Biomedical subjects

M Nadi

Publications and source records attributed to M Nadi.

11 recordsLinked to original sources

PubMed2003

Dielectric properties of blood: an investigation of haematocrit dependence.

We have investigated the haematocrit dependence of the electrical parameters (relative permittivity and conductivity) of blood. The measuring set-up, composed of an impedancemeter (HP 4291 A), an open-ended coaxial line and a temperature controlling set, was designed for dielectric measurements in the 1 MHz to 1 GHz frequency range. Measurements were performed on ex vivo animal (cow and sheep) blood at 37 degrees C. The two dielectric parameters appeared to be strongly dependent on the haematocrit. The permittivity versus frequency decreases then increases when the haematocrit decreases. The conductivity increases in the whole frequency range when the haematocrit decreases. Due to the lack of comparative data on the frequency range explored, we compare the dielectric profiles with those deduced from the Maxwell-Fricke theoretical model.

Animals↗

PubMed2003

[Relevance of in vitro studies for the immunity of cardiac implants in an electromagnetic field environment]].

The object of this article is to show the contribution of the vitro experimental approach, based on the basic rules of electromagnetic compatibility (EMC), as a complementary tool to the clinical studies. Results can be obtained by a experimental approach in vitro with electromagnetic phantoms associated to a bench of "standard" test to allow a possible comparison between various studies. After describing the protocol developed for the cardiac implants (pacemakers and defibrillators), examples of partial results are presented by way of illustration.

Defibrillators, Implantable↗

PubMed2002

Catheter ablation using very high frequency current: effects on the atrioventricular junction and ventricular myocardium in sheep.

BACKGROUND: Radiofrequency ablation is currently used in the treatment of various cardiac arrhythmias. However, this technique is limited by impedance rise, leading to coagulum formation and desiccation of tissue. We developed a new generator, providing very high frequency (27 MHz) current, which is in the intermediate range between radiofrequency and microwave energy. The aim of this study was to evaluate the results for catheter ablation of the atrioventricular junction and characteristics of the lesions obtained at ventricular sites. METHODS AND RESULTS: The generator was coupled to a specially designed 7-French coaxial catheter. The study included experiments performed on 10 sheep (Wt. 31- 42 kg). In seven sheep, the catheter was introduced into the femoral vein and advanced across the tricuspid annulus to record the largest possible His electrogram. VHF current was applied for 25 s, with increasing energies. The energy needed to obtain complete atrioventricular (AV) block ranged from 60 to 100 Watts. Six animals were observed for 6 to 21 days. Complete AV block was found to be persistent. In those seven sheep in whom AV junction was ablated and in three additional sheep, the ablation catheter was positioned toward the right ventricular apex using the same approach and into the left ventricle via the femoral artery, and 20 to 90 Watts energy was delivered in order to assess the size of the induced lesions. Side effects included ventricular tachycardia degenerating into ventricular fibrillation in six cases, but the same effect was observed in this animal model with radiofrequency energy. No cardiac perforation was noted. No thrombus was observed at the catheter tip. The size of the lesion ranged from 3 to 45 mm in width and 1 to 15 mm in depth. CONCLUSIONS: Catheter ablation using VHF current is feasible and appears effective in producing stable AV block when applied at the AV junction and results in substantial myocardial lesions. Further studies are needed to define its clinical interest and side effects.

Animals↗

PubMed2002

Acoustical characterization of bone using a cylindrical model and time of flight method: edge reconstruction and ultrasound velocity determination in cortical bone and in medullar marrow.

Our objective is to evaluate the external and internal dimensions of bone diaphysis and the speed of sound in cortical bone and in medullar marrow. The diaphysis is modelled by a cylindrical hollow tube. The theory of rays is used and an approximation allows us to break free from the data gained by ultrasonic field amplitude. Then, acoustical and dimensional parameters are only related to the time of flight of reflected and transmitted acoustic echoes in the tube. From the arrival time of particular echoes, the inverse problem resolution then allows us to experimentally determine the sought parameters. This method is validated in vitro on a bovine femur and gives satisfactory results.

Acoustics↗

PubMed2002

Dielectric properties of blood: an investigation of temperature dependence.

We have investigated the temperature dependence of the electrical parameters (permittivity and conductivity) of blood. The measuring system, composed of an impedancemeter (HP 4291 A), an open-ended coaxial line and a temperature controlling set, was designed for dielectric measurement in the frequency range of 1 MHz to 1 GHz. Measurements were performed on ex vivo blood of humans and animals (cow and sheep). The results obtained show the weak sensibility and a change of sign of the temperature coefficient of the relative permittivity (about 0.3% degrees C(-1) at 1 MHz and -0.3% degrees C(-1) at 1 GHz). The conductivity presents a more significant variation (of the order of 1% degrees C(-1) over the whole operating frequency range.

Animals↗

PubMed1995

Intracardiac high-frequency catheter ablatherapy: technical aspects.

