Effect of desynchronized inputs on compound sensory and muscle action potentials

Stimulation of the second (S1) or third (S2) digit elicits a median sensory potential at the wrist. Similarly, a shock applied to the median (Sm) or ulnar (Su) nerve at the wrist evokes a sensory potential of the fourth digit and a muscle potential over the thenar eminence. Hence, a concomitant application of S1 and S2 or Sm and Su with varying interstimulus intervals simulates the effect of desynchronized inputs. In 10 hands, a shift in latency on the order of 1 msec between S1 and S2 or Sm and Su caused a major reduction in sensory potential by as much as 30-40% but little change in muscle action potential. A latency difference slightly less than one-half the total duration of unit discharge maximized the phase cancellation between the two components and consequently the loss of area under the waveform.     

Interrelationship among nerve conduction velocity, amplitudes of compound muscle and compound nerve action potentials in diabetic neuropathy]

In order to clarify the relationship among amplitudes of compound nerve action potential (CNAP), compound muscle action potential (CMAP) and nerve conduction velocity parameters, data of nerve conduction studies were analyzed in 102 patients with diabetes mellitus. In motor conduction studies CMAP amplitudes after stimulations at the distal nerve trunk, and the polyneuropathy index (PNI), a mean percentage of normal for 12 indices from 4 nerves concerning to the velocity or long distance latency, were evaluated. CNAP was recorded in the median and ulnar nerves from an intrafascicularly inserted microelectrode at the elbow after wrist stimulation. CMAP amplitudes were high in the median and ulnar nerves, and were reduced in the tibial and peroneal nerves. A close relationship was found between PNI and CNAP amplitudes. Among CMAP amplitude parameters tibial nerve, not median or ulnar nerves, had a good correlation with PNI and CNAP amplitude. Along with the progression of diabetic neuropathy, neuropathic signs or symptoms become conspicuous, and nerve conduction velocity drops as is expressed by the PNI level, which reflects the change in nerve conduction velocity in the upper and lower limbs. At the same time CNAP amplitude or CMAP amplitude in the tibial nerve decreases, but in nerves of the upper limb CMAP amplitude doesn't always decrease. So, tibial nerve is best among CMAP amplitude parameters in evaluating the degree of diabetic neuropathy. It is necessary to judge the degree of diabetic neuropathy after due consideration of these facts.     

Intraoperative human vagus nerve compound action potentials

OBJECTIVE: Although electrical stimulation of vagus nerve is used widely for treatment of epilepsy the electrophysiological properties of human vagus nerve are not well characterized. Our objective was to measure compound action potentials of human vagus nerve fiber groups intraoperatively by stimulation using a commercially available generator and electrode system (Neurocybernetic Prosthesis System, NCP). MATERIAL AND METHODS: During NCP implantation we recorded compound action potentials evoked by stimulating the left vagus nerve through the NCP bipolar lead. Current intensities were varied from 0.25 to 3.0 mA. RESULTS: Vagus nerve compound action potential components conducting in the A, Adelta, and C velocity ranges could be elicited using either the NCP pulse generator or by a standard evoked potential instrument. A fiber potentials were recordable in all nerves, and were activated by very low stimulus currents. Adelta and C fibers were less reliably elicited, with C fibers requiring the highest currents. CONCLUSIONS: Three clearly identified fiber populations can be identified using therapeutic electrical stimulation of the human vagus. Intraoperative measurements of NCP-induced action potentials may potentially provide a marker for therapeutic stimulation and better insight into mechanisms of vagus nerve stimulation (VNS) efficacy.     

Far-field potentials in the compound muscle action potential

It has long been believed that the compound muscle action potential (CMAP) in motor-nerve conduction studies (MCSs) records the action potential beneath the active electrode over the muscle belly. However, recent studies have revealed the contribution of the reference electrode to the CMAP, most prominent in the tibial nerve, followed by the ulnar nerve. This “reference electrode potential” is recorded when the conventional reference electrode distal to the muscle belly is connected to a proximal reference. It must be a far-field potential (FFP) considering its distribution, although the precise mechanism of its generation has not been clarified. The conventional theory of termination of the action potential at the muscle-tendon junction is insufficient. Regarding the ulnar CMAP, interosseous muscles mostly contribute to the FFPs. New understanding of CMAP based on the FFP theory may provide new insights into the interpretation of MCSs and related techniques, including motor unit number estimation.     

