PubMed Health⌕ Search

Biomedical subjects

A Vinet

Publications and source records attributed to A Vinet.

54 records · Page 3Linked to original sources
PubMed1989

Model study of the spread of electrotonic potential in cardiac tissue.

This model study describes the electrotonic response of a cable model of cardiac tissue stimulated at one point. The stimulus is applied intracellularly in the form of a 2 ms pulse of current of near threshold amplitude. The attenuation of the electrotonic potential with distance and its mode of propagation along the cable are compared for equivalent passive, continuous and discontinuous cables. The three structures have the same basic physical and electrical characteristic and they differ either with respect to being active or passive or to the presence or absence of intercellular gap junctions. In the continuous cable a just subthreshold stimulus produces a local active response which propagates more slowly and is attenuated less rapidly with distance than in a passive cable. The spatial decrement of the local response in a discontinuous cable is faster than in a continuous cable of equal average resistivity. It is suggested that the larger time constant of the foot of the action potential observed in the longitudinal direction in cardiac muscle could be due in part to the electrotonic spread of the local response from the site of stimulation.

Action Potentials↗
PubMed1989

Piecework, repetitive work and medicine use in the clothing industry.

This study was designed to examine the potential effects of severe time constraints on workers' health. Medicine use is considered to be an indicator of non-specific morbidity that is worthy of interest in industrial health research when it is possible to compare workers who share the same culture and socio-economic characteristics, but are submitted to different work conditions. In the clothing industry, our hypotheses were that (1) piecework paid operators would have a higher percentage of medicine users than the hourly paid and (2) operators who did repetitive work would have a higher percentage of medicine users than those who did non-repetitive work. Women selected into the study were between the ages of 45 and 70, natives of Canada, spoke French and lived in the metropolitan region of Montreal. The occupational data came from the files of The Ladies' Clothing Joint Commission. They encompass the 30-year period 1956-85. Data on socio-economic characteristics, smoking status and medicine use of the 800 respondents were obtained by questionnaires administered by specially trained nurses. Among currently employed women, the probability of using stomach medication was higher for pieceworkers than among women who received an hourly wage: OR = 2.57 (1.19-3.96). The probability was also higher for women who did repetitive work than for women who did non-repetitive work: OR = 2.43 (1.26-3.60).

Aged↗
PubMed1989

Effect of duration of employment in piecework on severe disability among female garment workers.

This study measured the association between duration of employment in piecework and the prevalence of severe disability among 533 Quebec female garment workers who left employment between 1976 and 1985. Yearly information regarding occupational characteristics was available from a public agency for the 30-year period 1956-1985. Information on disability status was collected in a personal interview. Duration of employment in piecework was associated with the prevalence of severe disability. A multivariate analysis found that the association was independent of age, smoking habits, education, type of task and total length of employment. Workers who spent 5-9, 10-14, 15-19, and greater than or equal to 20 years in piecework had an increased prevalence of severe disability in comparison with the base-line category of 0-4 years. The adjusted risk ratios were 2.2 [95% confidence interval (95% CI) 1.0-4.6], 3.3 (95% CI 1.5-6.9), 3.6 (95% CI 1.5-8.4), and 2.3 (95% CI 0.8-6.6), respectively. The association was particularly strong for disability due to musculoskeletal problems and disability due to cardiovascular disorders although small numbers were involved.

Adult↗
PubMed1989

Disability among female garment workers. A comparison with a national sample.

An indicator of permanent disability was used to measure the chronic health problems associated with garment work. The study population comprised 800 female sewing-machine operators employed in the Quebec garment industry between 1976 and 1985. The workers were identified from public agency records. Their disability status was obtained in a personal interview. The disability prevalence of these workers was compared to national disability data of women employed in clerical work, services, and manufacturing industries. The garment workers who had left employment had an increased prevalence of severe disability (in comparison with that of workers who had left other types of employment) and an increased prevalence of moderate and slight disability. Currently employed garment workers had an increased prevalence of moderate and slight disability when compared with workers currently employed in other occupations. The risk ratios remained similarly elevated when the data were adjusted for age and smoking status.

