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Claims  |
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The embodiments of the present invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A patient monitoring system for plural persons, said system comprising
plural individual monitor units each being adapted to be associated with a
different person and movable therewith, each unit including a sensing
means adapted to be operatively connected with the associated person and
responsive to a body condition to produce a body condition signal, signal
processing means connected with the sensing means and including limit
detecting means for producing a recurrent alarm signal each time the body
condition signal deviates beyond a predetermined limit, first memory means
storing the value of said limit and connected with said limit detecting
means, each unit also including a signal transmitting means adapted to
transmit an emergency message comprising at least one occurrence of an
identifier code corresponding to said monitor unit, each said emergency
message having a duration which is several times shorter than the interval
between alarm signals, second memory means for storing said identifier
code, control means connected between said second memory means and said
signal transmitting means for applying said emergency message to the
transmitting means each time said alarm signal occurs, said control means
being exclusively responsive to said alarm signal for initiating
transmission of said emergency message, said control means of each monitor
unit being independent of the other monitor units of the system with the
respective alarm signals occurring independently so that the respective
emergency messages of two monitor units may be initiated at any time
relative to each other but with at least one identifier code of at least
one emergency message of each monitor unit occurring in the time interval
between the emergency messages of the other unit, said system also
comprising a central station including a signal receiving means, said
control means causing the signal transmitting means to initiate
transmission as aforesaid independently of any control by the central
station, decoding means connected with the receiving means for producing a
decoded identifier code in response to receipt of an emergency message,
and annunciating means connected with said decoding means and responsive
to a decoded identifier code for presenting the identifier code of the
monitor unit which produced an alarm signal.
2. The invention as defined in claim 1 wherein said sensing means produces
an analog condition signal, and said signal processing means is a digital
data processor with a computation section which includes said limit
detecting means, and an analog to logic level converting means connected
between said sensing means and said computation section, said converting
means being responsive to an attribute of the analog signal to produce a
train of logic pulses having a frequency corresponding to the value of the
body condition.
3. The invention as defined in claim 2 wherein said limit detecting means
comprises memory means for storing a data signal corresponding to said
predetermined limit for the value of said condition signal, and comparator
means having inputs connected with said converter means and said memory
means for comparing the value of the condition signal with the
predetermined limit.
4. The invention as defined in claim 3 including threshold means connected
between said sensing means and said converter means.
5. The invention as defined in claim 4 wherein said signal processing means
includes first clock means having a frequency higher than the frequency of
the logic pulses, counting means connected with said converting means and
said clock means for counting the clock pulses between said logic pulses
whereby said count of clock pulses is indicative of the time between said
logic pulses and, hence, the value of the body condition.
6. The invention as defined in claim 5 wherein the counting means
accumulates the number of clock pulses over a predetermined number of
periods of logic pulses, averaging means connected to said counting means
and said comparator means for producing an average value of the clock
pulses per period said average value being the average value of the body
condition for comparison with the predetermined limit.
7. The invention as defined in claim 6 wherein said counting means is an
up/down counter, decrementing means connected with the counting means for
decreasing the count after each period by an amount approximately equal to
the count for the first period of said predetermined number of periods.
8. The invention as defined in claim 7 wherein said memory means includes a
first register, and said averaging means comprises means connected with
said up/down counter for transferring bits from the counter to the first
register with the bit positions shifted to perform binary division by a
divisor equal to the number of periods.
9. The invention as defined in claim 8 wherein the decrementing means is
connected with said first register whereby the up/down counter is
decremented by the average count for the previous predetermined number of
periods.
10. The invention as defined in claim 8 including control means connected
with said clock means and with said averaging means and said comparator
means to cause operation thereof in a computation period immediately
following each logic pulse.
11. The invention as defined in claim 10 including second clock means
having a frequency higher than said first clock means and being connected
with said decrementing means to control the decrementing rate thereof.
12. The invention as defined in claim 11 wherein said memory means includes
a second register for storing said data signal, said first and second
registers being adapted to store data in binary form, said comparator
means being of the one-bit type, said control means including shift means
connected with said registers for transferring the counts in said
registers bit-by-bit to the respective inputs of the comparator means in
descending order of bit significance, said comparator producing said alarm
signal in response to a bit comparison indicative of a body condition
signal which exceeds said predetermined limit.
