Biomedical subjects

M Bourgeois

Publications and source records attributed to M Bourgeois.

At least 37 records · Page 2Linked to original sources

PubMed1999

Volumetric analysis of the right and left ventricle in a porcine heart model: comparison of three-dimensional echocardiography, magnetic resonance imaging and angiocardiography.

UNLABELLED: Three-dimensional echocardiography and magnetic resonance imaging allow the volumetric analysis of ventricular volumes independent of geometric assumptions. The aim of the study was to compare these methods and the common angiocardiography in a cardiac model of known volume. METHODS/MATERIALS: Right and left ventricular (RV, LV-) volumes were measured in a specific animal model directly ('true volume') and with different imaging techniques. Three-dimensional echocardiography (3D-Echo) and magnetic resonance imaging (MRI), both of which permit a volume estimation without necessitating geometric assumptions, and angiocardiographic volumetry which is based on the Simpson rule were used in this study. RESULTS: The best results were achieved with MRI (RV: r(2)=0.99, mean difference: -1. 9+/-3.3%; LV: difference r(2)=0.99,: 2.9+/-5.0%). Likewise, 3D-Echo showed a very good correlation with the true volumes (RV: r(2)=0.93, difference: 9.3+/-6.3%; LV r(2)=0.96, difference: 4.8+/-9.9%). The greatest deviations were observed during angiocardiographic volumetry (LV: r(2)=0.98; difference: 14.4+/-9.2%), particularly when measuring the right ventricle (RV: r(2)=0.82, difference: 57. 9+/-40.1%). Consequently, the direct comparison between 3D-Echo and the other methods yielded the best correspondence with MRI (RV: Bias: 3.7 ml, limits of agreement: 7.7 ml; LV: Bias: 3.7 ml, limits of agreement: 4.9 ml). In contrast, the differences between 3D-Echo and angiocardiography were marked (RV: Bias: 25.5 ml, limits of agreement: 11.1 ml; LV: Bias: 8.7 ml, limits of agreement: 13.2 ml). CONCLUSION: In a porcine cardiac model, 3D-Echo permits a relatively precise measurement of ventricular volumes with a slight under-estimation. MRI yielded the most precise volumetry, and the correlation between 3D-Echo and MRI was quite good. Particularly for the right ventricle, the angiocardiographic measurement was attached with the greatest error and thus appears ill-suited for the volumetry of geometrically more complex ventricles.

Analysis of Variance↗

PubMed1999

Volumetric analysis of the right ventricle in children with congenital heart defects: comparison of biplane angiography and transthoracic 3-dimensional echocardiography.

BACKGROUND: Three-dimensional echocardiography is a non-invasive imaging technique. The fact that it permits volumetric analyses independently of geometrical assumptions makes it a putatively useful method for the precise measurement of the volumes of the irregularly shaped right ventricles in children. The aim of this study was to assess the feasibility of this method and its agreement with angiocardiography based estimates of right ventricular volume in children with congenital heart disease. METHODS: We studied 102 children with congenital heart disease. The angiocardiographic right ventricular volumetry was performed using a biplanar technique using Simpson's rule and corrected with Lange's correction factors. The echo data sets were registered trans-thoracically with a rotating transmitter. Volumes were calculated after manual planimetry by adding the volumes of the individual slices. RESULTS: Calculation of right ventricular volume echocardiographically was possible only in 34% of patients, mostly infants and toddlers. In comparison to angiocardiography, the measured volumes were 1.1 +/- 6.9 ml (19.5 +/- 34.1%) or 6.3 +/- 9.4 ml (42.5 +/- 33.6%) smaller during systole or diastole, respectively. The limits of agreement were -12.5 and 13.6 ml, or 12.45 and 25.15 ml during systole or diastole, respectively. When plotted to a logarithmical scale, the correlation coefficients r2 were 0.70 for systolic and 0.79 for diastolic measurements. CONCLUSION: Transthoracic 3-dimensional echocardiography with a rotating transmitter is feasible for volumetry only in small children. The volumes measured were significantly smaller than the ones calculated from the angiocardiographic images. The correlation between the two methods is moderate.

Adolescent↗

PubMed1999

Balloon valvoplasty in infants with tetralogy of Fallot: effects on oxygen saturation and growth of the pulmonary arteries.

