Medical devices, systems, and methods that adjust physiological signal thresholds to control stimulation therapy
Medical devices that provide stimulation therapy that is adjusted based on sensed physiological signals compensate for drifting of those physiological signal values that can lead to stimulation control reaching limits and becoming less effective. The medical devices determine average values of the physiological signals and use those average values to compute adjusted physiological signal threshold(s). The adjusted threshold(s) bring the physiological signals closer to or within the threshold(s) to allow the stimulation adjustments to be made within stimulation limits that can influence the physiological signal to continue to be within the threshold(s) and provide more effective therapy.
1 . A medical device, the medical device comprising:
a stimulation generator configured to produce a stimulation signal having a stimulation characteristic; and
processing circuitry configured to:
control the stimulation generator to deliver the stimulation signal based on a first threshold;
obtain a measurement of a physiological signal sensed via electrodes,
compute a first average level of the physiological signal for a first time period,
adjust the first threshold to a second threshold based on the first average level of the physiological signal, and
control the stimulation generator for a next time period by comparing the level of the physiological signal over a current time period immediately preceding the next time period to the second threshold;
wherein to control the stimulation generator for the next time period, the processing circuitry is configured to, in response to the level of the physiological signal exceeding the second threshold during the current time period, adjust the stimulation characteristic of the stimulation signal for the next time period to a level that causes the physiological signal to no longer exceed the second threshold, wherein the physiological signal comprises local field potentials (LFPs) within neurological tissue and the stimulation characteristic is stimulation amplitude.
2 . The medical device of claim 1 , wherein the second threshold is a second upper threshold, wherein the processing circuitry further determines a second lower threshold based on the first average level of the physiological signal, and further controls the stimulation generator for the next time period by at least:
comparing the level of the physiological signal over the current time period immediately preceding the next time period to the second lower threshold; and
in response to the physiological signal being below the second lower threshold continuously during the current time period, adjusting the stimulation characteristic for the next time period to a level that causes the physiological signal to no longer be below the second lower threshold.
3 . The medical device of claim 1 , wherein the first average level of the physiological signal is an all day average level, and wherein the processing circuitry is further configured to compute a daytime average level of the physiological signal for the first time period and determine the first threshold based on the all day average level and the daytime average level.
4 . The medical device of claim 3 , wherein the processing circuitry is further configured to compute a nighttime average level of the physiological signal for the first time period and determine the first threshold based on the all day average level, the daytime average level, and the nighttime average level.
5 . The medical device of claim 4 , wherein the processing circuitry is further configured to determine the second threshold based on the all day average level, the daytime average level, and the nighttime average level, and control the stimulation generator for the next time period by at least comparing the level of the physiological signal over the current time period immediately preceding the next time period to the second threshold, and, in response to the physiological signal exceeding the second threshold continuously during the current time period, adjust the stimulation amplitude for the next time period to a level that causes the physiological signal to no longer exceed the second threshold.
6 . The medical device of claim 1 , wherein the first time period is a week.
7 . The medical device of claim 1 , wherein the processing circuitry is configured to obtain an average sample level of the measurements taken over a 10 minute span during the first time period, and wherein the processing circuitry is configured to compute the first average level from a collection of the average sample levels obtained during the first time period.
8 . The medical device of claim 7 , wherein the first time period is represented by a first in first out buffer and the processing circuitry is configured to continuously obtain the average sample levels at the 10 minute intervals to maintain the collection of the average sample levels within the first in first out buffer.
9 . The medical device of claim 8 , wherein the processing circuitry is configured to continuously compute the first average level at the 10 minute intervals and compute the first threshold on a daily basis.
10 . The medical device of claim 1 , wherein the first threshold is a first lower threshold and the second threshold is a second lower threshold, and wherein the processing circuitry is configured to:
control the stimulation generator to deliver the stimulation signal based on the first lower threshold and a first upper threshold;
adjust, based on the first average level of the physiological signal, the first upper threshold to a second upper threshold;
control the stimulation generator for the next time period by comparing the level of the physiological signal over the current time period immediately preceding the next time period to the second upper threshold; and
in response to the level of the physiological signal exceeding the second upper threshold during the current time period, adjusting the stimulation characteristic of the stimulation signal for the next time period to the level that causes the physiological signal to no longer exceed the second upper threshold.
