The study was carried out on 7 normal, healthy male volunteers in the age range of 29 to 55 years (mean + SD, 42.3 + 9.8 years). They were all committed meditators with experience ranging between 5 and 20 years. The details of the study were explained to the subjects and their signed informed consent was taken in accord with the ethical guidelines of the Indian Council of Medical Research, New Delhi.
Design of the study
Each session was of 32 min duration, of which 20 min were spent in meditation, preceded and followed by two 6 min periods of sitting relaxed, with eyes closed. Subjects were also studied in control sessions which were of the same duration as the meditation sessions, and similar in design except that the 20 min period was spent sitting relaxed with eyes closed, and non-targetted thinking (instead of meditation). Meditation involved mental chanting of "OM", while sitting comfortably, with eyes closed. Both types of sessions were repeated on three separate days.
Recordings of autonomic and respiratory variables were made on a 10 channel polygraph (Model 10, Polyrite, Recorders and Medicare systems, Chandigarh, India). EKG was recorded using the standard limb lead I configuration. Heart rate was obtained by counting the number of QRS complexes per 40-sec intervals continuously. Epochs of 40 sec were chosen to be able to correlate this data with that of subjects practicing other meditations (3). This has been described in the discussion. Palmar skin resistance (SR) was recorded using 2 silver chloride disc electrodes filled with electrode jelly (CSR Technocarta, Hyderabad, India), placed 4 cm apart on the palmar surface of the right hand. SR values were sampled continuously at 20-sec intervals. Skin blood flow was recorded using a photo-electric plethysmograph placed over the left thumb nail. The amplitude of six plethysmogram waveforms were calculated in each minute. Two nasal thermistors placed one at each nostril were used to record respiration. The number of breath cycles in each minute was calculated to give the respiratory rate. Oxygen consumption was recorded using the closed circuit Benedict-Roth apparatus. In this method, the subject breathed into an oxygen tank wearing a close fitting mask, and with a nose clip. The exhaled carbon dioxide does not enter the tank, as it is absorbed by soda lime. The difference between the initial and final volumes of oxygen in the tank is the amount of oxygen consumed by the subject in a given period of breathing (i.e. 5 min). The recording laboratory had a temperature of 25 ± 10C, with relative humidity about 70 percent. The values were corrected for standard temperature and pressure. The OC recordings were made before and after meditation, but not during meditation. Polygraphic recordings were made before, during, and after meditation. Values of the 5 variables mentioned above were averaged for each of the 3 periods of a session viz. before, during and after meditation (or the control procedure). Statistical analysis of these averaged values was done to reveal significant differences between (a) before versus during meditation (or control) and (b) during meditation versus during control periods, using the paired "t" test.