Search PubMed⌕ Search

Biomedical subjects

R Vollmer

Publications and source records attributed to R Vollmer.

54 records · Page 3Linked to original sources
PubMed1979

Combination chemotherapy (COMP protocol) and radiotherapy of anaplastic supratentorial gliomas.

Postoperative survival time and recurrence-free intervals in 116 consecutive patients with supratentorial grade III and IV gliomas (glioblastomas, gliosarcomas, anaplastic astrocytomas, and ependymomas) were compared in unselected groups receiving different forms of treatment. Postoperative high-voltage radiotherapy (31 patients, dosage 4,000--6,000 rads) and combined chemotherapy consisting of CCNU, vincristine, amethopterine, and procarbazine in 15-day circles (COMP protocol) (12 patients) showed the same median survival time of 10.6 months and comparable recurrence-free intervals of 6.8 and 7.0 months, respectively. These results were significantly different from a control group (39 patients) receiving best postoperative supportive (conventional) care (median survival 5.4 months, free interval 3.7 months). Combination of postoperative radiotherapy with simultaneous polychemotherapy (COMP protocol), evaluated in 18 patients, did not significantly change the recurrence-free interval (median 7.0 months), but increased the median survival time to 12.9 months, which was significantly superior to the two other treatment groups. The toxic side effects of COMP therapy were moderate and essentially haematological. In general, simultaneous radiation and chemical treatment was well tolerated after major tumour resection. These preliminary results of postoperative combination of radiation and polychemotherapy for anaplastic supratentorial gliomas appear encouraging, but further trials for optimization of combined therapeutic strategies are warranted.

Adult↗
PubMed1979

Coupling between neuronal activity and focal blood flow in experimental seizures.

Local blood flow, ECoG and single cortical neurone activity were recorded simultaneously from single microelectrodes in 17 cats. Seizures were induced by repeated intravenous injections of pentylenetetrazol (PTZ, 10-20 mg/kg) or by local application of 1 M Na-penicillin. Seven to 20 sec after appearance of burst activity in cortical neurones and ECoG, focal flow increased up to 300% of control. The extent of this flow increase was significantly correlated with the change in firing rate of the neurones. With cessation of seizure activity the flow returned to or below control values. Forty to 70 mg/kg PTZ caused status epilepticus with high voltage rhythmic discharges lasting 30 min-2 h. In 3 cats with status, the flow decreased below control despite persisting seizures, indicative of uncoupling between activity and flow. The delayed coupling between activity and flow during drug-induced seizures indicates a metabolic mediator. Uncoupling observed in cases with long lasting seizures may be due to brain oedema following increased permeability of the blood-brain barrier.

Animals↗
PubMed1979

[The propagation of acetylcholine-induced seizures (author's transl)].

Acetylcholine (ACh) injected into the cortex induces epileptic seizures which spread very slowly, with a propagation speed of some millimeters per minute over the cortex. To study this propagation mechanism the ECoG recorded with two rows of equally spaced electrodes, one row on the homolateral the other on the contralateral hemisphere, was analysed using correlation techniques and spectral analytical methods. Rabbits were used as experimental animals. If a cortical area is involved in the seizure of rhythmic fast and low activity of about 30 Hz is observed. The frequency decreases discontinuously and simultaneously the amplitudes increase. After one or more seconds the activity seems to stabilize showing a tonic pattern of about 9 Hz but a few seconds later this tonic pattern is replaced by an irregular seizure activity. This mechanism was found for the spreading of the primary focus as well as for the spreading of the mirror focus on the contralateral hemisphere which occurs about 2 hours after the injection of ACh. The analysis of the approximately 9 Hz tonic period yielded the following results: at the beginning, the 9 Hz activity of the cortical area already involved leads the activity of the adjacent area which is going to be involved. High coherences were found between both areas during this state. Then the coherence decrease, indicating an uncoupling of the two areas. The subsequent increase of coherence indicates a renewed coupling, but now the newly involved area is leading. This was found by correlation and phase analysis. From these results it can be concluded that the propagation of such seizures is based on a stepwise propagation of an active focus and that the propagation is strongly correlated with certain graphoelements and rhythms.

