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Biomedical subjects

A S Wee

Publications and source records attributed to A S Wee.

At least 19 recordsLinked to original sources
PubMed1991

Far-field recording of compound muscle action potentials produced during brachial plexus stimulation.

In 15 normal subjects, compound muscle action potentials (CMAPs) produced during electrical stimulation of the brachial plexus were obtained at a distance (far field) from their sources (upper-limb muscles). These far-field CMAPs were recorded at the forehead, neck, and tip of the middle finger and were referred to a relatively inactive region (contralateral forearm or knee). At the proximal recording site (neck or forehead), the far-field CMAPs were generally triphasic in appearance when all of the muscles of the upper limb were activated during brachial plexus stimulation. The initial component was a negative wave; this was followed by a positive component which terminated in a negative potential. At the distal recording site (tip of middle finger), the far-field CMAPs usually had a biphasic appearance, with an initial positivity followed by a period of negativity. The contours of the major components of the far-field CMAPs were frequently interrupted by a series of small amplitude negative and positive peaks or inflections.

Action Potentials↗
PubMed1991

Construction of an electrode for intraoperative nerve stimulation.

The electrode described in this paper consist of a barrel or handle with its conducting cable and a detachable stimulating tip. It is constructed of inexpensive and commercially available materials and is disposable. During the course of a stimulation study, electrode tips of different lengths or curvatures may be substituted without the need to replace the electrode barrel and cable.

Electric Stimulation↗
PubMed1990

Pathologic findings in brains of patients with focal epileptic seizures who had a craniotomy procedure.

This report reviews the pathologic findings in brains of 12 patients with focal epileptic seizures who had a craniotomy procedure. A majority of patients (seven) had either a cerebral neoplasm or a developmental abnormality (tuberous sclerosis and hamartoma), and these were found in six of the nine patients with chronic and intractable seizures. Four patients had cortical gliosis or scarring, and one had a bacterial brain abscess. Ten patients had a visible focal structural lesion during cranial imaging procedures, and in two instances, the MRI study was more sensitive than the CT in detecting a cerebral lesion.

Adolescent↗
PubMed1990

Multiple pterygium syndrome: neuromuscular findings in a case.

A woman with multiple congenital joint deformities and webbing (multiple pterygium syndrome) is described. The electrophysiologic study revealed normal sensory and motor nerve conduction velocities. However, the compound muscle action potential amplitude and the voluntary motor unit size were reduced, suggesting a decrease in the number of muscle fibers. The muscle biopsy was otherwise unremarkable histologically and histochemically. Possible explanations for these findings are discussed.

Adult↗
PubMed1990

Volume-conducted or "far-field" compound action potentials originating from the intrinsic-hand muscles.

When a recording electrode is situated at a relatively far and roughly equal distance from multiple muscle action potential (MAP) sources such as the intrinsic-hand muscles (far-field recording), the individual MAPs generated by muscle fibers may contribute to the resultant compound potential with nearly equal weights depending on the orientation of the individual MAP fields. This is in contrast to recording MAPs directly over the muscle (near-field recording), in which the resultant potential primarily reflects the MAPs that were near the recording electrode. Far-field recorded compound MAPs(CMAPs) thus may provide another dimension or perspective into viewing the overall spatio-temporal relationship among MAPs generated by a large number of muscle fibers. In this study, we described CMAPs from intrinsic-hand muscles that were recorded at a distance from their potential sources.

Action Potentials↗
PubMed1989

Cortical somatosensory evoked potentials during acute hemorrhagic hypotension.

Cortical somatosensory evoked potential (SEP) recording to lower-limb stimulation was performed on a patient to monitor surgery for scoliosis. Intraoperatively, the patient developed acute and irreversible hemorrhagic hypotension. Cortical SEPs were clearly present with systolic blood pressures in the low 50s and upper 40s (mm Hg). The potentials deteriorated significantly with systolic pressures in the low 40s and disappeared with further reduction in systemic blood pressures.

Child↗
PubMed1989

Construction of a simple multi-lead electrode for intraoperative nerve recording. Technical note.

In the operating room, a fast and accurate means of recording nerve action potentials (NAP's) is always desirable. The multi-lead recording electrode described in this paper contains these desirable features. It can survey and obtain a number of NAP's from different nerve segments at the same time and under the same recording condition. The fixed distances between the recording leads enable quick calculation of conduction velocities of different nerve segments. Construction of the electrode is simple, and it can be designed to suit individual needs. The cost is marginal, reflecting primarily the costs of the original subdermal needle electrodes. The device is both safe and disposable.

Action Potentials↗
PubMed1989

Relationship between the location of the ground electrode and size of electrical stimulus artifacts.

In simulated electrophysiologic recordings, electrical stimuli were applied to the upper limbs of ten subjects. Then, stimulus artifacts were recorded using different ground locations, while all other technical parameters were kept constant. Stimulus artifacts were relatively large (often reaching a maximum amplitude) when stimulating electrodes were between ground and recording electrodes. Artifacts were relatively small (commonly arriving at a minimum and never at a maximum value) when recording electrodes were between ground and stimulus sites. When the ground was situated between stimulating and recording electrodes, the stimulus artifacts had about an even chance (40-50%) of achieving either a maximum or a minimum amplitude value. These findings do not seem to support the traditional belief that the best ground location to reduce the size of the stimulus artifacts is between points of stimulation and recording.

Electric Stimulation↗
PubMed1986

Lack of cold sensitivity in hyperkalemic periodic paralysis.

The nosologic distinction between paramyotonia congenita and hyperkalemic periodic paralysis is somewhat blurred. Muscle membrane inexcitability induced by cooling seems to be characteristic of paramyotonia congenita. The effect of cooling on the maximal compound muscle action potential (CMAP) in patients with paramyotonia congenita was compared to that in patients with hyperkalemic periodic paralysis. Diminution in CMAP amplitude and area, which was observed in paramyotonia congenita, did not occur in hyperkalemic periodic paralysis. We suggest that this effect of cooling on the CMAP can be utilized in the differentiation of these two syndromes.

Action Potentials↗
PubMed1986

Scalp EMG in brain death electroencephalogram.

Electromyograms (EMGs) are usually considered artifacts during electroencephalographic (EEG) recording for determination of electrocerebral silence (ECS). Appearance of scalp motor unit activity, however, may reflect residual brainstem function and can introduce difficulty in establishing a secure diagnosis of brain death. In this study, ECS patients with and without scalp EMG were compared in terms of relationship to brainstem survivability. There was no correlation between length of survivability and presence of scalp EMG activity. No patient recovered brainstem function clinically. This study provides firm support for the usual practice of ignoring the EMG in brain death EEG. Scalp has no prognostic value.

Adolescent↗
PubMed1986

Unilateral asterixis: case report and comments.

Asterixis is usually bilateral. Occasionally, it may appear unilaterally. Hemiasterixis following infarction of the contralateral midbrain and thalamus is described. Mechanisms of asterixis and brain lesions associated with its unilateral appearance are reviewed. The mesodiencephalon is frequently implicated by the lesion either directly or indirectly, suggesting the importance of this structure in posture regulation.

Cerebral Infarction↗