ASIC based recorders of electrophysiological signals
The ability of application specific integrated circuits (ASICs) to minimise the size and power consumption of electronic circuitry, makes their application to the design of ambulatory monitoring equipment, an attractive option. To this end, a multi-purpose mixed analogue and digital ASIC has been fabricated and incorporated into both a long-term recorder of adult heart rate (HR) and a recorder of electrophysiological signals. The adult HR recorder has been employed in a study of long-term daily HR patterns, which verified the ambulatory nature of this instrument, as well as its suitability for investigating HR variability. The electrophysiological signal recorder uses the ASIC to amplify, filter and digitise signals, which are then stored directly into static RAM. The analogue front-end of this instrument is flexible in terms of gain, bandwidth and sampling frequency allowing it be applied to a whole range of signals. This instrument has been used to record the antepartum fetal HR, as part of the development of an ambulatory, ASIC based recorder of fetal HR (FHR). These recordings have shown that a usable signal can be obtained from a mother in her home environment, whilst in various postures. The electrophysiological signal recorder has also been used to record the electrohysterogram (EHG), which is the name given to the electrical activity of the uterus, from abdominal electrodes during labour. A strong correlation was found to exist between tocographs derived from the EHG and tocographs produced by conventional means.