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BACKGROUND OF THE INVENTION
1. Field of the Inventions
The present invention relates to a remote ECG monitoring system and, more
particularly, to a system for communicating ECG patient signals to
monitors at convenient locations anywhere within a facility equipped with
a master antenna television cable system.
2. Description of the Prior Art
Many patients in hospitals require constant monitoring of various, basic,
life-support functions due to the critical nature of their physical
condition. One of the most commonly monitored functions is a patient's
electrocardiogram (ECG) signals and a patient in intensive care is
typically equipped with a set of leads on his body and an ECG monitor
right by his bedside.
In spite of the necessity for constantly watching the individual ECG
monitors of all patients in an intensive care area, it is infeasible for a
single nurse or trained ECG watcher to effectively watch an entire room
full of monitors because of the physical space that each bed takes.
Therefore, the typical solution to this problem is to provide a hard-wired
connection between each ECG monitor positioned by the patient's bed and a
plurality of slave monitors which are aligned in a series, in front of a
console, at the nurse's station or some other convenient location. This
permits a qualified nurse or ECG watcher to substantially and effectively
monitor a number of patients at a single time.
Unfortunately, intensive care areas are either not large enough or too
expensive to handle all patients requiring ECG monitoring. A variety of
medical situations exist where doctors would like to be able to order an
ECG monitor on a patient without having to subject the patient to the
expense of intensive care. To achieve this, a portable monitor can be
brought to the patient's room and connected to him, but now there is a
problem of providing a qualified person to watch the monitor at all times.
Since qualified people are very limited in number, this is an ineffective
solution to the problem.
Another proposed solution is to use a form of telemetry. It has been
proposed to place the ECG leads on the patient and to provide the patient
with a transmitter which transmits radio waves containing the baseband ECG
information. In order to receive these radio waves at a central monitoring
station, it has been proposed to string antenna wires and amplifiers
throughout the hospital to receive, amplify, and conduct the radio waves
to the central monitoring station. Unfortunately, it is a relatively
expensive procedure to modify the hospital to incorporate the antennas and
amplifiers. Furthermore, because the Federal Communications Commission
limits the amount of energy that may be transmitted, satisfactory
performance requires substantial numbers of antennas and substantial
amplification systems to derive a satisfactory signal at the receiver, and
such systems provide for only a single receiver at a single location.
Still other problems exist with such a telemetry system. That is, since the
patient's transmitted signal can be picked up wherever the antenna goes,
it would not be possible to determine exactly where the patient is.
Furthermore, the signals tend to fade in and out as the patient moves from
place to place, into and out of close proximity to the antenna. Finally,
if the patient is in his room and an emergency condition results, it is
necessary to remove the leads from the patient and put a monitor on the
patient because the existing transmitter does not have facility for a
monitor.
SUMMARY OF THe INVENTION
According to the present invention, these problems are solved in a manner
unknown heretofore. With the present remote monitoring system, a patient
is provided with a portable transmitter unit which permits a certain
freedom of movement in relation to a receiver unit which is mounted right
in the patient's room to directly receive his transmitted signals. The
transmitter has sufficient power and the receiver has sufficient
sensitivity so that the patient can move around relatively freely without
affecting receipt of the signal by the receiver. The receiver, in turn,
after receiving the telemetry signal from the patient and demodulating it
to provide the baseband information, provides an output plug which is
adapted to receive a low-cost, non-isolated monitor which can be plugged
in at any time to immediately view the patient's heartbeat, right in his
room, without altering the patient's connections or hooking up something
to him. Furthermore, the room receiver remodulates a power FM transmitter
with the baseband information and applied it to the master antenna
television cable, which already exists in the hospital to bring television
signals to each patient's room. The carrier signal is chosen to be below
the frequencies used by the television system, but well within the
capability of the cable system, so that the signals may be readily carried
by the cable.
Adjacent the head end of the CATV system, where all branch wires lead from,
this signal is received, converted to some other frequency channel,
amplified, and coupled back into the master antenna television cable. Once
so inserted, this signal looks to the cable system just like any other
carrier signal that might be coming from the roof antenna, i.e. it has the
same basic strength and the same general frequency range, but on a
non-interfering channel. With such an arrangement, one can go to any wall
tap in the entire hospital and couple a receiver to the cable and receive
and demodulate the signal which originated at any place else within the
hospital. Furthermore, multiple monitors can be provided in different
locations in the hospital for monitoring by different personnel.
With the present system, a trained nurse or ECG watcher can effectively
monitor ECG and other patient information from widely scattered locations
within a hospital at a single monitoring station. This being the case, it
is unnecessary to put a patient in intensive care to monitor critical
life-support functions. When a patient is in trouble, the nurse knows
exactly where he is and a portable monitor can be immediately attached to
his local receiver for monitoring instantaneous ECG information. The
present system can be installed in a conventional hospital without any
rewiring or modification thereof, other than the installation of the
present equipment and the connection thereof to the conventional master
antenna wall taps.
