The evolution strategy-a search strategy used in individual optimization of electrical parameters for therapeutic carotid sinus nerve stimulation

Optimization problems, arising in the search for parameters and/or techniques of functional electrostimulation (FES) disproportionally increase when multiple electrodes, electrode configurations, electrical parameters, and stimulation modes are applied. When computational or investigational effort precludes systematic studies in FES, the use of Rechenberg´s evolution strategy is proposed. This strategy implements mutation and selection processes in analogy to biological evolution. The effect of combined multiple input variables on a quality function (Q) is experimentally evaluated. The actual computed value of Q serves as a selection criterion for those input variable combinations which lead Q to approach a target value (maximization), similar to a hill-climbing procedure. In radiofrequency-controlled, therapeutic electrical carotid sinus nerve stimulation (CSNS), combinations of pulse frequency and pulse amplitude parameters were varied according to the evolution strategy in individual patients. CSNS lowers blood pressure and decreases heart rate. Q was computed from blood-pressure and heart-rate responses to CSNS. The strategy individually optimized electrical parameters to achieve large depressor responses upon CSNS.