Abstract: A rate-responsive pacemaker measures a patient's level of activity and stores the results in an activity level histogram. The patient's average level of activity is maintained as a running average. Based on a prescribed base pacing rate, a prescribed maximum pacing rate, the average level of activity, and the measured levels of activity stored in the activity level histogram, the rate-responsive pacemaker automatically calculates the slope of the pacemaker transfer function. An activity deviation histogram is also maintained. Analysis of the activity deviation histogram allows the pacemaker to determine if the patient was usually inactive for an extended period of time, and to inhibit an automatic slope calculation under such conditions. If a patient desires to reach a prescribed target heart rate during exercise, the slope may be calculated using the target heart rate and a prescribed fraction of time each week that the patient devotes to exercise.

Abstract: A system and method are provided for modulating the base rate of a transfer function for a rate-responsive cardiac pacemaker. Activity sensor measurements are used to derive activity variance measurements, which in turn are used to modulate the base pacing rate. In one embodiment, a histogram is used to store activity variance measurements collected over a period of about a week. The histogram is used to derive an activity variance threshold, which is compared to current activity variance measurements to determine if the patient is sleeping. If the patient is deemed to be sleeping, the pacing rate is set to a rate that comfortably meets the patient's low metabolic demands during sleep. In alternative embodiments, the activity variance measurements are applied to a base rate slope to modulate the base pacing rate.