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Motor nerve conduction velocities in normal subjects with particular reference to the conduction in proximal and distal segments of median and ulnar nerve
314
ELECTROENCEPHAL(~RAPHY AND CLINICAL NEUROPHYSIOLOGY
MOTOR NERVE CONDUCTION
VELOCITIES
SUBJEC'I~ WITH PARTICULAR TO THE CONDUCTION
REFERENCE
IN PROXIMAL
SEGMENTS OF MEDIAN
IN NORMAL
AND DISTAL
AND ULNAR
NERVE
W. TROJABORG
Department of Clinical Neurophyslology, University Hospital, Copenhagen (Denmark) (Accepted for publication: December 6, 1963)
The muscle action potentials used to indicate the arrival of motor nerve impulses in man are recorded either with surface electrodes (Hodes et al. 1948, Wagman and Lesse 1952) or witb intramuscular needle electrodes (Bolzani 1954; Thomas et al. 1959). The nerve is stimulated either with surface electrodes (Hodes et al. 1948) or with needle electrodes (Poloni and Sala 1962). A systematic comparison of these procedures and of their uncertainties is not available. The velocity with which impulses are con. dueted over the proximal and distal portions of motor nerves is still a matter of dispute. With the mechanical latency as a gauge Helmholtz (1870) reported a higher ~elocity of impulse transmission in the median nerve when measured be. tween axilla and wrist than when measured from elbow to wrist. With the muscle action potential as indicator Norris et al. (1953) and Spiegel and Johnson (1962) found no difference between conduetion velocities measured in the upper arm segment and in the lower arm segment of the ulnar nerve, whereas Poloni and Sata (1962) and Mayor and Libman (1962) found a higher velocity in the upper segments of both the ulnar and the median nerves (difference 6 and 11 m/see). Bolzani (1954) and Redford (1958) reported similar findings in the ulnar nerve (difference 9 and 5 m/see) but both Redford (1958) and Thomas (1960) failed to demonstrate any similar difference in the median nerve. The purposes of the study presented in this report were (1) to compare the conduction velocities obtained by recording with surface and concentric needle electrodes and by stimulating with surface and needle electrodes, (2) to compare the conduction velocities in the proximal
and distal segments of the median and ulnar nerves in normal, subjects, (3) to evaluate the uncertainty of the procedure by comparing the conduction velocities in the right and left median, ulnar and anterior tibiat nerves. MATERIAL A N D M E T H O D
The examinations were performed on 47 subjeets without signs or symptoms of neuromuscular disorder, Thirty-six were between 20 and 50 years, eight more than 50 years and three below 20 years of age. Stimulation
The stimulus was a rectangular pulse of 0.10.7 mse¢ duration. It was obtained from a stimulator (DISA) with a double shielded output transformer (Buchthal et al. 1955). The output impedance was 15 kf~ and the maximum output current 15 mA. The stimulating current was 2 mA at threshold and 4=6 mA for supramaximal stimulation both with surface and with needle electrodes. This current was obtained with 10 and 25 V between the electrodes. A 50 /~secsignal was introduced to indicate the onset of the stimulus. The median and ulnar nerves were stimulated at three points along their course, at the level of the wrist (6-8 cm above the leading-off electrodes), the elbow (19-25 cm above the wrist) and the axilla ('17-25 cm above the elbow). The anterior tibial nerve was stimulated at the ankle (7-10 cm above the leading-off eleetro~es) and at the capitulum fibulae (29-39 cm above the ankle). The stimulus was applied through two electrodes placed 25 mm apart along the nerve: Electroeneeph. din. Nemephystoi., 19641 17:314-321
315
M O T O R C O N D U C T I O N VELO CI TY
Stirnulotion with | surfoce electrodes Recordi[g,, w,thneedle, electrodes cencentric nee~e e4~:trmle
surface efagtrode
bipolar meedle Mectro4e
c~ncentei¢ neeclie eiectrmfa
surface ~lm:trmle
b~olar nee41e electrode
Axillo
[=
- Elbow
3 crn
j~lOmV
]~mV
]•mV ÷
]•mv 4.
W~st S
Fig. 1 Muscle action potentials from m. abductor polli~isbrevisevoked by stimulating the median nerveat the axilia, elbow and wrist with surface electrodes(left) and with needle electrodes (right) and recording with concentricneedleelectrodes,skin electrodesand bipolar needleelectrodes.
