the illustration prepended to this PDF shows a South Asian man using the one-nostril 'nadi channels' variation of some pranayama practice -- not enough info to know which.. personally I find that the single nostril nadi constriction is a distraction or worse, actually detrimental, for some people, some amount of the time.

The breathing rhythms and GENTLE retentions discussed in the comments, are powerful tools and do affect physiology immediately. I suggest a) working with an experienced person at first, b) know your own body, c) do no include fancy extras in the practice, like the nadi channel restriction shown in the photo, rather focus on steady repitition and stable surroundings, at predictable times of day.

This practice has helped me a lot and I trust it will bring health and stability to others also.

Probably nadi shodana. You shouldn’t start this one right away, but only after you’ve already slowed down breathing.

I agree there’s also other techniques first, and if it is uncomfortable, stay away from it. That said, it’s a pretgood technique to know.

I dropped in here to say this. There's a book that just came out related to this called Breathe. I looks at breath from a cultural perspective also.