acce_ISF

acce_ISF determination and its impact

This represents the latest addition to autoISF and has been in operation since late December 2021.

For changes in variables like glucose or delta to occur, there must first be an acceleration. Therefore, acceleration recognizes such changes early and is employed by autoISF to take preemptive action. Glucose and delta, its first derivative, play a significant role in AAPS in determining the required insulin. However, acceleration, its second derivative, has not been considered until now. One reason for this omission might be its difficulty in extraction from glucose history, especially since delta needs to be averaged to provide a reliable signal. In autoISF, a best-fit algorithm is utilized to determine the parabola that best matches the glucose data.

Once the formula for the parabola is known, determining the acceleration becomes straightforward. In cases where the fit has poor correlation, indicating significant deviation from glucose readings, there is no contribution from acceleration, and acce_ISF = 1.

Otherwise, acce_ISF is calculated as follows:

acce_ISF = 1 + acce_weight * fit_share * cap_weight * acceleration

where:

• fit_share is a measure of fit quality, ranging from 0% for unacceptable fits to 100% for perfect fits.
• cap_weight is 0.5 below the target and 1.0 otherwise.
• acce_weight is bgAccel_ISF_weight for acceleration away from the target (mostly positive) or bgBrake_ISF_weight for acceleration towards the target (mostly negative).

Initially, it was assumed that the weights for acceleration and deceleration are of similar size. However, early experiences suggest that the weight while decelerating should be 30-40% lower than that for acceleration to reduce glucose oscillations. Often, the acce_ISF contribution plays a dominant role in autoISF, making it crucial and delicate. Weights for acce_ISF of 0 disable this contribution. It is advisable to start with small weights, like 0.02, and observe the results before increasing them. Keep in mind that negative acceleration may start occurring while glucose is still apparently rising, but the slope reduces. In such cases, acce_ISF will be <1, indicating growing sensitivity, and less insulin than normal will be required even before the glucose peak is reached.