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Testing neuromuscular fatigue in controls and patients
s104
Pofiter Sessions
years. compared to a control group. Supramaximal 0.1 msec 35 Hz continuous electrical stimulation was applied to the motor point and EMG was recorded from stimulated myofibers by means of a double differential electrode. By monitoring cross-correlation ratio between M-waves, following parameters were acquired: spectral median frequency (MDF), averaged rectified voltage (ARV) and muscle conduction velocity (CV). Force was recorded by means of a strain-gauge transducer. All data were acquired by a dedicated software, 1024 sampling frequency, and elaboratedisec during the protocol. Basally ARV and CV were significantly lower than controls. At the end of the contraction protocol while mean MDF, CV and normalized force decreased as in controls, ARV showed in about two third of MyD patients and differently from controls, a significant reduction. At the 15th set and at the end of the protocol a significant inverse correlation was observed between normalized MDF and ARV Alterations in excitability parameters seem to characterize muscle fatigue phenomena in MyD, as showed by ARV changes. A loss of myofiber activation can be explained by functional sarcolemmal impairment, like this hypothesized on the bases of Na+/K+ pump altered threshold reported in MyD.
/42-06 1SFEMG Studies in Experimental Autoimmune Myasthenia Aged Rats
Gravis. Differences
Between Young and
J. Verschuuren, E Spaans, A. Hoedemaekers, Y. Graus, M. de Baets University of Limburg, Maastricht, Netherlands Recently we found that aged Brown-Noway (BN) rats, in contrast to young BN-rats, are not susceptible to experimental autoimmune myasthenia gravis (EAMG). In order to further analyse this observation, young (11 weeks) and 5 aged (106 weeks) BN rats were investigated with stimulated (3, 5 and 10 Hz) SFEMG of the gluteal muscle before and after immunization with Torpedo acetylcholine receptor (AChR) in CFA (20 fig/l 00 g body weight). Before immunization mean MCD values in the young rats were 14.2 ps (SD 6.6). 15.6 ps (SD 7.6) and 14.9 ys (SD 9.8) at respectively 3, 5 and 10 Hz. in the aged rats these values were 20.3 bs (SD 15.3). 22.5 ps (SD 17.5). and 23.5 fis (SD 15.4) (all values significantly higher than those found in the young animals). Nine weeks after immunization the young rats, but none of the aged rats, showed clinical signs of disease. Mean MCV values in the aged rats were now respectively 20.4 fis (SD 11 .I), 26.4 ps (SD 15.6). and 30.6 ps (SD 23.1). At no stimulus frequency the MCD values were significantly increased. SFEMG studies were not repeated in the young rats because it is known from previous experiments that young rats with clinical symptoms of EAMG have considerably increased MCD values. Both young and aged rats produced similar anti-AChR antibody titers, and immunological studies showed no differences in the function of the immune apparatus between young and aged rats. It is hypothesized that structural changes at the endplate might explain as well the higher jitter values in the aged rats before immunization as the differences in susceptibility to EAMG. This work was supported by the ‘Prinses Beatrix Fonds’.
142-071Reliability of Transmission as a Function of Discharge Rate at Normal and Diseased Neuromuscular Junctions J,V Trontelj, M. Krian. E. StglbergUniversitylnstitute of Clinical NeurophysiologL: Ljubljana; *Department of Clinical NeurophysiologL: University Hospital, Uppsaia Jitter of a neuromuscular junction (NMJ) as recorded by single fibre EMG (SFEMG) is related to its safety factor. With repetitive activity at different rates, the safety factor changes as a result of two opposing, rate dependent, processes: potentiation (based on three different mechanism with different time constants) and depression. Jitter and the degree of blocking, when present, was assessed using SFEMG with axonal microstimulation in order to study rate dependent changes in safety factor in normal muscle, myasthenia gravis (MG). Lambert Eaton myasthenic syndrome (LEMS), botulism, in botulrnum-toxin injected muscles and in neurapraxia. In about a quarter of normal end-plates, safety factor was found to be relatively low at low discharge rates, but improved significantly at higher rates (IO Hz and above). In MG, the predominant pattern was temporary improvement of transmission at higher rates, however a reverse pattern predominated in
some patients. At the lowest rates (51 Hz) the transmission was most often, although not always, more reliable. In LEMS, the safety factor was lowest at the low rates and increased dramatically at 10 and 20 Hz A proportion of NMJs only transmitted at rates of 520 Hz. However, in some patients a proportion of NMJs showed the myasthenic pattern. ln botulism and botulinum toxin-injected muscles, the changes were similar to LEMS, but less dramatic. In cases of neurapraxia, the normal intertetanic potentiation was often completely missing, suggesting the failing presynaptic function.
