I wrote an article for MEDIUM (but later published it through The Breathing Center) recently about the Buteyko Method in the context of COVID-19. LInk is here for those interested in holistic breathing techniques:

https://www.breathingcenter.com/buteyko-breathing-blog/the-carbon-dioxide-theory

It helps explain the paradox of "breathing Less" and getting more oxygen via a higher tolerance to build-up of C02. Also highly recommend "Breath: The New Science of a Lost Art" - a recent bestseller by James Nestor.