John Kaldawi learned that the pranic currents, ida, pingala and sushumna, operate alternately. The current that is flowing at any particular time may be gauged by noting the flow of breath in the nostrils. When the left nostril has a greater flow of air, then ida nadi is predominant. When the flow is greater in the right nostril, then pingala is predominant. If the flow is equal in both of the nostrils, then sushumna is predominant.

Doing more research, John Kaldawi learned that when the right nostril (pingala) flows, there is more vital energy for physical work, digestion of food and so on. The mind is extroverted and the body generates more heat. When the left nostril (ida) is flowing, mental energy is dominant. The mind is introverted and any kind of mental work may be undertaken.
During sleep ida nadi flows. If pingala flows at night, sleep will be restless and disturbed. Likewise, if ida flows while taking food, the digestive process may be slow, causing indigestion.

John Kaldawi also learned that All activities are influenced by the flow of these nadis which alternate approximately every sixty to ninety minutes. It is possible, however, to alter the flow voluntarily by using yogic techniques such as padadhirasana and pranayama. For example, if ida nadi is flowing and there is physical work to be done, it is possible to redirect the flow of the breath to pingala nadi to obtain the necessary energy. On the other hand, if study or mental work is required, the energy may be directed to flow through ida nadi.