Balloon valvoplasty was undertaken in 27 patients with tetralogy of Fallot for first-stage palliation. Indications were arterial saturation of oxygen < 80%, hypoxic spells and duct-dependant pulmonary perfusion. The dilation was performed following diagnostic heart catheterization. Saturations improved from 75% +/- 8.5 before valvoplasty to 85% +/- 8.4 after the procedure, and worsened little to 83% +/- 9.6 at follow-up after 3.4 months. The pulmonary valvar orifice was hypoplastic in most patients (Z = -3.3 +/- 1.2), and did not change after the procedure. The cross-sectional area of the pulmonary arteries was diminished initially, reflected by a Nakata index of 186 +/- 95 mm2/m2. After valvoplasty, we found widening of the vessels (Nakata index 225 +/- 100 mm2/m2). At follow-up no further growth of the arteries was observed (Nakata index 209 +/- 109 mm2/m2). The procedure was complicated by hypoxic spells in three patients which were controlled by intravenous propranolol, and deep venous thrombosis in four patients. Our data demonstrate that balloon valvoplasty is feasible for initial palliation in patients with tetralogy of Fallot. It does not, however, produce growth of the pulmonary arteries or of the pulmonary valve.

Cardiac Catheterization↗

PubMed1999

Reduction in caregiver-identified problem behaviors in patients with Alzheimer disease post-hearing-aid fitting.

Studies and clinical procedures related to patients with Alzheimer disease (AD) largely have ignored the hearing ability of either the patient or caregiver. Yet the majority of treatment and investigation depends on or presupposes communication ability. Further, caregiver complaints often center around communication-based issues. Hearing deficits may be the most frequently unrecognized condition in patients with AD because patients either communicate adequately in quiet or the impairment is masked by other behavioral symptoms of AD. The current investigation identified individuals with AD with perceived and measured hearing impairment, provided amplification management, and evaluated the impact of treatment on caregiver-identified problem behaviors believed to be related to hearing status. Specifically, treatment compliance (hearing-aid use) and treatment efficacy (reduction in perceived hearing handicap and problem behaviors) were measured in the current investigation. A multiple-baseline design across individuals with multiple dependent variables was used to evaluate the reduction of problem behaviors post-hearing-aid treatment. Eight participants were included and 1 to 4 problem behaviors were significantly reduced for each patient after hearing-aid treatment. All participants were able to complete the necessary evaluation for hearing-aid fitting and wore their hearing aids between 5 and 15 hours per day by the end of the study. This investigation employed novel methodology in the areas of on-site hearing evaluation and hearing-aid selection, advanced hearing-aid technology, and primary data recording of caregiver-identified problem behaviors by caregivers.

Aged↗

PubMed1999

Reactivation of herpes virus after surgery for epilepsy in a pediatric patient with mesial temporal sclerosis: case report.

OBJECTIVE: This case report is presented to raise the awareness of the potential risk of reactivation of herpes simplex virus (HSV) encephalitis after intracranial surgery. CLINICAL PRESENTATION: The case of an 8-year-old male patient who suffered a reactivation of HSV encephalitis after undergoing amygdalohippocampectomy for complex partial seizures is reported. This patient had previously contracted HSV 1 meningoencephalitis at the age of 16 months. Six years later, a left amygdalohippocampectomy was proposed after the development of intractable partial epilepsy associated with left mesial temporal lesions. During the postoperative period, the patient suffered severe clinical deterioration with partial status epilepticus, aphasia, and hyperthermia, which resolved after intensive antiepileptic treatment supported by acyclovir. CONCLUSION: We advise prophylactic pre-, peri-, and postoperative treatment with acyclovir for patients with known histories of HSV encephalitis who undergo intracranial procedures.

Acyclovir↗

PubMed1999

Volume measurement of the left ventricle in children with congenital heart defects: 3-dimensional echocardiography versus angiocardiography.

