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Responses of forearm movers to torque disturbances: relations with preload and muscle background activity
$50
F28 FAMILIALAND LONGITUDINAL ELECTROPHYSIOLOGICALSTUDIES IN PATIENTS WITH CHARCOT-MARIE-TOOTH (CMT) DISEASE P. BOUCHEand H.P. CATHALA, Service d'Explorations Fonctionelles~ Neurologie~ HQpital de la SalP~tri#re, Paris, France I t is now widely accepted that patients with CMT disease could be subdivided into two main groups as f a r as nerve conduction v e l o c i t y is concerned. Patients of the f i r s t group are characterized by a marked reduction of motor and sensory nerve conduction v e l o c i t y (hypertrophic type). Patients of the second group have normal or s l i g h t l y reduced motor conduction v e l o c i t y but abnormal sensory p o t e n t i a l s (neuronal type). Such a c l a s s i f i c a t i o n is mainly based on the concordance of nerve conduction v e l o c i t y of r e l a t i v e s within f a m i l i e s . Three f a m i l i e s of each group were therefore studied. The e l e c t r o physiological results c l e a r l y confirm the great degree of concordance in nerve conduction v e l o c i t y , whatever the severity of the disease. All patients in one family belong to the same group e i t h e r hypertrophic or neuronal.Longitudinal e l e c t r o p h y s i o l o g i c a l studies were performed on patients from both groups. In the f i r s t group nerve conduction v e l o c i t y is markedly reduced, independent of the degree of involvement or denervation, as i t was already suggested by the f a m i l i e s ' study. In some cases a s l i g h t improvement in nerve conduction was noticed. In the second group values of nerve conduction seemed to be in r e l a t i o n with the degree of denervation.
F29 ELECTROP~YSIOLOGICALEVIDENCE FOR CROSSEDOLIGOSYNAPTIC TRIGEMINO-FACIAL CONNECTIONS IN NORMALMAN BOULU P, WILLER JC, DEHEN H, CAMBIER J, Clinique Neurologique, H~pital Geaujon, Clichy,
France
A crossed short latency component (RI) of the human blink r e f l e x can be e l i c i t ed in o r b i c u l a r i s oculi muscle to stimulation of the c o n t r a l a t e r a l suprao r b i t a l nerve, when i n f r a l i m i n a l conditioning stimulations are applied on various cutaneous afferents of the body ( f a c i a l , upper and lower limbs). The crossed RI responses appear when the time interval between the conditioning and the test stimuli is of 30 to 40 ms, 50 to 65 ms and 95 to 110 ms f o r f a c i a l , upper and lower limbs a f f e r e n t s , respectively. For the same time i n t e r v a l s , these conditioning volleys exert also a f a c i l i t a t o r y e f f e c t on the i p s i l a t e r a l RI responses. Furthermore, crossed RI responses are also obtained during supraspinal f a c i l i t a t i o n induced by a voluntary contraction of the eyelids. These data show that crossed oligosynaptic t r i g e m i n o - f a c i a l r e f l e x connections e x i s t in normal subjects which become functional when adequate f a c i l i t a t i o n or disi n h i b i t i o n of descending central influences are a v a i l a b l e .
F30 RESPONSESOF FOREARMMOVERSTO TORQUEDISTURBANCES: RELATIONS WITH PRELOAD AND MUSCLE BACKGROUNDACTIVITY BRINK EE, MACKEL R , Department of Neurology, Technical University of Munich, Moehlstrasse 28, 8000 Munich 80, FRG
The responses of forearm f l e x o r s and extensors to torque perturbations were examined in normal human subjects. EMG a c t i v i t y of b r a c h i a l i s and/or triceps was recorded intramuscularly; angular displacement and acceleration were also meas-
$51
ured. Torque perturbations displaced the forearms in a v e r t i c a l d i r e c t i o n ; subjects were asked to hold an i n i t i a l p o s i t i o n , with a 90 ° angle between the f o r e arm and upper arm and about 50 ° between the forearm and h o r i z o n t a l , a g a i n s t various torque preloads. The torque due to the weight of the machine arm and the human forearm was taken into account. Torque pulses produced sudden displacements of the forearm, and the typical early (MI) and l a t e r (M2-M3) r e f l e x responses. Generally, increasing preload produced three e f f e c t s : a) increased muscle background a c t i v i t y , a s muscles were required to generate more force to counteract higher imposed torques; b) smoother t r a j e c t o r i e s of the forearm, consistent with an increased s t i f f n e s s of the muscles; and c) increasedM1 responses. Deviations in the r e l a t i o n of MI to preload could be accounted f o r in part by s i m i l a r deviations of muscle background a c t i v i t y . When background a c t i v i t y spontaneously varied by 50% or more f or the same stimulus conditions, this was p a r a l l e l e d by v a r i a t i o n s of the same direction and magnitude in size of r e f l e x responses. Furthermore, depression of ref l e x responses by pharmacological agents was accompanied by and predictable from s i m i l a r depression of background a c t i v i t y . - The observations emphasize the close r e l a t i o n between background a c t i v i t y and r e f l e x size, and the need to examine e f f e c t on background a c t i v i t y in i n t e r p r e t i n g effects of any manipulations on r e f l e x responses. They also show up the v a r i a b i l i t y in the r e l a t i o n of muscle background a c t i v i t y to imposed preload, emphasizing that the two are not interchangeable.
