Comparison of four beat-to-beat cardiotachometer designs

Beat-to-beat cardiotachometers calculate the heart rate in beats per minute from two adjacent R wave pulses. These differ from cardiotachometers, which simply count the number of R wave pulses in a minute. The paper describes four beat-to-beat cardiotachometer systems using (a) divide-by-n counter; (b) calculator chip; (c) 1/t clock; (d) dual analogue voltage ramp. For each type a detailed description of operating principles based on a block diagram is presented. This is followed by a discussion of the performance of each system, the compromises that are required and the fundamental limitations of each system. One practical design of each system has been built and used successfully in a medical or biomedical situation. These are also described and compared.