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Biomedical subjects

I Daskalov

Publications and source records attributed to I Daskalov.

53 records · Page 3Linked to original sources
PubMed1975

On the total relaxation of the left ventricle in primary rheumocarditis in children. Apex-cardiographic studies.

Apexcardiographic studies were carried out on 100 healthy children and 120 children, aged 3-14 years, with primary rheumocarditis. An analysis of the results indicate that the duration of total relaxation of the left ventricle is prolonged in the group of children suffering from primary rheumocarditis. The prolongation of TR is due to the increased PD interval, as well as to the prolonged IVR. The changes described lead to a certain phasic delay of the aortal and opening of the mitral valves.

Adolescent↗
PubMed1975

Changes in the asynchronous contraction of the left ventricle in primary rheumocarditis in children.

An attempt has been made at studying in greater detail the changes in the AC of the left ventricle in primary rheumocarditis. The changes, evaluated with the help of an ACG, have been differentiated from such in the EMI and those in IVC. The studies werecarried out on 220 children, aged 3-14, divided into 2 groups: 100 healthy controls and 120 with primary rheumocarditis. An analysis of the results shows that the rheumatic process in the myocardium modifies the normal transformation of electrical events into mechanical ones, and prolongs the AC phase. The latter is due to the increase of EMI duration. IVC is practically unchanged. The prolonged duration of EMI may be connected with a certain compensatory reaction.

Adolescent↗
PubMedDate not supplied

Optimization of the defibrillation current density in the heart region by a two-layer segmented electrode.

Transthoracic defibrillation is a procedure applying high intensity electrical current through the thorax region by electrodes, in order to simultaneously activate most of the myocardial cells, thus enforcing them to reinstate a normal rhythm. A solution is proposed for analysis and synthesis of the current density distribution field in the heart region. In an attempt to reach uniform excitation of the greatest possible quantity of myocardial cells, a field image is searched for, with the J-vector uniformity distribution as a criterion. The finite element method and the method of approximating functions are used, as well as nonlinear programming. This approach resulted in designing a two-layer defibrillation electrode, with the layer applied to to the thorax divided in three different resistivity regions.

Algorithms↗
PubMedDate not supplied

Modelling transthoracic defibrillation waveforms.

Recent investigations connected with implantable defibrillators yielded new data on heart electrophysiology, resulting in reassessment of existing and advancing of new types of electrical impulses. Different electrical equivalent circuits were proposed for modelling intracardiac and transthoracic defibrillation pulse waveforms, comprising generator, electrode interface and tissue resistances. We attempted modelling of the transmembrane voltage Vm time course, induced by different applied voltage Vs waveforms, taking into account only the shapes and the relative Vs and Vm amplitudes. The excitable cell membrane impedance Zm was modelled with higher resistance and lower capacitance, so that a shunting effect on the generator and tissue resistances was avoided. The result was a very simple equivalent circuit. We proposed criteria for efficient defibrillation pulse waveforms yielding a straightforward approach to model existing and new pulses and to assess their efficiency.

Biomedical Engineering↗
PubMedDate not supplied

Automatic adjustment of biphasic pulse duration in transthoracic defibrillation.

Many studies have proven that biphasic defibrillation pulses are more efficient than the damped sinusoid monopolar waveform. Transthoracic resistance was shown to change during the two phases. On the other hand, it was proven that transthoracic resistance plays an important role in the defibrillation process, yielding the current for selected energy or voltage. Pre-shock measurement of the resistance may lead to improved selection. Stabilized current defibrillators are of low stored-to-delivered energy ratio. Therefore, automatic dynamic adjustment of some defibrillator parameters with respect to transthoracic resistance changes seems rational. An approach is known for modifying the pulse duration, in order to deliver a selected energy. A method is proposed here and an experimental defibrillator is developed for dynamic pulse duration adjustment with the purpose of obtaining a desired optimal time-course of the cardiac cell transmembrane potential.

Animals↗
PubMedDate not supplied

Assessment of balanced biphasic defibrillation waveforms in transthoracic atrial cardioversion.

Various electrical pulses have been used for defibrillation. The monophasic damped sinusoid waveform, initiated in 60 s, was adopted in virtually all defibrillators. Biphasic pulses were introduced recently, achieving success with less energy. A biphasic exponential waveform was modelled with 4 ms duration per phase with a balanced 3:1 ratio of the first to second phase peak voltages and implemented in a defibrillator. A version obtained by chopping the pulses with a 5 kHz frequency was also used. It was hypothesized that the modelled transmembrane voltage decay time is a parameter that could be associated with successful defibrillation. The results of cardioversion for two groups of patients with the 'classic' monophasic waveform and with the biphasic pulses were compared. The mean efficient energy with the damped sinusoid was 205 +/- 85 J, versus 88 +/- 43 J with the biphasic pulses, yielding a ratio of 2.32 (1.92 to 3.2 for fibrillation and flutter, respectively). An acceptable agreement between model data and clinical results was found. The transmembrane voltage decay time ratios for monophasic versus biphasic pulses was in the approximate range of 2.5 to 3.5.

