Search PubMed⌕ Search

Biomedical subjects

P Colli Franzone

Publications and source records attributed to P Colli Franzone.

8 recordsLinked to original sources
PubMed2006

Effects of transmural electrical heterogeneities and electrotonic interactions on the dispersion of cardiac repolarization and action potential duration: A simulation study.

It has been shown in the literature that myocytes isolated from the ventricular walls at various intramural depths have different action potential durations (APDs). When these myocytes are embedded in the ventricular wall, their inhomogeneous properties affect the sequence of repolarization and the actual distribution of the APDs in the entire wall. In this article, we implement a mathematical model to simulate the combined effect of (a) the non-homogeneous intrinsic membrane properties (in particular the non-homogeneous APDs) and (b) the electrotonic currents that modulate the APDs when the myocytes are embedded in the ventricular myocardium. In particular, we study the effect of (a) and (b) on the excitation and repolarization sequences and on the distribution of APDs in the ventricles. We implement a Monodomain tissue representation that includes orthotropic anisotropy, transmural fiber rotation and homogeneous or heterogeneous transmural intrinsic membrane properties, modeled according to the phase I Luo-Rudy membrane ionic model. Three-dimensional simulations are performed in a cartesian slab with a parallel finite element solver employing structured isoparametric trilinear finite elements in space and a semi-implicit adaptive method in time. Simulations of excitation and repolarization sequences elicited by epicardial or endocardial pacing show that in a homogeneous slab the repolarization pathways approximately follow the activation sequence. Conversely, in the heterogeneous cases considered in this study, we observed two repolarization wavefronts that started from the epi and the endocardial faces respectively and collided in the thickness of the wall and in one case an additional repolarization wave starting from an intramural site. Introducing the heterogeneities along the transmural epi-endocardial direction affected both the repolarization sequence and the APD dispersion, but these effects were clearly discernible only in transmural planes. By contrast, in planes parallel to epi- and endocardium the APD distribution remained remarkably similar to that observed in the homogeneous model. Therefore, the patterns of the repolarization sequence and APD dispersion on the epicardial surface (or any other intramural surface parallel to it) do not reveal the uniform transmural heterogeneity.

Action Potentials↗
PubMed2005

Simulating patterns of excitation, repolarization and action potential duration with cardiac Bidomain and Monodomain models.

Parallel numerical simulations of excitation and recovery in three-dimensional myocardial domains are presented. The simulations are based on the anisotropic Bidomain and Monodomain models, including intramural fiber rotation and orthotropic or axisymmetric anisotropy of the intra- and extra-cellular conductivity tensors. The Bidomain model consist of a system of two reaction-diffusion equations, while the Monodomain model consists of one reaction-diffusion equation. Both models are coupled with the phase I Luo-Rudy membrane model describing the ionic currents. Simulations of excitation and repolarization sequences on myocardial slabs of different sizes show how the distribution of the action potential durations (APD) is influenced by both the anisotropic electrical conduction and the fiber rotation. This influence occurs in spite of the homogeneous intrinsic properties of the cell membrane. The APD dispersion patterns are closely correlated to the anisotropic curvature of the excitation wavefront.

Action Potentials↗
PubMed1998

Spread of excitation in 3-D models of the anisotropic cardiac tissue. III. Effects of ventricular geometry and fiber structure on the potential distribution.

In a previous paper we studied the spread of excitation in a simplified model of the left ventricle, affected by fiber structure and obliqueness, curvature of the wall and Purkinje network. In the present paper we investigate the extracellular potential distribution u in the same ventricular model. Given the transmembrane potential v, associated with the spreading excitation, the extracellular potential u is obtained as solution of a linear elliptic equation with the source term related to v. The potential distributions were computed for point stimulations at different intramural depths. The results of the simulations enabled us to identify a number of common features which appears in all the potential patterns irrespective of pacing site. In addition, by splitting the sources into an axial and conormal component, we were able to evaluate the contribution of the classical uniform dipole layer to the total potential field and the role of the superimposed axial component.

Anisotropy↗
PubMed1993

Potential distributions generated by point stimulation in a myocardial volume: simulation studies in a model of anisotropic ventricular muscle.

