Biomedical subjects

R J Sclabassi

Publications and source records attributed to R J Sclabassi.

At least 19 recordsLinked to original sources

PubMed1996

Computer classification of sleep in preterm and full-term neonates at similar postconceptional term ages.

A classification strategy of neonatal sleep is being developed by comparing visually scored minutes of 21 channels of electroencephalographic (EEG)/polygraphic recordings with the corresponding values for each physiological signal derived from either visual or computer analyses. Continuous 3-hour sleep studies on 54 preterm and full-term neonates at similar postconceptional term ages were acquired under environmentally controlled conditions using a computerized monitoring system. An on-line event marker program recorded behavioral observations. One of three EEG sleep states was assigned to each of 8,995 minutes by traditional visual analysis criteria. EEG spectral values, spectral and nonspectral cardiorespiratory calculations and behaviorally observed movements, arousals and rapid eye movement counts were submitted for discriminant analysis. Based on the total minutes known for each of three states (i.e. active, quiet and awake), linear combinations of all specified digitized parameters were formed into an arithmetic algorithm by use of discriminant analysis, which served as the basis of a state assignment for each minute. Fifty percent of the data were arbitrarily used as the training set to derive the state classification model. The remaining fifty percent of the data were used as the cross-validation "test sample" to determine the accuracy of the classification when compared to the visually analyzed score for each corresponding minute. Thirteen out of 32 physiological measures best predicted state of both preterm and full-term neonatal groups. For both groups, the correct classification for active sleep was 90.3%, quiet sleep was 97.4%, awake was 97% and the overall accuracy was 93.3%. However, the order of significance for specific variables differed between these two neonatal groups. Differences in the order of variables that predict sleep states between preterm and full-term infants may reflect adaptation of brain function of the preterm infant to prematurity and/or prolonged extrauterine experience.

Child, Preschool↗

PubMed1995

Maturational trends of EEG-sleep measures in the healthy preterm neonate.

Five physiologic groupings of 45 EEG-sleep measures were acquired from serial 24-channel EEG-sleep recordings (i.e., sleep architecture, continuity, EEG spectral, phasic, and autonomic measures), utilizing 129 studies on 56 healthy preterm infants from 28 to 43 weeks postconceptional age (PCA) who were neurodevelopmentally normal on follow-up. Regression analyses chose the least number of measures that best reflected maturation. Four of 45 variables (i.e., spectral alpha energy during quiet sleep, total spectral EEG energy, arousal number during active sleep, and percentage of EEG discontinuity) most significantly explained brain maturation in neonates < 36 weeks PCA. Three of 45 variables (i.e., spectral theta and beta energies during active sleep and spectral alpha energy during quiet sleep) were most representative after 36 weeks PCA. Spectral EEG energies were the strongest indicators of maturation compared with other measures, particularly in near-term neonates.

Cardiovascular Physiological Phenomena↗

PubMed1995

Intraoperative urokinase infusion for embolic stroke during carotid endarterectomy.

Embolic stroke is an infrequent complication of carotid endarterectomy. Somatosensory evoked potential monitoring detected delayed acute neurological deterioration during endarterectomy performed on a 71-year-old woman. Intraoperative arteriography performed via an indwelling shunt revealed thrombus within the middle cerebral artery and distal branches. A microcatheter was placed into the internal carotid artery via the arteriotomy and advanced into the middle cerebral artery. Urokinase was infused into and around the thrombus until almost complete thrombolysis had been achieved. The patient recovered quickly and was discharged without neurological deficit.

Aged↗

PubMed1995

Neurophysiologic assessment in the management of spinal dysraphism.

Neurophysiologic techniques provide a valuable addition to the armamentarium of tools for the evaluation of sensory and motor function in the pediatric spinal cord. These techniques include median, radial, and ulnar nerve evoked potentials from the upper extremity; common peroneal and tibial nerve evoked potentials from the lower extremity; dermatomal potentials; and compound muscle action potentials and compound nerve action potentials. The techniques that evaluate the sensory system have been used extensively and effectively as research tools, as adjuncts to diagnostic evaluation, and for intraoperative monitoring. There is a considerable literature that describes the properties of SEPs in the infant and young child. Techniques for assessing the descending pathways have been developed in the last 10 years. These techniques hold great promise as both diagnostic and intraoperative monitoring tools. Many questions, however, still exist concerning their value and use. The rapidly increasing capability available in computer systems is also providing enhanced capability in the acquisition, display, and analysis of neurophysiologic data. It is now common to acquire multiple responses simultaneously, e.g. tibial SEPs, pudendal SEPs, and motor potentials. It is also possible to apply computationally intensive numerical algorithms in real time to enhance signal quality and reduce the time required to produce an interpretable display. Finally, it is possible to monitor multiple cases simultaneously from remote locations. These enhanced computational capabilities are helping to optimize the contribution of neurophysiologic monitoring to patient care.

