Abstract: An implantable device which acquires physiological data and status information. The physiological data is compressed, reducing the memory requirement of the implantable device and/or increasing the amount of data that can be stored. The compression technique uses variable resolution while maintaining desired accuracy. The physiological data, such as heart beat interval time, is converted into a digital value. The digital representation then is divided into sub-ranges, and various resolution values are assigned to each sub-range. Each resolution is selected to stay within the desired accuracy. The interval time is divided by the particular resolution to obtain a digital value for the interval time within that range. The digital value then is corrected based upon the sub-range to obtain the compressed encoded digital value, which can then be stored in memory together with other desired data.

Abstract: A pacemaker with a variable, asynchronous minimum heart rate and a second variable, synchronous heart rate. The second, variable heart rate has an absolute minimum, lower than the asynchronous minimum heart rate, which is preselected by the attending physician. The minimum heart rates can vary, conditioned upon sensed physiologic need. The cardiac pacemaker attempts to reestablish synchrony in every cycle, even if the intrinsic or natural atrial heart rate is below the asynchronous minimum heart rate in that cycle and can maintain cardiac synchrony at lower rates, thereby increasing cardiac efficiency and minimizing strain on the heart.

Abstract: A state machine for automatic gain control of sensing functions in an implantale cardiac stimulator. The state controls sensing levels based on present sensed conditions and on the prior state of the heart. Different rates of adjustment are selected under varying conditions so that the gain level for sense amplifiers can be adjusted without significant overshoot. The state machine comprises a set of four conditions or states together with interconnections or logical paths from one state to another. The rate of adjustment of sense amplifier gain is based on the path traversed in the state machine so that different effective time constants for the control function may be used for different conditions.