GB2048587A - Interconnection device for interconnecting a blood pressure monitor and a blood pressure waveform simulator device - Google Patents

Abstract

The interconnection device (152) is in the form of a cable (154) having a connector (156, 158) at each end. The cable (154) comprises a plurality of insulated conductors (172-188). A plurality of resistors (R58-R61) are provided to make a blood pressure waveform simulator to which connector (156) is connected compatible with a blood pressure monitor to which connector (158) is connected regardless of the type of blood pressure monitor being used. The resistors (R58-R61) are each connected at one end to a respective conductor (180-186). The other end of the resistors (R58-R61) are connected to a common conductor (180). Resistors (R58-R61) have different resistance values which provide different static pressure reading to the blood pressure monitor. <IMAGE>

Description

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SPECIFICATION

Interconnection device for interconnecting a blood pressure monitor and a blood pressure waveform 5 simulator device

The present invention relates to an interconnection device for interconnecting a blood pressure monitor and a blood pressure waveform simulator 10 device.

In U.K. Patent Application No. 7907239 (Serial No. 2 016 230) there is disclosed electronic circuitry for generating time-varying analog signals, preferably representing electrocardiographic and blood pres-15 sure waveforms. These waveforms can be coupled to remote display devices to check their operability.

A blood pressure monitor, when in actual use, monitors electrical waveforms derived from a transducer sensing the blood pressure of a live patient. 20 The blood pressure monitor provides an excitation signal to the transducer in order to initially energize the transducer. However, different types of blood pressure monitors have different types of transducers and provide different types of excitation signals, 25 these signals usually being of the pulsed, direct current (DC) or alternating current (AC) type.

It would be advantageous to provide a universal simulator device which is compatible with a wide variety of blood pressure monitors. Heretofore, 30 complex modifications have been necessary to make the particular monitor signals compatible with that of a simulator device.

It is an object of this invention to provide an interconnection device which permits the same 35 waveform simulatorto be utilized with a variety of different remote display devices.

According to the present invention there is provided an interconnection device for interconnecting a blood pressure monitor and a blood pressure 40 waveform simulator device, said blood pressure monitor providing an excitation signal and including means for receiving an input signal, said interconnecting device comprising a cable having a plurality of conductors, a first connector on one end of said 45 cable for coupling the conductors to the blood pressure monitor, a second connector at the other end of the cable for coupling said conductors to said simulator device, and a plurality of resistors connected at one end of one of the conductors for sup-50 plying the excitation signal from the blood pressure monitor to the simulator device, the other end of the resistors each being coupled to a separate terminal in one of said connectors to provide alternative conductive paths from the blood pressure monitorto 55 said simulator device.

The value of the resistors are chosen according to the particular characteristics of the blood pressure monitorto be tested. Thus, the same simulator device can be used to test a variety of different blood 60 pressure monitors, it merely being necessary to choose the interconnection device which is specifically designed for the monitor under test.

Embodiments of the present invention will hereinafter be described, by way of example, with 65 reference to the accompanying drawings, in which:—

FIGURE 1 is a front plan view of a waveform simulator device,

FIGURE 2 is a right side plan view of the device shown in Figure 1,

FIGURE 3 is a block diagram showing the major components of the circuitry of the simulator device,

FIGURES 4A-4C comprise a schematic diagram showing the circuitry of Figure 3 in more detail,

FIGURE 5 shows a blood pressure monitor and the simulator device shown in Figure 1 being coupled together by a cable of the present invention,

FIGURE 6 is a perspective view with parts broken away showing the structure of the cable shown in Figure 5,

FIGURE 7 is an electrical schematic diagram of the cable shown in Figure 6,

FIGURE 8 is a timing circuit illustrating the timing sequence of the circuitry shown in Figure 3, and

FIGURE 9 illustrates the electrocardiographic and blood pressure waveforms supplied by the simulator device.

