STRETCH REFLEX LATENCIES IN SPASTIC HEMIPARETIC SUBJECTS ARE PROLONGED AFTER TRANSCUTANEOUS ELECTRICAL NERVE-STIMULATION

Low-intensity repetitive electrical stimulation such as dorsal column and transcutaneous electrical nerve stimulation (TENS) reportedly decr eases spasticity and improves voluntary motor control. However, the me chanisms mediating these effects are unclear. Recent findings suggest that spasticity may be characterized more appropriately by a decrease in the stretch reflex threshold than by an increase in gain. Our objec tives were: (1) to examine possible changes in stretch reflex excitabi lity following 45 min of TENS, (2) to map out the time course of possi ble post-stimulation effects via both latency and magnitude (amplitude or area) measurements, and (3) to determine the role of segmental ver sus non-segmental mechanisms involved in mediating these changes. The effects of 45 min of segmentally and heterosegmentally applied TENS on lower limb reflexes in ten spastic hemiparetic subjects were contrast ed with those resulting from placebo stimulation. We found that both s egmentally and heterosegmentally applied TENS caused an immediate incr ease in soleus H reflex latencies that was evident for up to 60 minute s post-stimulation in over 75% of the subjects. Similar increases for up to 60 and 40 minutes post-stimulation was noted for the stretch ref lex latencies in 50% and 67% of the subjects respectively for segmenta l and heterosegmental stimulation. These results suggested that manipu lation of segmental and heterosegmental afferents for 45 min may lead to a decrease of the otherwise augmented stretch reflex excitability a ccompanying hemiparetic spasticity.