Blood-pressure gauge and method for measuring blood pressure

A blood-pressure gauge comprising:

• a pump;
• a bag-shaped pressure cuff that is connected to the pump, and extends along a circumferential direction of a measurement site in order to received supply of a pressurizing fluid from the pump;
• a sensing cuff that is not connected to the pump, includes a first sheet disposed to face an inner peripheral surface of the pressure cuff and a second sheet facing the first sheet, is configured in a bag shape, and extends in a circumferential direction so as to cross an artery passing portion of the measurement site;
• a back plate that is interposed between the pressure cuff and the sensing cuff, extends along a circumferential direction of the measurement site, and transmits a pressing force from the pressure cuff to the sensing cuff;
• an opening valve that is connected to the sensing cuff and is in either an open state in which an inside of the sensing cuff is conducted to outside air or a closed state in which the inside of the sensing cuff is not conducted to the outside air;
• a pressure cuff controller that controls the pressure cuff to either a compression state in which a fluid is supplied to the pressure cuff and the measurement site is compressed via the pressure cuff or a release state in which the fluid is discharged from the pressure cuff and the compression of the measurement site via the pressure cuff is released;
• an opening valve controller that controls the opening valve to be in either the open state or the closed state;
• and
• a blood pressure calculator that calculates a blood pressure on a basis of a pressure change of the sensing cuff when the opening valve is in the closed state,
• wherein the sensing cuff has restorability to make a volume in the sensing cuff a predetermined volume when the opening valve is in the open state.