Referring to Figures 1 and 2 of the drawing there is shown a substantially rectangular box defining a housing for a simulator device 10. A front plate 12 includes a pictoral representation of a patient 14 and a plurality of snap-type connectors 16 disposed relative to patient 14 for receiving disposable type electrode cables from an electrocardiogram machine being tested. A plurality of knobs 18 and 20,22, and 24 are coupled to particular components in the electrical circuitry internally contained by the housing. A series of jacks 26 on one side panel of the housing provide connections to electrocardiogram machine patient cables and may be color-coded to designate the connections as defined by the terminology adopted by the American College of Cardiology. An opposite side panel of the device 10 includes six pushbutton switches 28-38 and a nine socket receptacle 40 which are utilized when testing a blood pressure monitor as will be more fully discussed herein. Upon inspection of Figures 1 and 2, it will be seen that the simulator device 10 provides a compact tool which provides both simulated electrocardiographic waveforms via jacks 28 and simulated blood pressure waveforms via receptacle 40, which waveforms are advantageously utilized to check the operability of remote display units such as an electrocardiogram machine and a blood pressure monitor which are normally utilized to sense the physical characteristics of a live patient.

The block diagram shown in Figure 3 illustrates the major components of the electrocal circuitry of the simulator device 10. When the circuit is energized a clock circuit 42 generates a plurality of clock pulses which are fed to a first decade counter 44 which has a plurality of output stages represented by the lines emanating from the lower portion of counter 44. The clock pulses cause the counter 44 to count, thereby causing the output stages to successively change from a low state to a high state and back to the low state during a specific time period.

Particular output stages of counter 44 are connected to a first shaping and summing network 46. Network 46 shapes the particular outputs of counter

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44 to form particular segments of an electrocardiographic waveform. Network 46 then sums these segments to produce the complete waveform. The output of network 46 is coupled to amplifier48 whereat 5 the complete waveform is amplified.

The output of amplifier 48 is coupled to a divider network 50 that divides the waveform into a plurality of outputs having different amplitudes and to a potentiometer 52 for adjusting the high level output. 10 A calibration circuit 54 provides a one millivolt reference signal which is fed to divider 50. The reference signal is used for checking the gain of a display device such as an electrocardiogram machine to which divider network 50 may be connected, for 15 example, via jacks 26 shown in Figure 1.

Clock pulses from clock circuit 42 are also connected to a second decade counter 56 having a similar number of output stages and operating in the same manner as counter 44. Particular output stages 20 of counter 56 are coupled to a second shaping and summing network 58. Network 58 shapes particular output stage signals from counter 58 to provide a simulated blood pressure signal segments which are then summed to provide a complete waveform. It 25 should be noted thatthe circuit elements so far described in connection with Figure 3 are more fully explained in the above mentioned U.K. Application No. 7907239. Serial No. 2 016 230. Consequently, these elements will only be discussed in such detail 30 so that a full understanding of the claimed subject "matter of the present invention can be readily understood.

The output of network 58 is coupled to an amplifier 60 where the completed waveform is amplified. A 35 potentiometer 62 which is manually adjustable by knob 24 of Figure 1 regulates the amplitude of the blood pressure waveform to set the desired systolic level. The output of potentiometer 62 is coupled to a current regulator such as a transistor. In the prefer-40 red embodiment, the output of potentiometer 62 is coupled to the gate of a field effect transistor 64 whose source region is coupled to another potentiometer 66 for initially zeroing the output of the simulator device 10 when coupled to a blood pres-- 45 sure monitor as will be more fully discussed herein. The drain region of transistor 64 is coupled to a bridge network 68 to which an excitation signal is supplied from the blood pressure monitor under test. It is the feature of this invention that bridge 50 network 68 makes the simulator device of the present invention compatible with a variety of different blood pressure monitors which may supply correspondingly varied types of excitation signals. Regardless of the type of excitation signal from the blood 55 pressure monitor, the output of the bridge network 68 will provide a simulated blood pressure wave form which can be utilized to check the operability of the particular monitor under test.

