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Biomedical subjects

M Dujovny

Publications and source records attributed to M Dujovny.

At least 37 records · Page 2Linked to original sources
PubMed1999

Saturable transport of gabapentin at the blood-brain barrier.

Gabapentin readily crosses the blood-brain barrier and concentrates in brain tissue via an active transport process believed to be system-L. Blood-brain barrier system-L has a low K(m), making it particularly susceptible to substrate saturation. The purpose of this study was to determine whether the fraction of gabapentin crossing the blood-brain barrier remains constant over a broad range of doses. Using a rat model, microdialysis techniques were employed to determine if fluctuations in gabapentin concentrations in the brain extracellular fluid (ECF) coincided with proportional changes in plasma concentrations. Area under the concentration-time curve was calculated for plasma (AUCplasma) and brain extracellular fluid (AUCECF). The ratios of AUFECF to AUCplasma (AUCratio) and brain extracellular fluid to midpoint plasma gabapentin concentration for each collection interval (Cratio) were determined to provide indicators of the relative (i.e. fractional) amount of gabapentin crossing the blood-brain barrier. Analysis of the association between AUCECF and AUCplasma using linear regression analysis revealed a small, but significant relationship (r = 0.62; p < 0.01). Although higher AUCECF values were obtained with higher AUCplasma values, changes in AUCECF were less than proportional to observed changes in AUCplasma. Blood-brain barrier saturation of gabapentin transport was evident as the AUCratio decreased with increased AUCplasma. Collectively, these results support a trend towards saturation at higher plasma concentrations of the carrier-mediated transport mechanism of gabapentin through the blood-brain barrier.

Acetates↗
PubMed1999

Temperature distribution produced in brain tissue and other media by a radiofrequency hyperthermia generator.

The temperature distribution produced in living brain tissue by a radiofrequency, Neuro N-50, hyperthermia probe was measured as a function of probe temperature, heating duration, and distance from the heating probe by a sensor containing five thermocouples for durations up to 2 min. Brain sections were examined to determine the effects of heating at various temperatures. It was found that a simple theoretical conductive heat transfer model predicted the steady-state temperature distributions quite well. At distances up to 7.4 mm from the heating probe, a heating time of 20 s was sufficient to produce about 90% of the temperature rise measured at 120 s. The equilibrium temperature at any distance from the center of the probe was a linear function of the reciprocal of this distance. The time constant for heating was approximately 3 s at 0. 95 mm from the heating probe and about 10 s at 7.4 mm for brain tissue, while these values are about 5-20 s in egg white. For a given probe size, higher probe temperatures increased the size of the region of cell death. According to the heat transfer model, the diameter of the region of tissue that attains a given temperature is proportional to the diameter of the probe. The use of probe temperatures up to 90 degrees C would enable an increase in the volume of the region of cell death, or the use of a smaller diameter probe to produce a lesion of a given size.

Animals↗
PubMed1999

Anatomical basis for the lateral approach to the fourth ventricle.

This study focused on the posterior inferior cerebellar artery bifurcation and branching patterns in the fissures around the fourth ventricle. The vertebral arteries in 25 unfixed human cerebellum were cannulated and injected with polyester colored resin. The suboccipital surface of the cerebellum was exposed and the cisterna magna main landmarks localized. The average distance was 12.6 mm between the tonsillovermian notches and 21.8 mm between the inferior tips of the tonsils. The mean vertical distance between these horizontal planes was 14.5 mm. The posterior inferior cerebellar artery was found in the cerebellomedullary fissure in 42 of 50 cerebellar hemispheres, in seven cases the artery was absent and in one it was hypoplastic. The mean outer diameter was 1.8 mm and the average length was 27.9 mm. The posterior inferior cerebellar artery presented four bifurcation point patterns: superomedial, superolateral, inferomedial, and inferolateral. These patterns were characterized into subtypes based on the courses of the vermian and tonsillohemispheric branches. The perforating and choroidal branches originating in these segments were also studied. The mean number of perforating branches per hemisphere was 5.1. The range of the length was 2-10 mm and the range of the outer diameter was 0.1-0.3 mm. An average of 4.6 choroidal arteries originated from the tonsillomedullary and telovelotonsillar segments, a mean of 4 arose from both vermian and tonsillohemispheric branches. This information will facilitate surgical planning in approaching the fourth ventricle as well as the interpretation of cerebellar infarcts in the posterior inferior cerebellar artery area.

