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Biomedical subjects

N Chauveau

Publications and source records attributed to N Chauveau.

13 recordsLinked to original sources
PubMed1996

A multifrequency serial EIT system.

A multifrequency (1 kHz-1 MHz) serial electrical impedance tomography (EIT) system has been developed. It is based on 16 active electrodes and can be extended up to 32. Each active electrode can be programmed for current driving and for measuring either the injected current or the voltage difference between adjacent electrodes, and includes calibration facilities. Real and imaginary parts of the impedance are obtained by applying a parametric identification method (extended Prony), but other techniques are easily adaptable. Image reconstruction is carried out using the Sheffield filtered back-projection algorithm. Characteristic frequency images are under development and should be of great interest to distinguish between normal and tumorous tissues.

Algorithms↗
PubMed1996

Bioelectrical impedance techniques in medicine. Part I: Bioimpedance measurement. Second section: impedance spectrometry.

Electrical impedance spectrometry is an important application field of bioimpedance measurements. After introducing the electrical properties of biological tissues, this part presents instrumental aspects and applications of electrical impedance spectrometry. The main instrumental constraints encountered in spectrometric electrical impedance measurements are reviewed, focusing on low-frequency applications. Examples of impedance cells and probes are presented and several instrumental setups operating in the frequency and time domain are described. Some examples of applications are presented, including in vitro characterization and modeling of normal tissues, in vitro and in vivo characterization of cancerous tissues, and assessment of tissue perfusion/ischemia levels.

Breast Neoplasms↗
PubMed1995

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.

Animals↗
PubMed1995

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.

Animals↗
PubMed1994

Tissue characterization by impedance: a multifrequency approach.

Two experimental set-ups for in vitro characterization of electrical bio-impedance are described. The first one, based on a commercially available instrument, operates in the frequency range 1 Hz-10 MHz. The second one uses an identification process and operates in the frequency range 1 Hz-1 MHz. Some results are presented and discussed in the context of multifrequency electrical impedance tomography.

Animals↗
PubMed1993

Experimental acquisition system for impedance tomography with active electrode approach.

An experimental system for impedance tomography has been constructed. The acquisition system uses 16 multifunctional active electrodes, each including a current source and a voltage buffer. Images of active and reactive parts of different target impedances in a phantom filled with liquid have been obtained. The system performance has been compared with those of other systems using either a mesh phantom or rods as point sources used for the determination of the modulation transfer function.

Electric Impedance↗
PubMed1990

Evaluation of extracorporeal blood heat exchanger devices.

An accurate and easy to use test circuit has been developed for the performance evaluation of the heat exchangers used in cardiac surgery during extracorporeal circulation. The water part of the heat exchanger is fixed at a flow rate of 15 l/min and at a temperature of 40 degrees C. In the blood side, the flow rate is varied from 1 to 6 l/min and the temperature is 30 degrees C. The use of a precise thermometer (precision 0.01 degrees C) and of a microcomputer permits efficiency with a good reproducibility. The results obtained show a real improvement in the efficiency of the new extracorporeal blood heat exchangers devices.

Blood↗
PubMed1990

Automatic modules for extracorporeal circulation control.

Maintenance of a constant level in the oxygenator during surgical extracorporeal circulation (ECC) is of paramount importance. We propose a device able to regulate the pump speed accordingly to the level in the oxygenator, and an automatic clamp to control venous return from the patient. The level regulator permits pump speed control and also stops the pump when a prefixed low level is reached (during ECC). Linearization of the level sensor has been made in order to optimize the PI regulator. Simulation results are presented and the regulator is evaluated in a clinical environment. The automatic clamp provides a good solution for reproducible and easy transitions in venous return. When coupled with the level regulator, the pump speed will increase automatically from zero to the correct equilibrium speed, with variable duration (from 30 seconds to 5 minutes) chosen by the operator. The same technique is used for stopping the ECC. These two devices are, in fact, modules, making up part of an evolutive device for ECC automation. The modules can exchange data with a supervising microcomputer.

Automation↗
PubMed1986

[An electronic visual aid using a luminance amplifier in night vision disorders].

The efficiency of a light amplifier system for the improvement of night vision has been tested on 30 normal subjects and on subjects suffering from night blindness including 36 patients with pigmentary retinopathy, 18 myopic patients with night blindness and 12 patients with senile cataracts. In all cases, the scotopic vision presented a great improvement and it reached up to half of photopic vision. The use of the light amplifier would certainly provide a considerable improvement for subjects suffering from night blindness and mostly for those suffering from pigmentary retinopathy. But two conditions are necessary for this: miniaturization of the device and absence of major macular lesions in the patient.

Cataract↗
PubMedDate not supplied

[Free-living Amoebae in fresh water. Study of the water supply of the town of Poitiers (France) (author's transl)].

46 out of 76 samples of water originating from the water supply of the town of Poitiers, and concerning each stage of it, were found positive to free-living amoebae. 3/4 of the isolated strains belonged to the genus Acanthamoeba only 2 to the genus Naegleria, and the remaining to the genus Hartmanella. All the strains are insensible to 5-Fluoro-cytosin and Amphotericin B at concentrations compatible with human use. No experimental pathogen power could be demonstrated by inoculation to laboratory mice.

Amoeba↗