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Biomedical subjects

A Bardou

Publications and source records attributed to A Bardou.

At least 19 recordsLinked to original sources
PubMed2003

[Feasibility of prosthesis insertion by laparotomy as palliative treatment for malignant duodenal stenosis].

The authors report a preliminary series assessing the feasibility of duodenal stenting using a surgical approach. The study included 16 patients with a malignant duodenal outlet obstruction for whom a biliaryobstruction necessitated a laparotomyor following an endoscopic stenting failure. The stent was efficient in 15 patients with a complete relieve of obstruction. These patients could have oral intake at the end of the first postoperative week. No stent obstruction occurred. The duodenal stenting by laparotomy could be a good alternative to palliative gastroenteral anasotomosis.

Duodenal Neoplasms↗
PubMed2001

Numerically solving physiological models based on a polynomial approach.

Much research effort has been directed in different physiological contexts towards describing realistic behaviors with differential equations. One observes obviously that more state-variables give the model more accuracy. Unfortunately, the computational cost involved is higher. A new algorithm is presented for simulating a model described by a system of differential equations in which efficiency may not be altered by its size. In order to do this, the method is based on a polynomial description of the state-variables' evolution and on a computation distributed control. Evaluations and results performed with classical models like Fitzhugh Nagumo or Hodgkin Huxley, allow validation of the method and exhibits its potential to decrease the computational costs.

Algorithms↗
PubMed2000

Overview of CARMEM: a new dynamic quantitative cardiac model for ECG monitoring and its adaptation to observed signals.

Different approaches have been proposed in order to achieve knowledge integration for coronary care monitoring applications, usually in the form of expert systems. The clinical impact of these expert systems, which are based only on "shallow" knowledge, has not been remarkable due to the difficulties associated with the construction and maintenance of a complete knowledge base. Model-based systems represent an alternative to these problems because they allow efficient integration of the "deep" knowledge on the underlying physiological phenomena being monitored. In this work, a brief review of existing model-based systems for cardiac rhythm interpretation is presented, followed by the description of a new system for Cardiac Arrhythmia Recognition by Model-Based ECG Matching (CARMEM). Fundamental characteristics of CARMEM are presented; in particular, its ability to provide online parameter adaptation to simulate complex rhythms and to match observed ECG signals. The proposed model can be useful for the explanation of the origin of cardiac arrhythmias and contribute towards their robust characterization in the context of coronary care units.

Artificial Intelligence↗
PubMed1992

Interpretation of epicardial mapping by means of computer simulations: applications to calcium, lidocaine and to BRL 34915.

The aim of this work was to compare experimental investigations on effects of lidocaine, calcium and, BRL 34915 on reentries to simulated data obtained by use of a model of propagation based on the Huygens' construction method already described in previous works. Calcium and lidocaine effects are investigated on anisotropic conduction conditions. In both cases, reduction in conduction velocities are observed. In lidocaine case, a refractory area is located along the longitudinal axis. In agreement with experimental electrical mapping, the simulations show that the stabilization of reentrant excitation is mainly due to the existence of this refractory area around which the reentrant circuit can develop. The experimental study shows that BRL 34915 has both arrhythmogenic and antiarrhythmic effects. A detailed electrophysiological analysis has shown that drug infusion act on normal cardiac cells by decreasing the relative and absolute refractory period. BRL 34915 action is simulated by a decrease in the refractory period showing that the time frequency of the reentrant activity is increased and that the spatial size where the reentry is developing is becoming smaller. These two effects are arrhythmogenic, the simulated data being so in good agreement with the experimental ones.

Animals↗
PubMed1985

Quantitative ascending aortic Doppler blood velocity in normal human subjects.

We have developed digital, Apple II microcomputer-based methods for the numerical analysis of pulsed, range-gated, ultrasonic Doppler blood velocity signals. These methods were then used to analyse Doppler data recorded every 5 ms from the ascending aorta via the suprasternal notch in normal subjects ranging in age from 3 to 62 years. Normal values for peak velocity, the integral of velocity over the time of systole, and the rate of change of velocity in early ejection are reported. It was found that, after an initial step increase, the velocity of blood flow in early ejection increased in a linear manner in more than two thirds of the individual beats analysed. The time for which the linear acceleration in the aorta was constant (circa 50 ms) was unrelated to the age or size of the subject.

Adolescent↗
PubMed1985

Simultaneous Doppler blood velocity measurements from aorta and radial artery in normal human subjects.