142-081Testing ~s~rQ~~s~~la~
Fatigue in Controls and
Patients K. Wohlfarth, El?. G.
R. Dengler, M. Schubert, J, Elek, S. Zierz. University of Bonn,
Quantitative assessment of neuromuscular fatigue is clinically still not established. Therefore, we modified an exercise test described by Moussavi et al. (1989) for routine application in controls (n = 25) and patients with neuromuscular disorders. Patients with histologically and biochemically confirmed mitochondrial myopathies (n = 22) were selected because dysfunction of the respiratory chain may have caused relevant muscle fatigue. The adductor pollicis muscle was studied. The test (20 min.) included 120 cycles each consisting of 6 s voluntary contraction (50% of maximum) and 4 s rest. Compound muscle action potentials (CMAP) and twitch contractions (TC) were evoked by supramaximal ulnar nerve stimulation in the beginning and in 5 min. intervals. Controls showed only slight decreases of both CMAP amplitudes and twitch contraction forces of less than 30%. In the patients, CMAP amplitudes behaved similarly although a decrease of 40% was seen in two. TC forces were decreased by more than 30% in 15 patients with an extreme of 65% The above results, i.e. reduction of twitch forces associated with basically normal CMAPs, indicate that fatigue in mitochondrial myopathy is mainly of muscular origin. This is further supported by first results in 14 patients showing that abnormal muscle fatigue in the above test was mostly associated with pathologically increased lactate levels in the bicycle ergometer test. In our experience, the described test is easy to apply, yields reliable results and may be helpful in the assessment of the course of neuromuscular diseases and of treatment effects.
SESSION lNTRAOPERATlVE 43-01
43: MONITORING
1
Intraoperative Monitoring of Motor Evoked Potentials Using Direct Spinal Cord Stimulation and Controlled Neuromuscular Blockade
R.G. Emerson, D.C. Adams, E.J. Heyer. Columbia Presbyterian Medical Center, New York City The objective of this study was to evaluate the feasibility of intraoperative motor track monitoring using direct electrical simulation of the spinal cord with controlled neuromuscular blockade. Motor evoked potentials were recorded following electrical spinal cord stimulation (spe-MEPs) in 22 patients undergoing neurosurgical or orthopedic procedures. Anesthesia was maintairled using nitrous oxide, narcotic, and halogenated inhalational agents. Neuromuscular transmission was monitored continuously and titrated to 5% of baseline using a continuous vecuronium infusion. The spinal cord was stimulated using electrodes in either the interspinous ligaments, or the epidural or subarachnoid spaces. Compound muscle action potentials were recorded from quadriceps and tibialis anterior muscles. In all but one patient, well formed, stable spe-MEPs were recorded. That patient had a myelopathy clinically, and absent somatosensory evoked potentials. In one patient undergoing untethering of the spinal cord, spe-MEPs deteriorated, and a neurological deficit was present postoperatively. This study demonstrates the feasibility and utility of intraoperative motor track monitoring using spe-MEPs elicited by direct spinal cord stimulation. Controlled neuromuscular blockade permits recording of compound muscle action potentials while eliminating patient movement that would interfere with surgery. In contrast to motor evoked potentials elicited by transcranial stimulation, spe-MEPs are relatively resistant to effects of anesthetic agents.
