Motor nerve conduction velocity and latency in the dog

Supramaximal percutaneous nerve stimulation was used in motor nerve conduction velocity studies conducted in ten middle-aged, clinically normal dogs. Dogs were separated into two groups; dogs in one group weighted less than or equal to 7.5 kg and dogs in the other group weighted greater than or equal to 15.9 kg. Mean values and SEM were recorded for radial (72.1 +/- 1.9 m/s), median 65.6 +/- 2.1 m/s), ulnar (58.9 +/- 1.0 m/s), tibial (68.2 +/- 1.4 m/s), and peroneal (79.8 +/- 1.8 m/s) nerves. Values for latency, amplitude, and duration for proximal and distal evoked potentials were recorded. Analysis of mean nerve conduction velocity values for all nerves between the two groups indicated no statistical difference (P greater than 0.05). However, the two groups were statistically different (P less than 0.05) when values for distal latency and measurements of nerve length were compared. These data suggest that if latency is substituted for velocity measurements, various populations of dogs must be considered to clarify interpretation.     

Spinal-evoked potentials and spinal conduction velocity of the cat: reference values

Spinal conduction velocities of the fastest afferent fibers of the spinal cord were calculated from the onset latencies of averaged evoked responses elicited by stimulation of the tibial nerve sensory afferent fibers and were recorded at various sites on the spinal cord. Locations for stimulation and recording electrodes were identified. Waveforms, mean amplitudes, and duration of the evoked spinal potentials were described. The mean conduction velocity of the spinal cord afferents at T12-T13 was 74.25 m/s with a SD of +/- 9.81 m/s. The mean conduction velocity of the spinal cord afferents, determined at the cisterna magna, was 80.66 m/s with a SD of +/- 11.50 m/s. This is a slight increase over the spinal conduction velocity at T12-T13 (P = 0.05).     

Conduction velocities and reflexes of the proximal and distal parts of the saphenous nerve of the dog

The maximal conduction velocities of compound-action potentials in the proximal and distal parts of the saphenous nerve were determined by averaging potentials evoked and recorded through needle electrodes. Antidromic, triphasic compound-action potentials unipolarly recorded from the distal part of the saphenous nerve were of the same minimal latency as potentials having 4 phases which were recorded bipolarly from the same site. However, the unipolarly recorded potentials were of greater amplitude. Monophasic compound-action potentials were recorded through bipolar chlorided silver electrodes from the surface of fascicles of the distal part of the saphenous nerve. The maximal conduction velocity of these potentials was in agreement with the conduction velocity of compound-action potentials of the distal part of the saphenous nerve which were evoked and recorded through subcutaneous needle electrodes. The specificities of the stimulating and recording sites were verified by recording before and after the saphenous nerve was cut between the stimulating and recording sites. Mean conduction velocities were 62.3 +/- 2.0 m/s for the distal part of the saphenous nerve and 66.3 +/- 2.2 m/s for the proximal part of the saphenous nerve. Reflex-evoked muscle activity was elicited in the ipsilateral tensor muscle of the fascia lata and semimembranous muscle after electrical stimulation of the saphenous nerve through subcutaneous needle electrodes. The effects of various stimulus intensities on the latency and duration of these reflex-evoked muscle potentials were determined.     

Conduction velocities and myelinated fiber diameter spectra of the infraorbital and palpebral nerves of the dog

Maximum conduction velocities of compound-action potentials of the infraorbital (ION) and palpebral (PN) nerves were determined by averaging potentials evoked and recorded through subcutaneous needle electrodes. The specificity of the stimulating and recording sites was verified by recording before and after cutting the nerves. Conduction times for orthodromically and antidromically conducted potentials of the ION were essentially the same. The unipolarly recorded antidromic compound-action potentials of the ION were of higher peak-to-peak amplitude and were more reliably recorded than were the bipolarly recorded orthodromic action potentials. Areas of cutaneous innervation were not found for the PN. Neuromuscular blockade eliminated the volume-conducted muscle action potentials that were recorded after PN stimulation, allowing triphasic nerve action potentials to be recorded unobscured. Mean conduction velocities were: ION = 83.9 +/- 3.5 m/s; PN = 56.4 +/- 2.8 m/s. Distributions of the external diameters of myelinated fibers within the ION and the PN were determined.     

