The major and unexpected finding in this analysis of heart rate dynamics during these two forms of meditation in a small number of subjects was the presence of intermittent, extremely prominent oscillations in the 0.025-0.35 Hz band. For example, as shown in Figure 1, the heart rate varied over a 30-35 beat/min range within 5 sec in some of the subjects. These oscillations, observed in both Chi and Kundalini practitioners, correlated with slow breathing. Of note, these oscillations were significantly larger in amplitude than the variations associated with respiratory sinus arrhythmia observed during the pre-meditation control state, and other healthy young adults during metronomic or nocturnal breathing, as well as in elite triathlon athletes during sleep. Also of note was the highly complex nature of the fluctuations for the overall time series during the meditative states (Fig. 1).
These findings appear to contradict a conventional notion of meditation as only a psychologically and physiologically quiescent (``homeostatic'') state. Instead, the selected healthy individuals we studied showed marked dynamic variability in heart rate during a state subjectively perceived as one of profound relaxation. These findings raise several intriguing questions, including: 1) Do some forms of meditation involve a type of autonomic ``exercise'' mediated, at least in part, by specialized breathing maneuvers? 2) To what extent does the magnitude of heart rate oscillations relate to the rate and depth of respiration? 3) Are there ``universal'' physiological mechanisms involved in certain types of meditative states that are triggered by apparently disparate protocols developed in different cultures?
To answer the above questions, future studies should also include other useful physiologic signals, e.g., direct measurement of respiration and blood pressure. Further systematic, quantitative analysis of cardiopulmonary dynamics in a large number of healthy subjects in different age groups, as well as those with a variety of pathologic conditions, before, during and after various meditation regimes should broaden our understanding of an important class of mind-body interactions.