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Biomedical subjects

S Robin

Publications and source records attributed to S Robin.

32 records · Page 2Linked to original sources
PubMed2000

Implantable selective stimulator to improve bladder voiding: design and chronic experiments in dogs.

Among the treatments to enhance the bladder voiding, the sacral roots neurostimulation is one of the most promising techniques. The electrostimulation of sacral nerves provokes a simultaneous contraction of the detrusor muscle as well as the external urethral sphincter (EUS). A new simplified-architecture implantable stimulator with its wireless controller have been designed to investigate high-frequency inhibition stimulation strategies. This innovative technique based on high-frequency inhibition reduces sphincter activity during stimulation. Low-frequency current pulses also applied to the sacral roots induces contraction of the detrusor muscle resulting in low pressure voiding. Chronic experiments were carried out on ten male mongrel paraplegic dogs. One cuff electrode was implanted along with each stimulator for eight months. The animals were stimulated twice a day using the prototypes of our implantable selective stimulator while voided and residual urine volume were measured during the procedure. These experiments revealed that the proposed stimulation strategy enhances bladder voiding by more than 50% in comparison with low-frequency only stimulation. The residual urine volume was reduced to an average of 9% and low pressure micturition was achieved as shown by weekly cystourethrogram.

Animals↗
PubMed1999

A model for thermograms.

Thermograms are curves resulting from thermal analysis and are of great interest in the study of various food and biological products physical properties. A method to separate underlying peaks is proposed, and statistical properties of estimates for some characteristic parameters are derived. The total number of peaks can be estimated with a sequential analysis of the residual plots. For each new peak, a statistical criterion is proposed to check whether it is significantly different from the noise of the recording. As an example, the method is applied to a summer milk fat fusion thermogram.

Animals↗
PubMed1998

Implantable stimulation system dedicated for neural selective stimulation.

A functional electrical stimulation system is presented, which is dedicated for the selective neural stimulation of the bladder. The proposed system is composed of an internal stimulator (implant) and an external controller. The system is used to produce low-pressure voiding of the bladder in spinal cord injured patients. The implant is powered and operated by the external controller via radio-frequency electromagnetic coupling. All stimulation parameters are chosen externally using the controller and are sent to the implant, which produces the desired stimuli. These stimuli are applied directly to the S2 nerve which is linked to the sphincter and bladder muscles. A high-frequency signal is used to inhibit the contraction of the sphincter muscle, and low-frequency pulses stimulate the bladder muscle (the detrusor). Dedicated computer software is used by the physician to select the optimal parameters for each patient and to activate the implant through a parallel port interface with built-in transmitter. The parameters are then transferred to a hand-held controller which is used by the technical staff and by the patients themselves. Acute studies have been performed to validate the selective stimulation strategy, and chronic experimentation is currently underway in dogs.

Electric Stimulation Therapy↗
PubMed1998

Reduction of bladder outlet resistance by selective sacral root stimulation using high-frequency blockade in dogs: an acute study.

Detrusor-sphincter dyssynergia is a main problem in supra-sacral spinal cord injured patients. The problem of high pressure voiding is also encountered in most electrically induced micturition because of the mixed somatic and autonomic fiber components of the ventral sacral root. We studied the effect of selective high-frequency blockade at the sacral nerve root in an acute spinalized canine model to prevent the deleterious consequences associated with the elevated bladder outlet resistance. A new functional electrical stimulation system which can generate one signal composed of two independent adjustable current waveforms delivered via a single bipolar electrode was used in 11 dogs. The selectivity resulted from the inhibition of the sphincteric somatic innervation by a high frequency pulse while the low frequency stimuli activated the bladder autonomic fibers. Bladder and urethral pressure as well as electromyograms of external urethral sphincter were recorded to determine whether selective high-frequency blockade occurred. Our experiments showed that we were able to achieve selective blockade of the external urethral sphincter during the simultaneous detrusor stimulation, thus obtaining a more physiologic voiding.

Animals↗
PubMed1997

Magnesium deficiency increases vasoconstrictor activity without affecting blood pressure of aged spontaneously hypertensive rats.

