Analysis in Cardiac Stability over Thirty Minute Periods

Cardiac stability with little change in heart rate is important when studying the effect of cardiac interventions. The aim of this study was to analyse changes in heart rate during conditions expected to be stable. Subjects were studied during quiet relaxation to allow analysis of cardiac stability over thirty minute periods. Ten subjects with no known cardiac disease were enroled, and gave ethical consent. Their ages were 42±15 years (mean ± standard deviation). Subjects were given time for normal relaxation, but without any controlled conditions. After the study was explained, subjects were then asked to sit quietly on an office chair, while a single channel ECG was recorded to a computer for offline analysis. After a few weeks, subjects were instructed briefly in Zen meditation techniques, and rerecorded in similar conditions. There was a tendency for heart rate to fall and RR intervals to increase over the 30 min period, but overall this was not statistically significant, due primarily to individual subject variation resulting from respiratory effects, especially with the deeper regular breathing during meditation. There were small but significantly reduced heart rates with increased RR intervals during the meditation session, in comparison with relaxed sitting: mean RR interval increasing from 0.78 ± 0.10 s to 0.87 ± 0.13 s (p=0.002), with the mean minimum RR (associated with highest heart rate) increasing from 0.70 ± 0.10 s to 0.74 ± 0.10 s (p=0.008). With preceding uncontrolled relaxation, cardiac changes over a 30 minute period were small, and meditation generated an additional small overall reduction in heart rate, with increased RR intervals.