Development of a new conductance catheter system taking account of heterogeneous current distribution

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1.Using a simplified shape model of ventricle and thorax, we analyzed numerically how currents distribute heterogeneously over ventricular cavity, myocardium, and surrounding tissue in response to electrical stimulation from catheter ends.1)Development of numerical analysis and analysis of nonlinearity : In the first year, we characterized the problem as a solution of a partial derivative equation, Vxx+Vyy+Vzz=0 with boundary conditions Vn=0 at endocardium and V=+/-V0 at both stimulating electrodes. We expressed the equation using cylindrical coordinate system, due to its axisymmetrical nature, and substituted t=log(r), resulting in exp(-2t)Vtt+Vzz=0. These considerations led us to a method to efficiently discretize r with its logarithm equi-spaced. With this numerical analysis we identified the nonlinear relation between ventricular volume and its conductance.2)Numerical analysis in arbitray rotational shapes : We have developed a software to analyze current distribution and nonlinearity in arbitrary rotational shapes.3)Examination of nonlinearity in vitro : We examined the nonlinearity with a catheter of electrode width of 1mm and interelectrode distance of 1mm. We confirmed that 90% of currents were confined within 3.3mm from the catheter. Compared to the preveious reports, the range was wider ; however was similar to our numerical; analysis2.We developed a conductance volumetric system, in which generation of AC currents as well as determination of RMS values is performed digitally with a computer. This enables miniaturization and power-saving, and thereby continuous volumetry by an implanted device in a conscious small animals such as in rats. Data sampling synchronous to generated AC made RMS calculation at two frequencies possible with only addition and subtraction.