Adult↗
PubMed1998

Stereolithography: application to neurosurgery

Computer-aided design (CAD) and computer-aided manufacturing (CAM) by stereolithography are already being widely used in industry for the design and manufacture of new parts and have already shown accuracy in reproducing the desired model. The only shortcoming of this technique is that it can only make one model at a time, a "prototype." It cannot be used for mass production. It is precisely this property, namely making a prototype, that makes it so attractive in reconstructive surgery and implantation of prostheses, where each "part" has to be adapted to the unique anatomy of the patient. It was not until the early nineties that reports of the application of stereolithography to reconstructive surgery appeared in the literature, and even now they are scarce. However, it is a very promising technique, and we think that it is important for physicians to familiarize themselves with this concept.

Journal Article↗
PubMed1998

Failure of cerebral autoregulation in an experimental diffuse brain injury model.

The normal cerebral circulation has the ability to maintain a stable cerebral blood flow over a wide range of cerebral perfusion pressures and this is known as cerebral autoregulation. Autoregulation may be impaired in the injured brain. Closed head injury was induced in 28 Sprague-Dawley rats weighing 400-450 g. Four groups were studied: control and groups, head injured by weight drop from one meter height using 350 g, 400 g and 450 g respectively. CBF was monitored using laser-Doppler flowmetry along with monitoring of ICP and arterial blood pressure. If the correlation coefficient between CBF and CPP was > 0.85 and CPP was within normal range, loss of autoregulation was hypothesized. Loss of autoregulation was seen in all groups of injured rats during first four hours. A statistically significant difference (p = 0.041) was seen in the trequency of loss of autoregulation between injured and control animals. No loss of autoregulation was observed in the control group. In conclusion CBF and CPP provide information about loss of autoregulation in diffuse brain injury. Decrease in CBF and increase of ICP is observed as a result of loss of cerebral autoregulation. Knowledge of loss of autoregulation could help in the management of head injured patients.

Animals↗
PubMed1998

Bipolar coagulation in neurosurgery.

Coagulation is an essential part of a surgical procedure, especially in neurosurgery. Beginning in the early years of this century, various techniques have been used to control bleeding at the surgical site. Over the years, these techniques have led to the invention of the bipolar coagulator and its modifications. Prevention of charring and tissue adhesion have been the goals of bipolar coagulator manufacturers all over the world; new techniques and different metallurgical compositions for the forceps have been tried to achieve these results. The NS2000, with its microprocessor-based controlled coagulative sequence, can be a good system for reducing tissue adhesion and charring under desired limits of low output power ranges provided by the system. Comparable results can also be obtained with the Malis CMC III and Synergy Malis systems with irrigation channels. These systems have the additional advantages of providing higher power outputs at lower panel settings and a maximum power output greater than that of NS2000. For neurosurgeons who need the additional option of cutting, the Malis CMC III is the recommended system.

Electrosurgery↗
PubMed1998

Stereolithography for posterior fossa cranioplasty.

Posterior fossa cranioplasty has been suggested for improvement of neurological symptoms following craniectomy. However, there is no particular recommendation in the literature about techniques for prosthesis manufacture and implantation. We report our experience using rapid prototyping technology and stereolithography for pre-surgical implant design and production of cranioplasties.

Case Reports↗
PubMed1998

Head registration techniques for image-guided surgery.

Localization of the pathological structures in relation to the surrounding anatomy and understanding of the surgical anatomy are probably the most important keys to successful neurosurgery. Image-guided surgery is an important tool for understanding an individual's anatomy and for precisely locating the lesion. Head registration is the most important step in image-guided surgery, required by every system in use today, although these systems show great differences. In this study, head registration techniques and user algorithms in 83 image-guided surgery cases were analyzed. Several types of fiducials including skin markers, bone fiducials, and the stereotactic frame were used for registration. Clinical applications, ease of use, and computer-calculated accuracy values for each type were compared. The average accuracy was 1.50 mm. X-spot skin markers are the fiducials most commonly used with CT scan. The stereotactic frame was the most accurate method, with an accuracy of 0.69 mm. Disc-shaped fiducials were used when MRI was the imaging modality; they provided an average accuracy of 2.62 mm. Head registration is an important part of image-guided surgery; the procedure used for registration should be based on the requirements of each individual case. Our results indicated that the stereotactic frame is the most accurate method of registration; however, skin markers provide reasonable accuracy with significant ease of use and patient comfort.

