On Breathing and Thought

Then, proceeding further, you may begin to study in the human being something that is really much more difficult to observe, although it is generally thought to be easy — that is, to gain an understanding of how the human being takes breath, how he sets his rhythmic system in movement, and how the breath leads over into the blood circulation. This tremendously living play, which penetrates the whole body, is far more complicated than it is thought to be. The human being takes in the breath, the breath transforms itself into blood circulation, but on the other side the breath again passes over into the head and is related in a definite way to the whole activity of the brain. Thinking is simply a refined, delicate breathing. The blood circulation, again, passes over into the impulses of the movements of the limbs. - Rudolf Steiner, Karmic Relationships 

But it must not be forgotten that man has a twofold respiration, one of the spirit and another of the body; and that the respiration of the spirit depends on the fibers from the brains, and the respiration of the body on the blood-vessels from the heart, and from the vena cava and aorta. It is evident, moreover, that thought produces respiration; it is evident, also, that affection, which is of love, produces thought, for thought without affection is precisely like respiration without a heart, a thing impossible. From this it is clear that affection, which is of love, conjoins itself to thought, which is of the understanding (as was said above), in like manner as the heart does in the lungs - Emanuel Swedenborg, Divine Love and Wisdom 412