CARDIAC PACING RESPONSIVE TO MULTIPLE ACTIVITY TYPES

A variable rate implantable pacemaker responsive to patient exercise senses and distinguishes between distinct and different types of physical activity by the patient, and is programmed to respond by generating different response functions to control the pacing rate according to the specific type of physical activity detected. The response functions are algorithms, taken from the behavior of a healthy person with normally functioning cardiovascular system, of heart rates versus an appropriate parameter of a signal produced by a sensor carried by the patient, for the different types of activity requiring different algorithms, in which the parameter value varies in a predetermined way with exercise. The distinction between the different types of physical activity is derived by techniques including calculation of the absolute level of the sensor signal over time, calculation of the standard deviation relative to the mean of the parameter value of the sensor signal over time, performing pattern recognition by spectral analysis of the sensor signal and organizing different physical stress modes by comparing the various templates so observed with templates representing the different types of physical activity of interest, to determine the specific type of activity in which the patient is engaged, for use in controlling pacing rate.