Pofiter Sessions
years. compared to a control group. Supramaximal 0.1 msec 35 Hz continuous electrical stimulation was applied to the motor point and EMG was recorded from stimulated myofibers by means of a double differential electrode. By monitoring cross-correlation ratio between M-waves, following parameters were acquired: spectral median frequency (MDF), averaged rectified voltage (ARV) and muscle conduction velocity (CV). Force was recorded by means of a strain-gauge transducer. All data were acquired by a dedicated software, 1024 sampling frequency, and elaboratedisec during the protocol. Basally ARV and CV were significantly lower than controls. At the end of the contraction protocol while mean MDF, CV and normalized force decreased as in controls, ARV showed in about two third of MyD patients and differently from controls, a significant reduction. At the 15th set and at the end of the protocol a significant inverse correlation was observed between normalized MDF and ARV Alterations in excitability parameters seem to characterize muscle fatigue phenomena in MyD, as showed by ARV changes. A loss of myofiber activation can be explained by functional sarcolemmal impairment, like this hypothesized on the bases of Na+/K+ pump altered threshold reported in MyD.
/42-06 1SFEMG Studies in Experimental Autoimmune Myasthenia Aged Rats
Gravis. Differences
Between Young and
J. Verschuuren, E Spaans, A. Hoedemaekers, Y. Graus, M. de Baets University of Limburg, Maastricht, Netherlands Recently we found that aged Brown-Noway (BN) rats, in contrast to young BN-rats, are not susceptible to experimental autoimmune myasthenia gravis (EAMG). In order to further analyse this observation, young (11 weeks) and 5 aged (106 weeks) BN rats were investigated with stimulated (3, 5 and 10 Hz) SFEMG of the gluteal muscle before and after immunization with Torpedo acetylcholine receptor (AChR) in CFA (20 fig/l 00 g body weight). Before immunization mean MCD values in the young rats were 14.2 ps (SD 6.6). 15.6 ps (SD 7.6) and 14.9 ys (SD 9.8) at respectively 3, 5 and 10 Hz. in the aged rats these values were 20.3 bs (SD 15.3). 22.5 ps (SD 17.5). and 23.5 fis (SD 15.4) (all values significantly higher than those found in the young animals). Nine weeks after immunization the young rats, but none of the aged rats, showed clinical signs of disease. Mean MCV values in the aged rats were now respectively 20.4 fis (SD 11 .I), 26.4 ps (SD 15.6). and 30.6 ps (SD 23.1). At no stimulus frequency the MCD values were significantly increased. SFEMG studies were not repeated in the young rats because it is known from previous experiments that young rats with clinical symptoms of EAMG have considerably increased MCD values. Both young and aged rats produced similar anti-AChR antibody titers, and immunological studies showed no differences in the function of the immune apparatus between young and aged rats. It is hypothesized that structural changes at the endplate might explain as well the higher jitter values in the aged rats before immunization as the differences in susceptibility to EAMG. This work was supported by the ‘Prinses Beatrix Fonds’.
142-071Reliability of Transmission as a Function of Discharge Rate at Normal and Diseased Neuromuscular Junctions J,V Trontelj, M. Krian. E. StglbergUniversitylnstitute of Clinical NeurophysiologL: Ljubljana; *Department of Clinical NeurophysiologL: University Hospital, Uppsaia Jitter of a neuromuscular junction (NMJ) as recorded by single fibre EMG (SFEMG) is related to its safety factor. With repetitive activity at different rates, the safety factor changes as a result of two opposing, rate dependent, processes: potentiation (based on three different mechanism with different time constants) and depression. Jitter and the degree of blocking, when present, was assessed using SFEMG with axonal microstimulation in order to study rate dependent changes in safety factor in normal muscle, myasthenia gravis (MG). Lambert Eaton myasthenic syndrome (LEMS), botulism, in botulrnum-toxin injected muscles and in neurapraxia. In about a quarter of normal end-plates, safety factor was found to be relatively low at low discharge rates, but improved significantly at higher rates (IO Hz and above). In MG, the predominant pattern was temporary improvement of transmission at higher rates, however a reverse pattern predominated in
some patients. At the lowest rates (51 Hz) the transmission was most often, although not always, more reliable. In LEMS, the safety factor was lowest at the low rates and increased dramatically at 10 and 20 Hz A proportion of NMJs only transmitted at rates of 520 Hz. However, in some patients a proportion of NMJs showed the myasthenic pattern. ln botulism and botulinum toxin-injected muscles, the changes were similar to LEMS, but less dramatic. In cases of neurapraxia, the normal intertetanic potentiation was often completely missing, suggesting the failing presynaptic function.