Child↗

PubMed1994

Rectal temperature changes during sleep state transitions in term and preterm neonates at postconceptional term ages.

Mean rectal temperatures in neonates were investigated during sleep state transitions as assessed by visually analyzed electroencephalographic-polygraphic recordings. Continuous 3-hour studies were obtained on 3 term and 5 preterm infants at postconceptional term ages using a 24-channel computerized monitoring system. In the study, 1,461 min were assigned an EEG state by traditional criteria. Mean rectal temperature measurements were tabulated for each minute of sleep. Data were analyzed both as 1,461 consecutive minutes of sleep, and as 28 complete ultradian neonatal sleep cycles. Exploratory analyses were performed using t tests, Mann-Whitney U tests, and one-way analysis of variance. Decreases in mean rectal temperatures followed a transition from active to quiet sleep for only the term group. The preterm group had higher temperatures at sleep onset than the term group and demonstrated no changes during state transitions. Higher temperatures were maintained in the preterm group during both active and quiet sleep (i.e., 36.7 degrees C versus 36.4 degrees C, P = .02) when 28 complete cycles of sleep were compared and during the transition when 658 min of active sleep were compared to 617 min of quiet sleep. These findings are preliminary; however, the phenomenon of state-dependent changes in mean rectal temperature in neonates based on electroencephalographic sleep is unreported. Higher mean rectal temperatures during active sleep and altered temperature responses during transition to quiet sleep in the preterm infant suggest altered brain function because of the preterm infant's adaptation to the extrauterine experience.

Autonomic Nervous System↗

PubMed1994

Comparisons of EEG spectral and correlation measures between healthy term and preterm infants.

Continuous 12-hour electroencephalography (EEG)-sleep studies were acquired by a computerized monitoring system under environmentally controlled conditions for 2 groups of neonates. Eighteen health preterm infants at a postconceptional term age were matched to 18 term infants. These 2 groups were also matched for gender, race, and socioeconomic class. For the entire 12-hour recording, relative spectral power values (i.e., ratio of specific EEG power in specific frequency band compared to total EEG power) were significantly reduced in the preterm group for theta (P < or = .007), alpha (P < or = .001), and beta (P < or = .018) frequency bands, while delta remained unchanged. Correlations between 91 pairs of EEG channels were also calculated and the preterm infants had significantly higher correlation values in 27 of the 91 pairs of channels (P < .05); 14 interhemispheric, 8 intrahemispheric, and 5 sagittal combinations, while 3 intrahemispheric combinations were higher in the term group. Fewer functional neuronal aggregates generate less oscillatory potential (i.e., lower spectral power) in the theta through beta frequency ranges in the preterm infant, while greater cortical connectivity (i.e., higher correlations) exists in many brain regions by postconceptional term ages in this group. These findings suggest a functional alteration in brain development of the preterm infant as a result of prolonged extrauterine experience and/or prematurity.

Action Potentials↗

PubMed1994

Comparisons of EEG sleep state-specific spectral values between healthy full-term and preterm infants at comparable postconceptional ages.

Differences in state-specific electroencephalographic (EEG) spectral values are described between groups of preterm and full-term neonates at comparable postconceptional term ages. Eighteen healthy preterm neonates of < or = 32 weeks gestation were selected from an inborn population of a neonatal intensive care unit. Twenty-four-channel recordings were obtained at a full-term age and compared with studies of 22 healthy full-term neonates. The initial three hours of each 12-hour study were recorded on paper from which EEG sleep state scores per minute were visually assessed. Six mean spectral values (i.e. total EEG, electromyogram, delta, theta, alpha and beta energies) were calculated from each corresponding minute of digitized data, which was also assigned one of six EEG sleep states. Each neonatal group displayed statistically significant differences among sleep-state segments for all spectral values. The alpha- and beta-range spectral values of the preterm group, compared to the full-term control group, were lower during all sleep state segments. Spectral values for the theta band were lower during both quiet sleep segments only, whereas spectral values for delta were lower during all sleep stages, except tracé-alternant quiet sleep. Significant differences in EEG spectral values were noted among states of sleep for both preterm and full-term infants of similar postconceptional term ages. These data also suggest differences in central nervous system maturation between neonatal populations. These findings strengthen our previously stated contention that there is a functional alteration in brain development of the preterm infant as reflected in sleep organization that results from a prolonged extrauterine experience and/or prematurity.

