F-wave latency and F-wave conduction velocity for the tibial nerve in clinically normal dogs

OBJECTIVE: To establish a method of F-wave examinations and to determine values of F-wave conduction velocity (FWCV) and F-wave latency for the tibial nerve of clinically normal dogs. ANIMALS: 21 clinically normal dogs. PROCEDURE: The F-waves were elicited from the interosseous muscles via stimulation of the tibial nerve. The FWCV was determined by using the F-wave shortest value and the surface distance corresponding to the tibial nerve length. Correlation between the smallest latency value of the F-wave and the length of the tibial nerve and between the FWCV and rectal temperature were closely examined. RESULTS: F-wave latency was proportional to the length of the tibial nerve (correlation coefficient, 0.929). Mean +/- SD FWCV was 77.98 +/- 8.62 m/s. Regression equation was as follows: F-wave latency = 2.799 + (0.029 X length of the tibial nerve).The FWCV was increased when the measured rectal temperature was high. Correlation coefficient between FWCV and rectal temperature was 0.665. CONCLUSIONS AND CLINICAL RELEVANCE: In the study reported here, we established a reliable method for clinical evaluation of the F-wave. When assessing nerve conduction velocity, it is essential to measure nerve length along the pathway that the nerve impulse travels. This method of F-wave examination is a useful diagnostic tool for the evaluation of suspected dysfunction of the peripheral nervous system.     

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.     

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.     

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.     

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.     

Electrodiagnostic evaluation of peripheral nerve function in rheas and barred owls

OBJECTIVE: To establish reference values for electrodiagnostic evaluation of peripheral nerve function in birds. ANIMALS: 6 rheas and 6 barred owls. PROCEDURE: Birds were anesthetized with propofol or isoflurane in oxygen. Using a computer-based electromyograph system and needle electrodes for stimulation and recording, electromyography (EMG) was performed on the pectoral, biceps brachialis, and gastrocnemius muscles, and evoked EMG was performed on the tibial and ulnar nerves. Motor nerve conduction velocity (MNCV) was calculated. Repetitive stimulation was performed on these 2 nerves. Late F waves were recorded for each nerve, when possible. RESULTS: Activity was evident during insertion of the electrodes, but muscles tested were electrically quiescent after spontaneous EMG. Motor nerve conduction velocity was faster in the tibial nerve than ulnar nerve but did not differ significantly between species. Mean +/- SEM MNCV was 132.3+/-7.8 m/s for the tibial nerve and 59.7+/-7.8 m/s for the ulnar nerve. A significant difference was not observed in responses at the fourth or ninth stimulation during repetitive stimulation. Subsequent to the initial stimulation, amplitudes were +/-22.7% of the initial motor potential amplitude. Recorded F waves were inconsistent, which may have been associated with technique. CONCLUSIONS AND CLINICAL RELEVANCE: Reference range (mean +/-2 SEM) for MNCV was 34.1 to 75.3 m/s for the ulnar nerve and 116.7 to 147.9 m/s for the tibial nerve in barred owls and rheas. After repetitive stimulation, motor potential amplitudes may be +/-22.7% of the initial amplitude response.     

Cortical somatosensory evoked potentials in cows.

A method was developed to record cortical somatosensory evoked potentials (SEP) from thoracic and pelvic limb stimulation in cows. Recordings were similar in latency and amplitude to those reported for horses. Correction for conduction pathway length did not alter the average latency values because the cows of the study were uniform in size; however, the data provided will enable use of this normative data with smaller or larger individual animals. Although latency variability for the SEP peaks was low, variability of the amplitude measurements was high. This observed variability was similar to that seen in other species. Validity of the recorded responses was indicated by lack of a tibial nerve SEP in 1 cow that had been given a tibial nerve conduction block, using lidocaine, and by repeatability of the response in 2 recordings taken 1 year apart in the same cow.     

Transcranial magnetic stimulation of the motor cortex and percutaneous magnetic stimulation of the peripheral nervous structures in the dog

The motor cortex was transcranially and peripheral nervous structures (motor roots, plexus, peripheral nerves) were percutaneously stimulated by magnetic pulses in awake dogs and in dogs awaking from general anesthesia. The compound muscle action potentials were recorded by surface or needle electrodes. The central motor conduction time as an information about central motor tracts was obtained by subtracting the peripheral latency from the corticomuscular latency. The peripheral latency was assessed by high voltage electrical and magnetic stimulation of motor roots and by the F-wave technique. The motor conduction velocity of the tibial nerve was measured by percutaneous magnetic and by electrical stimulation and the resulting values were compared.     

