Biomedical subjects

V Barbaro

Publications and source records attributed to V Barbaro.

At least 37 records · Page 2Linked to original sources

PubMed2001

Pulsatile flow and atherogenesis: results from in vivo studies.

Compliance mismatch between prosthetic vascular replacement (possibly stented) and native artery is considered to be an important factor in implant failure due, e.g., to vascular remodeling, tissutal growth or intimal hyperplasia (IH). From an in vivo study involving altered vascular mechanics (and, consequently, compliance mismatch), carried out using the Moncada model of atherosclerosis development and smooth muscle cell (SMC) proliferation, the hemodynamic assessment was followed by means of real-time multigated ultrasound profilometry, of collared carotid artery using two different models: non-constrictive and constrictive plastic collars, wrapped around the vessel. The experiments provided the real-time measurement of velocity profiles in vivo and the subsequent estimation of wall shear stresses, locally responsible for the altered hemodynamics. Endothelium modifications were correlated with local hemodynamic alterations by using statistical regression analysis of the development of intimal hyperplasia and the mechanical stimulus applied to the endothelium by means of the two different manipulation models. Different correlations were found between wall shear rate and IH in the two models, showing the importance of the vascular pulsatility in determining SMC proliferation. This result could be useful in minimizing the negative consequences of clinical interventions such as graft and/or stent implantation.

Animals↗

PubMed2001

Extraction of physiological and clinical information from intra-atrial electrograms during atrial fibrillation: review of methods.

This paper presents a review of the evolution of methods and algorithms for the analysis of intra-atrial recordings, with special emphasis to the extraction of physiological and clinical information during atrial fibrillation. The principal time-domain and frequency-domain methods of electrogram analyses are described, and their physiological interpretation and clinical applications are discussed. In addition, the recent findings from complex system theory and chaos theory approaches are highlighted.

Arteries↗

PubMed2001

Deterministic patterns and coupling of bipolar recordings from the right atrium.

The presence of organization of atrial activation processes during atrial fibrillation has been investigated to assess whether the activation sequences are wholly random or are governed by deterministic mechanisms. We performed a linear analysis based on the cross correlation function and a non linear analysis based on two algorithms. The first one detects and qualifies recurrent patterns of the coupling between atrial period time series by means of the recurrence plot quantification approach; the second one estimates the non linear coupling between activation sequences in two sites following a multivariate embedding approach. The detection of spatio-temporal recurrent patterns and of non linear coupling together with the surrogate data results indicate that during atrial fibrillation a certain degree of local organization exists, likely caused by deterministic mechanisms of activation.

Adult↗

PubMed2001

Effect of atrial fibrillation organization on internal defibrillation threshold.

Aim of the present study is to assess the effect of the organization of atrial fibrillation in the right atrium on the minimum effective cardioversion energy. Thirteen patients were studied, selected a priori for low-energy internal cardioversion (LEIC). LEIC was carried out at increasing energy levels. All patients were monitored by a multipolar basket catheter in basal condition and during cardioversion. Our results showed that the mean organization correlates with the energy of successful cardioversion, and that after each shock no significant differences (Kruskal-Wallis test) were observed in the level of organization. Similar results have been obtained for the differences of organization values, immediately before and after each shock. These results prompt for further studies aimed at measuring electrophysiological properties to predict energy thresholds.

Atrial Fibrillation↗

PubMed2001

Clinical evaluation of disorganization during atrial fibrillation as a guide to radiofrequency ablation.

Aim of this study was to investigate the spatial patterns of organization of fibrillation in the right atrium using bipolar recordings from a basket catheter. Study population consists of 17 patients with persistent atrial fibrillation (AF), selected a priori for low energy internal cardioversion. Organization was measured by the number of occurrences--i.e. the percentage number of points laying on the baseline--which has been demonstrated to match Wells' criteria for the classification of AF. Well-defined and stable patterns of organization characterize the electrical activity of the right atrium in these patients. The organization in the entire right atrium showed an individual rather than common distribution. This may have implications in the choice of regions candidate for ablation.