Provision is made for simultaneously supplying 60 electrocardiographic and blood pressure waveforms in a timed sequence which correspond to the timed sequence of such waveforms which would be supplied by a live patient. This is accomplished by the interaction of monostable circuit 70, a first flip-flop 65 72 coupled to blood pressure counter 56, and a second flip-flop 74 coupled to electrocardiographic waveform counter 44. First flip-flop 72 is of the RS-type including set and reset inputs, and an output. The output is coupled to an enabling input (CE) of 70 counter 56. An intermediate stage of counter 44 is coupled to the set input of flip-flop 72. The last stage of counter 56 is coupled to an input of monostable circuit 70. In the preferred embodiment monostable circuit 70 is a one shot multivibrator which provides 75 a HIGH output pulse of a given pulse width upon receipt of a triggering pulse at its input. The output of monostable 70 is coupled to the reset input of flip-flop 74 which is also of an RS-type, as well as to the reset input of both flip-flop 72 and counter 56, 80 and to a disabling input of clock circuit 42. As will be discussed below, the setting of blood pressure flip-flop 72 by an intermediate stage of electrocardiogram counter 44 causes a delay in the initiation of the blood pressure waveform with respect to the begin-85 ning of the electrocardiographic waveform. The width of the output pulse from monostable 70 determines the period between successive waveforms. Means are provided via knob 22 of Figure 1 to vary the output pulse width from monost-90 able 70 such that the blood pressure waveform corresponds selectively to either 120,90 or 60 beats per minute.

The components illustrated in block diagram form in Figure 3 are shown in'more detail in Figure 4. The 95 details of some of the components are encompassed by dotted lines in Figure 4 to help the reader in ascertaining the connection between the various components.

Clock 42 employs a pair of inverting amplifiers 80 100 and 82, with the output of amplifier 80 connected to the junction of the input of the amplifier 82 and a resistor R1. A resistive-capacitive circuit consisting of resistor R1 and capacitor C1 determines the frequency of clock 44. The output of clock 42 is coupled 105 to the clock inputs of counters 44 and 56 via lines 84 and 86, respectively.

The output stages of counter 44 are labelled in this embodiment by the numerals 0-9 on the bottom portion of the block in the drawing. In this embodiment, 110 only stages 1,4,5,8, and 9 are utilized to initiate the shaping and summing network 46 which provides the electrocardiographic waveform. The shaping and summing network46 is described in more detail in the above referenced application. Briefly, the P 115 segment of the electrocardiographic waveform is obtained from the first period or stage counter 44 by summing this signal through resistor R6 to a common node N1. To derive the Q waveform segment, counter stage 4 is utilized. Since the Q wave is a 120 negative going wave and of different rise time than the P wave, the output of the stage 4 is coupled to a shaping circuit comprised of R8 and C6. This shaped waveform is then inverted by buffer 88 and then summed at node N1 through resistor R9. 125 Stage 5 is utilized to generate both the R and S electrocardiographic waveform segments. The S segment, like the Q segment, is a negative going waveform. The S wave is derived by shaping the output from stage 5 by resistor R7 and C5, then 130 inverting the wave by buffer 90 and finally summing

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this shaped signal through resistorRIO at node N1.

The output of stage 5 of counter 44 is also coupled to the set input of flip-flop 72 via line 92. Flip-flop 72 is comprised of two cross-coupled NOR gates 94 and 5 96 to form an RS-type flip-flop known in the art. The output of flip-flop 72 is coupled via line 96 to the enabling input (CE) of blood pressure counter 56.

The T segment of the electrocardiographic waveform is of a longer duration than any of the 10 other segments and therefore both stages 8 and 9 are utilized from counter 44. Stage 8 is coupled to summing junction N1 through resistor R4 and stage 9 is coupled to node N1 through resistor R5. The falling edge of the output of the stage 9 is utilized to 15 set flip-flop 74 via line 98. Flip-flop 74 is similarly an RS-type flip-flop comprised of cross-coupled NOR gates 100 and 102. Flip-flop 74 and 72 can be of a variety of known flip-flops. In this example, they are commercially available as a pair on one integrated 20 circuit component from Motorola as Component No. MC14001. As will be further described herein the falling edge of stage 9 of counter44 is used to set flip-flop 74 and disable counter 44 while blood pressure counter 56 times out in order to give the elec-25 trocardiographic and blood pressure waveforms the propertiming relationship.