Motor nerve conduction parameters in the cat

The electrophysiological characteristics of motor conduction in normal cats have been determined using an alligator clip as a surface electrode to record the compound muscle action potential (CMAP) following stimulation of the tibial, ulnar and fibular nerves. Data on nerve conduction velocity, residual latency and the amplitude and area of the CMAP have been determined using a computerised electromyography unit. Motor nerve conduction was substantially faster in cats than dogs and the site of stimulation had less effect on the size and area of the CMAP. Although a small decline in the amplitude of successive CMAPs was observed following repetitive stimulation of the tibial and ulnar nerve at 20 Hz, the decrement was less marked than in the dog.     

Comparison of genitoanal and bulbospongiosus reflexes and measurement of penile nerve conduction velocity in cats

The bulbospongiosus reflex, genitoanal reflex, and nerve conduction velocity of the dorsal nerve of the penis were evaluated in cats. Seven adult sexually intact or castrated male mixed-breed cats underwent surgical isolation of the bulbospongiosus (analagous to bulbocavernosus) branch, anal branch, and distal trunk of the pudendal nerve. The bulbospongiosus and genitoanal reflexes were recorded from the bulbospongiosus and anal branches, respectively, by electrical stimulation, in turn, of the distal pudendal trunk and the penis itself. Nerve conduction velocity of the dorsal nerve of the penis was calculated by measuring response latency differences in the anal branch after stimulation of 2 sites on the extruded penis. The bulbospongiosus reflex had response latencies of 8.1 to 10.3 ms (distal trunk stimulation) and 11.0 to 13.0 ms (penile stimulation). The genitoanal reflex had latencies of 8.1 to 10.5 ms (distal trunk stimulation) and 11.2 to 13.2 ms (penile stimulation). Response amplitudes diminished at stimulus rates of 5 to 10 Hz; responses were abolished at rates of 12 to 15 Hz, suggesting that the reflexes are polysynaptic. There was no significant difference between latency values for the bulbospongiosus and genitoanal reflexes. Mean +/- SD nerve conduction velocity in the dorsal nerve of the penis was calculated to be 3.8 +/- 0.34 m/s, which was considerably slower than that found in human beings. This may represent technical difficulties in performing the test in cats, but could also indicate a difference between cats and human beings in the predominant population of cutaneous sensory fiber types of the penis.     

Usefulness of combined electrophysiological examinations for detection of neural dysfunction in cats with lumbar hematomyelia

We conducted combined electrophysiological examinations including F-wave, motor nerve conduction velocity (MNCV), spinal cord-evoked potential (SCEP), and needle electromyography (EMG) in two cats involved in traffic accidents that consequently developed hind limb paralysis caused by lumbar hematomyelia. F-wave could no longer be elicited within 3 days after the accident, and the MNCV and compound muscle action potential (CMAP) amplitude decreased in a time-dependent manner, with CMAP no longer being evoked after 7 or 8 days. EMG showed abnormalities such as fibrillation and positive sharp waves after 6 to 8 days. These results suggest that such combined electrophysiological examinations may provide objective, quantitative data for motor nerve dysfunction in cats with lumbar hematomyelia.     

Cortical somatosensory-evoked potentials in the horse

Cortical somatosensory-evoked potentials (SEP) were recorded from thoracic and pelvic limbs in 15 horses (13 Thoroughbreds and 2 Quarter Horses). Ulnar nerve SEP were evoked by electrical stimulation of the lateral palmar branch of the ulnar nerve at the level of the metacarpophalangeal joint. Recordings were taken between electrodes at 2 cm lateral to the vertex (contralateral to the stimulated limb) and the midpoint of the interorbital line. Four peaks were found in all recordings: N1, P1, N2, and P2. Latencies to the peaks were 39.0 +/- 2.7, 45.5 +/- 5.3, 50.4 +/- 5.2, and 62.3 +/- 3.7 ms (mean +/- SD), respectively. Tibial nerve SEP were evoked by stimulation of the lateral plantar nerve branch of the tibial nerve at the level of the metatarsophalangeal joint. Recordings were taken between electrodes at the vertex (contralateral to the stimulated limb) and the midpoint of the interorbital line. Four peaks were also found in all tibial nerve SEP recordings: N1, P1, N2, and P2. Latencies to the peaks were 64.6 +/- 11.8, 84.5 +/- 9.7, 121.2 +/- 11.6, and 134.0 +/- 11.1 ms, respectively. Amplitude variability was high for the ulnar nerve and the tibial nerve SEP. There was no effect of sex seen on peak latency or amplitude, and peak latencies were not affected by body length.     

