Biomedical subjects

A Kemeny

Publications and source records attributed to A Kemeny.

12 recordsLinked to original sources

PubMed2001

Active, passive and snapshot exploration in a virtual environment: influence on scene memory, reorientation and path memory.

We investigated the importance of active, passive and snapshot exploration on spatial memory in a virtual city. The exploration consisted in traveling along a series of streets. 'Active exploration' was performed by giving directions to the subject who controlled his displacement with a joystick. During 'passive' exploration, the travel was imposed by the computer. Finally, during 'snapshot exploration', simple views of the scene were presented sequentially every 4 m. Travel velocity was the same in all cases. The three visual exploration modes were compared with three spatial memory measures: (1) scene recognition, (2) at the end of the path, reorientation toward the departure point and (3) drawings of the path shape. Scene recognition and estimation of the direction of the starting point of the path were not affected by the mode of exploration. In contrast, reproduction of the shape of the path was affected: the errors of reproduction were greater for the snapshot exploration than for the other two conditions; there was no difference between the other two conditions. These results suggest that (1) 2D image features from a visual scene are memorized. Moreover, (2) pointing towards the origin of the path relies on motion duration integration or a frame of reference integrated during displacement. Finally, (3) drawing the path shape involves a deliberate reconstruction process.

Adult↗

PubMed2001

Role of lateral acceleration in curve driving: driver model and experiments on a real vehicle and a driving simulator.

Experimental studies show that automobile drivers adjust their speed in curves so that maximum vehicle lateral accelerations decrease at high speeds. This pattern of lateral accelerations is described by a new driver model, assuming drivers control a variable safety margin of perceived lateral acceleration according to their anticipated steering deviations. Compared with a minimum time-to-lane-crossing (H. Godthelp, 1986) speed modulation strategy, this model, based on nonvisual cues, predicts that extreme values of lateral acceleration in curves decrease quadratically with speed, in accordance with experimental data obtained in a vehicle driven on a test track and in a motion-based driving simulator. Variations of model parameters can characterize "normal" or "fast" driving styles on the test track. On the simulator, it was found that the upper limits of lateral acceleration decreased less steeply when the motion cuing system was deactivated, although drivers maintained a consistent driving style. This is interpreted per the model as an underestimation of curvilinear speed due to the lack of inertial stimuli. Actual or potential applications of this research include a method to assess driving simulators as well as to identify driving styles for on-board driver aid systems.

Acceleration↗

PubMed2000

Radiosurgery for epilepsy associated with cavernous malformation: retrospective study in 49 patients.

OBJECTIVE: Microsurgical resection of a cavernous malformation (CM) with or without associated cortical resection can provide efficient treatment of drug-resistant associated epilepsy. To explore the potential alternative role of radiosurgery and to evaluate its safety and efficacy for this indication, we conducted a retrospective multicenter study. METHODS: We retrospectively reviewed the files of patients with long-lasting drug-resistant epilepsy, presumably caused by CM, who were treated by gamma knife (GK) surgery for the control of their epilepsy in five centers (Marseilles, Komaki City, Prague, Graz, and Sheffield). A satisfactory follow-up was available for 49 patients (mean follow-up period, 23.66 +/- 13 mo). The mean duration of epilepsy before the GK procedure was 7.5 (+/-9.3) years. The mean frequency of seizures was 6.9/month (+/-14). The mean marginal radiation dose was 19.17 Gy +/- 4.4 (range, 11.25-36). Among the 49 patients, 17 (35%) had a CM located in or involving a highly functional area. RESULTS: At the last follow-up examination, 26 patients (53%) were seizure-free (Engel's Class I), including 24 in Class IA (49%) and 2 patients with occasional auras (Class IB, 4%). A highly significant decrease in the number of seizures was achieved in 10 patients (Class IIB, 20%). The remaining 13 patients (26%) showed little or no improvement. The mediotemporal site was associated with a higher risk of failure. One patient bled during the observation period, and another experienced radiation-induced edema with transient aphasia. Postradiosurgery excision was performed in five patients, and a second radiosurgical treatment was carried out in one patient. CONCLUSION: This series is the first to specifically evaluate the capability of GK surgery to safely and efficiently treat epilepsy associated with CM. Seizure control can be reached when a good electroclinical correlation exists between CM location and epileptogenic zone. Although we do not recommend GK surgery for prevention of bleeding for a CM that has not bled previously, our findings suggest that GK surgery can be proposed for the treatment of epilepsy when the CM is located in a highly functional area.

