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Imagination and awareness are required to maintain the visualization.
A single inhalation and exhalation is one round. Practise 27 rounds.
Practice note: These practices help one become centred and increase the awareness. One can count each round mentally, starting from 54 or 27 and ending at zero. The awareness should be focused on the visualization and experience of the breath flowing in the nostrils and the counting.
Physiology of nadi shodhana
Nadi shodhana pranayama affects brain hemispherity by alternately stimulating the right brain and then the left brain. The flow of breath through the nostrils stimulates the opposite side of the brain, via nerve endings just beneath the mucous layer inside the nostrils. Each side of the body is governed by nerves originating in the opposite side of the brain. The stimulation of the nostrils by the flow of breath increases nervous activity in the brain on the opposite side of each nostril.
The autonomic nervous system is also stimulated and relaxed by this practice. The sympathetic nervous system is stimulated by increasing the flow of breath in the right nostril. This increases the heart rate, produces more sweaty palms, dilates the pupils and opens up the lungs - all part of the fight or flight reaction. By increasing the flow of breath through the left nostril, the parasympathetic nervous system is stimulated. This lowers the heart rate, relaxes the body and improves digestion.
The practice of nadi shodhana also brings about ionic field homogenization. The ida nadi is a storehouse of negative ions and the pingala nadi of positive ions. During the practice of nadi shodhana, as one inhales through the left nostril the negative ion concentration in ida nadi quickly increases from its rest or basal concentration. It then reaches a maximum and begins to fall off gradually, because the concentration of ions is greater in the regions of low pranic density (e.g. there
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