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.     

Establishment of a Method to Measure Length of the Ulnar Nerve and Standardize F-wave Values in Clinically Normal Beagles

We designed a new method of measuring the length of the ulnar nerve and determining standard values for F-wave parameters of the ulnar nerve in clinically normal beagles. Nerve length must be precisely measured to determine F-wave latency and conduction velocity. The length of the forelimb has served as the length of the ulnar nerve for F-wave assessments, but report indicates that F-wave latency is proportional to the length of the pathway traveled by nerve impulses. Therefore, we measured the surface distance from a stimulus point to the spinous process of the first thoracic vertebra (nerve length 1) and the anterior horn of the scapula (nerve length 2) as landmarks through the olecranon and the shoulder blade acromion. The correlation coefficients between the shortest F-wave latency and the length of nerves 1, 2 or the forelimb were 0.61, 0.7 and 0.58. Nerve length 2 generated the highest value. Furthermore, the anterior horn of the scapula was easily palpated in any dog regardless of well-fed body. We concluded that nerve length 2 was optimal for measuring the length of the ulnar nerve.     

Transcranial magnetic stimulation: normal values of magnetic motor evoked potentials in 84 normal horses and influence of height, weight, age and sex

REASONS FOR PERFORMING STUDY: Cervical spinal cord dysfunction is a common problem in equine medicine and the currently available tests give no objective information about the functionality of the nervous tracts. Therefore, transcranial magnetic stimulation (TMS) was performed in 84 healthy horses of different height in order to have an objective measure for the integrity of the descending motor tracts in normal horses. OBJECTIVES: To obtain reference values for onset latency and peak-to-peak amplitude of magnetic motor evoked potentials (MMEPs) and to evaluate the possible effect of height, age and gender on the neurophysiological measures. METHODS: All horses were sedated and stimulated transcranially by using a magnetic coil placed on the forehead. The stimulator triggered the sweep of an electromyogram machine that recorded MMEPs bilaterally from needle electrodes in the extensor carpi radialis and cranial tibial muscles. In that way, it was possible to measure latency between stimulus and onset of response. RESULTS: A significant difference was found between recordings made in the fore- and hindlimbs; MMEPs recorded in the front legs had a shorter onset latency and higher peak-to-peak amplitude. Mean +/- s.d. normal values for onset latency of 19.32 +/- 2.50 and 30.54 +/- 5.28 msecs and peak-to-peak amplitude values of 9.54 +/- 3.73 and 6.62 +/- 3.62 mV were obtained for extensor carpi radialis and cranial tibial muscles, respectively. The left-to-right difference in onset latency and peak-to-peak amplitude was not significant. In the same horse, differences up to 0.82 and 1.53 msecs for the extensor carpi radialis and cranial tibial muscles, respectively, lie within the 95% confidence limit and are considered normal. In contrast to onset latency, peak-to-peak amplitude showed a very large intra- and interindividual variability, even in the same muscle. To reduce the variability and predict normal values of new individual cases, influence of height, weight, age and sex on the MMEPs were determined. No significant effects of sex were observed on onset latency and peak-to-peak amplitude. The age of the horse had only a small but significant effect on peak-to-peak amplitude, with larger responses in older horses. Height at the withers and weight of the horse, parameters that strongly correlate with the size of the horse, had an important significant influence on onset latency but not on peak-to-peak amplitude. The age of the horse and height at the withers were used to predict peak-to-peak amplitude and onset latency, respectively, in normal horses. CONCLUSIONS AND POTENTIAL RELEVANCE: TMS is an excellent addition to the few tools we have for noninvasive imaging of the equine nervous system. Magnetically evoked potentials are highly reproducible and recent advances suggest that the applications of TMS in horses will continue to grow rapidly.     

