The selection of electromyographic needle electrodes.

Monopolar and concentric reusable and disposable EMG needle electrodes from several manufacturers were studied at various stages of usage. Needle tips were examined and measured microscopically, and needles were tested for spontaneous noise and resistive and capacitative characteristics at four different test signal frequencies. Resistive and capacitative characteristics were found to be frequency dependent. Needle tip areas differed by as much as 10 times among the various electrodes. The amount of noise correlated most highly with resistive characteristics. Monopolar and concentric needles differed in respect to tip area, noise, and all resistive and capacitative measures. Coaxial disposable and reusable electrodes did not differ significantly and minor differences were noted in electrical characteristics between reusable and disposable monopolar needles, even from the same manufacturer. There was considerable variability among manufacturers for both needle types. In choosing an electrode, consistent tip area is probably the most important consideration to ensure repeatable quantifiable results, but minimizing needle impedance is useful to reduce noise.

Antidromic sensory nerve conduction studies of medial and lateral plantar nerves in normals.

A reliable sensory nerve conduction study for the most distal lower extremities is needed in routine clinical electromyography. This paper reports a study of 150 medial and lateral plantar nerves in the foot in normals. An antidromic technique was used with stimulation at the ankle and recording from the small and large toes. Recordable responses were obtained in 149 instances. Conduction velocity in the medial branch distal to the tarsal tunnel was 40.5 +/- 4.0 m/sec and significantly slower than conduction in the lateral branch by 4.3 m/sec. The amplitude of the evoked response from the big toe was 3.46 +/- 2.2 microV and significantly larger than that in the small toe by 1.34 microV. Evoked response amplitude in the medial branch was greater in younger subjects.

The source of shoulder pain in hemiplegia.

Shoulder pain is a common problem in hemiplegia. This preliminary study attempted to identify pain-producing structures by evaluating the results of injecting 1% lidocaine into several sites in the shoulder area. Sixty-seven patients with shoulder problems were identified, examined, and characterized. The amount of pain was related most to loss of motion; it was unrelated to subluxation, spasticity, strength, or sensation. Of 28 patients who received a subacromial injection, approximately one-half obtained moderate or marked relief of pain and improved range of motion, suggesting that the subacromial area of the shoulder is a location of pain-producing structure in a significant number of cases.

Electromyography interference pattern decomposition.

Decomposition of an interference pattern enables examination of individual electromyography (EMG) motor units and their firing rates at more than minimal contraction forces. In this decomposition method, significant events with a constant occurrence (near motor unit action potentials) can be enhanced, and unwanted events (distant motor unit action potentials, artifacts) eliminated, by calculating the average accumulated change while sliding a fixed-width window along the digitized EMG interference pattern. Nonparametric statistical methods are then applied to these data to determine which information is significant at the .05 level. The exact duration of significant information is identified without the need for arbitrary thresholds and filters to eliminate unwanted information. Events are then classified into groups of similar events by comparing: (1) correlation coefficients, (2) point-to-point differences, (3) amplitudes, and (4) areas. The classification is further refined by the use of firing-rate information.

Differences in sensory conduction velocity between different sensory branches and segments of the median and ulnar nerves.

Abnormality of absolute values of median sensory conduction velocities and differences in conduction velocity between median and ulnar nerves are used as criteria for abnormality in the diagnosis of carpal tunnel syndrome. Detailed studies of sensory conduction in various median and ulnar branches and segments indicate that conduction velocities measured and calculated by standard methods are different in the different nerves, segments and branches. In particular, the velocity in the middle digit branch of the median nerve is slower than that in the index, and that in the 3-4 palmar branch is slower than that in the 2-3 palmar branch. Median and ulnar sensory conduction velocities are not well correlated in the same hand in the same individual, so comparison of these nerves for diagnostic purposes is subject to some risk. Palmar and digital conduction velocity in the same nerve may not be identical and the median nerve may have asymptomatic palmar slowing of no clinical significance. The conclusion that abnormality is present must take these factors into account.

Correlation studies of velocity, amplitude, and duration in median nerves.

Nerve conduction velocity is the parameter most often attended to when performing nerve conduction studies, but amplitude and duration of the nerve potentials should also provide important information about the status of the nerve examined. This study compared the results of amplitude and duration measurement to nerve conduction velocity to determine whether or not the various parameters correlated. Using standard techniques, median nerve motor and sensory conduction studies were performed on 390 unselected patients. The results were analyzed and correlation statistics calculated between the parameters of velocity, duration, and amplitude. Amplitude and duration of evoked potential correlated relatively poorly with conduction velocity (r2 = 0.26). Sensory and motor fibers were often affected differently in cases with probable carpal tunnel syndrome (CTS). Proximal motor conduction velocity correlated best with distal evoked potential amplitude (r2 = 0.27) in the CTS cases. The use of residual latency appeared to add little helpful diagnostic information. It was concluded that different parameters measure different physiologic processes that are to a considerable degree independent of each other.