Adult↗
PubMed1989

[Absence from work as an indicator of health: significance, measures and conditions for use].

This paper discusses the use of absence from work for health reasons and particularly absence of long duration as a non specific morbidity indicator in studies of occupational health. Until now, absence has been neglected by occupational health researchers because of methodological problems. The aim of this paper is to show when and how this indicator may be appropriately used. First, absence is discussed in the context of non specific morbidity. Secondly, different conceptions of and approaches to absence are reviewed with a special accent on absence for health reasons. Finally, methodological precautions for the use of the indicator in epidemiological studies are emphasized.

Absenteeism↗
PubMed1986

Reconstruction of propagated electrical activity with a two-dimensional model of anisotropic heart muscle.

The propagated electrical activity in normal anisotropic cardiac muscle is characterized by directionally dependent variations in the rising phase of the action potential. An important question concerns the relation between such variations and the propagation velocity and extracellular potentials. This problem was studied here in a sheet of cells, under conditions of uniform intracellular anisotropic resistivity and constant electrical membrane properties, through a numerical solution of the two-dimensional propagation equation. The numerical solution implies a lumping of the cytoplasmic and intercellular resistances into an equivalent junctional resistance to form a distributed resistive network representing the intracellular domain. The interstitial space is assumed isotropic and unbounded, with a resistivity of 100 omega X cm. The electrical properties of the cell membrane are represented by a Beeler-Reuter model. The stimulus current is applied to a small area of the sheet, and attention is focussed on the stable propagated events occurring some 5 or 6 length constants away from the stimulation site. The numerical solution is a good approximation of a continuous uniform structure when the cell size is less than 10% of the length constant along both major axes. Conditions of non-uniform propagation, with directionally dependent variations in the maximum rate of rise and time constant of the foot of the action potential were simulated by increasing the cell size to 30% of the length constant in the transverse direction of the sheet. Our results indicate that the directional changes in the maximum rate of rise correspond to small modifications of the extracellular potentials, while the directional changes in time constant of the foot are associated with the propagation velocity. The maximum effects are observed along the transverse direction as follows: a 19% increase in maximum rate of rise corresponds to a decrease of about 6% in the peak-to-peak amplitude of the extracellular potential, and a 24% increase in time constant of the foot is associated with a decrease of about 7% in the propagation velocity. Under the conditions of the present study, however, the simulated directional changes in maximum rate of rise are smaller than those experimentally observed so the corresponding changes in the extracellular potentials are probably underestimated.

Action Potentials↗
PubMed1985

Numerical integration in the reconstruction of cardiac action potentials using Hodgkin-Huxley-type models.

A comparison between traditional numerical integration methods and a new hybrid integration method for the reconstruction of action potential activity is presented, using a mathematical model of the cardiac Purkinje fiber (MNT model). It is shown that the hybrid integration method reduces importantly the overall computation time required for solving the Hodgkin-Huxley differential equations describing membrane electrical events. To accomplish this, the particular form of the gating variable equations is exploited to reformulate the step-by-step computation. In this way, the time increment can be made much larger compared with traditional methods when the membrane potential changes slowly. A mathematical analysis of the hybrid integration method is presented also, together with a numerical verification of its performance both for the propagated and nonpropagated membrane action potential. It is shown that the local error, that is the error arising at each integration step, and the cumulative integration error are strictly controlled by the membrane potential offset. Using the MNT model, the nonpropagated cardiac Purkinje action potential can be reconstructed in real time with an accuracy of 1% for the potential and 5% for the time of occurrence of its main features. In reconstructing propagated events, the hybrid integration method allows computation time savings by a factor of 10 or more compared to accurate Runge-Kutta schemes.

Action Potentials↗
PubMed1985

[Organization of work and mental health : repetitive work under time constraint ps.].

