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DISCUSSION
The present study has shown that breathing exclusively through the right nostril several times a day, for a month can significantly increase the baseline oxygen consumption by 37%, whereas repeated breathing through the left nostril alone, or through alternate nostrils produces a smaller increase, which was not statistically significant. Neither respiratory rate nor galvanic skin resistance changed with right nostril or alternate nostril breathing. In contrast, breathing through the left nostril exclusively repeated four times a day for a month produced a significant increase in the baseline level of volar galvanic skin resistance (GSR), suggestive of reduced sympathetic activity to the palmar sweat glands. Alternate nostril breathing repeated regularly for one month did not have this effect. All 3 types of Pranayamic practice caused a reduction in body weight (Mean 2.27, SD 0.61 kg). Since we had noted that previous groups of Yoga course participants had a similar percentage reduction in body weight, we attributed this reduction to their change in diet (a vegetarian diet devoid of saturated fat), as well as increased physical activity. We did not correlate their reduction in weight with any one of the three types of Pranayama practices, specially. We can speculate that right nostril breathing increases metabolism perhaps by increasing the output of adrenaline from the adrenal medulla, (reflected in the significant increases in baseline oxygen consumption and heart rate) while sympathetic output to the sweat glands does not change (stable GSR). In contrast left nostril breathing produced a marked decrease in sympathetic activity to the sweat glands whereas other subdivisions did not change as much (relatively smaller changes subdivisions did not change as much (relatively smaller changes in baseline oxygen consumption and heart rate). An interesting point is that in the same group (i.e. left nostril group) subjects, there was an increase in oxygen consumption (suggestive of increased sympathetic discharge to the adrenal medulla), and an increase in galvanic skin resistance (suggestive of reduced sympathetic tone to the palmar sweat glands and cutaneous blood vessels). This apparent disparity can be explained by the fact that each target of sympathetic innervation receives its own outflow, and the factors influencing it may differ from one part of the body to another. Hence the traditional concept of diffuse sympathetic tone cannot be maintained (7). It is also known that the sympathetic outflow to palmar sweat glands and cutaneous blood vessels change with the mental state (7). Since these nerves influence the GSR, we may speculate that reduced mental stress or arousal caused the increase in GSR, while some other (unknown) factor altered the sympathetic nervous system outflow to the adrenal medulla, to produce an increase in oxygen consumption. The exact mechanism by which nostril breathing influences the function of the autonomic nervous system is not known, though it has been speculated (2) that this is through a neural reflex mechanism in the superior nasal meatus. Further work is necessary to understand the mechanism, as well as to record changes during the actual practice. However, at this stage one may suppose that the effect of these pranayama practices can be used for therapeutic advantage. For example, several rounds of Surya Anuloma Viloma Pranayama, could be used to increase metabolism, in over weight persons, while the effects of the other two prayanamas would not be as marked. | 
