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Biomedical subjects

M R Nuwer

Publications and source records attributed to M R Nuwer.

At least 73 records · Page 4Linked to original sources
PubMed1990

Electrophysiologic evaluation and monitoring of spinal cord and root function.

The spinal cord can be monitored intraoperatively with somatosensory evoked potentials. Although this is only a posterior column test, it is sensitive to most acute cord impairment. Techniques have become standardized and include monitoring from scalp or around the spinal cord itself. Motor evoked responses are currently under investigation for possible OR use, and they may someday supersede somatosensory testing as the monitoring tool of choice.

Electrodiagnosis↗
PubMed1988

Frequency analysis and topographic mapping of EEG and evoked potentials in epilepsy.

Frequency analysis (spectral analysis) of both EEG and evoked potentials were studied prospectively in 52 patients with complex partial seizures to see if such tests could help localize the epileptic focus. Results were examined in line, bar and topographic head display formats. Asymmetries of fast and slow frequency components were identified in 26/52 patients. The existence and localization of such frequency alterations agreed with the overall results of other tests including the routine EEG, ictal EEG records, thiopental-activated EEG, CT or MRI, positron computed tomography (PET), and neuropsychometric testing. Changes were present in all 5 temporal lobe epilepsy cases that had a focal CT or MRI change, and in a majority (17/33) of cases in which the baseline EEG showed no focal slowing. These changes agreed with the preponderance of evidence in lateralizing the epileptic focus. Overall, EEG and evoked potential frequency analysis and topographic mapping do appear to offer data which are useful and complementary to other available test results, especially when a suspected lesion does not already show up as a defect on the CT scan or as a well-defined EEG slow focus. Considerable care needs to be taken to identify artifacts and normal EEG variants when interpreting these tests.

Adolescent↗
PubMed1988

Cortical evoked potential monitoring during spinal surgery: sensitivity, specificity, reliability, and criteria for alarm.

Cortical somatosensory evoked potentials (EP) were used for intraoperative monitoring of spinal cord integrity during 158 consecutive cases involving surgical correction of spinal deformities. Using a monitoring technique designed to optimize recording, 88% of patients had stable EP results at the time of spinal manipulation. However, five of six patients with preexistent neurological deficits did not have stable EPs. A persistent EP amplitude attenuation of greater than or equal to 40% was a sensitive and specific criterion for alarm. Seven patients had transient attenuations of greater than or equal to 40% after distraction that recovered, so that the distraction instrumentation could be left in place. Overall, this particular cortical somatosensory EP recording technique appears to be appropriate for clinical monitoring. Other recording techniques may be necessary for patients with preexisting neurological deficits.

Adolescent↗
PubMed1988

Use of somatosensory evoked potentials for intraoperative monitoring of cerebral and spinal cord function.

EPs can be used in the operating room for monitoring the integrity of many levels of the central nervous system. SEPs can monitor the spinal cord, brain stem, and cerebral hemispheres. Such monitoring can alert the surgical team to the presence of complications, allowing prompt correction in some cases so as to prevent postoperative neurologic deficits. Monitoring can be done from stimulation of either the lower or upper extremity. Recordings can be taken over the scalp or can be made from electrodes put into the surgical site itself. Monitoring of the spinal cord is most often done for surgery involving scoliosis, spinal tumors, or arteriovenous malformations, and during crossclamping of the thoracic aorta. Animal models and human surgical experience has shown that monitoring the posterior columns is an effective way to assess the status of the motor pathways of the spinal cord, because the two pathways are both affected in almost all acute circumstances. Monitoring can also assess the functional status of the cerebral hemispheres. This is most often applied during carotid endarterectomy or repair of aneurysms of the carotid artery and its branches. Occasionally, this has also been applied to monitoring the cortex during cardiopulmonary bypass. Such EP monitoring does not cover the wide areas of cortex that can be monitored using EEG, but the EPs do tend to change and disappear at a level of ischemia nearer to the true critical level. Intraoperative median nerve EPs can also be used to identify the hand level of the motor and somatosensory cortex. Such identification of motor cortex can help guide neurosurgeons in their choice of how or where to perform a biopsy, excision, and the like. Overall, intraoperative evoked potential monitoring is becoming widespread because it is a practical way to help avoid neurologic complications, and it can be carried out using equipment already available in many hospitals. A substantial further review in this field can be found in Evoked Potential Monitoring in the Operating Room.