Adult↗

PubMed1999

Gamma Knife radiosurgery of the glomus jugulare tumour - early multicentre experience.

Leksell Gamma Knife was used to treat 66 patients with glomus jugulare tumour at 6 European sites between 1992-1998. The age of the patients ranged between 18-80 years (median 54 years). Gamma Knife radiosurgery was a primary treatment in 30 patients (45. 5%). Open surgery preceded radiosurgery in 24 patients (36.4%), embolisation in 14 patients (21.2%) and fractionated radiotherapy in 5 patients (7.6%). The volume of the tumour ranged 0.5-27 cm(3) (median 5,7 cm(3)). The minimal dose to the tumour margin ranged between 10-30 Gy (median 16.5 Gy). After radiosurgery 52 patients were followed, the follow up period was 3-70 months (median 24 months). Neurological deficit improved in 15 patients (29%) and deteriorated in 3 patients (5,8%), one transient and two persistant. Neuroradiological follow up using MRI or CT was performed in 47 patients 4-70 months (median 24 months) after radiosurgery. Tumour size decreased in 19 patients (40%) while in the remaining 28 patients (60%) no change in the tumour volume was observed. None of the tumours increased in volume during the observation period. Control angiography was performed in 6 patients. Pathological vascularisation completely disappeared in one patient, reduced in two and there was no change in the remaining three. Radiosurgery proves to be a safe treatment for glomus jugulare tumour with no mortality and no acute morbidity. Because of its naturally slow growth rate, up to 10 years of follow up will be necessary to establish a cure rate after radiosurgery for these lesions.

Adolescent↗

PubMed1999

Gamma Knife radiosurgery for epilepsy associated with cavernous hemangiomas: a retrospective study of 49 cases.

A retrospective multicenter study was performed to evaluate the effectiveness of Gamma Knife radiosurgery (GKRS) in the treatment of drug resistant epilepsy associated with cavernous hemangiomas (CH). The mean duration of epilepsy before GKRS was 7.5 ¿ 9.3 years. The mean frequency of seizures was 6.9 ¿ 14/month. The mean marginal dose was 19.2 ¿ 4.4 Gy (range 11.3 to 36 Gy). The mean follow up was 23.7 ¿ 13 months. At the most recent follow-up examination, 26 (53%) patients were seizure-free (Engel s class I) including 24 in class IA (49%) and two (4%) patients with occasional auras (class IB, 4%). A highly significant decrease in the number of seizures was achieved in 10 (20%) patients, which is class lIB. The remaining 13 (2.6%) patients showed little or no improvement. A medial temporal location was associated with a higher risk of failure. In contrast, all patients with central region CH were seizure free. Two severe but transient complications were observed. There was hemorrhage in one patient and another patient suffered from radio-induced edema with transient aphasia. This series is the first demonstrating that GKRS can be used safely and efficiently to treat epilepsy associated to CH. Seizure control can be reached when a good electro-clinical correlation exists between CH location and epileptogenic zone. Our findings suggest that GKRS can be used to treat epilepsy for CH located in highly functional areas, particularly the central region.

Adult↗

PubMed1997

Prediction of obliteration of arteriovenous malformations after radiosurgery: the obliteration prediction index.

