Development of non-invasive and ambulatory monitoring system for cardiovascular haemodynamic parameters inclusive of cardiac output and blood pressure

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In recognition of the increasing need for health maintenance and disease prevention, an attempt was made to develop a non-invasive and ambulatory system capable of monitoring various cardiovascular parameters, naturally including cardiac output and blood pressure, during daily activities in a fully automatic manner. It is based on the electrical admittance cardiography and the volume-oscillometric method. The system mainly consists of (i) a finger cuff with a photo-plethysmographic sensor for detecting blood volume changes and tetra-polar electrodes for detecting the bio-admittance signal, (ii) a portable unit (104x64x32mm, 160g) which allows necessary measuring procedures and control, together with signal processing and data storage in a CMOS RAM,using a single-chip microcomputer, and (iii) data reproducing and analysing unit using a personal computer system. Asubject carries the former two during monitoring Long-term monitoring is made with a desired interval of 2,5 and 10 min preset … More , and after the monitoring the stored data are reproduced and analyzed by the computer, being displayd pulse rate (HR), pulse interval (PI), systolic (SBP)/meanMBP)/diastolic pressure (DBP), ventricular ejection time (Ts), stroke volume (SV), cardiac output (CO=HR・SV), peripheral vascular resistance (Rp=MBP/CO) and rate pressure product (RPP=HR・SBP) as an index of cardiac oxygen consumption in a trend manner.Besides the development of thissystem, a portable instrument for long-term ambulatory monitoring of human posture chnge has been designed, taking physiological importance and usefulness of such information along with cardiovascular haemodynamic parameters into consideration. It is based on the fact that almost all human postures in daily life, e. g. standing, sitting, lying, walking etc., can be estimated from the angles corresponding to the gravitational direction in three portions ; chest, thigh and lower leg. The instrument (58x94x25mm, 130g) includes preamplifiers, an A/D converter (6bit ; sampling interval, 0.1,0.2,0.5,1s), and a CMOS RAM (2MB) for storing the angles from electro-magnetic inclinometers placed on the three portions.Performance, availability and stability for monitoring by these two systems have been tested with successful and satisfactory results. Lots of 24-hour monitorings and data analyzes regarding the interactiive relation among the cardiovascular variables and the periodic construction of their circadian fluctuations using the maximum entropy method (MEM) have also been successfully made, suggesting that each proposed system appears promising as a method for use not only in further advanced basic and clinical cardiovascular researches but also in case of self care at home. Less