DISCUSSION

Fig. 1. Oxygen consumption, breath rate, tidal volume and minute ventilation in cyclic meditation (CM) and
shavasana (SH) sessions with a thirty minute post period (n=10).

CM was considered as four phases. The first three included the practice of yoga postures, while the fourth phase was of supine rest. The oxygen consumption increased in the first three phases of CM, returned to the baseline in the fourth phase and reduced by 19.3 percent compared to the baseline after the practice. The changes in minute ventilation, tidal volume, and breath rate were similar to the changes in oxygen consumption during and after CM.
In the shavasana session of supine rest (SH) the oxygen consumption decreased during SH and also decreased after SH by 4.8 percent. The tidal volume, minute ventilation and breath rate showed no change in the SH session. In a sub-sample of ten participants the same design was followed in a repeat session
with a longer ‘post’ recording (i.e., 30 min). The decrease in oxygen consumption in the first five minutes after CM was 18.3 percent and between 25 and 30 min post-CM, the percent decrease was 20.8. For the shavasana (SH) session in this sub-sample the decrease was 6.4 percent in the first five minutes post-SH and in the last five minutes (i.e., between 25 and 30 min) post-SH there was a 6.5 percent decrease. This showed that the changes which occurred 5 min after either CM or SH carried on for 30 min post practice. A longer duration post recording would be needed to understand how long the change persists.
The changes in oxygen consumption reported here show a similar trend as those in an earlier study, which had an identical design (Telles, Reddy, & Nagendra, 2000). However in the earlier study there was a 32.1 percent decrease in oxygen consumption after CM and a 10.1 percent decrease after SH practice, compared to a 19.3 percent and a 4.8 percent decrease respectively, in the present study. The difference in magnitude of change may be due to two factors: (i) the meditators in the previous study had an average experience of meditation of 32.9±19.8 months compared with the experience of the meditators in the present study which was 15.3±13.3 months, on an average, and (ii) the earlier study measured the oxygen consumption using a closed circuit apparatus which has been described as less precise (Judy, 1982; American Association for Respiratory Care, 1994). It is also to be noted that in the sub-sample of ten participants the same trend was seen during and after CM. When considering the changes in minute ventilation, it is known that ventilation increases linearly with the oxygen intake and with the carbon dioxide output upto approxi- mately 60 percent of the maximal oxygen consumption (Jones, 1997). Hence the similarity in the direction of change in oxygen consumption and minute ventilation during cyclic meditation is not unexpected. With regard to the changes in tidal volume and in breath rate, these may be explained by two facts (Jones & Rebuck, 1979). These are: (i) increases in minute ventilation are accompanied by an increase in tidal volume, and (ii) as the tidal volume reaches 50 to 60 percent of the vital capacity the breath rate increases as well. The changes in tidal volume,breath rate and minute ventilation after CM were of lesser magnitude in the present study compared to the earlier study (cited above). The reasons for these differences may be related to the fact that the closed circuit apparatus used earlier is less accurate (Matarese, 1997) and some people find it difficult to breathe through the closed circuit apparatus (Branson, 1990). During CM the yoga postures are practiced four times slower than classically described (Nagendra & Nagarathna, 1997). Practicing yoga postures slowly requires more effort than usual practice. Hence these practices were considered ‘activating’ when compared to the interspersed periods of supine rest. For this reason it is of interest to compare the post- CM changes in oxygen consumption (i.e., a 19.3 percent decrease) and breath rate (i.e., a decreaseby1.1breathsperminute),withthoseknowntooccurafterexercise.Afterexercise it is recognized that oxygen consumption increases (Borsheim & Bahr, 2003). This ‘excess post-exercise oxygen consumption (EPOC)’ may last for several hours after exercise or be transient and minimal. The magnitude of EPOC after aerobic exercise depends on both the duration and the intensity of exercise, as well as factors such as training status and gender. In low intensity, primarily aerobic exercise about one half of the total ‘Excess Post Exercise Oxygen Consumption (EPOC)’ takes place within thirty seconds of stopping the exercise and complete recovery can be achieved within several minutes, with the oxygen uptake returning to the pre exercise level. The EPOC was studied following a fifty minute run compared to two, twenty five minute run at seventy percent of peak oxygen consumption (Kaminsky, Padjen, & Latlam-Saeger, 1990). Following exercise, the oxygen consumption returned