Biomedical subjects

L M Alvarez

Publications and source records attributed to L M Alvarez.

6 recordsLinked to original sources

PubMed2000

Personal-computer-based system for three-dimensional anatomic-physiological correlations during stereotactic and functional neurosurgery.

This paper describes the automatic three-dimensional (3D) graphic possibilities that are supplied by the Neurosurgical Deep Recording System (NDRS) to facilitate anatomic-physiological targeting during stereotactic and functional neurosurgery using depth recording. This software has been developed to substitute the complex electronic equipment ordinarily used for deep brain electrical recording, display and processing by a personal computer. It may also help to improve on-line graphic analysis, automatic management of the recorded information and flexibility to implement different forms of signal analysis. It can automatically show a 2D or 3D representation of the electrode track, with the electrophysiological findings superimposed as well as the corresponding sagittal, coronal and axial views of a brain atlas using automatic scaling. The NDRS has already successfully been applied during more than 300 neurosurgeries in Spain and Cuba, enabling improved targeting accuracy and safety.

Brain Mapping↗

PubMed1999

Photooxidative bleaching of chlorophyllin.

Chlorophyllin, a water-soluble, copper-containing porphyrin, can be bleached rapidly in the light or slowly in the dark in a reaction which is oxygen dependent. Both the photo and the dark bleaching reactions are temperature dependent. Cyclic voltammetry measurements show that the copper in the bleached and nonbleached state remains in the +2 redox state and could be readily reduced. This would imply that there is no net oxidative change to the copper during the bleaching process. FT-IR absorption spectroscopy showed vibrations characteristic of a vinyl functionality disappeared upon bleaching. Aqueous solutions of chlorophyllin were not dialyzable through dialysis tubing of molecular weight cut-off, 6000-8000 molecular weight, indicative of an aggregate chlorophyllin micelle. Analysis of products by high performance liquid chromatography showed that the chlorophyllin mixture was more complex than originally anticipated and that two components were lost from the mixture upon photobleaching. One compound that is preferentially lost upon photobleaching has been identified by mass spectral analysis as Cu(II) chlorin e6.

Chlorophyllides↗

PubMed1998

Individual differences in memory and executive function abilities during normal aging.

The purpose of this study was to analyze the effects of some individual variables on memory and executive function test performance in normal aging individuals. Sixty subjects (21 males and 39 females), with a mean age of 69.66 (SD = 7.09) were selected. The following neuropsychological tests were selected. The following neuropsychological tests were administered: Associative Learning and Logical Memory from the Wechsler Memory Scale (WMS) (Wechsler, 1945), Associative Memory with Semantic Enhancement Test (AMSET) (Pineda, Galeano and Giraldo, 1991), Wisconsin Card Sorting Test (WSCT) (Heaton, 1981), and Verbal Fluency (phonologic and semantic). The effects of demographic (age, education, and sex) and some individual variables (academic history, working history, physical activity, and leisure activities) were measured. Age and education effects on test scores were observed, but no sex effect was found. Working history and leisure activities established significant differences in some test scores. A multiple regression analysis was performed. Not only demographic variables, but also individual variables were associated with memory, and albeit at a lesser extend, with executive function test scores. It was emphasized that not only demographic factors, but also individual variables have a significant effect on cognitive changes observed during normal aging.

Aged↗

PubMed1991

Triphenyltetrazolium chloride (TTC) as a marker for ischaemic changes in rat brain following permanent middle cerebral artery occlusion.

Triphenyltetrazolium chloride (TTC) was used to delineate ischaemic lesions in the rat brain at various times following middle cerebral artery occlusion. A comparison was made of TTC staining by immersion and perfusion techniques and conventional light microscopy. The lesions were quantified by measuring the ischaemic area at the sections corresponding to 7 mm in front of the AO line (atlas of Konig and Klippel). In animals examined 24 h after middle cerebral artery occlusion (MCAO), the area of infarction was 17.4 +/- 1.3 mm2 on the TTC perfused slices and 17.6 +/- 1.6 mm2 on the TTC immersed slices (mean +/- SEM). By contrast, there was a marked difference between the two TTC methods when tissues were examined at shorter intervals after artery occlusion. In the TTC-perfused animals, there was no significant difference between the mean areas of infarction measured at 5-20 min, 3-4 h, or 24 h post occlusion. Immersion in TTC, however, failed to reveal any consistent ischaemic damage when applied at the earlier post-occlusion times. Conventional histopathology demonstrated minimal lesions at 5-20 min but at 4 h or more the lesions were not significantly different from those demonstrated by TTC perfusion. TTC immersion staining can, thus, only be used as a reliable marker of cerebral ischaemia damage with post-occlusion survival periods of 24 h. TTC perfusion staining gives results not significantly different from histopathology at 4 h or more post-occlusion but at earlier intervals than 24 h it differs significantly from TTC immersion staining.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

[An automatic system for anatomophysiological correlation in three planes simultaneously during functional neurosurgery].

INTRODUCTION: The Neurosurgical Deep Recording System (NDRS) using a personal computer takes the place of complex electronic equipment for recording and processing deep cerebral electrical activity, as a guide in stereotaxic functional neurosurgery. It also permits increased possibilities of presenting information in direct graphic form with automatic management and sufficient flexibility to implement different analyses. OBJECTIVE: This paper describes the possibilities of automatic simultaneous graphic representation in three almost orthogonal planes, available with the new 5.1 version of NDRS so as to facilitate the analysis of anatomophysiological correlation in the localization of deep structures of the brain during minimal access surgery. MATERIAL AND METHODS: This new version can automatically show the spatial behaviour of signals registered throughout the path of the electrode inside the brain, superimposed simultaneously on sagittal, coronal and axial sections of an anatomical atlas of the brain, after adjusting the scale automatically according to the dimensions of the brain of each individual patient. This may also be shown in a tridimensional representation of the different planes themselves intercepting. RESULTS: The NDRS system has been successfully used in Spain and Cuba in over 300 functional neurosurgery operations. The new version further facilitates analysis of spatial anatomophysiological correlation for the localization of brain structures. CONCLUSION: This system has contributed to increase the precision and safety in selecting surgical targets in the control of Parkinson s disease and other disorders of movement.

Brain↗

PubMedDate not supplied

[The radiofrequency ablation of accessory pathways. The initial experience in Mexico].

Thirteen patients with paroxysmal supraventricular tachycardia (SVT) due to an accessory pathway were submitted to an electrophysiological study and radiofrequency ablation of the Kent bundle. There were 9 males and 4 females. The mean age was 22 years. Other than their SVT, none had any structural heart disease. Ten of them had Wolff-Parkinson-White syndrome, and three had concealed accessory pathways. Two different types of radiofrequency devices were used: one generating damped sinusoid waves, and two other generators producing pure continuous sinusoid waves. With the first type, two attempts were made: one patient with a concealed pathway and one with overt preexcitation. The successful ablation was not achieved because this wave type is 100 times more powerful, it desiccates the tissue, and thus does not produce the right kind of lesion. The other eleven patients were divided in three groups: I) With left overt preexcitation (7 pts) II) Concealed left Kent bundles (2 pts) III) Right Kent bundles. Ablation was 100% successful in group I, while in the other two groups, only one patient of each was successfully ablated. The overall successful rate of these 3 groups was 81.8%. Of the two patients that could not be treated, one had an anterior septal Kent bundle and the other had a concealed left Kent bundle. We believe that catheter ablation is a very promising therapeutic procedure for patients with SVT, besides being a extraordinary instrument that will enable us to be able to understand further clinical electrophysiology.

Adolescent↗