Patent GB-1376737-A (GB)
Title: Clinical measurement of blood pressure
IPC: A61B5/022
Filed: 1971-09-08
Abstract: 1376737 Sphygnomanometers WILKINSON SWORD Ltd 11 Aug 1972 [8 Sept 1971] 41812/71 Heading A5K [Also in Division G1] A sphygnomanometer comprises an inflatable cuff 5, Fig. 1, a reservoir 8 having a leak valve 12, a pivoted lever 22, having a chart marker 30 which is movable relative to the lever in directions generally transverse to the pivotal movement thereof, first pressureresponsive means 18 responsive to the pressure in cuff 5 and reservoir 8 and operative to move the lever 22 about its pivot, and second pressure-responsive means responsive to pressure variations in the cuff, caused by blood pulsations as the cuff pressure falls below systolic pressure, and operative to energise a motor 26 to oscillate the marker 30 relative to lever 22. The means 18 comprises a rolling-diaphragm piston-and-cylinder, or a bellows arrangement, connected to or located in reservoir 8 and operative to move lever 22 by means of a rod 20 as the pressure in the cuff falls following inflation by a pump 14. A temperature-sensitive resistor 52 senses blood-pulsations causing air pulses in a line 10 below the systolic pressure, and voltage variations across resistor 52 are effective to oscillate the marker, diastolic pressure being indicated by a decrease in oscillation amplitude. In a modification, Fig. 2 (not shown), lever 22 is a right-angle lever pivoted at the angle and carrying motor 26 at one end, the motor shaft carrying the marker, and the lever is pivoted in response to cuff-pressure variations by a nut on its other end engaged by a lead screw (90) driven by a motor (88) in one direction or the other in response to engagement of a contact on a bellows arrangement with one or the other of two contacts (80), (84) carried by the lever and connected to opposite poles of a centre-topped battery (86). A third embodiment, Figs. 3-5 (not shown) employs two overlapping cuffs and a bellows arrangement (134) in the reservoir 8 and responsive to cuff-pressure changes to swing a second-order lever 22 about a vertical axis, one end of the lever pivotally mounting a pulley (114) connected to one end of an arm (116) carrying the marker at its other end, the pulley (114) being oscillated relative to the lever by a drive cord (127) driven by a pulley (120) on the other end of the lever and driven by the lever-mounted motor. The lever is substantially balanced to avoid effects of tilting the apparatus. An electric circuit, Figs. 6A, 6B for driving motor 26, comprises a constant-current source 214 for the resistor 52, voltage variations on which are amplified by circuit 218 and passed to a differential amplifier 226 which supplies an output circuit 228 to drive motor 26 in the direction to adjust a potentiometer 240, coupled to the motor shaft, so that the difference beween the inputs to amplifier 226 from resistor 52 and from a potentiometer 248 is zero. Potentiometer 248 is manually adjustable to vary the trace position on a recording chart. A fault-sensing circuit 260 extinguishes a light-emitting diode 262 if open-circuiting of resistor 52 occurs, if the voltage on a +9V line 206 or a -9V line 210 falls too much towards a zero line 208, or if the output of a battery 200 becomes too low.