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Biomedical subjects

P Boon

Publications and source records attributed to P Boon.

At least 73 records · Page 4Linked to original sources
PubMed1995

EM-tomography of section collapse, a non-linear phenomenon.

Using back projection for reconstruction and tilt series of Epon or Lowicryl embedded and sectioned material, we demonstrated: (1) a reduction in thickness of 50% for Epon and 80% for Lowicryl sections, and (2) a non-uniform density distribution along the electron-optical axis in sections. The highest density was found at the vacuum exposed side of the section. The formvar side of the section showed a similar increase in density, but not to the same extent. Minimalization of electron exposure, even without pre-exposure, did not affect the reconstructed thickness, nor did it affect the non-uniform density distribution. However, parallax measurements showed that at 150K, collapse of Epon sections does not take place. For EM-tomography of plastic embedded material our findings imply that at the top and bottom portion of the sections the dimensions of the reconstructed structures are distorted, but that in the middle portion the dimensions are reliably retained.

Acrylic Resins↗
PubMed1995

Interictal and ictal dipole modelling in patients with refractory partial epilepsy.

Fifteen patients (7 men, 8 women) with mean age of 34 years and mean duration of refractory partial seizures of 17 years were included in a presurgical evaluation protocol. Neuroimaging (CAT, 1.5 T MR) demonstrated intracranial structural lesions (space-occupying: n = 9; atrophic: n = 6) and video-EEG monitoring showed complex partial seizures in all patients. Four patients underwent additional intracranial EEG monitoring that demonstrated hippocampal seizure onset in all. Voltage topography and spatiotemporal dipole mapping of interictal epileptic discharges revealed two distinct distinct dipole types. Patients with lesions in the medial (and lateral) temporal lobe uniformly presented with a negative voltage field with a steep gradient over the inferior temporal area and a stable, combined dipole that consisted of a radial and a tangential component with a high degree of elevation relative to the axial plane. Patients with extratemporal lesions had a more diffuse, less dipolar voltage field and a corresponding dipole which was less stable and had a predominant radial component. Dipole modelling of epochs of early ictal discharges revealed a striking correspondence with the interictal findings in individual patients. Interictal spike voltage topography and corresponding dipole mapping provided additional and reliable information that was relevant in surgical candidates for refractory partial epilepsy, e.g. by suggesting in some patients that the medial temporal structures were not primarily involved. Ictal dipole modelling revealed concordant results with interictal data. It shows promising but needs further confirmation and validation in a larger patient population with intracranial EEG recordings. Despite intrinsic limitations, spike voltage topography and dipole mapping contributes to a better localisation of the underlying brain source of epileptic discharges.

Adolescent↗
PubMed1994

Neurotropin treatment of brain edema accompanying acute middle cerebral artery infarction.

The present study is a second analysis of a randomized double-blind controlled trial on the efficacy of neurotropin on brain edema in a subgroup of patients with acute middle cerebral artery infarct treated within 24 hours. Neurotropin is a biological extract that specifically inhibits the release of bradykinin. The mortality rate was significantly lower in the neurotropin than in the placebo group. In the surviving patients the neurological deficit decreased to a significantly greater extent by neurotropin therapy after 15 days. The CT scan findings in the brain of the neurotropin-treated patients demonstrated a significant reduction in the size of the infarct and of the edematous area. Patients with middle cerebral artery infarct, which is prone to give rise to fatal intracranial hypertension, may derive great benefit from treatment of brain edema with neurotropin.

Aged↗
PubMed1994

Clinical and neurophysiological correlations in patients with refractory partial epilepsy and intracranial structural lesions.

