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BACKGROUND OF THE INVENTION
The present invention relates to a physiological monitoring device
including means for generating an alarm signal in the event the
physiological function rate falls above or below preset limits and for
displaying the alarm condition.
Electronic equipment has been used to monitor the physiological body
functions of a patient such as in the intensive care facility of
hospitals. The body functions may, for example, comprise diastolic and
mean blood pressures, heart rate, and the like. It has also been known to
provide such units with integral alarm circuits so that in the event the
physiological function deviates from preset bounds, an alarm is activated.
Heretofore, upon activation of such an alarm, it has been the duty of the
medical attendant to scrutinize the monitor device closely and to make a
determination of what change in the physiological function triggered the
alarm. In most instances, this may be determined by noting the
illumination of small front panel lamps. However, this requires that the
attendant return to the instrument and note the meter reading and lamp
status, to determine whether the alarm was triggered as a result of too
high or too low a reading.
In addition, it is possible for an alarm to be triggered by one extreme and
thereafter fall to a completely opposite extreme before the attendant has
an opportunity to view the display. For example, in a case where the
patient's heartbeat rate is being monitored his condition could be such
that the heartbeat rate changes from an overly high rate situation
(ventricular tachycandin) to an overly low rate situation (cardiac arrest)
in a very short period of time before an attendant would have an
opportunity to view and analyze the display. The attendant viewing the
display at the time of cardiac arrest would, probably, have no way of
knowing that the cardiac arrest was preceded by a high rate situation.
In view of the above, it is the principal object of the present invention
to provide a physiological function display device adapted to not only
indicate the numerical value of the physiological function at any time but
also to indicate whether the value exceeds or falls below preselected
limits in an error-proof and extremely visible manner.
A further object is to provide such a device with memory capabilities so
that in the event an alarm is triggered, the condition which first
triggered the alarm is preserved whether the function returns to a normal
condition or even swings to the opposite extreme.
SUMMARY OF THE INVENTION
In accordance with the present invention the above and other beneficial
objects and advantages are attained by providing a physiological function
monitor module comprising a physiological function rate detector circuit
adapted to receive an input from a patient and convert the same as a DC
voltage output signal proportional to the rate of the physiological
function of the patient under consideration. The module further includes
an alarm generator connected to the output of the detector circuit. The
alarm generator includes means for comparing the DC voltage level of the
detector circuit to a preselected level and for generating an alarm signal
in the event the DC level deviates beyond permissible bounds from the
preset level. The module also includes a digital display and an
analog/digital converter connected to the output of the detector circuit
in driving relationship with the digital display. A character generator is
connected to the output of the alarm generator and is also connected in
driving relationship to the digital display and parallel with the
analog/digital converter. The character generator drives the digital
display to produce mnemonics (such as HI, LO, OFF, etc.) which alternately
flash with the digital readout on the display in the event of an alarm
situation. Thus, both the alarm condition and patient data can be readily
determined with no chance of operator error.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a fragmentary perspective view of a physiological function
monitor module in accordance with the present invention depicting the
front control panel of the unit;
FIG. 2 is a simplified overall block diagram of the present module;
FIG. 3 is a more detailed block diagram of the detector block of FIG. 2;
and,
FIG. 4 is a more detailed view of various other blocks of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is illustrated in the accompanying drawings wherein
similar components bear the same reference numeral throughout the several
views. In the following description, the present invention is described in
the context of a heart rate monitor. It should be realized and readily
apparent to those familiar with the art that the identical or similar
technology could readily be used for monitoring some other desired
physiological function such as blood pressure, respiration, or the like.
