Patent ID: 7155280

Claim:
A cardiac pacemaker, comprising: a pacing channel for delivering pacing pulses to a heart; an exertion level sensor for measuring a patient's exertion level; a controller for controlling the delivery of pacing pulses through the pacing channel in accordance with a programmed mode, wherein the controller is programmed to pace a heart chamber in a demand mode at a sensor-indicated rate equal to a lower rate limit plus a function of the measured exertion level multiplied by a rate-response factor; wherein the controller is further programmed to compute the function of the measured exertion level as the amount, if any, by which a short-term average of the measured exertion level exceeds a long-term average of the measured exertion level; and, wherein the controller is further programmed to modulate the lower rate limit as a function of the long-term average of the measured exertion level and the maximum and minimum values of the long-term average of the measured exertion level during a defined extended time period, wherein the controller is programmed to modulate the lower rate limit according to the following formula: LRL=LRL min +( LRL max −LRL min )*( EXL lta −EXL ltaMin )/( EXL ltaMax −EXL ltaMin ) where LRL is the lower rate limit to be used by the pacemaker, LRL min and LRL max are programmed minimum and maximum values, respectively, for the LRL, EXL lta is the long-term average of the measured exertion level, EXL ltaMin is the minimum value of EXL lta during the defined extended time period, and EXL ltaMax is the maximum value of EXL lta during the defined extended time period.