That’s an interesting point @TinaT. First of all, I wonder how playing a sax compares with using a Frolov device. Second of all, even if they are comparable, I gather that even more important is how you are breathing the rest of the day. Even if you are breathing in a lot of CO2 with the Sax or Frolov device, how you are breathing when not engaged with those devices is paramount. Others here are much more knowledgeable on this subject and will perhaps chime in to correct me.