System and method for adjusting sensor threshold in a rate responsive

Abstract

There is provided a rate responsive pacemaker system and method employing an activity-type sensor for deriving signals for determining pacing rate, wherein the activity sensor threshold is automatically adjusted as a function of monitored sensor output. In a preferred embodiment, activity counts are categorized on a histogram basis, and the histogram data is stored over a selected period of time. The activity data in histogram form is then analyzed and compared to predetermined criteria to determine whether threshold seems to be proper, or whether threshold adjustment is indicated. The adjustment algorithm provides different degrees of adjustment depending upon the circumstances. Specifically, where the data suggests too many or too few counts within an expected range, the threshold is adjusted as a function of whether the analyzed outputs are only a little bit out of the expected range or quite a bit out of the expected range. The algorithm also determines whether the sensor response accurately reflects patient rest. Another specific feature of the invention is determination of when the sensor is picking up false positives and thus improperly responding to extraneous signals such as patient's cardiac contractions.