BACKGROUND: Volume measurement of the left ventricle is currently done by 2-dimensional echocardiography or angiocardiography. However, for the calculation of volumes by these methods, geometrical assumptions must be made. For a precise ventricular volumetry, independent of mathematical assumptions, imaging techniques as the 3-dimensional echocardiography (3D-echo) are required, which permit the imaging of the real ventricular shape. The aim of the study was therefore to detect, whether 3D-echocardiography is suitable for left ventricular volumetry in children with congenital heart disease and whether the 3D-echocadiographically measured volumes correlate sufficiently well with angiocardiographically measured left ventricular volumes. METHODS: 102 children with congenital heart disease were investigated. For angiocardiographic left ventricular volume measurement Simpson's rule was used. Results were corrected with Lange's correction factors. The 3D-echo data sets were registered with a rotating transthoracic transducer. Ventricular volumes were calculated after manual planimetry by summation of the volumes of the single slices. RESULTS: The left ventricular volume could be calculated by 3D-echo in 83% of patients of all ages. In comparison to angiocardiography, the measured volumes were 0.6 +/- 3. 3 ml (0.9 +/- 25.8%) or 7.1 +/- 28.4 ml (7.4 +/- 12.1%) smaller during systole or diastole, respectively. The correlation coefficients r(2) were 0.89 for systolic and 0.93 for diastolic measurements after logarithmic transformation. Pressure or volume overload did not influence significantly the difference between the two methods. CONCLUSION: Transthoracic 3D-echocardiography with a rotating transmitter is feasible for volumetry of the left ventricle in most children. The volumes measured by 3D-echo were significantly smaller than those calculated from the angiocardiography by Simpson's rule. The measurements were not influenced by the kind of load of the ventricle. The correlation between the two methods is good.

Adolescent↗

PubMed1999

The identification of ferritin in the nucleus of K562 cells, and investigation of a possible role in the transcriptional regulation of adult beta-globin gene expression.

We studied the subcellular distribution of ferritin in K562 cells by immunofluorescence techniques and have made a reappraisal of a direct binding interaction between ferritin and the proximal promoter region of the human beta-globin gene, as previously mentioned in the literature. Confocal microscopy indicates that ferritin, the iron-storage protein, is present in the nucleus of K562 cells, in addition to its expected cytoplasmic localisation. The stain distribution suggests that it is not directly associated with the nuclear matrix. Using a gel mobility shift assay, a protein that cross-reacts with monoclonal ferritin antibodies competitively binds to a double-stranded oligonucleotide spanning the region situated 150 base pairs upstream from the beta-globin transcription start site. Despite this antibody cross-reactivity, the protein is unlike cytosolic ferritin as it appears to be highly sensitive to both temperature and freeze-thaw cycles, and UV-crosslinking experiments indicate that the molecular mass of the protein factor lies between 90 and 100 kDa. In conclusion, while the intranuclear location of ferritin is described in the present study, ferritin is not in direct contact with the beta-globin promoter region.

Adult↗

PubMed1999

Benign cerebellar astrocytomas in children.

OBJECT: Cerebellar astrocytomas are benign tumors of childhood known to be associated with excellent long-term survival in patients in whom complete surgical resection is possible. However, the roles of other factors--clinical, radiological, histological, and therapeutic--in the survival of the patient, tumor recurrence, and long-term patient outcome remain imprecise. The goal of this study was to examine these factors and their relationships. METHODS: To clarify these issues a retrospective review was conducted of 168 children who were surgically treated for a cerebellar astrocytoma at Hôpital Necker-Enfants Malades between 1955 and 1995. These patients' clinical files were examined, the histological characteristics of their tumors were reviewed, and their outcomes were assessed according to Bloom's scale and the Wechsler intelligence quotient test. Of the 168 patients in the study, 91 were male and 77 were female with a mean age of 6.9 years and a mean follow up lasting 7.7 years. Tumors were identified as being strictly located in the cerebellum in 76.2% of the patients and as involving the brainstem (referred to as the "transitional form") in 23.8% of the patients. Complete surgical excision was possible in 88.7% of cases. There was a total mortality rate of 4.2% and a tumor recurrence rate of 9.5%. Fifty-eight percent of the patients had no neurological sequelae at follow-up evaluation. Pejorative factors that were discovered by multivariate analysis to be important included: a long preoperative duration of symptoms and the transitional form of tumor with respect to survival; incomplete tumor excision with respect to an increased risk of recurrence; and a long preoperative duration of symptoms, an early epoch during which surgery was performed (1955-1974), severe ventricular dilation, and the transitional form of tumor with respect to a poorer long-term patient outcome. CONCLUSIONS: The presence of brainstem involvement (tumor in the transitional form) emerged as a significant negative prognostic factor and should be treated as a distinct nosological entity. The extent of surgical excision has a significant bearing on the risk of tumor recurrence.

Adolescent↗

PubMed1999

Epilepsy in children with shunted hydrocephalus.

