Biomedical subjects

J L Chassé

Publications and source records attributed to J L Chassé.

7 recordsLinked to original sources

PubMed2002

Host patch selection induced by parasitism: basic reproduction ratio r(0) and optimal virulence.

The effects of parasites on the behavior of their hosts are well documented. For example, parasites may affect the habitat selection of the host individual. We used variables aggregation methods to investigate the way in which parasites affect the spatial pattern of susceptible hosts. We developed a simple epidemiological model, taking into account both the reproduction processes of hosts (density-dependent birth and death) and infection, considered separately on two different patches, and the migration of susceptible hosts between these two patches. We used the complete model of three equations to generate an aggregated model describing the dynamics of the combined susceptible and infected host populations. We obtained the basic reproduction ratio (R(0)) from the aggregated model, and then studied the effect of the migratory behavior of susceptible hosts on the ability of the parasite to invade the system. We also used the basic reproduction ratio to investigate the evolution of parasite virulence in relation to the migration decisions of susceptible hosts. We found that host investment in avoidance of the infected patch leads to an increase in optimal virulence if host investment is costly.

Animals↗

PubMed1999

Behavioral choices based on patch selection: a model using aggregation methods.

The aim of this work is to study the influence of patch selection on the dynamics of a system describing the interactions between two populations, generically called 'population N' and 'population P'. Our model may be applied to prey-predator systems as well as to certain host-parasite or parasitoid systems. A situation in which population P affects the spatial distribution of population N is considered. We deal with a heterogeneous environment composed of two spatial patches: population P lives only in patch 1, while individuals belonging to population N migrate between patch 1 and patch 2, which may be a refuge. Therefore they are divided into two patch sub-populations and can migrate according to different migration laws. We make the assumption that the patch change is fast, whereas the growth and interaction processes are slower. We take advantage of the two time scales to perform aggregation methods in order to obtain a global model describing the time evolution of the total populations, at a slow time scale. At first, a migration law which is independent on population P density is considered. In this case the global model is equivalent to the local one, and under certain conditions, population P always gets extinct. Then, the same model, but in which individuals belonging to population N leave patch 1 proportionally to population P density, is studied. This particular behavioral choice leads to a dynamically richer global system, which favors stability and population coexistence. Finally, we study a third example corresponding to the addition of an aggregative behavior of population N on patch 1. This leads to a more complicated situation in which, according to initial conditions, the global system is described by two different aggregated models. Under certain conditions on parameters a stable limit cycle occurs, leading to periodic variations of the total population densities, as well as of the local densities on the spatial patches.

Animals↗

PubMed1999

Role of the dispersion of refractoriness on cardiac reentries.

We used computer simulation to study the possible role of the dispersion of cellular coupling, refractoriness or both, in the mechanisms underlying cardiac arrhythmias. Local ischemia was first assumed to induce cell to cell dispersion of the coupling resistance (case 1), refractory period (case 2), or both (case 3). Our numerical experiments based on the van Capelle and Durrer model showed that vortices could not be induced. On the other hand, with cellular properties dispersed in a patchy way within the ischemic zone, a single activation wave could give rise to abnormal activities. This demonstrates the stability of the wave front under small inhomogeneities. Probabilities of reentry, estimated for the three cases cited above showed that a severe alteration of the coupling resistance may be an important factor in the genesis of reentry. Moreover, use of isochronal maps revealed that vortices were both stable and sustained with an alteration of the coupling alone or along with a reduction of the action potential duration. Conversely, simulations with reduction of the refractoriness alone, inducing only transient patterns, could exhibit functionally determined reentries.

Arrhythmias, Cardiac↗

PubMed1999

Incidence of dispersion of refractoriness and cellular coupling resistance on cardiac reentries and ventricular fibrillation.

We used computer simulations to study the possible role of the dispersion of cellular coupling, refractoriness or both, in the mechanisms underlying cardiac arrhythmias. Local ischemia was first assumed to induce cell to cell dispersion of the coupling resistance (Case 1), refractory period (Case 2), or both of them (Case 3). Our numerical experiments based on the van Capelle and Durrer model showed that vortices could not be induced by cell to cell variations. With cellular properties dispersed in a patchy way within the ischemic zone, a single activation wave could give rise to abnormal activities. This demonstrates the stability of the wave front under small inhomogeneities. Probabilities of reentry, estimated for the three cases cited above showed that a severe alteration of the coupling resistance may be an important factor in the genesis of reentry. Moreover, use of isochronal maps revealed that vortices were both stable and sustained with an alteration of the coupling alone or combined with a reduction of the action potential duration. Conversely, simulations with reduction of the refractoriness alone, inducing only transient patterns, could exhibit functionally determined reentries.

Cell Communication↗

PubMed1996

Modeling of cardiac electrophysiological mechanisms: from action potential genesis to its propagation in myocardium.

The aim of the present paper is to describe the different attempts at modeling cardiac electrophysiological mechanisms, mainly at the membrane and cellular level, from action potential genesis to its propagation in myocardium. The Hodgkin and Huxley model describing the nervous action potential's theoretical reconstruction is first recalled, for it represents the basic model for a large part of cardiac action potential models. These models (Beeler and Reuter, Van Capelle and Durrer, Luo and Rudy) are then successively studied as their main applications by diverse authors. Varied approaches, like the Fitzhugh-Nagumo model (derived from the Bonhoeffer-Van der Pol model of oscillatory systems) or cellular automata models applied to the study of ventricular activation wave propagation and diseases associated with its perturbation, are then presented and discussed. Other, different approaches, such as general studies of excitable media, are evoked. This paper concludes with a critical evaluation of these different methods of electrophysiological cardiac modeling and of the main domains in which they led to significant results and in which they appear able to generate future perspectives.

Action Potentials↗

PubMed1988

An example of circular statistics in chronobiological studies: analysis of polymorphism in the emergence rhythms of Schistosoma mansoni cercariae.

Chronobiological data concerning the emergence rhythms of Schistosoma mansoni cercariae were transformed into circular variables and analysed using circular statistics. The method proposed allowed three chronobiological patterns to be distinguished for the parasite populations studied, and statistical tests for the homogeneity of samples in each group and the significant differences between groups were also carried out.

Accidents, Traffic↗

PubMed1987

[Comparative analysis of the rhythm of cercariae emergence in three strains of Schistosoma bovis (trematoda: Schistosomatidae)].

A comparative experimental study of the rhythmic shedding of three geographic strains of Schistosoma bovis cercariae (Sardinian, Sudanese and Spanish) by Bulinus truncatus showed a significant difference in the emergence patterns. The results support the existence of a genetic variability of the emergence rhythms. The origin of the variability is discussed and could be found in the pastoral practice and the ecological characteristics of the different transmission foci.

Animals↗