11 . A method of controlling stimulation therapy, the method comprising:
producing a stimulation signal having a stimulation characteristic at a stimulation generator of the implantable medical device;
controlling, by processing circuitry, the stimulation generator to deliver the stimulation signal based on a first threshold;
obtaining, by the processing circuitry, a measurement of a physiological signal sensed via electrodes;
computing, by the processing circuitry, a first average level of the physiological signal for a first time period;
adjusting, by the processing circuitry, a first threshold to a second threshold based on the first average level of the physiological signal; and
controlling, by the processing circuitry, the stimulation generator for a next time period by comparing the level of the physiological signal over a current time period immediately preceding the next time period to the second threshold;
wherein controlling the stimulation generator for the next period comprises, in response to the level of the physiological signal exceeding the second threshold during the current time period, adjusting, by the processing circuitry, the stimulation characteristic of the stimulation signal for the next time period to a level that causes the physiological signal to no longer exceed the second threshold, wherein the physiological signal comprises local field potentials (LFPs) within neurological tissue and the stimulation characteristic is amplitude.
12 . The method of claim 11 , wherein the second threshold is a second upper threshold, and wherein the method further comprises:
determining a second lower threshold based on the first average level of the physiological signal; and
controlling the stimulation generator for a next time period by:
comparing the level of the physiological signal over the current time period immediately preceding the next time period to the second lower threshold; and
responsive to the physiological signal being below the second lower threshold continuously during the current time period, adjusting the stimulation characteristic for the next time period to a level that causes the physiological signal to no longer be below the second lower threshold.
13 . The method of claim 11 , wherein the first average level of the physiological signal is an all day average level, and wherein the method further comprises computing, by the processing circuitry, a daytime average level of the physiological signal for the first time period and determining, by the processing circuitry, the first threshold based on the all day average level and the daytime average level.
14 . The method of claim 13 , further comprising computing, by the processing circuitry, a nighttime average level of the physiological signal for the first time period and determining, by the processing circuitry, the first threshold based on the all day average level, the daytime average level, and the nighttime average level.
15 . The method of claim 11 , further comprising:
determining, by the processing circuitry, the second threshold based on the all day average level, the daytime average level, and the nighttime average level; and
controlling, by the processing circuitry, the stimulation module for a next time period by comparing the level of the physiological signal over the current time period immediately preceding the next time period to the second threshold and, responsive to the physiological signal exceeding the second threshold continuously during the current time period, adjusting the stimulation characteristic for the next time period to a level that causes the physiological signal to no longer exceed the second threshold.
16 . The method of claim 11 , wherein the first time period is a week.
17 . The method of claim 11 , further comprising obtaining, by the processing circuitry, an average sample level of the measurements taken over a 10 minute span during the first time period and computing, by the processing circuitry, the first average level from a collection of the average sample levels obtained during the first time period.
18 . The method of claim 17 , wherein the first time period is represented by a first in first out buffer, and wherein the method further comprises continuously obtaining the average sample levels at the 10 minute intervals to maintain the collection of the average sample levels within the first in first out buffer.
19 . A medical device comprising:
a stimulation generator configured to produce a stimulation signal having a stimulation characteristic; and
processing circuitry configured to:
control the stimulation generator to deliver the stimulation signal based on a first threshold;
obtain a measurement of a physiological signal sensed via electrodes,
compute an all day average level of the physiological signal for a first time period,
compute a daytime average level of the physiological signal for the first time period; and
adjust the first threshold to a second threshold based on the all day average level of the physiological signal and the daytime average level of the physiological signal,
control the stimulation generator for a next time period by comparing the level of the physiological signal over a current time period immediately preceding the next time period to the second threshold,
wherein to control the stimulation generator for the next time period, the processing circuitry is configured to, in response to the level of the physiological signal exceeding the second threshold during the current time period, adjust the stimulation characteristic of the stimulation signal for the next time period to a level that causes the physiological signal to no longer exceed the second threshold.
20 . The medical device of claim 19 , wherein the processing circuitry is further configured to:
compute a nighttime average level of the physiological signal for the first time period; and
determine the first threshold based on the all day average level, the daytime average level, and the nighttime average level.