Adult↗
PubMed1998

Transcranial cerebral oximetry in random normal subjects.

Near infrared optical spectroscopy is becoming a useful method for monitoring regional cerebral oxygenation status. The method is simple, reliable and noninvasive and the information which it provides is clinically significant in managing a growing number of neurological ailments. Use of this technique has been described previously by numerous authors. In the present study, regional cerebral oxygen saturation was measured at rest in 94 subjects randomly selected from a diverse population of individuals. This sample consisted of 38 males and 65 females (age range 18-70 years). There were 68 light-skinned individuals and 35 with darker skin comprising various ethnic and cultural backgrounds. Mean regional cerebral hemoglobin oxygen saturation was recorded as 67.14 +/- 8.84%. The association of the man regional cerebral hemoglobin oxygen saturation in various groups of individuals with relationship to their age, race, sex and skin color is examined.

Adolescent↗
PubMed1998

Microsurgical anatomy of the short central artery.

We studied the origin, length, external diameter, disposition, branching patterns and the perforators of short central artery in the circle of Willis in eighty fresh, unfixed cerebral hemispheres (40 brains). We also examined the relationship of the short central artery, the recurrent artery of Heubner, and M1 perforators to the anterior perforated substance, caudate and putamen. The short central artery arises at 5.2 +/- 3.36 mm from the origin of the anterior cerebral artery, hidden and overlapped by the internal carotid artery bifurcation. The recurrent artery of Heubner arises distally to the origin of the short central artery. Four main anatomical variations were found: 1. Presence of short central artery and recurrent artery of Heubner (37.5%). 2. Isolated presence of the short central artery (27.5%). 3. Isolated presence of the recurrent artery of Heubner (21.25%). 4. Absence of short central artery and recurrent artery of Heubner (13.75%). Two different branching patterns were observed: 1. 2-4 straight perforators from the short central artery, perforators from the recurrent artery of Heubner and lenticulostriate from the most medial portion of the M1, in 42 of 80 hemispheres (52.5%). 2. 8-10 perforators from only short central artery in 10 of 80 hemispheres (12.5%) with absent or hypoplastic recurrent artery of Heubner and lenticulostriates from M1 and M2.

Cerebral Cortex↗
PubMed1998

Third ventriculostomy, phase-contrast cine MRI and endoscopic techniques.

Endoscopic third ventriculostomy has become an increasingly popular procedure. This is mainly due to the improvement of the endoscopes. The progress in imaging techniques and Phase-Contrast Cine MRI in particular offers a reliable method of pre-and post-operative assessment of the patients. Two endoscopes, NeuroPEN and Channel Neuroendoscope (Medtronic PS Medical, CA, USA) have been evaluated in our center for third ventriculostomy. These instruments are light, have a good maneuverability and are disposable. The illumination and the quality of the image are excellent. We have performed Phase-Contrast Cine MRI pre-operatively and post-operatively for our patients. It offers a good assessment of the patency of the ventriculostomy and the fluid dynamics of the CSF pathways. Endoscopic third ventriculostomy is the technique of choice for the treatment of obstructive hydrocephalus. This is mainly due to two points: The progress in the endoscopic instrumentation (namely the reduction in size of endoscopes and introduction of disposable models), and the establishment of Phase-Contrast Cine MRI as the gold standard method for the pre- and post-operative evaluation of the CSF dynamics. However, to date, no technique can show the patency of the subarachnoid space, which is the most important predictive factor of surgical outcome.

Endoscopy↗
PubMed1998

Anatomy and embryology of the lateral sellar compartment (cavernous sinus) medial wall.

In order to study the microanatomy of the lateral sellar compartment (cavernous sinus) medial wall, serial histological sections of human fetuses and adults, as well as dissections under operative microscope, were performed. The results were compared to high resolution Magnetic Resonance Images in human, to microdissections and to serial histological sections in adult nonhuman primates (Papio Cynocephalus anubis). We were able to show that the sellar compartment and both lateral sellar osteodural compartments are not separated from each other by a dural wall, but by a more or less dense, interrupted, fibrous tissue which derived from the mesenchyme surrounding the hypophysis, carotid artery, cranial nerves and venous channels. In the human fetus, the previous mentioned structures are located in a unique interperiosteodural space. Histoarchitecture of the superior and lateral wall dura-mater was different from the underlying mesenchyme derived connective tissue and was easily distinguished through histological examination. These findings correspond to MRI data. We conclude that there is no medial dural wall limiting the lateral sellar compartment (cavernous sinus), both parasellar and the hypophyseal compartment should be considered as a unique extradural space. The only dense connective tissue surrounding the pituitary gland is its own glandular capsule and the periosteum.

