Simultaneous recording of arterial blood pressure, heart rate and ST segment in the ambulant patient: a new system

A system developed for the accurate and simultaneous recording of blood pressure, heart rate and ST segment level in the unrestricted patient is described, with laboratory validation and experience of its clinical use. The recording system uses a brachial artery cannula, a transducer/perfusion unit and a miniature f.m.e.c.g. tape recorder (Oxford Medilog Mark II), one channel of which is modified to enable the recording of a blood pressure signal. Data are initially presented as analogue trend charts, with further detailed analysis being carried out by an automated digital system with interactive software enabling data editing and averaging. Laboratory evaluation demonstrated that the modified blood pressure channel had a satisfactory frequency response, linearity, signal-tonoise ratio, and temperature stability. Battery depletion produced a consistent increase in gain which could be compensated by repeated calibration throughout the period of recording. The system has been found to be reliable when used for recording periods of up to 24 h on patients with ischaemic heart disease.