Women and men follow a monthly rhythm. With women it is associated with the menstrual cycle and changes of mood. With men it is associated mainly with a fluctuation of mood. There is also a twenty-four hour rhythm which induces changes in hormone secretion, blood pressure, body heat and so forth.
Modern scientists have now begun to realize that there is also a 90-minute rhythm. They have called it the ultradian rhythm and it relates to periodic swings of mood, mental alertness, stomach contractions and many other physical and mental changes. This last rhythm is directly related to ida and pingala and it is manipulation of this rhythm in order to induce meditation that is the main aim of hatha yoga and the practices that we will shortly describe.
Ida, pingala and the air flow in the nostrils
There is a direct relationship between the ida and pingala and the air flow through the two nostrils. The Rudra Yamala Tantra states: “On the left and right side of the sushumna are the ida and pingala. These go straight upwards, alternating from left to right. Having pierced all the chakras (the main ones in the spinal region) they proceed to the nostrils.”
It is because of this relationship that one can manipulate the flow of breath through the nostrils in order to bring balance in the ida and pingala at more subtle levels. On a gross level, the ida and pingala correspond to the breath in the left and right nostril respectively. This gross aspect has a direct relationship with the more subtle realms of ida and pingala in the mind and pranic body. Thus gross manipulation of the breath flowing through the nostrils has vast repercussions on a more subtle level of one’s being. This is the basis for most standard hatha yoga practices that attempt to control ida and pingala. The other forms of yoga attempt to gain the same control at more subtle levels without physical means.