OBJECT: The incidence of epilepsy among children with hydrocephalus and its relation to shunts and their complications, raised intracranial pressure (ICP), and developmental outcome are explored in a retrospective study. METHODS: The authors studied a series of 802 children with hydrocephalus due to varying causes, who were treated by ventriculoperitoneal shunt placement between 1980 and 1990, with a mean follow-up period of 8 years. Patients who had tumoral hydrocephalus and those whose files lacked significant data were excluded. Data extracted from medical records, including history of the hydrocephalus and history of seizures, if any, were analyzed. Thirty-two percent of the children had epilepsy, the onset of which frequently occurred at approximately the same time that the diagnosis of hydrocephalus was made. The majority of the affected children had severe uncontrolled epilepsy. The incidence of epilepsy was significantly affected by the original cause of the hydrocephalus. The presence of radiological abnormalities was also found to be a significant predictor of epilepsy. Similarly, shunt complications predisposed to epilepsy. Episodes of raised ICP related to hydrocephalus or in association with shunt malfunction may also predispose to epileptic seizures. Furthermore, the presence of a shunt by itself seems able to promote an epileptogenic focus. Finally, epilepsy appears to be an important predictor of poor intellectual outcome in hydrocephalic children with shunts. CONCLUSIONS: A prospective study is needed to identify clearly and confirm avoidable factors predisposing to seizures in these children so that we can strive to reduce the incidence of these seizures and, subsequently, improve these children's quality of life.

Birth Injuries↗

PubMed1999

Surgery of epilepsy associated with focal lesions in childhood.

OBJECT: Surgery in children with epilepsy is a new, evolving field. The important practical issues have been to define strategies for choosing the most suitable candidates and the type and optimal timing of epilepsy surgery. This study was undertaken to elucidate these points. METHODS: To identify the factors that correlated with outcome, the authors analyzed a series of 200 children (aged 1-15 years (mean 8.7 years) who underwent surgery between 1981 and 1996 at the Hôpital Necker-Enfants Malades. In 171 cases (85.5%) the epilepsy was medically refractory and was associated with focal cortical lesions. Surgery consisted of resection of the lesion without specifically attempting to identify and remove the "epileptogenic area. "In the group of children whose seizures were medically refractory, the mean follow-up period was 5.8 years. According to Engel's classification, 71.3% of these children became seizure free (Class 1a,) whereas 82% were in Class I. A multivariate statistical analysis revealed that among all the factors studied, the success of surgery in a patient in whom there was a good clinical/electroencephalogram/imaging correlation depended on the patient's having undergone a minimally traumatic operation, a complete resection of the lesion, and a short preoperative seizure duration. After the surgical control of epilepsy, behavior disorders were more improved (31% of all patients) than cognitive function (25%). The patient age at onset, duration and frequency of seizures, intractability of the disease to therapy, and seizure characteristics were correlated with cognitive, behavioral, and academic performance pre- and postoperatively. Multivariate statistical analysis revealed that cognitive dysfunction correlated highly with the duration of epilepsy prior to surgery, whereas behavioral disorders correlated more with seizure frequency. CONCLUSIONS: These data must be taken into account when selecting patients for surgical treatment and when deciding the timing of surgery. Early surgical intervention allows for optimum brain development.

Adolescent↗

PubMed1998

Improvement predictors in obsessive-compulsive disorder. An event-related potential study.

The treatment of patients with obsessive-compulsive disorder gives variable and unpredictable results. Numerous clinical features have been investigated as potential predictors of medication response but without consistent results. Preliminary findings have shown that some impairments of pre-treatment event-related potentials (ERPs) could be associated with future treatment outcome (Morault et al., 1997). The present study aimed to confirm the relationships between ERPs and treatment efficacy with larger sample sizes. ERP components were elicited during a verbal auditory 'oddball' paradigm and were recorded in 21 unmedicated patients compared to 21 control subjects. After a pharmacological treatment, the disorder improved in 12 patients. Pre-treatment ERP data were retrospectively compared between treatment responders, non-responders and control subjects. Patients who were to respond favorably to treatment had significantly reduced N2 amplitude and shorter N2 and P3 latencies compared to non-responders and control subjects. In contrast, no difference was shown between non-responders and control subjects. Our findings provide evidence for abnormalities of ERPs which could be considered as potential predictors of treatment response in patients with OCD. These results need to be tested in a prospective protocol.

Adult↗

PubMed1998

Transient overexpression of human H- and L-ferritin chains in COS cells.