The R waveform segment has steep rising and falling edges. This is obtained by using the output of counter 44 stage 5 and differentiating it through 30 capacitor C7 and resistor R12, with diode D1 causing capacitor C7 to recover quickly. Resistors R13 and capacitor C.O are used for shaping the wave, with buffer 104 and resistor R14 presenting the waveform at node N2. The P, Q, S, and T waveforms are sum-35 med at node N1, with this combined waveform being further summed with the R waveform segment at node N2 to provide the completed electrocardiographic waveform.

The completed electrocardiographic waveform is 40 coupled to output amplifier48 through an internally adjustable potentiometer R16 which is adjusted to provide the correct output level to the display under test. Amplifier 48 consists of a buffer amplifier 108 such as an LM324 integrated circuit having a feed-45 back line coupled to its inverting input. The output of amplifier48 is coupled to one side of potentiometer 52 which is adjustable by the user. Resistors R17 and R19 through resistor R31 form a divider network where the electrocardiographic signal is tapped off, 50 to be fed to the differential inputs of the remote display under test. Since all electrocardiographic monitors have a 1000:1 amplifier, resistor R16 is adjusted so thatthe RAto LA outputs provides a 1 millivolt output which, in turn, gives a grading of 1 55 volt on the electrocardiogram display.

The divider network 50 employs a parallel-series combination of resistors to divide the signal from the output of amplifier 48 into a plurality of outputs at jacks 26 which are color coded to provide the simu-60 lated electrocardiographic waveform with different amplitudes depending upon which jacks are connected to the display under test. A one millivolt output switch such as knob switch 18 shown in Figure 1 is utilized to provide a 1 millivolt output across jacks 65 labelled J1 and J2 when depressed. Potentiometer

R33 of calibration circuit 54 is adjusted to provide this one millivolt output. Potentiometer R18 is adjusted to provide the high level output taken across jacks J6 and J4A. The outputs labelled J1-J5 provide the electrode connections 16 on front panel 12 of device 10 shown in Figure 1. The jacks labelled J1A-J5Aand J7-J11 in Figure 4 correspond to the jacks 26 located on the side of the device housing.

As noted above, the same clock frequency is utilized to drive blood pressure decade counter 56. However, counter 56 is initiated after the initiation of electrocardiogram counter 44 since its enabling input is coupled to an intermediate stage (here,

stage 5) of counter 44 via line 96. The blood pressure waveform is one continuous waveform. Accordingly, almost all of the output stages of counter 56 are utilized. To achieve a rounding leading edge of the waveform, buffer amplifier 110 has its input coupled to the 0 stage of counter 56 and its output coupled to a summing node N3 through resistor R37. Stages 2 through 8 are coupled to node N3 through resistors R38-R44, respectively. Stage 8 of counter 56 is coupled via line 112 to monostable circuit 70 through capacitor C2. When stage 8 is activated, it provides a trigger pulse to monostable circuit 70 which in turn provides an output pulse of a predetermined pulse width. Monostable 70 includes 2 inverting amplifiers 114 and 116 which are connected together via capacitor C3. The width of the output pulse of monostable 70 is determined by the RC network comprised of capacitor C3 and the resistive network defined by potentiometer 118 which is series connected with either of resistors R3, R3A, or R3B through a four position switch SW1 such as switch 22 of Figure 1. Resistors R3, R3A, and R3B provide monostable 70 with an output pulse width of varying widths to define the periods between the electrocardiographic and blood pressure waveforms. According to a feature of this invention, resistors R3, R3A and R3B define a blood pressure waveform having a frequency corresponding to 90, 60 and 120 beats per minute, respectively,The output of monostable 70 is coupled to the reset input of blood pressure counter 56 via line 120. Counters 44 and 56 are commercially available from Motorola, Inc. as Component No. MC14Q17B. As it is known in the art, when such counters have a HIGH level applied at their reset input, the counter is disabled and will not count. Similarly, the output of monostable 70 is coupled to the reset input of flip-flop 72 and 74 via line 122 through diode D4 and inverters 124 and 126. Capacitor C13, resistor R57 and diode D3 cause a pulse to be generated when the simulator device is initially turned onto insure that the flip-flops 72,74 are reset. The output of monostable 70 is also coupled to clock circuit 42 through diode D2 which holds the clock circuit 42 in a disabled state for the duration of the monostable output pulse.