This present article first of all examines a general model of research concerned with the relationship between characteristics of a work organization and breaches in the workers' health and their mental and physical welfare. Thereafter this model is used in areas of mental health to study the consequences of a work organization where repetitive tasks are achieved under time restriction. The question is drawn out, followed by the results and methodological limitations of the researches done in this area. Then, the author describes a frame of analysis which integrates the acquired knowledge and the areas of research to be developed.

English Abstract↗
PubMed1984

Mastication after surgical reconstruction of the mandibular residual ridge.

A group of thirty-one female denture patients who underwent surgical reconstruction of their deficient residual ridges with ridge extension and skin graft or ridge augmentation with bone graft were evaluated with regard to their masticatory function before surgery, then at 8 months and 12 months post-operative with their new dentures. Two objectives tests of masticatory efficiency were used. The masticatory efficiency index (MEI), based on the size of chewed almond particles, determined the potential capacity of patients to masticate while the masticatory performance (MP) based on the time required to masticate food before swallowing assessed the individual ability of each patient to chew food. A subjective index of difficulty (SD) provided information on the patient's own assessment of chewing difficulty of certain foods selected for their hard texture. The evolution of each index and their interrelationship were statistically evaluated. It was shown that the masticatory performance (MP) and the subjective index of difficulty (SD) both improved significantly during the rehabilitation period and even more rapidly than the masticatory efficiency index (MEI). The discrepancy between the objective and the subjective tests and the overestimation from the patients indicate that the real benefit of the rehabilitation is not limited to improved chewing, but also to an acquired self-confidence in mastication.

Adult↗
PubMed1983

[Work and mental health : an issue to construct.].

This is a sphere of the field of health at work in wich knowledge is extremely limited and where research is truly slow in getting of the ground - the sphere of mental health. After providing a rapid synthesis of acquired knowledge, the author deplores the interpretive problems caused by having empirical research results without an adequate theoretical framework. With the help of a critical examination of work as social value on the one hand, and as reality element on the other, he attempts to lay down some guidelines of the new problem area. His hypothesis is based on the observation of an increasing disparity between the work ethic as it was thought to generations of workers, and the evolution of work structures in modern enterprises.

English Abstract↗
PubMed1982

Mandibular ridge augmentation and resorption with various visor procedures.

Modifications of the visor osteotomy for ridge augmentation are presented. Cases treated by these methods were studied for bone augmentation and resorption by measurements made on lateral cephalometric headplates, and compared with other procedures using interpositional or rib onlay techniques. It was found that the modified visor procedures fulfilled the criteria for the ideal ridge augmentation technique better than the other methods. Their main advantage is that they use the bone available from the mandible itself, with only a secondary role for the bone graft material in most instances.

Alveolar Ridge Augmentation↗
PubMedDate not supplied

The dynamics of sustained reentry in a ring model of cardiac tissue.

This paper describes the dynamics of circus movement around a fixed obstacle, using a one-dimensional continuous and uniform ring model of cardiac tissue to simulate sustained reentry. The membrane ionic current is simulated by a modified Beeler-Reuter formulation in which the kinetics of the fast sodium current were updated using more recent voltage-clamp data. Changes in the ring length are used to modify the dynamics of reentry. Reentry is stable if the ring length (X) exceeds a critical value (Xcrit) and complete block occurs if X is below a minimum (Xmin). Irregular sustained reentry is observed at intermediate ring lengths, as a narrow range of aperiodic reentry near Xcrit, and a larger range of quasi-periodic reentry at shorter ring lengths. The basic pattern of irregular reentry is an alternation between long and short cycle length, action potential duration (APD), diastolic interval (DIA), wavelength, and excitable gap. In aperiodic reentry cycle length variations are small, APD and DIA fluctuations are of medium amplitude, and conduction velocity over the whole pathway is essentially constant during successive turns. Much larger fluctuations in these various quantities occur during quasi-periodic reentry, and they increase in size as X approaches Xmin. The complexity of quasi-periodic reentry patterns is related to three factors: the slope of the APD versus DIA relation, which is greater than 1, the existence of a zone of slow conduction on the ring when the excitable gap becomes quite short, and the occurrence of triggered waves of secondary repolarization and excitability recovery. In the present model, quasi-periodic reentry with triggered secondary recovery covers most of the range of ring lengths, giving rise to sustained irregular reentry. There is very close agreement between our simulation results and experimental data obtained on rings of cardiac tissue.