Conduction velocityin m/sec Stimulating electrodes: surface needle Recordin$ electrodes: eoncentr, surface b i p o l a r concentr, surface axilia-elbow (21 era) 70,4 70.4 71.4 70.4 70.0 elbow-wrist (23 ¢m) 57,6 58.9 60,6 58.9 56.2 uilla-wrist (44 era) 63.8 64.7 65.2 64.7 62.8 distal latency(7-9 cm) msec 4.2 4.3 3,5 4.1 4.5
either through two cotton wick electrodes on the skin or through two needle electrodes (external diameter 0.4 ram) inserted close to the nerve. The cotton wick of the surface electrodes was soaked in salt solution before the electrodes were fixed to the skin. To reduce the skin resistanc~ the superficial corneal layer was removed by rubbing the skin lightly with fine sandpaper and by applying ether. The threshold was determined at high amplification (10 #V/ram) and, to ensure activation of all nerve fibres, the stimulus was supramaximal (two to three times threshold). To cheek the site of stimulation the polarity of the stimulating electrodes was reversed in every examina-
bipolar 71.4 58.9 64.2 3.6
tion (see Results). There was no evidence of anodal block when the cathode was placed proximally; the threshold was about the same with both types of stimulation,as were the amplitudesof the actionpotentialsevoked by supramaximal stimuli. The conduction time was measured as the average of the values obtained with both polarities. Recording Action potentials of the abductor pollicis brevis, abductor digiti quinti and extensor digitorum brevis muscles were used to indicate the arrival of the nerve impulse evoked by stimulaElectroeneeph. elin. Neurophysiol., 1964, 17:314-321
316
W. TROJAEORO
tion respectively of the median, ulnar and anterior tibial nerves, The muscle action potentials were recorded simultaneously by concentric needle electrodes (externaidiameter 0.45 ram) and by surface electrodes consisting of two tin plates (6 × 12 ram), one placed over the belly, the other over the tendon of the muscle, or by bipolar needle electrodes (external diameter 0.65 mm, distance between leading-off areas, 0.5 mm) to reduce interference from potentials from more distant muscles. When using surface electrodes the skin was prepared with electrode paste and the electrodes were covered with a thin layer of cotton and Bitted to the skin with a plastic solution. The earth electrode (lead plate) was placed between the distal stimulating electrode and the leading-off electrodes. The muscle action potentials were recorded with a 3-channel electromyograph (DISA). The time base was I msec/mm. The amplification was adjusted (0.5-1.0 mV/ ram) to give a peak to peak deflection of 35 mm. With ten times higher amplification a small potential might appear preceding the main deflection, indicating either a small portion of faster cotLducting fibres or a potential conducted from a more proximal muscle where the impulse arrives earlier. The conduction time was measured from the stimulus mark to the onset of the main steep negative deflection or to the inter. section of the steep positive-negative deflection with the base line. The distance in mm between two pairs of stimulating electrodes divided by the difference in msec between the onset of the slim, u|i and the muscle action potentials evoked by them gave the conduction velocity in m/see, Only potentials wi~h identical shape for all three stimulating positions were used to calculqte a velocity. In addition to conduction velocity the
voltage of the evoked muscle action potentials was measured. The temperature near the nerve was determined by a thermocouple mounted at the tip of a needle (diameter 0.7 mm, length 50 ram; EUab, type KS, TE3). RESULTS The conduction velocities of the motor fibres of the median and ulnar nerves were the same whether the muscle action potentials were led off' with surface or with concentric needle electrodes (Table I). When stimulating with surface electrodes it is difficult to localize the exact point of stimulation. This uncertainty is somewhat less with needle electrodes and the strength of the stimulus can be reduced about ten times at all three stimulating positions to restrict the spread of the stimulating current. Stimulus interference could be reduced further by le~ding off with bipolar needle electrodes. There was no significant difference in conduction velocity whether stimulation was effected with surface or with needle electrodes (Table !i). In an attempt to establish the site: of stimulation the polarity of the pulse was reversed in all examinations, resulting in a change in conduction time of about 0.5 msec. With a conduction velocity of 56-68 m/see this would correspond to a displacement of the site of stimulation of 28-34 ram, a value which is in reasonable agreement with the 25 mm distance between the stimulating elec, trodes. This indicates that, although the exact point of stimulation is unknown, the nerve is stimulated within a few mm from the cathode at all three positions; thus measurement of the distance from cathode to cathode gives the distance of conduction with good approxima,
TABLE I Motor conduction velocity in the median and uhmr nerves determined from muscle action potentials recorded with surface and with con~ntric needle electrodes
Recorded with Surface electrodes Needle electrodes
Median nerve Number Conductionvelocity of (elbow-wrist) nerves m/see 20 20
55.0d: 1,3 53.5-1-!,!
Ulnar nerve Number Conduction velocity of Celbow-wrist) nerves m/s~
S.D. m/see 5.6 5,0
a,
12 12
53.5±2,0 54.7q- 1,7
S,D. m/see 7.1 6.0
Electroencept~, clin, Neuropkysiol., 1964, 17:314-321
M O T O R C O N D U C T I O N VELOCITY
317
T A B L E II Conduction velocityof motor i'~ervowhen stimulatingwith surfaceand with needle electrodes
Stimulated with Surface electrodes Needle electrodes
Conduction velocity in m/sec in the median nerve
Number of nerves
axiila-elbow
S.D.
elbow-wrist
S.D.
axilla-wrist
S.D.
7 7
68.24-0.7 67.5+ 1.2
1.8 3. I
54.54-1.8 54.1 :[: 1.4
4.7 3.6
59.4-b 1. ! 58.64-1.0
2.8 2.7
TABLE HI Conduction velocity and difference in conduction velocity between right and left median (M), ulnar (U) and anterior tibial (AT) nerves
Conduction velocity Nerve investigated M M M U U U AT
axilla-elbow elbow-wrist axilla-wrist axilla-below elbow-wrist axilla-wrist capitulum-ankle
Number
Mean m/sec
S.D. m/see
24 36 24 22 30 22 22
67.9=[= 1.6 56.14-0.9 60.5± i.0 63.4:h 1.1 56.4:t:0.9 59.44-0.9 49.6:h0.9
7.7 5.3 4.8 5.3 4.8 4.1 4.2
Difference in conduction velocity between right and left Number Mean S.D. m/sec m/sec 12 18 12 I1 15 !I 11
6.7-1-1.3 4.14-0.8 3.7+0.5 6.0-1-1.5 2.84-0.6 4.4=[=0.9 2.84-0.7
4.4 3.2 1.9 5.0 2.2 2.9 2.3
TABLE IV Voltage of muscle action potential evoked at different levels in median, ulnar and anterior tibial nerves Muscle action potential evoked ~t
Proximal electrode Middle ©lectrod© Distal electrode
Median nerve Number Mean mV 24 36 36
18,5 :k 1.0 18,8~0.8 21.24-0,8
S.D. mV
Number
5,0 4,9 4,8
tion. The conduction velocities in the median and ulnar nerves were identical within the error of the method, as were the time intervals between the stimulus at the distal electrode and tile onset of the muscle action potential evoked by it (Table I!I and V). Motor conduction velocity in the anterior tibial nerve averaged 49.6 m/sec (S.D. 4.2 m/sec, 22 nerves); as previously shown by Hennksen (1956) it was slower than in the median and ulnar nerves. The voRage of the muscle action potential evoked by stimulation of the anterior tibial nerve was 1 !.4 mV (S.D, 3.8 mV, 22 nerves), i.e., significantly lower than that evoked by stimulation of the median and ulnar nerves.
22 30 30
Ulnar nerve Mean mV 14.1 ±0.9 14.4±0.9 16.84-t=0.8
S.D, mV
4.4 4.9 4,7
Anterior tibial nerve Number Mean S.D. mV mV 22 . . 22
.
