The effects of vertebral column tripolar electrical stimulation with various intensities on soleus and gastrocnemius H-reflex and Mh wave recruitment curve

To assess the effect of penetration depth of the surface tripolar electrical stimulation, Tripolar TENS was applied with different intensities (equal to sensory threshold (ST), 1.25 ST, 1.5 ST) on vertebral column of twenty healthy and three hemiplegic subjects. The cathode of TENS was laid on the T11 vertebra and anodes were put 3cm apart from cathode, longitudinally and in the anode-cathode-anode arrangement. Before, after and 10 min after TENS the recruitment curve of soleus and gastrocnemius H-reflex and M wave were recorded. Experiments were done in four separate sessions. One of them was control session and the TENS apparatus was off in it. In each of the test sessions, TENS was applied with one of the intensities. The results showed that the 1.5 ST TENS have a complex facilitatory-inhibitory effect on recruitment curve of soleus H-reflex in the way that slow motoneurons were inhibited and fast motoneurons were facilitated. So the positive slope of curve was increased and the intensity needed to evoke Hmax was decreased. Amplitude of Hmax and threshold of the curve were slightly decreased. Gastrocnemius was facilitated after 1.5 ST TENS. The threshold of the H-reflex curve and needed intensity to evoke Hmax were decreased, while peak to peak amplitude of Hmax was increased. After ST TENS, soleus was facilitated and gastrocnemius had little change. It seems that 1.5 ST TENS facilitate Ia, Ib, fast motoneurons and renshaw cells via stimulating the dorsal column of the cord and renshaw inhibit slow motoneurons, so a complex of facilitation and inhibition appears in soleus motoneurons. In the case of gastrocnemius which the renshaw cells had not strong effect, H-reflex curve was facilitated. In ST TENS which only the skin afferents were stimulated the renshaw cells were inhibited by skin afferents and H-reflex was facilitated, But because the gastrocnemius motoneurons are slightly under control of renshaw and skin afferents synapses with motoneurons are not engaged in reflex loop, facilitation of skin afferents synapses after TENS application had no effect on the H-reflex parameters of gastrocnemius.