Arrhythmia and conduction disorders can be treated by intracardiac ablation. The paper presents an original intracardiac catheter ablation method using a high-frequency (HF) electromagnetic power source. A high-frequency signal is emitted through an electrophysiological catheter introduced into the femoral vein and passed along the course of that vein into the heart. To prevent impedance rise, a problem encountered with other techniques, HF signal wave trains are used for half-period impedance match control and, where necessary, automatic impedance adjustment. Fully automated impedance matching combined with frequency-specific catheter design prevents power reflection between load and source. Resulting lesions can be controlled as to location, area and depth. In addition, HF pulses can be released independently of cardiac rhythm. Additional comprehensive animal experimentation is currently going forward.

Animals↗

PubMedDate not supplied

A methodological approach for the characterization of cardiac pacemaker immunity to low frequency interferences: case of 50 Hz, 60 Hz, 10 kHz and 25 kHz led disruptions.

The goal of this work is the implementation of a metrological set up dedicated to the characterization of cardiac pacemakers' immunity at low frequency electromagnetic disruptions. The studied frequencies are 50 Hz, 60 Hz, 10 kHz and 25 kHz. The assessment methodology that is applied is in accord with the electromagnetic compatibility. The tests are carried out on single-chamber pacemakers. The first approach, consisting of the application of the interfering signal directly between the housing and the electrode, enabled us to point out the influence of a preset detection sensitivity on the signal levels induced between the terminal and the pacemaker's housing. These attempts are completed by in vitro tests using an electromagnetic model which allows one to take into account the interface which constitutes the human body, and thus to get closer to a real life situation. The visualization of the pacemaker generated signal illustrates the performance of the pacemaker according to different test configurations. It is an initial approach meant to create a base for the creation of a metrological protocol.

Electromagnetic Fields↗

PubMedDate not supplied

Study of a new electromagnetic sensor for glycaemia measurement: in vitro results on blood pig.

In this paper, we develop a non-invasive method to measure glycaemia levels. The method is based on an electromagnetic sensor associated with a specific electronic card. Results obtained on whole pig blood show the influence of the temperature and the linearity between the glucose concentration and the process card signal output. Measurements are reproducible and the resolution obtained permits determination of the glucose level around 0.1 g l(-1).

Animals↗

PubMedDate not supplied

Non-invasive glycaemia blood measurements by electromagnetic sensor: study in static and dynamic blood circulation.

In this paper, we present the results of non-invasive blood glycaemia measurements. The blood used in the measurements was calf blood. The measurement method uses an electromagnetic sensor based on eddy currents, which allows the detection of blood glycaemia levels through the variation of the dielectric parameters of the blood. A change in blood glucose concentration causes a variation in the dielectric parameters, in particular conductivity. Detection is only possible at a resonant frequency. The measurements were taken in a static and dynamic state (with and without circulation of blood). The blood is inside a plastic tube placed within the sensor and is surrounded by gelatine, which simulates muscular tissue. The plastic tube simulates the vein where blood circulation occurs. The in vitro results in both cases (static and dynamic) are provided. Under unfavourable conditions we can detect a change of +/- 2 g/l of glucose. We present and discuss these results.

Animals↗

PubMedDate not supplied

Practical interstitial method of heating operating at 27.12 MHz.

A practical interstitial capacitive method of heating using thin flexible coated electrodes operating at 27.12 MHz is described. Advantages compared to classical interstitial methods are: uniform heating, control of the inserted length, compatibility with curie therapy, simplicity and low cost. The electrode geometry could be designed according to tumour site and volume. Restriction of longitudinal heating to a part of the wire is also possible. A simple matching circuit can be connected to the active wires to obtain a standing wave ratio (SWR) of less than 1.5. Individual power regulation of the electrode should be used and is feasible at this frequency. Numerical, experimental and clinical results demonstrate the practical value of this method.

Animals↗

PubMedDate not supplied

Dielectric properties of gelatine phantoms used for simulations of biological tissues between 10 and 50 MHz.

The use of gelatine phantoms for simulating the dielectric properties of human tissues is suggested. These phantoms are mainly made of gelatine and water and are therefore readily prepared at a low cost. They can be poured into moulds and adopt various shapes depending on the organ to be simulated. In addition, their preservation is not critical. We have studied, at 10, 27 and 50 MHz, the variations of relative permittivity and conductivity as a function of temperature between 15 and 50 degrees C. What is shown is that those values vary both as a function of gelatine concentrations and as a function of temperature. For example, at 37 degrees C and 27 MHz, variations of relative permittivity from 87 to 100 and variations of the conductivity from 0.27 to 0.45 S/m for concentrations of 10% to 40% are observed. At the above frequency, the permittivity of human and animal tissues range between 95 and 180 and the conductivity between 0.4 and 0.6 S/m. Furthermore, the addition of sodium chloride at variable concentrations enables both conductivity and permittivity values to be modified. We propose, as 'muscle-equivalent' phantoms at 27 MHz, a phantom consisting of 20% gelatine with an electrical conductivity from 0.27 to 0.48 S/m and a relative permittivity from 90 to 93 at temperatures between 15 and 50 degrees C. These gelatine, water and sodium chloride phantoms are adapted for easy and cheap simulation of most human tissues in a temperature range from 15 to 50 degrees C, for frequencies from 10 to 50 MHz.

Electric Conductivity↗