Respiration and postural sway: detection of phase synchronizations and interactions

The aim of the central nervous system in upright stance is to control an intrinsically unsta- ble plant. Internal disturbances, such as hæmodynamics and respiration, constitute an endog- enous threat to equilibrium. The way CNS reacts to those perturbations was studied in this work, through the analysis of summary scores taken from posturographic and pneumographic data. Signals were recorded simultaneously during trials administered on a sample population of healthy young adults, while sitting and standing and at paced and spontaneous uncon- trolled breathing. The extraction of posturographic and pneumographic parameters was accompanied by the utilization of techniques for the detection of phase synchronization in bivariate data, and the extraction of an interaction index, the mutual information MI. The effects of the biomechanical condition and respiratory amplitude on MI and summary meas- ures were tested with a two-way ANOVA. Summary scores clearly depend on posture condi- tion. Synchronization between breath and postural sway is always present, depends on both biomechanical condition and respiratory threat, and cannot be reduced to a simple linear relation