Adult↗
PubMed1998

A differential response of diffuse brain injury on the concentrations of endothelin and nitric oxide in the plasma and brain regions in rats.

In the present study, we hypothesized that acute diffuse brain injury (DBI) in rats would produce an increase in endothelin-1 (ET-1), a potent vasoconstrictor, and/or nitric oxide (NO), a potent vasodilator, in plasma and brain areas in rats. DBI was induced in anesthetized male Sprague-Dawley rats (350-400 g) using a 350 g weight dropped from 1 meter height impact through a device designed by Marmarou et al., 1994. Blood plasma and brain tissue (cerebral cortex, diencephalon and brain stem) samples were collected for estimation of ET-1 and NO at zero or 6 h from rats (n = 6) subjected to DBI as well as control rats (n = 6), i.e., not subjected to DBI. In a separate group of animals, cerebral blood flow (CBF) was recorded at 0, 5, 10, 15, 30, 60, 120, 240 and 360 min after induction of DBI or sham-DBI. Acute DBI produced a significant decrease in CBF at 120 min after induction of DBI. Plasma levels of ET-1 was found to be significantly increased (from 0.89 +/- 0.09 to 2.09 +/- 0.29 pg ml-1), at 6 h following DBI. DBI produced a significant decrease in the levels of ET-1 in diencephalon (from 70.97 +/- 9.47 to 57.64 +/- 2.65 pg g-1). In contrast to ET-1, DBI produced a significant increase in the concentrations of NO in the diencephalon, cerebral cortex and brain stem at 6 h post DBI. It appears that DBI-induced increase in the levels of NO in brain regions which might be down regulating the synthesis of ET-1 in diencephalon. It is concluded that ET and NO homeostatic mechanisms may play a role in the regional and vascular responses associated with acute DBI.

Analysis of Variance↗
PubMed1998

Cerebral oximetry--techniques.

The use of techniques to measure cerebral oxygen saturation is gradually gaining wide popularity. The main methods available today can mainly be classified as invasive or noninvasive. The invasive technology uses the parenchyma probes, which measure oxygen and biochemical parameters, depending upon the type of probe used. The noninvasive techniques use near infrared spectroscopy for transcranial cerebral oximetry. At present there is no universally accepted indication for the use of either technique but with time and wider use they are expected to become better understood. We discuss our experience and the techniques used in cerebral oximetry.

Brain↗
PubMed1997

Cranioplasty: cosmetic or therapeutic?

Cranioplasty is among the oldest surgical procedures. Trauma, infections, tumors and compression caused by brain edema are some of the reasons for the removal of bone. The indications for cranioplasty after resolution of the primary process that led to the bone defect were never well defined, and many were the "cosmetic" indications for cranioplasty. However, there are many theories suggesting that an underlying physiological alteration may occur which may require the correction of the bone defect; many patients improve after surgery. We discuss the physiopathological basis of the "syndrome of the trephined" and try to achieve a better understanding of the present status of cranioplasty and its possible therapeutic role.

Brain Injuries↗
PubMed1997

Magnetic characteristics of Yaşargil aneurysm clips.

BACKGROUND: Metallic bioimplants are subject to great scrutiny in order to ensure that they are totally harmless to patients. Aneurysm clips are no exception to this rule. Considering the number of aneurysm clips used and their potential for injury, they should be evaluated very meticulously. Determining the magnetic characteristics of these clips is an important part of the evaluation process. In this study, a new method for evaluating magnetism is described and the importance of that information is briefly discussed. METHODS: Twenty Yaşargil aneurysm clips were analyzed using a vibrating sample magnetometer under 1.5 Tesla. This device is highly sensitive, and is capable of measuring the magnetism of small objects. RESULTS: Our measurements showed magnetism of the aneurysm clips ranged from 0.0334-0.1369 electromagnetic units (emu). CONCLUSIONS: Magnetometer measurements and real life tests under magnetic resonance imaging (MRI) have shown that these clips have a very low magnetism and are safe to use in 1.5 Tesla MRI scanners. This study also proves that the vibrating sample magnetometer is a useful device for analyzing the magnetism of aneurysm clips, and their emu values can be used as another industry standard in the production line to increase the safety of these clips.

Aneurysm↗