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Biomedical subjects

R G Emerson

Publications and source records attributed to R G Emerson.

At least 19 recordsLinked to original sources
PubMed2001

Continuous EEG monitoring and midazolam infusion for refractory nonconvulsive status epilepticus.

BACKGROUND: Although cIV-MDZ has emerged as a popular alternative to barbiturate therapy for refractory status epilepticus (RSE), experience with its use for this indication is limited. OBJECTIVE: - To evaluate the efficacy of continuous intravenous midazolam (cIV-MDZ) for attaining sustained seizure control in patients with RSE. METHODS: The authors reviewed 33 episodes of RSE treated with cIV-MDZ in their neurologic intensive care unit over 6 years. All patients were monitored with continuous EEG (cEEG). MDZ infusion rates were titrated to eliminate clinical and EEG seizure activity; cIV-MDZ was discontinued once patients were seizure-free for 24 hours. Acute treatment failures (seizures 1 to 6 hours after starting cIV-MDZ), breakthrough seizures (after 6 hours of therapy), post-treatment seizures (within 48 hours of discontinuing therapy), and ultimate treatment failure (frequent seizures that led to treatment with pentobarbital or propofol) were identified. RESULTS: All patients were in nonconvulsive SE at the time cIV-MDZ was started; the mean duration of SE before treatment was 3.9 days (range 0 to 17 days). In addition to benzodiazepines, 94% of patients had received at least two antiepileptic drugs (AED) before starting cIV-MDZ. The mean loading dose was 0.19 mg/kg, the mean maximal infusion rate was 0.22 mg/kg/h, and the mean duration of cIV-MDZ therapy was 4.2 days (range 1 to 14 days). Acute treatment failure occurred in 18% (6/33) of episodes, breakthrough seizures in 56% (18/32), post-treatment seizures in 68% (19/28), and ultimate treatment failure in 18% (6/33). Breakthrough seizures were clinically subtle or purely electrographic in 89% (16/18) of cases and were associated with an increased risk of developing post-treatment seizures (p = 0.01). CONCLUSIONS: Although most patients with RSE initially responded to cIV-MDZ, over half developed subsequent breakthrough seizures, which were predictive of post-treatment seizures and were often detectable only with cEEG. Titrating cIV-MDZ to burst suppression, more aggressive treatment with concurrent AED, or a longer period of initial treatment may reduce the high proportion of patients with RSE who relapse after cIV-MDZ is discontinued.

Adult↗
PubMed2001

Attenuation of somatosensory evoked potentials during positioning in a patient undergoing suboccipital craniectomy for Chiari I malformation with syringomyelia.

Intraoperative electrophysiologic monitoring can diminish the risk of neurologic injury by enabling the detection of injury at a time when it can be reversed or minimized. This report describes a 14-year-old girl with a Chiari's malformation type I and syringomyelia who underwent a suboccipital decompression and dural patch grafting with concurrent somatosensory evoked potentials. When the patient was turned into the prone position and the neck was flexed, the left-sided somatosensory evoked potential deteriorated. After the patient's neck was repositioned, the left median nerve potential improved but did not return to baseline. Postoperatively, the patient had decreased proprioception of her left arm, which completely resolved at 2-week follow-up. This single case report does not establish the need for routine somatosensory evoked potential monitoring. Nevertheless, deterioration of the potential in this case led directly to a change in the surgical positioning, which may have significantly reduced the chances of a permanent neurologic injury.

Adolescent↗
PubMed1999

Spike detection II: automatic, perception-based detection and clustering.

OBJECTIVES: We developed perception-based spike detection and clustering algorithms. METHODS: The detection algorithm employs a novel, multiple monotonic neural network (MMNN). It is tested on two short-duration EEG databases containing 2400 spikes from 50 epilepsy patients and 10 control subjects. Previous studies are compared for database difficulty and reliability and algorithm accuracy. Automatic grouping of spikes via hierarchical clustering (using topology and morphology) is visually compared with hand marked grouping on a single record. RESULTS: The MMNN algorithm is found to operate close to the ability of a human expert while alleviating problems related to overtraining. The hierarchical and hand marked spike groupings are found to be strikingly similar. CONCLUSIONS: An automatic detection algorithm need not be as accurate as a human expert to be clinically useful. A user interface that allows the neurologist to quickly delete artifacts and determine whether there are multiple spike generators is sufficient.

Adolescent↗
PubMed1998

Evidence for unconscious memory processing during elective cardiac surgery.