The electrical signals from the output stages of blood pressure counter 56 are summed at summing junction N3. These signals are then shaped, first by capacitor C11, and then by the RC network comprised of resistor R45 and capacitor CI 2. The completed blood pressure waveform is then presented to the non-inverting input of buffer amplifier 60 where

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it is amplified. The output of amplifier 60 is coupled to a fine adjustment potentiometer 62 which is manually adjustable by the customer via knob 24 of Figure 1 to adjust the amplitude of the blood pressure 5 waveform. The varying analog signal biases the gate of field effect transistor Q1 through the divider network consisting of resistors R47 and R48. Resistor R50 and potentiometer 66, which is manually adjustable via knob 20 of Figure 1, adjusts the current 10 through the light emitting diode (LED) portion of photomodule 130. Photomodule 130 comprises an LED 132 which is optically coupled to a photosensitive resistance element 134. Photomodule 130 is part of one leg of the bridge network 68. Photomodule 15 130, series connected resistor R51 and parallel coupled resistor R52 form one leg of the bridge. Other legs of the bridge are comprised of resistors R53, R55 and R54. As used herein, the term resistive legs is meant to include other types of elements as well 20 as resistors which may be utilized in conjunction with a bridge network. Conductors 136 and 138 coupled to respective sockets in receptacle 40 connect the excitation signal from the blood pressure monitorto the bridge input. The output of the bridge 25 is coupled to other sockets in receptacle 40 via conductors 140 and 142. Conductor 140 is further coupled via line 144 to five of the pushbutton switches 28-38 of Figure 1. Switches 28-38 are of the known mechanically interlocking type by which when one 30 pushbutton is engaged, the other switches are automatically disengaged. In this embodiment, the wipers of the switches 28-38 contact the leftmost pole when disengaged and the rightmost pole when engaged. The wipers of switches 30-38 have a com-35 mon node. The wipers of switches 28-38 are shown positioned in Figure 4 as would be the case when zero button 30 is engaged. In such case, an external voltage source (+9V) is coupled via OFF switch 28 to the anode of LED 132 in photomodule 130. The cur-40 rent through transistor Q1 is then regulated via the adjustment of potentiometer 66 such thatthe output of the bridge over lines 138 and 140 would provide a zero indication on the blood pressure monitor under test.

45 Referring now to Figure 5, there is shown a typical interconnection between simulator device 10 and a blood pressure monitor 150 which are coupled together via interconnection device 152 according to this invention. Figure 6 shows the graphic details of 50 the interconnection device 152 and Figure 7 shows the electrical schematic diagram of its respective parts. Device 152 is in the form of a cable 154 having connectors 156 and 158 on each end. Connector"! 56 may be a commercially available multi-pin plug, 55 such as that manufactured by AMP Corporation. In this embodiment, connector 156 includes nine pins: P12A, P12B, P12C, P12D, P12E, P12F, P12H, P12J and P12K which serve as terminals which mate with sockets in receptacle 40 as shown in Figure 2. Nine insu-60 lated conductors coupled at one end to each of the pins of connector 156 are surrounded by a sheath 160 to form cable 154. Connector 158 in this embodiment has a screw type collar and includes a plurality of sockets 162-170 which are adapted to mate with 65 corresponding pins on the blood pressure monitor

150. Conductors 172 and 174 supply the output of bridge circuit 68 to blood pressure monitor 150. Conductor 176 supplies a ground signal between the two units. Conductors 178-188 supply the internally generated blood pressure monitor excitation signal coupled to sockets 168 and 170 to device 10.

