Terms and definitions of neural metrics
| Device utilization | The percent time the stimulator was on. Also referenced as percent time stimulating |
| Therapy utilization aka percent usage over ECAP threshold | The percent of preferred program use that the patient’s recorded ECAP amplitude was at or above ECAP threshold. Figure 1 histogram plots show the percent usage over ECAP threshold. |
| Therapy dose or dose ratio | The neural activation estimate normalized using each patient’s unique ECAP threshold and sensitivity. The median neural activation level (median ECAP amplitude) was calculated from the patient’s device logs. The dose ratio was calculated by matching the median ECAP amplitude to the fitted curve of the AP, identifying the corresponding current, and dividing that current by the ECAP threshold current to get a ratio. Ratios >1 are above threshold, while ratios <1 are below threshold, on average. Figure 1AP plots illustrate this relationship between median ECAP amplitude, ECAP threshold, and dose ratio. |
| Dose accuracy, inversely related to error in µV | Accuracy increases as error measured in µV decreases. The root mean squared error of the out-of-clinic measured feedback variable from the target, minus the contribution of measurement noise estimated as the SD in the subthreshold region of the AP. The accuracy metric was determined for patients whose target was set over threshold by taking the single-target ECAP amplitude histograms in the preceding week, taking the difference between each bin center and the target bin center, multiplying by the corresponding number of ECAPs in each bin, squaring and summing the differences, dividing by the number of measured ECAPs, subtracting the SD of the baseline noise of the loop in the subthreshold region, and taking the square root (equation in online supplemental materials). |
AP, activation plot; ECAP, evoked compound action potential.