System for measuring physical parameter utilizing vibration transmission

Abstract

A physical parameter measuring system is provided which measures a physical parameter such as a blood pressure of a person using oscillation transmission. The system includes a phase detector, an A/D converter, an arc center determining circuit, and a phase angle determining circuit. The phase detector detects a phase of a sensor signal produced, in sequence, by monitoring oscillations which are applied by an exciter and transmitted through a living body to map the signal on a two-dimensional plane as a sample point. The A/D converter converts the sample point signal into a digital sample point signal in sequence. The arc center determining circuit determines a center of an arc defined by a distribution of the sample points mapped for a given period of time. The arc determining circuit selects the sample points which are located at an interval greater than a given reference sample-to-sample distance to form a sample group consisting of at least three of the selected sample points and determines a center of a circle passing through the sample group as the center of the arc. The phase angle determining circuit determines a phase angle of the sample point as viewed from the arc center determined by the arc center determining circuit and provides it as a parameter used to determine a physical parameter of the subject.