Buyteko breathing at its simplest is breathing through your nose, practising shallow breathing, and practising holding your breath. It all increases the flow of oxygen to your lungs. It's about breathing from the diaphragm. Athletes and sports people have used it to improve their performance.
The more you practise holding your breath, the longer you will be able to do it. Breathe OUT through your nose then hold and count.
Here's the shallow breathing exercise:
(It's best done sitting up tall in a straight-backed chair, but I've been doing it in bed, sitting up or even lying down, and it's still proved helpful).
Close your eyes (and mouth) and focus on your breathing. Feel the air moving in and out of your nostrils. If your mind wanders, return to your nostrils and refocus on that sensation.
Relax your shoulders and any tension may be holding in your body, including your hands and face.
To check the volume of air flowing through your nostrils, place an index finger under your nose.
Now take shallow breaths, using your finger to gauge the rate of respiration. The moment you feel air hit your finger, start to breathe in again. This will reduce the volume of air flowing into your lungs while increasing the number of breaths. You are supposed to maintain this for three to five minutes, but because I've been ill I'm doing it for far shorter periods than that. I still find it helpful.
If you find yourself gasping, stop immediately.
Disclaimer - I was taught this by a professional practitioner many years ago, as a cure for asthma. It did and does help my asthma. But I am not an expert or professional or medical practitioner or any kind.