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Biomedical subjects

D B Sanders

Publications and source records attributed to D B Sanders.

At least 19 recordsLinked to original sources
PubMed1991

On the shape of the normal turns--amplitude cloud.

Factors that affect the shape of the so-called "normal cloud" of the turns and amplitude measurements of the electromyographic interference pattern are investigated. As the force of voluntary contraction increases from low to moderate levels, the number of turns in the signal increase faster than does the mean amplitude change between turns. This results in a cloud that is concave downward. At higher force levels, the pattern is reversed. The overall shape of the cloud thus depends on the maximum effort at which recordings are made, which is determined by the procedure of muscle activation.

Adult↗
PubMed1991

Recording characteristics of monopolar EMG electrodes.

Motor unit action potentials (MUAPs) and the electromyographic (EMG) interference pattern (IP) were recorded from the biceps muscle of 5 normal subjects using both a concentric needle (CN) and a disposable monopolar needle (MN) electrode. The MUAPs recorded by the MN electrode had higher amplitude and area and were more frequently complex than those recorded with the CN electrode. The MUAP duration and area: amplitude ratio were similar for both electrodes. Although the MN electrode had a larger recording surface, its dimensions (maximum diameter and length of the cone shaped tip) were similar to those of the CN electrode (minor and major axes of the elliptical recording tip). Based on these observations, we infer that the MN electrode may be more selective than the CN electrode, ie, the AP amplitude recorded by the MN electrode decreases faster than the AP amplitude recorded by a CN electrode when the distance of the muscle fiber from the recording electrode increases. Photomicrographs of the MN electrode after use demonstrated no evidence that the insulating material had peeled off. There was also no evidence that MUAP measurement values changed during the recordings as would be expected if the recording surface changed due to peeling of the insulating material.

Action Potentials↗
PubMed1991

Single-fiber EMG demonstrates reinnervation dynamics after nerve injury.

Serial single-fiber EMG (SF-EMG) studies in the frontalis muscle showed increased jitter with normal fiber density 15 days after facial nerve trauma. Both measurements were increased thereafter. The maximum increases occurred at 37 days, coincident with the initial return of function, and persisted until 67 days, when function had returned to normal. Thereafter, both features returned toward normal values, but were still elevated 34 months after injury.

Adult↗
PubMed1990

Quantitative EMG in inflammatory myopathy.

Fifty-four quantitative electromyographic (EMG) studies were made in 37 patients with inflammatory myopathy (IM) at different points in their clinical course and treatment. All studies were performed in the biceps brachii which varied in clinical strength. Motor unit action potentials (MUAPs) in 45 studies and EMG interference pattern (IP) in 48 studies were recorded using a concentric needle electrode. Macroelectromyographic (Macro-EMG) MUAPs were recorded from 10 patients in 14 studies. MUAP analysis revealed a myopathic pattern (decreased duration and/or area: amplitude ratio) in 69% of studies. IP analysis was more sensitive than MUAP analysis, demonstrating a myopathic pattern in 83% of studies. Macro-EMG MUAP amplitudes were reduced in two studies, minimally increased in one study and normal in the remainder; in 6 (40%) studies, fiber density was slightly increased. Thus, reinnervation does not seem to play an important role in motor unit remodeling in IM.

Action Potentials↗
PubMed1990

Recording and physical characteristics of disposable concentric needle EMG electrodes.

There is currently considerable interest in using disposable concentric needle (CN) electrodes for clinical electromyography (EMG). To determine how these electrodes compare with reusable CN electrodes, we have compared signals recorded by these two electrode types from the same muscle in normal subjects. We also made similar recordings with two groups of reusable electrodes. There was no difference in the features of motor unit action potentials (MUAPs) recorded by the two groups of reusable electrodes. Disposable electrodes performed satisfactorily in conventional EMG examination. However, compared to reusable electrodes, the disposable electrodes recorded MUAPs with smaller amplitude and area but with the same area:amplitude ratio and MUAP duration. The physical and electrical properties of the CNE groups were also investigated. Disposable electrodes had lower electrical resistance and greater capacitance than reusable electrodes when measurements were made in saline. Photomicrographs showed that the disposable electrodes had smaller recording surfaces and that the central wire was frequently eccentric in the cannula. The differences in electrical recording characteristics could be due to differences in the size of the recording surface, eccentric placement of the central wire in the cannula or differences in the metal used for the central wire. We conclude that electrical and physical testing may not predict the recording characteristics of needle electrodes. Electrophysiologic testing is necessary to determine how EMG signals recorded by new types of electrodes compare with those recorded by currently used electrodes.

Action Potentials↗
PubMed1990

Measurement of the amplitude of the EMG envelope.

When the force of muscle contraction is increased, the amplitude of the EMG envelope (ENAMP) increases. The ENAMP is usually assessed subjectively and its value in EMG analysis has been established. In this article we describe a method to make automatic measurements of the ENAMP. This method was tested on recordings of the EMG interference pattern (IP) from the biceps muscle of normal subjects. Normal values of this feature in the biceps muscle are described. There was a good concordance between the ENAMP measurements made by subjective assessment and by automatic analysis and the ENAMP values correlated strongly with a previously described feature of the IP called the upper centile amplitude. We infer that ENAMP is a robust feature of the IP that reflects the amplitude of the largest MUAP in the IP.

