RF dosimetry: a comparison between power absorption of female and male numerical models from 0.1 to 4 ghz.

Realistic numerical models of human subjects and their surrounding environment represent the basic points of radiofrequency (RF) electromagnetic dosimetry. This also involves differentiating the human models in men and women, possibly with different body shapes and postures. In this context, the aims of this paper are, firstly, to propose a female dielectric anatomical model (fDAM) and, secondly, to compare the power absorption distributions of a male and a female model from 0.1 to 4 GHz. For realizing the fDAM, a magnetic resonance imaging tomographer to acquire images and a recent technique which avoids the discrete segmentation of body tissues into different types have been used. Simulations have been performed with the FDTD method by using a novel filtering-based subgridding algorithm. The latter is applied here for the first time to dosimetry, allowing an abrupt mesh refinement by a factor of up to 7. The results show that the whole-body-averaged specific absorption rate (WBA-SAR) of the female model is higher than that of the male counterpart, mainly because of a thicker subcutaneous fat layer. In contrast, the maximum averaged SAR over 1 g (1gA-SAR) and 10 g (10gA-SAR) does not depend on gender, because it occurs in regions where no subcutaneous fat layer is present.

Development of numerical phantoms by MRI for RF electromagnetic dosimetry: a female model.

Numerical human models for electromagnetic dosimetry are commonly obtained by segmentation of CT or MRI images and complex permittivity values are ascribed to each issue according to literature values. The aim of this study is to provide an alternative semi-automatic method by which non-segmented images, obtained by a MRI tomographer, can be automatically related to the complex permittivity values through two frequency dependent transfer functions. In this way permittivity and conductivity vary with continuity--even in the same tissue--reflecting the intrinsic realistic spatial dispersion of such parameters. A female human model impinged by a plane wave is tested using finite-difference time-domain algorithm and the results of the total body and layer-averaged specific absorption rate are reported.

A semi-automatic method for developing an anthropomorphic numerical model of dielectric anatomy by MRI.

Complex permittivity values have a dominant role in the overall consideration of interaction between radiofrequency electromagnetic fields and living matter, and in related applications such as electromagnetic dosimetry. There are still some concerns about the accuracy of published data and about their variability due to the heterogeneous nature of biological tissues. The aim of this study is to provide an alternative semi-automatic method by which numerical dielectric human models for dosimetric studies can be obtained. Magnetic resonance imaging (MRI) tomography was used to acquire images. A new technique was employed to correct nonuniformities in the images and frequency-dependent transfer functions to correlate image intensity with complex permittivity were used. The proposed method provides frequency-dependent models in which permittivity and conductivity vary with continuity--even in the same tissue--reflecting the intrinsic realistic spatial dispersion of such parameters. The human model is tested with an FDTD (finite difference time domain) algorithm at different frequencies; the results of layer-averaged and whole-body-averaged SAR (specific absorption rate) are compared with published work, and reasonable agreement has been found. Due to the short time needed to obtain a whole body model, this semi-automatic method may be suitable for efficient study of various conditions that can determine large differences in the SAR distribution, such as body shape, posture, fat-to-muscle ratio, height and weight.

Numerical and experimental analysis of e-field scattering from the ground for base station antennae.

Based on the numerical determination of the complete irradiation volume of a commercial RBS antenna--performed using the FDTD method and the Kirchhoff integral formula for near to far field transformation--open site estimations of the electric field are made and compared with experimentally measured values. To describe the actual behaviour of the radiation field, the inherently complex phasic nature of plane waves is taken into account, together with their two independent states of polarisation. This information is contained in the radiation pattern previously deduced. Moreover, a reflected contribution from flat ground is introduced, along with the line-of-sight ray. Amplitude and phase of the reflected wave are calculated using Fresnel formulae for stratified ground and two polarisation states, i.e. normal and parallel to the plane of incidence. Good agreement with measured values is achieved only by using such assumptions.

Preparation, morphological characterization, and activity of thin films of horseradish peroxidase.

