MEASUREMENT OF VENTRICULAR VOLUME FROM BLOOD CONDUCTANCE USING 2-DIMENSIONAL FINITE-ELEMENT ANALYSIS

We used finite element analysis to study the relationship between the intraventricular blood conductance and the right ventricular volume. P revious studies reported a quasi-linear dependence between these two q uantities. We quantified the effects of the resistivities of the surro unding tissues (e.g. heart wall, lungs) on this relationship and perfo rmed simulations for four different right ventricular longitudinal sec tional areas to assess the linearity of the relationship. The relation ship was most significantly affected by the blood conductivity. Howeve r, the effects of the cardiac muscle and the lungs could not be neglec ted. The dependence of the intraventricular blood conductance on the v entricular volume was found to be non-linear. Although to some extent inaccurate, a linear approximation of this relationship is useful for the development of rate-responsive implantable cardiac pacemakers, whe re the pacing rate is adjusted based on the need for cardiac output. T he cardiac output is computed from the product of the heart rate and t he stroke volume. The stroke volume can be estimated by measuring the changes in the intraventricular blood conductance. The electrodes need ed for the stroke volume estimation can be placed on the same catheter as those used for pacing. The use of this method for clinical monitor ing or diagnosis has to be investigated further given that its errors in the estimation of the stroke volume are considerably larger than th ose corresponding to standard methods such as dye- or thermo-dilution,