Twenty patients (13 males, 7 females), who presented with refractory partial epilepsy and a CT and/or MR detected intracranial intra-axial structural lesion were admitted to the University of Gent Epilepsy Monitoring Unit. Mean duration of the epilepsy was 17 years (2-47 years). All patients were enrolled in a comprehensive presurgical protocol including neurological examination, video-scalp-EEG monitoring with prolonged interictal and ictal recording, neuropsychological assessment and positron emission tomography (PET). Intracranial EEG monitoring was performed in 5 patients in whom discrepancies between different tests were found during the non-invasive evaluation. Clinical neurological examination was normal in 16 patients; 4 patients had a mild contralateral hemiparesis. Lesions were mainly located in the temporal lobe (55%). Most patients presented with complex partial seizures (90%). Clinical seizure characteristics correlated well with the lesion location in 55% of patients. Interictal EEG showed focal epileptic activity and focal slowing in respectively 85% and 30% of patients. Interictal EEG lateralization was congruent with the side of the lesion in 17 patients (85%). Interictal EEG localization was congruent with the lobe of the lesion in 13 patients (65%). Ictal EEG lateralized correctly in 14 patients (70%) and localized correctly in 10 patients (50%). Neuropsychological assessment lateralized and localized congruently in respectively 8/17 (47%) and 7/17 (41%) of patients. Interictal PET showed focal interictal hypometabolism, congruent with the lesion, in 13/16 (81%) of patients. Intracranial EEG was congruent with the lesion location in 3 patients but non-congruent in 2 patients. All patients underwent surgical procedures: average follow-up was 14 months (6-24 months). Complete surgical removal of the lesion with free margins resulted in a more than 90% reduction of seizures without postoperative neurological deficit in 12/13 patients.

Adolescent↗
PubMed1994

Haemodilution study in major orthopaedic surgery experience as a technique of blood conservation.

Haemodilution and auto-transfusion were carried out in 103 consecutive patients having major orthopaedic surgery. The records of 99 patients were available for retrospective assessment of this technique. Fifty-six per cent of the patients did not require any homologous blood transfusion. Homologous blood transfusion was given to 44% of the patients, who used up 99 units of blood in their entire hospital stay. There was no morbidity such as transfusion reaction, infection, decrease in platelets or re-operation for bleeding associated with the procedure, although there was one death secondary to myocardial infarction. This technique offered an alternative method to reduce the use of homologous blood transfusion in major orthopaedic operations.

Adolescent↗
PubMed1994

Long-term video-EEG monitoring revisited. The value of interictal and ictal video-EEG recording, a follow-up study.

Between October 1990 and November 1992, 100 patients were monitored at the University of Gent Epilepsy Monitoring Unit. Sixty-three patients were referred for refractory epilepsy, 38 of whom were entered in the epilepsy surgery protocol. Thirty-seven patients were evaluated for the diagnosis of attacks of uncertain origin. Average duration of monitoring was 3.5 days (2-15 days). Prolonged interictal EEG was recorded in all patients. Ictal EEG was obtained in 63 patients; the average number of recorded episodes was 3 (1-15). Pre-monitoring tentative seizure diagnosis was available in 81 patients, 59 of whom had clinical attacks. Premonitoring diagnosis was confirmed in 31 patients and revised in 28 patients. As a result of the monitoring session, anticonvulsant medication was started in 10 patients, changed in 47, stopped in 5 and left unchanged in 23 patients. Twelve patients underwent surgery. Average follow-up after monitoring was 17 months (4-30 months). Four patients were lost to follow-up; 2 patients died of an underlying disease. In the nonsurgical group (85 patients), 60 patients became seizure-free or experienced significant reduction in seizure frequency. Outcome was unrelated to the availability of ictal recording. While prolonged interictal EEG monitoring is mandatory in the successful management of patients with refractory epilepsy, ictal video-EEG monitoring is very helpful but not indispensable, except in patients enrolled for epilepsy surgery or suspected of having pseudoseizures.

Adolescent↗
PubMed1994

Comparison of cerebral haemodynamic and oxygen metabolic changes due to cavernous angiomas and arteriovenous malformations of the brain. A positron emission tomography study.

