DISCUSSION

The present study has demonstrated a significant (paired t test) increase in OC (17%), systolic BP (9.4 mm of Hg on an average), and a significant decrease in digit pulse volume (45.7%), after SAV, with no change in these measurements after NB. After both SAV and NB there was a significant decrease (two Factor ANOVA, Tukey test) in SR.

The immediate effects of SAV on oxygen consumption shown in the present study are similar to the changes in baseline status reported after a month of SAV practice (Telles et al., 1994). This increase in oxygen consumption was considered especially interesting with a possible application in the obese who are known to have a lower Resting Metabolic Rate (RMR) in Kcal/kg/hour than the nonobese (the RMR is negatively correlated with the body mass index, or BMI) (Dudani et al., 1986). This effect is indeed in keeping with the name (‘surya anuloma viloma pranayama’), which means “heat generating breathing practice” (Nagendra et al., 1988). In this context it may be mentioned that in the earlier study (Telles et al., 1994) the practice of CAV (“chandra anuloma viloma pranayama” or ‘heat dissipating” breathing practice) also increased the OC though the increase was not significant and was of a lesser magnitude than that caused by SAV (24% versus 37%). Hence the name (“heat dissipating”) breathing practice may be mainly relative to SAV.

Apart from the effects on OC, the practice of SAV for a month caused an increase in heart rate, suggestive of increased cardiac sympathetic tone and/or reduced vagal tone (Telles et al., 1994). In the present study, immediately after SAV there was a significant reduction in skin resistance (SR) and in digit pulse volume (DPV), both indicative of an increase in sympathetic tone (to palmar sudomotor glands and cutaneous vasculature, respectively). These results support those of previous studies which have demonstrated the sympathetic stimulating effect of forced right nostril breathing (Backon, 1988; Shannahoff-Khalsa & Kennedy, 1993). The increase in systolic BP observed here was probably due to cutaneous vasoconstriction (as shown by the decrease in digit pulse volume). Both SAV and NB sessions caused a significant reduction in the SR. The reduction in SR after NB sessions could indicate an increase in the sympathetic activity in subjects sixty minutes after waking, as a “wearing off” of the increased SR known to occur during, sleep (Tart, 1967). All subjects-irrespective of which nostril was dominant at the start of the test session-showed these effects, suggestive of sympathetic stimulation.

It was interesting to note that at the end of the SAV test session, nine of twelve subjects reported feeling more relaxed, while at the end of the NB session eight subjects felt greater relaxation. Among these subjects there were six who reported feeling relaxed after both sessions. In the present study the subjects had practised yoga for three months prior to the study. The practice of yoga has been shown to reduce anxiety and increase quietitude (Hjelle, 1974). Hence, the earlier practice of yoga in the subjects of the present study may have added to the sympathetic stimulating effects of SAV, so that subjects felt more relaxed, though physically they showed signs of sympathetic stimulation. However, it is important to note that the subjects’ prior experience of yoga could be expected to condition their autonomic nervous systems, so that their response to SAV may not be the same as that of naive subjects who have no prior experience of yoga.

The way in which breathing through either nostril can influence autonomic functions is not well understood. A study of the electrographic activity generated by nasal (as opposed to oral) breathing (Kristof, Servit & Manas, 1981), showed that this activating effect could also be produced by nasal insufflation without inflating the lung. This neural reflex was abolished after injecting local anesthesia into the nasal mucosa. The afferents arising from the mucosa are believed to be connected to both the hypothalamus (hence the autonomic nervous system) and the cerebral cortex; however, these pathways have not been anatomically defined.

In summary, the practice of SAV may be of benefit in obesity, but in view of the increase.in systolic BP and cutaneous vasoconstriction, it may be best to avoid this practice in obese patients who are also hypertensive.