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Biomedical subjects

F Chagneau

Publications and source records attributed to F Chagneau.

12 recordsLinked to original sources
PubMed2002

[Evaluation of pendulum testing of spasticity].

OBJECTIVES: To identify valid measurements of spasticity derived from the pendulum test of the leg in a representative population of spastic patients. MATERIAL AND METHODS: Pendulum testing was performed in 15 spastic and 10 matched healthy subjects. The reflex-mediated torque evoked in quadriceps femoris, as well as muscle mechanical parameters (viscosity and elasticity), were calculated using mathematical modelling. Correlation with the two main measures derived from the pendulum test reported in the literature (the Relaxation Index and the area under the curve) was calculated in order to select the most valid. RESULTS, DISCUSSION: Among mechanical parameters, only viscosity was found to be significantly higher in the spastic group. As expected, the computed integral of the reflex-mediated torque was found to be larger in spastics than in healthy subjects. A significant non-linear (logarithmic) correlation was found between the clinically-assessed muscle spasticity (Ashworth grading) and the computed reflex-mediated torque, emphasising the non-linear behaviour of this scale. Among measurements derived from the pendulum test which are proposed in the literature for routine estimation of spasticity, the Relaxation Index exhibited an unsuitable U-shaped pattern of variation with increasing reflex-mediated torque. On the opposite, the area under the curve revealed a linear regression, which is more convenient for routine estimation of spasticity. CONCLUSION: The pendulum test of the leg is a simple technique for the assessment of spastic hypertonia. However, the measurement generally used in the literature (the Relaxation Index) exhibits serious limitations, and would benefit to be replaced by more valid measures, such as the area under the goniometric curve, especially for the assessment of therapeutics.

Adult↗
PubMed2001

A comprehensive model of spastic hypertonia derived from the pendulum test of the leg.

We propose a comprehensive model of spastic hypertonia based on clinical neurophysiology and validated using experimental data obtained from the pendulum test of the leg in 8 healthy volunteers and 15 spastic patients. This nonlinear computational model includes mechanical parameters and a stretch reflex representation involving three neural parameters: a threshold coefficient, the gain of the stretch reflex, and a time lag accounting for the reflex loop latency and the electromechanical coupling delay. Variation of the threshold coefficient alone allowed an overall reproduction of experimental data obtained from spastic and healthy subjects. We propose that this parameter could represent the supraspinal drive, supposed to be preserved in control subjects and decreased in spastic patients. No subsequent variation of the reflex gain was required to simulate spastic traces. Adjustment of the time lag influenced the duration of the swinging phase and oscillatory phenomena possibly occurring during the pendulum test. It could be related to the involvement of either short- or long-latency stretch reflex loops. With respect to current neurophysiological concepts of motor control, this modeling approach may help in understanding mechanisms underlying spastic hypertonia, and in predicting the clinical effect of antispasticity agents.

Adult↗
PubMed2001

Impact of torsional and bending inertia on root canal instruments.

The laws of applied mechanics can be used to analyze and predict the behavior of mechanical parts subjected to strain and distortion, such as endodontic instruments. Simple mathematical formulas can be used to represent the impact of torsional and bending inertias on stresses in endodontic instruments being used in root canals. The boundary integral method was applied to two theoretical models with the same diameters but different cross-sections to evaluate quantitatively and qualitatively the stresses produced in orthogonal cross-sections. The results confirmed the mathematical deduction concerning the impact of torsional and bending stresses. The results indicate that clinical protocols based on the torsional and bending properties of endodontic instruments must be strictly followed, and endodontic instrument manufacturers must adopt standardized criteria for describing these properties.

Dental Instruments↗
PubMed2000

Impact of two theoretical cross-sections on torsional and bending stresses of nickel-titanium root canal instrument models.