It is a feature of this invention thatthe interconnection device 152 is specifically designed forthe particular blood pressure monitor 150 being utilized. Different types of blood pressure monitors employ different types of excitation signals. For example, such excitation signals can be alternating current, direct current, or pulsed signals which are normally coupled to a transducer (not shown) mounted on a live patient for sensing his blood pressure. Typically such transducers provide a 50 microvolt output per volt of excitation signal when a pressure of one centimeter of mercury is applied to the transducer. In calibrating the blood pressure monitor 150, it is advantageous to provide electrical signals representing static pressure readings which would correspond to 100,80,50, and 15 millimeters of mercury pressure applied to the particular transducer normally utilized by monitor 150. Normally, when using such static pressure readings to check the monitor, the blood pressure waveforms are not generated. This is accomplished by removing the biasing voltage, (not shown) to the components in the waveform generator portion of the circuitry, for example by turning switch SW1 (via knob 22) to its OFF position. It is evident, however, that a simulator could not provide static pressure readings which would be compatible with every type of blood pressure monitor since different monitors employ not only different types of excitation signals, but the level of the excitation signal and the sensitivity of the transducer may be different for each monitor. Accordingly, resistors R58-R62 are provided to make the simulator and blood pressure monitor compatible regardless of the type of blood pressure monitor being utilized.

Resistor R62 is series connected with conductor 178 to bring excitation signal level to one volt at the input of bridge network 68 regardless of the level of the excitation signal utilized by blood pressure monitor 150. For example, if monitor 150 employs a 5 volt excitation signal, resistor R62 is chosen to provide a 4 volt drop across it. Resistors R58-R61 are coupled atone end to conductors 180-186, respectively. The other end of resistors R58-R61 are connected at a common node 190, along with the end of conductor 180. Node 190 is coupled to socket 170 of connector 158. Resistors R58-R61 have different resistance values which are chosen to provide static pressure readings corresponding to 100,80,50, and 15 millimeters of mercury to monitor 150 via conductors 172 and 174.

It should be noted that the resistance values of resistor R58-R61 will vary depending upon the particular blood pressure monitor being utilized. When interconnection device 152 is coupled between simulator 10 and monitor 150, resistors R58-R61 can be selectively placed in parallel with bridge resistor R54 depending upon the position of switches 32-38. By way of an example, assume that it is desired to

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provide a signal equivalent to a static pressure reading of 100 millimeters of mercury. Assume further that monitor 150 employs an excitation signal of 5 volts DC and normally utilizes a transducer having a 5 sensitivity of 50 microvolts per volt of excitation signal for a pressure applied of one centimeter of mercury. Push-button switch 32 is activated thereby placing its wiper on rightmost pole and the wiper of switch 30 on the leftmost pole. Thus, resistor R58 is 10 placed in parallel with resistor R54 of bridge network 68 thereby unbalancing the bridge. With the particular transducer sensitivity and excitation signal being utilized, the output required from the bridge network 68 would be 2.5 millivolts. The value chosen for R58 15 would be derived from the following equation:

Real = R( E;n 1)

4E0

20

= 2Kfl(1v -1)

4(2.5mv)

25

= 198KA

Where Ein is the voltage applied across the bridge, this being one volt due to the action of resistor R62, 30 E0 is the output voltage of bridge 68, this being the required 2.5 millivolts;

R = the value of resistor R54 in bridge network 68, this being 2Kfl in this example; and

Rcai = the resistance value necessary for R58. The 35 remaining resistance values of resistors R59-R61 can be chosen in the same manner.

