(a) Field of the Invention
The invention relates to an automatic noninvasive blood pressure monitor, i.e. an instrument for measuring the blood pressure in man on arteries being compressible from the surface by means of a pressure cuff or a pelotte equipped with a plethysmographic gauge, such as an impedance or a photo-electric one, which gauge is connected through at least one amplifier and a phase corrector to an electro-pressure transducer. All these components constitute the closed loop of a servosystem which continuously and instantaneously changes the pressure in the cuff and maintains thus the volume of the artery at a value corresponding to the zero tension of the arterial wall. The pressure within the cuff thus follows the instantaneous value of intraarterial pressure. In such instruments automatic setting and correction of the setpoint and gain is also possible.
(b) Description of the Prior Art
Similar instruments are known from the patent literature, e.g. Czechoslovak patent specification No. 133205, U.S. patent specification No. 4,510,940, as well as from articles in medical and technical journals. The instruments known up to now, however, either have no automatic initial setting of the setpoint and gain, or have no correction of these parameters during the measurement. Although an instrument with such a correction has been proposed, the correction is performed during short-lasting interruption of the measurement. Another instrument proposed is equipped with an additional cuff placed on another circulatory region so that a pair of cuffs is necessary. The proposed instruments permit measurement of the blood pressure on arteries of the finger or of another region which can easily be transilluminated, however continuous blood pressure measuring is impossible on other arteries especially on larger ones.