Autonomic System
Breathing in is for the sympathetic system which is the energizing system and breathing out is for the parasympathetic system which is the restful system. I believe the sympathetic system is also for our fight or flight response which due to constant stress may become the more dominant state which puts us physiologically in a state of anxiety. So by rebalancing our breathing to more parasympathetic state, we can reduce our anxiety. Such breathing practices over a period of months helped me to virtually eliminate prior panic and rage habits.