The understanding of the in vitro mechanisms of ferritin iron incorporation has greatly increased in recent years with the studies of recombinant and mutant ferritins. However, little is known about how this protein functions in vivo, mainly because of the lack of cellular models in which ferritin expression can be modulated independently from iron. To this aim, primate fibroblastoid COS-7 cells were transiently transfected with cDNAs for human ferritin H- and L-chains under simian virus 40 promoter and analysed within 66 h. Ferritin accumulation reached levels 300-500-fold higher than background, with about 40% of the cells being transfected. Thus ferritin concentration in individual cells was increased up to 1000-fold over controls with no evident signs of toxicity. The exogenous ferritin subunits were correctly assembled into homopolymers, but did not affect either the size or the subunit composition of the endogenous heteropolymeric fraction of ferritin, which remained essentially unchanged in the transfected and non-transfected cells. After 18 h of incubation with [59Fe]ferric-nitrilotriacetate, cellular iron incorporation was similar in the transfected and non-transfected cells and most of the protein-bound radioactivity was associated with ferritin heteropolymers, while H- and L-homopolymers remained iron-free. Cell co-transfection with cDNAs for H- and L-chains produced ferritin heteropolymers that also did not increase cellular iron incorporation. It is concluded that transient transfection of COS cells induces a high level of expression of ferritin subunits that do not co-assemble with the endogenous ferritins and have no evident activity in iron incorporation/metabolism.

Animals↗

PubMed1998

Is early adulthood a critical developmental stage for psychosis proneness? A survey of delusional ideation in normal subjects.

It has been hypothesized that late adolescence and early adulthood might be a brain developmental stage favoring the clinical expression of psychotic symptoms in psychiatric or neurological diseases. The aim of the present survey was to examine the relationship between age and delusional ideation in a sample of subjects with no psychiatric disorder. The survey was carried out with the Aquitaine Sentinel Network of general practitioners. Consecutive practice attenders were invited to complete the PDI-21 (Peters Delusional Inventory 21 items), a self-report questionnaire designed to measure delusional ideation in the normal population. The study concerned 444 patients who had no lifetime history of psychiatric disorder and who completed the PDI-21. A principal component analysis of the PDI-21 items was performed in order to identify delusional dimensions. An age-related decrease in the likelihood to report delusional ideas was found, younger subjects scoring higher on most dimensions of delusional ideation, such as 'persecution', 'thought disturbance', 'grandiosity' and 'paranormal beliefs'. 'Religiosity' was the only dimension positively associated with age. The results suggest that there may be a physiological neurodevelopmental stage favouring the expression of psychosis proneness in normal subjects, and support the hypothesis that the association between age and positive psychotic symptoms in functional and organic psychoses may be linked to the interaction between normal brain maturational processes and cerebral abnormalities involved in the aetiology of functional and organic psychoses.

Adolescent↗

PubMed1998

Systematic clinical methodology for validating bipolar-II disorder: data in mid-stream from a French national multi-site study (EPIDEP).

BACKGROUND: This paper presents the methodology and clinical data in mid-stream from a French multi-center study (EPIDEP) in progress on a national sample of patients with DSM-IV major depressive episode (MDE). The aim of EPIDEP is to show the feasibility of validating the spectrum of soft bipolar disorders by practising clinicians. In this report, we focus on bipolar II (BP-II). METHOD: EPIDEP involves training 48 French psychiatrists in 15 sites; construction of a common protocol based on the criteria of DSM-IV and Akiskal (Soft Bipolarity), as well as criteria modified from the work of Angst (Hypomania Checklist), the Ahearn-Carroll Bipolarity Scale, HAM-D and Rosenthal Atypical Depression Scale; Semi-Structured Interview for Evaluation of Affective Temperaments (based on Akiskal-Mallya), self-rated Cyclothymia Scale (Akiskal), family history (Research Diagnostic Criteria); and prospective follow-up. RESULTS: Results are presented on 250 (of the 537) MDE patients studied thus far during the acute phase. The rate of BP-II disorder which was 22% at initial evaluation, nearly doubled (40%) by systematic evaluation. As expected from the selection of MDE by uniform criteria, inter-group comparison between BP-II vs unipolar showed no differences on the majority of socio-demographic parameters, clinical presentation and global intensity of depression. Despite such uniformity, key characteristics significantly differentiated BP-II from unipolar: younger age at onset of first depression, higher frequency of suicidal thoughts and hypersomnia during index episode, higher scores on Hypomania Checklist and cyclothymic and irritable temperaments, and higher switching rate under current treatment. Eighty-eight percent of cases assigned to cyclothymic temperament by clinicians (with a cut-off of 10/21 items on self-rated cyclothymia) were recognized as BP-II. Evaluation of this temperament by clinician and patient correlated at a highly significant level (r=0.73; p <0.0001). Cyclothymia and hypomania were also correlated significantly (r=0.51; p < 0.001). LIMITATION: In a study conducted in diverse clinical settings, it was not possible to assure that clinicians making affective diagnoses were blind to the various temperamental measures. However, bias was minimized by the systematic and/or semi-structured nature of all evaluations. CONCLUSION: With a systematic search for hypomania, 40% of major depressive episodes were classified as BP-II, of which only half were known to the clinicians at study entry. Cyclothymic temperamental dysregulation emerged as a robust clinical marker of BP-II disorder. These data indicate that clinicians in diverse practice settings can be trained to recognize soft bipolarity, leading to changes in diagnostic practice at a national level.