I0, I ±0.8 . . I 1,8i0,8
3,8 3.8
Comparison of the conduction velocity in the distal and proximal segments of the median and uhmr nerves showed a significantly slower conduction in the distal than in the proximal portions of both nerves (by 18 and 11% respectively; "fable III), the voltage of action potentials evoked by ~timulating at the r roximal, middle and distal elect:redes did not show any significant differenc¢ (Table IV). As a temperature difference between the upper arm and the forearm might explain the slowing of conduction velocity in the distal segment of the nerve, the temperature was measured near the proximal and distal segments of the nerve in sevea subjects. The mean temperature in the Electroenceph. clin. Neurophysiol., 1964, 17:314-321
318
w. TROJAeOkO
upper arm was 36.0 u+ 0.3oc and in the forearm 35.4=i=0.3°C, i.e., a temperature differeace of 0.6~0.25°C (S.D. 0.65, P < 0.05, assuming a Gaussian distribution). If the distal slowing in conduction were due to the 0.6°C lower temperature in the forearm, it would correspond to a temperature dependence of conduction velocity in the median nerve (Table I!) of more than 20 m/see per degree centigrade. By examining the same nerve at different temperatures Henriksen (1956) found a change in conductiort velocity with temperature of 2.4 m/see per degree C; thus the difference in conduction velocity over proximal and distal segments of the nerve cannot be solely attributed to the difference in temperature be. tween upper arm and forearm. The variation in conduction velocity from subject to subject was 8.5--11.3%. The difference in conduction velocity between corresponding segments of the right and left zlerves was 5--10% (Table Ill). Assuming a normal distribution this difference can serve as basis for the determination of the experhnental error (~'): d
+++ +TB i/2 where d is the average difference in conduction velocity between right and left. in this way the experimental error in measuring conduction velocity in the median, ulnar and anterior tibial nerves was determined to amount to S-7%. Subtracting the experimental error from the variation from subject to subject the physiological
variation in conduction velocity from subject to subject was 5--7~. The experimental error in determining conduction time (Table V), obtained from a comparison of the corresponding segments of right and left nerves, was 7-17~. Including the experimental error the variation from subject to subject was 7-20%. Thus conduction velocity can be measured with greater accuracy than conduction time. DISCUSSION
The m o t o r nerve c o n d u c t i o n velocities in median, ulnar a n d anterior tibial nerves r e p o r t e d here are in general agreement with the reports o f
Wagman and Lesse (1952), Henriksen (1956), Thomas et ai. (1959), Johnson and Olsen (1960), Kato (1960), Lawrence and Locke (1961), Mulder et al. (1961), and SkiUman et al. (1961). The velocity of motor conduction was significantly slower in the distal than in the proximal segments of the median and ulnar nerves. A similar difference was observed in the proximal and distal portions of the ulnar nerve (Bolzani 1954; Poloni and Sala 1962), of the median nerve (Poloni and Sala 1962; Mayor and Libman 1962) and of the sciatic nerve (Gassei and Trojaborg 1964). Magladery and McDougal (1950) and Carpendate (I 956) found a decrease in conduction vetoc. ity along the lower portion of the ulnar nerve. On the other hand, the conduction velocity of sensory fibres was identical in the forearm and in the upper arm segment of the median nerve (Rosenfalck and Buchthat 1963).
[TABLE V Conduction time and difference in conduction time between right and left median (M), ulnar (U) and anterior tibial (AT) nerves ~onduction time Stimulation at M M M U U U AT AT
proximal electrode middle ,, distal ,, proximal ,, middle ,, distal ,, proximal ,, distal ,,
Number 24 36 36 22 30 30 22 22
Mean
S.D.
msec
m~
13.4:E0.2 10.1:E0.2 6.2+0.2 13.210.2 10.1~:0.3 5.8=[=0.2 14.5=[=0.4 8.0-4-0.3
1.4 1.3 1,2 0.9 1.3 1.2 1.8 1.4
Difference in conduction time between right and left Number Mean S.D. 12 18 18 11 15 15 11 11
m~
m$~:
1,2-t-0.2 i.0:1:0.2 1.1 :[:0.1 !.i+0.3 1.0-1-0.2 1.1-1-0.2 1.2-1-0.3 0.9-4-0.3
0,7 0.7 0.6 0.8 0.2 0.8 1.0 0.9
Electroenceph. clin. Neuroph.w'toL, 1964, 17:314-321
MOTOR CONDUCTION VELOCITY
The distal slowing in motor nerve conduction might be due to (1) a systematic error in measuring the length of the nerve in the forearm and upper arm, (2) a systematic displacement of the site of stimulation, (3) a systematic change in the point of the potential used for measurement of conduction time, (4) the lower temperature in the forearm, and (5) a diminished fibre diameter in the forearm. (I) The possible error introduced by inaccuracy of determining the distance between different sites of stimulation has been discussed by Simpson (1956) and by Christie and Coomes (1960), both of whom prefer measurements of conduction time; but I found both the standard deviation and the experimental error to he up to two times greater when the conduction time was measured than when conduction velocity was determined. The lower conduction velocity in the forearm would correspond to an average error of 2.5-4.5 cm in the measurement of nerve length. This is unlikely; Carpendale (1956) compared the length of median and ulnar nerves found on dissection of the forearm with the resuits of surface measurement and concluded that errors introduced in this way were of little importance, the surface distance being only 0.30.8 mm shorter than the actual length. In the examinations presented in this report errors in the measurement of distance were reduced by fixing the stimulating electrode. Especially in the axilla, where the skin is loose, manual pressure could lead to an erroneous estimation of the point of stimulation. By using needle electrodes for stimulation this error is practically eliminated. (2) Even with these precautions the lower conduction velocity in the forearm might be due to systematic differences in the distribution of the stimulating current associated with tissue conductivity at the different sites of stimulation. Thus the stimulus might spread such that the conduction distance was shorter in the upper arm and longer in the forearm than measured on the surface. With displacements of the sites of stimulation of 0.5-0.7 cm the proximal velocity would be reduced by 4 m/see and the distal velocity would increase 1.5 m/see, reducing the 12-7 m/see difference between proximal and distal velocities by 5.5 m/see. The uncel~ainty in the site of stimulation was reduced by measuring
319
