PubMed Health⌕ Search

Biomedical subjects

R J Sclabassi

Publications and source records attributed to R J Sclabassi.

70 records · Page 4Linked to original sources
PubMed1985

A non-linear analysis of afferent modulatory activity in the cat somatosensory system.

The effects of prior input on afferent activity in the somatosensory system of the cat have been studied using both twin-pulse experiments and random stimulus trains for which evoked activity is characterized by a set of mathematical functions known as kernels. The kernels quantitatively characterize transformational processes occurring in the system. The first-order kernel is analogous to a classical averaged evoked potential, but to temporally interacting stimuli; the second-order kernel may be likened to a generalized recovery function. Responses to superficial radial nerve stimulation were obtained at sensory (S1) cortex, thalamic n. ventralis posterolateralis (VPL), and the nucleus cuneatus of the dorsal column nuclei (DCN). Comparison of first-order kernels with averaged evoked potentials showed good agreement in chronic awake, chronic anesthetized, and acute anesthetized animals. Second-order kernels indicated complex interactions with an overall depression of subsequent response amplitudes. Comparison between second-order kernels and the results of the two-pulse experiments at both S1 cortex and VPL showed good agreement for early latency response components, but significant deviations for later components suggest higher than second-order non-linearities for this system.

Animals↗
PubMed1985

Early detection of brainstem glioma using brainstem auditory evoked potentials.

Brainstem tumor was suspected in an 11-year-old boy presenting with a painless lateral rectus palsy, on the basis of abnormal brainstem auditory evoked potentials (BAEP), despite normal computed tomographic studies, the diagnosis being confirmed by biopsy. The BAEP improved after radiation therapy, but their later deterioration heralded the onset of recurrence two weeks before any adverse clinical symptoms appeared. The value of BAEP studies in the early detection of brainstem lesions and in monitoring their progress, is discussed.

Astrocytoma↗
PubMed1985

Use of the Cavitron ultrasonic surgical aspirator and evoked potentials for the treatment of thalamic and brain stem tumors in children.

We subtotally removed nine pediatric central gliomas (five brain stem and four thalamic) with the Cavitron ultrasonic surgical aspirator (CUSA). Greater than 70% of the tumor was removed in eight of the nine cases. Evoked potentials were monitored during six of the operations. Of the six children who were operated on with monitoring, four had no deficit and two had single cranial nerve palsies. Of the three children who were operated on without evoked potential monitoring, one had no deficit, one was in a permanent state of obtundation, and one died of a pulmonary embolus 6 weeks postoperatively. Because the prognosis of children with malignant astrocytomas correlates with the extent of tumor removal, extensive tumor removal with the CUSA is probably indicated for some children with relatively discrete, enhancing central gliomas. Evoked potential monitoring may be useful during such operations.

Adolescent↗
PubMed1985

Cavitron ultrasonic surgical aspirator and visual evoked potential monitoring for chiasmal gliomas in children. Report of two cases.

The Cavitron ultrasonic surgical aspirator (CUSA) and intraoperative visual evoked potentials (VEP's) were found to be helpful in treating two children with difficult chiasmal gliomas. Approximately 60% of one tumor and 85% of the other was resected without change in the intraoperative VEP's and with no change in postoperative visual fields or acuity. The CUSA-VEP technique is useful in the infant to "buy time" for brain maturation, delaying or obviating subsequent radiotherapy. This approach may be helpful in the older child to reduce the tumor burden for subsequent chemotherapy. Chiasmal gliomas can be subtotally resected with the CUSA while visual function is monitored by intraoperative VEP's.

Child↗
PubMed1984

Visual evoked potentials in hydrocephalus: relationship to head size, shunting, and mental development.

Flash-evoked visual cortical potentials were measured in 54 infants and children with symptomatic hydrocephalus; 54 shunted, asymptomatic infants and children; and 57 controls. All patients were evaluated for head size, mental development, and history of infection of the nervous system. Hydrocephalic infants up to 60 weeks of conceptional age showed significant changes in the maturation curve of the latency to the main positive peak P2 (P100), particularly when their hydrocephalus was associated with an enlarged head or with infection. Older children of normal mental development presenting with acute hydrocephalus of recent onset had normal latencies to P2. Some persistent ventriculomegaly after shunting was also compatible with normal visual evoked potentials (VEPs). After shunting, the latency to P2 became normal in most of the patients who showed normal mental development, whereas retarded hydrocephalic children of all ages continued to have abnormal VEPs.

