US Patent No. 3,926,179 December 16, 1975
This invention provides apparatus for accurately measuring and continuously monitoring blood pressure. The apparatus comprises a blood pressure probe adapted to engage a body member such as one arm of the patient. The probe includes a pressure applying member for engaging the surface of the body member over an artery which is near the surface. For example, the pressure applying member may be located over the radial artery in the wrist of the patient’s arm. The probe also includes pressure exerting means, such as a solenoid, for pressing the pressure applying member against the surface of the body member, so as to produce partial flattening of the artery. The pressure app lying member includes a pressure sensor adapted to engage the surface of the body member over the artery for sensing the blood pressure pulses in the artery. The sensor includes a transducer for producing electrical signals corresponding to the blood pressure pulses. The apparatus includes control means for operating the pressure exerting means to maximize the electrical signals corresponding to the pulse pressure. For example, a feedback circuit may be provided to energize the solenoid to such an extent as to maximize the pulse pressure signals. Generally, the signals will be maximized when the artery is flattened approximately halfway. The true or corrected waveform of the blood pressure signals may be derived and displayed on an oscilloscope for continuously monitoring the blood pressure variations. Means may also be provided for deriving and indicating the systolic and diastolic blood pressure values, and also the pulse pressure. The blood pressure measuring apparatus is highly accurate, continuous in operation, and noninvasive, in that it is not necessary to invade the artery. Moreover, the function of the artery is not impaired, since the device is nonocciusive. The blood pressure probe, together with the supporting apparatus, is called a tonometer.