Influence of Volume and Flow Change on the Electrical Impedance Signal (In Vitro)

摘要

On the basis of preliminary results, rheoencephalography (REG) shows promise as a practical, noninvasive and continuous monitoring modality of brain injuries. However, REG literature reflects uncertainty about whether the signal reflects flow or volume. Presented here are results of in vitro studies manipulating flow/volume to model clinical conditions (such as brain ischemia and vasospasm) while recording the electrical impedance signal. A loop was created using tubing filled with 0.9 % NaCl. This loop was comprised of a Doppler in-line flow probe connected to an ultrasound flow meter, a peristaltic pump, a pressure transducer and home-made electrical impedance measuring cell, incorporating a balloon catheter. Bipolar impedance amplifiers were used for measuring impedance pulse waves. Data were stored on a PC and processed off-line. This in vitro study confirmed that (1) Doubling flow rate influenced the pulse amplitude and mean flow of the Doppler signal; (2) Doubling flow rate had no influence on the amplitudes of the pressure or electrical impedance signals; (3) An increase in amplitude was observed in the pressure and electrical impedance signals when the first derivative was taken. (4) Balloon inflation decreased electrical impedance and Doppler flow pulse amplitudes; (5) With balloon inflation, Doppler and electrical impedance signals showed an identical relationship to decreased flow (R sq=0.966).