BACKGROUND: Many anesthetic drugs have been shown to disrupt conscious recall (explicit memory) in volunteers. However, unconscious processing (implicit memory) of intraoperative auditory material may occur during general anesthesia and may provide an opportunity for intraoperative therapeutic intervention. In this study, we examined patients undergoing elective cardiac surgery for evidence of intraoperative implicit and explicit memory. METHODS AND RESULTS: Twenty-five subjects provided written informed consent and underwent general anesthesia and cardiopulmonary bypass for cardiac surgery. During the operation, patients were randomized to receive 1 of 2 different audiotapes of associated word pairs. Postoperatively, a blinded observer conducted a standardized interview to determine the extent of intraoperative implicit and explicit memory. With the use of free association, significant intraoperative implicit memory was found. In contrast, no patient had spontaneous or directed recall of intraoperative events, and we did not find evidence of intraoperative explicit memory with a recognition task. CONCLUSIONS: Patients undergoing general anesthesia for cardiac surgery were reliably able to reinforce associations between word pairs solely on the basis of their intraoperative presentation. This provides further evidence that patients are capable of processing intraoperative auditory information.

Adult↗
PubMed1998

Evoked potentials in clinical trials for multiple sclerosis.

Multiple sclerosis produces disruption of conduction in the central nervous system by a variety of mechanisms, relating, in part, to loss of the myelin sheath. Although often not well correlated with the clinical course of the disease in individual patients, the resulting evoked potential (EP) disturbances can serve as measures of an accumulating disease burden, particularly in longitudinal population studies. Accordingly, EPs can serve as useful instruments for assessing the effectiveness of therapeutic agents which may alter the course of the multiple sclerosis. Furthermore, since EPs measure conduction within the central nervous system, they provide a means of directly assessing symptomatic treatments designed to improve central conduction.

Clinical Trials as Topic↗
PubMed1996

Intraoperative monitoring of motor evoked potentials: a review of 116 cases.

We reviewed the results of motor evoked potential (MEP) and somatosensory evoked potential (SEP) monitoring during 116 operations on the spine or spinal cord. We monitored MEPs by electrically stimulating the spinal cord and recording compound muscle action potentials from lower extremity muscles and monitored SEPs by stimulating posterior tibial or peroneal nerves and recording both cortical and subcortical evoked potentials. We maintained anesthesia with an N2O/O2/opioid technique supplemented with a halogenated inhalational agent and maintained partial neuromuscular blockade using a vecuronium infusion. Both MEPs and SEPs could be recorded in 99 cases (85%). Neither MEPs nor SEPs were recorded in eight patients, all of whom had preexisting severe myelopathies. Only SEPs could be recorded in two patients, and only MEPs were obtained in seven cases. Deterioration of evoked potentials occurred during nine operations (8%). In eight cases, both SEPs and MEPs deteriorated; in one case, only MEPs deteriorated. In four cases, the changes in the monitored signals led to major alterations in the surgery. We believe that optimal monitoring during spinal surgery requires recording both SEPs and MEPs. This provides independent verification of spinal cord integrity using two parallel but independent systems, and also allows detection of the occasional insults that selectively affect either motor or sensory systems.

Evoked Potentials, Motor↗
PubMed1995

Propagation patterns of temporal spikes.

In standard EEG recordings, spikes appear as single events characterized mainly by the scalp location of the their peak voltage. The signal-to-noise ratio of raw EEG is usually too high to permit more detailed analysis. We used spike averaging to improve the resolution of interictal spikes in 40 patients with temporal lobe epilepsy. Spikes were identified visually in raw, digitally stored EEG. When multiple spike types were present in a patient, they were grouped separately. Spikes were synchronized for averaging by aligning their negative peaks in a designated channel. Sixteen patients demonstrated spike propagation from anterior temporal to posterior temporal electrode locations. Thirty-six patients demonstrated spread of spikes from anterior temporal to fronto-polar electrode sites. While anterior temporal and fronto-polar spikes were often synchronous, fronto-polar spikes followed anterior temporal discharges in 25% of cases and preceded them in 13%. Spike averaging revealed propagation patterns not apparent on visual inspection of raw EEG. We speculate that these patterns may reflect inherent physiological properties of temporal and frontal neuronal circuits, possibly utilized by the epileptogenic process.

Adolescent↗
PubMed1995

Implantable cardioverter-defibrillator. Evaluation of clinical neurologic outcome and electroencephalographic changes during implantation.

