I use a breathing technique called Buteyko breathing normally. It is used to improve breathing for asthmatics. It is a little controversial but seems to work well for me. I managed to teach myself the technique without having the official classes. The upshot of it is that I run about three percent lower on O2 sats than most people. It involves training the body to breathe gently and become tolerant of higher CO2 levels in the blood.
Will this help me or hinder me if I happen to get CV19? I don't know. I am hoping any particles I inhale don't go as far into the lungs, so maybe that is a positive. I hope I don't have to find out either way on this question.