13. The invention as defined in claim 12 including a first alarm store
connected with the output of the comparator means and responsive to an
alarm signal for producing a first alarm store signal, a third register
adapted to store the identifier code of the monitor unit, said first alarm
store being connected with the third register to cause said identifier
code to be applied to said transmitting means, and first alarm counting
means for causing said identifier code to be applied to said transmitting
means a number of times in excess of a predetermined number.
14. The invention as defined in claim 12 wherein said second register of
the memory means includes first and second portions for storing first and
second data signals corresponding to lower and upper limits, respectively,
for the value of said condition signal.
15. The invention as defined in claim 12 wherein said central station
comprises a time generator adapted to produce successive timing pulses
separated by an adjustable time interval, a calibrating counter, circuit
means for connecting the first clock output of one of said monitor units
to said calibrating counter, means for adjusting said time generator
according to a desired limit of the value of said body condition, said
circuit means being adapted to stop and start said calibrating counter
upon the occurrence of successive pulses from said timing generator
whereby said second register in said monitor unit may be preset according
to a prescribed limiting body condition value for a given patient.
16. The invention as defined in claim 13 including a malfunction detecting
means connected with a selected portion of said monitor unit, a second
alarm store connected with the malfunction detecting means and with said
third register to cause said identifier code to be applied to said
transmitting means, and second alarm counting means for causing said
identifier code to be applied to said transmitting means a number of times
equal to said predetermined number.
17. The invention as defined in claim 1 wherein said sensing means
comprises a transducer for producing an electrical signal indicative of
the occurrence of successive heartbeats.
18. The invention as defined in claim 17 wherein said transducer comprises
at least two electrodes adapted to be electrically connected to the body
of the patient.
19. A patient monitor unit comprising a sensing means adapted to be
operatively connected with a patient and responsive to a body condition
thereof to produce a body condition signal, first memory means for storing
a data signal corresponding to a predetermined value of said body
condition, comparator means connected with said sensing means and said
first memory means for producing a recurrent alarm signal each time the
body condition signal deviates beyond the predetermined value, said unit
also including a signal transmitting means connected with said comparator
means and adapted to transmit an emergency message comprising at least one
occurrence of an identifier code corresponding to said monitor unit, each
said emergency message having a duration which is several times shorter
than the interval between alarm signals, second memory means for storing
said identifier code, control means connected between said second memory
means and said signal transmitting means for applying said emergency
message to the transmitting means each time said alarm signal occurs, said
control means being exclusively responsive to said alarm signal for
initiating transmission of said emergency message, whereby emergency
messages may be transmitted by the monitor unit at any time relative to
the emergency message of another monitor unit but with at least one
identifier code of at least one emergency message of the monitor unit
occurring in the time interval between the emergency messages of said
another monitor unit, said control means being independent of any signal
originating externally of the monitoring unit.
20. The invention as defined in claim 19 wherein said sensing means
produces an analog condition signal, said first memory means and said
comparator means being parts of a computation section in a digital data
processor, an analog to logic level converting means connecting between
said sensing means and said computation section, said converting means
being responsive to an attribute of the analog signal to produce a train
of logic pulses having a frequency corresponding to the value of the body
condition, and threshold means connected between said sensing means and
said converting means.
21. The invention as defined in claim 20 wherein said signal processing
means includes first clock means having a frequency higher than the
frequency of the logic pulses, counting means connected with said
converting means and said clock means for counting the clock pulses
between said logic pulses.
22. The invention as defined in claim 21 wherein the counting means
accumulates the number of clock pulses over a predetermined number of
periods of logic pulses, averaging means connected to said counting means
and said comparator means for producing an average value of the clock
pulses per period, said average value being the average value of the body
condition for comparison with the predetermined value.
23. The invention as defined in claim 22 wherein said counting means is an
up/down counter, decrementing means connected with the counting means for
decreasing the count after each period by an amount approximately equal to
the count for the first period of said predetermined number of periods.
24. The invention as defined in claim 23 wherein said averaging means
includes a first register connected with said up/down counter with means
for transferring bits from the counter to the register with the bit
positions shifted to perform binary division by a divisor equal to the
number of periods.
