“The force which gives you life is called praana. The force which maintains you is called udyaana. The force which is the eliminating faculty in you, is called apaana. So these forces are the principle vayus, powerful air currents. Udyaana relates to your nervous system. Praana gives you energy and apaana takes away what is not needed by you. These are three automatics and you can have conscious control of them if you are conscious enough.” Yogi Bhajan