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Biomedical subjects

M Laurent

Publications and source records attributed to M Laurent.

At least 37 records · Page 2Linked to original sources
PubMed2002

[Platypnoea-orthodeoxia syndrome. Diagnosis, etiology, treatment].

Platypnoea-orthodeoxia (P.O.) syndrome is the association of dyspnoea and arterial oxygen desaturation aggravated in the erect position and relieved in the supine position. Initially considered very rare (20 cases reported over fifty years) and occurring essentially in patients having undergone pneumonectomy, it in fact occurs much more frequently if only it is looked for (20 extra cases reported in a single year). Some new aetiologies have been described, in particular dilatations or aneurysms of the ascending aorta. Diagnosis is made easier if the oxygen saturation is measured in the supine position when it is normal, and in the erect position when it falls considerably. Another argument is added by the small effect of inspiration of high concentrations of oxygen. Contrast echocardiography confirms the right-left shunt and allows estimation of the site. This is usually situated at the atrial level, via an inter-atrial communication or more often a patent foramen ovale; as a rule the area of dehiscence having been modified by the associated pathology allowing the right-left shunt despite normal right pressures. Exceptionally the shunt is situated at the vascular or pulmonary parenchymal level. Poor tolerance of P.O. syndrome justifies a therapeutic procedure; this is usually closure of the septal fault with an occluder introduced percutaneously; the results are generally highly spectacular.

Aortic Aneurysm↗
PubMed2002

[Neuropathology of the cerebral vessels of centenarians].

Neuropathological study of brain and brain vessels was performed in two series of 12 and 20 centenarians, focusing on the prevalence of small vessel lesions, infarction, Alzheimer's changes and mental status. These are discussed as a function of vascular risk factors. In the first series (12 cases), there was no correlation between the severity of small vessel lesions: hyalinosis (12/12), mineralisation (10/12), amyloid angiopathy (9/12), vascular risk factors (high blood pressure or diabetes), Alzheimer's lesions. However, there was a tendency for an association between amyloid angiopathy and high density of neurofibrillary tangles. In the second series (20 cases), small infarcts and lacunes were found in 9/20 cases, neurofibrillary tangles and diffuse deposits of A beta peptide were constant, senile plaques were very frequent (19/20). Five patients were demented (one vascular dementia, one Alzheimer dementia, and 3 mixed dementias). These data indicate that: 1) Lesions of the walls of small cerebral vessels do not seem linked to the vascular risk factors observed at the end of the life of centenarians. 2) Cerebral infarcts and lacunes are frequent in these patients, and are responsible, at least in part, for a high proportion of the cognitive dysfunctions. The study of larger series is needed for a better understanding of relationships between vascular and degenerative lesions in the oldest old.

Aged↗
PubMed2001

Spatially constrained locomotion under informational conflict.

This study investigates the informational based that supports intentional adaptation of locomotion to spatial environmental constraints. A virtual reality setup was used to present subjects with targets providing normal as well as abnormal optical expansion during locomotor pointing (i.e. positioning of a foot on a visible target on the floor during walking). The manipulation dissociated two variables providing temporal information about time-to-passage (TTP): TTP(beta alpha) which encompasses target expansion, and TTP(alpha) which is independent of target expansion. While a previous study showed TTP(alpha) to be sufficient, the present results reveal that TTP(beta alpha) may be used when it is available. This finding indicates that both variables play a role that varies according to the circumstances. Furthermore, the present results provide evidence of the operation of a security principle for action in conflicting situations.

Adaptation, Psychological↗
PubMed2001

Interplay of biomechanical and neuromuscular constraints on pattern stability and attentional demands in a bimanual coordination task in human subjects.