Aged↗

PubMed2001

Different atrial regional patterns of activation during atrial fibrillation: is there any relationship with the anatomy?

Right atrial (RA) mapping has been recently more carefully examined in patients with idiopathic atrial fibrillation (AF) in order to improve radiofrequency (RF) catheter-mediated ablation lines to control recurrences. The aim of this study was to map right atrial activation during AF to analyze relationship between anatomy and atrial activation for specific sites. Twenty-four patients with recurrent, drug-refractory, paroxysmal AF underwent an extensive mapping of the RA before attempting RF linear lesion catheter ablation. A typical pattern of atrial activation was recorded in all patients which was consistent with a more regular activity on the trabeculated right atrium (type I AF) and a more fragmented and complex activation on the posterior and the anterior septum (type II and III AF). This paper helps to understand the influence of the anatomic barriers to atrial activation during atrial fibrillation.

Atrial Fibrillation↗

PubMed2001

Management of patients with atrial fibrillation: different therapeutic options and role of electrophysiology-guided approaches.

At present the approach to atrial fibrillation treatment is based on the electrophysiological patterns of atrial fibrillation (on the basis of multiple intra-atrial recordings or sophisticated new mapping techniques) only in a restricted minority of patients, those who are candidate to ablation of the substrate and/or of the triggers. Atrial fibrillation has a broad spectrum of clinical presentations and a heterogeneous electrophysiological pattern. The treatment of this arrhythmia, both with drugs and non pharmacological treatments, has been based, classically, on empirical basis and on a clinically-guided staged-approach. The limitations of pharmacological treatment led in recent years to the development of a wide spectrum of non pharmacological treatments. This implies a change in the approach to atrial fibrillation and the need to identify potentially ideal candidates to complex and expensive treatments. In this view it is currently under investigation the possibility to identify potential responders to a definitive treatment or a combination of treatments (both pharmacological and non-pharmacological) on the basis of the electrophysiological pattern.

Anti-Arrhythmia Agents↗

PubMed2000

On the monodimensional approach to the estimation of the highest reynolds shear stress in a turbulent flow.

The measurement of the Reynolds stress tensor, or at least of some of its components, is a necessary step to assess if the turbulence associated with the flow near prosthetic devices can damage blood constituents. Because of the intrinsic three dimensionality of turbulence, in general, a three-component anemometer should be used to measure directly the components of the Reynolds stress tensor. However, this can be practically unfeasible, especially in vivo; therefore, it is interesting to investigate the possibility of characterizing the turbulent flows that may occur in the circulatory system with the monodimensional data that a less complete equipment (e.g., a pulsed ultrasound Doppler) can yield. From the general expression of the Reynolds stress tensor, the highest shear stress can be deduced, as well as the Reynolds normal stress in the main flow direction. The relation between these two quantities, which is an issue already addressed in previous works, can thus be rigorously formulated in terms of some characteristic parameters of the Reynolds stress tensor, the principal normal stresses and the angles that the directions that define them form with the main flow direction. An experimental verification of the ratio of the two above-mentioned quantitites for the flow across bileaflet valves, investigated by means of two-dimensional laser Doppler anemometry, will illustrate the limitations of the monodimensional approach estimating the maximum load on blood constituents.

Algorithms↗

PubMed2000

Hemodynamic performance of small-size bileaflet valves: pressure drop and laser Doppler anemometry study comparison of three prostheses.

Laser Doppler anemometry (LDA) is a single-point technique which is unparalleled to detect accurately the local properties of the velocity field in a turbulent flow, such as that generated by a prosthetic heart valve (PHV). We propose a correlation between the structure of the flow field in three 19 mm bileaflet PHVs (Sorin Bicarbon, St. Jude Standard, St. Jude HP), investigated at peak systole (6 L/min cardiac output [CO]) with LDA, in kinematic and geometric similarity, and the global parameter of transvalvular pressure drop measured in both steady and pulsatile conditions. The pressure transducers of the same apparatus were used to characterize pressure drops at different flow rates whereas the steady-flow case was studied with a highly accurate tester built in our laboratory. The 2 St. Jude models rank according to their internal orifice diameter (ID) with the standard model (with a smaller ID) providing higher pressure drops for each flow rate. Sorin Bicarbon, due to its leaflet geometry, generates a more complex flow field with respect to the 2 St. Jude flat-leaflet models and shows improved hemodynamical behavior in pulsatile conditions with respect to the stationary case due to differences in pressure recovery. This study can provide insights into a PHV's local flow structure and global hemodynamical parameters.

