ELECTRICAL ADMITTANCE CUFF FOR NONINVASIVE AND SIMULTANEOUS MEASUREMENT OF HEMATOCRIT, ARTERIAL-PRESSURE AND ELASTICITY USING VOLUME-OSCILLOMETRIC METHOD

An improved technique based on the electrical admittance cuff was desi gned for the non-invasive measurement of haematocrit (Hot), together w ith blood pressure (BP) and arterial elasticity represented as volume elastic: modulus (E,), in human fingers. This device is made of a rigi d annular chamber installed with a surrounding thin-walled tube (cuff) , which is filled with electrolyte solution. A tetrapolar method is us ed to detect the admittance signals, both in the solution and in a fin ger segment placed through the cuff With this device, it is theoretica lly shown that the resistivity of blood flowing into the segment is eq ual to that of the solution multiplied by the ratio of the admittance variation in the solution to that in the segment. Thus, the blood resi stivity and therefore Hct can be non-invasively determined from the el ectrolyte resistivity and these two admittance variations. On Vie othe r hand, BP and E, are also simultaneously measured from the admittance signals following the gradual change of the chamber pressure based on the volume-oscillometric method. Experiments were successfully made i n 14 subjects, showing that the indirect Hct values agreed well with t he direct Values obtained from sampled blood and that this simle techn ique was significant for the non-invasive ad simultaneous measurement of these physiological variables.