25. The invention as defined in claim 24 wherein the decrementing means is
connected with said register whereby the up/down counter is decremented by
the average count for the previous predetermined number of periods.
26. The invention as defined in claim 24 including control means connected
with said clock means and with said averaging means and said comparator
means to cause operation thereof in a computation period immediately
following each logic pulse.
27. The invention as defined in claim 26 including second clock means
having a frequency higher than said first clock means and being connected
with said decrementing means to control the decrementing rate thereof.
28. The invention as defined in claim 27 wherein said memory means for
storing said data signal comprises a second register, said first and
second registers being adapted to store data in binary form, said
comparator means being of the one-bit type, said control means including
shift means connected with said registers for transferring the counts in
said registers bit-by-bit to the respective inputs of the comparator means
in descending order of bit significance, said comparator producing said
alarm signal in response to a bit comparison indicative of a body
condition signal which exceeds said predetermined limit.
29. The invention as defined in claim 28 including a first alarm store
connected with the output of the comparator means and responsive to an
alarm signal for producing a first alarm store signal, said second memory
means including a third register adapted to store the identifier code of
the monitor unit, said first alarm store being connected with the third
register to cause said identifier code to be applied to said transmitting
means, and first alarm counting means for causing said identifier code to
be applied to said transmitting means a number of times in excess of a
predetermined number.
30. The invention as defined in claim 28 wherein said second register of
the memory means includes first and second portions for storing first and
second data signals corresponding to lower and upper limits, respectively,
for the value of said condition signal.
31. The invention as defined in claim 29 including a malfunction detecting
means connected with a selected portion of said monitor unit, a second
alarm store connected with the malfunction detecting means and with said
third register to cause said identifier code to be applied to said
transmitting means, and second alarm counting means for causing said
identifier code to be applied to said transmitting means a number of times
equal to said predetermined number.
32. The invention as defined in claim 20 including a casing adapted to be
mounted upon the body of said patient and being readily portable thereby,
said sensing means being disposed externally of said casing, said
converting means and digital data processor being disposed internally of
said casing.
33. The invention as defined in claim 32 including mounting means connected
with said casing and adapted to encircle a portion of the anatomy of said
patient, said transmitting means being a radio transmitter including a
radio transmitting antenna formed by a portion of said mounting means.
34. The invention as defined in claim 19 wherein said sensing means
comprises a transducer for producing an electrical signal indicative of
the occurrence of successive heartbeats.
35. The invention as defined in claim 34 wherein said transducer comprises
at least two electrodes adapted to be electrically connected to the body
of the patient.
36. The invention as defined in claim 19 wherein said transmitting means is
a radio transmitter. |
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Claims |
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Description |
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FIELD OF THE INVENTION
This invention relates to monitoring systems and more particularly to a
system which comprises a plurality of monitoring stations all of which may
report to a single central station. In a particular application, this
invention relates to a system for monitoring selected life functions of
several persons such as patients in a hospital.
BACKGROUND OF THE INVENTION
In caring for patients in a hospital, such as those requiring intensive
care, it is desired to provide continuous observations of one or more life
functions of each patient; however, the common technique of providing such
observation by trained nurses not only requires a large number of nurses
but also actually falls short of continuous uninterrupted observation. It
is therefore desired to provide a system for accomplishing the continuous
observation of multiple patients by means of instrumentation and a single
attendant who need not be highly trained.
Patient monitoring systems of various types have been proposed in the prior
art. For the most part, these prior art systems may be characterized as
telemetering systems wherein the patients or persons being monitored are
fitted with one or more sensors which produce signals corresponding to a
selected vital function of the person. The signals representing the vital
function as detected by the sensors are then transmitted as data signals
to a central processing station where the significance of the signals
relative to the given patient is determined manually or by a data
processing system. Patient monitoring systems of this type are described
in the following U.S. Pat. Nos. Vogelman et al 3,572,316, Pacela et al
3,608,542, Buxton et al 3,646,606, and Greatbatch 3,639,907. The
difficulty with these prior art systems is that they are very complex,
especially at the central station in that they require computer or data
processing equipment of relatively large capacity. Additionally, such
prior art systems need a fairly sophisticated communication system between
the patient monitoring stations and the central station. Because of the
complexity and high cost, patient monitoring systems have not been used
extensively and there remains a great need in providing multiple patient
intensive care without exorbitant costs associated with presently known
techniques.