Recent debate has focused upon the issue of whether general principles and laws of movement coordination may be derived without reference to anatomical, mechanical and physiological mechanisms. It has been proposed that self-generated movement involves the interaction of biomechanical and neuromuscular constraints. Biomechanical constraints are usually considered of as arising from the pendular dimensions of the limb or limb segments whereas neuromuscular constraints are commonly associated with nervous and metabolic control processes. The present study aims to investigate the interplay between these two different constraints on bimanual pattern stability and attentional demands. Five subjects were asked to execute an anti-phase coordination pattern (180 degrees of relative phase), while gradually increasing the frequency of oscillation and changing the rotational inertia of the joysticks. Frequency manipulation was expected to affect the neuromuscular constraints. Inertial manipulation was expected to affect biomechanical constraints. Attentional demands, reflecting the central cost associated with the maintenance of the coordination pattern was assessed using a dual-task paradigm. The results showed that: (1) increasing the oscillation frequency altered both coordination dynamics and attentional demands associated with the maintenance of bimanual coordination patterns; (2) manipulation of rotational inertia of the joysticks also altered pattern stability (standard deviation of relative phase) and coordination dynamics (i.e. the number of phase transition and the before transition), but these alterations were not paralleled by a change in attentional demands.

Adrenergic Agonists↗
PubMed2001

Prion diseases: dynamics of the infection and properties of the bistable transition.

Prion diseases are thought to result from a pathogenic, conformational change in a cellular protein, the prion protein. The pathogenic isoform seems to convert the normal isoform in an autocatalytic process. In contrast to the conditions used for in vitro studies of enzyme kinetics, the concentration of the catalyst is not much lower than that of the substrate in the course of infection. This feature may endow the system with a time-hierarchy allowing the pathogenic isoform to relax very slowly in the course of infection. This may contribute to the long incubation periods observed in prion diseases. The dynamic process of prion propagation, including turnover of the cellular prion protein, displays bistable properties. Sporadic prion diseases may result from a change in one of the parameters associated with metabolism of the prion protein. The bistable transition observed in sporadic disease is reversible, whereas that observed in cases of exogenous contamination is irreversible. This model is consistent with the occurrence of rare, sporadic forms of prion diseases. It may also explain why only some individuals of a cohort develop a prion disease following transient food contamination.

Animals↗
PubMed2001

Shared dynamics of attentional cost and pattern stability.

This paper examines the informational activity devoted by the CNS to couple oscillating limbs in order to sustain and stabilize bimanual coordination patterns. Through a double-task paradigm associating a bimanual coordination task and a reaction time (RT) task, we investigated the relation between the stability of preferred bimanual coordination patterns and the central cost expended by the CNS for their stabilization. Ten participants performed in-phase and anti-phase coordination patterns in a dual task condition (coordination + RT) at several frequencies (0.5, 0.75, 1.0, 1.5, and 2.0 Hz), thereby decreasing the stability of the bimanual patterns. Results showed a U-shaped evolution of pattern stability and attentional cost, as a function of oscillation frequency, exhibiting a minimum value at the same frequency. These findings indicate that central cost and pattern stability covary and may share common, high order dynamics. Moreover, the attentional focus given to the bimanual coordination and the RT task was also manipulated by requiring either shared attention or priority to the coordination task. Such a manipulation led to a tradeoff between pattern stability and RT performance: The more stable the pattern, the more costly it is to stabilize. This suggests that stabilizing a coordination pattern incurs a central cost that depends on its intrinsic stability. Conceptual consequences of these results for understanding the relationship between attention and coordination are drawn, and the mechanisms putatively at work in dual tasks are discussed.

Adult↗
PubMed2001

[Monitoring of tinzaparin in a ten day treatment dose in elderly patients].

