A new gastric impedancemeter for detecting the development of a visceral edema: a proof-of-concept study on an experimental endotoxemic shock.

Visceral congestion and edema are important features of advanced heart failure. Monitoring the evolution of fluid content in the gastric wall might provide an index of the development of this phenomenon and therefore constitute an innovative marker to early detect acute decompensated heart failure episodes. The evolution of the fluid content in the gastric wall is measured using a device implanted in the submucosa layer of the fundic region of the stomach. The device composed of two electrodes measures the bioimpedance values that reflects the water content of the tissue.An in-vivo experiment in a pig was carried out to validate the feasibility of detecting the gastric bioimpedance variations during the development of an experimental acute visceral edema caused by an endotoxemic shock. Our preliminary results confirm the possibility to monitor the bioimpedance variations due to moderate changes in tissue water content (10%) with a two-electrode configuration device implanted in the submucosa of the stomach.

In vitro tissue characterization and modelling using electrical impedance measurements in the 100 Hz-10 MHz frequency range.

In vitro electrical impedance spectrometry was performed on tissue samples excised from sheep. Measured data have been processed to reduce dispersion in measurements and to provide criteria useful for tissue comparison. Two electrical models are proposed for tissues exhibiting a one-circle impedance locus and a two-circle impedance locus. Measurement results and electrical parameters of tissues and models fitted to experimental data are presented. Model sensitivity to parameter variations is discussed.

Closed loop control of PaCO2 during ECC.

A prototype for the control of blood gases during extracorporeal circulation (ECC) has been built. It is composed of a CDI300 continuous gas blood analyzer, a programmable gas blender and an IBM PC. The air blender is composed of three mass flow controllers (air, oxygen and total flow rate). The microcomputer commands these controllers in order to obtain the desired mixture of air and oxygen. The system acquires the data sent by the blood gas analyzer every 6 seconds and commands the gas blender in order to maintain the desired arterial dioxide partial pressure (PaCO2) in the arterial line. The first experimental results on sheep show that if blood gas parameters are stable when beginning the closed loop control, then the desired PaCO2 value may be obtained. Otherwise, the value of PaCO2 under control is slightly different but a stable value is obtained after 10 minutes. More experiments must be done in order to establish the real limits of such a system and optimize the gain of the control system.