Adult↗

PubMed1998

Managing hearing loss in a patient with Alzheimer disease.

This case study reports the management of hearing loss in a patient with Alzheimer disease (AD) living at home with a spouse care giver. The report highlights the interaction between symptoms associated with AD and hearing loss and the lack of data regarding remediation of hearing loss in this population. Specifically, the case illustrates the modifications in evaluation and verification of the hearing aid fitting that may be advisable when working with patients with AD. The data for this patient illustrate some novel measurement techniques that may assist the professional in documenting the impact of treatment in this population.

Aged↗

PubMed1997

Psychophysiological and clinical value of event-related potentials in obsessive-compulsive disorder.

To investigate brain correlates of cognitive function in obsessive-compulsive disorder (OCD), event-related potentials (ERPs) were recorded in a group of thirteen unmedicated OCD patients and thirteen normal controls for verbal auditory stimuli in an oddball paradigm. The patients showed longer latencies of the N1 and P2, shorter latency of the P3, and reduced amplitude of the N2. These results suggest that OCDs stress the speed of task-dependent processes (i.e., by showing shorter N2 and P3 latencies) and have impairment of task-independent ones (i.e., by showing longer N1 and P2 latencies and reduced N2 amplitude). The components were more positive in the left hemisphere in OCDs and in the right hemisphere in normal controls. Future responders to treatment had significantly reduced N2 and enhanced P3 amplitudes relative to future nonresponders. So ERPs might provide psychophysiological profiles in OCDs with clinical and pharmacological implications.

Adult↗

PubMed1997

Post-partum blues and mild depressive symptomatology at days three and five after delivery, A French cross sectional study.

This cross-sectional work studies the prevalence of post-partum blues on days 3 and 5 after delivery and the links between post-partum blues and depressive symptomatology, using standardised interviews and rating scales (Kennerley and Gath Blues Scale. MADRS) to screen a consecutive series of 104 women on days three and five after a normal delivery. This study stresses the possibility of a difference between the symptomatology of a benign "classical" post-partum blues, and that of a more intense blues closer to the spectrum of depressive mood disorders and perhaps post-natal depression.

Cross-Sectional Studies↗

PubMed1997

Evidence of a preprogrammed deactivation of the hamstring muscles for triggering rapid changes of posture in humans.

Normal subjects were asked to make rapid flexions of the legs from a stationary initial standing posture in a self-paced mode. Because this movement implicates a rapid change in posture, questions were asked about the type of central command which must include the rupture of the erect posture and the accomplishment of the goal directed movement. Movements of the different segments of the body were recorded and analyzed using the optoelectronic ELITE system. Electromyographic (EMG) activities of 8 muscles of the lower limb on one side were recorded, rectified and integrated. The time relationships of the different EMG signals (activation or deactivation) were analyzed with respect to selected kinetic measures of the related segments of the body. In the majority of the subjects, before the movement onset, EMG events included a specific deactivation of the tonic EMG activity of the semimembranous (SM) and semitendinous (ST) muscles (time onset relative to the onset of the legs flexion: -196.9 +/- 96.4 ms and -180.5 +/- 89.7 ms, respectively). A second event was a phasic activation of the tibialis anterior (TA) muscle (time onset: -60.5 +/- 117.6 ms). Conjugate cross-correlation analysis of these EMG signals demonstrated the existence of a common coordinated strategy between the deactivation of the hamstring and the TA activation. Even though a small horizontal displacement of the head was recorded prior to leg movement, it occurred too late to induce deactivation of the hamstring muscles. These results demonstrate that for rapid legs flexion, where the gravity forces are the main source of joint angle acceleration, the deactivation of the SM and ST muscles acts in conjunction with the phasic activation of the TA. The preprogrammed deactivation of the SM and ST muscles represents the early phase of the central command to switch from the standing to the squatting posture.

Adult↗