SUMMARY OF THE INVENTION
According to this invention, a monitoring system, especially adapted for
hospital patient monitoring, is provided which develops and processes data
at the monitor station and transmits an identification signal to the
central station only in case of an emergency. This is accomplished by
assigning a monitor unit or station to each patient with a suitable
identification code and providing a programmed data processor or computer
within the monitor station so that the emergency status of the patient is
decided at the monitor station. If an emergency exists, a transmitter at
the monitor station is activated and transmits the station identification
to the central station. The central station decodes the identification
signal and produces an alarm display to invoke an emergency procedure for
treatment of the patient in distress.
Further, in accordance with this invention, the monitor station is portable
by the patient, preferably as a wrist-unit or as a pendant on a necklace.
This is accomplished by implementing the processor electronics in
microcircuits and minimizing the need for communication between the
monitor station and the central station. Additionally new signal
processing means have been developed to permit the processor to be
implemented with a minimum number of stages while affording ample capacity
in programming and computation.
A more complete understanding of this invention may be obtained from the
detailed description that follows taken with the accompanying drawings in
which:
FIG. 1 is a block diagram of the monitor system;
FIG. 2 is a side view with parts cut away of the monitor station in the
form of a wrist-unit;
FIG. 3 is a plan view of the wrist unit;
FIG. 4 is a block diagram of the analog signal processing stages;
FIG. 5 is a waveform diagram of the heartbeat signal and logic signal;
FIG. 6 is a block diagram of the transmitter;
FIG. 7 is a block diagram of the central station;
FIG. 8 is a block diagram of the programming means for the monitor station;
FIG. 9 is a block diagram of a test apparatus for the monitor station;
FIGS. 10 and 11 are timing diagrams;
FIGS. 12, 13 and 14 taken together represent the digital processor of the
monitor station; and
FIG. 15 is a timing diagram pertaining to the computation cycle of the
digital processor.
DETAILED DESCRIPTION
Referring now to the drawings, there is shown an illustrative embodiment of
the invention in a patient monitoring system; in particular, the
illustrative embodiment is a system for monitoring the pulse or heartbeat
rate of multiple persons in a hospital or clinic. It will be appreciated
as the description proceeds, that the invention is applicable to the
monitoring of other life functions of persons or animals. Additionally, it
will be seen that the invention is not limited in its use to the
monitoring of life or vital functions; instead, it may be used in the
monitoring of physical conditions at multiple stations, such as may be
desired in industrial plants or in military applications and the like.
As alluded to above, the subject invention in the illustrative embodiment
is adapted for continuous monitoring of a selected life function of one or
more persons and reporting to a central station when a predetermined
condition occurs. In the particular illustrative embodiment to be
described, the invention is adapted for use in a hospital for monitoring
the heartbeat rates of multiple patients. Each individual patient is
supplied with a monitor station or remote unit which is suitably attached
to the patient. The monitor station may be attached in various ways such
as by a wrist band or as a pendant on a neck band; in the illustrative
embodiment it takes the form of a wrist-mounted unit, in the manner of a
wristwatch. Each monitor station is adapted to sense a selected condition
relating to a life function of the person, develop data signals
corresponding thereto, process the data signals and transmit an alarm to
the central station in the event that the monitored condition reaches a
predetermined value. The central station, which is attended by an
operator, is effective upon receipt of a transmitted signal to produce a
display or audible alarm which identifies the individual monitor station
which originated the transmission.
FIG. 1 is a block diagram representation of the monitoring system including
a monitoring station 10 and a central station 12. The monitoring station
includes a sensor 14 which is adapted to produce a signal indicative of a
physical condition; for example, the sensor 14 may be a transducer in the
form of two electro-cardiograph electrodes, an acoustical transducer
responsive to the pulse at a person's wrist, or a thermometer adapted to
produce an electrical output signal corresponding to temperature. The
sensor output signal, which is in the form of an electrical analog signal,
is converted to logic signal form by an analog to logic level converter 16
and then applied to the input of a digital processor 18. The digital
processor performs specified mathematical computations or other
manipulations of the input data and, under certain circumstances, produces
an output signal which is applied to a transmitter 20. A transmitting
means including a transmitter 20 and a communications channel, such as a
radio link indicated by the arrow 22, is adapted to send a coded signal to
the central station 12. The central station comprises a signal receiver 24
which is capable of accepting transmitted signals through the
communications link 22 from any one of a multiplicity of individual
monitor units 10. The output of the receiver 24 is applied to a decoder 26
which is operative in response to the transmitted signal to produce an
identification signal which is applied to the input of a display or alarm
means 28 which is adapted to identify the transmitting monitor station to
the operator attending the central station.