Brain Diseases↗
PubMed1988

Quantitative EEG: I. Techniques and problems of frequency analysis and topographic mapping.

Quantitative EEG techniques include frequency analysis (spectral analysis), significance probability mapping, and other analytic techniques. Each can be done on spontaneous EEG in various states or in conjunction with sensory stimulation. Several types of displays are available, including topographic mapping of scalp electrical activity. Assessment of normality in these records must take into account age, gender, state of alertness, medications, and other factors. Substantial statistical issues are critical in these assessments and must be thoroughly understood by all users. Other problems can easily mislead the interpretations of these tests, sometimes in subtle ways. References are often active. Traditional EEG artifacts can appear in surprising ways, and new artifacts can be caused by computer processing and display format. Important technical choices must be made in recording quantitative EEG, and the correct choices are not clearly known. These choices include references, number of channels, epoch length, number of epochs acquired, and artifact rejection criteria. This review summarizes a variety of the techniques commonly used. Advantages of particular methods are contrasted. Problems with these techniques are discussed at length, with emphasis on the difficulties and choices facing users of typical commercial quantitative EEG machines. As quantitative EEG techniques come into some clinical use, issues of nomenclature, technique, normality, and problems will become widely understood. For now, clinicians should respect the problems inherent in these techniques. Quantitative EEG tests should only be interpreted along with the traditional paper EEG tracing that represents the raw data on which the quantitative analysis was performed. A thorough familiarity with traditional EEG is a prerequisite to understanding the meaning of the quantitative EEG results.

Arousal↗
PubMed1988

Quantitative EEG: II. Frequency analysis and topographic mapping in clinical settings.

The results of many studies using quantitative EEG techniques in clinical settings have been published. Those reports are reviewed here, with emphasis on those that used EEG frequency analysis and topographic mapping. In cerebrovascular disease, these methods can confirm the existence of lesions that are too mild to show up on routine EEG or too mild or too early to show up on computed tomography. The results correlate well with cerebral blood flow studies. These EEG tests can be done continuously in an intensive care unit or operating room. However, exact localization ability is inferior to that seen using traditional neuroimaging tests. In epilepsy, quantitative EEG techniques have found subtle degrees of background EEG changes near epileptic foci. Other methods can quantify epileptic spikes in useful ways and can indicate which region is driving other regions during seizures. Quantification is also useful for measuring drug effects when drugs (such as thiopental) are given deliberately to provoke acute EEG changes. Other measurements of drug effects may become useful in the future. In patients with mass lesions and metabolic encephalopathies, quantitative EEG changes do occur, and some of these correlate with the clinical state. However, in the latter settings, the clinical advantages for patient care are not yet clear, especially in comparison to available neuro-imaging studies and other routine medical tests. For dementia, quantitative EEG techniques are being developed. Some of these tests are accurate in moderately or severely demented patients, but there is still poor accuracy for early or borderline cases. For dyslexia, schizophrenia, and depression, there is a considerable volume of research reports but still no consensus about how to use quantitative EEG tests for care of individual patients. These tests require substantial user expertise in EEG. At present, these tests should be viewed as adjunctive to traditional EEG testing: such routine EEG testing should serve as the foundation for any clinical use of quantitative EEG tools.

Brain↗
PubMed1988

Clinical experience with azathioprine: the pros.

We performed a randomized, placebo-controlled, double-blind, comparative clinical trial of 36 weeks of methylprednisolone and 3 years of azathioprine in 98 patients in the chronic progression phase of multiple sclerosis (MS). We demonstrated a trend in favor of the combination therapy for limiting progression. The relapse rate in the azathioprine recipients was half that of the control group, and visual evoked potential latencies were stabilized in those who received the combination. We think that a therapeutic trial of continuous use of the combination of adrenal steroids with azathioprine would be worthwhile if administered early in the course of the disease.

Azathioprine↗
PubMed1988

Computed electroencephalographic topographic brain mapping. A new and accurate monitor of cerebral circulation and function for patients having carotid endarterectomy.

