Patent GB-1499516-A (GB)
Title: Patient's vital sign recording apparatus
IPC: A61B5/00
Filed: 1975-02-11
Abstract: 1499516 Recording apparatus AMERICAN OPTICAL CORP 11 Feb 1975 [11 Feb 1974] 5802/75 Headings G1J and G1N(E) Apparatus for recording physiological measurements from a patient, e.g. an electrocardiogram, comprises a looped record carrier 351 (a chart secured round a drum 200, or an endless loop passing round parallel rollers) which is moved continuously past a recording member 300 responsive to signals representing said measurements to trace a record thereof on the record carrier, and means 304, 302 to move the recording member 300 progressively in a direction transverse to the direction of motion of the record carrier, to prevent overlapping of the record trace. This transverse movement may be continuous, so that the trace has a helical base line, or stepwise, once per revolution of the record carrier. In Fig. 3, a rectangular chart 351 is wrapped round a drum 200 and its ends secured in a slot 201 by a clamp 352. A motor 305 rotates the drum via gears 307. A carriage 304 slidable on a rod 303 parallel to the drum axle 350 carries a galvanometer 301 driving a pen 300. A lead screw 302 driven from the gears 307 moves the carriage 304 downwards as the drum rotates, until a limit switch 306 is tripped to stop the motor 305. Fig. 5 shows part of a typical chart for a single input channel, the end 2 of the first trace line corresponding to the start 2 of the second trace line. If several input channels are used, each with a respective pen galvanometer, the carriage 304 must move far enough per drum revolution to avoid any overlap of traces for different channels. An E.C.G. signal from a patient 101 Fig. 1 passes via an amplifier 103, a selector switch 105, and a galvanometer drive circuit 107 to the galvanometer 109 (301 in Fig. 3) to control the pen 300 to produce an E.C.G. trace 502. Amplifier 103 output also passes to a heart rate module 117 which produces a D.C. voltage proportional to the heart rate. This is applied to a comparator 208 Fig. 2 in the selector switch 105 circuitry. A clockpulse generator 202 drives a counter 204 which in turn drives a ramp generator 206 supplying a second input to the comparator 208. When the two inputs are equal, the comparator energizes a monostable trigger circuit 214 to cause a switch 212 to block the E.C.G. signal 104 and inject a dither voltage 135 from a dither circuit 134 Fig. 1 to the galvanometer circuit 107 to cause the pen to make a mark 505 above a pulse rate scale 506 to record the mean pulse rate. This is arranged to occur once per revolution of the drum by electro-optical elements 113 on the drum which pass a fixed element on the base-plate 400 to cause a reset unit 213 to zero the counter 204 once per drum revolution. A manual input 116 to the trigger circuit 214 enables a mark 521 to be applied at any point on the trace to indicate an event, such as start of exercise, or administration of drugs. A reset switch button, when pressed, causes a speed control 150 to rapidly advance the motor 129 (305 on Fig. 3) to bring the starting line O of the chart under the pen (see straight trace up to 3'), the electro-optical elements 113 providing limit signals to return the motor to its normal speed.