Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to an electronic circuit
for generating complex time-varying analog signal wave-
forms. More particularly, it involves apparatus for
slmulating electrocardiographic and/or blood pressure
waveforms which can be utilized to test remote display
devices.
In our U.S~ Patent No. 4,204,261 which issued
on May 20, 1980, disclosed electronic circuitry for gen-
erating time-varying analog signals, preferably repre-
senting electrocardiographic and blood pressure 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 for a live
patient. The blood pressure monitor provides an excita-
tion signal to the transducer in order to lnitially
energize the transducerO However, different types of
blood pressure monitors provide different types of ex-
citation signals, these signals usually being of the
pulsqd, direct current (DC) or alternating current (AC)
type. ~ simulator device must utilize the excitation
signal from the blood pressure monitor. In the above-
referenced U.S. application, there is provided two separate
interface circuits, one for a DC excitation signal and
- 25 one for an AC excitation signal. Unfortunately, this
necessitates increased costs for a user who has
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different types of blood pressure monitors to be checked.
For example, a hospital may carry a wide variety of blood
pressure monitors which have different types of excitation
signals.
In checking the operability of the remote display
devices, it is advantageous for the simulator device to simu-
late waveforms which closely represent the waveforms that
would ordinarily be supplied by a live patient. Under true
operating conditions, where the patient is being simulta-
neously monitored by an electrocardiogram machine and a blood
pressure monitor, the blood pressure waveform will appear
delayed from the electrocardiographic waveform. However,
the simulator device of the above referenced U.S. Patent
initiated both simulated waveforms at the same time.
While this has provided reliable means for checking the
operability of the displays, it would be further advantageous
to provide these waveforms in a timed sequence corresponding
; to the waveforms actually provided by a live patient.
s noted above, it would be advantageous to provide
a universal simulator device which is compatible with a wide
~ variety of blood pressure monitors. According to another
; aspect of this invention, there is provided an intercon-
nection cable which is specifically designed ~or use with
a particular blood pressure monitor. Since each monitor
may utilize a particular type of transducer and supply a
certain type of excitation signal, complex modifications
had heretofore been necessary to make the particular monitor
signals compatible with that of a simulator device. To
overcome this problem, the interconnection device of the
present invention is specifically designed for the par-
ticular blood pressure monitor being utilized so as to make
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its signals compatible with the simulator device. Therefore,
the same simulator device can be utilized in conjunction with a
variety o~ different blood pressure monitors merely by changing
the cable specifically designed for the monitor under test.
Therefore~ it is an object of the invention to provide
a waveform simulator which is compatible with a variety of
remote display devices having different types of excitation
signals.
It is another object of the present invention to pro-
vide simulated electrocardiographic and blood pressure waveforms
in a timed sequence corresponding to those waveforms which would
be derived from a live patient.
A further object of this invention is to provide an
interconnection device which permits the same waveform simulator
to be utilized with a variety of different remote display
devices.
According to a broad aspect of this invention there
is provided apparatus for simulating waveforms utilized to check
the operability of a remote display device, said remote display
device providing an excitation signal which is normally coupled
to a transducer for sensing physical characteristics of a live
patient, said apparatus comprising: generator means ~or provid~
ing electrical signals representing simulated waveforms; and an
interface circuit for coupling said waveforms to the remote dis-
: play device, said interface circuit including: means defining
a bridge network having a plurality of legs, and a variable
impedance element in one of said legs coupled to said generator
means; means for coupling the excitation signal from the remote
display device to an input of said bridge network; means for
coupling an output of said bridge to the remote display device
whereby said electrical signals from said generator means cause
the impedance of said variable impedance element to correspond-
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ingly vary and unbalance the bridge network to provide said
simulated waveforms to the remote display device.
Accordingly, either AC, DC or pulsed excitation
signals can be utilized with the simulator apparatus.