The cerebral haemodynamic and metabolic changes due to cavernous angiomas in three patients and to arteriovenous malformations in four patients were compared by positron emission tomography, using the steady state technique with 15O. In the brains with a cavernous angioma no important changes in blood flow were observed. Only a decreased oxygen consumption was present in the cortex supplied by the arterial branches of the angioma, most probably related to neuronal deafferentation. In the four cases of arteriovenous malformation cerebral blood flow was significantly increased in the territory of the feeding vessels of the angioma. In the two huge ones the oxygen extraction rate was increased in the other vascular areas remote from the supply territory of the angioma, indicating chronic ischaemia. The present study confirms that chronic vascular steal phenomena can occur in large arteriovenous malformations, while cavernous angiomas do not induce important haemodynamic changes.

Adult↗
PubMed1993

A positron emission tomography study of patients with acute carbon monoxide poisoning treated by hyperbaric oxygen.

Seven patients with an acute and severe carbon monoxide intoxication were treated with hyperbaric oxygen and underwent a positron emission tomographic examination 2-5 days after the acute event. Although the final clinical outcome was good in all patients, ischaemic changes were observed. Three patients with temporary sequelae after hyperbaric oxygen treatment showed the most severe changes, mainly in striatum and thalamus. Although positron emission tomographic examination cannot predict the final outcome, it can show the regions at risk for development of late complications following carbon monoxide poisoning.

Adult↗
PubMed1992

Brain abscess after esophageal dilatation for stenosis.

The case is presented of a 28-year-old female with a brain abscess after esophageal dilatation for stricture, secondary to an acute necrotizing esophagitis. Other causes of brain abscess were excluded. To our knowledge this is the first documented case of brain abscess after dilatation for esophageal stricture in adult life. Some reports in the pediatric literature have been published previously.

Adult↗
PubMed1991

Controllable and uncontrollable footshock and monoaminergic activity in the frontal cortex of male and female rats.

Effects of controllable and uncontrollable footshock on monoaminergic activity in the frontal cortex and plasma corticosterone levels were studied in male and female rats. Subjects were exposed to a shuttle-box procedure for a period of either 30 min (60 shocks) or 90 min (180 shocks). A shuttle response ended shock presentation for escape subjects, whereas their yoked, same-sex, counterparts were unable to escape from shock presentation. A third group was exposed to the experimental environment, but did not receive any shocks. Concentrations of noradrenaline, serotonin and dopamine and their major metabolites were measured in the frontal cortex by high performance liquid chromatography with electrochemical detection. Plasma corticosterone was measured by radioimmunoassay. Results of this experiment show that: (1) exposure to the experimental environment without shock already increased the activity of all 3 transmitter systems. In particular, serotonin was very responsive to mere confinement to the shuttle-box. Changes induced by exposure to the experimental environment were similar for males and females. (2) Presentation of footshocks further increased transmitter activity. The activation of noradrenaline and dopamine was larger after uncontrollable shock than after controllable shock. Moreover, uncontrollable shock resulted in higher serotonin levels than controllable shock. (3) Sex-dependent effects of controllability were found for noradrenaline and dopamine, but not for serotonin. Differences in catecholaminergic activity between controllable and uncontrollable shock were larger in females than in males. (4) In both males and females, corticosterone levels in plasma were increased by exposure to the experimental environment. A further elevation was found in response to footshock presentation, which was independent of the controllability of shock.

Animals↗
PubMed1991

A carbohydrate-directed heterobifunctional cross-linking reagent for the synthesis of immunoconjugates.

