The present study revealed a significant decrease in heart rate during mental chanting of "OM", which is suggestive of psychophysiological relaxation. The non- significant trend of reduction in oxygen consumption also has a similar interpretation. This change is similar to that caused by TM (4), though of smaller magnitude.
However, it is important to note that the actual pre-meditation (or control) values of oxygen consumption of the (senior) meditators of the present study were noticeably higher than those of other meditators (4), and of the general population. Since it is usually thought that yoga practitioners have lower oxygen consumption values than those who do not practise yoga, these results are difficult to explain. There is a report (5) in the literature which demonstrated an increase in the basal metabolic rate (BMR) with six weeks experience in yoga, compared to the period before learning yoga. The BMR decreased, but did not return to the initial value after continuing yoga practice for six weeks. In contrast to the present study, the subjects were not practising meditation, but were practising specific postures (yogasanas) and breath regulation (pranayama). Hence no direct correlation can be made between the two studies, and further assessments are necessary to come to a definite conclusion.
The significant decrease in finger plethysmogram amplitude (i.e. increased peripheral vascular resistance) which occurred during both meditation and control periods is a sign of increased sympathetic tone and hence is also not expected during meditation (4)
While attempting to explain these seemingly contradictory results, it is to be noted that the same individual may simultaneously show changes in two variables indicating opposite states of arousal, e.g. a decrease in heart rate along with reduced skin resistance. While explaining similar contradictory changes in Ananda Marga meditators (6), the authors described the reduced skin resistance as an attempt to prevent intrusion of sleep during the session. Since reduced skin blood flow is known to occur when the subject is alert, as while solving arithmetic problems mentally (7), the present study might indicate that chanting "OM" mentally causes increased alertness (reduced finger plethysmogram amplitude), even though the subject was more relaxed (reduced heart rate).
This study was designed and carried out under the expert guidance of (the late) Dr. T Desiraju (NIMHANS, Bangalore). The contributions of the other staff of "Project Consciousness", are gratefully acknowledged.