The use of nickel-titanium in the manufacture of endodontic instruments has given rise to continuous-rotation canal preparation techniques. These techniques involve unidirectional torque, meaning that files are under constant stress and strain when operating. The study presented herein compares torsional and bending stresses in triple U and triple helix models. This was done by applying the boundary integral method to theoretical cylindrical models. The two theoretical models underwent very different torsional stresses, both in terms of intensity and distribution. Bending stresses were much more similar, but to obtain the same curvature, bending moments had to be different. The results of the mathematical calculations indicated that triple U and triple helix instruments should be used for different operating procedures.

Dental High-Speed Equipment↗
PubMed2000

[Changes in the enamel after in vitro debonding of brackets bonded with a modified glass ionomer cement].

The aim of this study was to assess the incidence on the enamel behavior of debonding two types of orthodontic brackets, bonded with two different adhesives. Ninety recently extracted human premolars were bonded with two types of brackets (30 Minitrim and 60 Discovery). Two bonding protocols were used. The first one consisted in bonding 30 Minitrim and 30 Discovery brackets on etched and dried enamel surfaces with No Mix orthodontic resin. The second one consisted in bonding 30 Discovery brackets on unetched and wet enamel surfaces with a modified glass ionomer cement, Fuji Ortho LC. Teeth were stored in hydrated ambiance at 37 degrees C for 7 days before debonding. A LLOYD (LR 30K) testing machine was used to evaluate the orthogonal tensile bond strength. The debonded base brackets were examined with a scanning electron microscope (JEOL JSM 6400) and qualitatively analyzed with an OXFORD-LINK-ISIS to assess the site of bond failure and the enamel detachments. An Enamel Detachment Index (EDI) was defined. The results showed that the types of orthodontics brackets and adhesives influenced the bond strength and the enamel detachment. The Discovery/No Mix couple presented higher bond strength (214.9 N) than observed with the Discovery/Fuji Ortho LC (98.5 N) or the Minitrim/No Mix (82.3 N) couples. The surfaces of enamel detachment were insignificant and not extended for all brackets. Nevertheless, the Discovery/No Mix couple presented 42% of an EDI score of 1, compared to the Discovery/Fuji Ortho LC and Minitrim/No Mix couples which presented, respectively, 8% an 20% of an EDI score of 1. The laser sculpted base (Discovery) bonded on unetched and wet enamel surfaces with the modified glass ionomer cement (Fuji Ortho LC) offers a good resistance to debonding forces and preserve enamel integrity.

Acid Etching, Dental↗
PubMed1996

Effects of dimethylformamide on in vivo fatigue and metabolism in rat skeletal muscle measured by 31P-NMR.

Dimethylformamide (DMF) is widely used as an industrial solvent in spite of well-established hepatotoxicity and adverse effects on in vitro muscle contractility. The doses used in the studies describing these effects were higher than the doses required to solubilize drugs to be injected at very low levels and the potential effects of DMF at very low levels has not yet been explored. The goal of this work was to study the effects of an acute, low dose of DMF (3 mu/100 g body weight, administered i.p.) on mechanical parameters and energy metabolism of contracting rat skeletal muscle. Metabolic changes were followed by 31P nuclear magnetic resonance spectroscopy. Tension was significantly lower during the fatigue test in DMF-treated rats than in controls. Phosphomonoesters and inorganic phosphorus level were lower, and intracellular pH was higher in DMF-treated rats than in controls, showing that energy metabolism was activated to a lesser degree, in relation with the lower mechanical performance, after DMF. Skeletal muscle is a target organ for dimethylformamide which has a major effect on muscle contractility by decreasing the tension developed. The effects of DMF suggest that it is unsuitable for use as a drug vehicle for in vivo injections, even at a very low nonhepatotoxic doses.

Animals↗
PubMed1992

Stroboscopic computerized determination of humeral rotation in overarm throwing.

Analysis of the final phase of the overarm handball throw was carried out by a microcomputerized treatment of photographic images taken simultaneously in two grid layouts. Reflective stickers on the joints of the throwing arm (shoulder, elbow, wrist) allowed the coordinates of these three points to be measured against a reference on the wall. Using a mathematical treatment and Euler matrices, the movement could be studied in space. The results confirmed that humeral rotation occurs during the overarm handball throw. Initial external rotation was immediately followed with internal rotation about 40 ms before ball release.

