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Neuromuscular changes in fatigue and effects of training
ABSTRACTS Although the program works automatically, the user can intervene at any time in order to influence the computer decisions. Shape analysis only, which is important for a neuromuscular diagnosis, completes for a 10 see EMG signal in about 1 rain, whereas an exhaustive irmervafion-statistic requires up to 10 min.
PS. A new color display method for evoked potentials. H.T.M. Haenen (Dept. Clinical Neurology, University Hospital, 9700 RB Groningen, The Netherlands) One methodological problem with EPs is the number of stimuli to be applied. In order to address this problem we developed a pictorial color display showing all the details of how the EP averaging proceeds. For this purpose, the average EP curve is color coded in amplitude after each stimulus applied. Then a map is built containing all color codes for all stimuli given. The important EP curve features become after a while visible in the map as tracks with a specific color. One can easily see whether an EP average is stable or not and, if stable, after which number of stimuli. Artifacts that have 'slipped' into the average are visible as spots, with specific colors. When used concurrent with EP recordings these maps provide an on-line tool for EP reliability. The dynamic maps are video-taped for demonstration. We investigated these maps for a group of 20 normal SEPs and found that, on average, they become stable already after half the number of stimuli applied normally (200). We also determined for several SEP protocols which derivations are most sensitive in view of stability of the average.
SMi. Muscle power reduced by gamma-loop interruption. K.-E. l-lagbarth, EJ. Kunesch, M. Nordin, R. Schmidt and E.U. Wallin (Dept. of Clin. Neurophysiol., Akademiska Sjukhuset, S-751 85 Uppsala, Sweden) Previous Ia recordings in man have shown that the gamma-loop normally is activated during voluntary isometric muscle contractions. In attempts to obtain a preferential block of the gamma motor fibers, a dilute solution of a local anesthetic drug was injected around the deep peroneal nerve in healthy subjects. The resulting reduction in foot dorsiflexion power was partly due to a voluntary disability to maintain steady, high frequency motor unit firing rates in the pretibial muscles. This disability could be overcome by agonist muscle vibration whereas antagonist calf muscle vibration had the opposite effect, i.e., accentuated the paresis of the pretibial muscles. The results indicate that signals normally conveyed via the gammaloop in maximal force tasks not only assist in the voluntary activation of agonist alpha motoneurons but also 'protect' these neurons from reciprocal inhibition exerted by antagonist Ia afferents.
$43 SKi. Neuromuscular changes in fatigue and effects of training. - K. Hainaut, and J. Duchateau (Lab. of Biology and Brain Research Unit, University of Brussels, I.S.E.P.K., B-1050 Brussels, Belgium) The effects of electrically triggered sustained and intermittent contractions on peripheral electro-mechanical failures are studied in human muscles. Sixty second sustained contractions are compared with series of sixty 1 sec contractions separated by 2.0, 1.0 and 0.5 sec intervals for an identical total duration of tension development. No significant difference of force reduction is observed during sustained and intermittent series of I sec contractions separated by 1 sec intervals, but the concomitantly recorded electrical changes appear to be considerably different. The analysis of the electrical failure indicates that slowing of conduction along nerve and muscle membranes, as well as a possible increase of synaptic delay are present during peripheral fatigue. The comparison of electrical and mechanical failures, for an identical decrease of muscle force, shows that the electrical failure does not explain the mechanical failure. It is suggested that intracellular processes play the major role in the changes of contractility observed during fatigue. The effects of training by voluntary contractions or by the electrical stimulation of the muscle are discussed in relation with muscle fatigue in man.
PS. Towards a physiological stimulation method in electrophrenic respiration. - V. ITt~inen *, P. Talonen * * and G. Baer * (* Dept. of Neurophysiology and Anaesthesiology, Tampere University Central Hospital, 8F-33520 Tampere, Finland, and * * Computer Systems Laboratory, Tampere University of Technology, SF-33101 Tampere, Finland) In long-term electrophrenlc respiration the criteria for physiologic stimulation can be described as follows: (1) Electrode: which electrode configuration stimulates the phrenic nerve most economically (with lowest amount of charge and current), prevents the nerve from being injured mechanically and chemically, limits the spread of stimulating current to the outside tissue, and allows an easy surgical installation? (2) Stimulus pulse: which pulse shape minimizes the corrosion of the electrode and prevents the cells from being damaged by the products of the electrochemical processes occurring during stimulation; which pulse shape electronically separates the thresholds of different size fibers most widely, allowing a smooth and graded control of stimulus response? (3) Stimulus pulse train: which pulse train configuration most effectively delays the onset of diaphragm fatigue, preserves the total number of functioning (trained) motor units as high as possible during continuous submaximal stimulation, and thus allows the control of tidal volume in a sufficient wide range? Compared to conventional stimulation methods, multipolar nerve stimulation seems to be the only way to fulfill these demands. We have performed animal and human examinations with phrenic nerve stimulators utilizing 2-pole and 4-pole Cuff dec-
PS. A new color display method for evoked potentials. H.T.M. Haenen (Dept. Clinical Neurology, University Hospital, 9700 RB Groningen, The Netherlands) One methodological problem with EPs is the number of stimuli to be applied. In order to address this problem we developed a pictorial color display showing all the details of how the EP averaging proceeds. For this purpose, the average EP curve is color coded in amplitude after each stimulus applied. Then a map is built containing all color codes for all stimuli given. The important EP curve features become after a while visible in the map as tracks with a specific color. One can easily see whether an EP average is stable or not and, if stable, after which number of stimuli. Artifacts that have 'slipped' into the average are visible as spots, with specific colors. When used concurrent with EP recordings these maps provide an on-line tool for EP reliability. The dynamic maps are video-taped for demonstration. We investigated these maps for a group of 20 normal SEPs and found that, on average, they become stable already after half the number of stimuli applied normally (200). We also determined for several SEP protocols which derivations are most sensitive in view of stability of the average.