the conduction velocity with each of the electrodes in turn as cathode (see above). (3) The point ofthepotentialused for measurement of conduction time may either be the onset of the action potential or its positive-negative deflection. If the leading off electrode is at the end-plate zone and the onset of the action potential is negative and is abrupt even at high amplification, the onset is well defined and well suited as point of reference for measurement at the different levels of stimulation. If hcwever the electrode is at some distance from the end-plate zone, the onset of the potential is gradual and positive, so that the "latency" is less well defined and depends on the amplification. Therefore, the intersection ofthe positive-negative deflection with the base line may give a more reproducible point of measurement for the determination of velocity between different levels of stimulation, provided that the shape of the potential is identical when evoked from the different points. Moreover, activity from distant muscles does not affect the time to the positive-negative deflection. This is of special importance when stimulating in the axilla where the median and ulnar nerves are often stimulated simultaneously. Thereby the onset of the muscle action potential led off from the thenar muscle group, for example, may be distorted by potentials generated from muscles of the hand innervated by the ulnar nerve, and vice versa. (4) Progressive lowering of the temperature of the nerve towards the periphery might contribute to the slowing of conduction. Helmholtz (1870) reported a diminution in winter in the conduction velocity in the median nerve to less than half the velocity in summer. Henriksen (1956) found a less drastic dependence of 2.4 m/see per degree centigrade within the range of 29 to 38°C, i.e., 4% per degree of cooling. Carpendale (1956) found that the conduction time from the wrist to the hypothenar muscle group was prolonged by about 0.2 msec per degree fall in temperature within the range o f 25 to 35°C, i.e., 8~ per degree of cooling. With the skin temperature at the wrist as a measure of temperature the conduction velocity changed by 1.2 m/see per degree centigrade at 20-.37°C (Kat3 1960). The change in external temperature can he assumed to affect the temperElectroenceph. clin. Neurophysiol., 1964, 17:314--321
W. TgOJABOgO
320
ature near the nerveless thanthe skin temperature, explaining the apparently lower temperature dependence in Kate's experiments. Kate found no difference in conduction velocity in the ulnar nerve between the upper arm and the forearm when measured at room temperature of about 30°C. On the other hand Mayor and Libman (1962) found that the differonce in velocity between the proximal and the distal segment of the median nerve persisted even when the temperature gradient along the arm was reduced by dry heat. We have found an average difference in temperature between the upper arm and forearm of 0.6°C measured near the median and ulnar nerves. This agrees with the difference in temperature of about one degree centigracle found by Buchthai et al. (1944) in the muscles of the upper arm and forearm and by Bazett et al. (1948) and Pennes (1948) between the warm brachial artery and the cool deep forearm. With a temperature dependence of 2.4 m/ sec per degree centigrade a 0.6°(: difference in temperature could account for a slowing of 1.4 m/see. In the case ofthe ulnar nerve a systematic displacement in the site of stimulation and a 0.6°C reduction in temperature in the forearm might account for the slowing of 7 m/see in distal conduction. However, in the median nerve the difference was 12 m/sec, and a further possible cause of slowing must be considered. (5) Mayor and Libman (1962) present the argument making it most likely that a gradual distal decrease in diameter of motor nerve fibres explains the distal reduction in conduction velocity. In animal experiments Gasser and Grundfest (1939) showed that the conduction velocity is proportional to the diameter of the axon. The distal slowing of conduction velocity, which has also been found in the sciatic nerve of frog (Marshall and Gerard 1933), might then reflect a decrease in diameter of the nerve fibres from the axilla to the small muscles of the hand, Indeed such a change in diameter has been demonstrated histologically in rabbits; motor nerves decrease in diameter distally not only because of branching but also because the individual fibres taper distally (Fernand and Young 1951). SUMMARY
Motor nerve conduction velocity in the
median, ulnar and anterior tibial nerves has been determined in 47 subjects, as well as the voltage of the evoked muscle action potential and the time interval between stimulus and the muscle action potential evoked from the distal electrode (Tables III-V). There was no significant differonce in conduction velocity when stimulating with needle and surface electrodes. In the median and ulnar nerves, conduction velocity was significantly slower in the distal than in the proximal portion of the nerve, and the difference was not due solely to differences in temperature; it may be attributable to a decrease in fibre dian~ter from the proximal to the distal part of the nerve. The difference in conduction velocity between the right and left extremities in the same subject and the variation from person to person averaged
5-10%. RtSUMt L, VITESSSDE CONDUCT,ONNeaveuse UO~lCe CHEZ DES SUJETS NORMAUX Se RAPPORTANT EN PARTICULIER ~ LA CONDUCTION DE LA PORTION PgOXIMALE ET DlSTALE DES NERFS MI~DIAN El" CUBITAL
La vitesse de conduction nerveuse motrice, ramplitude des potentiels musculaires ~voqu6s, ainsi que le temps de latence entre stimulation par 61ectrode distale et los r6ponses musculaires ont 6t6 d6termin6s dana 47 cas pour los nerfs m6dian, cubitai et sciatique poplit6 externe (Tableaux Ill-V). li n'existe pas de diff6renee significative entre les vitesses de conduction avec stimulation par ~lectrodes de surface ou par aiguilles. Pour los nerfs m~ian et cubitai la vitesse de conduction est plus lento darts le segment distal que dens le segment proximal des nerfs, Cette r~duction de vitesse ne s'explique pas seulement par des diff6rences de temperature; elle pourrait etre doe tt une diminution du din. m~tre des fibres nerveuses dans le segment distal. Los diff6rences de vitesse entre los extr6mit~ts droites et gauchos chez la memo personne et cellos entre cliff,rents sujets sent de 5-10% en moyenne. REFERENCES
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Electroenceph. clin. Neurophysiol., 1964, 17:314--321
M O T O R CONDUC'I ION VELOCITY
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MAOLADEBY,J. W. and McDOUOAL, D. B. Electrophysio-
Reference: TROJABORG,W. Motor nerve conduction velocities in normal subjects with particular reference to the conduction in proximal and distal segments of median and ulnar nerve. Electroenceph. din. NeurophysioL, 1964, 17: 314-321.