Analysis of Variance↗

PubMed1994

A comparison of conventional and matched filtering techniques for rapid eye movement detection of the newborn.

This paper compares an extended conventional filter technique for automated detection and analysis of rapid eye movements (REM) in neonates, using amplitude, synchrony, velocity, and coherence threshold criteria, with a matched filtering technique using the morphology of the REM waveform. Analyses of both simulated and real data were carried out. Automated REM tabulations are compared with visual scoring by a trained observer. Both preterm and fullterm neonates were used to test these methods. Both the advantages and disadvantages of these two techniques are discussed as compared with conventional methods which use only amplitude and synchrony threshold criteria. The major advantage of the extended conventional over the conventional method, as well as the matched filtering over the extended conventional technique, is the increased REM detection rate for ten minute intervals of artifact-free sleep. More accurate methods of automated REM detection that can be applied over extended monitoring periods are still needed.

Computer Simulation↗

PubMed1994

Cardiorespiratory behavior during sleep in full-term and preterm neonates at comparable postconceptional term ages.

Cardiorespiratory behavior during sleep has been investigated by comparing visually analyzed minutes of EEG sleep with the digitized values of these two physiologic variables for each corresponding minute. Continuous 3-h nighttime sleep studies on 37 full-term and preterm neonates at comparable postconceptional term ages were acquired under controlled conditions, using a 24-channel computerized monitoring system and an automated event-marker program. Five thousand, two hundred ninety-four minutes were assigned an EEG state by traditional criteria. Eighteen preterm infants were compared with 19 full-term infants with respect to six cardiac and six respiratory measures: two nonspectral calculations (i.e. average per minute and variance of the means) and four spectral calculations of the cardiorespiratory signal (i.e. bandwidth, spectral edge, mean frequency, and ratio of harmonics). The relative capabilities of these measures to predict a sleep state change were investigated using discriminant analysis. A stepwise selection algorithm in discriminant analysis was used to identify the order of significance for the remaining variables. Eight cardiorespiratory measures were then submitted to multivariate analysis of variance to assess sleep state or preterm-full-term differences: mean frequency, bandwidth, average per minute, and ratio of harmonics for cardiac signals; and spectral edge, mean frequency, logarithm of variance, and ratio of harmonics for respiratory signals. Differences among the sleep states and between neonatal groups were highly significant (p < 0.0001). Interaction between sleep state and neonatal group was also significant (p < 0.034). Two variables differentiated preterm from full-term respiratory behavior: ratio (p < or = 0.001) and mean frequency (p < or = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular Physiological Phenomena↗

PubMed1993

Recovery of hippocampal dentate granule cell responsiveness to entorhinal cortical input following norepinephrine depletion.

Hippocampal dentate granule cell responsivity to excitatory input from entorhinal perforant path fibers was examined in the chronic rabbit preparation following norepinephrine (NE) depletion induced with the neurotoxin DSP4. To examine granule cell responsivity as a function of perforant path activation, constant low frequency stimulation (0.1 Hz) was applied to the perforant path using an ascending intensity series. To examine granule cell responsivity to more complex patterns of stimulation, a train of impulses, with a random interstimulus interval (Poisson distribution; mean frequency of 2 Hz), was applied to the perforant path. Both single impulse and random interval impulse stimulation revealed that NE depletion increased the average amplitude of the perforant path-granule cell population spike. The random interval impulse stimulation revealed that NE depletion also increased the magnitude and duration of second order inhibitory interactions. These changes were transient, however, and recovered over the 21 day test period. Hippocampal NE levels were reduced an average of 80% between 23 and 38 days post-DSP4. The activity of the rate-limiting enzyme for NE synthesis, tyrosine hydroxylase (TH), was reduced an average of 60%. That NE levels were reduced to a greater extent than was TH activity is suggestive of increased NE synthesis within the remaining nerve terminals. Such an increase in NE synthesis may reflect a compensatory response underlying the functional recovery of electrophysiological responsiveness following partial NE depletion.

