ELECTRICAL-IMPEDANCE OF LAYERED ATHEROSCLEROTIC PLAQUES ON HUMAN AORTAS

Electrical impedance measurements were performed on 13 atherosclerotic human aortic segments at 67 measuring spots in order to determine whe ther or not on the basis of these data a distinction can be made betwe en atherosclerotic lesions and normal tissue. Stenosis localization an d guidance of interventional techniques could be among the application s of an impedance measuring technique implemented on a catheter system . The experimental results, obtained with a two-electrode measuring te chnique, show that the apparent resistivity of an atherosclerotic spot does not necessarily deviate much from the resistivity of normal tiss ue. This is clarified by histology which shows that the majority of le sions has a surface layer of connective, fibrous tissue having almost similar conducting properties as the normal arterial wall. For gaining a deeper understanding of the way in which the measured data come abo ut, a physical model of an atherosclerotic lesion is presented and con fronted with the data. Both experimental data and theoretical consider ations lead to the conclusion that only when the superficial fibrous l ayer is absent or very thin in relation to the size of the measuring e lectrode, the measured resistivity at a lesion is much higher than at normal spots. This occurs as a consequence of the high ohmic propertie s of the calcified or lipid deposits in the atherosclerotic lesion.