THORACIC GEOMETRY AND ITS RELATION TO ELECTRICAL-CURRENT DISTRIBUTION- CONSEQUENCES FOR ELECTRODE PLACEMENT IN ELECTRICAL-IMPEDANCE CARDIOGRAPHY

In thoracic impedance cardiography (TIC) measurements the neck electro des are often positioned at the basis of the neck, close to the neck-t horax transition. Theoretically, this neck-thorax transition will caus e inhomogeneities in the current density and potential distribution. T his was simulated using a 30 finite element method, solely representin g the geometrical neck-thorax transition. The specific conductivity wa s 7 10(-3) (Omega cm)(-1) and the injected current was 1 mA. As expect ed, the model generated inhomogeneities in the current distribution at the neck-thorax transition, which reached as far as 5 cm into the nec k and 20 cm into the thorax. These results are supported by in vivo me asurements performed in 10 young male subjects, in which the position of the neck electrodes was varied. A two-way ANOVA revealed that the s troke volume of the lowest neck position was significantly different f rom the other positions. Small shifts in the position of the neck elec trode resulted in large changes in impedance and stroke volume (127 to 82 ml for the Kubicek equation). To standardise the electrode positio n, the authors strongly recommend placement of the neck electrodes at least 6 cm above the clavicula.