Our blood have a pH around the 7.0, when we hold the breath our cells still breathing, and the release [tex]CO_2[/tex], this compound react with water (hydrolysis).
[tex]H_2O+CO_2\leftrightharpoons H_2CO_3[/tex]
This compound formed by this reaction is acid, carbonic acid.
Them the pH will get lower them normal, and our buld send an action to our body, and this reaction will be the breathing.