PURPOSE: Renal impairment, which is frequently observed in elderly patients, raises the question of low molecular weight heparins treatment dose adjustment in this population. Thus, we conducted a prospective study to determine whether tinzaparin, administered subcutaneously at treatment dose (175 anti-Xa IU/kg) once daily for 10 days, does accumulate in patients older than 70 years of age. METHODS: Accumulation criteria were an increase of plasma anti-Xa and anti-IIa levels determined prior to the first injection and on days 2, 5, 7 and 10. The characteristics of the 30 consecutive included patients receiving tinzaparin at treatment dose (six men, 24 women) were: age 87.0 +/- 5.9 years (range: 71-96 years), body weight: 62.7 +/- 14.6 kg (range: 38-90 kg) and creatinine clearance 40.6 +/- 15.3 mL/min (range: 20-72 mL/min). RESULTS: None of the patients required a dose adjustment of tinzaparin over the 10-day treatment period. Anti-Xa and anti-IIa activity levels on day 2 were 0.66 +/- 0.20 IU/mL (range: 0.26-1.04 IU/mL) and 0.33 +/- 0.10 IU/mL (range: 0.18-0.55 IU/mL), respectively. These levels did not significantly change over the 10 days. These results favor the absence of the accumulation effect of tinzaparin. There was no correlation between anti-Xa and anti-IIa activities and age, weight, or creatinine clearance. Concerning the side-effects, only one minor hematoma at the injection site was reported. CONCLUSION: Tinzaparin may thus be administered in older patients with renal impairment, at a treatment dose (175 anti-Xa IU/kg/d) for a 10-day treatment period, without accumulation effect nor hemorrhagic side-effect in patients with creatinine clearance greater than 20 mL/min.

Age Factors↗
PubMed2001

Long-term follow-up of percutaneous vena cava filters: a prospective study in 100 consecutive patients.

OBJECTIVES: the long-term outcome in following insertion of inferior vena cava (IVC) filters remains unclear. DESIGN: prospective study. MATERIAL AND METHODS: one hundred consecutive patients received percutaneous vena cava filters between 1988 and 1993. The patients underwent clinical examination, abdominal X-rays and duplex ultrasound of the IVC, right internal jugular vein and legs after a mean follow-up duration of 38+/-11 months. RESULTS: forty patients died after implantation (median 11.3 months; IQR: 1.8--20.4 months). The cause of death was known in 33 cases, and pulmonary embolism (PE) was suggested in three. Multivariate analysis revealed the mortality rate to be significantly higher in cancer patients (relative risk of 2.13). The 3-year survival was 20% for cancer patients and 71% for patients without cancer. Among the 60 living patients, thrombi were trapped in the filter in 10 cases, the filter tilted in four, was malpositioned in five and migrated in 29. These incidents were recorded as asymptomatic complications, as opposed to seven IVC thromboses and 23 recurrent lower limb thromboses, which were considered as symptomatic complications. CONCLUSION: long-term major complications are not frequent. As expected, cancer was the only factor predicting mortality. IVC filters seem effective in preventing PE.

Adult↗
PubMed2001

Altered expression of novH is associated with human adrenocortical tumorigenesis.

NOVH belongs to the CCN (CTGF/CYR61/NOV) family of proteins, some of which have chemotactic, mitogenic, adhesive, and angiogenic properties. Whereas ctgf and cyr61 are growth factor-inducible, immediate-early genes, nov is expressed in growth-arrested or quiescent cells. As nov expression has been shown to be altered in both avian and human nephroblastomas and to be a target of WT1 regulation, NOV may play important roles in normal nephrogenesis and the development of Wilms' tumors. The aim of this study was to determine whether changes in novH expression were associated with tumorigenesis in tissues other than those of the kidney. We showed by Northern blotting and immunohistochemistry that among human adult endocrine tissues, the adrenal gland is a major site of novH expression, and that in adult and fetal adrenal tissue, novH is primarily expressed in the adrenal cortex. Studies with 12 benign and 18 malignant adrenocortical tumors revealed that the levels of novH mRNA and protein decreased significantly (P < 0.004) with progression of adrenocortical tumors from a benign to a malignant state. Although the localization of NOVH did not change, the N-glycosylation profile of benign and malignant tumors differed considerably from that of normal adrenocortical tissue, and these differences may affect the biochemical properties of the molecule. The properties of NOVH here provide the first evidence that this member of the CCN family could be involved in adrenocortical tumor development.