SMi. Muscle power reduced by gamma-loop interruption. K.-E. l-lagbarth, EJ. Kunesch, M. Nordin, R. Schmidt and E.U. Wallin (Dept. of Clin. Neurophysiol., Akademiska Sjukhuset, S-751 85 Uppsala, Sweden) Previous Ia recordings in man have shown that the gamma-loop normally is activated during voluntary isometric muscle contractions. In attempts to obtain a preferential block of the gamma motor fibers, a dilute solution of a local anesthetic drug was injected around the deep peroneal nerve in healthy subjects. The resulting reduction in foot dorsiflexion power was partly due to a voluntary disability to maintain steady, high frequency motor unit firing rates in the pretibial muscles. This disability could be overcome by agonist muscle vibration whereas antagonist calf muscle vibration had the opposite effect, i.e., accentuated the paresis of the pretibial muscles. The results indicate that signals normally conveyed via the gammaloop in maximal force tasks not only assist in the voluntary activation of agonist alpha motoneurons but also 'protect' these neurons from reciprocal inhibition exerted by antagonist Ia afferents.
$43 SKi. Neuromuscular changes in fatigue and effects of training. - K. Hainaut, and J. Duchateau (Lab. of Biology and Brain Research Unit, University of Brussels, I.S.E.P.K., B-1050 Brussels, Belgium) The effects of electrically triggered sustained and intermittent contractions on peripheral electro-mechanical failures are studied in human muscles. Sixty second sustained contractions are compared with series of sixty 1 sec contractions separated by 2.0, 1.0 and 0.5 sec intervals for an identical total duration of tension development. No significant difference of force reduction is observed during sustained and intermittent series of I sec contractions separated by 1 sec intervals, but the concomitantly recorded electrical changes appear to be considerably different. The analysis of the electrical failure indicates that slowing of conduction along nerve and muscle membranes, as well as a possible increase of synaptic delay are present during peripheral fatigue. The comparison of electrical and mechanical failures, for an identical decrease of muscle force, shows that the electrical failure does not explain the mechanical failure. It is suggested that intracellular processes play the major role in the changes of contractility observed during fatigue. The effects of training by voluntary contractions or by the electrical stimulation of the muscle are discussed in relation with muscle fatigue in man.
PS. Towards a physiological stimulation method in electrophrenic respiration. - V. ITt~inen *, P. Talonen * * and G. Baer * (* Dept. of Neurophysiology and Anaesthesiology, Tampere University Central Hospital, 8F-33520 Tampere, Finland, and * * Computer Systems Laboratory, Tampere University of Technology, SF-33101 Tampere, Finland) In long-term electrophrenlc respiration the criteria for physiologic stimulation can be described as follows: (1) Electrode: which electrode configuration stimulates the phrenic nerve most economically (with lowest amount of charge and current), prevents the nerve from being injured mechanically and chemically, limits the spread of stimulating current to the outside tissue, and allows an easy surgical installation? (2) Stimulus pulse: which pulse shape minimizes the corrosion of the electrode and prevents the cells from being damaged by the products of the electrochemical processes occurring during stimulation; which pulse shape electronically separates the thresholds of different size fibers most widely, allowing a smooth and graded control of stimulus response? (3) Stimulus pulse train: which pulse train configuration most effectively delays the onset of diaphragm fatigue, preserves the total number of functioning (trained) motor units as high as possible during continuous submaximal stimulation, and thus allows the control of tidal volume in a sufficient wide range? Compared to conventional stimulation methods, multipolar nerve stimulation seems to be the only way to fulfill these demands. We have performed animal and human examinations with phrenic nerve stimulators utilizing 2-pole and 4-pole Cuff dec-