Abstract— The assessment of the autonomic cardiovascular regulation provides important diagnostic and prognostic information. The aim of this study was to investigate the alterations of this autonomic regulation in the progress of a normal pregnancy and in several pregnancy disorders associated with hypertension, especially pre-eclampsia, applying the method of Joint Symbolic Dynamics (JSD). The JSD reveals nonlinear interactions/ coupling between two time series. Continuous, non-invasive 30 min blood pressure recordings from women with normal pregnancies (CON), with chronic hypertension (CH), with pregnancy-induced hypertension (PIH) and with pre-eclampsia (PE) were analyzed. It could be shown that the cardiovascular regulation system was changed considerably between a first and a second part of gestation in normal pregnancy. These changes were revealed by the analysis of the interactions of heart rate and blood pressure applying the bivariate method JSD. Further on, significant changes of these interactions led to a significant differentiation between normal pregnancy and pre-eclampsia and between chronic or pregnancy-induced hypertension and pre-eclampsia. The JSD provides new information about interaction and coupling between heart rate and blood pressure, increases the ability to diagnose pathological changes and finally may assist the physician to avoid serious maternal and prenatal complications. I. INTRODUCTION VER the last decades several studies have shown that applying nonlinear methods to assess the cardiovascular regulation provides additional diagnostic and prognostic information and therefore complement traditional time- and frequency domain analyses. There are various methods of nonlinear dynamics extracting different indices to describe the complexity and/or interaction of heart rate and blood pressure time series. Some of those indices have been proven to be of diagnostic relevance or have contributed to risk stratification [1]. One of these methods, the Joint Symbolic Dynamics (JSD), revealed significant results in the risk stratification of patients with heart failure [2]. Analyzing the autonomic Manuscript received April 1, 2010. This work was supported by a grant of the University of Applied Sciences Jena, Germany and by the Deutsche Forschungsgemeinschaft (Vo505/4-1, Vo505/4-2). A. Voss is with the University of Applied Sciences, Department of Medical Engineering and Biotechnology, 07745 Jena, Germany (phone: +49-3641-205625; fax: +49-3641-205626; e-mail: voss@fh-jena.de). A. Seeck is with the University of Applied Sciences, Department of Medical Engineering and Biotechnology, 07745 Jena, Germany M. Baumert is with the University of Adelaide, School of Electrical & Electronic Engineering, Australia. regulation in patients suffering from depression this method indicated considerable alterations of the interactions between heart rate and systolic blood pressure [3]. It is already known that the maternal cardiovascular regulation system is strongly affected by pregnancy [4]. Voss et al. reported significant changes of heart rate variability (HRV) and spontaneous baroreflex sensitivity (BRS) between non-pregnant and normal pregnant women applying standard linear parameters. In addition the nonlinear univariate method of Symbolic Dynamics (SD) was applied and revealed also significant indices for the differentiation between non-pregnant and pregnant women. Furthermore, it was investigated if there are any differences of the autonomic regulation in pregnant women depending on different gestational stages. Only two linear parameters were found to differentiate these stages significantly [5]. Faber et al. demonstrated that the assessment of HRV and blood pressure variability (BPV) can reveal early indicators for the development of pathologic conditions, as for example hypertensive disorders which can lead to serious maternal and prenatal complications [6]. The same group proved for the first time that the application of JSD is suitable to differentiate between non-pregnant and normal pregnant women [7]. The aim of this study was to investigate if the nonlinear JSD method, extracting indices of interaction and coupling between two time series, is capable to describe a modification of the autonomic cardiovascular regulation in the progress of normal pregnancy. On the basis of these results it should be further investigated if various hypertensive disorders during pregnancy show different regulatory patterns and finally if it is possible to identify women with pre-eclampsia, which has the worst perinatal outcome of all analyzed disorders [8]. II. METHODS A. Data for analysis of normal pregnancies In this part of the study 21 pregnant women (mean age 27.8 years, range 17-35 years, standard deviation (std) 5.4 years) were enrolled from the Department of Obstetrics, University of Leipzig. These women had normal single pregnancies with normal outcome. Data were recorded at three different gestational stages; before week 20, between week 20 and 30 and after week 30 of gestation. Women with any blood pressure disorders before or during the pregnancy or any other cardiovascular or renal diseases or diabetes were excluded. Altered interactions of heart rate and blood pressure during normal and abnormal pregnancy Voss A., Seeck A., and Baumert M. O 32nd Annual International Conference of the IEEE EMBS Buenos Aires, Argentina, August 31 - September 4, 2010 978-1-4244-4124-2/10/$25.00 ©2010 IEEE 1695