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Biomedical subjects

A N Guthkelch

Publications and source records attributed to A N Guthkelch.

At least 19 recordsLinked to original sources
PubMed1995

Influence of a 'brain protector' drug 21-amino steroid on the effects of experimental embolic stroke treated by thrombolysis.

This study was designed to evaluate the effects of tissue-type plasminogen activator (tPA) and 21- amino steroid (U74006F) in experimental embolic stroke in rabbits. The size of infarction from embolism was compared to controls with tPA alone, 21-amino steroid alone, and in combination. The middle cerebral artery of the rabbit was embolized by injecting an arterial ('white') thrombus in the right internal carotid artery. The rabbit treatment was 2 mg kg-1 of tissue-type plasminogen activator and/or 3 mg kg-1 of 21 amino steroid started at 2 h post-embolization. The animals were terminated 4 h post-treatment and brains were examined for evidence of ischemia and/or hemorrhage. Administration of tissue-type plasminogen activator and/or 21-amino steroid in the raw data show that there is a tendency for all treatments to reduce the ischemic volume when compared to the control group, also it is evident the standard deviation of these estimates is rather large when compared to the differences between treatments. The results of the analysis of variance shows that the differences expressed are not statistically significant. (No statistical differences were found between the treatment groups and the control group.) The results show that administration of tissue-type plasminogen activator and/or 21 amino steroid at 2 h post-embolization alone or in simultaneous administration does not significantly reduce the volume of infarction. Further studies need to be addressed in regards to the region of viable brain in the peri-infarct area, in reducing the time to treatment.

Animals↗
PubMed1995

Posterior tibial somatosensory evoked potentials a comparative study of responses elicited by transcutaneous and percutaneous stimulation at the popliteal fossa.

Nine healthy volunteers underwent posterior tibial nerve stimulation at the popliteal fossa with recordings of averaged potentials being taken from the lumbar spine and cortex. Stimulation was attempted in all subjects both transcutaneously and percutaneously. A comparison of the responses to the two stimulating methods was made.

Adult↗
PubMed1992

Dorsal root entry zone stimulation for deafferentation pain.

Dorsal root entry zone (DREZ) stimulation was performed in 12 patients with chronic pain syndromes after extensive trials of medical therapy, sympathectomy or peripheral nerve stimulation had failed, with 50% of them obtaining excellent long-term benefit. Evoked potential monitoring to facilitate positioning of electrodes under either general or spinal anesthesia, and postoperatively to explore the mechanism of action, revealed findings distinct from those reported with conventional spinal cord stimulation (SCS). DREZ stimulation may function on a different neurophysiologic basis than conventional SCS, involving intersegmental processing and influencing tract of Lissauer functions or the dorsal horn directly.

Chronic Disease↗
PubMed1992

Influence of tissue plasminogen activator and heparin on cerebral ischemia in a rabbit model.

BACKGROUND AND PURPOSE: The aims of this study were to verify that tissue-type plasminogen activator given either 1 or 2 hours after experimental embolic stroke in rabbits diminishes the volume of resulting ischemic brain and to ascertain the effect of the simultaneous administration of heparin. METHODS: We embolized the middle cerebral artery of rabbits by injecting performed autologous arterial ("white") thrombus into one internal carotid artery. Treatment with 2 mg/kg tissue-type plasminogen activator, alone or in combination with heparin, was commenced either 1 or 2 hours after embolization. The animals were killed 5 hours after treatment commenced, and their brains were examined for evidence of ischemia and hemorrhage. RESULTS: Administration of tissue-type plasminogen activator significantly diminished the size of the resulting brain ischemia. Administration of heparin, with or instead of tissue-type plasminogen activator, did not result in a significant decrease in the volume of cerebral ischemia, but it also did not lead to hemorrhagic transformation of the stroke. CONCLUSIONS: In the rabbit model, administration of tissue-type plasminogen activator within 2 hours diminished the volume of brain rendered acutely ischemic by embolic stroke. Since the simultaneous administration of heparin during this same period did not result in any instances of hemorrhagic transformation, tissue-type plasminogen activator may have some place for use in such circumstances to mitigate a tendency to further embolic or thrombotic events.

Analysis of Variance↗
PubMed1991

Treatment of malignant brain tumors with focused ultrasound hyperthermia and radiation: results of a phase I trial.

Hyperthermia delivered by scanned focused ultrasound was combined with external beam radiation to treat 15 patients with primary malignant tumors of the brain. A preliminary craniectomy was performed to avoid attenuation of the ultrasound beam by the skull, and multiple thermal sensors were employed to ascertain intratumoral temperatures. The target temperature was 42.5 degrees C at the tumor boundary. This was attained at more than one point during every complete treatment, while a mean temperature in excess of 42 degrees C was achieved within the scanned tumor volume during at least 1 treatment in 11 patients. Technical problems and toxicities are described.

Adolescent↗
PubMed1990

Interstitial thermoradiotherapy of brain tumors: preliminary results of a phase I clinical trial.

