Special-purpose orthonormal basis functions--application to motor unit action potentials.
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Action Potentials↗
Biomedical subjects
S D Nandedkar
Publications and source records attributed to S D Nandedkar.
Simulation of single muscle fibre action potentials.
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Action Potentials↗
Digital reproduction of biopotential waveforms for neurophysiological studies.
A simple biological signal generator capable of reproducing complex biopotential waveforms is described. It is constructed by a combination of digital and analog circuit components and can be used under different experimental conditions, such as in calibration of biomedical instrumentation systems, or simply as a function generator providing voltage outputs of various waveforms. The biopotential waveform to be generated is sampled at a high frequency and the samples are stored sequentially in a programmable read only memory (PROM). The samples are then fed in the same sequence to a digital-to-analog (D/A) converter and the resulting output is amplified and a DC offset is added. External controls are provided to adjust the DC offset, amplitude and repetition rate of the signal generated. The reproduced voltage signals are stable and superior in quality to those produced by conventional biological signal generators.
Animals↗
Simulation and analysis of the electromyographic interference pattern in normal muscle. Part II: Activity, upper centile amplitude, and number of small segments.
We have defined three new features of the electromyographic (EMG) interference pattern (IP): activity, upper centile amplitude (UCA), and number of small segments (NSS). These parameters were measured in simulated IPs constructed by adding together motor unit action potentials (MUAPs) recorded with a concentric needle EMG electrode. The activity increases linearly with the number of MUAP discharges to approximately 80% of its theoretical maximum value. The UCA correlates strongly with the peak-to-peak amplitude of the largest MUAP in the IP and the mean segment amplitude and does not depend on the discharge rate of the largest MUAPs. We infer that the UCA defines the upper limit of the peak-to-peak amplitude of the MUAPs contained in the IP. The NSS increases with the number of MUAP discharges, but reaches a constant value at higher MUAP discharge rates, probably because small amplitude MUAPs are masked by the large amplitude MUAPs. The potential value of these parameters in automated IP analysis is discussed.
Action Potentials↗
Automatic analysis of the electromyographic interference pattern. Part II: Findings in control subjects and in some neuromuscular diseases.
The electromyographic (EMG) interference pattern (IP) was measured in the biceps muscle of 16 normal male and 17 normal female subjects. The activity, upper centile amplitude (UCA), and the number of small segments (NSS) (defined in a companion paper) were measured from 500-msec epochs of the IP. The normal values of these features were defined separately for men and women by plotting the UCA and NSS values against activity for each epoch and defining an area on these plots, called a "cloud," that contained more than 90% of the datum points from each study. The mean deviation of the individual datum points from the overall mean values was also calculated for each study. A study in one muscle is considered to be normal if more than 90% of the datum points from that muscle are within the normal clouds and the deviation values are within their normal range. In patients with neuropathy, the characteristic pattern was increased UCA with normal or decreased NSS. In patients with myopathy, NSS was increased and the UCA was normal or decreased. In all studies, the interpretations of the IP from the plots agreed with qualitative assessments of the IP made independently by an electromyographer. The use of these features to understand and quantitate the changes in the motor units produced by disease is demonstrated by serial studies performed in a patient with motor neuron disease.
Action Potentials↗
Motor unit action potential duration recorded by monopolar and concentric needle electrodes. Physiologic implications.
Controversy exists regarding motor unit action potentials (MUAPs) recorded with monopolar v concentric needle electrodes. All investigations to date have used different instrumentation parameters combined with different motor unit potential populations to assess comparative durations for MUAPs. In this investigation, the same MUAP was analyzed for both monopolar and concentric needle electrodes with identical instrumentation parameters. Monopolar needle electrodes were found to record MUAPs with slightly longer durations, a result that reached statistical significance. Manual wideband high-resolution MUAP analysis demonstrated durations approaching 30 ms for both electrodes, which is different from the approximately 10 ms presently measured for both electrode types. A hypothesis was proposed whereby the total duration of current flow, which is directly proportional to muscle fiber length, is the primary determinant of MUAP duration. The physiologic implications of this hypothesis are discussed.
Action Potentials↗
Influence of the surface EMG electrode on the compound muscle action potential.
The recording characteristics of surface EMG electrodes were investigated. Compound muscle action potential (CMAP) and surface recorded motor unit action potentials were recorded from different muscles, using different surface electrode shapes and sizes. The CMAP was smaller for larger surface electrodes. This was more pronounced in smaller muscles. The CMAP was minimally affected by the geometry of the recording surface. With larger surface electrodes, shunting contributes to the reduction in MUAP amplitude. This is offset by a larger uptake area which gives a much smaller reduction in the CMAP amplitude for the larger muscles.
Adult↗