During placement of implantable cardioverter-defibrillators, ventricular arrhythmias are induced to test the function of the devices. Although cerebral hypoperfusion and ischemic electroencephalographic changes occur in patients while implantable cardioverter-defibrillators are being tested, no investigation has assessed neurologic outcome in these patients. Nine patients having either implantation or change of an implantable cardioverter-defibrillator underwent neurologic examination and neuropsychometric tests before and after the operation. After induction of general anesthesia and insertion of implantable cardioverter-defibrillator leads (when needed), ventricular fibrillation, ventricular flutter, or ventricular tachycardia, was induced by means of programmed electrical stimulation. Implantable cardioverter-defibrillator testing continued until satisfactory lead placement was confirmed. The intraoperative electroencephalographic recording was analyzed for evidence of ischemic change. In all, an electroencephalogram was recorded during 50 periods of circulatory arrest. Mean duration of the arrest periods was 13.6 seconds. By means of conventional visual inspection of the raw electroencephalogram, high-amplitude rhythmic delta or theta, voltage attenuation, or loss of fast frequency activity was observed in 30 of the arrests. By means of an automated technique of electroencephalographic interpretation based on power spectral analysis, electroencephalographic changes were correctly identified in 26 of the arrests. The incidence of these electroencephalographic changes was dependent on the arrest duration. The mean interval from arrest onset to electroencephalographic change was 7.5 seconds (standard deviation +/- 1.8 seconds). In patients with electroencephalographic changes during multiple arrests, no downward trend in this interval was detected in later arrests and no evidence of persistent ischemic change was observed in electroencephalograms recorded after the conclusion of implantable cardioverter-defibrillator testing. Postoperative neurologic and neuropsychometric testing was completed in eight patients, none of whom exhibited a new neurologic deficit, exacerbation of a preexisting neurologic condition, or significant deterioration in neuropsychometric performance. We conclude that the brief arrest of cerebral circulation induced during insertion of an implantable cardioverter-defibrillator is not associated with permanent neurologic injury.

Adult↗
PubMed1995

The reliability of quantitative electroencephalography as an indicator of cerebral ischemia.

The electroencephalogram (EEG) has been used to detect episodes of cerebral ischemia during various surgical procedures. Recently, computerized systems for recording and interpreting the quantitative EEG (QEEG) have been used by anesthesiologists because of their ease of application, clarity of display, and reported ability to identify ischemic EEG changes. However, the extent to which automated techniques of QEEG interpretation reliably differentiate cerebral ischemia from the confounding effects of anesthetics and other sources of "artifact" is not completely established. In this study, EEGs were recorded before and after defibrillator testing in patients undergoing implantable cardioverter defibrillator (ICD) placement and during analogous time periods in control patients undergoing abdominal surgery. EEGs were subjected to standard visual inspection by an experienced electroencephalographer and QEEG analysis with a commercially available system was used for automated EEG interpretation in order to evaluate the reliability of this quantitative technique. The CIMON technique identified episodes which met previously defined criteria for QEEG cerebral dysfunction and ischemic pattern in both groups, despite the presumed absence of cerebral ischemia in the control patients. Since there was no evidence of cerebral ischemia in the raw EEGs of either the ICD patients or the controls, these QEEG changes were not confirmed by conventional techniques of EEG interpretation. Our results suggest that caution is warranted when using automated systems for intraoperative interpretation of EEG.

Adult↗
PubMed1993

Monitoring during supratentorial surgery.

Electroneurophysiological monitoring is employed during various supratentorial surgical procedures. EEG and evoked potential monitoring are used to detect and to facilitate the timely correction of cerebral ischemia during carotid endarterectomy and aneurysm surgery. Direct cortical recording and stimulation is used to identify areas or cortex that would be likely to produce clinical deficits if removed. Electrocorticography is used to identify epileptogenic cortex intraoperatively during surgical treatment of epilepsy.

Brain Ischemia↗
PubMed1993

Monitoring of intraoperative motor-evoked potentials under conditions of controlled neuromuscular blockade.

Motor-evoked potentials were recorded after electrical spinal cord stimulation in 19 patients undergoing neurosurgical or orthopedic procedures. Anesthesia was maintained with nitrous oxide, opioids, and inhaled anesthetics. Vecuronium was infused sufficient to eliminate 90% of twitch tension. The spinal cord was stimulated using either epidural or subarachnoid electrodes. Compound muscle action potentials were recorded from quadriceps and tibialis anterior muscles. Well-formed, stable motor-evoked potentials were recorded in all but one patient, in whom a preexisting myelopathy was felt to preclude recording. Intraoperative deterioration of motor-evoked potentials occurred in one patient who had a postoperative neurologic deficit. This study demonstrates the feasibility and utility of intraoperative motor tract monitoring using direct spinal cord stimulation. Controlled neuromuscular blockade permits recording of compound muscle action potentials while eliminating patient motor activity that could interfere with surgery.