ELECTROENCEPHAL(~RAPHY AND CLINICAL NEUROPHYSIOLOGY
MOTOR NERVE CONDUCTION
VELOCITIES
SUBJEC'I~ WITH PARTICULAR TO THE CONDUCTION
REFERENCE
IN PROXIMAL
SEGMENTS OF MEDIAN
IN NORMAL
AND DISTAL
AND ULNAR
NERVE
W. TROJABORG
Department of Clinical Neurophyslology, University Hospital, Copenhagen (Denmark) (Accepted for publication: December 6, 1963)
The muscle action potentials used to indicate the arrival of motor nerve impulses in man are recorded either with surface electrodes (Hodes et al. 1948, Wagman and Lesse 1952) or witb intramuscular needle electrodes (Bolzani 1954; Thomas et al. 1959). The nerve is stimulated either with surface electrodes (Hodes et al. 1948) or with needle electrodes (Poloni and Sala 1962). A systematic comparison of these procedures and of their uncertainties is not available. The velocity with which impulses are con. dueted over the proximal and distal portions of motor nerves is still a matter of dispute. With the mechanical latency as a gauge Helmholtz (1870) reported a higher ~elocity of impulse transmission in the median nerve when measured be. tween axilla and wrist than when measured from elbow to wrist. With the muscle action potential as indicator Norris et al. (1953) and Spiegel and Johnson (1962) found no difference between conduetion velocities measured in the upper arm segment and in the lower arm segment of the ulnar nerve, whereas Poloni and Sata (1962) and Mayor and Libman (1962) found a higher velocity in the upper segments of both the ulnar and the median nerves (difference 6 and 11 m/see). Bolzani (1954) and Redford (1958) reported similar findings in the ulnar nerve (difference 9 and 5 m/see) but both Redford (1958) and Thomas (1960) failed to demonstrate any similar difference in the median nerve. The purposes of the study presented in this report were (1) to compare the conduction velocities obtained by recording with surface and concentric needle electrodes and by stimulating with surface and needle electrodes, (2) to compare the conduction velocities in the proximal
and distal segments of the median and ulnar nerves in normal, subjects, (3) to evaluate the uncertainty of the procedure by comparing the conduction velocities in the right and left median, ulnar and anterior tibiat nerves. MATERIAL A N D M E T H O D
The examinations were performed on 47 subjeets without signs or symptoms of neuromuscular disorder, Thirty-six were between 20 and 50 years, eight more than 50 years and three below 20 years of age. Stimulation
The stimulus was a rectangular pulse of 0.10.7 mse¢ duration. It was obtained from a stimulator (DISA) with a double shielded output transformer (Buchthal et al. 1955). The output impedance was 15 kf~ and the maximum output current 15 mA. The stimulating current was 2 mA at threshold and 4=6 mA for supramaximal stimulation both with surface and with needle electrodes. This current was obtained with 10 and 25 V between the electrodes. A 50 /~secsignal was introduced to indicate the onset of the stimulus. The median and ulnar nerves were stimulated at three points along their course, at the level of the wrist (6-8 cm above the leading-off electrodes), the elbow (19-25 cm above the wrist) and the axilla ('17-25 cm above the elbow). The anterior tibial nerve was stimulated at the ankle (7-10 cm above the leading-off eleetro~es) and at the capitulum fibulae (29-39 cm above the ankle). The stimulus was applied through two electrodes placed 25 mm apart along the nerve: Electroeneeph. din. Nemephystoi., 19641 17:314-321
315
M O T O R C O N D U C T I O N VELO CI TY
Stirnulotion with | surfoce electrodes Recordi[g,, w,thneedle, electrodes cencentric nee~e e4~:trmle
surface efagtrode
bipolar meedle Mectro4e
c~ncentei¢ neeclie eiectrmfa
surface ~lm:trmle
b~olar nee41e electrode
Axillo
[=
- Elbow
3 crn
j~lOmV
]~mV
]•mV ÷
]•mv 4.
W~st S
Fig. 1 Muscle action potentials from m. abductor polli~isbrevisevoked by stimulating the median nerveat the axilia, elbow and wrist with surface electrodes(left) and with needle electrodes (right) and recording with concentricneedleelectrodes,skin electrodesand bipolar needleelectrodes.
