@allenJo - The whole point of the oxygenation index is to figure out how much oxygen you’re getting, not how hard you’re breathing.
If you want to circulate more oxygen throughout your body, I’d recommend you get on a treadmill or engage in some other aerobic exercise routine. Do that for thirty minutes in the evening before you sleep and see if it improves your sleep.
Of course, I’m not a doctor. You get no warranties with this advice, express or implied.