The reference values of the T-wave of the patellar tendon reflex in normal dogs

The T-wave of the patellar tendon reflex (PTR) was recorded in 24 neurologically normal dogs. The surface electromyogram (EMG) was recorded as the T-wave from the vastus lateralis muscle (VL) in response to percussion of the patellar tendon. The distance of the reflex arc (DRA) was measured along the straight line between the spinous process of L5 and the greater trochanter (GT), and between GT and the patellar ligament (PL). There was a significant correlation (P<0.001) of the latency with the DRA on each side, but no difference in the slopes of the relationships between right and left VL was shown. The regression line between the DRA and the latency of all data was Y = 0.0216X + 1.693, where Y = latency in ms, X = DRA in mm. The mixed sensory-motor conduction velocity was estimated as 84.6 +/- 5.5 m/s. In contrast, there was no significant correlation between the DRA and the amplitude of the T-waves. The mean (mean-CV) and standard deviation (SD-CV) of all CV (coefficient of variation) in each dog were 9.14 +/- 3.65% in latency and 3.54 +/- 1.14% in amplitude, indicating that the use of a simple hand-held reflex hammer is sufficient to record the reproducible T-wave of the PTR even in unanesthetized dogs. This method was applied to a case with minimal paraparesis, and the latency of the T-wave of the PTR in the right hind limb with slight proprioceptive deficit was outside of the upper limit of the 95% confidence interval between latency and the DRA. In conclusion, this method may be used in neurological diagnosis to quantify more precisely the PTR in dogs.     

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.     

The effect of the tarsal joint positions on the tibial nerve motor action potential latency in dog: electrophysiological and anatomical studies

This study has been carried out to determine the effect of neutral position, hyperextension and hyperflexion of the tarsal joint on the tibial nerve, motor action potential latency and tarsal canal compartment pressure in dogs with the aid of electrophysiological and anatomical methods. Totally twenty healthy mongrel dogs were used. Latency of motor nerve action potential (MNAPL) studies of tibial nerve via surface stimulating and needle recording electrodes was performed on right hind limbs of all the dogs. The compartment pressures of the tarsal canal with the pressure transducer were determined from both limbs from ten of the dogs. In one dog, tarsal regions of both left and right limbs were demonstrated using magnetic resonance imaging (MRI). Two dogs were euthanatized and tarsal regions of the dogs were sectioned for correlative anatomy. Nerve conduction studies showed that the MNAP latency of the tibial nerve were 3.55 +/- 0.097 ms, 3.76 +/- 0.087 ms and 3.39 +/- 0.097 ms in neutral, hyperextension and hyperflexion positions, respectively. Hyperflexion of the tarsal joint caused prolongation of the MNAP latency of the tibial nerve with the highest pressure value being determined in tarsal canal. From the anatomical viewpoint, the distance between the flexor hallucis longus muscle and the superficial digital muscle was the shortest during hyperflexion and the plantar branch of saphenous artery, lateral and medial plantar nerves located more laterally in cadaver and MR imaging sections. As a result of this study, it is thought that tarsal region diseases as well as long time splint in the hyperflexion position as applied in the Ehmer sling can affect the compartment pressure and nerve tension because of occupying in the tarsal canal. Raising pressure and nerve stretching in the tarsal canal compartment could cause deficiencies in the conduction velocity of the tibial nerve. This might be a result of tarsal tunnel syndrome in the dog. Clinicians could consider this syndrome in cases of tarsal region diseases as well as application of long time splint in hyperflexion of tarsal joints in dogs.     

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).     

Compound-action potentials of myelinated fibers in the saphenous nerve of the dog: in situ electrophysiologic and behavioral studies

Compound-action potentials (CAP) were recorded directly from the surface of fascicles of the distal portion of the saphenous nerve (SN) of dogs in situ. Potentials were evoked through needle electrodes and were recorded through bipolar stainless steel electrodes. Stimuli of 10-microseconds duration and of 0.4 +/- 0.15-mA amplitude evoked a monophasic CAP. Sensory conduction velocities of afferent fibers, the action potentials of which contributed to this evoked compound potential, ranged from 62.4 +/- 2.8 m/s for the most rapidly conducting fibers to 30.5 +/- 2.4 m/s for the least rapidly conducting fibers. Stimuli of 25-microseconds duration and of 2.2 +/- 0.8-mA amplitude evoked a second, longer latency CAP in addition to the first CAP. Sensory conduction velocities of afferent fibers, the action potentials of which contributed to this evoked compound potential, ranged from 20.4 +/- 2.9 m/s for the most rapidly conducting fibers to 13.7 +/- 1.0 m/s for the least rapidly conducting fibers. Low-amplitude, negative peaks were recorded between the first and second major potentials elicited by the longer duration stimuli. Stimuli of still longer duration and higher currents induced contractions of the caudal part of the sartorius muscle by current spread in 9 of 12 dogs. In 3 dogs, a third monophasic CAP was evoked, having a maximal conduction velocity of 1.7 +/- 0.2 m/s. After section of the distal portion of the SN on one side in each of 2 dogs, an absence of signs of sensory deficit was found on clinical neurologic examination. The area of cutaneous innervation of the cranial branch of the distal portion of the SN was determined electrophysiologically.