Conduction velocityin m/sec Stimulating electrodes: surface needle Recordin$ electrodes: eoncentr, surface b i p o l a r concentr, surface axilia-elbow (21 era) 70,4 70.4 71.4 70.4 70.0 elbow-wrist (23 ¢m) 57,6 58.9 60,6 58.9 56.2 uilla-wrist (44 era) 63.8 64.7 65.2 64.7 62.8 distal latency(7-9 cm) msec 4.2 4.3 3,5 4.1 4.5
either through two cotton wick electrodes on the skin or through two needle electrodes (external diameter 0.4 ram) inserted close to the nerve. The cotton wick of the surface electrodes was soaked in salt solution before the electrodes were fixed to the skin. To reduce the skin resistanc~ the superficial corneal layer was removed by rubbing the skin lightly with fine sandpaper and by applying ether. The threshold was determined at high amplification (10 #V/ram) and, to ensure activation of all nerve fibres, the stimulus was supramaximal (two to three times threshold). To cheek the site of stimulation the polarity of the stimulating electrodes was reversed in every examina-
bipolar 71.4 58.9 64.2 3.6
tion (see Results). There was no evidence of anodal block when the cathode was placed proximally; the threshold was about the same with both types of stimulation,as were the amplitudesof the actionpotentialsevoked by supramaximal stimuli. The conduction time was measured as the average of the values obtained with both polarities. Recording Action potentials of the abductor pollicis brevis, abductor digiti quinti and extensor digitorum brevis muscles were used to indicate the arrival of the nerve impulse evoked by stimulaElectroeneeph. elin. Neurophysiol., 1964, 17:314-321
316
W. TROJAEORO
tion respectively of the median, ulnar and anterior tibial nerves, The muscle action potentials were recorded simultaneously by concentric needle electrodes (externaidiameter 0.45 ram) and by surface electrodes consisting of two tin plates (6 × 12 ram), one placed over the belly, the other over the tendon of the muscle, or by bipolar needle electrodes (external diameter 0.65 mm, distance between leading-off areas, 0.5 mm) to reduce interference from potentials from more distant muscles. When using surface electrodes the skin was prepared with electrode paste and the electrodes were covered with a thin layer of cotton and Bitted to the skin with a plastic solution. The earth electrode (lead plate) was placed between the distal stimulating electrode and the leading-off electrodes. The muscle action potentials were recorded with a 3-channel electromyograph (DISA). The time base was I msec/mm. The amplification was adjusted (0.5-1.0 mV/ ram) to give a peak to peak deflection of 35 mm. With ten times higher amplification a small potential might appear preceding the main deflection, indicating either a small portion of faster cotLducting fibres or a potential conducted from a more proximal muscle where the impulse arrives earlier. The conduction time was measured from the stimulus mark to the onset of the main steep negative deflection or to the inter. section of the steep positive-negative deflection with the base line. The distance in mm between two pairs of stimulating electrodes divided by the difference in msec between the onset of the slim, u|i and the muscle action potentials evoked by them gave the conduction velocity in m/see, Only potentials wi~h identical shape for all three stimulating positions were used to calculqte a velocity. In addition to conduction velocity the
voltage of the evoked muscle action potentials was measured. The temperature near the nerve was determined by a thermocouple mounted at the tip of a needle (diameter 0.7 mm, length 50 ram; EUab, type KS, TE3). RESULTS The conduction velocities of the motor fibres of the median and ulnar nerves were the same whether the muscle action potentials were led off' with surface or with concentric needle electrodes (Table I). When stimulating with surface electrodes it is difficult to localize the exact point of stimulation. This uncertainty is somewhat less with needle electrodes and the strength of the stimulus can be reduced about ten times at all three stimulating positions to restrict the spread of the stimulating current. Stimulus interference could be reduced further by le~ding off with bipolar needle electrodes. There was no significant difference in conduction velocity whether stimulation was effected with surface or with needle electrodes (Table !i). In an attempt to establish the site: of stimulation the polarity of the pulse was reversed in all examinations, resulting in a change in conduction time of about 0.5 msec. With a conduction velocity of 56-68 m/see this would correspond to a displacement of the site of stimulation of 28-34 ram, a value which is in reasonable agreement with the 25 mm distance between the stimulating elec, trodes. This indicates that, although the exact point of stimulation is unknown, the nerve is stimulated within a few mm from the cathode at all three positions; thus measurement of the distance from cathode to cathode gives the distance of conduction with good approxima,
TABLE I Motor conduction velocity in the median and uhmr nerves determined from muscle action potentials recorded with surface and with con~ntric needle electrodes
Recorded with Surface electrodes Needle electrodes
Median nerve Number Conductionvelocity of (elbow-wrist) nerves m/see 20 20
55.0d: 1,3 53.5-1-!,!
Ulnar nerve Number Conduction velocity of Celbow-wrist) nerves m/s~
S.D. m/see 5.6 5,0
a,
12 12
53.5±2,0 54.7q- 1,7
S,D. m/see 7.1 6.0
Electroencept~, clin, Neuropkysiol., 1964, 17:314-321
M O T O R C O N D U C T I O N VELOCITY
317
T A B L E II Conduction velocityof motor i'~ervowhen stimulatingwith surfaceand with needle electrodes
Stimulated with Surface electrodes Needle electrodes
Conduction velocity in m/sec in the median nerve
Number of nerves
axiila-elbow
S.D.
elbow-wrist
S.D.
axilla-wrist
S.D.
7 7
68.24-0.7 67.5+ 1.2
1.8 3. I
54.54-1.8 54.1 :[: 1.4
4.7 3.6
59.4-b 1. ! 58.64-1.0
2.8 2.7
TABLE HI Conduction velocity and difference in conduction velocity between right and left median (M), ulnar (U) and anterior tibial (AT) nerves
Conduction velocity Nerve investigated M M M U U U AT
axilla-elbow elbow-wrist axilla-wrist axilla-below elbow-wrist axilla-wrist capitulum-ankle
Number
Mean m/sec
S.D. m/see
24 36 24 22 30 22 22
67.9=[= 1.6 56.14-0.9 60.5± i.0 63.4:h 1.1 56.4:t:0.9 59.44-0.9 49.6:h0.9
7.7 5.3 4.8 5.3 4.8 4.1 4.2
Difference in conduction velocity between right and left Number Mean S.D. m/sec m/sec 12 18 12 I1 15 !I 11
6.7-1-1.3 4.14-0.8 3.7+0.5 6.0-1-1.5 2.84-0.6 4.4=[=0.9 2.84-0.7
4.4 3.2 1.9 5.0 2.2 2.9 2.3
TABLE IV Voltage of muscle action potential evoked at different levels in median, ulnar and anterior tibial nerves Muscle action potential evoked ~t
Proximal electrode Middle ©lectrod© Distal electrode
Median nerve Number Mean mV 24 36 36
18,5 :k 1.0 18,8~0.8 21.24-0,8
S.D. mV
Number
5,0 4,9 4,8
tion. The conduction velocities in the median and ulnar nerves were identical within the error of the method, as were the time intervals between the stimulus at the distal electrode and tile onset of the muscle action potential evoked by it (Table I!I and V). Motor conduction velocity in the anterior tibial nerve averaged 49.6 m/sec (S.D. 4.2 m/sec, 22 nerves); as previously shown by Hennksen (1956) it was slower than in the median and ulnar nerves. The voRage of the muscle action potential evoked by stimulation of the anterior tibial nerve was 1 !.4 mV (S.D, 3.8 mV, 22 nerves), i.e., significantly lower than that evoked by stimulation of the median and ulnar nerves.
