微肌肉振動對手指牽張反射之影響

Abstract

對正常人手指肌肉施予微振動刺激能提高被振動手指肌肉之運動誘發電位。振動對於運動誘發電位的影響可分為大腦皮質與脊髓兩階段。雖然微肌肉振動對大腦皮質可激度對於運動誘的影響已被多個研究證實，但脊髓神經通路在此由振動造成的可激度的變化仍待確認的貢獻。本研究之目的為利用牽張反射這種基本上為脊髓的神經生理反應來釐清振動對於脊髓可激度的影響。十名男性健康受測者(年齡平均為24.1±1.5歲，身高平均為178.1±5.4公分，體重平均為76.3±14.3公斤)參與本研究。實驗以自製之手指牽動裝置分別牽動受測者手部之第一背側骨間肌(first dorsal interosseus)，外展拇短肌(abductor pollicis brevis)與外展小指肌(abductor digiti minimi)，藉由肌電訊號的量測量化上述肌肉分別在受到振動(80Hz；0.3~0.7mm振幅)與沒有振動時牽張反射的潛伏期與峰值大小。結果顯示有振動比無振動之牽張反射短潛期峰值降低了17.8%，而潛伏期沒有顯著改變。然而在長潛期反射之峰值與潛伏期均無明顯差異。因此基於振動抑制短潛期反射發現，脊髓神經通路在微肌肉振動引發中樞神經可激度增加之現象上應不具正向的效果，其影響可能為負向效果或是沒有影響。

Previous studies have shown that muscle vibration, below the threshold of inducing illusory movement or tonic vibration reflex, could modulate motor-evoked potential (MEP) of pathways controlling hand muscles in intact and chronic stroke individuals. It is evident that this type of sub-threshold muscle vibration provides corticomotor modulations on the pathways controlling the vibrated and adjacent non-vibrated muscles. However, spinal-level contribution to the muscle vibration-induced changes in MEPs is not clear. The purpose of this study was to investigate the effects of muscle vibration on the excitability of the spinal neural pathway. Ten healthy male subjects (age, 24.1±1.5 years; body height, 178.1±5.4 cm; body weight, 76.3±14.3 kg) volunteered for this study. Muscle vibration (MV) was applied to the muscle belly of first dorsal interosseus (FDI), abductor pollicis brevis (APB) and abductor digiti minimi (ADM) by an electrodynamic shaker with a custom-made 7mm-diameter probe. Muscle activities were recorded using surface electromyography (EMG). The vibration frequency was set at 80Hz, and the amplitude was adjusted to be just below the threshold of inducing tonic vibration reflex or illusory movement. A custom-made finger stretching device driven by a servo motor was used to stretch the hand muscles to induce a rapid adduction/abduction. Custom-designed software written in LabVIEW was used to control the device. The onset of stretching finger was randomized from 1s to 3s after onset of vibration. The duration of vibration was extended to offset of stretching finger after 1s. Subjects were instructed to perform an isometric contraction in the target muscle at 20% MVC before stretching the finger and maintain the activity level until the trial ended. Our results indicate that the amplitude of M1 of the three finger muscles was depressed 17.8% during muscle vibration as compared to that with no vibration; however, there was no significant difference in the amplitude of M2 between with and without muscle vibration. In addition, muscle vibration did not affect the latency of either M1 or M2. These findings suggest that muscle vibration-induced MEP facilitation may not occur in the spinal-level pathway.