Hi Eula, the CO2 levels can change quickly if you breathe more slowly or hold the breath, particularly holding the air out. Your nervous system sensitivity to CO2 (determining to some extent how fast you respire when at rest) can be gradually conditioned when you take on a daily breathing practice where you focus on slowing down the breath as well as introducing holds or pauses. I hope this helps.
@@eularichardson9270 The most direct way to influence this is through slowing down your breath in a disciplined, regular practice as well as making sure you are breathing through your nose and not your mouth. It's not really a matter of exercise and I'm not aware of any foods or drinks that will influence this. If you go for walks, only breathe through your nose. Try my free course on breathyoga.com and learn the basics of resonance frequency breathing and practice it daily for a week to see what you notice is changing within you. I hope that helps!
cold water immersion is something separate but Wim Hof breathing definitely lowers CO2 very quickly. But done in a short practice followed by a breath suspension then a breath hold and it is a potentially therapeutic process. The point about having low CO2 is more about chronic, unconscious overbreathing. Most conscious breathing practices will take the person towards a generally more healthy breathing pattern even when they are not paying attention to it!