A novel, highly water-soluble, heterobifunctional cross-linking reagent, S-(2-thiopyridyl)-L-cysteine hydrazide (TPCH), was synthesized which contains a hydrazide moiety for coupling to aldehyde groups generated in the carbohydrate residues of antibodies by mild periodate oxidation, and a pyridyl disulfide moiety for coupling to molecules with a free sulfhydryl group. Since the carbohydrate moieties are distal to the antigen binding region of antibodies, derivatization with this cross-linker minimizes impairment of the antigen binding function. Derivatization of the human monoclonal IgM antibody 16-88 against human colon carcinoma cells with as many as 16 TPCH cross-linker molecules did not impair its antigen binding capability. Using mild oxidation conditions for antibody derivatization, sialic acid residues were identified as attachment sites for the cross-linker molecules, since after desialylation of antibody 16-88 by neuraminidase virtually no cross-linker molecules could be incorporated. Comparison of TPCH with S-(2-thiopyridyl)mercaptopropionic acid hydrazide and S-(2-thiopyridyl)-L-cysteine, two related cross-linking reagents, revealed that TPCH is most efficiently incorporated into periodate-treated antibody. Based on the structural differences of the cross-linkers, the more efficient incorporation of TPCH appears to be a function of the presence of a hydrazide moiety with an adjacent amino group. When three to four molecules of pyridyl disulfide-derivatized barley toxin were coupled to TPCH-derivatized antibody 16-88, the antigen binding capability remained uncompromised. In addition, no significant impairment of toxin activity upon coupling to the antibody was observed. Based on these data, TPCH may be very useful for the synthesis of immuno-conjugates with no or only minimal impairment of the antigen binding function.

Antibodies, Monoclonal↗
PubMed1991

Pancreatic encephalopathy. A case report and review of the literature.

Pancreatic encephalopathy is an uncommon condition found in patients with acute pancreatitis. The present report shows the interest of MRI in the diagnosis of this disorder. Patchy white matter signal abnormalities, resembling plaques seen in multiple sclerosis, may reflect the lesions that are found in the cerebral white matter of post-mortem confirmed cases.

Brain↗
PubMed1990

Villaret's syndrome due to thrombosis of the jugular vein.

Villaret's syndrome is an extremely uncommon condition in which the four lower cranial nerves and the cervical sympathetic are selectively affected. Most cases described thus far have been attributed to either trauma or space-occupying lesions in the posterior retroparotid space. This report demonstrates a first case of "pure" Villaret's syndrome caused by jugular vein thrombosis secondary to previous mastoiditis.

Cerebral Angiography↗
PubMed1990

Corpus callosum agenesis, spastic quadriparesis and irregular lining of the lateral ventricles on CT-scan. A distinct X-linked mental retardation syndrome?

This report gives a description of 4 male patients, two of whom are sibs, two of whom are uncle and cousin. They appear to have psychomotor retardation, spastic quadriparesis and on CT (partial) agencies of the corpus callosum, and irregular lining of the lateral ventricles, without craniofacial abnormalities or seizures. Although the mode of inheritance of agenesis of the corpus callosum is still difficult to establish, in these 4 male patients an X-linked recessive inheritance is the most likely mode. A review of the literature with concern to the heredity of agenesis of the corpus callosum is presented. The clinical and neurological findings in the present four male patients allow for the delineation of a new X-linked mental retardation syndrome.

Adult↗
PubMed1988

Sex differences in passive avoidance depend on the integrity of the central serotonergic system.

Effects of the neurotoxin para-chloroamphetamine (PCA) on sex differences in passive avoidance were studied. Seven days prior to passive avoidance training and testing, male and female rats were injected with PCA (5 mg/kg) or physiological saline (SAL). Treatment effects on brain monoamines levels were evaluated in brains collected shortly after the passive avoidance test. Compared to SAL-treated control groups PCA severely reduced both serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA) in the frontal cortex of males and females. Levels of dopamine (DA) and homovanillic acid (HVA) in the frontal cortex were not affected. These data are indicative of a strong and selective depression of the central 5-HT activity. PCA- and SAL-treated male and female rats were trained and tested in a two-compartment step-through passive avoidance apparatus. Sex differences in passive avoidance were clearly observed in the SAL-treated control groups; a higher number of males did not enter either compartment within the maximum test duration. After PCA treatment sex differences in passive avoidance were abolished, mainly resulting from an increase in the number of PCA-males reentering. Irrespective of sex or treatment subjects seldom failed to choose the nonshock compartment when entering during the passive avoidance test, indicating that disturbance of memory or learning cannot explain for the present results. Rather, the data are discussed in terms of a sex-specific role of central 5-HT in punishment-induced behavioral suppression.

Animals↗