Active uniform films of horseradish peroxidase (HRP) have been prepared by covalent binding on Si/SiO(2) or glass supports previously activated by silanization and succinylation. Labeling by fluorescent or by Electron Spin Resonance (ESR) probes was used to quantify the surface density of active groups and of horseradish peroxidase. Atomic Force Microscopy (AFM) imaging was used to characterize the surface morphology. We observed that a non-uniform protein adsorption due to physical interactions was present when the supports were not activated for covalent binding and was, in large part, removed by washing. The enzyme deposited by covalent binding formed homogeneous layers with a height in the range 60-90 A. By using a fluorescent label, we calculated a protein density of 3.6 x 10(12) molecules cm(-2) on Si/SiO(2), corresponding to an estimated area per molecule of 2800 A(2) which is in agreement with the value expected on the basis of the crystallographic data considering the formation of a monomolecular layer. The protein density of the layer immobilized on glass was similar (1.9 x10(12) molecules cm(-2)). The enzyme immobilized on both supports showed a k(cat)/K(M) being of the order of 3-5x10(5) M(-1)s(-1) that is 1/20th of free HRP. The half-life time of the activity of the enzyme immobilized by covalent binding was longer than 40 days at 6 degrees C.

[Paroxysmal supraventricular tachycardias due to re-entry via concealed retrograde atrio-His bypass (author's transl)]. / Tachicardie parossistiche sopraventricolari coinvolgenti un by-pass atrio-His a conduzione solo retrograda.

Recently there have been proposed electrophysiologic criteria for the diagnosis of a concealed atrio-His bypass tract in patients with paroxysmal supraventricular tachycardia (PST). In order to verify the reliability of the proposed criteria--among the patients we studied for PST without ventricular preexcitation and in whom retrograde His bundle activation was recorded--we have chosen those with normal anterograde A-V conduction, with constant (or minimal increases) V-A interval during ventricular pacing and with short (less than 50 msec) and constant H2-A2 interval during ventricular premature stimulation. We encountered 15 patients with these electrophysiologic characteristics (37-73 years). H2-A2 interval (measured from the end of the His bundle deflection to the earliest atrial activity) ranged 20-45 msec (mean: 33 msec). The prolongation of S2-A2 interval observed in all patients was always within the S2-H2 tract. The retrograde effective refractory period of the A-V nodal region was always short, but not evaluable in any of the patients since it was shorter than that of ventricular myocardium (14 cases) or of His-Purkinje system (1 case). The S1-H2 interval was measured to evaluate whether during ventricular premature stimulation the retrograde His bundle activation was in fact anticipated. In 14 out of 15 patients this interval varied within a very narrow range: 0-20 msec. For this reason we believe that the differential diagnosis between a concealed atrio-His bypass and an accelerated retrograde A-V conduction can only be made if during electrophysiologic study a tachycardia is induced; in such case the detection of an H-Ae interval identical to H2A2, together with a normal retrograde atrial activation, is indicative of a bypass of the A-V node. A concealed atrio-His bypass tract must be differentiated also by a concealed septal Kent bundle; also in this case we believe that the detection of an H-Ae interval identical to H2-A2 indicates the former type of bypass. We conclude that a concealed atrio-His bypass can be diagnosed only if, besides the electrophysiologic criteria proposed by other authors, there is an H-Ae interval the same as H2A2.

Double atrial tachycardia with functional atrial dissociation.

A 57-year-old man with hypertensive and coronary heart disease and bradycardia-tachycardia syndrome suffered from paroxysmal palpitations, during which ECG showed a low atrial tachycardia at a rate of 150-200 beats/min with Wenckebach A-V block. During electrophysiological study an episode of atrial tachycardia appeared, characterized by: - atrial potentials in the high atrial electrocardiogram with regular cycle length (500-530 msec); - atrial potentials in the His bundle electrocardiogram with cycle length (570-580 msec), interrupted by premature atrial beats with coupling interval of 420-480 msec and with an atriogram of identical morphology. A-V conduction showed Wenckebach A-V block. After the cycles of 570-580 msec the low atrial potentials were simultaneous or preceded or followed the high atrial potentials by 10-20 msec. After the cycles of 420-480 msec the low atrial potentials preceded the high ones by 40-70 msec. Then, high atrial tachycardia abruptly stopped and the low atrial tachycardia only persisted with the same cycle length (570-580 msec); the high atrium was captured by the low atrial impulses with a low atrium - high atrium interval of 70 msec. These findings suggest that during the first part of tachycardia a conduction neither from high to low atrium, nor from low to high atrium can be possible. It is therefore a particular case of double atrial tachycardia - to our knowledge never before described in literature - sustained a few seconds because of functional atrial dissociation, induced by refractoriness related to the impulses delivered by the two tachycardia foci. The double atrial tachycardia was not diagnosed in the surface ECG leads. The two foci both appear to be localized at atrial level. The electrophysiological mechanism and the differential diagnosis with tachycardias at different sites are discussed.