In a preferred embodiment in which the remote display
device comprises an electrocardiogram machine and a blood
pressure monitor, the generator means further comprises: first
waveform generator means for providing simulated electrocardio-
; graphic waveform segments; second waveform generator means for
providing simulated blood pressure waveforms; and control means
coupled between said first and second generator means for auto- -
matically initiating said blood pressure waveform after a pre-
determined number of the ~lectrocardiographic waveform segments
have been generated so that said electrocardiographic and blood
pressure waveforms are provided in a time sequence corresponding
to waveforms that would ordinarily be supplied by a live patient.
In a specific embodiment of this invention an inter-
connection device for coupling a blood pressure monitor to the
simulator aevice is provided. The interconnection device is
in the form of a cable having a plurality of conductors therein
and terminating in connectors on either end of the cable. A
plurality of impedances are contained within one of the connec-
tors and have a common node coupled to one of the conductors
for supplying the excitation signal from the blood pressure
monitor. The other end of the impedances are each attached to
separate terminals in one of the connectors to provide alter-
native conductive paths which may be selectively coupled to the
simulator device to modify its output signal. The values of
the impedances are chosen according to the particular character-
istics o~ the blood pressure monitor being tested.
These and other objects and advantages of this inven-
33~l3~
tion will become apparent upon reading the following specific-
ation and by reference to the accompanying drawing in which:
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FIGURE 1 is a front plan view of the waveform simu-
lator device of the present invention;
FIGURE 2 is a right side plan view of the device shown
in FIGVRE l;
FIGURE 3 is a block diagram showing the major compon-
ents of the circuitry of the present invention;
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 simu-
lator device shown in FIGURE 1 being coupled together by a
cable according to another aspect of this invention;
FIGURE 6 is a perspective vlew 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 electrocardiographi~ and
; blood pressure waveforms supplied by the simulator device of
the present invention~ ;
DESCRIPTION OF THE PREFERRED EMBODIMENTS
. General Description
Referring to Figures 1 and 2 of the drawing there is
shown a substantially rectangular box defining a housing for
the simulator device 10 of the present invention. A front plate
12 includes a pictoral representation of a patient 14 and a
plurality of sn~p-type connectors 16 disposed relative to patient
14 for receiving disposable type electrode cables from an elec-
trocardiogram machine being tested. A plurality of knobs 18
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and 2~, 22, and 24 are coupled to particular components in the
electrical circuitry internally contained by the housing. A
series of jac~s 2Ç on one side panel of the housing Drovide
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
s~itches 28-¢38 and a nine socket receptacle 40 which are utilized
when testing a bIood pressure monitor as will be more fully
discussed herein. Upon inspection of Figures 1 and 2, it
will be seen that the simulator device 1~ of the present in-
vention pr~vides a compact tool which provides both simulated
eIectrocardiographic waveforms via jacks 28 and simulated blood
~ 15 pressure waveforms via receptacle 4~, which waveforms are ad-
; vantayeously utilized to check the operahility of remote
display units such as an eIectrocardiogram 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 electrical circuitry of the present
invention. 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 emanatiny from the lower portion of
, counter 44. ~he 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.
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Particular output stages of counter 44 are con-
nected to a first shaping an~ summing network 46. Network
46 shapes the particular outputs of counter 4~ to form
particular segments of an electrocardiographic waveform.
Network 46 then sums these segments to produce the com~
plete waveform. The output of network 46 is coupled to
amplifier 48 whereat 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 potentio-
meter 52 for adjusting the high level output. A cali-
bration 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 example, via jacks 26 shown
in Figure l.
Clock pulses from clock circuit ~2 are also con-
~ nected to a second decade counter 56 having a similar num-
; 20 ber of output stages and operating in the same manner as
counter 44. Particular output stages of counter 56 are
- coupled to a second shaping and summing network 58. Net-
work 58 shapes particular output stage signals from counter
58 ot provide a simulated blood pressure signal seqments
which are then summed to provide a complete waveform.