It should be emphasized thatthe particular types of connectors 156 and 158 can be varied, as can be the location of resistors R58-R62 in the interconnec-40 tion device 152. In this embodiment, it has been found to be easierto include resistors R58-R62 in the larger type connector utilized for connector 158. However, this is clearly a matter of choice and may be readily varied as is known by a person skilled in 45 the art.

Referring now especially to Figures 3,8 and 9, the operation of the simulator device 10 will now be described. Upon energization of the circuit, clock 42 provides a series of clock pulses as is most clearly 50 shown in Figure 8. Flip-flops 74 and 76 are initially in their reset state. Since the enabling input of counter 44 is grounded, it begins to count upon receipt of the clock pulses from clock circuit 42. The stages 0-9 of electrocardiogram counter 44 are sequentially acti-55 vated as noted by the numerals above the pulses from counter 44 shown in Figure 8. However, the blood pressure counter 56 is not enabled until the set input of flip-flop 72 receives the rising edge of the pulse emanating from stage 5 of counter 44. When 60 the flip-flop 72 is set, a HIGH signal from flip-flop 72 coupled to the enabling input of counter 56 starts the blood pressure counter 56 to begin counting. Hence, the initiation of the blood pressure waveform is delayed by a predetermined period of time from the 65 beginning of the electrocardiographic waveform. As can be seen most clearly in Figure 9, since output stage 5 of counter 44 is coupled to the subnetwork in network 46 which creates the S electrocardiographic waveform segment, this causes the respective timed 70 sequence of the two simulated waveforms to represent that which would actually be experienced in monitoring a live patient.

The trailing edge of the output pulse from stage 9 of counter 44 causes flip-flop 74 to change to its set 75 or HIGH level which in turn disables counter 44 by providing the output of flip-flop 74 to the reset input of counter 44. Consequently, decade counter 44 stops counting.

The trailing edge of the pulse from output stage 8 80 of counter 56 provides a triggering pulse to monostable 70 which in turn provides an output pulse of predetermined width depending upon the position of switch SW1. As noted above, the position of switch SW1 as set by knob 22 of Figure 1 determines 85 the period of frequency of the respective electrocardiographic and blood pressure waveforms. The HIGH level monostable output pulse disables clock 42 by providing a HIGH signal at the input of inverter 80. Consequently, counter 44 does not count even 90 though flip-flop 74 has been reset by the pulse from monostable 70. Similarly, the monostable output pulse resets flip-flop 72 and associated blood pressure counter 56. Hence for the duration of the HIGH level of the monostable output pulse, both the elec-95 trocardiographic and blood pressure waveforms are not provided by the simulator device 10. As also noted above, the position of SW1 via knob 22 selects the frequency of the blood pressure waveform to correspond to 120,90, or 60 beats per minute. 100 When the output pulse from monostable 70

returns to its LOW level, the clock circuit 42 is again enabled to provide pulses which drive counter 44 to initiate a second electrocardiographic waveform. However, due to the interaction of the intermediate 105 stage of counter 44 and flip-flop 72, the second blood pressure waveform is not initiated until afterthe appropriate time has elapsed.

Turn now to the details of the bridge network 68 shown in Figure 4. When the particular blood pres-110 sure monitor 150 is connected to simulator 10 via interconnection device 152, switch SW1 is turned OFF and zero button 30 is engaged by the user to zero the output of the bridge before any blood pressure waveform is generated. Potentiometer 66 is 115 adjusted so that the output of bridge network 68 provides a zero indication on the monitor 150. Static pressure readings of 100,80,50, or 15 millimeters of mercury can be provided by pressing buttons 32-38 respectively, as described above. Afterthe 120 waveform generator circuitry is energized via knob 22, the amplitude or systolic level of the blood pressure waveform can be adjusted via potentiometer R62. Hence, the visual indications of the simulated blood pressure waveform on monitor 150 will have a 125 systolic level as determined by potentiometer 62 and a minimum DC or diastolic level as established by the setting of switches 30-38. When the electrical signals emanating from shaping and summing network 58 are applied to the gate of transistor Q1, the 130 conduction between the source and drain regions

