Objective: Foot dorsiflexion evokes a short- (SLR) and a medium- latency EM G response (MLR) in the soleus of standing subjects. SLR is mediated by spindle group Ia, while group II fibres contribute to MLR through an ...Objective: Foot dorsiflexion evokes a short- (SLR) and a medium- latency EM G response (MLR) in the soleus of standing subjects. SLR is mediated by spindle group Ia, while group II fibres contribute to MLR through an oligosynaptic circu it. We studied the effects of Achilles’ tendon vibration on both responses in spastic patients to disclose any abnormal excitability of these pathways. Method s: SLR and MLR were evoked in 11 hemiparetics and 11 normals. The vibration- in duced changes in both responses were correlated to the Ashworth score of the aff ected leg. Results: There were no differences between normals and patients in th e size of control SLR or MLR. Vibration decreased SLR to 70% in normal subject s, but increased it to 110% in patients, in both affected and unaffected leg. Vibration did not affect MLR in normals, but increased it to 165% on the affec ted and 120% on the unaffected side of patients. Ashworth score was solely cor related with the degree of vibration- induced increase of MLR. Conclusions: Whi le the lack of inhibitory effect of vibration on SLR confirms a reduced inhibiti bility of the monosynaptic reflex, the increased MLR indicates a disin hibition of group II pathway in patients, connected to the loss of descending control on group II interneurones. Spastic hypertonia depends on release of gro up II rather than group Ia reflex pathways. Significance: These findings give a neurophysiological support for the pharmacological treatment of spastic hyperton ia and suggest a method for the assessment of its effects.展开更多
文摘Objective: Foot dorsiflexion evokes a short- (SLR) and a medium- latency EM G response (MLR) in the soleus of standing subjects. SLR is mediated by spindle group Ia, while group II fibres contribute to MLR through an oligosynaptic circu it. We studied the effects of Achilles’ tendon vibration on both responses in spastic patients to disclose any abnormal excitability of these pathways. Method s: SLR and MLR were evoked in 11 hemiparetics and 11 normals. The vibration- in duced changes in both responses were correlated to the Ashworth score of the aff ected leg. Results: There were no differences between normals and patients in th e size of control SLR or MLR. Vibration decreased SLR to 70% in normal subject s, but increased it to 110% in patients, in both affected and unaffected leg. Vibration did not affect MLR in normals, but increased it to 165% on the affec ted and 120% on the unaffected side of patients. Ashworth score was solely cor related with the degree of vibration- induced increase of MLR. Conclusions: Whi le the lack of inhibitory effect of vibration on SLR confirms a reduced inhibiti bility of the monosynaptic reflex, the increased MLR indicates a disin hibition of group II pathway in patients, connected to the loss of descending control on group II interneurones. Spastic hypertonia depends on release of gro up II rather than group Ia reflex pathways. Significance: These findings give a neurophysiological support for the pharmacological treatment of spastic hyperton ia and suggest a method for the assessment of its effects.