[The bundle branch block anatomically located in HIS bundle (author's transl)]. / Problematica dei blocchi di branca a localizzazione anatomica nel fascio di HIS.

Bundle branch block (BBB) patterns are commonly considered to represent conduction block in the corresponding bundle branch. However, several histological and experimental studies demonstrated the possibility of a BBB related to an anatomical lesion within the His bundle. Recently there has been demonstrated, also in clinical setting, the possibility of evaluation whether a left bundle branch block (LBBB) is related to an anatomical within such bundle. For this purpose the selective stimulation of the His bundle has been utilized. A distal simulation of such bundle (which can be evaluated by a stimulus-QRS interval shorter than HV interval) normalizing the QRS complexes compresses an anatomical lesion within the proximal His bundle. Such normalization cannot be attributed to a right septum stimulation since the LBBB pattern should be increased instead of disappearing. The Authors think that an anatomical localization within the His bundle can be evaluated only in LBBB. In fact it is possible that a right bundle branch block pattern, if a septal calcification or fibrosis is present, could be normalized also in the presence of an isoelectric line placed between the artificial stimulus and the QRS complex. There is criticized the concept supported by other Authors that normalization of the QRS complex may be related to a summation effect between the sinusal impulse and that artificially induced. In fact such effect can be easy excluded by analizing the temporal relationship between the ventriculograms registered during His bundle stimulation and the atriograms. The clinical implications of the LBBBs in relation with an anatomical lesion within the His bundle are discussed.

Effects of dobutamine on electrophysiological properties of the specialized conduction system in man.

The electrophysiological effects of Dobutamine, a new beta adrenergic drug, were investigated using intracardiac electrograms and the extrastimulus method, in 19 patients with 1:1 AV conduction and in 10 other patients, five with second and five with third degree AV block. The electrophysiological effects were studied at three concentrations of the drug: 5, 10 and 15 micrograms/Kg/m'. Dobutamine induces: 1) an enhancement of SA node automaticity, showed by a decrease of the sinus cycle length (P less than 0.001 at the first concentration) and by a decrease in the corrected sinus node recovery time (P less than 0.001 at the second concentration); 2) a decrease in the effective atrial refractory period (P less than 0.001 at the first concentration); 3) an improvement of AV conduction, showed by a decrease in AH interval (P less than 0.001 at the first concentration) and by a shortening of functional and effective refractory periods (P less than 0.001 at the first concentration); 4) no change in the HV interval; 5) an improvement of conduction in patients with second degree AV block proximal to the His bundle; and 6) a minimal increase in the heart rate in patients with complete AV block distal to His bundle.

2:1 and phase 4 peri-infarction block.

A patient with acute inferior and anteroseptal myocardial infarction initially developed a 2 : 1 AV block with alternate conducted ventricular complexes showing aberrancy, and later Wenckebach-type, 2nd-degree AV block with aberrancy of the beats following a long diastolic pause. Intracavitary recording suggested that aberrancy was related to an intraventricular block. ECG and VCG recordings excluded the site of block as being in the main bundles or in the fascicles of the left bundle. The patient therefore showed evidence for a 2 : 1 and later a phase 4 peripheral block, defined also as a peri-infarction block because of the underlying etiology of the block. The block could be localized in the posterior wall of the right ventricle, by the marked rightward and posterior orientation of the middle and terminal electrical forces evident in the vectorcardiogram.

[External recording of His bundle electrical activity (author's transl)]. / Registrazione esterna dell'attività elettrica del fascio di His.

A noninvasive method to record His' potentials in man is described. In several patients who needed intracardiac recording, a bipolar lead was placed across the chest, directed as conveniently as possible for the recording of His bundle electrical activity. A signal filtered (70-300 Hz) and amplified (X 100.000), was processed by a multichannel analyzer for averaging. The temporal regime of the averager was determined by a trigger which established a fiducial point on the ECG. For this purpose a QRS detector fed to a normal peripheral bipolar lead was used. The temporal stability of the system was continually checked in order to reject the recordings over the limits of +/- 1 msec. The computer program was chosen in order to select a window (usually 200 msec) which occurred up to 150 msec prior and 50 msec after the trigger signal. The sampling rate was 5 KHz for 1024 samples and the sweep counts were fixed from 128 to 512. At the same time, the D1, D2 and D3 were recorded in the other three channels of the analyzer for a more accurate measurement of the HV interval. Then an example comparing the external and interval recording was presented. Finally several external recordings were measured and the exact reproducibility of the G wave was confirmed. In conclusion we can say that the G wave is significant and suggests the electrical activity of the bundle of His.