Electromyographic evaluation of conduction time and velocity of the recurrent laryngeal nerves of clinically normal dogs

In 25 adult dogs of various breeds, recurrent laryngeal nerve fibers were electrically stimulated at 2 points along their extralaryngeal course. Evoked compound muscle action potentials were recorded in the ipsilateral intrinsic laryngeal muscles, using a percutaneous needle electrode. Latencies, amplitudes, and durations were measured. Latencies were correlated with neck length (r = 0.88 on left and 0.82 on right). Five of the dogs were euthanatized, and the nerve length between the 2 stimulating needle electrodes was measured; calculated conduction velocities (mean +/- SD) were 55 +/- 6 m/s (left) and 57 +/- 6 m/s (right). In 38 additional canine cadavers, the lengths of the exposed left and right recurrent laryngeal nerves were correlated with neck length (r = 0.44 on left and 0.56 on right). A linear regression model is proposed for predicting normal latencies, despite variations in neck length among different breeds of dogs.     

Morphologic and morphometric studies of the vagus and recurrent laryngeal nerves in clinically normal adult dogs

Morphologic and morphometric studies were performed on the vagus nerve and its major branch, the recurrent laryngeal nerve (RLN): (1) to determine normal histologic data in myelinated fibers of clinically normal young adult dogs, (2) to establish reference values for mean fiber diameter in the vagus nerve and in the proximal and distal portions of the RLN, and (3) to delineate relative frequency distribution curves for each nerve. Few degenerative changes were observed in single teased-nerve fiber preparations. There was no statistical difference between left and right sides of the vagus nerve or between the proximal and distal portions of the RLN (right and left sides). In contrast to the unimodal distribution of fibers in the vagus nerve and the proximal portion of the RLN, the distribution of fibers in the distal portion of the RLN was bimodal. Mean (+/- SD) fiber diameters of the vagus nerve and in the proximal portion of the RLN (3.02 +/- 1.44 microns and 3.63 +/- 1.49 microns, respectively) were not significantly different, despite a shift to large-diameter fibers in the latter. However, mean fiber diameters of distal and proximal portions of the RLN (5.56 +/- 1.88 microns and 3.63 +/- 1.49 microns, respectively) were significantly (P less than 0.001) different. Approximately 86% of fibers in the vagus nerve and 76% of fibers in the proximal portion of the RLN, had a diameter less than 5 microns, and about 70% of fibers in the distal portion of the RLN had a diameter greater than 5 microns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distal denervating disease: a degenerative neuropathy of the distal motor axon in dogs

A group of ten dogs affected by an apparently identical denervating disease, is described. There was no breed or age predisposition but females were preferentially affected (70%). The rate of onset of signs was variable from a week to greater than 1 month. Quadriparesis was present to varying severities and in two dogs the head and neck could not be supported. Mastication, swallowing, respiration and bladder function were unimpaired. Pain sensation was normal, tone was usually decreased and the local limb reflexes depressed or absent. Muscle atrophy was often prominent. All cases bar one recovered but another dog was also destroyed. Electrophysiology revealed diffuse spontaneous activity in the muscles and the motor nerve conduction velocities were at the lower end of or just below the normal range. The evoked muscle potentials were reduced in amplitude. Sensory nerve potentials were normal. The pathology showed a degeneration of the distal intramuscular axons with collateral axonal sprouting. The muscle changes were typical of neurogenic atrophy. The disease has been called distal denervating disease (DDD) until the precise aetiology can be determined.     

Sensory action potentials in the ulnar and radial nerves of dogs: effect of stimulation site and voltage