INTRODUCTION: We present simulations of extracellular potential patterns elicited by delivering ectopic stimuli to a parallelepipedal slab of ventricular tissue represented as an anisotropic bidomain incorporating epi-endocardial fiber rotation. METHODS AND RESULTS: Simulations were based on an eikonal model that determines wavefront shapes throughout the slab at every time instant during the depolarization phase, coupled with an approximate model of the action potential profile. The endocardial face of the slab was in contact with blood and the composite volume was surrounded by an insulating medium. The effect of a simplified Purkinje network was also studied. RESULTS: (1) For all pacing depths, except endocardial pacing, a central negative area and two potential maxima were observed at QRS onset in all intramural planes parallel to the epicardium. In all planes, the axis joining the two maxima was approximately aligned with the direction of fibers in the plane of pacing. Endocardial pacing generated a different pattern, but only when blood was present; (2) During later stages of excitation, outflowing currents (from the wavefront toward the resting tissue) were always emitted, at all intramural depths, only from those portions of the wavefront that spread along fibers. At any given instant, the position of the two potential maxima in a series of planes parallel to the epicardium and intersecting the wavefront rotated as a function of depth, following the rotating direction of intramural fibers. Purkinje involvement modified the above patterns. CONCLUSION: Epicardial and endocardial potential maps provided information on pacing site and depth and on subsequent intramural propagation by reflecting the clockwise or counter-clockwise rotation of the deep positivity. Results may be applicable to epicardial and endocardial potential maps recorded at surgery or from endocavitary probes.

Action Potentials↗
PubMed1990

Wavefront propagation in an activation model of the anisotropic cardiac tissue: asymptotic analysis and numerical simulations.

In this paper we present a macroscopic model of the excitation process in the myocardium. The composite and anisotropic structure of the cardiac tissue is represented by a bidomain, i.e. a set of two coupled anisotropic media. The model is characterized by a non linear system of two partial differential equations of parabolic and elliptic type. A singular perturbation analysis is carried out to investigate the cardiac potential field and the structure of the moving excitation wavefront. As a consequence the cardiac current sources are approximated by an oblique dipole layer structure and the motion of the wavefront is described by eikonal equations. Finally numerical simulations are carried out in order to analyze some complex phenomena related to the spreading of the wavefront, like the front-front or front-wall collision. The results yielded by the excitation model and the eikonal equations are compared.

Electrocardiography↗
PubMed1976

Numerical determination of intestinal membrane diffusing constants by a gradient method.

Optimisation problems arising in the identification of kinetic parameters of intestinal membranes are here considered. The dynamic behaviour of the membrane is described by means of a linear compartmental model. Using optimisation techniques of a gradient type, the intestinal kinetic parameters are identified, minimising a quadratic criterion between experimental data of D-histidine transport and model prediction. Numerical results are reported and their physiological implications discussed. The quantitative assessment of the asymmetry of diffusion constants with respect to diffusion direction seems to be an important result of this work.

Biological Transport↗
PubMedDate not supplied

Impact of the introduction of laparoscopic cholecystectomy on the population aged 70 and over.

BACKGROUND/AIMS: Laparoscopic cholecystectomy is reported to be better tolerated than open cholecystectomy by patients aged 70 and over. We evaluate its impact on patients aged 70 and over, from one single center. METHODOLOGY: We review 427 cholecystectomies performed in one single centre, from November 1992 through November 1999. We consider 23 patients, 70 years old or older at the time of surgery. The following objective parameters were considered and compared with the younger population: length of stay in the hospital; mean preoperative stay; mean postoperative stay; incidence of risk factors; postoperative complications. A questionnaire was also mailed to all individual 427 patients. RESULTS: Length of stay in the hospital declined in both population, during the time interval considered. The incidence of risk factors, both major and minor, increases consistently with age from less than 1% below the age of 30 to about 62% in the eighth decade and over. Major postoperative complications were 4.34% in patients > or = 70 vs. 2.8% in patients < 70 years of age. Mortality was nil in both groups. Ninety percent reported complete disappearance of preoperative symptoms. CONCLUSIONS: Laparoscopic cholecystectomy in geriatric patients is safe and risks are reasonably low. Selection of patients must be done on strict indications.

Aged↗