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Subclinical lead neuropathy in man
718
INTERNATIONAL FEDERATION - 7TH CONGRESS
lying pathology is discussed.
16.
Motor unit frequency control in facial neuropathy.-J. H. Petajan (College, Alaska, U.S.A.).
Using audiovisual feedback of motor unit action potentials, the ability of 11 patients with facial neuropathy to control firing rate was examined. The following mean interspike intervals were determined when firing rate was: (1) at its lowest most stable level, o n s e t interval and (2) increased to a level at which recruitment of a second motor unit occurred, r e c r u i t m e n t interval. Mean onset interval was decreased while mean recruitment interval was unchanged. In 20% of orbicularis oris and 12% of frontalis motor units studied a second motor unit was not recruited despite high firing rates while in normal subjects recruitment always occurs. The findings can be explained by a loss of larger motor units as would be produced by ischemia or pressure block. Regardless of the number of motor units lost in any territory, if recruitment can occur, then it occurs when the primary unit reaches a critical firing rate, the normal recruitment interval.
17. Threshold and conduction velocity in human median nerve sensory fibers.-W. C. Wiederholt (Columbus, Ohio, U.S.A.). Fast conducting nerve fibers have a lower threshold than slow conducting fibers. Contrary to this generally accepted fact, Hodes et al. concluded from study of human motor nerves that fibers of low threshold conduct more slowly than those of high threshold. Recently, Wiederholt demonstrated in isolated mixed mammalian nerves that increasing stimulus intensities produce progressive shortening of latency, no change of conduction velocity, but movement of the effective point of excitation away from the stimulating cathode. Conduction velocity in median nerve sensory fibers and its relation to stimulus intensity was studied in 30 normal subjects. Sensory fibers were stimulated with square pulses (0.1 msec, 30 to 110V) at the base of the third digit. Evoked nerve action potentials were recorded simultaneously from electrodes distal and proximal to the carpal tunnel. The distance from the distal electrode to the first electrode proximal to the carpal tunnel averaged 3.8 cm and between electrodes proximal to the carpal tunnel 1.94 cm. Conduction times between electrodes were used to calculate conduction velocities. With just supramaximal stimulation conduction velocity across the carpal tunnel was 54.4+10.3 (S.D.) m/sec and proximal to the carpal tunnel 64.3-+9.3 m/sec. When stimulation was increased from minimal (30 to 40 V) to just
supramaximal (80 to 110 V), latency from shock artifact to beginning of the evoked potential (proximal to carpal tunnel), decreased from 2.24:ff).24 msec to 2.085:0.23 msec but conduction velocity remained the same. This could result from movement of the effective point of excitation 1.04:b0.32 cm away from the stimulating cathode. The results suggest that (1) the fastest conducting sensory fibers in the human median nerve have a lower threshold than slower conducting fibers, and (2) the effective point of excitation moves away from the stimulating cathode as intensity of stimulation is increased.
18. Effect of local temperature on resting membrane potential in rat musele.-T. Nakanishi and F. H. Norris, Jr. (San Francisco, Calif., U.S.A.). The resting membrane potential (RMP) of human muscle has been measured as a diagnostic tool, but large variations have made determination of the normal range difficult. As o n e of the technical causes of such variation, the effect of local temperature on the RMP was investigated in rat muscle in vivo. The longissimus dorsi medialis muscle was irrigated with Liley's solution at various temperatures and RMPs measured within a depth of 1 mm from the surface using 3 M KCl-filled micropipette electrodes. The muscle RMP increased and decreased as the local temperature was raised and lowered between 25 and 44°C. Two experiments were performed. In one, fibers were studied for long periods of time while serial RMP measurements were made. The coefficient of the RMP was 1.3-+0.6 (S.D.)/aV per degree with a Q I 0 of 1.215:0.03 for increasing temperatures; the coefficient was 1.4:b0.7/aV per degree with a Q10 of 1.25:!:0.05 for decreasing temperatures. In the second experiment, 20 different fibers were impaled successfully at each of several temperatures. The coefficient of the RMP was 1.0-+0.4 /zV per degree with a Q10 of 1.155:0.08 for increasing temperatures; the coefficient was 1.1-+0.3/2V per degree with a Q I 0 of 1.16-+0.07 for decreasing temperatures. These linear relationships of RMP and temperature might account for some of the reported variations of the normal RMP.
19.
Subclinical lead neuropathy in man.-P. M. Fullerton and M. J. G. Harrison (London, G.B.).