It should be noted that the circuit elements so far des
cribed in connection with Figure 3 are more fully explained
in our U.S. Patent No. 4,204,261 which issued on ~lay 20,
1980. Consequently, these elements will only be discussed
in such detail so that a full understanding of the claimed
subject
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matter of the pre ent invention can be readily understood~
The output of network 58 is coupled to an amplifier
60 where the completed waveform is amplified~ A potentiometer
62 which is manually adjustahle by knob 24 of Figure 1 regulates
the am~litude of the klood pressure waveform to set the desired
systolic level. The output of potentiometer 62 is coupled to
a current regulator such as a transistorO In the preferred
embodiment, the output of potentiometer 62 is coupled to the
gate of a fieId 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-
sure monitor as will be more fully discussed herein. The drain
reaion of transistor 64 is coupled to a bridge network 68 to
which an excitation signal is supplied from the hlood pressure
monitor under test. It is the feature of this invention that
bridge network 68 makes the simulator device of the present
; invention compatible with a variety of different blood pres-
~ sure monitors which may supply correspondingly varied types of
".,~
excitation signals. Regardless of the type of excitation signal
from the blood pressure monitor, the output of the bridge net-
work 68 will provide a simulated blood pressure waveform which
,:.
can be utilized to check the operability of the particular
monitor under test.
Pursuant to the present invention, provision is also
25 made for simultaneously supplying electrocardiographic and blood ~;;
pressure waveforms in a timed se~uence which correspond to the
timed s-equence of such waveform$ which would be supplied by a
live patient. This is accomplished by the unique interaction
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VAL-121
of monostable circuit 70, a first flip-flop 72 coupled to blood
pressure counter 56, and a second flip-flop 74 coupled to elec-
trocardiographic 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 counter 56.
An intermediate stage of counter 44 is coupled to the se-t input
of flip~flop 7~. The last stage of counter 56 is coupled to an
input of monostabIe circuit 70O In the preferred embodiment
monostabIe circuit 70 is a one shot multi-vlbrator which provides
a HIGE 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 iIlpUt 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, and to a disabling input of clock circuit 42.
As will be di.scussed below, the setting of blood pressure :
fl.ip-flop 72 by an intermediate stage of electrocardiogram
counter 44 causes a delay in the initiation of the blood pressure .
~ waveform wit~ respect to the beginning of the electrocardiographic
~ waveform. ~he width of the output pulse from monostable
7~ determines the period between successive waveforms. Aecording
- to another aspect of this invention, means are provided via
knob 22 of Figure 1 to vary the output pulse width from mono-
stabIe 70 such that the blood pressure waveform co.rresponds
selecti~ely to either 120, 90 or 60 beats per minute.
B. Detailed Description
The components illustrated in block diagram form in
Figure 3 are shown in more detail in Figure 4. The details
of some of the components are encompassed by dotted lines in
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VAL-121
Figure 4 to help the reader in ascertaining the connection be-
tween the various components
Clock ~2 employs a pair of inverting amplifiers 80
and 82, with the output of amplifier 80 connected to the junction
of the input of the amplifler 82 and a resistor Rl. A resistive-
capacitive circuit consisting of resistor Rl and capaci-tor Cl
determines the frequency of clock 44. The output of clock 42
is coupled 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~ only stages 1 r 4, 5, 8,
and 9 are utilized to initiate the shaping and s~ming network
46 which provides the electrocardiographic ~aveform. The
shaping and summing network 46 is described in more detail in
the above referenced application. Briefly, the P segment of
the electrocardiographic waveform is obtained from the first
period or stage counter 44 by summing this signal through
2~ resistor R6 to a common node Nl. To derive the Q waveform seg-
ment, counter stage 4 is utilized. Since the Q wave is a
negative going wave and of different rise time than the P wave,
the output of the stage 4 is coupled to a shaping circuit com-
prised of R8 and C6. This shaped waveform is then inverted
by buffer 88 and then summed at node Nl through resistor R9.
Stage 5 is utilized to generate both the R and S
electrocardiographic waveform segments. The S segment, like the
Q seyment, is a negative going waveform. The S wave is derived
by shaping the output from stage 5 by resistor R7 and C5, then
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inverting the wave by buffer 90 and finally summing this shaped
signal through resistor R10 at node Nl~
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 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 S6.
