RESUMO
We studied the effects of prolonged high-frequency stimulation in normal rat tail nerves. Nerves could conduct impulses at 50 Hz for 5 hours without complete conduction block. However, over time there was a significant decrease in amplitude and increase in latency of the compound nerve action potential (CNAP), which gradually became desynchronized. Changes were influenced by the frequency of stimulation. When stimulating over 30 minutes at 20, 50, 100, and 143 Hz the amplitude decreased to 89%, 79%, 67%, and 65% of baseline values, respectively, whereas the latency was only significantly increased at 100 and 143 Hz. All changes were reversible upon cessation of stimulation. Changes could not be attributed to focal block at the site of stimulation. These changes in the CNAP may reflect functional limitations of the axon membrane which may have pathophysiological implications for the study of neuropathies and focal nerve lesions.
Assuntos
Nervos Periféricos/fisiologia , Potenciais de Ação , Animais , Estimulação Elétrica , Masculino , Fibras Nervosas/fisiologia , Ratos , Ratos Endogâmicos , Cauda/inervação , Fatores de TempoRESUMO
A case of poisoning with the insecticide carbaryl, a cholinesterase inhibitor, was studied using repetitive stimulation and edrophonium administration. Without edrophonium, repetitive stimulation studies were normal. After 5mg of edrophonium was administered intravenously, a 40% decrement was recorded using 3Hz stimulation and an 80% decrement was seen with 30Hz stimulation. It is concluded that edrophonium is useful in testing for poisoning with cholinesterase inhibitors when other electrophysiologic studies are normal. These changes are most likely due to a recently described fast desensitization of the acetylcholine (ACh) receptor induced by high ACh concentrations.
Assuntos
Carbaril/intoxicação , Edrofônio/farmacologia , Junção Neuromuscular/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Adulto , Eletromiografia , Feminino , Humanos , Nervo Mediano/efeitos dos fármacos , Nervo Mediano/fisiopatologia , Tentativa de Suicídio , Nervo Ulnar/efeitos dos fármacos , Nervo Ulnar/fisiopatologiaRESUMO
Isokinetic strength testing has been widely used to assess athletic populations. The purpose of this study was to measure isokinetic strength in nonathletic able-bodied subjects to provide a subsequent comparison with nonathletic injured patients. Using a standard isokinetic protocol, with continuous verbal encouragement, a single investigator tested 16 women and nine men aged 20 to 30 years on an isokinetic dynamometer. Subjects had minimal athletic experience, and none were varsity performers. Peak torque as a percentage of body weight was statistically greater for men than for women in most joints tested both at 60 degrees and 180 degrees per second. The ratio of the last five to the first five of 25 repetitions at 180 degrees/second (Endurance Ratio = ER) rarely (ie, 5/154 tests) fell below the commonly accepted value of 50%. Many subjects had an endurance ratio of 100% or greater (range 4% to 171%). Peak torques were well below and endurance ratios well above those published for similarly aged athletes. The results suggest that before isokinetic testing is considered as a possible way to distinguish malingerers among injured patients, normal values in an age-matched, nonathletic, working population should be clearly defined. The endurance ratio may reflect the level of athletic training or the level of vigorous participation in an exercise program.