The volume-oscillometric and volume-compensation methods, previously developed by us, are a useful and helpful means for non-invasive measurement of blood pressure. These methods are usually applied for digital arterial pressure measurement. During the continuous measurement of finger arterial pressure by the volume-compensation method, a band-type cuff wrapped around the finger has been conventionally used. However, this causes venous blood congestion at the distal portion of the cuff site due to occlusion of all veins under the cuff, resulting in uncomfortable and painful feeling for a subject. In order to reduce such congestion, we have previously designed a disk-type cuff unit for local pressurization to the digital artery. This local pressurization-cuff technique needs practice in proper attachment of the cuff unit: It is important to correctly place the cuff just above the digital artery concerned. It is therefore necessary to facilitate the determination of a proper cuff-position for practical use. To address this practical problem, the present study describes a definite method of this determination based on the nonlinear nature of arterial pressure-volume characteristics. We have also investigated the cuff-pressure transmission through the tissue by a finite element method. From the experimental and numerical investigations, we have developed the determination method together with a new cuff unit. To evaluate accuracy of the blood pressure measurement with this method, comparison experiments with the direct measurement of radial artery were made using healthy volunteers under informed consent. The results clearly indicate that a proper cuff-attachment could be easily achieved by this determination method and that the indirect finger arterial pressure showed good agreement with the direct radial artery pressure. The present technique with the volume-compensation method seems available for long-term as well as ambulatory arterial pressure monitoring.