The T segment of the eIectrocardiographic waveform
is of a longer duration than any of the other segments and there-
fore both stages 8 and 9 are utilized from counter 44. Stage 8
~- is coupled to summing junction Nl through resistor R4 and stage9 is coupled to n~de Nl through resistor R5. The falling edge
of the output of the stage 9 is utilized to set flip-flop 74
yia 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 in-
tegrated circuit component from Motorola as Component No.
MC14001. As will be further described herein the falling edge
of stage 9 of counter 44 is used to set flip-flop 74 and
disable counter44 while hlood pressure counter 56 times out in
order to give the electrocardiographic and blood pressure wave~
forms the proper timing relationship.
The R waveform se~ment has steep rising and falling
edges. This is obtained by using the output of counter 44
stage 5 and differentiating it through capacitor C7 and resistor
R12, with diode Dl ca~sing capacitor C7 to recover quickly.
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VAL-121
ResistorsR13 and capacitor C10 are used for shaping the wave,
with buffer 10~ and resistor R14 presenting the waveform at
node N2. The P, Q, S, and T waveforms are summed at node Nl,
with this combined waveform being further summed with the R
waveform segment at node N2 to provide the completed electro-
cardiographic waveform.
Thb completed eIectrocardiographic waveform is coupled
to output amplifier 48 through an internally adjustable potentio-
meter ~16 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-
- back line coupled to its inverting input. The output of amplifier
48 is coupled to one ~ide of potentiometer 52 which is adjust-
able by the user. Resistors R17 and Rl9 through resistor R31
form a divider network where the electrocardiographic signal is
tapped off, to be fed to the differential inputs of the xemote
display under test. Since all electrocardiographic moni-tors
have a 1000 1 ampli~ier, resistor R16 is adjusted so that the
RA to LA outputs provides a 1 millivolt output which, in turn,
gives a rading of 1 ~olt 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 simulated electrocardiographic
waveform with different amplitudes depending upon which jacks
are connected to the display under test. A one millivolt output
sw-itch such as knob switch 18 shown in Figure 1 is utilized
to provide a 1 millîvolt output across jacks labelled Jl and J2
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VAL-121
~hen depressed. Potentiometer R33 of calibration cireuit 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 Jl-J5 provide the elec-
trode eonnections 16 on front panel 12 of deviee 10 shown in
Figure 1. The jacks labelled JlA-J5A and J7-Jll in Figure 4
eorrespond to the jaeks 26 loeated on the side of the device
housing.
As noted above, the same eloek frequeney is utilized
~ ~
to drive blood pressure deeade eounter 56. However, eounter 56
is initiated after the initiation of eleetroeardiogram counter 44
~ since its enabling input is eoupled to an intermediate stage
; (here, stage 5) of eounter 44 via line 96. The blood pressure
waveform is one continuous waveform. Aeeordingly, almost all
of the output stages of eounter 56 are utilized. To achieve
a rounding leading edge of the waveform, buffer amplifier 110
has its input eoupled to the O stage of eounter 56 and its out-
- put coupled to a summing node N3 through resister R37. Stages 2
2~ through 8 are coupled to node N3 through resistors R38-R44,
respeetively. Stage 8 of eounter 56 is coupled via line 112 to
monostable eireuit 70 through eapacitor 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. ~onostable 70 ineludes 2 inverting amplifiers
114 and 116 which are connected together via capaeitor C3.
The width of the output pulse of monostable 70 is determined by
the RC network eomprised of capacitor C3 and the resistive
network defined by potentiometer 118 which is series conneeted
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with either of resistors R3, R3A, or R3B through a four position
switch SWl such as switch 22 of Figure 1. Resistors R3, R3A,
and R3B provide monostable 70 with an output pulse width of
varying widths to de~;ne the periods between the electrocardio-
~raphic and blood pressure waveforms. According to a feature
of this invention, resistors R37 R3A and R3B define a blood
pressure waveform having a frequency corresponding to gO, 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 NoO MC14017B. 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. Sim~
~` ilarly, the output of monostable 70 is coupled to the rese-t
input of flip-flop 72 and 74 via lirJe 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
i ~,
initially turned on to insure that the flip-flops 72j 74 are
reset. The output of monostable 70 is also coupled to clock
circuit 42 throu~h 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 Cll, and then by
the RC network comprised of resistor R45 and capacitor C12.