Action Potentials↗
PubMedDate not supplied

Simulation of two-dimensional anisotropic cardiac reentry: effects of the wavelength on the reentry characteristics.

A two-dimensional sheet model was used to study the dynamics of reentry around a zone of functional block. The sheet is a set of parallel, continuous, and uniform cables, transversely interconnected by a brick-wall arrangement of fixed resistors. In accord with experimental observations on cardiac tissue, longitudinal propagation is continuous, whereas transverse propagation exhibits discontinuous features. The width and length of the sheet are 1.5 and 5 cm, respectively, and the anisotropy ratio is fixed at approximately 4:1. The membrane model is a modified Beeler-Reuter formulation incorporating faster sodium current dynamics. We fixed the basic wavelength and action potential duration of the propagating impulse by dividing the time constants of the secondary inward current by an integer K. Reentry was initiated by a standard cross-shock protocol, and the rotating activity appeared as curling patterns around the point of junction (the q-point) of the activation (A) and recovery (R) fronts. The curling R front always precedes the A front and is separated from it by the excitable gap. In addition, the R front is occasionally shifted abruptly through a merging with a slow-moving triggered secondary recovery front that is dissociated from the A front and q-point. Sustained irregular reentry associated with substantial excitable gap variations was simulated with short wavelengths (K = 8 and K = 4). Unsustained reentry was obtained with a longer wavelength (K = 2), leading to a breakup of the q-point locus and the triggering of new activation fronts.

Action Potentials↗
PubMedDate not supplied

Spontaneous changes in ventricular tachycardia cycle length and their relation to earliest sites of epicardial activation in a canine model.

BACKGROUND: The purpose of this study was to examine the spontaneous changes in cycle length during episodes of sustained monomorphic (MVT) and polymorphic (PVT) ventricular tachycardias and to relate these changes with the earliest epicardial activation site of the beat. METHODS: Isochronal activation maps were obtained from 127 unipolar electrograms recorded from the surface of both ventricles with a sock electrode array in 24 open chest anesthetized dogs. After atrioventricular block, the left anterior descending coronary artery was occluded for 60 min under ventricular pacing (140/min), followed by reperfusion. In 7 dogs the left stellate ganglion was stimulated 5 min after reperfusion. RESULTS: In 7 MVTs (reperfusion) and 4 PVTs (sympathetic stimulation), cycle length changes showed an initial acceleration, reaching a minimum cycle length and then decelerating before termination. Isochronal maps showed radial spread from earliest activation, without conduction block. Cycle length (481 +/- 80 msec) in MVT had beat to beat variations of 15 +/- 17 msec corresponding to small shifts in sites of the earliest activation, clustered along the border of the ischemic myocardium. In PVTs the cycle length (352 +/- 90 msec, p < 0.01) had a variability of 62 +/- 23 msec, corresponding to wide changes in the sites of earliest activation in right and left ventricles. Linear regression analysis showed a strong and significant correlation between cycle length variability and the number of electrodes with the earliest activation (r = 0.77, p < 0.0001). CONCLUSION: In these models of monomorphic and polymorphic ventricular tachycardias, cycle length variability showed a significant correlation with the number of electrodes with the earliest activation. MVTs showed concentrated origins with regular cycle length, whereas PVTs showed dispersed origins with irregular cycle length. These results suggest that the earliest epicardial activation site of the beat could be a factor in determining the dynamics in the cycle length.

Animals↗