THE MONITOR STATION
An exemplary embodiment of the monitor station in the form of a remote unit
30 is shown in FIGS. 2 and 3. This remote unit comprises a case 32,
preferably constructed of metal and hermetically sealed, which is fitted
with a wrist strap 34 adapted to be fitted around a host person's wrist,
as by a buckle, not shown. The case 32 includes a removable metal lid 36
to permit access to the interior of the case for servicing. An electronics
package or assembly 38 is mounted upon a substrate 40 which in turn is
supported upon a base member 42 inside the case. A battery 44 is connected
by suitable electrical leads to conductors on the substrate 40 to supply
electrical power to the electronics assembly. As will be described
subsequently, the electronics assembly 38 takes the form of a large scale
integrated circuit, preferably of the type known as complementary symmetry
metal oxide semiconductor (CMOS) integrated circuits. This technique of
circuit manufacture permits a vast number of transistors to be disposed
within a very small volume. The CMOS integrated circuit exhibits an
exceedingly small power drain on the power supply. The electronics
assembly 38 comprises the analog to logic level converter 16, the digital
processor 18, and the transmitter 20 which were described with reference
to FIG. 1. An electrode 44 and an electrode 46, both of the
electro-cardiograph type, are mounted upon the case 32 exteriorly thereof
for electrical connection with the body of the host person at selected
points. The electrodes are adapted to produce an electrical signal
indicative of the heartbeat of the host person in a well-known manner. The
electrodes are insulated from and extend through the wall of the case 36
into electrical connection with the electronics assembly 38. The
electrodes 44 and 46 constitute the sensor 14 which was referred to in
connection with FIG. 1. The remote unit 30 is also provided with an
antenna lead 48 which is insulated from the case and extends through the
wall thereof from the electronics assembly 38 to a metal wrist band 50
which constitutes a transmitting antenna and comprises a portion of the
transmitter 20.
The electronics system preferably includes sensor signal processing stages
for producing a logic level signal as illustrated in FIG. 4. The sensor
14, in the form of the electrodes 44 and 46, detects an electrical signal
52, such as that shown graphically in FIG. 5. This electrical signal has a
peak amplitude of a few millivolts and each of the impulses corresponds to
a heartbeat of the host person. Each impulse is characterized by an
initial, high amplitude positive pulse followed by a negative pulse of
lesser amplitude which in turn is followed by a trailing low amplitude
positive pulse. Each impulse which corresponds to a heartbeat typically
has a duration of around twenty milliseconds. The interval between
heartbeat impulses typically varies from about 1/2 second to about 2
seconds.
The signal received by the sensor 14 is applied through isolation means 54
to prevent accidentally applied or spurious excessive voltages from
reaching the electronic devices and to prevent the application of
electronic system signals to the host person. The sensor signal is also
applied through a bandpass filter 56 to exclude noise which might
accompany the signal. The output of the filter is applied to the input of
an amplifier 58 to increase the signal strength to a workable level. The
output of the amplifier is applied to a threshold device 60 which is
adapted to recognize significant signal characteristics, such as amplitude
or time period. The filtered and amplified signal 62 is shown in FIG. 5.
The threshhold device 60 is of the amplitude responsive type and as shown
in FIG. 5, produces a rectangular pulse 64 in response to the signal 62
exceeding the threshhold level. It is noted that the amplifier may be of
fixed gain followed by a variable threshhold device or, alternatively, a
variable gain amplifier may be followed by a fixed threshhold device. The
output of the threshhold device 60 is applied to a logic pulse generator
66 which produces a constant amplitude fixed duration logic level pulse
DS, as shown in FIG. 5, corresponding to each pulse 64. The threshhold
device 60 and pulse generator 66 correspond to the analog to logic level
converter 16 referred to in connection with FIG. 1. The pulse DS has a
duration of about 1 millisecond and, as indicated in FIG. 5, has a pulse
period or time interval between pulses equal to the interval between
successive heartbeats which typically may range from 1/2 to 2 seconds.