Temperature dependence of normal sensory nerve action potentials

Summary Sensory conduction velocities of normal subjects are increasing linearly with rising temperature. The duration of the compound sensory action potentials recorded from the median nerve at the wrist and elbow shows a negative temperature coefficient. The peak-to-peak amplitude of these potentials increases from 22° to approximately 26°C and then decreases progressively again up to 36°C. It is believed that this behavior is due to a combination of decreasing temporal dispersion, height and duration of the individual spike potentials.Dedicated to Prof. F. Buchthal on the occasion of his 70th birthday     

Correlation between distal motor latency and compound muscle action potential in amyotrophic lateral sclerosis

OBJECTIVES: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder, characterized by a selective progressive degeneration of the motor system. Electromyography is essential for the diagnosis of ALS. The measurement of motor conduction of peripheral nerves is of major importance to recognize other possible causes of progressive muscle wasting. However, there are also pathologic changes in nerve conduction studies in ALS patients. METHODS: In this study we analysed the values of distal motor latency (DML), compound muscle action potential (CMAP) and motor nerve conduction velocity (MNCV) in 95 patients with definite ALS. RESULTS: We found slight slowing of MNCV and moderate to strong reduction of CMAP and a prolongation of DML. We found no significant correlation between MNCV and CMAP. DISCUSSION: The main finding of the present work was the negative correlation between DML and CMAP. It is interpreted as a very distal axonal damage as the main reason for prolongation of DML in ALS patients.     

Relationships between the changes in compound muscle action potentials and selective injuries to the spinal cord and spinal nerve roots.

OBJECTIVE: Compound muscle action potentials (CMAPs) evoked by transcranial electrical stimulation have been widely introduced to monitor motor function during spinal surgery. They may reflect segmental injuries as well as injuries to motor-related tracts in the spinal cord. However, we have experience with some patients who developed postoperative segmental motor weakness without any potential changes during surgery. To evaluate the efficacy of this method, we used a cat model to observe the relationships between potential changes and selective injuries to the white and gray matters of the spinal cord and spinal nerve roots. METHODS: Ten CMAPs were obtained before and after injury to the spinal cord and spinal nerve roots in 20 cats. Changes in the amplitude, latency, and duration of CMAPs were analyzed. RESULTS: CMAPs decreased in amplitude significantly after the insult to the motor-related tracts in the spinal cord in all cats, while the potentials did not always change when the insult was restricted to a limited area in the anterior horn of the spinal cord or to the single spinal nerve root. CONCLUSIONS: CMAPs may not exactly reflect segmental injury, and careful attention should be paid to the interpretation of CMAPs.     

Intracranially recorded compound action potentials from the human trigeminal nerve

Potentials from the sensory root of the trigeminal nerve in the cerebello-pontine angle, evoked by electrical stimulation of the different trigeminal divisions, were recorded during neurosurgical operations. Two components of the compound action potential could be distinguished: one early with large amplitude and one late with small amplitude. It is concluded that the two components represent activity in A alpha and A delta fibers respectively.     

动眼神经电刺激对健康Beagle犬下斜肌CMAP的影响研究

目的 研究动眼神经电刺激对Beagle犬下斜肌复合动作电位（CMAP）的影响,为动眼神经损伤后的电刺激治疗提供依据.方法 对10只健康雌性Beagle犬行常规开颅,暴露动眼神经海绵窦后段,以不同强度电刺激动眼神经,采集下斜肌CMAP.结果 随着电刺激强度的递增,下斜肌CMAP峰值逐渐增加.直接刺激动眼神经干的适宜强度为0.9～1.6 V,可使下斜肌CMAP峰值达到500 μV左右.结论 给予动眼神经一定强度的电刺激,可以在眼外肌上诱发出稳定的动作电位.该结果对动眼神经损伤后的功能重建有潜在的应用价值.     