F31
EPIDURALRECORDINGOF ROOT AND SEGMENTALSPINAL CORD POTENTIALS
W.F. BROWN, M.F. DAVIS, C l i n i c a l Neurological Sciences, University Hospital, 339 Windermere Road, London, Ontario, Canada, N6A 5A5 Lesions which involve the plexus or roots are sometimes hard to l o c a l i z e when there is no denervation and the resolution of root and segmental spinal cord p o t e n t i a l s as recorded by skin electrodes is poor. Epidural needle electrodes in the lumbosacral regions can s u b s t a n t i a l l y improve the resolution of these p o t e n t i a l s and when combined with stimulation at other proximal-distal sites make i t possible to much better l o c a l i z e lesions involving the roots or plexuses. Furthermore, in selected cases, insulated lumbar puncture needles inserted in to the lumbosacral subarachnoid space (LI-2 and L4-5) may be used to stimulate the ventral roots and this combined with the stimulation at more d i s t a l sites makes i t possible to measure motor conduction v e l o c i t i e s and assess conduction block across the more proximal segments of the peripheral nervous system. The l a s t has been most valuable in the evaluation of patients with Guillain-Barr@ n e u r i t i s . The techniques have also proven valuable in the i n v e s t i g a t i o n of other lesions involving the lumbosacral plexus, roots and lumbosacral spinal cord.
F28 FAMILIALAND LONGITUDINAL ELECTROPHYSIOLOGICALSTUDIES IN PATIENTS WITH CHARCOT-MARIE-TOOTH (CMT) DISEASE P. BOUCHEand H.P. CATHALA, Service d'Explorations Fonctionelles~ Neurologie~ HQpital de la SalP~tri#re, Paris, France I t is now widely accepted that patients with CMT disease could be subdivided into two main groups as f a r as nerve conduction v e l o c i t y is concerned. Patients of the f i r s t group are characterized by a marked reduction of motor and sensory nerve conduction v e l o c i t y (hypertrophic type). Patients of the second group have normal or s l i g h t l y reduced motor conduction v e l o c i t y but abnormal sensory p o t e n t i a l s (neuronal type). Such a c l a s s i f i c a t i o n is mainly based on the concordance of nerve conduction v e l o c i t y of r e l a t i v e s within f a m i l i e s . Three f a m i l i e s of each group were therefore studied. The e l e c t r o physiological results c l e a r l y confirm the great degree of concordance in nerve conduction v e l o c i t y , whatever the severity of the disease. All patients in one family belong to the same group e i t h e r hypertrophic or neuronal.Longitudinal e l e c t r o p h y s i o l o g i c a l studies were performed on patients from both groups. In the f i r s t group nerve conduction v e l o c i t y is markedly reduced, independent of the degree of involvement or denervation, as i t was already suggested by the f a m i l i e s ' study. In some cases a s l i g h t improvement in nerve conduction was noticed. In the second group values of nerve conduction seemed to be in r e l a t i o n with the degree of denervation.