The completed blood pressure ~ave~orm is then presented to the
noninYertin~ input of buffer amplifier 60 where it is amplified.
The output of amplifier 60 is coupled to a fine adjustment
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potentiometer 62 which is manually adjustable by the customer
via knob 24 of Figure 1 to adjust the amplitude of the blood
pressure waveform. The varying analog signal biases the gate
of field effect transistor Ql through the divider network con-
sisting of resistors R47 and R48. Resistor R50 and potentio-
meter 56, which is manually adjustable via knob 20 of Figure 1,
adjusts the current through the light emitting diode (LED)
portion of photomodule 130. Photomodule 130 comprises an LED
132 which is optically coupled to a photosensitive resistance
~; 10 element 134. Photomodule 130 is part of one leg of the bridge
network 68. Photomodule 130, series connected resister 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
~ ~v~c e_
15 types of~elements as well 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 sig-
nal from the blood pressure monitorto the bridge input. The output
of the bridge is coupled to other sockets in receptacle 40 via
20 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 pushbutton is engaged, the other swi-tches are
automatically disengaged. In this embodiment, the wipers of the
25 switches 28-38 contact the leftmost pole when disengaged and the
rightmost pole when engaged. The wipers of switches 30-38 have
a common node. The wipers of switches 28=38 are shown positioned
in Figure 4 as would be the case when ~ero button 30 is engaged.
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In such case, an external voltage source (+9V) is coupled
~ia OFF switch 28 to the anode of LED 132 in photomodule 130.
The current through transistor Ql is then regulated via the
adjustment of potentiometer 66 such that the output of the bridge
^ 5 over lines 138 and 140 would provide a zero indication on the
blood pressure monitor under test.
C. The Interconnection Device
Referring now to Figure 5, there is shown a typical
interconnection between simulator device lQ and a blood pressure
; 10 monitor 150 which are coupled together via interconnection device
152 according to another aspect of this invention. Figure 6
; shows the graphic details of the interconnection device 152 and
Figure 7 shows the electrical schematic diagram of its respec-
tive parts. Device 152 is in the form of a cable 154 having
connectors 156 and 158 on each end. Connector 156 may be a
commercially available multi-pin plug, 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 recep-
tacle 40 as shown in Figure 2. Nine insulated 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 em-
bodiment has a screw type collar and includes a plurality of
sockets 162-170 which are adapted to mate with 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.
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It is a feature of this invention that the inter-
connection device 152 is specifically designed for the 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 tnot shown~ mounted on a live patient
for sensing his blood pressure~ Typically such transducers pro~
vide a 50 microvolt output per volt of excitation ~ignal 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 milli-
meters of mercury pressure applied to the particular transducer
normally utilized by monitor 1500 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 ~omponents in the wave-
form generator portion of the circuitry, for example by turning
5witch S~l ~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 dif-
ferent types o~ excitation signals, but the l~vel of the excita-
tion signal and the sensitivity of the transducer may be differentfor each monitor. Accordingly, resistors R59-62 are provided
to make the simulator and blood pressure monitor compatible
regardless of the type of bIood pressure monitor being utilized.
Resistor R62 is series connected with conductor 178
to bring excitation signal leveI 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
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to provide a ~ volt drop across it~ Resistors R58-R61 are
coupled at one end to conductors 180-186, respectively~ The
other end of resistors R58-R 61 are connected a-t a common
node l9Q, along wi-th the end of conductor 188. Node 190 is coupled
to socket 170 of connector .158~ Resistors R58-R6.1 have different
resista.nce val.ues 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
RS8-R61 can be selectively placed in parallel with bridge resist-
or R54 depending upon the position of switches 32-38. By way
of an example, assume that it is desired to 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 sens.itivity 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 the
rightmost pole and the wiper of switch 30 on the leftmost pole.