Cerebrospinal Fluid Shunts↗
PubMed1982

Changes in the visual evoked potentials of hydrocephalic children.

The visual evoked potentials (VEPs) of a group of 84 hydrocephalic children, aged between 2 days and 15 years, were studied. The variables analyzed were age, ventriculomegaly, head size, and the presence or absence of a functioning shunt. In infants, an increase in the latency of the primary positive wave (P2) was confirmed, but this was present consistently only when ventriculomegaly was accompanied by increased head size. Improvement in the VEP was slow to follow shunting. No change in the latency of P2 was found during hydrocephalic episodes in older children.

Adolescent↗
PubMedDate not supplied

Comparison of orthogonal search and canonical variate analysis for the identification of neurobiological systems.

In this paper, we investigate two general methods of modeling and prediction which have been applied to neurobiological systems, the orthogonal search (OS) method and the canonical variate analysis (CVA) approach. In these methods, nonlinear autoregressive moving average with observed inputs (ARX) and state affine models are developed as one step predictors by minimizing the mean-squared-error. An unknown nonlinear time-invariant system is assumed to have the Markov property of finite order so that the one step predictors are finite dimensional. No special assumptions are made about model terms, model order or state dimensions. Three examples are presented. The first is a numerical example which demonstrates the differences between the two methods, while the last two examples are computer simulations for a bilinear system and the Lorenz attractor which can serve as a model for the EEG. These two methods produce comparable results in terms of minimizing the mean-square-error; however, the OS method produces an ARX model with fewer terms, while the CVA method produces a state model with fewer state dimensions.

Electroencephalography↗
PubMedDate not supplied

Real time signal processing in the clinical setting.

We routinely use a variety of real time signal acquisition, enhancement, and display techniques in the operating room to provide the surgeon with functional information. This enables reduction of surgical morbidity in cases which present a significant risk to the nervous system. Here we present regression based signal processing algorithms which produce considerable signal-to-noise-ratio enhancement with corresponding reduction in the time required to obtain an interpretable neurophysiological signal. We also present the approach we have applied to fault tolerance and distributed data display for our workstation cluster environment.

Algorithms↗
PubMedDate not supplied

Protective effects of combined superoxide dismutase and deferoxamine on recovery of cerebral blood flow and function after cardiac arrest in dogs.

Oxygen free radicals generated during reoxygenation after cardiac arrest may impair recovery of cerebral blood flow and function. In a randomized study in vivo, we tested the following anti-free radical combination therapy administered at the beginning of cardiopulmonary resuscitation after apnea-induced cardiac arrest of 7 minutes: 1) ventilation with 100% nitrogen for 30 seconds to allow the delivery of therapy before oxygen, 2) 10 mg/kg i.a. superoxide dismutase followed by 10 mg/kg i.v. over 1 hour to scavenge the superoxide anion radical, and 3) 20 mg/kg i.v. deferoxamine over 1 hour to prevent membrane lipid peroxidation. We evaluated the effects of this combined treatment on the recovery of cardiovascular variables, cerebral blood flow and oxygen consumption, and somatosensory evoked potentials in 20 dogs 6 hours after resuscitation. Compared with standard treatment (n = 10), the combined treatment (n = 10) did not affect cardiovascular variables, significantly mitigated cerebral blood flow changes after cardiac arrest, and enhanced recovery of somatosensory evoked potentials. We conclude that oxygen free radicals play a role in the pathogenesis of the arrest-related derangements of cerebral blood flow and function that are effectively reduced by this combined treatment; we recommend evaluation of its components in outcome studies.

Animals↗
PubMedDate not supplied

Time-varying evoked potentials.

In an important subset of surgical procedures, the procedure itself poses a significant threat to the patient's nervous system. In order to reduce this threat, neurophysiological function of the structures at risk may be monitored during surgery using time-locked sensory or motor-evoked responses. A simple but powerful extension of the segmented and sliding average techniques currently in wide use is described and demonstrated. By fitting polynomial functions of time to capture time variations in the evoked response, signal/noise enhancement comparable with that of averaging is obtained. More importantly, a considerable improvement in time resolution is gained. In the demonstration data set presented in the figures, clinically significant changes were identifiable in one-sixth of the time required using signal averaging.

Aged↗