Adrenergic Agents↗

PubMed1993

Assessing brain stem function.

Intraoperative neurophysiologic monitoring provides objective measures of nervous system function that are of value when operating in proximity to the brain stem. Real-time measurements of function can be correlated to operative manipulations in order to reduce the risk of damage in critically important regions. Techniques for evaluating brain stem function clinically and electrophysiologically are presented along with their applications during surgery of the brain stem.

Brain Diseases↗

PubMed1992

Instantaneous characterization of time-varying nonlinear systems.

A nonlinear system may be characterized by an orthogonal functional power series (FPS) computed from cross correlations between input and output variables. "Is the response changing over the course of the experiment?" is a fundamental question encountered in the analysis of both FPS and evoked potentials (EP's). Regression on closed-form functions of time produces a time-varying FPS or EP. Evaluation of these functions at a specified time point produces a system characterization for that instant.

Evoked Potentials↗

PubMed1992

Intraoperative somatosensory evoked potential monitoring of pelvic and acetabular fractures.

The efficacy of intraoperative somatosensory evoked potential (SSEP) monitoring was evaluated in the surgical management of 82 patients with pelvic and acetabular fractures. The injuries consisted of 45 acetabular fractures, 30 pelvic ring disruptions, and seven combined injuries. Preoperative neurological deficits were recorded in 34% of the study group (29% of those with an acetabular fracture and 47% of those with a pelvic ring injury). Three patients sustained an iatrogenic sciatic nerve injury during the study period (all of which were documented in the first 40 cases). Two patients sustained an exacerbation of an existing sciatic nerve injury. In the group of pelvic fractures, hazardous parts of the exposure, reduction, and fixation were identified by the SSEP monitoring. Removal of the provocative stimulus by the surgeon led to reversal of the SSEP abnormalities, and none of this group of patients sustained an iatrogenic injury. When the intraoperative SSEP changes were noted during an acetabular fracture fixation, immediate attempts were made to relieve the excessive tension on the sciatic nerve by replacing or removing a retractor, flexing the knee, extending the hip, or dividing the femoral insertion of the gluteus maximus. None of the SSEP changes were associated with the lacerative injury to the sciatic nerve. For the method to be clinically effective in reducing the incidence of neurological deficit, even subtle changes in the SSEP tracing must be recognized immediately by the neurophysiologist so that a corresponding corrective measure can be rapidly undertaken by the surgeon to remove the offending stimulus.

Acetabulum↗

PubMed1991

Kindling-induced potentiation of excitatory and inhibitory inputs to hippocampal dentate granule cells. I. Effects on linear and non-linear response characteristics.

Epileptiform activity is known to alter both excitatory and inhibitory circuits within the network of neurons that comprise the hippocampal formation. In the present experiment, kindling-induced alterations in the functional properties of the rabbit perforant path-dentate circuit were analyzed using non-linear system analytic procedures. System input consisted of a random train of impulses applied to the perforant path. System output was the perforant path-granule cell population spike amplitude evoked by each impulse in the train. The results of non-linear systems analysis were compared with the results from twin impulse analysis of kindling-induced alterations within the hippocampal dentate gyrus. Compared to twin impulse procedures, non-linear systems analytic procedures revealed a reduced duration and magnitude of kindling-induced inhibitory interactions to interstimulus intervals of 10-200 ms. The increased magnitude of inhibitory interactions did not decay to prekindled magnitude until 16 weeks postkindling. In contrast, kindling-induced potentiation of the population spike had decayed within 10 weeks of the last stage 5 seizure. Despite the decay of electrophysiological responses to prekindled levels, only a few kindling stimulations were required to evoke fully kindled seizures. Thus, electrophysiological alterations within the first synaptic relay of the hippocampal trisynaptic circuit, the dentate gyrus, cannot explain the long duration of the kindling effect.

Animals↗

PubMed1990

Effects of combined superoxide dismutase and deferoxamine on recovery of brainstem auditory evoked potentials and EEG after asphyxial cardiac arrest in dogs.