Blood Flow Velocity↗

PubMed2000

Automated classification of human atrial fibrillation from intraatrial electrograms.

The assessment of the degree of organization and the classification of atrial fibrillation (AF) according to the types defined by Wells usually resorts to the visual inspection of bipolar intraatrial electrograms. The focus of this study was to test seven parameters aimed to quantify the degree of organization of the electrograms, and then to design a final classification scheme based on a multidimensional, minimum-distance analysis. The following parameters were tested: mean atrial period (AP) and its coefficient of variation (CV); number of points lying at the baseline (NO) and the Shannon entropy (EN) of the amplitude probability density function (APDF); depolarization width (F-WIDTH); and correlation waveform analysis (CWA) and electrogram bandwidth (BW). The signal database consisted in a set of 160 AF strips of Type I, II, and III AF, scored by an expert cardiologist (60 Type I, 40 Type II, 60 Type III) and further divided in a training set (60) and a test set (100). Strips were 6 seconds long and were recorded with 5-mm interspace bipolar catheters from electrically induced (n = 13) and chronic (n = 10) patients. A classification algorithm based on a minimum-distance (Mahalanobis distance) discriminant analysis was tested. Using a single parameter, the best discriminations were provided by NO, F-WIDTH, and CV. F-WIDTH was found strongly inversely correlated to NO (r = -0.90). Of all the two-parameter combinations, CV-NO provided the best classification: 92 of 100 segments were correctly classified with sensitivity > 90% and specificity > 92%. A further improvement was obtained by including BW as a third parameter (93/100 correctly classified). The use of more than three parameters not only failed to improve, but even degraded the classification.

Algorithms↗

PubMed2000

Laser Doppler anemometry study of bidimensional flows downstream of three 19 mm bileaflet valves in the mitral position, under kinematic similarity.

Three small-size (nominal size: 19 mm) bileaflet valves, CarboMedics R (CM), St Jude Standard (SJ) and Sorin Bicarbon (SB), have been tested by means of a two-component laser Doppler anemometry (LDA) system, in the mitral position, in order to assess the potential damage to blood elements entailed by the turbulent flow through them. A high regime (6 l/min cardiac output) was chosen to perform measurements for the worst case in generated turbulence. Two half-diameter profiles, at 13 and 26 mm downstream of the valve plane, have been investigated for each model. Besides velocity profiles, turbulence shear stresses (TSS) are reported, after the application of the stress analysis technique, in order to assess the maximum values of TSS (TSSmax) exerted on blood particles. Results show the typical bileaflet-type velocity profile for SB and SJ, with three jets exiting the valve, whereas CM lacks the central jet, due to instabilities of its flow field. As for TSSmax, CM reaches the highest values, presumably due to leaflets fluttering. SJ's TSSmax profiles maintain similar shapes at the two downstream locations, whereas SB presents an unexpected increase in the peak value of TSSmax, from 13 to 26 mm downstream of the valve plane, probably due to the curved leaflet design. The three prosthetic heart valves (PHVs) tested show many differences as for their turbulence properties, although they are similarly constructed.

Biomechanical Phenomena↗

PubMed2000

Recurrent patterns of atrial depolarization during atrial fibrillation assessed by recurrence plot quantification.