Adolescent↗
PubMed2001

[Results of surgical treatment of calcified aortic valve stenosis: report of a series of 4,129 interventions].

Aortic stenosis (AS) is the most common lesion currently encountered among valvular heart disease, particularly in elderly people. Severe functional impairment and risk of sudden death explain that surgical treatment is largely accepted. We report a retrospective analysis of institutional experience with aortic valve replacement (AVR) for AS from 1971-1997 in 4,129 patients. Age ranged from 13 to 91 years (mean 68 +/- 10) and degenerative disease was largely predominant (86%). For AVR, mechanical prostheses were used in 2,054 patients (50.2%) and bioprostheses in 2,075 (48.8%) in elderly group. Coronary artery revascularization was associated in 670 patients (16%). Operative mortality was 7% (303 pts) and main cause was left ventricular failure (52%). Late results were studied with a maximum follow-up of 26 years. Total follow-up represents 21,533 pt-years. Late death occurred in 1,108 patients between 1 month and 24 years after operation (mean 6.6 years). Reoperation was necessary in 136 cases. Actuarial survival--including operative mortality--was 77% and 56% at 5 and 10 years. A large functional improvement was observed in the vast majority of patients, 73% being I or II subgroups of the NYHA classification. Incremental risk factors for death (immediate as well as late) were older age, preoperative functional status, emergency, presence of cardiac failure, coronary artery lesions and associated morbidity. The choice of valvular prosthesis remains controversial, but the results show that AVR is the procedure of choice for the vast majority of patients wtih significant aortic valve disease.

Adolescent↗
PubMed2001

[Patient information and coronary angiography: experience of the Rennes group].

The object of this study was to assess the degree of patient information of subjects referred for coronary angiography and their reaction to a detailed protocol of information. The enquiry was performed in 3 stages: an oral evaluation of the degree of information with a standardised questionnaire; the giving of written documents from the French Federation and Society of Cardiology mentioning the risks of the procedure; the continuation of the interview with evaluation of the degree of satisfactions with the information provided. Two hundred and thirty one patients referred by cardiologists for non-urgent coronary angiography were interrogated (175 men, 56 women; mean age 63 years, range: 27-83 years). In the 164 subjects who had never had this investigation: 56 (34.1%) did not appreciate the invasive nature of the procedure 111 (67.6%) totally ignored the risks of the procedure 70 (42.6%) were not informed of the possibility of a surgical procedure or of an angioplasty as a result of the procedure. 89% were satisfied with the information concerning the risks of the investigation. In a second group of 100 patients, the comprehension of the information was checked by the same questionnaire used a posteriori. These results show that patient information is very often incomplete. Despite some reticence, the new procedures seem to be globally well accepted but would be more effective if used before hospital admission.

Adult↗
PubMed2001

A dynamical framework to understand performance trade-offs and interference in dual tasks.

This study demonstrated that the dynamic pattern approach may reconcile resource and outcome conflict theories to explain performance in dual tasks. Participants performed a bimanual coordination task and a reaction time task with different conditions of attentional priority. Results showed a trade-off between pattern variability and reaction time when priority was given to the coordination task. Such a trade-off was indicative of resource allocation. An analysis of perturbation in the bimanual coordination revealed interference, a reputed sign of outcome conflict. Moreover, interference diminished substantially when priority was given to the bimanual task. The coexistence of performance trade-off and outcome conflict suggests that these two phenomena are not mutually exclusive. Rather, both may follow from modifying the coupling between the limbs through attention.

Adult↗
PubMed2001

[Heparin therapy in pregnant women].