Guinea pigs given lead acetate orally for several months often develop peripheral neuropathy, associated in some instances with considerable slowing of conduction. Pathological changes of segmental demyelination have been demonstrated in such animals.
FREE COMMUNICATIONSIN EMG Although lead poisoning is still a common industrial problem, paralysis is rare. Nevertheless, it is possible that subclinical damage might be reflected in abnormalities of nerve conduction. Nineteen men who had worked in a lead battery factory for between 5 months and 13 years were therefore examined. All had raised blood lead levels and some were anemic, but none had any abnormal neurological symptoms or signs. Twelve age matched control subjects were studied for comparison. The lateral popliteal nerve was stimulated at knee and ankle and the muscle action potential recorded through surface electrodes over extensor digitorum brevis. The afferent volley was recorded from the lateral popliteal nerve at the head of the fibula following stimulation at the ankle. There was no statistical difference between the two groups for maximal motor conduction velocity, nor for the velocity or amplitude of the afferent volley. If slowing of conduction occurred in only a proportion of the nerve fibers, then maximal velocity might remain normal, but the muscle action potential would become increasingly dispersed the longer the conduction distance. As an indication of dispersion, the amplitude of the muscle response following stimulation at the knee was expressed as a percentage of that following stimulation at the ankle. The value for the lead workers was 84.8% (S.D. 12.7) and for the control group was 95.4% (S.D. 6.9). These differences are statistically significant and suggest that some fibers in the lead workers were conducting at a reduced velocity. 20.
Stretch reflex and shortening reaction. A quantitative analysis of phasic and tonic stretch reflex in clinical .states of spasticity and rigidity.-E. Esslen (Zurich, Switzerland).
A method (Electro-Tono-Myography) is described, to perform strictly defined active and passive extension and flexion movements and to record and analyse quantitatively phasic and tonic stretch reflexes in patients suffering from central motor disorders. In the course of these investigations a new phenomenon has been observed, called shortening reaction. It is mainly manifest in extrapyramidal diseases. Stretch reflex and shortening reaction are based on normal neurophysiological mechanisms, controlled by higher brain centers. In central motor disorders they are more or less released from central control. Comparisons of stretch reflex and shortening reaction before and after stereotactic operations on the thalamus reveal a differential effect on both. 21.
A study of the diseased nerve in carpal tunnel s y n d r o m e . - K . Meehelse and B. Matricali
719
(Leyden, The Netherlands). In patients with a carpal tunnel syndrome, the conduction velocity of the exposed median nerve was measured during operation. After section of the ligamentum carpi transversum, a number of electrodes with fixed distances of one centimetre were placed on the nerve. The nerve was then stimulated successively through the various electrodes and the muscle response recorded from the m.abductor pollicis brevis. Voltage of the threshold stimulus and the latency of the muscle response were measured. Then the nerve response was recorded from various points of the nerve which was stimulated either distally or proximally at different distances from the recording point. The result was that in most cases the threshold voltage of the muscle response was significantly higher in a certain part of the nerve. Sometimes the muscle response obtained by stimulating this part was either absent or of lower amplitude. Conduction velocity as derived from the latency and distance measurements increased clearly distal to this point. Further studies of the nerve response seem to confirm that nerve conduction is slowed and refractory period is longer particularly in this part of the nerve. Anatomical changes, when present, were observed in this part of the nerve. In all operations performed, the m.opponens pollicis originated across the median nerve on the ligamentum carpi transversum. In a number of hands studied on the dissecting table, this origin never crossed the median nerve except in one case with a clear cut partial thenar atrophy. It is concluded that these carpal tunnel syndromes are related to the action of an aberrantly originating muscle on the nerve.
22. Motosensory afferents in human peripheral nerve to mechanical stimulation of muscle receptors.-H. M. Krott and H. M. Jacobi (Dietenbronn, Germany). There have been many unsuccessful attempts to record the afferent discharge in the human peripheral nerve preceding the ankle jerk to mechanical stimuli. In the positive report of Hagharth and Vallboit is difficult to distinguish between afferents from muscle, joint and skin. Methods: In order to get exclusively muscle afferents with the T-reflex, records were taken from the femoral nerve and from the ramus muscularis of the tibial nerve by means of semimicroelectrodes. The criterion for a correct position of the electrode tip in the nerve was an optimal H-reflex following threshold stimulus, with M-response and without any sensation. The contact of the hammer-stimulator with the Achilles or patellar tendon, respectively, was used
INTERNATIONAL FEDERATION - 7TH CONGRESS
lying pathology is discussed.