This study examines the effect of long-term magnesium-deficient diet on blood pressure and vascular reactivity in aged spontaneously hypertensive rats (SHR) with established hypertension. Thirty-one-week old male SHR received control (0.15 per cent magnesium) and magnesium-deficient (0.015 per cent magnesium) diets for 30 weeks. Systolic blood pressure was measured by tail-cuff method. At the end of the study, the heart, aorta and kidney were collected to measure total magnesium and calcium concentrations; the ex vivo effects of the different magnesium diets on vascular reactivity were examined in isolated aorta and in the isolated perfused mesenteric vascular bed. After 30 weeks, magnesium deficiency had no effect on systolic blood pressure and heart rate of SHR. The tissue concentrations of total magnesium in aorta, heart and kidney were not modified by magnesium deficient diet. Total calcium concentration was significantly higher in the heart of the SHR fed the magnesium-deficient diet (p < 0.01). The aortic responsiveness to contractile agents norepinephrine, endothelin-1, CaCl2 and KCl, and to vasorelaxant agents acetylcholine and isoproterenol were not modified by magnesium deficiency. The vasoconstrictor activity to norepinephrine, CaCl2 and KCl was significantly enhanced in the isolated perfused mesenteric vascular bed of magnesium-deficient SHR (p < 0.05). In conclusion, magnesium deficient diet fails to elevate blood pressure in aged SHR maintained on deficiency for 30 weeks despite an enhanced ex vivo vasoconstrictor activity.

Aging↗
PubMed1997

Peripheral neurological involvement as the first manifestation of spina bifida occulta.

A 42-year-old male was admitted for right-sided sciatica with asymptomatic septic arthritis of the fifth toe of the right foot. He had a history of active chronic hepatitis C and septic arthritis of the fifth toe of the left foot. His symptoms included low back pain, poorly systematized right-sided sciatica, impairment of all forms of sensation in both lower limbs, absent ankle jerks, episodes of urinary retention, urgency, and painless septic arthritis of the fifth toe of the right foot. Roentgenograms showed a spina bifida occulta of L5 and a bony erosin in the distal interphalangeal joint of the right fifth toe. Distal denervation in the territory of L5 was demonstrated by the electromyographic study. Magnetic resonance imaging disclosed an area of high signal on T1 and T2 images, located within the spinal canal opposite L4 and suggestive of an intraspinal lipoma, as well as tethering of the spinal cord in an abnormally distal position. Antimicrobial therapy was effective in ensuring resolution of the infectious arthritis. The low back pain and sciatica responded to nonsteroidal antiinflammatory drug therapy and did not recur subsequently. Many patients who have roentgenograms taken to evaluate low back pain and sciatica are found to have a spina bifida occulta. This complex birth defect involving the spinal canal, meninges and spinal cord or cauda equina can cause neurologic and/or urinary symptoms in adulthood. Magnetic resonance imaging is essential in this situation to evaluate the spinal cord and to look for an intraspinal lipoma.

Adult↗
PubMed1996

Effects of long-term high manganese intake on magnesium metabolism in rats.

The effects of long-term high manganese intake on the magnesium metabolism in rats were studied. One group of rats was fed a normal diet and the treated group received a normal diet and distilled water containing 2 g/litre manganese (as MnCl2). Metabolic studies showed that after 11 weeks of treatment, manganese supplementation modified magnesium metabolism by increasing urinary magnesium excretion and decreasing magnesium balance.

Animals↗
PubMed1994

Influence of geometrical factors on the behavior of lumbar spine segments: a finite element analysis.

The main objective of this study was the assessment of the influence of geometrical factors on the behavior of lumbar segments. To this end, a three-dimensional, parameterized, finite element model of the lumbar spine was used, and the results were compared with inhouse experimental results and with the few published experimental results available concerning either the geometry of the tested samples or the differences observed at different vertebral levels. Furthermore, in order to appreciate the relative importance of the geometry, the influence of the variation of some other parameters was studied, such as the orientation of the facet joints, the gap between the articular processes, and the Young's modulus of the disk fibers. As a first approach, a series of computations was carried out in order to evaluate the role of geometry in the mechanical behavior differences observed at different levels. It has been found that geometrical factors do exert a noticeable influence on the behavior of the spine, especially those which interfere with the dimensions of the intervertebral disk.

Biomechanical Phenomena↗
PubMed1993

A biomechanical analysis of short segment spinal fixation using a three-dimensional geometric and mechanical model.

