When they become pure, the breath gets controlled gradually. Complete control of breath is called suddha kumbhaka.
Others, that is, jnānis, define rechaka as giving up the idea ‘I-am-the-body’, pooraka as the quest for the Self, and kumbhaka as sahaja-sthiti or abidance in the Self.
Also by repetition of mantras, the mind gets controlled. Then the mantra becomes one with the mind and also with the prāna.
When the syllables of the mantra become one with the prāna, it is termed dhyāna and when dhyāna becomes deep and firm it leads to sahaja sthiti.