A noise-protected digital heart ratemeter

In many experimental and diagnostic studies of heart rate, a simple averaging ratemeter is not satisfactory. This is due to the difficulty of obtaining an instrument response sufficiently fast to follow the rapid changes in rate, and at the same time keeping the ripple to an acceptable level. This paper describes an instantaneous-frequency cardiotachometer with some unique design features. It focuses particular attention on the digital period-to-frequency converter and a protection system designed to reject spurious noise pulses, such as those caused by muscle artefacts during exercise studies and those occurring during foetal heart rate monitoring.