Patent GB-1224510-A (GB)
Title: Sphygmomanometer
IPC: A61B5/022
Filed: 1968-12-24
Abstract: 1,224,510. Sphygmomarometers. PHELPS DODGE COPPER PRODUCTS CORP. 24 Dec., 1968 [31 Jan., 1968], No. 61253/68. Heading A5K. [Also in Division G1] A sphygmomarometer, for automatically determining blood pressure, comprises an inflatable occluding cuff 32 for placing around the upper arm, a second blood-pulse detecting cuff 60, for placing around the lower arm, a pressure transducer for detecting the pressure in the cuff 32 and a pulse-detecting transducer for detecting pulses in the artery under the cuff 60. A pressure bulk 10 is used to inflate the cuffs through conduits 16, 41 and 42 and via a non-return valve 11 and a pneumatic integrator 12, which is designed to increase the pressure in the cuffs gradually by absorbing the sharp constrictions of the bulb 10. After the pressure in the pneumatic system reaches approximately 30 mm. Hg above atmospheric a solenoid winding 36, energised by control logic (850), closes a normally-open valve 34, thereby isolating a closed pulse detecting pneumatic system including the cuff 60, a non- flexible air reservoir 40, and a metallic chamber 44. This chamber comprises two compartments 46 and 48, the former being connected in the pneumatic system and containing a tungsten wire 50 having a non-linear resistance characteristic, and the latter compartment 48 being closed and isolated from the pneumatic system and containing a similar resistance wire 52. These wires are placed in adjacent arms of a pulse-detecting bridge circuit (400). After the valve 34 is closed, the pressure in the cuff 32 is further raised to above the maximum expected systolic blood pressure. The pressure in the occluding cuff 32 is detected by a transducer comprising a potentiometer 20 connected to measuring circuitry (800), the position of the potentiometer top being determined by the pressure in the conduit 16 and the cuff 32. A permanently-open exhaust orifice 24 is connected to the conduit 16 to slowly relieve the pressure in the cuff 32 after cessation of pressurisation. When the pressure in the cuff 32 equals and is then less than the systolic blood pressure, blood pulses flow through the artery under the cuff 60 and cause a slight expansion of its inner wall displacing some air toward the reservoir 40. The air flows through the chamber 46 and cools the wire 50 hence unbalancing the detector bridge and giving rise to an electrical output pulse. The amount of air-flow, and hence the amplitude of the electrical pulse, is a direct function of the blood pulse amplitude. The systolic blood pressure equals the pressure in the cuff 32 at which the pulses start and electronic logic and measuring circuitry indicates this pressure on a meter (740). This circuitry includes systems to check that the measured signal is not a spurious signal, the systems being arranged to store the systolic pressure indicated by the occluding pressure transducer and lock the systolic pressure meter (740) onto this pressure only when two pulses of increasing amplitude are received from the pulse detector in a predetermined time. Reliable diastolic blood pressure readings are said to be indicated by the pressure transducer when a signal from the pulse-detecting bridge is received having a peak amplitude 0.7 of the largest peak pulse amplitude measured as the pressure in the cuff 32 decreases in a given test. Logic circuitry detects such a pulse and locks a diastolic bloodpressure meter (1240) to read the pressure obtaining in the cuff 32 at that instant. When both the systolic and diastolic blood pressures have been measured and displayed, the logic and control circuitry opens an air valve 26, reducing the pressure in the pneumatic system to atmospheric. When the pressure in the cuff 32 and conduit 16 is reduced to below 30 mm. Hg gauge, the valve 34 is also opened allowing the cuff 60, conduit 42, reservoir 40 and chamber 46 to exhaust through the valve 26. A resetswitch (1135) resets all the logic circuitry and unlocks the systolic (740) and diastolic (1240) blood pressure meters for another test.