22 30 30
Ulnar nerve Mean mV 14.1 ±0.9 14.4±0.9 16.84-t=0.8
S.D, mV
4.4 4.9 4,7
Anterior tibial nerve Number Mean S.D. mV mV 22 . . 22
.
I0, I ±0.8 . . I 1,8i0,8
3,8 3.8
Comparison of the conduction velocity in the distal and proximal segments of the median and uhmr nerves showed a significantly slower conduction in the distal than in the proximal portions of both nerves (by 18 and 11% respectively; "fable III), the voltage of action potentials evoked by ~timulating at the r roximal, middle and distal elect:redes did not show any significant differenc¢ (Table IV). As a temperature difference between the upper arm and the forearm might explain the slowing of conduction velocity in the distal segment of the nerve, the temperature was measured near the proximal and distal segments of the nerve in sevea subjects. The mean temperature in the Electroenceph. clin. Neurophysiol., 1964, 17:314-321
318
w. TROJAeOkO
upper arm was 36.0 u+ 0.3oc and in the forearm 35.4=i=0.3°C, i.e., a temperature differeace of 0.6~0.25°C (S.D. 0.65, P < 0.05, assuming a Gaussian distribution). If the distal slowing in conduction were due to the 0.6°C lower temperature in the forearm, it would correspond to a temperature dependence of conduction velocity in the median nerve (Table I!) of more than 20 m/see per degree centigrade. By examining the same nerve at different temperatures Henriksen (1956) found a change in conductiort velocity with temperature of 2.4 m/see per degree C; thus the difference in conduction velocity over proximal and distal segments of the nerve cannot be solely attributed to the difference in temperature be. tween upper arm and forearm. The variation in conduction velocity from subject to subject was 8.5--11.3%. The difference in conduction velocity between corresponding segments of the right and left zlerves was 5--10% (Table Ill). Assuming a normal distribution this difference can serve as basis for the determination of the experhnental error (~'): d
+++ +TB i/2 where d is the average difference in conduction velocity between right and left. in this way the experimental error in measuring conduction velocity in the median, ulnar and anterior tibial nerves was determined to amount to S-7%. Subtracting the experimental error from the variation from subject to subject the physiological
variation in conduction velocity from subject to subject was 5--7~. The experimental error in determining conduction time (Table V), obtained from a comparison of the corresponding segments of right and left nerves, was 7-17~. Including the experimental error the variation from subject to subject was 7-20%. Thus conduction velocity can be measured with greater accuracy than conduction time. DISCUSSION
The m o t o r nerve c o n d u c t i o n velocities in median, ulnar a n d anterior tibial nerves r e p o r t e d here are in general agreement with the reports o f
Wagman and Lesse (1952), Henriksen (1956), Thomas et ai. (1959), Johnson and Olsen (1960), Kato (1960), Lawrence and Locke (1961), Mulder et al. (1961), and SkiUman et al. (1961). The velocity of motor conduction was significantly slower in the distal than in the proximal segments of the median and ulnar nerves. A similar difference was observed in the proximal and distal portions of the ulnar nerve (Bolzani 1954; Poloni and Sala 1962), of the median nerve (Poloni and Sala 1962; Mayor and Libman 1962) and of the sciatic nerve (Gassei and Trojaborg 1964). Magladery and McDougal (1950) and Carpendate (I 956) found a decrease in conduction vetoc. ity along the lower portion of the ulnar nerve. On the other hand, the conduction velocity of sensory fibres was identical in the forearm and in the upper arm segment of the median nerve (Rosenfalck and Buchthat 1963).
[TABLE V Conduction time and difference in conduction time between right and left median (M), ulnar (U) and anterior tibial (AT) nerves ~onduction time Stimulation at M M M U U U AT AT
proximal electrode middle ,, distal ,, proximal ,, middle ,, distal ,, proximal ,, distal ,,
Number 24 36 36 22 30 30 22 22
Mean
S.D.
msec
m~
13.4:E0.2 10.1:E0.2 6.2+0.2 13.210.2 10.1~:0.3 5.8=[=0.2 14.5=[=0.4 8.0-4-0.3
1.4 1.3 1,2 0.9 1.3 1.2 1.8 1.4
Difference in conduction time between right and left Number Mean S.D. 12 18 18 11 15 15 11 11
m~
m$~:
1,2-t-0.2 i.0:1:0.2 1.1 :[:0.1 !.i+0.3 1.0-1-0.2 1.1-1-0.2 1.2-1-0.3 0.9-4-0.3
0,7 0.7 0.6 0.8 0.2 0.8 1.0 0.9
Electroenceph. clin. Neuroph.w'toL, 1964, 17:314-321
MOTOR CONDUCTION VELOCITY
The distal slowing in motor nerve conduction might be due to (1) a systematic error in measuring the length of the nerve in the forearm and upper arm, (2) a systematic displacement of the site of stimulation, (3) a systematic change in the point of the potential used for measurement of conduction time, (4) the lower temperature in the forearm, and (5) a diminished fibre diameter in the forearm. (I) The possible error introduced by inaccuracy of determining the distance between different sites of stimulation has been discussed by Simpson (1956) and by Christie and Coomes (1960), both of whom prefer measurements of conduction time; but I found both the standard deviation and the experimental error to he up to two times greater when the conduction time was measured than when conduction velocity was determined. The lower conduction velocity in the forearm would correspond to an average error of 2.5-4.5 cm in the measurement of nerve length. This is unlikely; Carpendale (1956) compared the length of median and ulnar nerves found on dissection of the forearm with the resuits of surface measurement and concluded that errors introduced in this way were of little importance, the surface distance being only 0.30.8 mm shorter than the actual length. In the examinations presented in this report errors in the measurement of distance were reduced by fixing the stimulating electrode. Especially in the axilla, where the skin is loose, manual pressure could lead to an erroneous estimation of the point of stimulation. By using needle electrodes for stimulation this error is practically eliminated. (2) Even with these precautions the lower conduction velocity in the forearm might be due to systematic differences in the distribution of the stimulating current associated with tissue conductivity at the different sites of stimulation. Thus the stimulus might spread such that the conduction distance was shorter in the upper arm and longer in the forearm than measured on the surface. With displacements of the sites of stimulation of 0.5-0.7 cm the proximal velocity would be reduced by 4 m/see and the distal velocity would increase 1.5 m/see, reducing the 12-7 m/see difference between proximal and distal velocities by 5.5 m/see. The uncel~ainty in the site of stimulation was reduced by measuring
