Electric conductivity measurements on microscopic as well as macroscopic scale of different muscles in vivo

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FI09 THE CEREBRAL REFRACTORYPERIOD OF MEDIAN NERVE SEP, TIBIAL NERVE SEP AND VEP IN PATIENTS WITH DIABETES MELLITUS GERHARD H, K~EIJE~VELD WS, RI~4PEL I , LEHMANNHJ~ Neurology C l i n i c , U n i v e r s i t y Hospital of Essen, FRG The cerebral r e f r a c t o r y time is a functional test of the a f f e r e n t sensory system and of the optic system. By t h i s method l a t e n t lesions of the sensory and optic system of diabetics with and without sensory-motor polyneuropathy can be detected. Twelve patients without polyneuropathy and f i v e patients with polyneuropathy were examined. The t i b i a l nerve SEP showed a pathological r e f r a c t o r y period in about h a l f of the cases of patients without polyneuropathy. In three out of f i v e cases with polyneuropathy i t showed a pathological r e f r a c t o r y period. These results are compared to r e f r a c t o r y period f i n d i n g s in peripheral (sural) nerves.

F110 H-REFLEX CHANGESAT DIFFERENT LENGTH OF RELAXED AND ISOMETRICALLY VOLUNTARY ACTIVATED TRICEPS SURAL MUSCLE GERILOVSKY,L., TSVETINOV,P. and TRENKOVA,G.~ Central Lab. of Biophysics, Bulgarian Academy of Sciences, Sofia, Bulgaria Using monopolar and bipolar surface recording technics, H - r e f l e x - p o t e n t i a l s recorded from triceps surae muscle have been investigated. The monopolar recordings were s u b s t a n t i a l l y higher than the b i p o l a r ones. The monopolar/bipolar amplitude r a t i o varied s i g n i f i c a n t l y along the d i f f e r e n t l e a d i n g - o f f areas, e s p e c i a l l y upon voluntary a c t i v a t i o n . In a relaxed muscle and 9o° ankle j o i n t p o s i t i o n , the b i p o l a r l y recorded H-potentials showed highest a m p l i t u d e s along the medial l i n e of the soleus muscle, about three cm below the two gastrocnemial muscles. The respective "best point" for monopolar recordings was about f i v e cm downwards. By passive stepwise muscle shortening (90 ° to 13o° plantar foot f l e x i o n ) , the H-amplitudes increased and both "best points" s h i f t e d upwards. These phenomena could hardly be explained only by changes in monosynaptic r e f l e x e x c i t a b i l i t y . Several peripheral factors could be considered such as an angle increase between the muscle f i b r e s and the skin surface, an increase in f i b r e diameter when shortening, etc. Similar amplitude changes of single motor u n i t potentials accompanying a muscle shortening are in support of t h i s suggestion. The above mentioned peripheral factors could play an essential role in an estimation of evoked potentials as well as summated EMG-#ctivity in muscles with f i b r e s i n c l i n e d to the muscle surface.

F111 ELECTRICCONDUCTIVITY MEASUREMENTSON MICROSCOPICAS WELL AS MACROSCOPIC SCALE OF DIFFERENTMUSCLES IN VIVO GIELEN FLH, WALLINGA-DE JONGE W~ Twente University of Technology; PO Box 217, 7500 AE Enschede, The Netherlands A correct analysis of d i f f e r e n t EMG signals should be based on e l e c t r i c volume conduction theory, in which the e l e c t r i c c o n d u c t i v i t i e s of skeletal muscle tissue are important parameters. On a scale, that corresponds with the so-

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c a l l e d 'pick-up area of single f i b e r EMG electrodes' ( c i r c l e with a radius of about 5 to 6 f i b e r diameters), the tissue is c e r t a i n l y not homogeneous. In that case a microscopic e f f e c t i v e e l e c t r i c c o n d u c t i v i t y has to be used to characterize the tissue. This c o n d u c t i v i t y is d i f f e r e n t from the commonly used macroscopic c o n d u c t i v i t y . Now results are presented from conductivity measurements on d i f f e r e n t muscles in vivo ( r a t and rabbit;243 measurements on 30 d i f f e r e n t muscles). The results show a s i g n i f i c a n t difference between conductivity measurements on a large scale and a small scale, r e f l e c t i n g macroscopic respectively microscopic e f f e c t i v e e l e c t r i c c o n d u c t i v i t i e s of skeletal muscle tissue. RESULTS: Notation: t= transverse; l= l o n g i t u d i n a l ; ~o= conductivity (real part) ~ = conductivity (imaginary p a r t ) ; ~ = / c o n d u c t i v i t y / . All results are given in a frequency range between 10Hz and 10 kHz. Microscopic: 0.09<~ <0.17(~m) - I Macroscopic: 0.09<~ <0. lO(F~m)-~

0.20<~t<0.71(gm)-I 0.01

< i < we /do 0.33 t t

0.02
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0.36<~<0.42(~m)-I 0.02
<0"30

~ u O.03
F112 RECOVERYOF NERVE CONDUCTIONAFTER TRANSIENT ISCHEMIA GIERON,M.A., MAKI,T., KORTHALS,J.K., Univ.of South F l o r i d a , College of Medicine, Tampa, F l o r i d a , USA The e f f e c t of t r a n s i e n t ischemia on nerve conduction was studied in 5o cats. Nerve ischemia was produced by simultaneous clamping of the d i s t a l aorta, r i g h t i l i a c and r i g h t femoral artery f o r l to lo hours. Nerve conduction to the plantar muscles of the r i g h t foot was examined. The nerves were stimulated at the s c i a t i c notch and the ankle. Complete conduction block developed in a l l cats between the thigh and the ankle 20-3o minutes a f t e r clamping of the a r t e r i e s . Af t er clamp removal, conduction recovery occurred in a l l cats a f t e r I-9 hours of ischemia and in 2 cats a f t e r lo hours of ischemia. Conduction did not return in 3 cats subjected to lo hours of ischemia. Conduction between the ankle and the foot muscles e i t h e r was present during the e n t i r e period of ischemia or was abolished between 2 and lo hours a f t e r clamping of the a r t e r i e s and returned a f t e r clamp removal. Ligation of the aorta or femoral a r t e r y alone produced e i t h e r minimal or no changes in nerve conduction. The f i r s t pathologic changes occurred in the upper portions of the t i b i a l and peroneal nerves a f t e r 5 hours of ischemia. The severity of changes was d i r e c t l y proportional to the duration of ischemia. (Supported by VA Medical Research).