142-081Testing ~s~rQ~~s~~la~
Fatigue in Controls and
Patients K. Wohlfarth, El?. G.
R. Dengler, M. Schubert, J, Elek, S. Zierz. University of Bonn,
Quantitative assessment of neuromuscular fatigue is clinically still not established. Therefore, we modified an exercise test described by Moussavi et al. (1989) for routine application in controls (n = 25) and patients with neuromuscular disorders. Patients with histologically and biochemically confirmed mitochondrial myopathies (n = 22) were selected because dysfunction of the respiratory chain may have caused relevant muscle fatigue. The adductor pollicis muscle was studied. The test (20 min.) included 120 cycles each consisting of 6 s voluntary contraction (50% of maximum) and 4 s rest. Compound muscle action potentials (CMAP) and twitch contractions (TC) were evoked by supramaximal ulnar nerve stimulation in the beginning and in 5 min. intervals. Controls showed only slight decreases of both CMAP amplitudes and twitch contraction forces of less than 30%. In the patients, CMAP amplitudes behaved similarly although a decrease of 40% was seen in two. TC forces were decreased by more than 30% in 15 patients with an extreme of 65% The above results, i.e. reduction of twitch forces associated with basically normal CMAPs, indicate that fatigue in mitochondrial myopathy is mainly of muscular origin. This is further supported by first results in 14 patients showing that abnormal muscle fatigue in the above test was mostly associated with pathologically increased lactate levels in the bicycle ergometer test. In our experience, the described test is easy to apply, yields reliable results and may be helpful in the assessment of the course of neuromuscular diseases and of treatment effects.
SESSION lNTRAOPERATlVE 43-01
43: MONITORING
1
Intraoperative Monitoring of Motor Evoked Potentials Using Direct Spinal Cord Stimulation and Controlled Neuromuscular Blockade
R.G. Emerson, D.C. Adams, E.J. Heyer. Columbia Presbyterian Medical Center, New York City The objective of this study was to evaluate the feasibility of intraoperative motor track monitoring using direct electrical simulation of the spinal cord with controlled neuromuscular blockade. Motor evoked potentials were recorded following electrical spinal cord stimulation (spe-MEPs) in 22 patients undergoing neurosurgical or orthopedic procedures. Anesthesia was maintairled using nitrous oxide, narcotic, and halogenated inhalational agents. Neuromuscular transmission was monitored continuously and titrated to 5% of baseline using a continuous vecuronium infusion. The spinal cord was stimulated using electrodes in either the interspinous ligaments, or the epidural or subarachnoid spaces. Compound muscle action potentials were recorded from quadriceps and tibialis anterior muscles. In all but one patient, well formed, stable spe-MEPs were recorded. That patient had a myelopathy clinically, and absent somatosensory evoked potentials. In one patient undergoing untethering of the spinal cord, spe-MEPs deteriorated, and a neurological deficit was present postoperatively. This study demonstrates the feasibility and utility of intraoperative motor track monitoring using spe-MEPs elicited by direct spinal cord stimulation. Controlled neuromuscular blockade permits recording of compound muscle action potentials while eliminating patient movement that would interfere with surgery. In contrast to motor evoked potentials elicited by transcranial stimulation, spe-MEPs are relatively resistant to effects of anesthetic agents.