to baseline within thirty minutes for all three exercise trials. There are no reports to our knowledge of a reduction in oxygen consumption post- exercise or after exercise followed by rest. The depth (and also for strenuous exercise, the rate) of breathing increases with the onset of exercise, followed by a brief pause, after which there is a further, more gradual increase (Ganong, 2005). Ventilation decreases at the end of exercise and gradually declines to pre-exercise values. Again there is no description of a decrease in breath rate following exercise. In the present study the decrease in breath rate following meditation may be a manifestation of decreased arousal (Ax, 1953). There is no evidence of it being a rebound effect as no such decrease follows exercise. It is also to be noted that the participants were not following specific instructions to regulate their breathing. The changes which occurred after CM are more like the changes which have been de- scribed after the practice of TM i.e., a 17 percent decrease in oxygen consumption, decrease in breath rate and minute ventilation (Wallace, Benson, & Wilson, 1971). A similar trend of a decrease in oxygen consumption and in breath rate also followed meditation on OM (Telles, Nagendra, & Nagarathna, 1998). In the early reports on the effects of TM and in subsequent studies the hypometabolic state has been suggested to be due to decreased mus- cle metabolism based on decreased forearm lactate secretion and related changes (Jevning, 1988). A decrease in oxygen consumption has also been reported following the practice of the relaxation response in early and recent reports (Benson, Dryer, & Hartley, 1978; Dusek et al., 2006). The relaxation response resulted in generalized decreased sympathetic nervous system activity and more recently the response has been reported to be mediated by nitric oxide. Whether similar mechanisms as described for TM or for the relaxation response were responsible for the post-CM changes is not known. SinceCMincludesthepracticeofyogaposturestheeffectswerealsoconsideredworth comparing to the practice of Tai-Chi-Qui-Gong (TCQG) which includes 54 movements (Chao, Chen, Lan, & Lai, 2002). Based on energy expenditure and cardio respiratory responses TCQG was described as a low intensity exercise. The changes after the practice were not reported. Hence the changes during the practice of yoga postures in CM appear similar to those during TCQG. In summary, the practice of CM reduces oxygen consumption compared to the pre- ceding period, as well as compared to a period of supine rest of equal duration. Similarly a reduction in oxygen consumption has been reported following other meditation practices and the relaxation response. Hence an understanding of the physiological and clinical im- plications of a decrease in oxygen consumption is desirable. The oxygen consumption is considered as a general index of increased physiological activity (Bonnet & Anand, 2003). Also in an investigation of effects of psychological parameters on resting metabolic rate (RMR), a significantly greater RMR was found in a high-trait anxious group than in a low trait anxious group (Schmidt, O’Connor, Cochrane, & Cantwell, 1996). This suggests that a higher rate of oxygen consumption may be associated with higher anxiety. This is of interest as high anxiety levels are generally associated with a greater incidence of stress related ailments (Grinde, 2005). However on the other hand, it has been shown that the long-term maintenance of weight loss has been found to be associated with highly restrained eating, regular physical activity, and perhaps with increased anxiety (Sarlio-Lahteenkorva & Riassanen, 1998). Whether the practice of techniques such as CM over time modifies the ability to maintain weight or weight loss remains to be studied. Another possible benefit of reducing oxygen consumption may be extrapolated from a study on cellular metabolism (Hand & Hardewig, 1996). This report mentions that the survival time of organisms during exposure to those environmental stresses which limit energy availability is directly related to the degree to which metabolic rate decreases. However all these possible consequences of a decrease in oxygen consumption are speculations. The present study reports a decrease in oxygen consumption consistent with the earlier study of identical design (Telles, Reddy, & Nagendra, 2000). The changes following CM may be ascribed to the traditional concept on which the technique is based says that, ‘in a state of mental inactivity awaken the mind, when agitated, calm it; between these two states realize the possible abilities of the mind. If the mind has reached a state of perfect equilibrium do not disturb it again.’ The reduction in oxygen consumption may hence be a possible manifestation of physiological changes occurring while approaching a state of ‘perfect equilibrium.’ Further research is required to understand the mechanisms underlying the change and the long-term consequences of the practice.