Vertebral stabilization using spinal fixation devices is a widely used technique. A three-dimensional geometric and mechanical finite element model has been used as a simulation tool for the evaluation of the mechanical behavior of spinal devices. The geometry of lumbar vertebrae was parameterized, which allows the construction of the geometric model for a given lumbar segment from the digitization of two roentgenographs. This procedure was used to construct a finite element model for a three-vertebra segment with simulation of fractures in the middle vertebra, and with simulation of a restoration using an osteosynthesis device, implemented in a frame fashion with four screws and two rods linked by two transverse rods, and/or an anterior bone graft. Compression force and torsion moment were considered, and different cases were investigated, by varying the severity of the fracture, the geometric characteristics of the device, and the mechanical characteristics of the material joining the two intact vertebral bodies. Results were analyzed considering the mobility of the vertebral segment, which indicates the ability of the restoration system to stabilize the vertebral segment, and considering the forces and moments distribution in the device, which gives information on part of the forces that pass through the device in each situation. Results show that maximum values of forces and moments in the device are more important in compression than in torsion. Adding an anterior bone graft has an effect mainly for compression, whereas in torsion its effect is negligible. For a rigid fixation device, no significant difference was found between different fracture models, indicating that the posterior arch does not play an important role for an instrumented segment. For compression, a rigid posterior wall, or the presence of a bone graft, reduces greatly the mobility of the instrumented segment. For torsion, suppressing the two transverse rods in the device greatly increases the mobility of the instrumented segment. Using a finite element model of a lumbar vertebral segment appears to be an interesting tool to analyze the behavior of an instrumented spine and to compare between different stabilization systems.

Biomechanical Phenomena↗
PubMed1992

Three-dimensional geometrical and mechanical modelling of the lumbar spine.

The main objective of this study is to design a three-dimensional geometrical and mechanical finite element model of the lumbar spine. The model's geometry is constructed using six parameters per vertebra. These parameters are digitized from two X-rays (anterio-posterior and lateral), thus yielding an individualized model which can be arrived at from the radiographs of a tested specimen. This procedure makes the model validation easier, as geometry is generally a factor of dispersion in experimental results. The geometrical reconstruction, in the form of a finite elements mesh, was effected for the whole lumbar spine. The global coherence of the model was verified.

Humans↗
PubMed1991

Tuberculosis, poverty, and "compliance": lessons from rural Haiti.

Tuberculosis (TB) is the leading cause of death among rural Haitian adults, and TB control in Haiti is widely acknowledged to be a failure. The causes of both the endemicity of TB and the failure of attempts to address it are briefly reviewed before data from a study conducted in rural, central Haiti are presented. Members of one group of patients with active TB were given free medical care; members of a second group were given free care as well as financial aid, incentives to attend a monthly clinic, and aggressive home follow-up by trained village health workers. Comparing the two groups shows significant differences in mortality, sputum positivity after 6 months of treatment, persistent pulmonary symptoms after 1 year of treatment, average amount of weight gained, ability to return to work, and cure rate. The roles of human immunodeficiency virus and cultural factors are also examined. When adequate nutrition and access to free care were assured, drug-dependent and patient-dependent factors were shown to be of secondary importance in determining treatment outcome. Based on these data from a small, community-based TB-control project, the authors conclude that high cure rates can be achieved if the primacy of economic causes of TB is acknowledged and addressed.

Acquired Immunodeficiency Syndrome↗
PubMed1976

Citric acid metabolism in hetero- and homofermentative lactic acid bacteria.

The effect of citrate on production of diacetyl and acetoin by four strains each of heterofermentative and homofermentative lactic acid bacteria capable of utilizing citrate was studied. Acetoin was quantitatively the more important compound. The heterofermentative bacteria produced no acetoin or diacetyl in the absence of citrate, and two strains produced traces of acetoin in its presence. Citrate stimulated the growth rate of the heterofermentative lactobacilli. Acidification of all heterofermentative cultures with citric acid resulted in acetoin production. Destruction of accumulated acetoin appeared to coincide with the disappearance of citrate. All homofermentative bacteria produced more acetoin and diacetyl in the presence of citrate than in its absence. Citrate utilization was begun immediately by the streptococci but was delayed until at least the middle of the exponential phase in the case of the lactobacilli.

Acetoin↗