Electrical properties of commercial concentric EMG electrodes

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an especially constructed platform with t h e i r heads and knees f i x e d , t h e i r eyes closed (exclusion of s t a t o - t o n i c , s t a t o - k i n e t i c and visual c o n t r o l ) . The p l a t form designed f o r mechanical evocation of unloading r e f l e x was connected with a DISA Electromyograph 13A09 and a M u l t i s t i m 13G04. High-speed cinematography was used to study the body movements. The f i l m was run at 1000 frames/s. The s i l e n t period and rebound of the unloading r e f l e x in i d i o p a t h i c s c o l i o s i s , s t a t i c s c o l i o s i s and normal subjects were analysed.

F75 PATTERNRECOGNITION OF MUP's IN NEEDLE EMG RECORDS: PHYSICAL AND STATISTICAL MODELS OF A MYOELECTRICSIGNAL DONCARLI,C! and GUIHENEUC,P~, I . Lab. of Automatic Control, E,N.S.M. and 2. Lab. of Physiology, U.E.R. M~decine, F-44o35 Nantes Cedex, A myoelectric (ME) s i g n a l , recorded with a concentric needle electrode, is composed of: a) useful signals, which are the p o t e n t i a l s to be detected, and b) a c e r t a i n amount of noise, instrumental and b i o l o g i c a l in o r i g i n . I f d i f f e rent c h a r a c t e r i s t i c s (amplitude, frequency, power spectrum) are assumed for these two components, a d i g i t a l f i l t e r can be elaborated to produce segment a t i o n of the signal into noise zones (without s i g n i f i c a n t p o t e n t i a l ) and s i g n i f i c a n t zones (useful signals disturbed by noise). A s t a t i s t i c a l model of such a ME signal is derived. Noise zones are represented by a white noise v ( t ) , of very weak spectrum q, twice integrated, with an a d d i t i v e white noise w(t) of variable spectrum r. S i g n i f i c a n t zones are characterized by a steep increase of the q spectrum of v ( t ) . The parameters q and r of the signal are estimated through 2 p a r a l l e l f i l t e r s and the detection of the useful areas d i r e c t l y given by the value of q. Besides, an optimal Kalman f i l t e r can be derivated from the s t a t i s t i c a l model and the additive noise can be cancelled. But t h i s method is s t i l l too time consuming. The n r i n c i p l e of a fast f i l t e r i n g algorithm is described, based upon recursive cbmputa~ion of the variance of the signal through receeding horizon f i l t e r s .

F76

ELECTRICALPROPERTIES OF COMMERCIALCONCENTRIC EMG ELECTRODES

DORFMAN,L.j., CUMMINGS,K.L. and McGILL,K.C., Stanford U n i v e r s i t y Med. School, Dept. of Neurology, Stanford, C a l i f o r n i a 943o5, USA Five e l e c t r i c a l c h a r a c t e r i s t i c s - impedance, broadband noise generation, l i n e noise s e n s i t i v i t y , signal d i s t o r t i o n , and common-mode conversion - were measured in f i v e concentric needle EMG electrodes (approximate diameter 0.5 mm) from each of six commercial manufacturers. Untreated electrodes showed considerable v a r i a t i o n in impedance and broadband noise c h a r a c t e r i s t i c s , both w i t h i n and among manufacturers. E l e c t r o l y t i c t r e a t ment reduced impedances by a f a c t o r between 1.5 and 4.0, and lessened w i t h i n manufacturer v a r i a b i l i t y . Average post-treatment impedances at 2o0 Hz ranged from 25 to 5o0 kOhm, r e f l e c t i n g in part the range of core surface areas. Treatment also reduced the broadband noise to the level of the instrumentation noise f o r a l l but the highest impedance electrodes. D i s t o r t i o n and common-mode conversion varied predictably with impedance, and were n e g l i g i b l e f o r the lowest impedance electrodes. Line noise from a nearby power cord was completely suppressed only by those electrodes with f u l l y shielded cables, and then only when the electromyographer also was grounded. We conclude that

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( I ) there are consistent differences in the properties of electrodes from d i f f e r e n t manufacturers, (2) e l e c t r o l y t i c treatment improves the performance of a l l electrodes and tends to lessen the differences among then, and (3) both active and passive electrode cable shields are e f f e c t i v e in reducing extraneous l i n e noise.

F77 DISTURBANCESOF SOME INTERHEMISPHERAL INTERACTION AFTER ISCHAEMIC STROKE DROBNY, M., PITHOVA, B., FUNDAREK, J., Neurologic C l i n i c Faculty of Medicine, Martin, CSSR The authors investigated 31 patients after ischaemic hemispheral stroke by means of the passive sinusoidal forearm movements, of the evaluation of part i c u l a r SEPs components and of the polyelectromyographical r e g i s t r a t i o n of the isometric recruitment paradigms of the leg muscles during exteroceptive i r r i t a t i o n of the Babinski's zone. Excessive deviations from control patterns in the coordination of voluntary and r e f l e x a c t i v i t i e s in the followed parameters were found. Similar disturbances also appeared in the sensory i n t e r action between the hemispheres, as evaluated, f o l l o w i n g the late SEPs components i p s i l a t e r a l l y to the median nerve s t i m u l a t i o n . B i l a t e r a l l y ( i . e . also in so-called "unaffected" leg) pathologic paradigm of the isometric leg muscle contractions were found, together with high values of the basic r e f l e x muscle tonus, as ascertained by the passive sinusoidal movements. Reflex tonus values did not correlate with the grade of pathologic changes of the recruitment leg muscles paradigmes: high grade of the pathologic paradigm was often found together with the low r e f l e x muscle tonus in the EMG picture but with high grade of the muscular resistance at the c l i n i c a l i n v e s t i g a t i o n performed by means of the passive manual muscle stretch.

F78 PHYSIOLOGICALLYVERSUS ELECTRICALLY EVOKED SOMATOSENSORYCORTICAL POTENTIALS DUCATI A, SCHIEPPATI M., I n s t i t u t e s of Neurosurgery and of Human Physiology, U n i v e r s i t y of Milano, Italy A simple method for skin s t i m u l a t i o n has been implemented using an a i r puff with c o n t r o l l e d i n t e n s i t y and time course. In 10 normal volunteers, the somatosensory c o r t i c a l potential (SCP) has been obtained using an e l e c t r i c a l and a physiological stimulus on the r i g h t index. SCP from e l e c t r i c a l s t i m u l i were in agreement with most l i t e r a t u r e data. P h y s i o l o g i c a l l y evoked SCP d i f f e r e d somewhat; the f i r s t negative d e f l e c t i o n could be measured with a 3 ÷ 0.5 msec delay as compared to e l e c t r i c a l l y evoked SCP, t h i s latency being Eonsistent with receptor'stransducing time; the N20-P30 complex was ampler by 1.2 pV on the mean; f i n a l l y , the primary response was followed by larger l a t e waves. In the same subject, repeated tests were v i r t u a l l y i d e n t i c a l , provided that the stimu l a t i o n and recording c h a r a c t e r i s t i c had not been changed. The SCP from an a i r puff in the second trigeminal branch has also been recorded in the same subjects. This has a t y p i c a l waveform, s t a r t i n g with a negative d e f l e c t i o n at I I + 1.5 msec, followed by 5 p o s i t i v e peaks and a large negative wave at I00 msec.-