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Biomedical subjects

R G Emerson

Publications and source records attributed to R G Emerson.

31 records · Page 2Linked to original sources
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↗
PubMed1986

Electrophysiologic features of abetalipoproteinemia: functional consequences of vitamin E deficiency.

We performed electrophysiologic testing in 10 patients with abetalipoproteinemia (ABL). Peripheral nerve studies implied an axonal disorder. Visual evoked potentials demonstrated prolonged P100 latency in three patients and abnormal electroretinograms in six. Somatosensory evoked potentials indicated dorsal column dysfunction in eight patients. Brainstem auditory evoked potentials were normal. Findings were consistent with the known neuropathology of ABL and of experimental vitamin E deficiency. Stabilization or improvement in electrophysiologic findings occurred with vitamin E supplementation. Neurophysiologic tests document retinal, central somatosensory and peripheral nerve lesions in vitamin E deficiency and provide an objective indication of response to treatment.

Abetalipoproteinemia↗
PubMed1985

Treatment of cerebrotendinous xanthomatosis with chenodeoxycholic acid.

We describe a patient with cerebrotendinous xanthomatosis who was treated for one year with chenodeoxycholic acid. Modest clinical improvement was accompanied by marked improvement in visual and brainstem auditory evoked potentials. Improved central nervous system function coincided with return of plasma and cerebrospinal fluid cholestanol levels to normal.

Adult↗
PubMed1985

Phase synchronized triggering: a method for coherent noise elimination in evoked potential recording.

While standard evoked potential recording techniques reliably attenuate gaussian and white noise, they are not similarly effective in reducing coherent noise such as that induced by power lines. We have presented a technique that will effectively eliminate coherent noise. This technique is especially appealing for clinical settings where 60 Hz artifact and a few discrete frequencies are most troublesome, such as in operating rooms or intensive care units. An added advantage of the technique is that it is especially well suited to applications requiring small sample sizes.

Electricity↗
PubMed1985

Real-time reconstruction of evoked potentials using a new two-dimensional filter method.

Standard techniques for evoked potential recording extract a stimulus-locked event from accompanying noise by averaging a large number of sequentially obtained responses. This approach is valid only to the extent that the nervous system's electrical response to successive stimuli is identical. The technique is suboptimal for recording unstable evoked potentials which vary with the subject's state and attention. Similarly, standard methods are suboptimal for efficiently analyzing rapid changes such as may be seen in the operating room. We developed an evoked potential recording method that reconstructs the individual evoked responses (or small subaverages of evoked potentials) to a series of stimuli. First, the raw data from an entire series of one to several hundred responses are recorded digitally. Using a frequency domain two-dimensional filter, the data are then filtered twice, once along the data sequence axis for each trial, and again along the cross-trial sequence axis for comparable frequency coefficients in sequential trials. The reconstructed filtered evoked potentials are plotted, with successive responses stacked for easy tracking of component changes.

Electroencephalography↗
PubMed1985

Intraoperative BAER monitoring and hearing preservation in the treatment of acoustic neuromas.

We treated 20 cases of acoustic neuromas in the last 2 1/2 years using the suboccipital approach with intraoperative monitoring of eighth nerve function in an attempt to preserve hearing. Total tumor removal was accomplished in 18 cases. Three tumors were small (less than 2 cm in size); 3 tumors were moderate sized (2 to 3 cm) and 14 tumors were large (greater than 3 cm). In 15 cases, all BAER components were lost during surgery. These patients had no postoperative hearing. In five patients there was intraoperative preservation of some or all BAER components. These included the three patients with small tumors and two other patients with moderate sized tumors. One patient with a moderate size tumor had preservation of wave 1 only, and had no postoperative speech discrimination. One patient with a small tumor retained all 5 BAER components, but had no postoperative hearing. Three patients in our series retained functional hearing after surgery, including 3 of 5 patients with tumors 2 cm or smaller. Intraoperative BAER monitoring appears to be useful in predicting postoperative hearing. Tumor size seems to be the primary factor in preservation of hearing following acoustic neuroma surgery.