In FIG. 1, the front panel of a monitoring module 10 in accordance with the
present invention is disclosed. The function monitor front panel 12 bears
a title 14 ("Heart Rate") indicating the body function being monitored
which, in this case, is the heart rate. In addition, the front panel
includes a 3-digit digital display 16 which indicates the heart rate and a
light 18 which flashes with each heartbeat. The front panel further
includes an alarm reset button 20, the dials and controls 22 and 24 for
setting the upper and lower limits for the alarm and a push-pull, rotary
control knob 26 which serves the double function of setting the volume of
an audible alarm as well as controlling the illumination display 16 and
light 18. The latter provides a nighttime operating feature of the unit
designed to eliminate patient annoyance with the unit especially at
nighttime. As will be described in detail forthwith, this feature permits
the display lights to be turned off and remain off as long as the
patient's body is functioning properly. In the event of an alarm
condition, both the lights and the audible alarm automatically activate.
As will also be described in detail forthwith, the display 16 is adapted to
produce a 3-digit readout of the physiological function being monitored.
In addition, the display is adapted to be driven to form the following
mnemonics indicative of the condition of the patient or monitoring device:
HI, LO, and OFF. The HI and LO signals flash intermittently with a numeric
reading of the physiological function and their value is determined by the
setting of controls 22 and 24. Thus, for example, if a high limit of 120
is set and exceeded, the mnemonic HI will flash intermittently with an
actual reading of the heart rate which, at some later time, could still be
above or possible below 120.
The OFF signal appears in the event of a malfunction in the patient sensor
as for example, if the patient electrode lead falls off him. Other
mnemonics may be provided for particular physiological function. Thus, a
respirator monitor could be adapted to indicate if the patient monitored
goes into an apnea condition by producing a suitable mnemonic such as
"AP".
Referring to FIG. 2, a simplified block diagram for the present
physiological function monitor circuit 28 is shown. The circuit includes a
function detector circuit 30 which is shown in more detail in FIG. 3. In
the present example of a heart rate monitor, the detector 30 detects the
QRS of a patient's heartbeat. The inputs to the detector 30 are an ECG
signal which is fed on line 32 and a BLANKING- input fed on line 34. In
the following description, a minus sign after a signal (e.g., BLANKING-)
indicates an active negative-going signal. The BLANKING- signal serves to
momentarily blank the ECG signal which would be required to prevent
inadvertent triggering of the alarms if a patient had a pacemaker and
pacemaker pulses were being delivered to the patient.
The QRS detector 30 accepts a suitably amplified patient EDG input and
converts it to a DC level output proportional to the input heart rate as
will be described forthwith. It also generates an R-pulse output,
coincident with each R-wave, which is fed through line 36 to flash the
indicator light 18 on display panel 12 and through line 38 to speaker 40
to produce an audible "beep".
The DC output of detector 30 is fed through line 42 to an analog to digital
converter 44 which serves to provide a 7-segment output signal to drive
the display 16 which comprises three gas discharge digit indicators
visible through the front panel 12.
The DC output of detector 30 is also fed on line 48 to an alarm generator
circuit 50. The alarm generator 50 compares the DC level of the QRS
detector with fixed inputs 52 determined by the setting of control knobs
22 and 24. In the event the DC level on line 48 does not fall within the
permissible bounds determined by the settings of controls 22 and 24, the
alarm generator 50 generates an alarm signal which is fed on line 54 to
the character generator 56 and on line 58 to the audible alarm 40. The
alarm generator 50 also has an ALARM INHIBIT- input through line 60. This
input is in effect a fault detector which recognizes a fault indication
such as a lead being off the patient. This signal causes the alarm signals
to be inhibited which causes the character generator to drive the display
to read OFF.
The character generator 56 receives the output of the alarm generator 50
through line 54 and generates suitable 7-segment output signals through
line 62 and 64 to drive the display 16 to produce the mnemonic HI or LO
indicative of the alarm condition or OFF indicative of the alarm inhibit
condition.
A somewhat more detailed description of the above general description of
the various blocks will now follow.
QRS Detector
As stated, the QRS detector 30 converts the ECG input from the patient to a
DC voltage proportional to the patient's heart rate and generates an
R-pulse signal coincident with each R-wave. The circuitry utilized in
fairly common and employed in existing digital monitoring equipment such
as that heretofore available from the Electrodyne Division of Becton,
Dickinson and Company of Sharon, Massachusetts, assignee of the present
invention.