The aim of this study was to determine the presence of organization of atrial activation processes during atrial fibrillation (AF) by assessing whether the activation sequences are wholly random or are governed by deterministic mechanisms. We performed both linear and nonlinear analyses based on the cross correlation function (CCF) and recurrence plot quantification (RPQ), respectively. Recurrence plots were quantified by three variables: percent recurrence (PR), percent determinism (PD), and entropy of recurrences (ER). We recorded bipolar intra-atrial electrograms in two atrial sites during chronic AF in 19 informed subjects, following two protocols. In one, both recording sites were in the right atrium; in the other protocol, one site was in the right atrium, the other one in the left atrium. We extracted 19 episodes of type I AF (Wells' classification). RPQ detected transient recurrent patterns in all the episodes, while CCF was significant only in ten episodes. Surrogate data analysis, based on a cross-phase randomization procedure, decreased PR, PD, and ER values. The detection of spatiotemporal recurrent patterns together with the surrogate data results indicate that during AF a certain degree of local organization exists, likely caused by deterministic mechanisms of activation.

Adult↗

PubMed1999

A discussion on the threshold limit for hemolysis related to Reynolds shear stress.

Turbulence-related damage to blood is a major problem with the use of prosthetic devices, such as mechanical heart valves. An often-cited paper by Sallam and Hwang (1984). Biorheology 21, 783-797) quantified the threshold for hemolysis to be about 400 N m(-2), a value that has hitherto contributed to the evaluation of the potential dangerousness of a medical implantable device. We propose a discussion of the mentioned experiment, based on the application of stress analysis concepts to the original measurements: this is necessary to assess the peak turbulence shear stress value that could have been found in Sallam and Hwangs experiment, with a suitable orientation of the measurement axes. The result of our theoretical discussion is that the threshold value of 400 N m(-2) could probably be considerably underestimated: following this point of view, a 3-D stress analysis shows that the peak turbulence shear stress at the inception of hemolysis should be at least 600 N m(-2). This result, obtained on the basis of the study of RBCs' response to a turbulent environment, indicates that blood particles are probably more resistant to short-time shear stresses than it was thought.

Blood Physiological Phenomena↗

PubMed1999

Electromagnetic interference of digital and analog cellular telephones with implantable cardioverter defibrillators: in vitro and in vivo studies.

The present study examines the potential electromagnetic interference effects induced by cellular telephones on ICDs. We developed ad hoc protocols to conduct both in vitro and in vivo trials on most of the implantable cardioverter defibrillators available on the international market. Trials were conducted with three cellular telephones: two GSM (Global System for Mobile Communication) and one TACS (Total Access Communication System). A human trunk simulator was used to carry out in vitro observations on six ICDs from five manufacturers. In vivo tests were conducted on 13 informed patients with eight different ICD models. During the trials in air, GSM telephones induced interference effects on 4 out of the 6 cardioverter defibrillators tested. Specifically, pulse inhibition, reprogramming, false ventricular fibrillation, and ventricular tachycardia detections occurred, which would have entailed inappropriate therapy delivery had this been activated. Effects were circumscribed to the area closely surrounding the connectors. When the ICD was immersed in saline solution, no effects were observed. Three cases of just ventricular triggering with the interfering signal were observed in vivo.

Aged↗

PubMed1999

The role of usable length in the compliance measurement of vascular prostheses.

In this study we investigated the dependence of the mechanical properties and in particular of the radial compliance of a vascular prosthesis as a function of its usable length. Radial compliance was measured at 60 bpm and in the pressure range 80-120 mmHg. Starting from compliance measurements a simple model was used to calculate the pulse wave velocity and the reflection coefficients between 6 mm and 8 mm grafts (knitted and woven) with iliac and subclavean artery of similar diameter. The results provide an indication of the influence of usable length on the compliance and diameter mismatch at the anasthomosis between graft and host artery.

Blood Vessel Prosthesis↗

PubMed1998

Principal stress analysis in LDA measurement of the flow field downstream of 19-mm Sorin Bicarbon heart valve.

