Patent GB-990381-A (GB)
Title: Blood pressure apparatus
IPC: A61B5/022
Filed: 1961-12-06
Abstract: 990,381. Sphygmometers. AIR-SHIELDS Inc. Dec. 6, 1961 [Dec. 9, 1960], No. 43689/61. Heading A5K. Blood pressure sensing apparatus comprises a cuff adapted to be distended by the admission of fluid under pressure greater than the blood pressure, pressure-sensing means connected to the cuff when so distended, means for bleeding off the pressure from the cuff, transducer means responsive to a pulse during said bleeding off, and circuit means responsive to the translation of a pulse by the transducer means to disconnect the pressure-sensing means from the cuff. A cuff 10 is connected by a flexible tube 11 to a duct 12 connectible by a normally closed solenoid-operated valve 14 to an air-pressure source 13, and provided with a bleed port 15. Pressure gauges 16 and 18 are connectible by respective normally closed solenoid-operated valves 17 and 19 to duct 12, and a normally open relief valve 20 is also connected to duct 12. During an initial period valves 14, 17 and 19 are opened and valve 20 is closed to charge duct 12 to a pressure in excess of the systolic pressure. Valve 14 then closes and air pressure in duct 12 falls progressively till it reaches the systolic pressure, when the resultant pulse is picked up by a microphone connected in a circuit so arranged as to close valves 17 and 19. The circuit is also so arranged that valve 19 opens momentarily at each subsequent pulse. Gauge 16 thereby registers the systolic pressure, and gauge 18 the pressure of the last transmitted pulse, namely, the diastolic pressure. A step-down transformer 42 is connected by the poles 44, 45 of a two-way switch and lines 46, 50 to a pair of micro-switches 47, 51 adapted to be closed by a pair of coupled cams 49, 53 which complete one rotation in 4 minutes. The cams are so arranged that both switches are closed for 3 seconds, when lines 58 and 59 are connected to transformer 42, while switch 47 remains closed for the succeeding 27 seconds when earthed line 58 is disconnected and line 59 remains live. Connected between lines 58 and 59 are the solenoid valve 14, a suppression relay 25 and a relay 26a for unlatching the armature 61 of a switch relay 26. Armature 61 in the unlatched condition connects contacts a and b and contacts d and e. In the latched condition armature 61 connects contacts b and c and contact e to a blind contact f. Valves 17 and 19 are connected between earth returns X and contacts e and b respectively. Line 59 is connected, via a line 64, to contacts a and d. Valve 20 is connected between line 59 and an earth return X. A microphone 21 is connected to an amplifier 23, the output of which is connected via a sensitive relay 66 to a slave relay 24. The arrangement is thereby such that during the initial 3 second period, valves 14, 17 and 19 are opened and valve 20 is closed to charge duct 12, while relay 25 is energized to suppress the transmission of pulses from microphone 21 to relay 24, and relay 26a is energized to withdraw latching armature 60 from the latched armature 61 of relay 26. At the end of the three-second period, valve 14 closes and the pressure in duct 12 falls progressively until the systolic pressure is reached, when a pulse transmitted from the microphone closes the contacts of relay 24 to connect line 59 via a line 68 to the solenoid 69 of relay 26 and to contact c, armature 61 being held in the energized position by the armature 60 of relay 26a. The connection to valve 17 will thereby be broken and gauge 16 will register the systolic pressure, while a connection to valve 19 will be momentarily established via the contacts b and c. At each successive pulse valve 19 will thereby be opened momentarily, and consequently on the cessation of pulses gauge 18 will register the diastolic pressure. A lamp 72 connected in parallel with valve 19 lights up each time the latter is energized. At the end of the 30- second period switch 47 opens and valve 20 thereby opens to exhaust duct 12. Microswitches 48, 52 connected in parallel with switches 47, 51 and arranged with their actuating elements disposed at 180 degrees from those of the latter, may be placed in circuit by a switch 54, 55 to reduce the cycle time to 2 minutes. For manual operation, switch 44, 45 is shifted from contacts 2 to contacts 1, whereby line 59 alone is live, and operation then controlled by a manual switch 73 connecting line 58 to an earth return X.