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Human muscle fatigue: simultaneous analysis of force, EMG and 31P nuclear magnetic resonance spectroscopy
S12,1
Vlll C O N G R E S S OF E M G A N D R E L A T E D C L I N I C A L N E U R O P H Y S I O L O G Y
still believed to function by way of antidromic activation of the dorsal columns giving rise to inhibition of nociceptive signals at the first relay in the dorsal horn. A supraspinal loop may also be involved. The neurohumoral mechanisms of pain relief with spinal stimulation are not known. This form of stimulation is preferentially effective for pain classified as neurogenic, i.e., pain due to injury of the nervous system itself. Recently, it has been demonstrated that spinal stimulation may be effective for ischemic pain but it is not known whether pain relief occurs as a result of improvement of peripheral circulation produced by the stimulation. Intracerebral stimulation m a y be performed in two different target regions corresponding to the activation of different mechanisms of pain suppression. Stimulation in the periventricular region is exclusively effective for nociceptive pain whereas stimulation in the sensory thalamic nuclei may influence neurogenic pain. The former type of stimulation is at least partly dependent upon endorphinergic and serotonergic mechanisms whereas the biochemical, as well as the neurophysiological, background to the latter one is poorly understood.
SKi. Human muscle fatigue: simultaneous analysis of force, EMG and 3tp nuclear magnetic resonance spectroscopy. - R.G. Miller, H.S. Milner-Brown, D. Giannini, R.B. Layzer, D. Hooper and M.W. Weiner (Children's Hospital of San Francisco and the University of California at San Francisco, San Francisco, CA, U.S.A.) We have utilized 31p nuclear magnetic resonance ( N M R ) measurements of the h u m a n adductor pollicis (AP) with simultaneous measurements of M-wave, force and rectified integrated E M G (RIEMG) to evaluate the relative contribution of impulse propagation failure, high energy phosphate depletion, lowered pH, and impaired excitation-contraction coupling in h u m a n muscle fatigue and recovery. During fatigue m a x i m u m voluntary contraction force (MVC) fell by 90%, p H fell to 6.4, and phosphocreatine fell to 0. Neuromuscular efficiency ( f o r c e / R I E M G ) was reduced to 40% of control at the end of the fatiguing contraction, twitch tension was reduced to 25% of control, and the M-wave was reduced in amplitude and prolonged in duration. During recovery the M-wave returned to control levels within 4 min; pH, high energy phosphates and MVC within 20 rain; and neuromuscular efficiency and twitch tension did not recover within 60 min. These studies prove the feasibility of studying different elements of fatigue and recovery in h u m a n muscle, in vivo, with simultaneous 31p N M R , E M G and force recording. The data provided thus far show a close correlation between changes in MCV, pH and high energy phosphates, both during fatigue and recovery. A long-lasting impairment of twitch tension and N M E , which is independent of any N M R or M-wave alteration, probably reflects impaired excitationcontraction coupling.
SY. Lambert-Eaton myasthenic syndrome (LEMS): a presynaptic autoimmune disorder aff~ting neuromuscular transmission. - J. Newsom-Davis (Dept. of Neurological Science, Royal Free Hospital School of Medicine, London NW3, U.K.) LEMS is characterized by muscle weakness and autonomic dysfunction. In a personal series of 50 consecutive cases, cancer was present in 23, small cell lung carcinoma (SCLC) histologically proven in 20. Neurophysiologically there is a reduction in the number of nerve evoked acetylcholine packages (quanta) and in the rate of non-quantal release (molecular leakage) of transmitter at the neuromuscular junction. Experiments in which LEMS tgG preparations were injected intraperitoneally into mice have shown that, in both cancer-associated and cancer-unassociated LEMS, the neurophysiological abnormalities can be accounted for by an IgG antibody that reduces the number of functional presynaptic voltage-dependent Ca 2÷ channels (VDCC). Freeze fracture electron microscope studies of the nerve terminal in LEMS have revealed paucity of active zone particles (that are thought to be the morphological correlate of VDCCs) and disorganization of their normal array; these changes can also be transferred to mice by injection of LEMS lgG. SCLC may be of neuro-ectodermal origin, and voltage-dependent Ca 2+ flux can be demonstrated in cultured h u m a n SCLC cell lines, using a 45Ca 2÷ flux assay. Flux is significantly reduced in cells grown in LEMS IgG from caneer-associated and non-cancer cases. Thus the primary immune response in the former m a y be against VDCCs on the cancer cell; the stimulus in non-cancer cases is at present unknown.
PS. Percutaneously and subcutaneously evoked nerve potentials of supedicial peroneal, tibial and sural nerves. B. Radanovi¢~,A. Jm~ii~ and N. Fronjek (Dept. of Neurology, General Hospital, Osijek, and Center for Neuromuscular Diseases, Zugreb, Yugoslavia) In 40 healthy young men and in 15 patients the method of evoking nerve potentials according the description of Ju~i6 et al. was applied. In all healthy volunteers the nerve potentials of sufficient synchrony were recorded. In patients with polyneuropathy the latencies were prolonged or no potential was recorded. In 8 patients with trophic skin changes or edema the stimulation with bipolar not isolated needle electrodes easily yielded nerve potentials. The electrodes were placed not in parallel along the dorsum, as the strip electrodes of the previously described method, but left-right over the proximal boundary of the peroneus profundus sensory innervation region. The possibility to evoke tibial nerve potential by subcutaneous needle electrodes was limited also to the transversal placement of needle electrodes proximally to the first metatarso-phalangeal joint. Nerve potential was biphasic and only lower than the mean of the amplitudes in normal controls, and the latencies were more or less prolonged. Therefore the absence of the nerve potential can be considered definitive if there is no response on subcutaneous needle stimulation.