The influence of stimulation site and voltage on amplitude, wave form, conduction time, and velocity of sensory action potentials in the ulnar and radial nerves was evaluated in 25 healthy dogs. A 5-fold increase in stimulation voltage above threshold caused a 300% increase in the amplitude of evoked sensory nerve potentials. An additional 2-fold increase in stimulation voltage (to 10 times threshold) resulted in an additional 40% increase in amplitude. An absolute saturation voltage was not found. Latency velocity was increased by increasing stimulation voltage, but conduction velocity was not affected. Multicomponent nerve action potentials were frequently found at the proximal recording sites. The number of components was not affected by stimulation voltage. Proximal displacement of the stimulation site resulted in an increase in amplitude of the nerve action potentials, increased latency velocity, and fewer components; conduction velocity was not affected. As a consequence of these findings, preference was given to simultaneous recording at 2 sites along the nerve, stimulation at the more proximal stimulation site distal to the carpus, and stimulation voltages between 5 and 10 times the threshold. The occurrence of multicomponent wave forms, the absence of an absolute saturation voltage, and the lowering of the number of components by proximal displacement of the site of stimulation may all be related to the relatively small number of sensory nerve fibers that can be activated at the stimulation site.     

Age-related effects on motor nerve conduction velocity in chickens.

Compound motor-nerve action potentials evoked by supramaximal stimulation of the proximal and distal aspects of the tibial nerve were evaluated in chickens 1 to 15 weeks old. Motor-nerve conduction velocity increased from a mean of 22.6 m/s at week 1 to a mean of 52.7 m/s at week 15. The increase in conduction velocity was greatest for the first few weeks, and reached a plateau at 10 weeks. Subcutaneous limb temperature, limb length, and proximal latency measurements also increased with age; however, distal latency measurements were not significantly influenced by age. A quadratic equation was calculated to predict mean motor-nerve conduction velocity for maturing chickens.     

A new method for recording and analysing evoked motor potentials from dogs

Normal values for motor conduction in the tibial, ulnar and fibular nerves of dogs have been determined using a new method for recording and analysing evoked motor potentials. The use of an alligator clip as a roving surface electrode for recording, and a personal computer to analyse the evoked potentials has facilitated faster and more reproducible motor conduction studies. Compound muscle action potential (CMAP) and motor nerve conduction velocity data are in good agreement with previous studies. Normal values for CMAP area, residual latency and proximal to distal ratios for CMAP area and amplitude are presented for the first time.     

Normal values for radial,peroneal and tibial motor nerve conduction velocities in adult sheep,with comparison to adult dogs

A technique for measuring motor nerve conduction velocities (NCV) in sheep was developed using 15 clinically normal ewes. Mean ±SD values were determined for the radial (76.3±12.5 m/s), peroneal (103.9±12.7 m/s), and tibial (98.6±13.1 m/s) nerves. The recording needle electrode was located in the extensor carpi radialis, tibialis cranialis, and gastrocnemius muscles, respectively. Latencies, amplitudes and durations of the proximal and distal evoked compound muscle action potentials are given. To investigate further the unexpectedly high NCVs calculated for the peroneal and tibial nerves, analogous stimulating and recording electrode sites were used in 7 clinically normal dogs. The corresponding canine peroneal (88.1±8.3 m/s) and tibial (89.2±12.4 m/s) NCVs were higher than the standard sciatic-tibial NCV recorded from the interosseous Myelinated nerve fiber diameters were measured on semithin transverse sections of peroneal and tibial nerve specimens taken from a clinically normal ewe and bitch. A possible explanation for the relative species difference in the proximal peroneal and tibial NCV values is the presence of fibers in both the peroneal and tibial nerves of the sheep which were as much as 3 wider than the largest fibers found in the dog.     

Failure of neuromuscular transmission after complete nerve section in the dog.

After the ulnar nerve was surgically transected, nerve conduction velocity in the distal segment and the evoked motor unit potential (EMUP) from the interosseous muscle were recorded until neuromuscular transmission failed. In five of the six dogs in the experiment, functional conduction ceased by 4.8 days, as determined by failure of both proximal and distal stimulation of the distal segment to evoke a muscle response. From the time of section until neuromuscular failure, the nerve conduction velocity remained unchanged. The amplitude of the EMUP from the interosseous muscle, however, decreased markedly during this time. Changes in other features of the EMUP are also presented. Fibrillation (denervation) potentials did not appear until the first day that muscle response could not be detected by stimulating the nerve. These data present a principle which would enable a determination of relative extent and progression of peripheral nerve damage.     