F29 ELECTROP~YSIOLOGICALEVIDENCE FOR CROSSEDOLIGOSYNAPTIC TRIGEMINO-FACIAL CONNECTIONS IN NORMALMAN BOULU P, WILLER JC, DEHEN H, CAMBIER J, Clinique Neurologique, H~pital Geaujon, Clichy,
France
A crossed short latency component (RI) of the human blink r e f l e x can be e l i c i t ed in o r b i c u l a r i s oculi muscle to stimulation of the c o n t r a l a t e r a l suprao r b i t a l nerve, when i n f r a l i m i n a l conditioning stimulations are applied on various cutaneous afferents of the body ( f a c i a l , upper and lower limbs). The crossed RI responses appear when the time interval between the conditioning and the test stimuli is of 30 to 40 ms, 50 to 65 ms and 95 to 110 ms f o r f a c i a l , upper and lower limbs a f f e r e n t s , respectively. For the same time i n t e r v a l s , these conditioning volleys exert also a f a c i l i t a t o r y e f f e c t on the i p s i l a t e r a l RI responses. Furthermore, crossed RI responses are also obtained during supraspinal f a c i l i t a t i o n induced by a voluntary contraction of the eyelids. These data show that crossed oligosynaptic t r i g e m i n o - f a c i a l r e f l e x connections e x i s t in normal subjects which become functional when adequate f a c i l i t a t i o n or disi n h i b i t i o n of descending central influences are a v a i l a b l e .
F30 RESPONSESOF FOREARMMOVERSTO TORQUEDISTURBANCES: RELATIONS WITH PRELOAD AND MUSCLE BACKGROUNDACTIVITY BRINK EE, MACKEL R , Department of Neurology, Technical University of Munich, Moehlstrasse 28, 8000 Munich 80, FRG
The responses of forearm f l e x o r s and extensors to torque perturbations were examined in normal human subjects. EMG a c t i v i t y of b r a c h i a l i s and/or triceps was recorded intramuscularly; angular displacement and acceleration were also meas-
$51
ured. Torque perturbations displaced the forearms in a v e r t i c a l d i r e c t i o n ; subjects were asked to hold an i n i t i a l p o s i t i o n , with a 90 ° angle between the f o r e arm and upper arm and about 50 ° between the forearm and h o r i z o n t a l , a g a i n s t various torque preloads. The torque due to the weight of the machine arm and the human forearm was taken into account. Torque pulses produced sudden displacements of the forearm, and the typical early (MI) and l a t e r (M2-M3) r e f l e x responses. Generally, increasing preload produced three e f f e c t s : a) increased muscle background a c t i v i t y , a s muscles were required to generate more force to counteract higher imposed torques; b) smoother t r a j e c t o r i e s of the forearm, consistent with an increased s t i f f n e s s of the muscles; and c) increasedM1 responses. Deviations in the r e l a t i o n of MI to preload could be accounted f o r in part by s i m i l a r deviations of muscle background a c t i v i t y . When background a c t i v i t y spontaneously varied by 50% or more f or the same stimulus conditions, this was p a r a l l e l e d by v a r i a t i o n s of the same direction and magnitude in size of r e f l e x responses. Furthermore, depression of ref l e x responses by pharmacological agents was accompanied by and predictable from s i m i l a r depression of background a c t i v i t y . - The observations emphasize the close r e l a t i o n between background a c t i v i t y and r e f l e x size, and the need to examine e f f e c t on background a c t i v i t y in i n t e r p r e t i n g effects of any manipulations on r e f l e x responses. They also show up the v a r i a b i l i t y in the r e l a t i o n of muscle background a c t i v i t y to imposed preload, emphasizing that the two are not interchangeable.
F31
EPIDURALRECORDINGOF ROOT AND SEGMENTALSPINAL CORD POTENTIALS
W.F. BROWN, M.F. DAVIS, C l i n i c a l Neurological Sciences, University Hospital, 339 Windermere Road, London, Ontario, Canada, N6A 5A5 Lesions which involve the plexus or roots are sometimes hard to l o c a l i z e when there is no denervation and the resolution of root and segmental spinal cord p o t e n t i a l s as recorded by skin electrodes is poor. Epidural needle electrodes in the lumbosacral regions can s u b s t a n t i a l l y improve the resolution of these p o t e n t i a l s and when combined with stimulation at other proximal-distal sites make i t possible to much better l o c a l i z e lesions involving the roots or plexuses. Furthermore, in selected cases, insulated lumbar puncture needles inserted in to the lumbosacral subarachnoid space (LI-2 and L4-5) may be used to stimulate the ventral roots and this combined with the stimulation at more d i s t a l sites makes i t possible to measure motor conduction v e l o c i t i e s and assess conduction block across the more proximal segments of the peripheral nervous system. The l a s t has been most valuable in the evaluation of patients with Guillain-Barr@ n e u r i t i s . The techniques have also proven valuable in the i n v e s t i g a t i o n of other lesions involving the lumbosacral plexus, roots and lumbosacral spinal cord.