Action Potentials↗
PubMed1991

Repetitive high magnetic field stimulation: the effect upon rat brain.

The effect on rat brain of a large number of stimulations with a high strength pulsed magnetic field was investigated in 31 rats: 10 naive controls, 10 anesthetized controls, and 11 stimulated and anesthetized rats. An investigational magnetic stimulating device with a circular 5.5 inch diameter stimulating head was used. The stimulating coil was energized by 1000 V, 8000A, 200 microseconds half sine pulses at a rate of 8 Hz. The peak field strength was 3.4 T, and the peak field flux was approximately 53,000 T/sec. Stimulation was performed for 20 min at a rate of 8/stimuli per second, for a total of at least 10,000 stimulations. The rats were sacrificed after 8 days, and their brains were examined using light microscopy with hematoxylin and eosin staining, or electron microscopy. Histological samples were taken from the neocortex, the hippocampus, the basal ganglia, and the cerebellum. No significant changes were seen.

Animals↗
PubMed1988

Normal brain-stem auditory evoked potentials with abnormal latency-intensity studies in patients with acoustic neuromas.

Brain-stem auditory evoked potentials (BAEPs) are highly sensitive for detecting acoustic neuromas but false-negative results occur. We studied BAEPs preoperatively in 39 cases of acoustic neuroma. Absolute and interpeak latencies ipsilateral to the tumor, and interaural latency differences, were normal in four patients with small tumors. In three of these, however, results of latency-intensity studies were abnormal. In one patient, the latency-intensity result became normal postoperatively. If acoustic neuroma is suspected, and BAEPs are normal by usual criteria, latency-intensity functions should be examined to maximize chances of detecting a small tumor.

Acoustic Stimulation↗
PubMed1988

State-dependent changes in the N20 component of the median nerve somatosensory evoked potential.

Short-latency components of median nerve somatosensory evoked potentials are generally assumed to be unaffected by sleep and level of arousal. We found that sleep prolongs the latency and alters the morphology of the N20 component in normal subjects. These changes may represent differential effects of sleep on various elements contributing to generation of the N20. Failure to control for patient state may degrade the reliability of clinical somatosensory evoked potential testing.

Adult↗
PubMed1988

Anatomic and physiologic bases of posterior tibial nerve somatosensory evoked potentials.

Following stimulation of the posterior tibial nerve, lumbar electrodes record a response that is the composite of two signals, one (PV) corresponding to the afferent volley in the cauda equina and gracile tract, and another (N22) generated postsynaptically in the gray matter of the lumbar cord. Subcortical structures generate two distinct, widely distributed signals, recordable from scalp electrodes using a noncephalic reference, P31 and N34. P31 is most likely generated by the afferent volley in the caudal medial lemnicus. N34 probably reflects subcortical postsynaptic activity in brain stem and/or thalamus, respectively. The "primary" cortical response, P38/N38, has a complex scalp distribution reflecting the location of the leg area on the mesial aspect of the postcentral gyrus, within the interhemispheric fissure. It is most likely a composite waveform with multiple cortical generators.

Evoked Potentials, Somatosensory↗
PubMed1986

Dissociation of frontal N100 from occipital P100 in pattern reversal visual evoked potentials.

We studied the relationship between occipital P100 and frontal N100 in visual evoked potentials produced by pattern reversal in normal subjects and two groups of patients. Recording derivation was critical for interpretation since both Fz and Oz electrode sites are active. In 9 patients, but no normal subjects, P100 was absent. In these patients, use of a standard Oz-Fz montage resulted in the erroneous impression of a 'normal' P100 since a downward deflection was produced by the inverting effect of the amplifier on an intact N100 at Fz. When both P100 and N100 were present (at Oz and Fz respectively), their latencies were usually similar but not identical which contributed to apparent latency shifts or W-shaped wave forms in the Oz-Fz derivation. We conclude that use of a non-cephalic or relatively inactive scalp position (such as the mastoid) should be used as a reference site in addition to Fz to reduce interpretive errors.

Adolescent↗
PubMed1986

Effect of cervical spinal cord lesions on early components of the median nerve somatosensory evoked potential.

Clinical interpretation of median somatosensory evoked potentials (SEPs) is usually based on latency measurements of selected waveforms. The "cervicomedullary" potential (N14) is commonly recorded by measuring the voltage difference between cervical spine and frontal electrodes. This cervicomedullary potential is actually a composite waveform that is generated by several distinct neural structures. We present evidence that placement of additional recording electrodes to delineate the multiple cervical components of the median SEP enhances ability to detect and localize cervical cord lesions.

Adult↗