Myelinated axons in peripheral nerves of adult beagle dogs: morphometric and electrophysiological measurements

The myelinated fibre composition and conduction velocities were measured for the ulnar, saphenous and caudal cutaneous sural nerves of 10 healthy beagle dogs. A systematic random sampling technique was used to estimate the fibre diameter frequency distributions and densities. Conduction velocities were measured from evoked compound nerve action potentials. All nerves showed bimodal diameter frequency distributions with modes being approximately the same for each nerve (2 to 4 microns and 8 to 10 microns or 10 to 12 microns). The variation in the average densities and in the shapes of histograms of the different nerves was slight; however, there was a wide variation for the same nerve in different individuals. The conduction velocities for the fastest conducting axons in the nerves ranged from 63 to 79 m s-1. These normal quantitative processes affecting peripheral nerves in the dog.     

Nature of the late potentials and F-ratio values in dogs

There is controversy about the nature of the late potentials (F-waves and H-reflexes) in dogs. This work has attempted to clarify the problem by comparing late potentials in eight intact and four chronically deafferented dogs. Pure H-reflexes were recorded inconsistently from intact preparations at voltages below the threshold for the M-wave. At stimulation voltages giving maximum direct responses, there was no statistically significant difference between the amplitude and latency of the late potentials of the two groups. However, there was a tendency for the late potentials to be of larger amplitude and longer duration in intact preparations. Late potentials in intact preparations had a composite waveform consisting of both F-waves and H-reflex components. F-waves only were present in deafferented limbs, and their amplitude was proportional to the intensity of the stimulus. F-ratios could be calculated by using the latencies of the late potentials, because the F-wave did not have a longer latency than the H-reflex. The following reference values for the F-ratio are proposed: 1.954 +/- 0.086 when stimulating at the hock and 0.883 +/- 0.052 when stimulating at the popliteal fossa.     

Assessment of dorsal nerve root and spinal cord dorsal horn function in clinically normal dogs by determination of cord dorsum potentials

OBJECTIVE: To establish normal predictive values for cord dorsum potential (CDP) onset latency after thoracic and pelvic limb sensory or mixed nerve stimulation in adult dogs. ANIMALS: 26 clinically normal adult dogs. PROCEDURE: Sensory nerve action potentials (SNAP) were recorded proximally from tibial and lateral superficial radial nerves after distal stimulation. The CDP were recorded from the L4-L5 interarcuate ligament for the tibial nerve and from the C7-T1 interarcuate ligament for the radial nerve. Linear regression analyses were performed for CDP onset latency, and mean +/- SD was calculated for CDP onset to peak latency differences and sensory nerve conduction velocities (SNCV). RESULTS: For the tibial nerve, expected CDP onset latency (CDPOL) = -1.194 + 0.014 X pelvic limb length (mm; R2 = 0.912); CDPOL = -2.156 + 0.011 X pelvic limb/spinal length (mm; R2 = 0.911); and CDPOL = 0.941 + 2.197 X tibial nerve SNAP latency (milliseconds; R2 = 0.903). For the radial nerve, CDPOL = -0.9 + 0.014 x thoracic limb length (mm; R2 = 0.873); and CDPOL = 1.454 + 1.874 X radial nerve SNAP latency (milliseconds; R2 = 0.903). Mean +/- SD for CDP onset to peak latency difference for tibial and radial nerves was 3.1+/-0.3 and 3.0+/-0.4 milliseconds, respectively. CONCLUSIONS: Strong linear associations exist between CDPOL and a number of easily measured peripheral independent variables in dogs. There is also a narrow range of normal values for CDP onset to peak latency differences that is independent of limb length. CLINICAL RELEVANCE: CDP evaluation can be used to accurately assess functional severity and distribution of abnormalities in proximal sensory nerves, dorsal nerve roots, and spinal cord dorsal horns in dogs with suspected neuropathy, radiculopathy, or myelopathy involving the brachial or lumbosacral intumescences.     