16.
Motor unit frequency control in facial neuropathy.-J. H. Petajan (College, Alaska, U.S.A.).
Using audiovisual feedback of motor unit action potentials, the ability of 11 patients with facial neuropathy to control firing rate was examined. The following mean interspike intervals were determined when firing rate was: (1) at its lowest most stable level, o n s e t interval and (2) increased to a level at which recruitment of a second motor unit occurred, r e c r u i t m e n t interval. Mean onset interval was decreased while mean recruitment interval was unchanged. In 20% of orbicularis oris and 12% of frontalis motor units studied a second motor unit was not recruited despite high firing rates while in normal subjects recruitment always occurs. The findings can be explained by a loss of larger motor units as would be produced by ischemia or pressure block. Regardless of the number of motor units lost in any territory, if recruitment can occur, then it occurs when the primary unit reaches a critical firing rate, the normal recruitment interval.
17. Threshold and conduction velocity in human median nerve sensory fibers.-W. C. Wiederholt (Columbus, Ohio, U.S.A.). Fast conducting nerve fibers have a lower threshold than slow conducting fibers. Contrary to this generally accepted fact, Hodes et al. concluded from study of human motor nerves that fibers of low threshold conduct more slowly than those of high threshold. Recently, Wiederholt demonstrated in isolated mixed mammalian nerves that increasing stimulus intensities produce progressive shortening of latency, no change of conduction velocity, but movement of the effective point of excitation away from the stimulating cathode. Conduction velocity in median nerve sensory fibers and its relation to stimulus intensity was studied in 30 normal subjects. Sensory fibers were stimulated with square pulses (0.1 msec, 30 to 110V) at the base of the third digit. Evoked nerve action potentials were recorded simultaneously from electrodes distal and proximal to the carpal tunnel. The distance from the distal electrode to the first electrode proximal to the carpal tunnel averaged 3.8 cm and between electrodes proximal to the carpal tunnel 1.94 cm. Conduction times between electrodes were used to calculate conduction velocities. With just supramaximal stimulation conduction velocity across the carpal tunnel was 54.4+10.3 (S.D.) m/sec and proximal to the carpal tunnel 64.3-+9.3 m/sec. When stimulation was increased from minimal (30 to 40 V) to just
supramaximal (80 to 110 V), latency from shock artifact to beginning of the evoked potential (proximal to carpal tunnel), decreased from 2.24:ff).24 msec to 2.085:0.23 msec but conduction velocity remained the same. This could result from movement of the effective point of excitation 1.04:b0.32 cm away from the stimulating cathode. The results suggest that (1) the fastest conducting sensory fibers in the human median nerve have a lower threshold than slower conducting fibers, and (2) the effective point of excitation moves away from the stimulating cathode as intensity of stimulation is increased.
18. Effect of local temperature on resting membrane potential in rat musele.-T. Nakanishi and F. H. Norris, Jr. (San Francisco, Calif., U.S.A.). The resting membrane potential (RMP) of human muscle has been measured as a diagnostic tool, but large variations have made determination of the normal range difficult. As o n e of the technical causes of such variation, the effect of local temperature on the RMP was investigated in rat muscle in vivo. The longissimus dorsi medialis muscle was irrigated with Liley's solution at various temperatures and RMPs measured within a depth of 1 mm from the surface using 3 M KCl-filled micropipette electrodes. The muscle RMP increased and decreased as the local temperature was raised and lowered between 25 and 44°C. Two experiments were performed. In one, fibers were studied for long periods of time while serial RMP measurements were made. The coefficient of the RMP was 1.3-+0.6 (S.D.)/aV per degree with a Q I 0 of 1.215:0.03 for increasing temperatures; the coefficient was 1.4:b0.7/aV per degree with a Q10 of 1.25:!:0.05 for decreasing temperatures. In the second experiment, 20 different fibers were impaled successfully at each of several temperatures. The coefficient of the RMP was 1.0-+0.4 /zV per degree with a Q10 of 1.155:0.08 for increasing temperatures; the coefficient was 1.1-+0.3/2V per degree with a Q I 0 of 1.16-+0.07 for decreasing temperatures. These linear relationships of RMP and temperature might account for some of the reported variations of the normal RMP.
19.
Subclinical lead neuropathy in man.-P. M. Fullerton and M. J. G. Harrison (London, G.B.).
