Cardiovascular regulation during sleep quantified by symbolic coupling traces

The different sleep stages modulate the autonomous functions blood pressure and heart rate as well as their complex interactions. The method of symbolic coupling traces (SCT) is used to analyse and quantify time-delayed couplings of these measurements. The SCT is defined by the difference of the symmetric and diametric traces of a bivariate word distribution matrix. It is applied to the signals of healthy controls as well as normo- and hypertensive patients with sleep apneas over night. We found significant different couplings not only between the deep sleep and the other sleep stages (p<;0.05, Kruskal-Wallis test) but also between healthy subjects and patients. Thereby, SCT yields additional information which can not be measured by standard parameters of heart rate- and blood pressure variability. The proposed method may help to indicate pathological changes in cardiovascular regulation and also effects of continuous positive airway pressure therapy on the cardiovascular system.