Acetylcholine↗
PubMed1978

[Neurophysiology of epileptic seizures (author's transl)].

The paper is a review of the progress made over the past years in the understanding of electrical processes occurring during epileptic seizures as elicited by the local application of penicillin. The events at the cellular level of the neocortex are discussed, as well as cortico-subcortical relationships and microtopography of the seizure patterns. The increased excitability under penicillin induces a great number of feedback processes, the electrical effects of which become visible in the seizure EEG with its high degree of organization. Neocortical architectonics is of great importance for the shape of the potentials and their distribution. Seizure patterns of different shape are found in the different layers of the cortex.

Animals↗
PubMed1977

A technique for recording local blood flow and neuronal activity with a single microelectrode.

A technique is presented for recording both local blood flow, by means of hydrogen clearance method, and neuronal activity of the cat's cortex using a single microelectrode. The requirements of electrodes for recording cerebral blood flow are different from those for recording extracellular spikes. Only electrodes within a small range of impedance (measured at 10 Hz) are suitable to record both. A bridge method is used for the recordings. The bridge signal is split in order to amplify cell activities and H2 responses separately. Three examples demonstrate the method and the importance of appropriately selected electrodes.

Animals↗
PubMed1977

[The phenomenon of synchronization in the status epilepticus produced by penicillin and its changes after Clonazepam (author's transl)].

The purpose of this series of experiments was to understand how Clonazepam changes the mechanisms of synchronization in seizures. Penicillin was applied to the rabbits cortex. Interictal spikes and seizures were recorded with multiple electrodes from both the cortical surface and intracortically. The spatio-temporal relationships during these electrical events were studied by topographical methods. Moreover, power spectrum and coherence estimates were performed. A most characteristic feature seen with low doses of Clonazepam is a regularization of the spatio-temporal behaviour of both spikes and seizures. The number of tonic phases considerably increases at the cost of clonic phases. The seizures take more time to become generalized. The generator-zones become larger. This is explained by a decrease of the number of neurones--by Clonazepam--which are still left to produce "paroxysmal depolarization shifts". The findings confirm the increase of postsynaptic cortical inhibition under Clonazepam, as demonstrated by various authors.

Animals↗
PubMed1976

[Endoscopic diagnosis of carcinoma in the operated stomach].

In 24 000 gastroscopies at 4 medical departments 705 subjects with gastric operations done more than 5 years before had been studied. 39 of 608 patients with Billroth II, 5 of 81 with Billroth I and 4 out of 15 with gastroenterostomy were found to be suffering from carcinoma of the gastric stump. The primary gastric operations were performed at a medium age of 40 years. The interval between surgery and development of carcinoma averaged 24 years and was shorter in patients operated at a higher age. Besides age and interval since operation risk factors were apparently former gastric ulcers or polyps. Indications for endoscopic follow-up studies of gastrectomized patients to improve surgical results with carcinoma of the gastric stump have been suggested.

Adenocarcinoma↗
PubMed1976

[Intracortical electrogenesis: spontaneous activity, sleep and epileptic seizure (author's transl)].

Various electrical activities were recorded in rabbits from within the cortex by means of a multielectrode carrying, on a glass needle, 8 Ag-AgCl contacts (50X50 micronm) at 300 micronm distances. The records were stored on tape and analyzed (power spectrum, coherence and phase). Generally, the relatively uniform pattern of the cortical surface is paralleled by a spatio-temporally very complex intracortical activity. In all activities a zone of minimum activity ("zero zone") was found between roughly 500 and 800 micronm below surface. Beyond this zone, activities often appear like a mirrorimage of the surface activities although true phase-reversals never occur. In spontaneous activities this zone remains constant, during seizures it may shift and broaden. The maximum power is usually found below this zone. The transcortical power profile often changes during seizures. Tonic patterns, although fairly uniform in the ECoG from the surface of the cortex, turn out to be composed of several components when studied intracortically. The "generator zones" of the various intracortically identifiable graphoelements have various vertical position and extension. These findings demonstrate that a certain neuronal circuitry may be responsible for the shape of the potential recorded. This circuitry is far from rigid but may change in different stages of synchronization. For a better spatio-temporal resolution of intracortical activities, the interelectrode distance has still to be reduced.

Animals↗