As described with reference to FIG. 1, the logic pulses DS are applied to
the digital processor 18 for such computation or manipulation as may be
required to determine whether an alarm or emergency signal should be
transmitted to the central station. A typical example of the data
processing which is performed by the processor 18 in the monitor station
will now be described. (A detailed description of the processor itself
will be given subsequently.) In the illustrative embodiment, the life
function being monitored is the heartbeat rate of the host person wearing
the monitor station in the form of the remote unit of FIGS. 2 and 3. The
data processing function will be described with reference to a selected
patient (host person) in a hospital environment. It will be assumed that
the patient's physician has determined that the patient's heartbeat rate
should be monitored continuously and that the patient's condition is such
that he should be attended to immediately in the event that his heartbeat
rate on a time average basis, drops below 40 beats per minute or if it
exceeds 120 beats per minute. Further, the physician specifies that the
heartbeat rate should be determined as a time average with the average
being calculated for a base period corresponding to eight successive
heartbeats of the patient. If the heartbeat rate of the patient should be
outside the low and high limits specified by the physician, the remote
unit is to transmit a medical emergency signal which will summon medical
help.
In addition to the patient monitoring function specified by the physician,
the remote unit is adapted to perform a self-checking function and report
the occurrence of a malfunction so that its capability in monitoring the
condition of a patient will be known at all times. For this purpose, one
or more self-checking means are provided within the remote unit and
signals are developed or supplied to the processor. Such signals are
utilized by the processor to determine whether a malfunction exists and,
if so, a malfunction emergency signal is transmitted to the central
station.
As described above, the monitor station (wrist unit) is independently
capable of ascertaining whether the patient's condition (heartbeat rate)
is inside or is outside the limits specified by the physician. This
ascertainment is made at the monitor station by digital data processing
which comprises the production of a signal quantity which is the function
of two or more variables and comparison thereof with one or more reference
quantities. The performance of the data processing at the monitor station
eliminates the need for communication with the central station except in
the case of an emergency situation. In particular, a transmission need be
made regarding the patient condition only if and when the condition is
outside the specified limits; then, it is only necessary to transmit an
identification code word or signal which identifies the monitor station
which produces the alarm so that the attendant at the central station can
dispatch medical help to the patient in distress. Additionally, the
monitor station will send an emergency signal transmission when the
self-checking means of the monitor station signifies that a malfunction
exists in the monitor station. In this case, only a signal identifying the
monitor station with the malfunction need be transmitted so that the
attendant at the central station knows that the monitor station cannot be
relied upon until the malfunction is corrected. In the case of the medical
alarm, i.e., with the heartbeat rate outside the specified limits, the
emergency signal T, which is a burst of identification code words, is
transmitted repeatedly for an indefinite number of times. Preferably, the
emergency signal T is transmitted repeatedly until medical aid reaches the
patient in distress or until the battery is run down and the remote unit
is unable to continue transmission. For functional alarm where a
malfunction occurs in the monitor station the emergency signal T is
transmitted a definite number of times, preferably four times, and then
the transmission is terminated.
This arrangement, including data processing at the monitor station and
transmission only of a identification signal, permits simplified
signalling with a common signal channel for all monitor stations. Since no
raw or intermediate data is transmitted to the central station, the
communication link is passive until an emergency occurs at one of the
monitor stations. There is no problem of bandwidth requirement for the
communication link and there is no problem of crosstalk among the several
transmitting stations. If simultaneous emergency transmissions occur the
overlap will be limited (as discussed further below) so both stations can
be identified.
