Figure 1.

Neural activation and activation accuracy during open-loop and closed-loop SCS. Neural activation accuracy is the ability of the SCS device to adhere to the target neural response (ie, ECAP, prescription (Rx)) (black line at 50 µV in this example). In open-loop (gray line), with a fixed amplitude of 1.1 µC/pulse, over the course of 150 s, there was an average deviation from the target of 68 µV, which produced an erratic neural activation (elicited ECAP). In closed-loop (orange line), performing the same posture assessment, with the stimulation amplitude continuously modified with each pulse for a range of 0.5–1.4 µC, there was an average deviation of 3 µV, which produced a neural activation of 50 µV (aligned with the target ECAP). The neural activation (elicited ECAP) is more accurate in closed-loop (orange line), on average only deviating 3 µV from the ECAP target of 50 µV. In contrast, the neural activation is less accurate in open-loop, as can be observed by the more erratic gray line, on average deviating 68 µV from the ECAP target. Data are from two postural assessments (open-loop and closed-loop) for a single patient. ECAP, evoked compound action potential; SCS, spinal cord stimulation.