Guinea pigs given lead acetate orally for several months often develop peripheral neuropathy, associated in some instances with considerable slowing of conduction. Pathological changes of segmental demyelination have been demonstrated in such animals.
FREE COMMUNICATIONSIN EMG Although lead poisoning is still a common industrial problem, paralysis is rare. Nevertheless, it is possible that subclinical damage might be reflected in abnormalities of nerve conduction. Nineteen men who had worked in a lead battery factory for between 5 months and 13 years were therefore examined. All had raised blood lead levels and some were anemic, but none had any abnormal neurological symptoms or signs. Twelve age matched control subjects were studied for comparison. The lateral popliteal nerve was stimulated at knee and ankle and the muscle action potential recorded through surface electrodes over extensor digitorum brevis. The afferent volley was recorded from the lateral popliteal nerve at the head of the fibula following stimulation at the ankle. There was no statistical difference between the two groups for maximal motor conduction velocity, nor for the velocity or amplitude of the afferent volley. If slowing of conduction occurred in only a proportion of the nerve fibers, then maximal velocity might remain normal, but the muscle action potential would become increasingly dispersed the longer the conduction distance. As an indication of dispersion, the amplitude of the muscle response following stimulation at the knee was expressed as a percentage of that following stimulation at the ankle. The value for the lead workers was 84.8% (S.D. 12.7) and for the control group was 95.4% (S.D. 6.9). These differences are statistically significant and suggest that some fibers in the lead workers were conducting at a reduced velocity. 20.
Stretch reflex and shortening reaction. A quantitative analysis of phasic and tonic stretch reflex in clinical .states of spasticity and rigidity.-E. Esslen (Zurich, Switzerland).
A method (Electro-Tono-Myography) is described, to perform strictly defined active and passive extension and flexion movements and to record and analyse quantitatively phasic and tonic stretch reflexes in patients suffering from central motor disorders. In the course of these investigations a new phenomenon has been observed, called shortening reaction. It is mainly manifest in extrapyramidal diseases. Stretch reflex and shortening reaction are based on normal neurophysiological mechanisms, controlled by higher brain centers. In central motor disorders they are more or less released from central control. Comparisons of stretch reflex and shortening reaction before and after stereotactic operations on the thalamus reveal a differential effect on both. 21.
A study of the diseased nerve in carpal tunnel s y n d r o m e . - K . Meehelse and B. Matricali
719
(Leyden, The Netherlands). In patients with a carpal tunnel syndrome, the conduction velocity of the exposed median nerve was measured during operation. After section of the ligamentum carpi transversum, a number of electrodes with fixed distances of one centimetre were placed on the nerve. The nerve was then stimulated successively through the various electrodes and the muscle response recorded from the m.abductor pollicis brevis. Voltage of the threshold stimulus and the latency of the muscle response were measured. Then the nerve response was recorded from various points of the nerve which was stimulated either distally or proximally at different distances from the recording point. The result was that in most cases the threshold voltage of the muscle response was significantly higher in a certain part of the nerve. Sometimes the muscle response obtained by stimulating this part was either absent or of lower amplitude. Conduction velocity as derived from the latency and distance measurements increased clearly distal to this point. Further studies of the nerve response seem to confirm that nerve conduction is slowed and refractory period is longer particularly in this part of the nerve. Anatomical changes, when present, were observed in this part of the nerve. In all operations performed, the m.opponens pollicis originated across the median nerve on the ligamentum carpi transversum. In a number of hands studied on the dissecting table, this origin never crossed the median nerve except in one case with a clear cut partial thenar atrophy. It is concluded that these carpal tunnel syndromes are related to the action of an aberrantly originating muscle on the nerve.
22. Motosensory afferents in human peripheral nerve to mechanical stimulation of muscle receptors.-H. M. Krott and H. M. Jacobi (Dietenbronn, Germany). There have been many unsuccessful attempts to record the afferent discharge in the human peripheral nerve preceding the ankle jerk to mechanical stimuli. In the positive report of Hagharth and Vallboit is difficult to distinguish between afferents from muscle, joint and skin. Methods: In order to get exclusively muscle afferents with the T-reflex, records were taken from the femoral nerve and from the ramus muscularis of the tibial nerve by means of semimicroelectrodes. The criterion for a correct position of the electrode tip in the nerve was an optimal H-reflex following threshold stimulus, with M-response and without any sensation. The contact of the hammer-stimulator with the Achilles or patellar tendon, respectively, was used