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correspondingly vary as is known in the art. Hence, transistor Q1 provides a variable current source to the photomodule 132, with the current level depending upon the amplitude of the generated blood pres-5 sure waveform at the output of potentiometer 62. The intensity of LED 132 proportionally varies pursuant to the current through transistor Q1. Accordingly, the output of bridge 68 over lines 138 and 140 provides the simulated blood signals to monitor 150 10 since the resistance of photosensitive resisto r 134 is dependent upon the light intensity of LED 132.

It is now evident that the interface network is compatible with a wide variety of blood pressure monitors regardless of the type of excitation signal 15 employed. The bridge network emulates the transducer circuitry that would ordinarily be used with monitor 150 to sense the blood pressure of a live patient. Since the photomodule 130 optically isolates the waveform generator portions of the simulator 20. device 10, the excitation signal from the monitor under test does not effect the waveform generation irrespective of the type of excitation signal employed. Consequently, the simulator device can be univerally used to check the operability of a variety 25 of blood pressure monitors even though they employ different types of excitation signals.

Therefore, while various aspects of this invention have been described in connection with particular examples thereof the scope of the invention 30 described herein should not be limited to such examples since modifications will be obvious to one skilled in the art. Hence, the scope of this invention should be determined in accordance with the following claims.

35 Copending Application No. 7930268 (2030394A) from which the present Application is divided, describes and claims apparatus for simulating waveforms including an interface circuit for coupling said waveforms to a remote display device. 40 Copending Application No. 8014018 (Serial No. 2045559) (Agents ref: 51412/JN), which is also divided from Application No. 7930268 (2030394A), describes and claims apparatus for simulating electrocardiographic and blood pressure waveforms. 45 CLAIMS

1. An interconnection device for interconnecting a blood pressure monitor and a blood pressure waveform simulator device, said blood pressure monitor providing an excitation signal and including

50 means for receiving an input signal, said interconnecting device comprising a cable having a plurality of conductors, a first connector on one end of said cable for coupling the conductors to the blood pressure monitor, a second connector at the other end of 55 the cable for coupling said conductors to said simulator device, and a plurality of resistors connected at one end of one of the conductors for supplying the excitation signal from the blood pressure monitorto the simulator device, the other end of the 60 resistors each being coupled to a separate terminal in one of said connectors to provide alternative conductive paths from the blood pressure monitorto said simulator device.

2. A device as claimed in Claim 1, wherein at

65 least four conductors are provided of which the first and second conductors supply said excitation signal to the simulator device, and of which the third and fourth conductors couple the output signals of the simulator device to said blood pressure monitor.

70 3. A device as claimed in Claim 2, further comprising an additional resistor serially connected with said first conductor, said additional resistor having a resistance value such that a portion of said excitation signal from the blood pressure monitor is dropped

75 thereacross.

4. A device as claimed in any preceding claim, wherein said plurality of resistors each have different resistance values which are chosen to provide a plurality of different static pressure readings from

80 said simulator device to said blood pressure monitor.

5. A device as claimed in any preceding claim, wherein said second connector is coupled to an interface network in said simulator device, said inter-

85 face network including a resistive bridge network having a plurality of resistive legs.

6. A device as claimed in Claim 5, wherein said plurality of resistors comprises four in number, and wherein coupled to one of the resistive legs of said

90 interface network the first resistor conditions said simulator device to provide a static pressure reading corresponding to 100 millimeters of mercury, said second resistor conditions said simulator device to provide a static pressure reading of 80 millimeters of

95 mercury, said third resistor conditions said simulator device to provide a static pressure reading of 50 millimeters of mercury, and said fourth resistor conditions said simulator device to provide a static pressure reading of 15 millimeters of mercury.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1980.

Published at the Patent Office, 25 Southampton Buildings, London, WC2A1 AY, from which copies may be obtained.