To determine the usefulness of computed electroencephalographic (EEG) topographic (CET) brain mapping to monitor neurologic function during carotid endarterectomy (CEA), 46 consecutive patients having CEA were monitored preoperatively, intraoperatively, and immediately postoperatively by CET brain mapping and simultaneous 16-lead EEG. Preoperative studies revealed that 7 of 16 asymptomatic patients, 5 of 11 patients with amaurosis fugax, and 8 of 12 patients with transient ischemic attacks (TIAs) had abnormal CET brain mapping suggestive of previous subclinical stroke. EEG was abnormal in only 8 of the 20 patients with abnormal CET brain mapping. Intraoperatively during carotid cross-clamping, ischemic changes were seen on CET brain mapping in 23 patients whereas EEG detected these changes in only 13 patients. Ischemic changes detected by intraoperative CET brain mapping were more likely to occur in patients with previous stroke (six of seven) than in patients without previous stroke (17 of 39), p less than 0.05. Patients with changes detected by intraoperative CET brain mapping had an average carotid back-pressure of 38 mm Hg, in contrast to 57 mm Hg for patients without CET brain mapping changes, p less than 0.05. After endarterectomy, CET brain mapping revealed new ischemic changes in one patient who awoke with a mild stroke and in one patient who had TIAs and amaurosis fugax within 6 hours of surgery. We conclude that CET brain mapping is a sensitive, accurate, and useful noninvasive monitor of cerebral circulation and function for patients having CEA.(ABSTRACT TRUNCATED AT 250 WORDS)

Blindness↗
PubMed1987

Recording electrode site nomenclature.

Several additions and extensions to the 10-20 System have been proposed. The major sets of proposals are reviewed here. The principal uses of these additional scalp recording sites are for clinical evoked potential testing and for acquisition of EEGs from very large numbers of scalp sites. Three separate systematic nomenclatures have arisen for filling in the half-step gaps in the 10-20 placements. These are compared and contrasted here.

Electroencephalography↗
PubMed1987

The centrifugal effect and other spatial artifacts of topographic EEG mapping.

Topographic maps of EEG can contain artifacts that are foreign to clinical electroencephalographers trained to read traditional EEG records. Several spatial artifacts are described and discussed here, including the centrifugal effect, ring enhancement, spatial aliasing, electrode hills and holes, color-step effects, and restriction of minima/maxima to electrode sites. Users of quantitated EEG with topographic maps should be aware of these artifacts and should have a high suspicion for other analogous artifactual spatial phenomena when interpreting individual patient records.

Color↗
PubMed1987

Evoked potentials predict the clinical changes in a multiple sclerosis drug study.

Visual, brainstem auditory, and median nerve somatosensory evoked potential (EP) tests were performed annually during a 3-year, double-blind, placebo-controlled study of azathioprine with or without steroids in chronic progressive MS. Treatment-related visual and somatosensory EP changes became statistically different 1 year before corresponding differences were seen in the Standard Neurological Examination scores. The statistical significance of EP changes was substantially greater than seen for changes in other clinical scales. The degree of significance was increased by using EP latency values, rather than simple criteria for change. EPs are sensitive, objective measurements useful in MS therapeutic trials.

Adult↗
PubMed1987

Evaluation of stroke using EEG frequency analysis and topographic mapping.

Frequency analysis and topographic mapping of EEG were studied in 20 consecutive patients with mild stroke and in 20 age-matched normal subjects. Abnormally large increases in delta and decreases in alpha activity were seen over the scalp in 17 of 20 patients and in no normal subjects. Theta was unreliable by itself. The scalp area so localized appeared correct in each case compared with signs, symptoms, and neuroimaging studies. These computerized EEG analysis techniques were abnormal significantly more often than routine EEGs. The results obtained here with simple techniques agree with past studies done with more complex types of EEG analysis.

Aged↗
PubMed1986

Postoperative neurological deficits may occur despite unchanged intraoperative somatosensory evoked potentials.

We describe 6 patients who demonstrated postoperative neurological deficits despite unchanged somatosensory evoked potentials during intraoperative monitoring. Although there is both experimental and clinical evidence that somatosensory evoked potentials are sensitive to some types of intraoperative mishap, the technique should be employed with an awareness of its possible limitations.

Adolescent↗