OBJECTIVE: To describe the response to single dose photon stereotactic radiosurgery of arteriovenous malformations (AVMs) so that the probability of success or failure of treatment may be predicted for the individual patient. METHOD: The obliteration prediction index (OPI) was calculated for AVMs by dividing the marginal dose of radiation in Gray (Gy) by the lesion diameter in centimetres in cohorts of 42 patients treated with the modified linear accelerator at Toronto-Sunnybrook Regional Cancer Centre and 394 patients treated with the gamma unit at the Royal Hallamshire Hospital, Sheffield, United Kingdom. Patients were grouped into ranges by OPI and the proportion of success and failure was calculated for each group. An exponential function [P = 1-A.e(-B.OPI)] was fitted to the data by the least squares method. RESULTS: Despite systematic differences in radiation treatment, that is, marginal doses of 15 and 20 Gy in Toronto and most Sheffield patients with a marginal dose of 25 Gy, the resultant data points exhibited similar behaviour. CONCLUSION: The function [P = 1-A.e(-B.OPI)] partly describes the biological effect of radiation and is independent of the radiation device used. Radiosurgery centres can use this model to facilitate predictions of successful treatment for individual patients.

Follow-Up Studies↗

PubMed1996

The use of single fraction Leksell stereotactic radiosurgery in the treatment of uveal melanoma.

Fourteen patients with posterior uveal melanomas were treated using single fraction stereotactic radiosurgery. In each case a dose of 70 Gy was administered to the periphery of the tumour. Regression of the tumour has been observed in 13 patients, whilst the lesion has remained unchanged in one patient. The visual acuity has deteriorated in all 14 patients. Significant radiation induced adverse reactions were noted in 13 patients and include; retinopathy, optic neuropathy, rubeosis iridis, and secondary glaucoma. Two patients have required enucleation because of intractable rubeotic glaucoma. One patient has died from proven metastases. Although stereotactic radiosurgery appears to be a practical and effective method of treating uveal melanomas, its usefulness is limited by a high incidence of radiation induced adverse reactions. Further work is required to refine the current treatment protocol and establish an optimal prescription dose.

Adult↗

PubMed1992

Factors associated with alcohol use in university students.

A survey was conducted of drinking, drug use attitudes, beliefs, personality and demographic characteristics of students on a university campus. Gender, ethnic and social group differences were also examined. It was concluded that a biopsychosocial matrix of determinants influenced alcohol consumption and its excessive consumption. Two general factors emerged from analyses of the results. They may be interpreted as entering into a complex approach-avoidance conflict where the net approach tendency determines overall alcohol consumption. Personality characteristics and presumably their biological correlates, as well as set and setting, or attitudes, beliefs and environmental influences contribute to the approach-avoidance conflict that determines abstinence or varying amounts of alcohol consumption.

Adult↗

PubMed1986

Variation of surface density and other parameters in remodeling of trabecular bone in various conditions.

To appreciate the remodeling of the trabecular bone, the static morphometric parameters of surface density (SV(TRAB/BONE] and volumetric fraction (VV(TRAB/BONE] of cancellous bone were measured and compared to remodeling parameters, i.e., the surface extents of active/inactive resorption, active bone formation and nonmineralized bone. Iliac bone biopsies from 28 subjects with spasmophilia, osteoporosis and primary hyperparathyroidism were studied by means of a Nachet-France NS 2000 automatic image analyzer and a Zeiss ocular integrator; the results obtained in each group showed comparable values for the two methods (r = .8 for each group, with P less than .01). The remodeling parameters measured by means of the ocular integrator were compared with the variation measurements of the trabecular surface density, SV(TRAB/BONE). The correlation between the inactive osteoid surface and the coefficient of variation of the mean (CVM of SV(TRAB/BONE] on sections was significant for the three pathologic groups. The average mean values and standard errors of the mean of this latter parameter for the spasmophilia and hyperparathyroidic groups were, respectively, 0.063 +/- 0.008 and 0.092 +/- 0.012. Analysis of the experimental data shows that the simple global measurement of CVM (SV(TRAB/BONE] by means of an automatic image analyzer supplies information on the skeletal state during tissue remodeling.