A radio communication link between a monitor station and the central
station is shown in FIG. 6 and FIG. 7. The radio transmitter 70 is a pulse
code modulated transmitter with a carrier wave at an assigned fixed
frequency. The carrier frequency is the same for all the monitor stations
which communicate with the same central station. The digital processor 18,
as described with reference to FIG. 1, is operative to control the
transmission by the transmitter 70. When an alarm signal is developed by
the processor, the transmitter 70 is turned on and the modulator thereof
receives the identification code word in binary form in a serial feed of
the code bits. The identification code word is supplied to the transmitter
a definite number of times, e.g. eight times, in the case of a functional
alarm signal from the processor and then the transmitter is turned off. In
the case of a medical alarm signal being developed by the processor, the
transmitter is turned on and the identification code word is fed to the
modulator a larger number of times, for example, sixteen times, followed
by a delay interval of, for example, 4 seconds duration. The burst or
series of identification code words followed by the delay interval is
repeatedly transmitted an indefinite number of times. Each of the
identification code words is a binary word, which includes an identifier
code ID and programming code Y. In the preferred embodiment, the
identification code word is a 14 bit word with eleven bits allotted to the
identifier code which is assigned to the particular monitor station and
which distinguishes it from other monitor stations. Some of the eleven
bits of the identifier code may be used for an error checking code. The
remaining three bits in the identification code word are allotted to the
programming code Y for use by the processor; in the illustrative
embodiment, this programming code Y specifies the number of heartbeats
which is to be used as the basis for determining the average heartbeat
rate. A typical identification code word or signal, as emitted by the
transmitter 70, is illustrated in FIG. 6 showing the allocation of bits
for the identifier code ID and the programming code Y.
THE CENTRAL STATION
The central station for the monitoring system utilizing a radio
communication link is shown in FIG. 7. A radio receiver 72 is tuned to the
radio frequency carrier wave assigned to the monitor system. The emergency
signal T is received and demodulated by the receiver 72 and the resulting
identification code word is applied to the input of a decoder 74 which
converts the code word into a digital signal. The decoder includes a code
signal verification means wherein the received alarm code in digital form
is compared with the list of alarm codes which have been assigned to
monitor stations in the system. The many repetitions of the transmitted
code word are compared with each other to verify the identification of the
monitor station sending the alarm signal. The decoder 74 converts the
binary code word into a corresponding decoded identifier word such as a
decimal number assigned to the monitor station. Alternatively, the decoder
may translate the binary code word into the patient's name. The decoder 74
produces an output signal which represents the decoded identifier word.
The output signal from the decoder is applied to the input of a latch
circuit 76 which stores the decoded identifier word which corresponds to
the monitor station represented by the identification code word. The latch
circuit 76 is connected with an annunciator preferably in the form of a
display means 78 which produces illuminated characters corresponding to
the number or name of the monitor station which transmitted the alarm
signal. The display 78 is disposed within view of the central station
attendant and may be accompanied by an audible alarm to draw attention to
the display means.
The aforementioned display means may be used as a main display means to
signify a current or existing alarm in conjunction with plural auxiliary
display means to signify previous alarms. The main display means, of
relatively large size, receives the number or name of the monitor station
directly from the latch circuit 76 immediately upon receipt of the
emergency signal. The number or name is held in the main display means
until the attendant acknowledges receipt of the alarm by operating a
switch. This causes the number or name to be transferred to an auxiliary
display means and the main display means to be cleared. The number or name
is held in the auxiliary display means until manually cancelled when the
emergency is over.
LOADING AND TESTING OF MONITOR STATION
Before any of the monitor stations is put into use for monitoring the
heartbeat rate of a given patient, it must be provided with certain data
which is relevant to the patient to be monitored. The supply, or inputting
of data, also referred to as programming, is accomplished by means shown
in FIG. 8. In general, there are two types of data to be loaded into the
monitor station. One type is the identifier code which identifies the
particular monitor station and, hence, the patient to which it is
assigned. The other type of input data relates to parameters of the
monitoring function; in particular, for the monitoring of the heartbeat
rate, the acceptable limits of the heartbeat rate must be specified. While
these limits may be specified in various ways, e.g., as beats per minute
or as pulse period, it is desirable to use an average value taken over a
specified time period. For example, the attending physician of a given
patient may specify that an emergency signal must be sent if the patient's
heartbeat rate falls below an average of 40 beats per minute or if it
rises above an average of 120 beats per minute, the average being taken
over the time period of the last 16 beats. This time period for deriving
the average heartbeat rate, referred to herein as the averaging period,
may be selected from a wide range of values.