Adult↗
PubMed1984

Somatosensory evoked potentials following median nerve stimulation. I. The cervical components.

Median somatosensory evoked potentials were studied in 20 normal adult volunteers. Recording electrodes were positioned over posterior, anterior and lateral neck, as well as on the scalp. Three distinct cervical potentials were identified. Immediately after the afferent volley passes Erb's point, a travelling wave is recorded in the lateral cervical electrodes ipsilateral to the side of stimulation. This represents the afferent volley approaching the spinal cord in the proximal brachial plexus and cervical roots and has been designated the 'proximal plexus volley' (PPV). Following PPV, a second travelling wave is recorded which increases in latency from low to high cervical levels. It represents the afferent volley in the dorsal column, and has been designated the 'dorsal column volley' (DCV). Following DCV, a stationary potential, designated CERV N13/P13, is recorded with characteristics of a transverse midline dipole having maximal negativity posteriorly and maximal positivity anteriorly. This potential may be generated by interneurons in the dorsal grey of the cervical cord. Each of these cervical travelling waves is accompanied by a negative far-field potential recorded at the scalp. The PPV is accompanied by a negative scalp deflection with a nominal latency of 10 ms (N10), and the peak of DCV at SC1 is accompanied by a scalp negativity with a nominal latency of 12 ms (N12). In view of these observations, it is necessary to reexamine assumptions regarding the polarity of scalp-recorded potentials generated by remote neural events.

Adolescent↗
PubMed1983

Spinal and early scalp-recorded components of the somatosensory evoked potential following stimulation of the posterior tibial nerve.

Somatosensory evoked potentials (SEPs) were elicited by stimulation of the posterior tibial nerve (PTN) in 12 normal adults. Recording using both cephalic and non-cephalic references were obtained from multiple electrodes placed over the spine and scalp. Following PTN stimulation, the fastest recorded potentials of the afferent sensory volley proceeds up the spinal cord at constant velocity. After arrival of the volley at cervical cord levels, 3 widely distributed waves, P28, P31 and N34, are recorded from scalp electrodes. These 'far-field' potentials are followed by a localized positivity (P38) which has a peak voltage either at the vertex or just laterally toward the side of stimulation. A contralateral negativity (N38) was present in most individuals. We propose that P28 arises from medial lemniscus; that P31 is generated by ventrobasal thalamus; and that N34 is probably the result of further activity in thalamus and/or thalamocortical radiations. The P38/N38 complex represents the primary cortical response to PTN stimulation. Its most consistent characteristic is a positivity at the vertex or immediately adjacent scalp areas ipsilateral to the stimulated leg. The topography of the P38/N38 potential varies slightly from individual to individual in a manner consistent with a functional dipole situated in the leg and foot area on the mesial aspect of the postcentral gyrus, whose exact location and orientation changes in accordance with known variations in the location of the leg area.

Adolescent↗
PubMed1981

Toxoplasmosis: a treatable neurologic disease in the immunologically compromised patient.

A 10-year-old girl with aplastic anemia developed seizures and a mild hemiparesis following a bone marrow transplant. Based on serologic evidence and a computed tomography scan, which showed a left parietal lucency with ring enhancement, a diagnosis of toxoplasmosis was considered. A brain biopsy of the lucent area demonstrated the inflammation and necrosis but no organisms were seen. During a six-week course of pyrimethamine, sulfadiazine, and folinic acid therapy there was clinical and neuroradiologic resolution. The short course of therapy as well as the inadvertent substitution of folic acid for folinic acid and trimethoprim-sulfamethoxazole for sulfadiazine resulted in the reappearance of neurologic deficits. Reinstitution of appropriate therapy produced gradual improvement over a nine-month period. Serial computer tomography scans correlated with the clinical course. In the immunologically compromised host CNS toxoplasmosis should be considered in the differential diagnosis of an evolving CNS syndrome. Early detection and prolonged therapy with appropriate drugs can result in a favorable outcome. Computed tomography scanning may be helpful in diagnosis and follow-up.

Anemia, Aplastic↗