Heart rate variability associated with different modes of respiration during Zen meditation

To understand the effect of respiration modes on hemodynamic events elicited by deep Zen meditation during Zazen, we studied heart rate in 2 intermediate Zen meditators. The study took place over 9 sets of Zen meditations in a quiet, Zen practice hall. Each set of Zazen lasted at least for 25 minutes. The first sets were used for habituation, and the data obtained from the following eight sets were used for analysis, where 2 modes of respiration, i.e., fast inhalation followed by slow exhalation (FISE) and slow inhalation followed by fast exhalation (SIFE), were allocated alternately. Power spectrum analysis showed distinctive change in frequency components. Very low frequency (VLF) components decreased for FISE (p=0.05). Most notably, detrended fluctuations analysis (DFA) of HRV were around 1/2 for FISE and 0.74 for SIFE. During Zen practice, we seat ourselves in a lotus posture, practice Tanden respiration, i.e., lower abdominal breathing, and keep mind free from specific state of consciousness. We attribute the decrease of VLF components and DFA exponent in FISE to the spontaneous and passive regulation of respiratory muscles during slow exhalation, as contrasted with the active use of respiratory muscles during slow inhalation in SIFE.