Adolescent↗
PubMed1992

[Early weight-bearing after osteosynthesis by THS hip screw in cervico-trochanteric fractures].

A second generation hip screw was designed in the laboratory to allow unlimited immediate weight-bearing in elderly patients with cervico-trochanteric fractures. The use of this device in 300 operated patients demonstrated that it provided the same capacity for weight-bearing as total hip prostheses, but with a lower morbidity and better and longer lasting functional results. Thus, in patients with a mean age of 77 years, one half of whom suffered from an unstable fracture: the operation was minimally traumatic (reduction on an orthopaedic table, no surgical access to the fracture site, operating time less than one hour); complications were consequently rare (no deep sepsis, no dislocation) in contrast with 5 to 10% of deep sepsis or dislocation with prostheses; early unlimited weight-bearing was permitted by the 5th day in every case and was achieved by the 10th day in more than 80% of cases (30% of whom were able to walk unassisted with crutches); an essential point, the design of the material prevented dismantling on weight-bearing and preserved the morphology of the hip (telescoping of the fracture site never exceeded 20 mm, mean:11 mm). Consolidation was obtained in every case by 6 to 8 weeks. The mortality at 3 months was identical to that observed with prostheses (18%, related to physiological age). The length of hospital stay and the duration of rehabilitation were considerably shortened, as 37% of patients returned to their previous residence by the 45th postoperative day. This resulted in a marked saving in medical costs for each patient (as patients previously returned home after an average of 145 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Phosphocreatine and pH recovery without restoration of mechanical function during prolonged activity of rat gastrocnemius muscle: an in vivo 31P NMR study.

Metabolic impairment in skeletal muscle was suggested to be involved in the development of local mechanical fatigue but until now results have dealt with short activity periods whereas little data on exhaustive and prolonged exercises are available. Stimulations of rat leg muscle lasting 45 min were induced by tetanic trains delivered via sciatic nerve at five different rhythms. Energy metabolism of the stimulated gastrocnemius muscle was followed by 31P NMR spectroscopy using surface coil while mechanical function was recorded. Our data showed a decrease in the force level to very low values a few minutes after exercise onset. This mechanical impairment only induced a transient metabolic failure followed by rapid restoration of high phosphocreatine (PCr) values and intracellular pH, without mechanical recovery. In addition, at the end of exercise, the PCr content was proportional to the fatigue level. As these experiments could not have impaired neuromuscular junction, the data would indicate that fatigue was maintained by a mechanism which does not appear to depend directly on muscle cell energy stores.

Adenosine Triphosphate↗
PubMed1987

[Weight-bearing early after osteosynthesis of the femoral neck by nail-plate (100 cases)].

One hundred trochanteric or transcervical fractures, 64 of which were in patients more than 75 years old, were treated by internal fixation with a THS nail-plate. This device is characterised by a better bending strength than a one-piece nail-plate and a design which limits the risk of displacement of the screw in the head so that immediate weight-bearing can be allowed. Weight was borne on the limb in 81 cases at the tenth post-operative day. It did not improve the mortality, there being 17 deaths by the third month but it greatly helped post-operative care and rehabilitation without producing any additional complications. As a result, 43 per cent of patients could return home by the 45th post-operative day and 74 per cent had recovered their previous level of autonomy within three months of operation. There were only four mechanical complications, all in transcervical fractures: one crack fracture in the femoral head and three displacements following inadequate reduction, treated by prosthetic replacement. The follow-up of 80 patients at three months showed that consolidation always developed between the 45th and 90th day with full weight-bearing and a stable radiological picture. There was no intra-articular penetration or bending of the screw and no break-out of the implant. Whilst it is a definite advance in the treatment of trochanteric fractures, a longer follow-up is needed to determine its place compared with prostheses in transcervical fractures.

Aged↗