GB956094A - Automatic blood pressure meter - Google Patents

Abstract

956,094. Sphygmometers. GODART-MANIMEX N.V. July 13, 1962 [July 18, 1961; March 29, 1962], No. 27079/62. Heading A5K. An automatic blood-pressure measuring device including at least one inflatable cuff and a pressure meter, comprises a member responsive to the phase difference between the bloodpressure impulses in two closely-spaced inflatable cuffs 1, 2, the moment at which this phase difference disappears indicating when the pressure in the cuffs is the diastolic pressure. The two cuffs 1, 2 are attached to each other so that when applied to the patient's arm they overlap. One cuff 2 communicates with the other cuff 1 through conduits 11D, 15, a damping chamber 10 and conduits 14, 12 in a block 9, a thermistor 13 being located between conduits 14 and 12. A third cuff 7 located in a lower position on the same arm is connected to a pressure pulse detector 8. In use, the three cuffs are inflated until the pulse stops. The pressure in the cuffs is then gradually released through a passage 11F in the block 9. As the pressure falls, bloodpressure pulses in the two upper cuffs are out of phase and produce a cooling air current over the thermistor to vary the voltage across it. This voltage is amplified (Fig. 3) and then divided, a major portion being rectified and applied through a cathode follower 23 to a resistor 24. The other portion is similarly rectified and applied to a resistor 29 through a high discharge time constant condenser 27 and a cathode follower 28, the voltage across the resistor 29 thus being maintained at its maximum value. The diastolic pressure is measured when the pressure in the cuffs 1, 2 has fallen to such a value that blood starts to flow freely, the phase difference between the pulses in the two upper cuffs then disappearing so that the air current traversing the thermistor and the voltage generated across it suddenly fall to a minimum. This causes the voltage across resistor 24 to fall below that across the resistor 29. This operates a member 30, comprising a galvanometer, a galvanometer relay or an electromagnetic relay, which either indicates that the pressure in the cuffs should be measured or operates a switch 37 in a measuring circuit (Fig. 4), which includes a pressure meter 43. The measuring circuit includes a transducer having a core 33 which is moved between primary and secondary windings 31, 32 in dependence upon pressure in the uppermost cuff 1 so that a voltage proportional to the pressure is produced and applied through the switch 37 to a resistor 40 to be compared by the meter 43 with a fixed voltage applied to a resistor 41. Systolic pressure is also indicated by the meter 43, the switch 37 in the measuring circuit being operated by the detector 8 when blood-pressure pulses first appear in the lower cuff as the cuff pressure is falling. The detector comprises either a thermistor associated with the lower cuff or a transducer similar to that used in the measuring circuit.