Assessment of high coherent states using heart rate variability, pulse transit time and respiratory signals

Goal: the purpose of this study is to introduce a novel index, called Global Coherence Index (GCI), for the estimation of physiological coherence (PhyCoh), which includes the assessment of synchronization among signals. Methods: 34 volunteers (14 men) were randomly selected to be part of the study (84% sample power). Participants were asked to perform a 20-min test while electrocardiography, photoplethysmography and respiration signals were acquired. The test consisted of a basal measurement (stage 1), laboratory mental stress (stage 2 and 3), and controlled breathing (stage 4). PhyCoh was estimated in each of the stages using both GCI and the traditional estimation method based on HRV. The estimated PhyCoh values obtained in each stage were compared using repeated-measures analysis of variance, and the agreement between the measurements was assessed using the Bland-Altman analysis. Results: GCI behaves similarly to the traditional measurement of PhyCoh, while including more information regarding the synchronization of body systems; it has a moderate agreement with the traditional measurement. Conclusion: GCI reflects PhyCoh states and enables the assessment of signal synchronization and a broader revision of the PhyCoh state. An accurate evaluation of physiological coherence based on more than heart rate variability signals is feasible using the proposed index. Significance: The novel index allows for a more comprehensive and reliable estimation of physiological coherence states.