Ultrasound-guided needle positioning near the sciatic nerve to elicit compound muscle action potentials from the gastrocnemius muscle of the rat

The use of ultrasound-guided electrode positioning in near-nerve myography was investigated. This is a minimally invasive technique that allows repeated measurements to increase accuracy and hence decreases animal numbers. Ultrasound imaging of the sciatic nerve was performed in nine rats using a 55 MHz high-end transducer. Once visualised, a monopolar needle electrode was placed through the skin near this nerve. Upon stimulation, two surface electrodes, placed over the gastrocnemius muscle, recorded compound muscle action potentials (CMAPs). Reproducibility was tested having two teams of investigators perform the recordings consecutively. Reliability of the procedure was determined by comparing the ultrasound method to the conventional technique, which requires an incision through muscle and skin to expose the sciatic nerve. In all animals the sciatic nerve was visible on ultrasound images. Both methods showed CMAP latencies (duration was determined as the time interval between the onset latency and positive peak). The conventional method had a mean latency of 3.4±0.5 ms, our method had a mean latency of 3.3±0.5 ms. Reproducibility was excellent (observed latencies and amplitudes: 3.3 versus 3.3 ms and 25.6±5.1 mV versus 22.5±8.8 mV) resulting in a coefficient of variation for duration of 2.1% and for amplitude 6.7%. Interclass correlation coefficient was 0.828 for duration. Comparing the three different measurements no significant differences were found and our new method can therefore be considered reliable and comparable to the conventional method. Ultrasound-guided near-nerve needle positioning is a reproducible and reliable minimally invasive method for selectively eliciting CMAPs, which allows repeated CMAP measurements for studying nerve regeneration in rats.     

Compound muscle action potentials during repetitive nerve stimulation

When using repetitive nerve stimulation to examine neuromuscular transmission, the change in compound muscle action potential (CMAP) size is usually assessed by measurement of negative-peak or peak-to-peak amplitude. Technological developments now allow automatic measurement of CMAP area, but some patients show increment of CMAP amplitude and decrement of CMAP area. This study systematically analyzed the changes in these CMAP parameters in 23 neurologically healthy subjects. CMAPs were recorded when the ulnar nerve was stimulated at frequencies of 1, 2, 5, 10, 20, 30, and 50 HZ (five pulses per train). CMAP amplitude showed significant increment within a train when stimulus frequency was above 5 HZ (probably due to increased muscle-fiber conduction velocity), whereas CMAP area hardly changed at any frequencies. Measurement of CMAP area produces less ambiguous results than amplitude measurement in repetitive nerve stimulation studies.     

The optimal recording electrode configuration for compound sensory action potentials.

There is no uniformity in the published literature from different laboratories on the optimal electrode configuration for recording nerve action potentials, and a number of standard texts omit any reference to the effects that interelectrode distance and electrode orientation can have on the shape, amplitude and latency of nerve action potentials. The sensory action potential from the digital nerves of the index finger was recorded at wrist and elbow using bipolar electrodes with the "active" electrode over the median nerve and the "reference" placed 4 cm laterally or proximally along the nerve using interelectrode distances of 4, 3 and 2 cm. These potentials were compared with that recorded using a remote reference on the ipsilateral shoulder, the assumption being that this configuration eliminated the contribution of the reference electrode to the compound nerve action potential. With different electrode configurations, there were significant differences in the shape of the potential, the latencies to onset and peak and the rising- and falling-phase amplitudes. The shorter the distance between the electrodes the greater the distortions. Overall, the distortions were least with the 4 cm interelectrode separation, particularly for short conduction distances.     

