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Dauphin, and A. Bouzerdoum, “Image analysis using anisotropic local contrast,” in Proc. 2004 Int. Symp. Intelligent Multi- media, Video, Speech Processing, 2004, pp. 506–509. [20] S. J. Huang, “Adaptive noise reduction and image sharpening for dig- ital video compression,” in Proc. Int. Systems, Man, Cybernetics Conf., 1997, vol. 4, pp. 3142–3147. Cardiovascular Oscillations of the Carotid Artery Assessed by Magnetoelastic Skin Curvature Sensor Eugenijus Kaniusas*, Helmut Pfützner, Lars Mehnen, Jürgen Kosel, Giedrius Varoneckas, Audrius Alonderis, and Linas Zakarevicius Abstract—The present study concerns the nondisturbing assessment of cardiovascular oscillations of the carotid artery using a novel skin curvature sensor on the neck. The mechanical oscillations of the skin reflect changes of the artery radius and thus relevant physiological data such as cardiac and respiratory activities, their mutual dependencies, and even changes of blood pressure. The skin curvature sensor is easy to handle and it minimally disturbs the patient, which is relevant for many medical areas such as sleep monitoring. Index Terms—Cardiovascular system, carotid artery, physiological sen- sors, skin curvature sensor. I. INTRODUCTION T HE assessment of cardiovascular oscillations shows distinct im- portance from a physiological and clinical point of view. The rel- evance of oscillations is given in many medical areas, such as sleep monitoring, biomechanic feedback, or athlete/driver monitoring. The cardiovascular oscillations of blood pressure , as shown in Fig. 1(a) using the data from [1], are mainly driven by time-dependant pressure gradients due to periodic heart beats. Generally, is deter- mined by the product of the stroke volume and the arterial impedance. The corresponding change of the artery radius (Fig. 1(b)), is strongly determined by the elastic properties of the artery wall. In particular, the wall stiffness increases nonlinearly with increasing (or ) in order to prevent an over-distension of the wall [2]. At low values of , this yields a strong increase of for increasing . On the other hand, a saturation of results for higher values of , as can be observed in Fig. 1(b). Furthermore, the waveforms of pressure and diameter are more similar during systole than diastole [3]. In addition, smooth muscles within the artery wall contribute significantly to the nonlinear behaviour of the wall elasticity, especially for periods of time that exceed the duration of the cardiac cycle. Throughout the cardiac cycle, the carotid artery—as the investiga- tion object of this study—yields a moderately pronounced nonlinear dependence between and under normal physiological conditions [1], [3]. The low wall stiffness at low can be attributed to the content of elastin in the artery wall while high stiffness at increased distention arises because of collagen [2]. Within the present work, the cardiovascular oscillations of the carotid artery were assessed by a novel noninvasive skin curvature Manuscript received July 12, 2006. This work was supported by the EU project B-SENS (No. G5RD-CT-2002-00690). Asterisk indicates corre- sponding author. *E. Kaniusas is with the Institute of Fundamentals and Theory of Electrical Engineering/E351, Bioelectricity and Magnetism Laboratory, Vienna Uni- versity of Technology, Gusshausstrasse 27-29/351, A-1040 Vienna, Austria (e-mail: kaniusas@tuwien.ac.at). H. Pfützner, L. Mehnen, and J. Kosel are with the Institute of Fundamentals and Theory of Electrical Engineering, Bioelectricity and Magnetism Labo- ratory, Vienna University of Technology, A-1040 Vienna, Austria (e-mail: pfutzner@tuwien.ac.at). G. Varoneckas, A. Alonderis, and L. Zakarevicius are with the Institute of Psychophysiology and Rehabilitation, Kaunas University of Medicine, LT-5720 Palanga, Lithuania (e-mail: giedvar@ktl.mii.lt). Digital Object Identifier 10.1109/TBME.2007.899355 0018-9294/$25.00 © 2007 IEEE