The QRS complex input on line 32 is fed to a unity-gain slew rate limit
circuit 66 which limits the rate of change of the input signals. The
output of circuit 66 is fed through a band pass filter 68 to a full wave
rectifier circuit 70. The band pass filter circuit 68 includes a low pass
filter, the gate of which can be adjusted by control 72 to allow the
detector sensitivity to be varied. The band pass filter 68 further
includes a high pass filter which, together with the low pass filter,
comprises an inverting band pass filter which filters the R-wave from the
QRS complex. A further input to the band pass filter 68 is the output of
blanking circuit 74 which, in turn, receives a BLANKING- signal on lead 34
to blank the input to the band pass filter when a pacer blanking signal is
present on lead 34. This prevents pacemaker pulses from triggering the
detector.
The filtered R-wave output of rectifier 70 is fed to a peak detector 76 and
comparator 78 to trigger a one-shot 80 that provides the R-pulse signal
for driving the QRS indicator lamp 18 and audible alarm 40 on lines 36 and
38 respectively. The output of the one-shot is also attenuated and fed to
a 3-pole filter 82 which converts the attenuated pulse to a DC voltage
directly proportional to the rate of pulses. This DC voltage is applied
through lines 42 and 48 respectively to the analog to digital converter 44
as well as the alarm generator 50.
Analog/Digital Converter
The analog/digital converter 44 shown in detail in FIG. 4 is also of
conventional design. The A/D converter receives the DC output of the QRS
detector circuit on line 42 and converts it into 7-segment digital form
for driving the display 16. To this end, a DC signal is applied to
integrator 84 through FET switches 86 and 88. Switch 86 is normally kept
on and switch 88 is kept on by counter 90 until the counter counts to
10,000 which is equal to a fixed time interval of approximately 170 ms.
During this interval, the output of integrator 84 ramps to a negative
value proportional to the DC input. On a 10,000 count, switch 88 switches
to apply a voltage to the integrator driving its output to zero. When the
output of integrator 84 crosses zero, comparator 92 switches states
producing a pulse which, through control logic 94, generates a reset
signal which is fed to counter 90 on line 96 after a 60 .mu.s delay. The
reset pulse restarts the counter so that the integration cycle is
repeated.
The output of comparator 92 is also used to clock a 4-stage binary counter
stage of control logic 94 which, together with a coder, generates one
pulse for every 16 integration cycles. The positive edge of this pulse is
used to generate a transfer pulse which transfers the count, which
corresponds to the time required for the integrator output to ramp up to
zero, into four storage latches within counter 90 through line 98. This
count is directly proportional to the input heartbeat rate fed into the
QRS detector 30 on line 32.
An internal scan oscillator in counter 90 sequentially transfers the count
in the storage latches, scanning from the most significant digit to the
least significant digit, to the binary coded decimal outputs 100 of the
counter. The internal oscillator also generates a digit select output 102
corresponding to a selected latch. This turns on appropriate switches in
the analog driver 104 so that a voltage is applied to the selected digit
of display 16. The binary coded decimal outputs 100 from counter 90 are
applied to the numeric display driver 106 where they are decoded into
7-segment high voltage outputs for driving the cathodes of the display. A
zero blanking circuit 108 interposed between counter 90 and decoder 106
blanks the leading zeros until the first non-zero number or least
significant digit occurs.
