Beat-to-beat variability in the heart period is intrinsic to healthy cardiac functioning. Cardiac chronotropy is chiefly regulated by the parasympathetic (most often vagal) and sympathetic nervous systems. These divisions of the autonomic nervous system have distinctly different activity levels and latencies. Time and frequency domain analyses of heart rate variability (HRV) provide information on the levels of activity of each of these divisions of the autonomic nervous system and other physiological factors which affect variations in heart rate. HRV can increase our understanding of the effects of mind-body interventions (MBIs), which can influence mental and physical functions. MBIs include yoga, biofeedback, meditation, imagery, yoga, Tai Chi and Qi gong, acupuncture, and relaxation techniques, among others. Many health benefits of MBIs are believed to occur by shifting the autonomic balance towards parasympathetic dominance. In most MBIs, changes in HRV have been studied to better understand the mechanisms underlying the therapeutic benefits of these practices.

Several mind-body practices include volitional slowing of respiration. Recording HRV during these practices poses challenges in separating respiratory-driven low-frequency HRV components from those mediated by neural regulation. However, these practices also offer the opportunity to evaluate low-frequency HRV components in healthy volunteers trained in these practices and to further understand the contribution from different physiological sources. The acquisition of electrocardiogram signals could be contaminated by particular sources of artifacts, for example, mind-body practices which include rhythmic movement could cause movement artifacts. Hence, the acquisition, analysis, and interpretation of HRV recorded in MBIs have specific challenges and opportunities for research.

This Special Issue aims to further our knowledge of HRV and the autonomic effects of MBIs. We welcome studies on HRV in healthy volunteers and in clinical populations receiving MBIs, as well as the use of different analytical approaches to widen our understanding of the physiological significance of HRV components. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• HRV in combination with other physiological recordings indicative of autonomic activity, such as cutaneous blood flow or electrodermal activity, to better understand the effects of a mind-body intervention on the autonomic nervous system
• HRV recordings in volitional breathing to understand the contribution of respiratory modulation to HRV
• Comparing mind-body interventions, including both calming or activating practices, to determine the different effects on HRV
• HRV recordings in a mind-body intervention related to emotion valence testing
• HRV recordings in a mind-body intervention and directed attention or consciously regulated mental states
• HRV, mind-body intervention, and specific clinical populations
• New information about the physiological significance of the HRV
• Analysis for additional HRV feature extraction to improve our understanding of mind-body interaction
• Improvement in HRV signal-to-noise ratio in mind body interventions with rhythmic movement