Action Potentials↗
PubMed1989

Myasthenic U-shaped decrement in multifocal cervical radiculopathy.

A middle-aged man with lymphomatous meningitis developed acute cervical radiculopathy. Repetitive stimulation of an affected nerve revealed a "U-Shaped" decrement. The decrement was absent 10 days later. We hypothesize that the decrement was secondary to simultaneous denervation of many motor units and disappeared as denervation became complete in those motor units.

Electromyography↗
PubMed1989

Evaluation of an automatic method of measuring features of motor unit action potentials.

This study was performed to evaluate an automatic method of motor unit action potential (MUAP) analysis developed in our laboratory. MUAPs were recorded from the biceps brachii muscle of 68 normal subjects and 122 patients with nerve or muscle disease. The values of mean MUAP durations from normal subjects obtained by automatic analysis were similar to those reported in the literature. However, the normal range of MUAP amplitude and the incidence of polyphasic MUAPs were much higher. Normal ranges of mean MUAP area, area/amplitude ratio, and the number of turns were also defined. Automatic analysis demonstrated an abnormality of at least one MUAP feature in 70% of patients. There was concordance between automated analysis and visual assessment of MUAPs in 76% of patients with neuropathy but in only 50% of patients with myopathy. The relationships between different MUAP features seen in neuropathy and myopathy are explained in physiologic terms.

Action Potentials↗
PubMed1989

The effect of cholinesterase inhibitors of SFEMG in myasthenia gravis.

We report four patients with myasthenia gravis (MG) in whom single-fiber electromyography (SFEMG) jitter measurements were normal in some muslces while they were taking pyridostigmine and became abnormal 2-14 days after the medication was discontinued. When the abnormality of neuromuscular transmission in MG is mild, cholinesterase inhibitors may mask the findings of increased jitter on SFEMG.

Action Potentials↗
PubMed1989

Simulation of myopathic motor unit action potentials.

Normal motor units (MUs) were simulated and their architecture altered to simulate the changes produced by myopathy. The concentric needle electromyographic recordings of motor unit action potentials (MUAPs) from the MUs were then also simulated. These simulated MUAPs showed features that are seen in myopathy: normal amplitude and slightly reduced area, MUAPs with simple waveform and reduced duration, and complex MUAPs with normal or increased duration. The MUAP waveforms were complex because of increased variability of fiber diameter and not because of loss of muscle fibers. The MUAP duration increased when the variability of fiber diameter increased. Finally, MUAPs similar to those seen in neurogenic diseases were produced from MUs in which the only abnormality was increased variability of fiber diameter.

Action Potentials↗
PubMed1989

Principal component analysis of the features of concentric needle EMG motor unit action potentials.

Motor unit action potentials (MUAPs) were recorded from the biceps muscle of normal subjects and of patients with nerve or muscle diseases. Principal component analysis of the MUAP amplitude, area, area/amplitude ratio, duration, and the number of turns and phases produced three components that among them contained 90% of the variance of the data set. Thus the dimensionality of data was reduced from six to three. The first component reflected changes in the size of the MU, whereas the second reflected variations in the arrival time at the recording electrode of the action potentials of muscle fibers in the motor unit. The third factor reflected local loss of muscle fibers within the MU territory. Patterns of variations in the three components were different in patients with neuropathy and myopathy.

Action Potentials↗
PubMed1989

Ephaptic transmission in hemifacial spasm: a single-fiber EMG study.

In two patients with hemifacial spasm (HFS), single-fiber EMG recordings in facial muscles demonstrated low jitter in the late responses produced by stimulation of peripheral branches to other facial muscles. Surgical decompression of the facial nerve in one patient was followed by clinical improvement and disappearance of the abnormal late responses. These observations are consistent with the hypothesis that there is ephaptic transmission among peripheral branches of the facial nerve at the site of compression in HFS.

Action Potentials↗
PubMed1988

Simulation of concentric needle EMG motor unit action potentials.

Computer simulations of motor unit action potentials (MUAPs) as measured by a concentric needle (CN) electromyography (EMG) electrode in normal motor units (MUs) indicated that the MUAP amplitude is determined mainly by the proximity of the electrode to the closest muscle fiber. The area and duration of the simulated MUAPs were affected by all muscle fibers in front of the active recording surface but mainly by those that were less than 2 and 2.5 mm, respectively, from the active recording surface. The MUAP area was also affected by the proximity of the electrode to the closest muscle fiber. The number of phases of the simulated MUAPs increased when the dispersion of the arrival times of individual muscle fiber APs at the electrode was increased. Increased temporal dispersion of APs decreased the MUAP amplitude and area slightly but did not affect the MUAP duration. It is inferred that different features of the CN MUAP are determined by the distribution of muscle fibers within different portions of the MU territory and thus provide complementary information about the MU architecture.

Action Potentials↗