Patent GB-1206014-A (GB)
Title: Apparatus for separating a data signal from a composite signal
IPC: A61B7/04
Filed: 1968-01-05
Abstract: 1,206,014. Electro medical measurements. INTERNATIONAL BUSINESS MACHINES CORP. 5 Jan., 1968 [9 Jan., 1967], No. 732/68. Heading H4J. [Also in Division G1] Automatic indirect systolic and diastolic pressure measurement is performed using circuits sensitive to 40 and 100 c/s. components occurring in an audio input generated by a microphone 11 (Fig. 1) positioned under an inflatable arm cuff 10 placed over a patient's brachial artery. Simultaneous outputs derived from these components occurring at a time when the patient's instantaneous circulatory pressure is stable or increasing cause a signal to be transmitted to a circuit which co-operates with a 1000 c/s. frequency selector to trigger a further circuit to record the instantaneous cuff pressure if the pulse does not occur within 50 ms. following occurrence of a 1000 c/s. component in the audio input. A further rejection circuit prevents the recording if a 1000 c/s. component is detected within 250 ms. following the occurrence of the blood pressure pulse. The cuff 10 is inflated by an air supply 12 controlled by a unit 14 which thereafter causes the cuff 10 to be deflated gradually. A pressure transducer 16 determines the cuff pressure and this is recorded in response to "digitize" and "record" signals (described later). The output of microphone 11 is transmitted through a double emitter follower buffer 24 to an amplifier 26 and thence to filter 30, passing a 100 c/s. signal, and to filter 32 (40 c/s.) and to filter 34 (1000 c/s.). Buffer 24 also feeds an inverter 61 and slope detector 60. The outputs of filters 30, 32, 34 are applied through A.M. detectors 40, 42, 44 to Schmidt triggers 50, 52, 54 which provide a square wave pulse. The slope detector 60 provides a negative square wave pulse when the output from buffer 24 is of negative slope. When the output is of zero or positive slope a transistor 65 is held non-conductive and a line 66 is positive. As the output from buffer 24 drops (i.e. negative slope) transistor 65 is turned on and the voltage on line 66 goes negative and stays negative as long as the buffer output decreases. An "AND" circuit 70 generates an output provided there is positive output from line 66 together with pulses from Schmidt triggers 50, 52. However, if a 1000 c/s. input signal occurs, this is not caused by a blood pressure signal and the output of trigger 54 inhibits "record" through a circuit 80. A pulse on line 55 causes multivibrator 81 to generate a 50ms. positive output which is inverted (81a) and fed to "AND" 83. A signal on line 71 is also applied to "AND" 83. Pulses on line 55 cause multivibrator 81 to decondition "AND" 83 so that pulses on line 71 do not provide "digitize" pulses for the 50 ms. period, thereby eliminating invalid blood pressure readings. Each pulse from "AND" 83 sets a latch 88 causing its output to go positive. Also, a multivibrator 85 generates a positive pulse of 250 ms. whose output partially conditions "AND" 82 whereby during the 250 ms. pulse any signal on line 55 is gated by "AND" 82 through "OR" 87 to reset latch 88 to cause its output to go negative. At the end of the 250 ms. pulse a positive signal is sent by an inverter 85a through a delay 86 to "OR" 87, and to an output "AND" 89. If at this time latch 88 is still positive a positive record pulse is transmitted from "AND" 89. The output of "AND" 89 is positive for the period of delay 86 whereupon the outputs of latch 88 and "AND" 89 are negative. A pulse on line 55 in the 250 ms. period resets latch 88 through "AND" 82 and no record signal is generated. Thus each "record" signal confirms that no pulse was on line 55 in the 250 ms. period following the preceding "digitize" pulse. An A.G.C. circuit 27 causes the gain of amplifier 26 to decrease with increased background noise in the output of filter 30 to prevent undesired firing of Schmidt triggers. Alternatively the threshold level of the Schmidt triggers may be variable in accordance with the noise level.