Computerized synthesis of electromyographic interference patterns.

Computer simulation is a process that appears to have wide application in many disciplines. Electromyographic (EMG) interference patterns can be computer-synthesized by inputting parameters of individual motor unit action potentials (MUAPs) such as amplitude, duration, and phases, and recruitment parameters of number of motor units, and the firing rate and its standard deviation. The resulting simulated EMG interference patterns can then be used to test hypotheses regarding the effect of alteration of the individual MUAP parameters on the interference pattern. An example of the usefulness of simulation is demonstrated by the analysis of the simulated patterns by the Fast Fourier Transform (FFT), which indicates that the major frequency band in the FFT results from the duration of the individual phases of the MUAP. The motor unit's recruitment rate is superimposed on the FFT envelope in the low-frequency end. The variability of the firing rate influences the distinctness of the low-frequency peaks. The MUAP amplitude and number of motor units in the recruitment pattern are reflected in the FFT power. Simulation appears to be a useful tool for further investigation and development of EMG signal analysis techniques.

Measurement of loads on the lumbar spine under isometric and isokinetic conditions.

Ten male and ten female subjects were tested for their ability to exert maximal force about the lumbo-sacral junction (as is done during lifting) under controlled isometric and isokinetic conditions. The myoelectric activity of ten trunk muscles, intra-abdominal pressure, and torque produced by the back were monitored. There are prominent differences in the manner in which subjects utilize the musculature of the trunk for the production of torque statically and dynamically. A significant lag was identified between the onset of intra-abdominal pressure and torque, and this lag increased with increasing trunk velocity. These differences between isometric and isokinetic exertions suggest that isokinetic trunk testing provides a means of controlled evaluation that is appropriate for manual materials handling situations.

Calculated nerve conduction velocity dependence upon the method of testing.

Nerve conduction velocities using the evoked nerve potential can be calculated using six different methods. The latency may be measured to the onset of the negative potential or to the negative peak, using techniques of single or dual stimulation and single or dual recordings. Each method produces a value that is dependent on the method used for latency measurement and velocity calculation. The major factor producing the variability is the measurement of latency to the negative peak of the evoked potential. Awareness of these calculation artifacts is necessary to set standards and compare values.

Axillary F-loop latency of ulnar nerve in normal young adults.

F waves were studied with stimulation of the ulnar nerve in normal subjects (25 men and 15 women, with an average age of 26.5 years) using an EMG machine that permits the simultaneous display of 8 sweeps. The axillary F-loop latency (AFLL), defined at the conduction time between the axilla (25cm from the sternal notch) and the spinal cord, was 9.17 +/- 0.81msec when 8 F responses were measured but was 8.57 +/- 1.00msec when 40 F responses were used. Data from men and women showed no significant statistical difference. The mean plus 2 standard deviations were 10.8 and 10.6msec for 8 and 40 responses, respectively. On the basis of these findings, an AFLL longer than 11msec should be considered abnormal in the young adult. Four measures repeated at weekly intervals showed no significant difference from week to week, indicating that the technique can be consistently and reliably applied at different times. The average duration of the F complex was 15.78 +/- 2.55msec and was about 80% of the average duration of the M wave.

Peripheral nerve regeneration in primates during D-penicillamine-induced lathyrism.

We have attempted to alter collagen metabolism in young squirrel monkeys by inducing lathyrism with D-penicillamine to weaken scar tissue. We then tested the effectiveness of this drug in improving regeneration of transected peripheral nerves at the wrists using a dose of 200 mg/kg/day. We did find a significant increase (doubling) in the soluble collagen in Ivalon sponge samples that had been implanted 3 weeks after the onset of drug treatment. We also compared the control and treated groups in terms of :(1) the rate of appearance of evoked muscle action potentials, (2) the amplitude of evoked muscle action potentials, and (3) the nerve conduction velocities. Using these tests we were not able to demonstrate any improvement in the quality or rate of nerve regeneration. The possible explanations for these observations are discussed.

Dantrolene sodium suspension in treatment of spastic cerebral palsy.

A double-blind study was carried out on 20 children with spasticity secondary to cerebral palsy, in order to compare the effects of dantrolene sodium suspension and a placebo. The drug was found to be physiologically active in reducing the force of muscle contraction, but objective functional improvement, as measured by multiple performance tests, was irregular and probably not significant.

Dantrolene sodium: long-term effects in patients with muscle spasticity.

Seventy-seven patients with muscle spasticity secondary to central nervous system pathology were treated with dantrolene sodium for periods of up to two years. The drug was effective in reducing muscle spasms, clonus, muscle tone, and the force of muscle contraction elicited by Achilles tendon tap and tibial nerve stimulation, but improvement of function was seen less often. The incidence of side-effects was considerable, and poses a problem regarding patient acceptance of drug treatment.