I was scrolling Tik-Tok one day and saw Bas Ruttens o2 Trainer videos.
Having a printer, I knew I could make one.
This device could possibly help you train your lung and diaphragm muscles so that you can breath deeper and get more O2. YMMV.
You will need to purchase a Snorkel Mouthpiece to put on the device.
I still have kinks to work out on the caps, as the larger ones whistle, but the 3mm and 4mm do not. You're welcome to make changes and fix the problems.
Default PLA settings, 3 walls, 15% gyroid infill.
I edited the following models to make my device:
https://www.thingiverse.com/thing:1596643
https://www.thingiverse.com/thing:469540