319
the conduction velocity with each of the electrodes in turn as cathode (see above). (3) The point ofthepotentialused for measurement of conduction time may either be the onset of the action potential or its positive-negative deflection. If the leading off electrode is at the end-plate zone and the onset of the action potential is negative and is abrupt even at high amplification, the onset is well defined and well suited as point of reference for measurement at the different levels of stimulation. If hcwever the electrode is at some distance from the end-plate zone, the onset of the potential is gradual and positive, so that the "latency" is less well defined and depends on the amplification. Therefore, the intersection ofthe positive-negative deflection with the base line may give a more reproducible point of measurement for the determination of velocity between different levels of stimulation, provided that the shape of the potential is identical when evoked from the different points. Moreover, activity from distant muscles does not affect the time to the positive-negative deflection. This is of special importance when stimulating in the axilla where the median and ulnar nerves are often stimulated simultaneously. Thereby the onset of the muscle action potential led off from the thenar muscle group, for example, may be distorted by potentials generated from muscles of the hand innervated by the ulnar nerve, and vice versa. (4) Progressive lowering of the temperature of the nerve towards the periphery might contribute to the slowing of conduction. Helmholtz (1870) reported a diminution in winter in the conduction velocity in the median nerve to less than half the velocity in summer. Henriksen (1956) found a less drastic dependence of 2.4 m/see per degree centigrade within the range of 29 to 38°C, i.e., 4% per degree of cooling. Carpendale (1956) found that the conduction time from the wrist to the hypothenar muscle group was prolonged by about 0.2 msec per degree fall in temperature within the range o f 25 to 35°C, i.e., 8~ per degree of cooling. With the skin temperature at the wrist as a measure of temperature the conduction velocity changed by 1.2 m/see per degree centigrade at 20-.37°C (Kat3 1960). The change in external temperature can he assumed to affect the temperElectroenceph. clin. Neurophysiol., 1964, 17:314--321
W. TgOJABOgO
320
ature near the nerveless thanthe skin temperature, explaining the apparently lower temperature dependence in Kate's experiments. Kate found no difference in conduction velocity in the ulnar nerve between the upper arm and the forearm when measured at room temperature of about 30°C. On the other hand Mayor and Libman (1962) found that the differonce in velocity between the proximal and the distal segment of the median nerve persisted even when the temperature gradient along the arm was reduced by dry heat. We have found an average difference in temperature between the upper arm and forearm of 0.6°C measured near the median and ulnar nerves. This agrees with the difference in temperature of about one degree centigracle found by Buchthai et al. (1944) in the muscles of the upper arm and forearm and by Bazett et al. (1948) and Pennes (1948) between the warm brachial artery and the cool deep forearm. With a temperature dependence of 2.4 m/ sec per degree centigrade a 0.6°(: difference in temperature could account for a slowing of 1.4 m/see. In the case ofthe ulnar nerve a systematic displacement in the site of stimulation and a 0.6°C reduction in temperature in the forearm might account for the slowing of 7 m/see in distal conduction. However, in the median nerve the difference was 12 m/sec, and a further possible cause of slowing must be considered. (5) Mayor and Libman (1962) present the argument making it most likely that a gradual distal decrease in diameter of motor nerve fibres explains the distal reduction in conduction velocity. In animal experiments Gasser and Grundfest (1939) showed that the conduction velocity is proportional to the diameter of the axon. The distal slowing of conduction velocity, which has also been found in the sciatic nerve of frog (Marshall and Gerard 1933), might then reflect a decrease in diameter of the nerve fibres from the axilla to the small muscles of the hand, Indeed such a change in diameter has been demonstrated histologically in rabbits; motor nerves decrease in diameter distally not only because of branching but also because the individual fibres taper distally (Fernand and Young 1951). SUMMARY
Motor nerve conduction velocity in the
median, ulnar and anterior tibial nerves has been determined in 47 subjects, as well as the voltage of the evoked muscle action potential and the time interval between stimulus and the muscle action potential evoked from the distal electrode (Tables III-V). There was no significant differonce in conduction velocity when stimulating with needle and surface electrodes. In the median and ulnar nerves, conduction velocity was significantly slower in the distal than in the proximal portion of the nerve, and the difference was not due solely to differences in temperature; it may be attributable to a decrease in fibre dian~ter from the proximal to the distal part of the nerve. The difference in conduction velocity between the right and left extremities in the same subject and the variation from person to person averaged
5-10%. RtSUMt L, VITESSSDE CONDUCT,ONNeaveuse UO~lCe CHEZ DES SUJETS NORMAUX Se RAPPORTANT EN PARTICULIER ~ LA CONDUCTION DE LA PORTION PgOXIMALE ET DlSTALE DES NERFS MI~DIAN El" CUBITAL
La vitesse de conduction nerveuse motrice, ramplitude des potentiels musculaires ~voqu6s, ainsi que le temps de latence entre stimulation par 61ectrode distale et los r6ponses musculaires ont 6t6 d6termin6s dana 47 cas pour los nerfs m6dian, cubitai et sciatique poplit6 externe (Tableaux Ill-V). li n'existe pas de diff6renee significative entre les vitesses de conduction avec stimulation par ~lectrodes de surface ou par aiguilles. Pour los nerfs m~ian et cubitai la vitesse de conduction est plus lento darts le segment distal que dens le segment proximal des nerfs, Cette r~duction de vitesse ne s'explique pas seulement par des diff6rences de temperature; elle pourrait etre doe tt une diminution du din. m~tre des fibres nerveuses dans le segment distal. Los diff6rences de vitesse entre los extr6mit~ts droites et gauchos chez la memo personne et cellos entre cliff,rents sujets sent de 5-10% en moyenne. REFERENCES
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M O T O R CONDUC'I ION VELOCITY
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