THE EFFECTS OF SURFACE ANESTHESIA ON THE AUTONOMIC DYSREFLEXIA RESPONSE DURING FUNCTIONAL ELECTRICAL-STIMULATION

Recently, increases in blood pressure (BP) and concomitant bradycardia , suggestive of autonomic dysreflexia (AD), have been documented durin g functional electrical stimulation (FES) in individuals with a high s pinal cord injury (SCI). If uncontrolled, this response could preclude the safe use of FES among such individuals. FES induced pain is partl y related to stimulation of skin nociceptors. Therefore, measures to r educe skin sensitivity may reduce the risk of AD during FES. The purpo se of this study was to determine if topical anaesthetic applied over the site of electrical stimulation could minimize the AD cardiovascula r and hormonal responses to FES in individuals with SCI above the T6 l evel. Seven subjects with a SCI above T6 received FES to the quadricep s muscle of each leg under two conditions on two different testing day s. The two treatment conditions, topical anaesthetic and placebo cream s, were double blinded and randomized. The cream was administered to a n area the size of the electrode (10x10 cm) Ih prior to stimulation. S timulation began at 0 mAmps and increased by 16 mAmps every 2 min unti l an intensity of 160 mAmps was achieved. HR and BP were measured at e ach stimulation intensity level. Catecholamines were analyzed three ti mes during the stimulation protocol (pre, mid and post stimulation int ensities). At the end of the stimulation protocol, FES induced isometr ic quadriceps contraction force at 160 mAmps intensity was measured us ing a hand held dynamometer. As FES stimulation intensity increased, s ignificant rises in systolic and diastolic BP were seen, with a concom itant progressive drop in HR. The AD response to stimulation was not s ignificantly different between the topical anaesthetic and placebo con ditions. Serum catecholamine (epinephrine and norepinephrine) levels t ended to rise with increasing FES intensity levels but did not reach s tatistical significance. The two treatment conditions did not signific antly affect serum catecholamine levels or FES-induced quadriceps cont raction force. In summary, FES application to the quadriceps muscle in high level SCI subjects resulted in significant increases in BP, decr eases in HR (AD-like response), a trend towards elevations in catechol amine levels, and no difference in quadriceps muscular strength. Howev er, these responses were unaffected by the use of topical anaesthetic cream on the skin at the stimulation site. This suggests that other me chanisms than skin nociception are operative in FES-induced AD.