We used two independent, pulsed, range-gated, ultrasonic, Doppler blood velocity meters to record blood velocities in the aorta and a peripheral artery in 32 normal subjects aged 8 to 62 years. Aortic signals were obtained from an unfocussed transducer in the suprasternal notch using a 2.25 MHz instrument. Simultaneous tracings were obtained from the radial or posterior tibial artery using an 8 MHz instrument. The audio Doppler signals were subjected to spectral analysis and mean velocity was calculated at 5 ms intervals during 11 successive heart beats at each site. The increase in mean velocity at the start of systole in the aorta followed a linear pattern for the first 45 ms of ejection in two thirds of the beats, irrespective of the age or size of the subject. A similar linear velocity increase in early systole was seen in the peripheral arterial signals after a delay due to the time taken for the flow wave to pass to the periphery. Thus the constant acceleration seen in aortic blood velocity tracings is transmitted to peripheral arteries in an attenuated and delayed but undistorted form.

Adolescent↗
PubMed1984

Effect of descending thoracic aorta clamping and unclamping on phasic coronary blood flow.

Myocardial infarctions during aortic surgery often occur after aortic clamping and unclamping. In order to investigate the aortic blood pressure (AoBP)-coronary blood flow (CBF) relationship, hemodynamic parameters and phasic circumflex CBF in 15 anesthetized and open-chest dogs during clamping and unclamping of the thoracic descending aorta have been recorded. During clamping, mean aortic blood pressure (MAoBP) rose from 97 + 17 to 150 + 42 mm Hg (P less than 0.001), and total combined left-ventricular power (Wtc) from 692 + 232 to 923 + 402 mW (P less than 0.001) while the ascending aortic blood flow (AoBF) and heart rate did not change significantly. The mean circumflex blood flow (MCBF) increased from 67 + 30 to 88 + 30 ml/min. The increase in systolic coronary blood flow (+73%) was larger than that in diastolic coronary blood flow (DCBF) (19%). The late coronary resistances were increased 39%. Conversely, after unclamping, MAoBP decreased while AoBF and Wtc increased. During the first cardiac cycles after aortic unclamping DCBF decreased 50% with a decrease in the diastolic blood pressure (DBP). Four cycles later, DCBF reincreased while DBP kept on decreasing. This may be related to an active coronary vasodilatation. A linear relationship between DCBF and DBP has been obtained during acute change in DBP due to clamping or unclamping. From these linear relationships, the change in diastolic zero flow pressure (PfO) has been found to be about + 40 mm Hg during clamping. This change in PfO may be responsible for the observed large fall in DCBF during unclamping. The decrease in DCBF associated with the increase in Wtc accounts for the delayed active vasodilatation.

Animals↗
PubMed1981

Study of relations between arterial oscillation period and heart rate.

This study was performed to determine the relationship between variations of arterial cross-section and cardiac period. Relative section variations were recorded by impedance rheography. In 176 anesthetized adult mongrel dogs, aortic and femoral rheograms, femoral pressure, and ECG were recorded. The cardiac period (Tc) and the interval between the systolic and the dicrotic wave, i.e., the arterial intrinsic period (Ta), were measured and related to each other (Tc/Ta ratio). In 125 dogs, the dicrotic wave appeared spontaneously. In these cases Tc/Ta 1.98 +/- 0.16. In 51 dogs, no dicrotic wave appeared spontaneously. Lengthening of cardiac period was obtained in 25 of these dogs by vagus stimulation. As related to the cardiac period before vagal stimulation Tc/Ta was then 0.98 +/- 0.08. In the remaining 26 dogs, such a lengthening was obtained by inducing a premature ventricular depolarization. In this group, Tc/Ta was 1.00 +/- 0.03. The results of the present study suggest that a constant adaptation exists between ventricular ejection and arterial dynamics. The physiologic implications are discussed.

Animals↗
PubMed1977

Impedance rheography: a new method for recording spontaneous arterial section variation.

The aim of this work is to define, on the basis of impedance rheography, a method to record arterial section variations without either inertia or the production of wall-strain. High frequency current (2 MHz) is employed to measure the impedance variations of the deforming artery. The modulating envelope is representative of arterial section variations. This method permits the recording of arterial section variations by a peri-arterial method or an external method on superficial arteries (without denudation). A comparison between arterial section variations and arterial pressure variations at the same point shows that the arterial wall behaves as a non-linear pressure gauge: Rheogram-pressure curves are similar to volume-arterial pressure curves. The great precision with which this method describes the chronology of arterial deformations is of great interest in defining viscous properties of the arterial wall and following their evolution during pathologic alterations such as atherosclerosis.

Animals↗
PubMed1977

A hardware device for recognition of P and QRS waves.

A new hardware device has been constructed to detect QRS and P complexes for the purpose of automatic arrhythmia interpretation. This apparatus can operate in noisy conditions and provide synchronized pulses representative of P complex, QRS complex, wide QRS, and premature QRS to different output channels. P wave identification is achieved with a high degree of reliability through a specially designed bipolar electrode catheter. The device could minimize demands on central processor time and core storage computer.

Arrhythmias, Cardiac↗