In a normal condition we receive the vibration and rhythm of the great ocean of life, and respond to it, but at times the mouth of the inlet seems choked up with debris, and we fail to receive the impulse from Mother Ocean, and inharmony manifests within us.
You have heard how a note on a violin, if sounded repeatedly and in rhythm, will start into motion vibrations which will in time destroy a bridge.

The same result is true when a regiment of soldiers crosses a bridge, the order being always given to "break step" on such an occasion, lest the vibration bring down both bridge and regiment.
These manifestations of the effect of rhythmic motion will give you an idea of the effect on the body of rhythmic breathing.

The whole system catches the vibration and becomes in harmony with the will, which causes the rhythmic motion of the lungs, and while in such complete harmony will respond readily to orders from the will.

With the body thus attuned, the Yogi finds no difficulty in increasing the circulation in any part of the body by an order from the will, and in the same way he can direct an increased current of nerve force to any part or organ, strengthening and stimulating it.
In the same way the Yogi by rhythmic breathing "catches the swing," as it were, and is able to absorb and control a greatly increased amount of prana, which is then at the disposal of his will.

He can and does use it as a vehicle for sending forth thoughts to others and for attracting to him all those whose thoughts are keyed in the same vibration.