A Phase I clinical trial has been initiated to determine the feasibility, tolerance, and toxicity of interstitial thermoradiotherapy in the treatment of high-grade supratentorial brain gliomas. Hyperthermia was delivered by means of thermally-regulating ferromagnetic implants afterloaded into stereotactically placed plastic catheters. Heat treatments were given immediately before interstitial irradiation; in addition, five patients received a second heat treatment at the completion of brachytherapy. The desired target temperature for the 60-minute hyperthermia session was between 42 degrees C and 45 degrees C. Following hyperthermia, the catheters were afterloaded with Ir-192, which delivered a variable radiation dose of 14-50 Gy depending on the clinical situation. Interstitial irradiation was supplemented with external beam radiotherapy (40-41.4 Gy) in patients with previously untreated tumors. A total of 14 patients (4 males, 10 females) have been treated to date on this protocol. Eleven of the patients had a diagnosis of glioblastoma multiforme, whereas three had anaplastic astrocytoma. The mean implant volume was 61.5 cm3 (range: 9-119 cm3); the median number of interstitial treatment catheters implanted was 19 (range: 7-33). Continuous temperature monitoring was performed by means of multisensor thermocouple probes inserted in the center as well as in the periphery of the tumor. Of the 175 monitored intratumoral points, 83 (47%) had time-averaged mean temperatures of greater than 42 degrees C, and only 12 sensors (7%) exceeded a temperature of 45 degrees C. Among the 19 heat treatments attempted, there have been four minor acute toxicities, all of which resolved with conservative medical management and one major complication resulting in the demise of a patient. These preliminary results indicate that ferromagnetic implants offer a promising new approach to treating brain tumors with hyperthermia.

Adult↗
PubMed1990

Observations of the posterior tibial nerve SEP of patients requiring extradural spinal surgery.

The cortical potentials evoked by posterior tibial nerve stimulation were examined in a series of 141 hospital patients requiring extradural spinal surgery. One hundred and five patients were neurologically intact, while in 36 some deficit was present. In the intact subjects, the absolute latencies of the main medium-latency peaks (N30, P40, N50, P60) were found to vary with height and age. There were no additional gender-related differences. The latencies of the deficit group were longer than those of the intact group but only marginally useful as a clinical discriminator; their amplitudes were not significantly lower than those of the intact group. A model for variations in SEP latency is suggested.

Age Factors↗
PubMed1987

Effect of low concentration stable xenon on the EEG power spectrum.

The effect on the central nervous system of inhaled stable xenon, at concentrations of 25%, 30% and 35%, was assessed by evaluating changes in power spectra computed on the electroencephalogram. Ten normal adult subjects were studied in a protocol designed as a repeated measures experiment. Synchronous changes in the EEG power spectra were observed with stable xenon inhalation. These changes were equivalent for symmetrical electrode pairs, but the time history of the changes differed depending on the cortical region being measure. This suggests regional effects of stable xenon inhalation on the mechanisms producing the EEG.

Adult↗
PubMed1987

The relationship of the latency of the visual P100 wave to gender and head size.

Six separate recordings of the pattern-reversal visual evoked potentials of 8 male and 8 female healthy adults were made. The average resulting latencies to P100 (LP100) were correlated with head length and circumference as well as with gender and latency to N70 (LN70). There was better correlation of LP100 with head circumference than with gender, and no significant correlation of LP100 with head length or with LN70. Also, using head circumference as a predictor of LP100, the addition of gender to the regression equation did not improve the prediction. These results indicate that a major determinant of differences in LP100 in adults is head size rather than gender. These differences are suggested to be due to differences in the geometry of the head rather than to more general biological differences between males and females.

Adult↗
PubMed1987

Management of high cervical-intracranial internal carotid artery traumatic aneurysms.

The successful surgical management of a patient with a traumatic aneurysm of the internal carotid artery (ICA) at the base of the skull and a second traumatic aneurysm of the ipsilateral superficial temporal artery is described. EC-IC bypass was not necessary, and graded occlusion of the ICA was employed. Direct repair was not chosen because of its high risk of distal embolization. Electrophysiologic monitoring techniques are helpful in predicting hemispheric ischemia.

Adult↗
PubMed1987

Patterns of cervical spine injury and their associated lesions.

Motorcycle riding and diving into shallow water continue to present a high risk of cervical spine injury, often complicated by spinal cord damage. In patients with high cervical cord trauma, differentiation of arterial hypotension due to losing vasomotor control from the effects of internal hemorrhage can cause difficulty. In a series of 123 consecutive cases of cervical spine injury, no evidence was found that either early surgical treatment or steroid administration exert a favorable influence on recovery from traumatic myelopathy. When compared with other series, differences were found in the nature, frequency and severity of both spinal and associated injuries, resulting from the relative frequency among the population studied of trauma due to a particular mechanism-traffic accident, diving, industrial injury-and the special functions and location of the hospital from which information is gathered.

Accidents↗
PubMed1986

Prognostic factors in pediatric brain-stem gliomas.

The clinical, computerized tomography (CT), and histological findings from 84 children with brain-stem gliomas were reviewed to determine whether any of these features correlated with outcome. Clinical data were available from all children, CT data from 62 children, and biopsy data from 54 children. Actuarial life tables were constructed for each clinical, CT, and histological feature and the differences between these were analyzed. The period of survival was significantly shorter in children who presented with cranial nerve palsies (p less than 0.0001), and such children were more likely to have malignant tumors. Two CT features correlated with a significantly decreased survival time: a hypodense tumor prior to contrast administration and a tumor that involved the entire brain stem. Tumor enhancement was not associated with any alteration in survival times. Children with tumor biopsies that were histologically benign survived significantly longer than those whose tumors were malignant (p less than 0.0001). The histological feature associated with the poorest survival time was the presence of mitoses; features associated with the best prognosis were Rosenthal fibers and calcification. The data indicate that brain-stem gliomas are not a homogeneous group of tumors as far as their clinical, CT, and pathological features are concerned. These features may be useful in assessing prognosis and in developing future treatment protocols.

Brain Neoplasms↗