zeroed.
We try to minimize this within the software by performing the volume correction, after the pod/spirometer has warmed up, and at
the beginning of the experiment as it can vary per person, per day, and per equipment.