Objective: The breathing processes are known to modulate cardiac autonomic tone and improve psychological status. We investigated cardiac autonomic tone following long Sudarshan Kriya Yoga (SKY) using heart rate variability (HRV) and skin conductance level (SCL).
Methods: Thirty healthy volunteers (age 28.3 ± 8.4 years; 23 M: 7 F) participated in the study. Electrocardiogram (ECG) and SCL were recorded for 5 min each, before and after long SKY. Long SKY is a combination of pranayama and cyclic rhythmic breathing and is performed by following the guided audio instructions. HRV analysis was used for the assessment of cardiac autonomic tone. Time and frequency domain parameters of HRV were calculated by using RR interval of ECG. SCL was acquired using Galvanic skin response (GSR) amplifier of PowerLab in microSeimens (μS).
Results: Time domain parameters of HRV, including mean RR interval (p = 0.000), respiratory sinus arrhythmia (RSA) (p = 0.037), standard deviation of all NN intervals (SDNN) (p = 0.013), NN50 count divided by the total number of all NN intervals (pNN50) (p = 0.004), and square root of the mean of the sum of the squares of differences between adjacent NN intervals (RMSSD) (p = 0.002) increased, and mean heart rate decreased (p = 0.000) following long SKY. In frequency domain analysis, power of low-frequency (LF) component (p = 0.010) and LF/HF ratio (p = 0.008) decreased significantly, whereas power of high frequency (HF) significantly increased (p = 0.010). SCL decreased following long SKY, although it did not attain statistical significance.
Conclusions: The results suggest that long SKY induces significant oscillations in cardiac autonomic tone. Parasympathetic activity increases and sympathetic activity decreases and sympathovagal balance improves following long SKY. Decrease in sympathetic activity is also demonstrated by decrease in conductance although it did not reach statistical significance. From this study it can be concluded that long SKY has a beneficial effect on cardiac autonomic tone, and psychophysiological relaxation. It may serve as a tool to improve HRV, which is the marker of cardiovascular health.
Keywords: cardiac autonomic tone; heart rate variability; long Sudarshan Kriya Yoga; skin conductance level.