The prescription of heparin during pregnancy is an uncommon situation but a difficult one to manage because there are no reported therapeutic trials. The main indications are thromboembolic disease, valvular or congenital heart disease, cardiac arrhythmias and patients at high risk of thrombosis with blood clotting disorders. Non-fractionated heparin is the commonest form of anticoagulation in these circumstances as it does not cross the placental barrier; there are no teratogenic or haemorrhagic risks to the foetus. However, its dosage is difficult in pregnant women and this may lead to complications such as haemorrhage, heparin-induced thrombocytopaenia and osteoporosis; in addition, the duration of the treatment is often long and it can affect tolerance. Low molecular weight heparins are a promising alternative because of their long half-lives which give a more predictable dose-effect and reduce the number of daily injections. The risk of heparin-induced thrombocytopaenia is lower. At present, their legal prescription is limited to enoxaparin during the 2nd and 3rd terms of pregnancy as prophylactic treatment. The recommendations described in this article are the result of the 6th Consensus of the ACCP on antithrombotic treatment, which cautions the use of low molecular weight heparin during pregnancy. Different therapeutic regimes are presented according to the degree of thromboembolic risk. In patients with mechanical valvular prostheses, the recommendations are variable, with many workers, especially European groups, preferring anticoagulation to heparin from the 12th to the 36th week of pregnancy because of the greater efficacy of this particular indication. Peridural anaesthesia may be carried out with heparin therapy providing the level of anticoagulation is monitored and the procedure is performed under well controlled conditions. In cases presenting formal contra-indications to heparin therapy, heparinoids may be used instead. In future, low molecular weight heparin therapy will probably play a larger role in anticoagulation during pregnancy and in all the potential therapeutic indications.

Adult↗
PubMed2000

Effects of attention on phase transitions between bimanual coordination patterns: a behavioral and cost analysis in humans.

The present study aimed to obtain a behavioral analysis of the effects of attentional focus on the dynamics of phase transitions in bimanual coordination and to evaluate the central cost expended by the central nervous system to maintain and stabilize such coordination patterns before and after the transition. Eight subjects were asked to execute an anti-phase coordination pattern (180 degrees of relative phase), while gradually increasing the frequency of oscillation. The central cost was assessed using a dual-task paradigm associating the bimanual coordination task with a reaction time task. Results showed that: (1) the transition process was significantly altered by focusing attention on the bimanual coordination task; and (2) the cost involved in sustaining the bimanual patterns was determined by their coordination dynamics.

Acoustic Stimulation↗
PubMed2000

The control of human locomotor pointing under restricted informational conditions.

Since a perception-action coupling type of control (Kugler, P.N. and Turvey, M.T., Information, Natural Law, and Self-Assembly of Rhythmic Movements, Erlbaum, Hillsdale, 1987, 481 pp.) continuously operates during locomotor pointing tasks (e.g. long jumping) (Montagne, G., Cornus, S., Glize, D., Quaine, F. and Laurent, M., A 'perception-action coupling' type of control in long-jumping. J. Motor Behav., (2000) in press), the information sources underlying this control have to be dealt with. Under the assumption that subjects use information about the first-order time remaining before they pass the target, we identify in the literature four different sources of information that specify this physical property. Only one of these sources is inevitably present under all possible environmental conditions containing at least a continuously visible target on the floor. This study aimed to test its sufficiency to perform a locomotor pointing task. The use of a virtual reality set-up permitted us to compare locomotor pointing executed with all four information sources or only with the aforementioned one. The likeness found between those two conditions, as far as the pointing performance and the mode of control are concerned, expresses the evoked sufficiency.

Biomechanical Phenomena↗
PubMed2000

Bleaching of ESR signals by the sunlight: a laboratory experiment for establishing the ESR dating of sediments

A laboratory bleaching experiment was performed in order to improve the method of ESR dating of sediments. Several sedimentary, volcanic, and granitic quartz samples showed consistent bleaching response for the exposure to halogen lamps. It was found that the most sensitive signals are the Ti-H and Ti-Na centers. There was no difference observed within the samples exposed to light filtered by several color glass plates, according to the present preliminary result.

Journal Article↗