[Evolution of ventricular depolarization in the acute phase of inferior and posteroinferior myocardial infarction (author's transl)]. / Evoluzione della depolarizzazione ventricolare nella fase acuta dell'infarto inferiore e postero-inferiore

Twenty-five patients, hospitalized within 24 hours from the beginning of the precordiaglia due to acute diaphragmatic infarction, with or without a posterior extension, underwent the ECG and VCG recordings for the first consecutive twenty days and on the fortieth day, in order to study the development of ventricular depolarization. To diagnose an infarction of the diaphragmatic and posterior walls the usual ECG and VCG paramaters were used; the ECG was found to be less useful above all for the difficulty of measuring the variations, in the loss of the electrical forces. The electrodes were always placed in the same points suitably signed. Several evolutive modalities of the diaphragmatic infarction were observed; in 52% of the cases the loss of the inferior electrical forces reaches its maximum expression quickly, then it remains almost constant. In 12% of the cases the necrosis increases very clearly, tardily, between the ninth and fourteenth day. In 24% a precocious reduction of the electrical extension of the infarction on the eighth-twelfth day is observed. In 12% of the cases there are irregular oscillations during the whole acute phase. In all cases more or less stressed daily or cyclic oscillations were present. In nine cases an extension of the infarction to the posterior wall was evident; among these in five, two peaks are present; in two an initial increase, in the other two an initial decrease of the electrical extension of the necrosis; then, more or less stressed daily or cyclic oscillations. In another nine cases a single reading of the tracings do not let us diagnose a posterior extension; this is possible only through an "in series" reading. The clinical course and the humoral data do not give any contribution to the interpretation of the founded evolutive variabilities. The necrosis, therefore, must not be considered a zone of homogeneous and global stuffing, but composed of cellular groups in several and variable anatomo-metabolic situations conditioning the observed electrical instabilities.

Physiopathological and diagnostic hypotheses in peripheral block.

Delays and conduction blocks may occur in Purkinje fibers, junctions and muscular cells. Since such blocks may take place everywhere in the ventricles and not only in the free walls, we prefer to use the term peripheral instead of parietal block. The electrophysiologic problems connected with such blocks are discussed. The localization of the ventricle affected by the block is usually simple using VCG recording and is based on the orientation of terminal vectors. It is more difficult to recognize the ventricular walls affected by the block, the intraparietal localization and the source of the block: Purkinje fibers, junctions or muscular fibers. We maintain the concept that peripheral blocks alter not only the terminal phases of ventricular depolarization, but sometimes also the initial ones, in that the Purkinje-junction-muscular fibers system can be damaged in the septum with the major conduction pathways remaining intact. Several discrepancies found between the prescence of electric patterns of septal necrosis and autopsy data may be explained by peripheral blocks localized in the left septum.

Left bifascicular block with normally conducting middle fascicle.

A case of aortic insufficiency showing an ECG pattern of left ventricular hypertrophy and strain has been followed over time. One year after the initial observation, the ECG and VCG recordings showed the appearance of a left bifascicular block, due to involvement of the anterior and posterior fascicles, with normal septal activation. It is suggested that the normally functioning middle fascicle activates the inferior two-thirds of the septum. This hypothesis is discussed in light of recent experimental data.

[Idiopathic sick sinus syndrome with a-v and intraventricular conduction disturbances in a child. (first report in childhood) (author's transl)]. / "Sick sinus syndrome" idiopatica con turbe della conduzione A-V ed intraventricolare in un bambino. Primo rapporto in età pediatrica.

This report presents a ten-year old child suffering from sick sinus syndrome, in the "Bradycardia-tac hycardia-asystole" variant. A long observation and an ECG made when he was 7 have never shown a sinusal rhythm. An involvement of the A-V node is also present, made clear by a block of the second degree with not very high atrial rates and by prolonged refractory periods, as well as an involvement of the intraventricular conduction, made evident by an incomplete right bundle branch block and by a long refractory period of the anterior fascicle. The clinical, laboratory and hemodynamic data excluded either a congenital or an acquired cardiopathy. The ECGs of the patient's relatives excluded a familiar type of S.S.S. It is, therefore, an idiopathic S.S.S., which is very rare in children. The nosological set in the still vague field of the idiopathic degenerations of the conduction tissue is discussed.