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Biomedical subjects

A N Lebedev

Publications and source records attributed to A N Lebedev.

At least 37 records · Page 2Linked to original sources
PubMedDate not supplied

The neurophysiological parameters of human memory.

The images of human working memory are coded by systems of cyclically repeating cerebral processes. The dominant frequency of the cyclical oscillations in an alpha rhythm focus, approximately 10 Hz, and the duration of the relative refractoriness after the impulse discharge of the neuron, approximately 0.01 sec, determine the diversity of the character of the bioelectrical activity of the human brain, and thereby determine the capacity and speed of working memory. The higher the frequency and the briefer the refractory state, the greater the capacity and the speed of memory. Methods for the assessment of both parameters on the basis of the individual characteristics of the human electroencephalogram in the state of its relative rest are indicated. Formulas are presented for the calculation of the capacity of memory and the duration of the operations of collation of images perceived and those stored in memory.

Alpha Rhythm↗
PubMedDate not supplied

[X-ray findings in meningiomas of the tentorium cerebelli].

A roentgenological investigation of 38 patients with meningiomas of the tentorium cerebelli of the supra-subtentorial growth revealed signs of hypertension in 31 of them. The destruction of the squama occipitalis and of the superior edge of the apex of the petrous pyramid was found in 17 of these patients. Opacification of the ventricular system discerned a combination that included compression of the inferior contour of the posterior segments of the lateral ventricles or a filling defect of the trigonum of the left ventricle with deformation of the posterior segment of the III ventricle and a displacement forward of the aqueductus Sylvii. An angiographic investigation of the carotid and basilar systems determine a typical picture of simultaneous shifts, viz, upwards--of the median cerebral artery, medially--of the internal occipital artery; outwards--of the temporal-occipital artery, medially and downwards--of the superior cerebral artery. Obliteration of the sinuses rectus and transversalis comes into evidence. Opacification of the meningioma vasculature above and underneath the tentorium cerebelli makes the topical diagnosis quite convincing.

Adolescent↗
PubMedDate not supplied

[Assessment of learning capacity by electroencephalographic parameters].

Problems in the objective assessment of intellectual endowments are considered. In the authors' opinion, electroencephalographic (EEG) parameters are one of their measures. An examination of about 300 schoolchildren revealed signs of a correlation of EEG parameters with study progress. The methods and results of the examination are presented.

Age Factors↗
PubMedDate not supplied

[Experience with transcranial surgery of hypophyseal adenomas].

The article generalizes experience in intracranial operations on 453 patients performed at the Institute of Neurosurgery, AMS, USSR in 1983-1987. The tumors had a pronounced extrasellar growth in most cases. The surgical approaches and the peculiarities of surgical techniques in removal of pituitary adenomas are described. The importance of microsurgical techniques which raise the radical character of the surgical interventions and improve their results is discussed.

Adenoma↗
PubMedDate not supplied

[Complex x-ray diagnosis of craniopharyngioma in adults].

The authors analyse the findings of craniography, linear tomography, radiocontrast examination, computed tomography (CT), and magnetic-resonance tomography (MRT) in 322 patients 16 to 69 years of age with craniopharyngiomas. Calcification of the craniopharyngiomas was demonstrated on craniograms in 38.8% of cases and by computed tomography in 57.4% of cases. Endosuprasellar localization of the craniopharyngioma was encountered in 99 cases, in the stalk in 122, intra-extraventricular--in 80, and intraventricular--in 21 cases; among these cases 30 were with giant craniopharyngiomas. CT and MRT give an idea of the size of the nodular, petrified, and cystic parts of the craniopharyngioma and the topographic relations of the tumor to the various parts of the brain and the vascular and C.S.F. systems, which is very important for the tactics of treatment, the volume of the surgical intervention.

Adolescent↗
PubMedDate not supplied

[Diagnosis of neurinomas of the Gasserian ganglion].

The article analyses the findings of clinical and X-ray examination in 39 patients in two types of growth of neurinoma of the gasserian ganglion: with localization within the boundaries of the middle cranial fossa (22) and with the formation of tumor nodes in the middle and posterior cranial fossae (17). The first symptoms of the disease were paresthesia or numbness and continuous pain mostly in the zone innervated by the 1st--2nd pair of the trigeminal nerve, absence of corneal reflexes, high lumbar cerebrospinal fluid pressure, and protein-cellular dissociation in the cerebrospinal fluid. The craniograms revealed destruction of the floor of the middle cranial fossa with involvement of the walls of the f. ovale, spinosum et lacerum and the apex of the pyramid of the temporal bone. Carotid angiography demonstrated typical displacement of the carotid siphon to the midline, to the front, or to the back. The middle cerebral artery was moderately displaced upward and an arched art. chorioidea, anterior was noted. Growth of the neurinoma into the posterior cranial fossa was attended with displacement and deformity of a. basilaris et cerebellaris superior and the veins of the posterior cranial fossa. The ventriculograms showed compression of the inferior horn of the lateral ventricle and moderate compression of the caudal parts of the fourth ventricle and aqueduct of Sylvius. Comprehensive generalization of all the findings gained from examination of the patient is necessary in determining the topics and type of the growth of a neurinoma of the gasserian ganglion.

Adolescent↗
PubMedDate not supplied

[Pituitary tumors extending into the nose, their topography, diagnosis and principles of treatment].

Tumors of the hypophysis grow into the nose in 5.5% of cases. In 33 of 40 patients the new growth was very large and spread both into the cranial and the nasal cavity; less frequently (in 7 cases) the tumor was only infrasellar, growing into the nasal cavity. The initial signs of the growth of a hypophyseal tumor into the cavity of the nose are detected by purposeful anterior rhinoscopy of the deep anteroposterior parts of the nose and cytological examination of the aspirate from the tumor in the nose. X-ray examination and computer tomography usually reveal growth of the tumor into the nasal cavity only in the later stages of development. According to the size of the intranasal part of the tumor, the authors distinguish small (in 30 patients), of moderate size (1 case), and large (9 cases) tumors. Each group was marked by characteristic rhinoscopic and X-ray features. The choice of the method of treatment was guided by the ratio of the size of the intracranial and intranasal parts of the tumor, the extent of destruction of the base of the skull, and by other factors. Transnasal-transsphenoidal removal is recommended for a tumor growing only into the sphenoidal sinus and the nasal cavity. A tumor growing for the most part intracranially was removed from the cavity of the skull. Intracranial and endonasal rhinological removal is recommended in cases of a large tumor located in the nasal cavity and intracranially.

Adenocarcinoma↗