Heart valve replacement has become, since many years, a common surgical practice. Along with the improvement that the patients' health has derived from it, however, a certain amount of risk could not be avoided, bound to the inevitable hemodynamic disturbances that an artificial device generates. A major shortcoming, often reported, is the formation of thrombus on the edge of the prosthetic valve, with a possible obstruction of the orifices through which blood should normally flow undisturbed. Hemolysis is another possible consequence of the implantation of a mechanical heart valve, generally correlated to turbulence downstream of prosthetic heart valves (PHV). As it is agreed upon by many researchers, the risk of thrombogenicity or hemolysis is higher in those valves that are more subject to promote turbulence and flow separation in the flow through them. In the following paper, we present a study of the turbulence-related shear stress downstream of a bileaflet valve of minimum size (19 mm external diameter) Sorin Bicarbon. This size was chosen, accordingly to the Food & Drug Administration (FDA) draft guidance suggestion to investigate the worst case in turbulence promoted by PHVs, in order to have the highest velocity gradients and shear stresses for the FDA-stated cardiac output (6 1/min), related to maximum Reynolds number conditions. Velocity data were collected with the two-dimensional laser Doppler anemometry (LDA) technique; whereas this approach does not investigate directly all three components of the flow field, in the present case (bileaflet valves) it is not a limitation to the assessment of the maximum turbulence shear stress (TSS), thanks to the two-dimensional flow nature downstream of bileaflet models. Data taken in coincident mode were elaborated in order to determine the maximum shear stress in the measured points in the flow field, using the 2D Principal Stress Analysis (PSA). The consequences of a variable principal normal stress direction all along the measured profile will be illustrated in terms of differences between measured and maximum shear stresses. Results show the need to estimate the maximum values for the TSS and the direction along which it is obtained to correctly define the turbulent flow field downstream of PHVs.

Blood Flow Velocity↗

PubMed1997

A portable unit for remote monitoring of pacemaker patients.

The number of people with pacemakers has been steadily increasing over the past 20 years. At present there are about 2,500,000 in the world. All these patients must have a checkup twice a year in hospital, which involves the allocation of significant resources by the national health systems, not to speak of the inconvenience it entails for elderly subjects. Telemedicine can provide a partial solution to these problems. The present work describes a prototype system that transmits the patient's electrocardiograms and the main characteristics of the pacemaker to a monitoring centre. This remote monitoring system will be beneficial to patients and health-care organizations in terms of quality of life for the former, and costs and efficiency for the latter.

Electrocardiography, Ambulatory↗

PubMed1997

A statistical approach to the quantitative comparison of pulsatile flow in vitro data of prosthetic heart valve testing.

BACKGROUND AND AIMS OF THE STUDY: In vitro evaluation and animal testing are fundamental steps in the assessment of prosthetic heart valves before their use in clinical practice. Valve testing under pulsatile conditions is the best in vitro simulation of cardiac valve function, and the ensuing results should support the surgeon's decision concerning the time of valve replacement. However, limits in hydraulic reproduction of cardiac function and differences in protocol implementation of in vitro testing lead to difficulties in obtaining reliable and comparable results. Debate among researchers and standardizing bodies about discrepancies in results becomes critical in light of the European CE certification of implantable medical devices. An interlaboratory environment has been created at the Biomedical Engineering unit of the Istituto Superiore di Sanita in Rome, which uses differing test apparatus to evaluate prosthetic heart valves in vitro, in order to define significant measurement parameters and procedures that produce comparative data. METHODS: Two prosthetic valves-a tilting disc and a bileaflet valve-each sized 29 mm, were tested in the aortic position on two different pulse duplicators (PDs), namely the Dynatek MP1 and a system developed at the University of Sheffield. The common protocol adopted was the FDA Interlaboratory Comparison Testing Protocol. Original software was used to manage all test phases, thus minimizing operator-dependent variability in both systems and imposing strict control of experimental conditions. Statistical analysis performed on the data followed two approaches: (i) separate fitting of the two regression equations of pressure drop-flow rate relationship obtained for each valve on both PDs, and (ii) application of a multiple regression model, to fit a single regression equation of pressure drop-flow rate relationship, using data obtained from both PDs for each valve. In addition, an additional independent (dummy) variable was introduced. RESULTS AND CONCLUSIONS: Using this approach, the valve parameter range was obtained and, by imposing strict control of the experimental set-up, the coincidence of the two valve power laws, estimated by each of the two PDs, was studied.

Heart Valve Prosthesis↗