Atrial Fibrillation↗
PubMedDate not supplied

Automatic detection of atrial fibrillation and flutter by wave rectification method.

Rapid detection of atrial flutter or fibrillation is needed in intensive care or home ECG monitoring with alarm generation, and in portable monitors with warningfunction, etc. Detection and assessment of these atrial abnormalities is necessary in computerized morphological analysis as well, to decide whether parameter measurements should be rejected, restricted to QRS and/or T wave only, or limited to those leads where atrial flutter orfibrillation waves are less expressed. A method for the detection and measurement of atrial flutter and fibrillation in the T-P segments of the ECG is proposed. An atrial flutter/ fibrillation parameter (AFF) is defined as the mean value of the differentiated filtered and rectified signal in these segments. The AFF has been measured in 329 patients from an annotated atrial flutter-fibrillation database. A threshold of AFF=0.35% with respect to the maximum signal excursion was chosen by a heuristic algorithm, to separate patients with atrial arrhythmia. The accuracy of the method was 91.8 %. The positive and negative detection errors of the AFF classification are discussed.

Atrial Fibrillation↗
PubMedDate not supplied

Possibilities for predictive measurement of the transthoracic impedance in defibrillation.

Transthoracic electrical defibrillation is administered by high voltages and currents applied through large size electrodes. Therefore, the defibrillator load impedance becomes an essential factorfor the efficacy of the procedure. Attempts at prediction of transthoracic impedance by pre-shock measurement with low-amplitude high-frequency current have yielded apparently promising results. A reassessment was undertaken of the comparison between transthoracic impedance measured over a wide frequency range (bioimpedance spectroscopy) and measured during the shock. An estimation of the possibilities for pre-shock 'prediction ' of the impedance was performed, to allow adequate selection of the defibrillation energy or current with the intention of increasing the possibility for positive results with the first shock. Data were obtained from experimental fibrillation/defibrillation cycles on dogs andfrom cardioversion of atrial fibrillation or flutter in patients. The final results suggest that high-frequency low-amplitude impedance measurements cannot predict the corresponding value during the shock with very high accuracy, as differences up to 15-17% were found using biphasic pulses in patients. However, the method can be used for approximate assessments.

Adult↗
PubMedDate not supplied

Electrical current distribution under transthoracic defibrillation and pacing electrodes.

The known effect of high current density under the perimeter of defibrillation electrodes, leading to skin damage and even severe burns in some cases, has been considered by many investigators. Two main approaches for improvement were proposed: (i) interfacing with layers of varying and high resistivity and (ii) lengthening and shaping the perimeter line. Using finite element and physical modelling, it is shown that the second approach does not yield significant improvement in the distribution uniformity. Moreover, the application of high resistivity layers is unacceptable in dibrillation. The use of a low resistance layer with a diameter covering and extending over the metal plate by at least 2.5 mm results in better uniformity. A similar effect can be obtained by recessing the metal plate in an isolating support--an approach adopted from implantable neurostimulation electrodes. These two versions can be applied in combination.

Cardiac Pacing, Artificial↗
PubMedDate not supplied

Automatic adjustment of chopping-modulated defibrillation pulses to patient transthoracic resistance.

Defibrillation of the heart requires a high amplitude short duration current pulse to be passed through large electrodes placed on the patient's chest. The current meets a virtually active resistance, which can vary in the approximate range of 25 to 180 Omega. As the delivered current or energy depends on the resistance, several methods have been developed to reduce or compensate its influence. For example, pre-shock resistance has been measured by a high-frequency current and the current or energy set accordingly; measurements have been made from the initial tilt and the pulse durations adjusted; and pre-shock measurements have been made by a sub-shock pulse to generate an appropriately selected constant current. A method is proposed using high-frequency chopped biphasic pulses, with pulse-width and period modulation of the elementary pulses. Patient resistance is measured with the first elementary pulse and depending on its value a modulated waveform is generated, selected by a micro-controller from a preprogrammed set. Thus the selected energy is accurately delivered to the patient. In addition, this method allows the shaping of a desired mean patient current waveform, maintaining adequate charge balance between the two phases and securing an appropriate time course of the model-derived transmembrane potential.

Adult↗
PubMedDate not supplied

[Report of a case of congenital vesico-uterine fistula with vaginal atresia associated with an exterior uterine cervix and agenesis of the right kidney].

In a 27-year-old patient with cyclic hematuria a complex congenital malformation was diagnosed: the atresia of the upper third of the vagina and the external uterine cervix, a vesico-uterine fistula, and agenesis of the right kidney. The patient was treated surgically in two phases: first, the vesico-uterine fistula was closed abdominally and then, vaginally, the cervix was lowered down to its normal anatomic site and the external cervical orifice was opened. The postoperative course was normal and the patient was discharged from hospital 20 days after surgery. After 2 months the findings of the follow-up examination were normal, and so were the menstrual cycle and urination.

Abnormalities, Multiple↗