A means to slowdown your exhale speed, breath slower and push the breath downwards to the belly (so Diaphragm get to work) for otherwise healthy persons.
Per, Strength stairs
If you have a medical condition linked to the respiratory system, you should of course talk to your doctor or physiotherapist before using these techniques.
Lessons
Resistance breathing with the lips
PreviewResistance breathing with equipment
PreviewFor you who want to take your resistance breathing to next level or make the resistance a bit more exact there are good and cheap equipment to achieve this. Per, Strength stairs Performance Common questions