Progressive axonopathy: an inherited neuropathy of Boxer dogs. 1. Further studies of the clinical and electrophysiological features

The clinical and electrophysiological findings in 14 Boxer dogs with progressive axonopathy (PA) are described. The salient clinical features are hind-limb ataxia which may later involve forelegs, proprioceptive defects, hypotonia, patellar areflexia, absence of muscle atrophy and, in a few instances, ocular tremor and head bobbing. The outward signs are often observed by 2–3 months of age but clinical testing can reveal patellar areflexia at 1 month of age. After an initial progression, the signs may stabilize and dogs are alive at 4 years of age having shown no deterioration over the previous 2 years. The electrophysiology shows reduced motor nerve conduction velocities and evoked potential amplitudes after about 4 months of age. The F-wave latency is considerably increased. Sensory nerves also show a marked reduction in the amplitude of their evoked potentials and eventually cease to conduct. Abnormal spontaneous activity is not a feature on electromyography. The conduction defects probably reflect to some degree the reduced nerve fibre diameters and myelin sheath changes found in PA although other factors may also be operating. The study shows that PA can be diagnosed with reasonable confidence by routine clinical testing at an early age.     

Influence of limb temperature on sensory nerve conduction velocity in horses

Sensory nerve conduction velocity was measured in the lateral palmar nerve of 8 horses. The limb temperature was manipulated by external means and monitored. Alterations in the nerve conduction velocity related to limb temperature variation were identified at both increased and decreased temperatures. These were quantified and a mean value of 2.15 +/- 0.2 m/s/degree Celsius was determined. The effect of altered limb temperature should be considered in nerve conduction velocity determinations.     

Effect of tissue temperature on ulnar nerve conduction velocity in the dog.

The motor conduction velocity of the ulnar nerve of 19 mature dogs anesthetized with pentobarbital was electromyographically determined before and at tissue temperature decrements of 2 degrees (C) during cooling of the forelimb. Precooling (37 C) conduction velocity was 56 +/- 7.6 m/second (mean +/- standard deviation). At a tissue temperature of 20 C, conduction velocity was reduced to 31 +/- 6.3 m/second. Regression analysis indicated that conduction velocity decreased linearly by 1.7 m/second for each degree of decrease in tissue temperature between 37 and 20 C.     

Trigeminal nerve-evoked potentials in the dog

Brain stem and cerebrocortical potentials were evoked by electrical stimulation of the infraorbital nerve of dogs and recorded through needle electrodes placed adjacent to the contralateral parietal bone. Five individual, short latency peaks were recorded in each averaged trigeminal nerve-evoked potential and were identified as I, II (A and B), III (A and B), PI (A, B, and C), and NI. Mean peak latencies +/- 1 SD were as follows: I = 0.9 +/- 0.1 ms, IIA = 1.7 +/- 0.1 ms, IIB = 2.5 +/- 0.1 ms, IIIA = 3.6 +/- 0.15 ms, IIIB = 4.1 +/- 0.2 ms, PIA = 5.2 +/- 0.15 ms, PIB = 6.4 +/- 0.2 ms, PIC = 7.3 +/- 0.3 ms, and NI = 11.0 +/- 0.6 ms. Trigeminal nerve-evoked potentials recorded through needle electrodes were essentially the same as potentials evoked by direct stimulation of the infraorbital nerve and recorded directly from the dura mater overlying the contralateral rostral suprasylvian gyrus. The specificity of the stimulating site was verified by recording before and after the infraorbital nerve was cut proximal to the stimulating site.     

Intraoperative Monitoring of Ischiatic Nerve Function with Sensory Evoked Potentials

Serial recordings of sensory evoked potentials (SEP) generated in response to stimulation of each tibial nerve were obtained from 23 anesthetized dogs. Five dogs were anesthetized for 3 hours to evaluate changes in serial SEP during general anesthesia. Nonsurgical and surgical manipulations were performed on one hind limb of five dogs to determine the effects of limb positioning and nerve retraction on SEP. In 13 dogs, the ischiatic nerve was exposed surgically and retracted until the SEP deteriorated and disappeared, to determine the relationship between amount of tension on the nerve and the time to complete deterioration of the SEP. Sensory evoked potential waveforms, which consisted of two to five peaks, were stable throughout the anesthetic period. The first two peaks were the most stable. Latency of the first two peaks was the easiest and most reliable parameter to evaluate. Although the peak latency in recordings from the superior hind limb was always slightly longer, SEP recordings from the inferior limb were good controls to monitor nerve function. There was considerable variation in sensitivity to nerve retraction. The technique proved to be a reliable way to monitor nerve function in normal anesthetized dogs.