Recording compound action potentials from the optic nerve in man and monkeys

Compound action potentials were recorded from the optic nerve in patients undergoing neurosurgical operations and in rhesus monkeys. The stimuli were short light flashes delivered by light-emitting diodes that were bonded to plastic contact lenses positioned on one or both eyes, and potentials were recorded simultaneously from electrodes placed on the scalp. Potentials recorded from the optic nerve in man have an initial small positive deflection, with a latency of about 45 msec, followed by a negativity with a latency of 60-70 msec. The wave form depends on the recording site on the optic nerve and, occasionally, oscillations with a frequency around 100 Hz were seen in the responses from the optic nerve. There was considerable individual variation in the shape and size of the recorded potentials, but most potentials recorded simultaneously from an electrode placed on Oz with a reference electrode on the forehead appeared as positive deflections with latencies of about 80 msec and, occasionally, with a small positivity with a latency of about 45 msec. Compound action potentials recorded from the optic nerve near the ocular globe in the rhesus monkey in response to similar light flashes appeared as negative deflections with latencies of about 17 msec. The potentials recorded at the chiasm appeared as initial positive deflections, with the latency of the earliest peak being about 35 msec, on which oscillations with frequencies of about 100-150 Hz occasionally could be seen. The recordings from electrodes placed on the scalp (Cz-Oz and Cz-shoulder) in the monkey showed a positive peak with a latency of about 65 msec.(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle force,motor nerve conduction velocity and compound muscle action potentials after parathyroidectomy for secondary hyperparathyroidism

OBJECTIVE: We studied the motor nerve conduction velocity (MNCV) and the amplitude of compound muscle action potentials (CMAP) in patients with symptomatic secondary hyperparathyroidism at preoperative and 3 months post-operative period, to find the factors affecting muscle force after parathyroidectomy. METHODS: Twenty-six patients with symptomatic secondary hyperparathyroidism with levels of intact parathyroid hormone (iPTH) over 6.8 pmol/l who underwent total parathyroidectomy and autotransplantation of 60 mg of tissue were included in this research. Extension force of the quadriceps muscle was measured at 60 degrees of right knee flexion and expressed as Newtons (N) in peak force and average force. Nerve conduction studies of four limbs were checked and the MNCV and CMAP of right femoral and tibial nerves were analyzed and correlated with the muscle force. RESULTS: Three months after operation, the peak force increased from 272 +/-108 to 315 +/- 123 N (P=0.015) and the average force from 215 +/- 94 to 253 +/- 103 N (P=0.006). MNCV and latencies of femoral and tibial nerves did not show definite change, but the amplitude of CMAP increased significantly from 7.1 +/- 4.1 to 10.7 +/- 3.2 mV (P=0.005) at femoral stimulation and from 9.8 +/- 4.6 to 11.7 +/- 4.3 (P=0.007) and 13.2 +/- 5.9 to 14.9 +/- 6.0 (P=0.011) at proximal and distal tibial stimulation. CONCLUSION: The improvement of muscle force after surgery was found to be parallel to the increment of the amplitude of CMAP but not to nerve conduction velocity or latency. We propose that the weakness of the patients with secondary hyperparathyroidism is probably related to alteration of muscle fiber contraction.     

The optimal distance between two electrode tips during recording of compound nerve action potentials in the rat median nerve简

The distance between the two electrode tips can greatly influence the parameters used for record- ing compound nerve action potentials. To investigate the optimal parameters for these recordings in the rat median nerve, we dissociated the nerve using different methods and compound nerve action potentials were orthodromically or antidromically recorded with different electrode spac- ings. Compound nerve action potentials could be consistently recorded using a method in which the middle part of the median nerve was intact, with both ends dissociated from the surrounding fascia and a ground wire inserted into the muscle close to the intact part. When the distance be- tween two stimulating electrode tips was increased, the threshold and supramaximal stimulating intensity of compound nerve action potentials were gradually decreased, but the amplitude was not changed significantly. When the distance between two recording electrode tips was increased, the amplitude was gradually increased, but the threshold and supramaximal stimulating intensity exhibited no significant change. Different distances between recording and stimulating sites did not produce significant effects on the aforementioned parameters. A distance of 5 mm between recording and stimulating electrodes and a distance of 10 mm between recording and stimulating sites were found to be optimal for compound nerve action potential recording in the rat median nerve. In addition, the orthodromic compound action potential, with a biphasic waveform that was more stable and displayed less interference （however also required a higher threshold and higher supramaximal stimulus）, was found to be superior to the antidromic compound action potential.