In a randomized study in 23 dogs, we tested the following anti-free radical combination therapy, administered at the beginning of CPR, following apnea-induced cardiac arrest of 7 min: a) ventilation with 100% nitrogen for 30 s to allow the delivery of therapy before oxygen; b) superoxide dismutase (10 mg/kg i.a. followed by 10 mg/kg i.v. over 1 h) to scavenge the superoxide anion radical; and c) deferoxamine (20 mg/kg i.v. over 1 h) to prevent membrane lipid peroxidation. We evaluated the effects of this treatment on the recovery of cardiovascular and cerebral variables short term (6 h) after resuscitation. We reported previously that this treatment mitigated the post-arrest cerebral blood flow changes and enhanced the recovery of somatosensory evoked potentials. This is a secondary report from the same study concerning the effects of this treatment on the recovery of brainstem auditory evoked potentials (BAEPs) and EEG. Compared to control (n = 10), the experimental treatment (n = 10) did not exert a clearcut, significant effect on the recovery of BAEP which normalized in both groups at 1 h post-arrest and enhanced the post-arrest recovery of EEG spectra total power by reducing the post-arrest increase in slow frequency bands. However, the relative distribution of EEG frequencies never recovered the pre-arrest pattern in either group, during the 6 h post-arrest observation period. We conclude that the combination treatment tested enhances the recovery but does not normalize cerebral function post-arrest, suggesting that other treatments should also be entertained or that, indeed, such an insult may not be completely ameliorated by any such treatments.

Animals↗

PubMed1990

Computer analyses of EEG-sleep in the neonate: methodological considerations.

Neonatal EEG interpretation can aid in the estimation of central nervous system maturation, as well as provide diagnostic and prognostic information of the high-risk infant. However, one cannot easily visualize the complex interrelationships coupling EEG and polysomnographic components of the EEG-sleep rhythm. This is particularly relevant for the preterm neonate, in whom a rudimentary sleep cycle has not yet been clearly delineated. Computer analysis can augment the information derived from the visual interpretation of scalp-generated EEG activity. Automated techniques for EEG-sleep analysis have only recently been applied to a neonatal population. Such studies have been limited to full-term rather than preterm infants and rely on conventional methods that assume stationarity of neurophysiologic signals. We describe a computer system that simultaneously compares behavioral and electrographic components of EEG-sleep in a manner that preserves the integrity of the signals over time, while investigating the time- and frequency-dependent relationships among signals. Strategies for on-line and off-line editing, data storage, and off-line signal processing are described. Computational algorithms regarding analyses of EEG power, motility, and cardiorespiratory data are being used to study the ontogeny of EEG-sleep in asymptomatic preterm and full-term neonates. Computer strategies are based on both principles of stationarity and nonstationarity of physiologic signals and are applied depending on the temporal resolution required for specific signal processing needs.

Computer Systems↗

PubMed1990

Acoustic recordings from experimental saccular aneurysms in dogs.

In an effort to isolate and characterize the emission of acoustic signals from saccular aneurysms, we made a series of invasive microphone recordings from experimental aneurysms created on the common carotid arteries of dogs using the vein pouch technique. Using a modified probe microphone, we compared recordings from the common carotid artery before creation of the aneurysm to recordings from the aneurysmal surface, both before and after clip occlusion. We then performed spectral analysis, band-pass filtering, and spectrographic analysis to compare the dominant frequency and width of the frequency range of both the aneurysmal and carotid recorded signals. The aneurysmal signals had a significantly higher dominant frequency (p less than or equal to 0.05) and a significantly wider frequency range (p less than or equal to 0.05) than the carotid signals. Aneurysmal signals recorded under conditions of systemic hypotension had a significantly lower frequency (p less than or equal to 0.05) than aneurysmal signals recorded under conditions of hypertension. Our results support the assumptions that acoustic signals from experimental saccular aneurysms are distinct from those of the parent vessel and that the aneurysmal signal can be characterized using passive microphone recordings.

Animals↗

PubMed1989

Delirium: a subcortical phenomenon?

Evoked potentials of 23 patients with chronic liver disease and delirium were compared with those of matched controls without delirium. Delirious subjects had significantly worse scores on the Mini-Mental State Exam and Trail Making Tests. Mean peak activity from computerized spectral analysis of the EEG was lower in delirious subjects than in nondelirious subjects (7.5 +/- 3.8 cycles per second (cps) and 9.5 +/- 3.2 cps, respectively). Mean auditory brainstem evoked potentials were abnormal in both groups, with delirious subjects showing a bimodal distribution of latency values and a greater proportion of abnormal values. Somatosensory evoked potentials were abnormal for delirious patients and normal for controls, and the differences were significant. The data suggest that the underlying pathophysiology of delirium may lie, at least in part, at the subcortical level.

Adolescent↗