Changes in Autonomic Variables Following Two Meditative States Described in Yoga Texts

Objectives: In ancient yoga texts there are two meditative states described. One is dharana, which requires focusing, the second is dhyana, during which there is no focusing, but an expansive mental state is reached. While an earlier study did show improved performance in an attention task after dharana, the autonomic changes during these two states have not been studied. Methods: Autonomic and respiratory variables were assessed in 30 healthy male volunteers (group mean age +/- SD, 29.1 +/- 5.1 years) during four mental states described in traditional yoga texts. These four mental states are random thinking (cancalata), nonmeditative focusing (ekagrata), meditative focusing (dharana), and effortless meditation (dhyana). Assessments were made before (5 minutes), during (20 minutes), and after (5 minutes), each of the four states, on four separate days. Results: During dhyana there was a significant increase in the skin resistance level (p < 0.001; post hoc analysis following ANOVA, during compared to pre) and photo-plethysmogram amplitude (p < 0.05), whereas there was a significant decrease in the heart rate (p < 0.001) and breath rate (p < 0.001). There was a significant decrease in the low frequency (LF) power (p < 0.001) and increase in the high frequency (HF) power (p < 0.001) in the frequency domain analysis of the heart rate variability (HRV) spectrum, on which HF power is associated with parasympathetic activity. There was also a significant increase in the NN50 count (the number of interval differences of successive NN intervals greater than 50 ms; p < 0.001) and the pNN50 (the proportion derived by dividing NN50 by the total number of NN intervals; p < 0.001) in time domain analysis of HRV, both indicative of parasympathetic activity. Conclusions: Maximum changes were seen in autonomic variables and breath rate during the state of effortless meditation (dhyana). The changes were all suggestive of reduced sympathetic activity and/or increased vagal modulation. During dharana there was an increase in skin resistance. The changes in HRV during ekagrata and cancalata were inconclusive.