Vlll C O N G R E S S OF E M G A N D R E L A T E D C L I N I C A L N E U R O P H Y S I O L O G Y
still believed to function by way of antidromic activation of the dorsal columns giving rise to inhibition of nociceptive signals at the first relay in the dorsal horn. A supraspinal loop may also be involved. The neurohumoral mechanisms of pain relief with spinal stimulation are not known. This form of stimulation is preferentially effective for pain classified as neurogenic, i.e., pain due to injury of the nervous system itself. Recently, it has been demonstrated that spinal stimulation may be effective for ischemic pain but it is not known whether pain relief occurs as a result of improvement of peripheral circulation produced by the stimulation. Intracerebral stimulation m a y be performed in two different target regions corresponding to the activation of different mechanisms of pain suppression. Stimulation in the periventricular region is exclusively effective for nociceptive pain whereas stimulation in the sensory thalamic nuclei may influence neurogenic pain. The former type of stimulation is at least partly dependent upon endorphinergic and serotonergic mechanisms whereas the biochemical, as well as the neurophysiological, background to the latter one is poorly understood.
SKi. Human muscle fatigue: simultaneous analysis of force, EMG and 3tp nuclear magnetic resonance spectroscopy. - R.G. Miller, H.S. Milner-Brown, D. Giannini, R.B. Layzer, D. Hooper and M.W. Weiner (Children's Hospital of San Francisco and the University of California at San Francisco, San Francisco, CA, U.S.A.) We have utilized 31p nuclear magnetic resonance ( N M R ) measurements of the h u m a n adductor pollicis (AP) with simultaneous measurements of M-wave, force and rectified integrated E M G (RIEMG) to evaluate the relative contribution of impulse propagation failure, high energy phosphate depletion, lowered pH, and impaired excitation-contraction coupling in h u m a n muscle fatigue and recovery. During fatigue m a x i m u m voluntary contraction force (MVC) fell by 90%, p H fell to 6.4, and phosphocreatine fell to 0. Neuromuscular efficiency ( f o r c e / R I E M G ) was reduced to 40% of control at the end of the fatiguing contraction, twitch tension was reduced to 25% of control, and the M-wave was reduced in amplitude and prolonged in duration. During recovery the M-wave returned to control levels within 4 min; pH, high energy phosphates and MVC within 20 rain; and neuromuscular efficiency and twitch tension did not recover within 60 min. These studies prove the feasibility of studying different elements of fatigue and recovery in h u m a n muscle, in vivo, with simultaneous 31p N M R , E M G and force recording. The data provided thus far show a close correlation between changes in MCV, pH and high energy phosphates, both during fatigue and recovery. A long-lasting impairment of twitch tension and N M E , which is independent of any N M R or M-wave alteration, probably reflects impaired excitationcontraction coupling.
SY. Lambert-Eaton myasthenic syndrome (LEMS): a presynaptic autoimmune disorder aff~ting neuromuscular transmission. - J. Newsom-Davis (Dept. of Neurological Science, Royal Free Hospital School of Medicine, London NW3, U.K.) LEMS is characterized by muscle weakness and autonomic dysfunction. In a personal series of 50 consecutive cases, cancer was present in 23, small cell lung carcinoma (SCLC) histologically proven in 20. Neurophysiologically there is a reduction in the number of nerve evoked acetylcholine packages (quanta) and in the rate of non-quantal release (molecular leakage) of transmitter at the neuromuscular junction. Experiments in which LEMS tgG preparations were injected intraperitoneally into mice have shown that, in both cancer-associated and cancer-unassociated LEMS, the neurophysiological abnormalities can be accounted for by an IgG antibody that reduces the number of functional presynaptic voltage-dependent Ca 2÷ channels (VDCC). Freeze fracture electron microscope studies of the nerve terminal in LEMS have revealed paucity of active zone particles (that are thought to be the morphological correlate of VDCCs) and disorganization of their normal array; these changes can also be transferred to mice by injection of LEMS lgG. SCLC may be of neuro-ectodermal origin, and voltage-dependent Ca 2+ flux can be demonstrated in cultured h u m a n SCLC cell lines, using a 45Ca 2÷ flux assay. Flux is significantly reduced in cells grown in LEMS IgG from caneer-associated and non-cancer cases. Thus the primary immune response in the former m a y be against VDCCs on the cancer cell; the stimulus in non-cancer cases is at present unknown.
PS. Percutaneously and subcutaneously evoked nerve potentials of supedicial peroneal, tibial and sural nerves. B. Radanovi¢~,A. Jm~ii~ and N. Fronjek (Dept. of Neurology, General Hospital, Osijek, and Center for Neuromuscular Diseases, Zugreb, Yugoslavia) In 40 healthy young men and in 15 patients the method of evoking nerve potentials according the description of Ju~i6 et al. was applied. In all healthy volunteers the nerve potentials of sufficient synchrony were recorded. In patients with polyneuropathy the latencies were prolonged or no potential was recorded. In 8 patients with trophic skin changes or edema the stimulation with bipolar not isolated needle electrodes easily yielded nerve potentials. The electrodes were placed not in parallel along the dorsum, as the strip electrodes of the previously described method, but left-right over the proximal boundary of the peroneus profundus sensory innervation region. The possibility to evoke tibial nerve potential by subcutaneous needle electrodes was limited also to the transversal placement of needle electrodes proximally to the first metatarso-phalangeal joint. Nerve potential was biphasic and only lower than the mean of the amplitudes in normal controls, and the latencies were more or less prolonged. Therefore the absence of the nerve potential can be considered definitive if there is no response on subcutaneous needle stimulation.