Alarm Generators
The alarm generator 50 is also shown in detail in FIG. 4. The principal
function of the alarm generator is to detect an alarm condition and to
produce the signals that are used by the character generator 56 to drive
the digital display to produce the HI and LO characters during the alarm
condition and the OFF character during an alarm inhibit condition. The
alarm generator also includes an audio alarm which sounds in the event of
an alarm condition to call immediate attention to the unit. The alarm
circuits are enabled by depressing the ALARM RESET switch 20 on the face
of the unit. This serves to enable flip flops 110 and causes the alarm
reset lamp 112 that appears on the face of the unit to turn on. To set the
alarm limits, the alarm set toggle switch 24 is moved from a neutral
center position to a SET HI or SET LO position. This results in producing
the following conditions:
a. A gate within the control logic 94 of the analog/digital converter 44 is
enabled through lines 114 and 116 to switch the converter to a fast
up-date mode;
b. Switch 86 is turned off thereby disconnecting the DC from the A/D input
and the SET LO or SET HI potentiometer 118 is switched to the A/D input
along line 120 so that the setting may be read on display 16.
c. The alarm logic 122 (described in detail forthwith) is inhibited so that
all alarm conditions are inhibited;
d. The remote inhibit logic 124 (described in detail forthwith) is
inhibited so that the digital remote display is disabled.
The alarms are set by varying potentiometers 118 by turning knob 22 on the
front panel. The alarm set potentiometers are connected through lines 126
and 128 (low and high settings respectively) with comparators 130 which
also receive the DC input signal along line 48 from the QRS detector 30.
If the DC reference exceeds the HI set point, the output of the high
comparator after a 3-second delay produced by delay circuit 132 sets an
alarm HI flip flop 110 the output of which drives display logic 134 and
alarm logic 122. Similarly, if the DC reference drops below the LO set
point, the output of the low comparator sets an alarm LO flip flop 110.
Since flip flops 110 can only be reset by depressing the RESET switch 20
the first to occur of a HI or LO signal will continue to drive the display
logic 134 thereby providing a memory of the alarm condition even if that
condition subsequently subsides or even swings to an opposite alarm
condition. The alarm logic drives audio alarm 40 to generate a continuous
tone. The alarm logic also overrides the volume control 26 for the audio
alarm. That is, even though the volume during ordinary monitoring may have
been turned down or off, under an alarm condition, the audio alarm sounds
at a predetermined level.
The display logic 134 also receives an input from timer 138 which causes
the display logic to alternate between a high and low state. During the
high state, a blanking signal is sent to decoder 106 of the A/D converter
on line 136 while the HI (or LO) generate signal is fed to the character
generator on line 137. In the low state, no signal is fed to the character
generator and decoder 106 is not inhibited so that display 16 alternates
between displaying HI (or LO) and the QRS reading.
A display light switch 140 which is a push-pull function of the volume
control switch 26 is also provided. This switch serves to connect the
display logic 134 with ground when closed to produce a constant blanking
signal for decoder 106 along line 136. In this manner, the display may be
turned off as may be desired, for example, during nighttime operating
where the display would otherwise annoy the patient and possible interfere
with his sleep. It should be noted, however, that the setting of switch
140 would not interfere with either the display of the alarm condition (HI
or LO) or the audio alarm in the event of an alarm condition.
The alarm generator 50 also receives an alarm inhibit signal along line 60.
This signal, is generated, when for example, the ECG electrode is off the
patient so that no ECG signal is being received. The alarm inhibit signal
is fed through a 7-second delay circuit 142 to a flip flop 144 which is
set by alarm logic 122 when an alarm signal is generated by flip flops
110. The output of flip flop 144 is fed to the display logic 134 to
produce the necessary driving signal for the character generator so that
OFF is displayed.
Character Generator
The character generator 56 is also shown in FIG. 4. The character generator
accepts the output from display logic 134 and decodes it into the proper
7-segment outputs for displaying the HI, LO and OFF characters as
required. To this end, the output of display logic 134 is fed through line
137 into a binary coded decimal decoder 148 which converts the output of
the display logic into the binary coded decimal code required by the
character display driver 150 to generate the 7-segment outputs which are
fed to the display 16.
As stated, the present invention is disclosed herein in the context of a
heartbeat rate monitoring module. With slight modification, the invention
could be adapted to monitor some other desired physiological rate such as
respiration or pulse.
Thus, in accordance with the above, the aforementioned objects are
effectively attained.
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