Referring now to FIG. 8, the input data for programming the monitor station
is supplied through a manually controlled input means 82, preferably in
the form of a keyboard. The identification code word ID+Y for the monitor
station is fed serially by bit into a memory section, such as a shift
register, of the integrated circuit chip. The programming word Y is
comprised of three bits which specify the value of the averaging period as
1, 2, 4, 8, 16, or 32 heartbeat periods. Also, the data input means 82
accepts the specification of the lower and upper limits of heartbeat rate.
This input is in the form of a data word B which is comprised of fourteen
binary bits with the lower limit being expressed in the first 7 bits and
the upper limit being expressed in the last 7 bits. The data input for the
data word B is suitably expressed in heartbeats per minute at the
keyboard.
The output of the data input means 82 is applied to a data converter 84
which is operative to convert the input data to the format required by the
processor. The ID code and the programming code Y are applied directly
from the converter 84 to a loader 86. The loader 86 supplies the data word
ID+Y in serial fashion to the assigned register in the processor.
The data word B, which represents the lower and upper limits of the
heartbeat rate, may also be supplied directly to the loader 86 which is
operable to feed the data word B in serial fashion into the assigned
storage register of the processor. However, for the purpose of providing a
high degree of accuracy in the timing function of the monitor station,
additional means are provided for loading the monitor station with the
data word B. Since the heartbeat rate is of critical importance in the
monitoring function it must be measured accurately at the monitor station;
while this could be accomplished with a precision local oscillator or
clock in the monitor station, such means are costly in terms of components
and space requirements. Instead of a precision clock, an oscillator having
a relatively wide frequency tolerance is provided and the output thereof
is compared with a precision time base generator prior to loading the
monitor station with the data word B. As shown in FIG. 8, the data word B
is supplied to the data converter 84 and the output thereof is applied to
a time base generator 88. The first 7 bits of the word B specifies the
lower limit of the heartbeat rate in beats per minute which, or course,
corresponds to a heartbeat period which is expressed in a definite number
of milliseconds. The data converter applies a signal to the time base
generator indicative of the heartbeat period and the time base generator
produces an output signal of the specified duration. This time base signal
is applied to the input of a counter 90 to enable the counter for the
duration of the time base signal. During this loading process, the clock
oscillator is running in the monitor station 10 and the low frequency
clock signal CLL is applied to the count input of the counter 90. In the
illustrative embodiment, the low frequency clock signal has a nominal
frequency of 80 Hz and typically the frequency of a given monitor station
will be different from the nominal frequency by as much as 10%. During the
time base signal from the generator 88, the counter 90 will accumulate a
count equal to the number of low frequency clock pulses which occur during
the specified low limit period. For example, it may be assumed that the
low frequency clock has a nominal frequency of 80 Hz and that the low
limit specified by the attending physician for the given patient is to be
48 heartbeats per minute, which is equivalent to a pulse period of 1.25
seconds. Accordingly, the time base generator 80 provides a timing pulse
of 1.25 seconds duration to a high degree of accuracy. During this timing
pulse the counter 90 reaches a count of 110 which means that the low
frequency clock is 10% fast and the low limit to be established in the
monitor station is a low frequency clock pulse count of 110. The same
means and technique are utilized for establishing the high limit for the
heartbeat rate in the monitor station. The output of the counter 90 is
applied to the loader 86 which feeds a low limit code and a high limit
code into an assigned shift register in the processor.
After the monitor station is loaded with the required data as just
described, it is desirable to test the monitor station for proper
functioning before it is put into use on the assigned patient. This
testing is performed in a manner indicated by the process flow diagram of
FIG. 9. The monitor station 10 to be tested is connected with a body
signal simulator 92 which, in the illustrative embodiment, supplies
simulated electrical heartbeat signals to the two electrodes of the
monitor station. The simulated heartbeat signals are supplied at various
heartbeat rates under the control of a variable signal generator 94. A
program control unit 96 applies a control signal to the variable signal
generator 94 to cause the signal variation and hence the simulated
heartbeat signals to vary in accordance with a predetermined program. The
monitor station 10 responds to the simulated heartbeat signals and, if it
is functioning properly, it will transmit the medical alarm in the event
the heartbeat rate falls outside the limits and it will transmit a
functional alarm in the event of a malfunction in the monitor station. If
the simulated heartbeat rate remains within the lower and upper limits and
if there is no malfunction, there will be no transmission from the monitor
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