Abstract:
Effects of isometric FES and dynamic FES on cardiovascular parameters on an active tilt-table stepper

Thrasher TA, Keller T, Lawrence M, Popovic MR.
E-mail: adam.thrasher(at)utoronto.ca

Functional Electrical Stimulation (FES) has the potential to address orthostatic hypotension, which is a common problem in acute Spinal Cord Injury, by activating the skeletal muscle pump in the lower extremities. A randomized cross-over study was performed in which two interventions were compared: isometric FES and dynamic FES combined with constrained stepping movements. 16 young, able-bodied subjects participated. Each subject performed three trials on separate days in random order. Subjects were tilted to 75 degrees from horizontal for a maximum of 30 minutes. The protocol for the three trials were: A) subjects were immobilized and received no FES; B) subjects were immobilized and cyclical FES was applied; C) subjects’ legs were moved in a stepping pattern and FES was applied. Of the 16 subjects, 5 experienced syncope or pre-syncope during the control trial (A). Those 5 plus one more experienced syncope or pre-syncope during the static FES trials (B), however it occurred on average 6.5 minutes later than in the static trials. No one experienced syncope or pre-syncope during the FES-stepping trials (C). Isometric FES appeared to cause short-term increases in blood pressure and heart rate, but these were not maintained over the long term. Dynamic FES produced much better results. We conclude that FES has potential to counteract orthostatic stress, however it should be combined with movement of the legs.