A plurality of receiver/monitors can be provided in a central nurse's
station for monitoring simultaneously all patients. Furthermore, a chief
cardiologist or other individual may have a single, tunable monitor in his
office with provision for tuning in any one of the multiple patient
stations. A patient unit and a receiver/retransmitter unit may be provided
in the emergency room of the hospital so that a qualified watcher can
view, from a central location, an ECG on a patient within a few minutes or
seconds after the patient arrives in the emergency room. A patient unit
and a receiver/retransmitter unit may also be provided in each operating
room so that the anesthesiologist may obtain an opinion from a
cardiologist without the cardiologist having to scrub up and come into the
operating room to view the monitor the anesthesiologist is watching.
Briefly, the present remote monitoring and telemetry system for use in a
facility equipped with a master antenna television cable system comprises
a patient unit comprising: means for deriving baseband information from a
patent; means for generating a first frequency signal; means for
modulating said first frequency signal with said baseband information; and
antenna means for transmitting said first modulated signal; a
receiver/retransmitter unit comprising: means for receiving and
demodulating said first modulated signal to derive said baseband
information; means for generating a second frequency signal different from
said first frequency signal; means for modulating said second frequency
signal with said derived baseband information; and means for coupling said
second modulated signal to said master antenna television cable; a
converter/amplifier unit positioned adjacent the head end of said master
antenna television cable comprising: means coupled to said master antenna
television cable for receiving said second modulated signal; means
operatively coupled to said receiving means for converting said second
modulated signal to a third modulated signal having a frequency different
from said second frequency; means for amplifying said third modulated
signal; and means for coupling said amplified third modulated signal to
said master antenna television cable; and a monitoring unit comprising;
means coupled to said master antenna television cable for receiving and
demodulating said third modulated signal to derive said baseband
information.
OBJECTS
It is therefore an object of the present invention to provide a remote ECG
monitoring system.
It is a further object of the present invention to provide a system for
communicating ECG signals from a patient in a hospital to another point in
the hospital where viewing is more convenient.
It is a still further object of the present invention to provide a remote
ECG monitoring system for a hospital which utilizes the hospital's master
antenna television cable.
It is another object of the present invention to provide a remote ECG
monitoring system which eliminates the necessity for rewiring a hospital.
It is still another object of the present invention to provide a remote ECG
monitoring system whereby ECG information can be simultaneously monitored
at a variety of locations within a hospital.
Still other objects, features, and attendant advantages of the present
invention will become apparent to those skilled in the art from a reading
of the following detailed description of the preferred embodiment
constructed in accordance therewith, taken in conjunction with the
accompanying drawings wherein like numerals designate like or
corresponding parts in the several figures and wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the present remote ECG monitoring system;
FIG. 2 is a block diagram of the patient sensor/transmitter unit of the
system of FIG. 1;
FIG. 3 is a block diagram of the receiver/demodulator unit of the system of
FIG. 1;
FIG. 4 is a block diagram of the converter/amplifier unit of the system of
FIG. 1; and
FIG. 5 is a block diagram of the receiver/demodulator unit of the system of
FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings and, more particularly, to FIG. 1, there is
shown a remote monitoring and telemetry system, generally designated 10,
for use in a hospital 11 for simultaneously monitoring, at one or more
central monitoring stations 12, ECG or other baseband information from one
or more patients 13 located in rooms 14 scattered throughout hospital 11.
The only requirement is that hospital 11 be equipped with a conventional
master antenna television (MATV) cable system, generally designated 15,
typically including a roof antenna 16 connected via a power amplifier 17
to a cable 18, which has a myriad of splitters and taps (not shown) so as
to extend throughout hospital 11 to a plurality of wall taps 19 to which
televisions 20 may be connected for receiving conventional television
programs. System 10 combines telemetry plus two-way, coaxial cable
communication techniques to communicate ECG or other patient information
from patient 13 to monitors 43 positioned at station 12 or any other
convenient location in hospital 11 where a wall tap 19 exists.
Broadly speaking, patient 13 is connected via a plurality of electrical
leads 21 to a portable, battery-operated, rechargeable, patient
sensor/transmitter unit 22 which, by virtue of being battery-operated,
eliminates any possibility of electrical shock to patient 13. As will be
described more fully with regard to FIG. 2, patient unit 22 includes a
range switch 23 which permits adjustment of the gain of a differential
amplifier 24 within unit 22 to accommodate different energy levels that
come from different patients. Patient unit 22 also includes an indicator
light 25 that blinks in synchronism with the heartbeat of patient 13.
Light 25 may be adjusted not to blink if the heartbeat is too weak or if
the sensitivity is turned too low, so as to serve as a convenient gauge
for establishing the position of switch 23. Indicator light 25 may also be
used to indicate when the battery in unit 22 is low and requires
recharging.
