Sensitivity of the tetrapolar lead configurations on the impedance changes of the lungs

Abstract

We have been developing wearable and wireless impedance measurement device for monitoring impedance changes caused by change in lung conductivity. The measurement is conducted with tetrapolar electrode configuration. The distance of the electrodes is limited to 15 cm and thus there is need for optimization of the electrode locations. In the present study we studied the sensitivity of the electrode configurations on changes of impedance in the lungs by modeling and preliminary measurements. We studied the sensitivity distributions of impedance measurements by applying reciprocal lead field approach. We modeled 35 tetrapolar electrode combinations, 21 vertical and 14 horizontal, with a finite difference method in a realistic model of a human thorax. We analyzed the modeled impedance with two lung conductivities, deflated and inflated. We also measured impedances from two male testees with same 35 leads. The results of the study show lead configurations in upper thorax, both vertical and horizontal, are optimal to measure the impedance changes caused by conductivity changes of the lungs. The study also shows that results from modeling and measurements have fairly good correlation and thus the presented modeling methods are applicable in analyzing the sensitivity of leads to the changes of thoracic impedance. © Springer-Verlag 2007.