Pacemaker with improved distributed rate pacing

A rate responsive implantable pacemaker comprising:

• a rate control parameter generator for generating a rate control parameter;
• a pulse generator for generating pacing pulses on demand in accordance with a rate control signal;
• and
• a controller including a histogram generator for generating an initial histogram including a first initial histogram portion and a second initial histogram portion for said rate control parameter, a normalizer for generating a normalized histogram from said initial histogram, said normalized histogram including said first initial histogram portion for a first rate range and a normalized histogram portion for a second rate range, said normalized histogram portion having predetermined characteristics, and a selector for selecting said rate control signal in accordance with said normalized histogram in response to an instantaneous rate control parameter, wherein said rate control signal is determined by said initial histogram portion when said instantaneous rate control parameter corresponds to said first rate range and wherein said rate control signal is determined by said normalized histogram portion when said instantaneous rate control parameter corresponds to said second rate range.

A method of generating pacing pulses on demand for a patient using an implantable pacemaker, said method comprising the steps of:

• generating a rate control parameter;
• generating an initial parameter histogram for said rate control parameter over an extended time period of at least a day, said initial parameter histogram including a first initial histogram portion and a second initial histogram portion;
• converting said initial parameter histogram into a normalized parameter histogram having predetermined characteristics, said normalized parameter histogram including a first normalized histogram portion corresponding to said first initial histogram portion and a second normalized histogram portion generated by normalizing said second initial histogram portion;
• selecting a control rate based on said normalized parameter histogram using an instantaneous rate parameter, wherein said control rate is selected using said first normalized histogram portion for a first range of said instantaneous rate parameter and wherein said control rate is selected using said second normalized histogram portion for a second rate of said instantaneous rate;
• and
• generating demand pacing pulses at said control rate.

An implantable pacemaker comprising:

• a pacing pulse generator for generating pacing pulses in accordance with a control signal;
• a cardiac sensor for sensing intrinsic cardiac beats and for generating corresponding sensed signals;
• a metabolic sensor for sensing a metabolic demand and for generating a corresponding metabolic demand signal;
• and
• a controller for generating said control signal responsive to said sensed signal and said metabolic demand signal;
• a histogram generator for generating an initial demand histogram for said metabolic demand, an initial sensor histogram for said cardiac beats and a normalized histogram derived from one of said initial histograms in accordance with a preselected criteria, said normalized histogram including a portion of said one initial histogram, and a normalized histogram portion , and a demand generator for generating said demand rate from said normalized histogram.