Thus, resistor R58 is placed in parallel with reslstor 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 millivoltsO The value chosen for R58 would be derived
from the following equation:
R - R( in - 1)
cal 4E
= 2KQ(lv -1)
4(-2-.5mv)
= 198KQ
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Where Ein is ~he voltage applied across the bridge,
this being one volt due to the action of resistor R62;
Eo is the output voltage of bridge 68, this being
the required 2.5 milliYo].ts;
R= the value of resistor R54 in bridge network 68,
this being 2KQ in this example; and
RCal = the resistance value necesaary for ~58.
The remaining resistance values of resitors R59-R6I can be
chosen in the same manner.
It should be emphasized that the particular types of
connectors 156 and 158 can be varied, as can be the location of
resistors R58 R62 in the interconnection device 152. In this
embodiment, it has been found to be easier to 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 the art.
D. Simulator Operation
Referring now especially to Figures 3, 8 and 9, the
operation of the simulator device 10 according to the present
in~ention will now be described. Upon energization of the _-
circuit, clock 42 provides a series of clock pulses as is most
clearly 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 actiYated as noted by the numerals
aboye the pulses from counter ~ 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
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emanating from stage 5 of counter 44. When 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 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 respec-
lQ tive timed sequence of the two simulated waveforms to representthat which would actually be experienced in monitoring a live
patient.
The trailing ed~e of the output pulse Erom stage 9
of counter ~4 causes flip-flop 74 to change to its set or HIGH
level which in turn disables counter 44 by providing the output
of flip-flop 74 to the reset input oE counter 44. Consequently,
decade CQUnter 44 stops counting.
The trailing edge of the pulse from output stage 8
of counter 56 ~rovides a triggering pulse to monostable 70 which
in turn provides an output pulse of predetexmined width depen-
ding upon the position of switch SWl. As noted above, the
position of switch 5~1 as set by knob 22 of Figure 1 determines
the period or frequency of the respecitve electrocardiographic
and blood pressure waveforms. The HIGH level monostable output
pulse disables clock 42 hy providing a HIGH signal at -the input
of inverter 80. Consequently, counter 44 does not count even
though flip-flop 7~ 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
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duration of the HIGH level of the monostable output pulse, both
the electrocardiographic and blood pressure waveforms are not
provided by the simulator de~ice 10. As also noted above, the
position of SWl via knob 22 selects the frequency of the blood
pressure waveform to correspond to 120, 90, or 60 beats per
minute.
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 electrocardio-
graphic waveform. However, due to the interaction of the inter-
mediate stage of counter 44 and flip-flop 72, the second blood
pressure waveform is not initiated until after the appropriate
time has elapsed.
Turn now to the details of the bridge network 68 shown
in Figure 4. ~hen the particular blood pressure monitor 150
is connected to simulator 10 via interconnection device 152,
switch SWl 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 adjusted so that the
output of bridge network 68 provides a zero indicati~n 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. After the 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
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 Ql,
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V~L-121
the conduction between the source and drain regions correspond-
ingly vary as is known in the art. ~Ience, transistor Ql provides
a variable current source to the pho~omodule 132, with the
current level depending upon the amplitude of the generated
blood pressure waveform at the output of potentiometer 62.
The intensity ~f LED 132 proportionally varies pursuant to the
current through transistor Ql. Accordingly, the output of
bridge 68 over lines 138 and 140 provides the simulated blood
signals to monitor 15Q since the resistance of photosensitive
resistor 134 is dependent upon the light intensity of LED 132.
It is now evident that the interface network of the
present invention is compatible with a wide variety of blood
pressure monitors regardless of the type of excitiation signal
employed~ The bridge netwark of the present invention emulates
lS
the transducer circuitry that would ordinarily be used with
monitor 150 to sense the blood pressure of a live patient.
: Since the photomodule 13~ optically isolates the waveform gener-
ator portions of the simulator 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 of the present invention can
be universally used to check the operability of a variety 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 as required by the patent statutes, the scope of the
invention described herein should not be limited to such ex-
amples since modifications will be obvious to one skilled in
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3L~33~
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the art. Hence, the spirit and scope of this invention should
be determined in accordance with the following claims.
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