Precision of Various Indices of Heart Rate Variability in Sitting and Upright Positions and Between the Two Groups

ABSTRACT The purpose of this study was to evaluate the precision of various heart rate variability (HRV) analysis parameters during postural changes between sitting and upright postures, with a particular focus on Tone–Entropy analysis, and to verify the absolute evaluability and high reproducibility of Tone–Entropy analysis. Fifteen healthy young men (age 20.7 ± 1.5 years) from two different groups participated in the study, and their heart rates (HRs) were recorded during sitting and upright postures. The postural changes were repeated twice, and each posture was maintained for 2 min. Precision was evaluated by defining the error rate for each HRV index. As a result, Entropy showed almost the same precision as HR. On the other hand, standard frequency domain indices such as low frequency (LF), high frequency (HF), and LF/HF ratio showed consistently low precision. Furthermore, our results support the usefulness of Tone–Entropy analysis to date, as it can allow absolute evaluation in Tone–Entropy space even for different groups of subjects and experimental conditions, and the reproducibility of Entropy is also high. In conclusion, it is suggested that Tone–Entropy analysis has high reliability and reproducibility and that frequency power spectrum analysis lacks sufficient precision to be applied to long‐term monitoring analyses in young male subjects.