Patent GB-1253501-A (GB)
Title: Apparatus for following systolic or diastolic blood pressure
IPC: A61B5/022
Filed: 1970-01-06
Abstract: 1,253,501. Monitoring diastolic and systolic blood pressure. INTERNATIONAL BUSINESS MACHINES CORP. 6 Jan., 1970 [8 Jan., 1969], No. 569/70. Heading A5K. [Also in Division G3] An apparatus for following and monitoring the diastolic or systolic blood pressure of a patient comprises an inflatable occluding cuff 601 (Fig. 4) for applying pressure to an artery, a microphone (Fig. 1) for detecting Korotkoff sounds, logic voltage comparators 103, 104 which compare the detected sounds with reference levels V1, V3 and produce output signals corresponding to acceptable and loud sounds respectively, counters 107, 108 for counting each signal during a sampling period, logic circuits (Figs. 2 and 3, not shown) which receive the outputs of said counters and produce command signals which are fed together with actual cuff pressure signals from a strain gauge 604 to a pressure servo system 605 for varying the cuff pressure toward the diastolic or systolic blood pressure depending upon which is being monitored. The pressure servo maintains the cuff pressure constant throughout a sampling period as determined by a pre-set counter 114 (Fig. 1), which counts heart beats detected by EKG electrodes,-the period may be five heart beats. For a Korotkoff pulse to be acceptable it should occur within a certain lag time after the QRS portion of the EKG waveform detected by the electrodes. The lag time is provided by delay unit 113. After a predetermined number of heartbeats have been counted a single shot unit 115 is energized and opens AND gates 109, 110 so that the contents of the counters are released to analysing and decisional logic circuits Fig. 2 (not shown). The logic circuitry (Fig. 2, not shown) samples the signals from the counters 107, 108 and from systolic and diastolic blood pressure measurements derived by logic circuitry (Fig. 3, not shown) and produces UP and DOWN command signals which are applied to single shot units (301), (302), (Fig. 3). Both up and down signals are also applied to reset the counters 107, 108, 114 in Fig. 1 to start a new sampling period. A register (309) Fig. 3 (not shown) contains a digital number equal to the prior average systolic (or diastolic) blood pressure. The up and down signals from the decisional logic operate respective single shot units (301), (302) and cause pre-set pressure increment (equivalent to 4 mm. mercury) to be added to or subtracted from the value held in the register (309). The new digital value is converted to an analogue value in a D/A converter and fed to a comparator 605 (Fig. 4) of a pressure servo. In Fig. 4, a strain gauge 604 senses the actual pressure in cuff 601 and produces an output which is compared in a servo comparator 605 with an input 3A from the D/A converter and which is significant of the required pressure. The servo 605 operates a solenoid valve 602 or 603 to inflate or deflate the cuff to maintain a zero difference between actual and required pressure. An accurate reading of the systolic or diastolic blood pressures is obtained by averaging the cuff pressures over a plurality of sampling periods. Only those cuff pressures which result in at least one Korotkoff sound, being averaged. This averaging is effected by counters, adders, dividers in Fig. 3, the output from a divider (508) representing in digital form the systolic blood pressure. Like logic components obtain the diastolic pressure.