The goal of this project is to develop a technique to permit the rapid and accurate measurement of pulmonary edema by measuring changes in electrical impedance of the thorax. By designing and building an electrical conductivity measuring instrument with high sensitivity and spatial resolution, we will test the feasibility of detecting and displaying changes in electrical impedance in the lungs associated with their accumulation of fluid. By synchronizing these measurements with the events of the cardiac cycle, it may be possible to distinguish fluid which moves in a pulsatile fashion in the intravascular space from extravascular fluid, which is stagnant. By comparing changes in the reactive component of impedance with changes in its real component changes in the reactive component of impedance with changes in its real component, or resistivity, an added method of distinguishing blood from interstitial fluid may be developed. We have discovered several innovative approaches to this problem. We have built a prototype instrument, obtained data and produced images of greater spatial resolution and conductivity resolution than those available to earlier methods. We will use both the reactive and resistive components of impedance to test the hypothesis that images of the cross-section of the thorax can be produced having sensitivity and spatial resolution sufficient to distinguish clinically important levels of regional pulmonary edema. This prototype instrument applies patterns of electric current through an array of 32 electrodes on the surface of the body, and records the voltages that result on all 32 of those electrodes. From the measured voltages, the system generates and displays an approximate reconstruction of the electrical conductivity within that body. This reconstruction provides an image of the tissues in that body based on their differing electrical conductivities. this system is adaptive in that the successive patterns of current applied to the body are determined from the previous voltage measurements. this method achieves a theoretically predicted maximum signal-to-noise ratio, which exceeds that previously obtained in other systems. A further innovation is the use of algorithms to model the presence of electrodes on the body surface to account for their shunting the applied currents around rather than through the body being studied.
| Newell, J C; Peng, Y; Edic, P M et al. (1998) Effect of electrode size on impedance images of two- and three-dimensional objects. IEEE Trans Biomed Eng 45:531-4 |
