Evaluation of the efficacy of the new selective interface for electrical stimulation

Electrical stimulation of sensory-motor systems when applying surface electrodes is becoming a conventional therapeutic modality (e.g., pain reduction, muscle strengthening, activation of paralysed muscles, and training of sensory-motor mechanisms). Common to all uses of surface electrodes for stimulation is that it requires a great deal of skill and patience of the user and/or the therapist to place the electrodes in the optimal position for the function to be performed. It is impossible to know precisely the pathways of the electrical charge that should be delivered to sensory-motor systems under the skin.  It is therefore difficult to predict precisely which anatomic structures will be activated for any given position and electrode configuration. Very often self-adhering electrodes are used, which must be taken off completely before they can be repositioned at a different location on the skin. This process is not only frustrating and time-consuming, but can also be painful and compromises the adhesion of the electrode to the skin, leading to an increased consumption of electrodes. Further, it is difficult to try many different electrode sizes, even if this may have an important effect on the function and subjective perception of the stimulation. For these reasons a non-optimal electrode position and electrode size are often chosen. We are addressing the problem of the effective use of surface electrodes that partly resolves the said problems by using the electrode array. We developed a prototype of a multiple contact surface stimulation electrode combined with an easy-to-use interface, which allows the user to rapidly emulate many different electrode sizes and positions, without actually removing the electrode from the skin during the process. The relation between the selectivity and the size of the conductive field were analysed in details, and the results suggested that the size of about 1 cm2 is optimal. The new interface comprises an array-electrode (Actitrode(R), patent pending), and programmable stimulator (Actigrip CS(R), patent pending).