Adult↗

PubMed1984

Study on static morphometric parameters for a diagnostic approach of osteoporosis.

The diagnostic value of the morphometric parameters Vv,Sv, dtrab of cancellous bone and relations between them were examined. Iliac bone biopsies of osteoporotic and spasmophilic subjects were studied by means of a Mop 1 semi automatic digitizer tablet joint to a C B M 3032 microprocessor. Both the average Sv and Vv values were significantly different between the two groups. Concordance of Sv values with the radiological diagnosis was closer than Vv ones. The global estimation of mean trabecular thickness is discussed. In conclusion the confrontation of experimental data shows that simple global measure of Sv completes and precise the knowledge of skeleton state.

Adult↗

PubMed1984

A perimeter algorithm applied to lung pathology.

A new image analyser, the NS 2000, explores the image using 256 photodiodes and, according to an adjustable threshold, converts it into a set of digital points of logical level 0 or 1. The method of fitting squares of increasing size consists of checking the presence of a square of a given size and of a given logical value throughout the image studied and gives the areas of successive erosions of the image. Using the parameters provided by the device one can obtain the total boundary BA per unit area for the phase studied, which is proportional to the number of squares having points of the two logical levels. Errors in length measurement as a function of orientation and for isotropic structures are compared to other automatic perimeter algorithms and to manual square grid measurement. Using the parameters provided by the device for the quantitative evaluation of lesions of elastase induced emphysema in hamster lungs, the values obtained for internal surface area (ISA) of alveoli, are lower by about 40% in elastase treated hamsters when compared to normal controls. This difference is highly significant (P less than 0.001) and the results obtained by the described method are in good agreement with those obtained by the classical manual procedure. Efficiency, defined as the precision of the estimate per unit measurement time on a given set of sample units (pictures in this paper), is given for both NS 2000 and manual procedures. The results obtained show comparable values but the automatic procedure includes a statistical treatment and it is significantly faster on histological sections than on micrographs, which was not the case with the manual method.

Animals↗

PubMed1984

Pharmacological activation of gamma-aminobutyric acid-system blunts prolactin response to mechanical breast stimulation in puerperal women.

To evaluate whether the gamma-aminobutyric acid (GABA)ergic system participates in the control of PRL secretion during the puerperium, different doses of sodium valproate (DPA), a drug that increases endogenous GABA activity, were administered orally to puerperal women who did not wish to breast feed their infants. Two groups of five women were each given DPA in doses of 400 and 800 mg, respectively. PRL levels were measured in plasma samples collected before and after drug administration. Another group of five puerperal women was treated with 800 mg DPA 60 min before mechanical breast stimulation using an electric breast pump for 15 min. Circulating PRL levels were measured in samples obtained before, during, and after breast stimulation. No drug-associated side effects were observed. After placebo administration, no significant variations in plasma PRL levels occurred in any subject. The lower dose of DPA (400 mg) induced a slight decrease in plasma PRL levels, but 800 mg of the drug induced a significant fall (P less than 0.05 vs. baseline values) in PRL, with a maximum percent decrease (68.2 +/- 4%) 180 min after DPA treatment. Mechanical breast stimulation performed after placebo treatment induced a significant increase (P less than 0.01) in plasma PRL levels, with peak values (37 +/- 10% above baseline values) 10 min after the onset of stimulation. When DPA was administered to the same women, a significant decrease (23 +/- 3%) in plasma PRL occurred during breast stimulation. Thereafter, PRL values continued to fall in spite of breast stimulation. PRL levels were significantly decreased after DPA treatment compared to both basal values (P less than 0.01) and the levels found in the same patients during control tests (P less than 0.05). These results demonstrate that enhancement of endogenous GABAergic tone induced by DPA significantly decreases basal PRL levels and blunts PRL release after mechanical breast stimulation. In agreement with animal data, a possible physiological role of GABA in the control of PRL release during puerperium may be suggested.

Adult↗