Separate Quantification of Reflex and Nonreflex Components of Spastic Hypertonia in Chronic Hemiparesis

Experimental setup for instrumented Achilles’ tendon reflex test and motorized passive movement test. (A) The leg was strapped to the leg support at 60° of knee flexion. The thigh and trunk were strapped to the seat and backrest, respectively, with the hip at 85° of flexion. The foot and cast were clamped and strapped to the attachment with appropriate alignment. The footplate was mounted onto a torque sensor measuring the ankle flexion torque, which was connected to a servo motor. (B) The instrumented tendon hammer with a force sensor mounted at its head and the rubber pad are shown. Abbreviations: DSP, digital signal processor, LED, light-emitting diode, PC, personal computer.

(A, B) The tendon tapping force, (C, D) reflex-mediated ankle plantarflexion electromyographic (EMG) response, (E, F) reflexive ankle plantarflexion torque (Torq), (G, H) impulse responses (IR) of the reflex-mediated electromyographic response, and (I, J) torque. The 2 columns correspond to representative results from a spastic stroke patient (left column) and healthy subject (right column). The peak values of tapping force and 2 impulse responses correspond to the threshold in tapping force (f_th), electromyographic reflex gain (G_er), and torque reflex gain (G_tr). The solid and dashed lines give the mean and mean ± SD, respectively.

Representative signals during passive movement trials on a stroke patient (left column) with a spastic ankle and a control subject (right column). (A, B) The top and the (C, D) second rows correspond to the ankle joint angle (positive for dorsiflexion) and ankle joint torque (positive for plantarflexor resistance torque), respectively. (E, F) The electromyography signals from the soleus (sol) muscles are shown. (G, H) Plotting the ankle joint torque (ordinate) at each corresponding ankle joint angle (abscissa) generates multiple hysteresis curves, moving clockwise as time progresses as indicated by the arrows. (I, J) The multiple curves are averaged for further measurements of the nonreflex properties. For simplicity, (I) the dorsiflexion angle at 10Nm of passive resistant torque (A_10Nm) is shown while (J) the passive resistant torque (T_10df) and the stiffness (K_10df) at 10° of dorsiflexion angle are shown. The slope of the thick oblique segment in panel J gives the stiffness (K_10df).

Scattergraphs of the quantitative data as a function of the clinical measures in 17 normal (open circles) and 17 stroke (filled squares) subjects. (A, B) The peak reflex gain (G_tr) and ankle joint angle at 10Nm of passive resistant torque are plotted versus the tendon reflex scale (DTR) versus (C, D) the manual dorsiflexion ROM, and (E, F) the MAS. The ρ indicates the Spearman correlation coefficient, and r indicates the Pearson correlation coefficient. *The correlation coefficients higher than the critical values (ρ>.449 or r>.455 with P<.01).