Slow breathing, unless you are doing it to an extreme, doesn't actually significantly alter blood oxygen levels. Mostly you are dealing with carbon dioxide leve

Slow breathing, unless you are doing it to an extreme, doesn't actually significantly alter blood oxygen levels. Mostly you are dealing with carbon dioxide levels. In fact, due to the dilation of the blood vessels caused by CO2, cellular oxygen levels can go up when breathing slows down, as more blood is delivered to the cells themselves. It takes quite a lot of stress for O2 to drop for normal people who haven't pre-trained themselves into getting comfortable with raised CO2, quite longer than any sort of remotely comfortable breathing technique. In other words, the urge to breathe is actually generated by increasing CO2, not falling O2. If you put yourself in a chamber with normal CO2 and abnormally low O2, you wouldn't feel an urge to breathe faster, you'd just eventually become delirious. So the analogy of caloric restriction to O2 restriction isn't actually applicable for gentle, even mildly uncomfortable, breathwork. But it's still an interesting idea.