Patient unit 22 derives the ECG information from patient 13 and transmits,
via an antenna 26, a signal having a first frequency, which signal is
modulated with the baseband information. Each patient unit 22 will have a
different first frequency within the frequency band selected for patient
units 22, as will be described more fully hereinafter.
The signal transmitted by antenna 26 is received by the antenna 30 of an AC
powered, wall-mounted, receiver/demodulator/modulator unit 31 which is
connected via a line 32 to television set 20 and by a line 33 to the MATV
wall tap 19 in room 14. Unit 31 allows signals to come from master antenna
wall tap 19 straight through to television set 20 without interfering with
the normal operation thereof. Unit 31 also demodulates the signal received
from antenna 30 to derive the baseband information and provides an output
tap 34 for receipt of a conventional non-isolated ECG monitor for viewing
of ECG information in room 14. Unit 31 also couples to MATV wall tap 19 a
second signal having a second frequency, different from the first
frequency of unit 22, and modulated with the ECG information. Each unit 31
will have a different second frequency within the frequency band selected
for units 31, as will be described more fully hereinafter.
It is the nature of master antenna television cable systems that the most
effective and direct path from each wall tap 19 is to the head end of
cable 18, typically on the roof, where antenna 16 and amplifier 17 exist
to bring television signals to hospital 11. Accordingly, system 10
includes a directional coupler 35 in cable 18, adjacent the output of
amplifier 17, including a lead 36 connected to a converter/amplifier unit
37. Directional coupler 35 is a conventional item that directs signals on
cable 18 to amplifier 17 or converter/amplifier unit 37, and vice versa,
but signals will not be directly coupled between amplifier 17 and unit 37.
In any event, unit 37 converts the received signals from units 31 to a
different frequency band, amplifies the signals and couples a third set of
signals back into cable 18 via directional coupler 35, the third signals
being similar to the signals normally received by cable 18 from antenna
16. Therefore, the baseband information from all patient units 22 in room
14 and other rooms in hospital 11 is now on cable 18 is transmitted to all
portions of hospital 11 where cable 18 goes. Thus, at central monitoring
station 12, there is provided one or more receiver/demodulator units 40
which are coupled to wall tap 19 via a line 41. Each unit 40 receives and
demodulates the signal from one of patient units 22 to derive the baseband
information.
Referring now to FIG. 2, patient unit 22 includes a differential amplifier
24 connected to patient 13 via leads 21 and a range switch 23 coupled to
amplifier 24 for varying the sensitivity thereof. Range switch 23 permits
adjustment of the gain of amplifier 24 to accommodate for the different
energy levels that come from different patients. The use of a differential
amplifier 24 provides common mode rejection and noise elimination. Thus,
the output of differential amplifier 24 is a voltage analog of the
hearbeat of patient 13. Such signal is applied to a voltage controlled
oscillator 45 which provides a subcarrier signal having, for example, a
center frequency of 2 kHz which is frequency modulated by the ECG analog.
The baseband signal from the patient 13 is in the frequency range of DC to
150 Hz and this signal is used to modulate the subcarrier provided by
oscillator 45. The resultant output of oscillator 45 is a subcarrier
signal having a frequency which is representative of the instantaneous
voltage amplitude at the output of amplifier 24. The output of oscillator
45 is conducted to an FM oscillator 46 which is preferably crystal
controlled to provide stability. The signal from oscillator 46 is
frequency modulated by the output of oscillator 45 and applied via a
matching network 47 to antenna 26.
Oscillator 46 preferably operates in the 174 to 216 MHz range, which is the
frequency range established by the Federal Communications Commission for
use in low power medical telemetry broadcasting. Providing a bandwidth of
200 kHz per channel, a hospital could be provided with a multiplicity of
patient units 22 where the oscillators 46 therein are adjusted to 174 MHz,
174.2 MHz, etc., to provide a different frequency for each patient unit
22.
The signal from differential amplifier 24 is also processed within unit 22
to convert both positive and negative ECG pulses from patient 13 into
uniform pulses, one per heartbeat, by an R wave pulse generator 48. The
output of generator 48 is applied via an OR gate 49 and an amplifier 50 to
indicator light 25, so that a nurse may take the pulse of patient 13
simply by watching the blinking of indicator light 25. A battery level
detector 51 may also be connected to indicator light 25 via OR gate 49 so
as to light indicator 25 permanently when the battery within unit 22
requires recharging.
Referring now to FIG. 3, the signal radiated by antenna 26 is received by
antenna 30 of unit 31 mounted within room 14. The power of unit 22 and the
sensitivity of unit 31 would be such as to permit freedom of movement of
patient 13 within a range of approximately 100 feet without affecting the
operation of system 10. Antenna 30 is coupled to a conventional FM
receiver and demodulator 52 which is tuned to the specific frequency of
oscillator 46, so that receiver 52 picks up signals only from patient unit
22 and not from other patient units 22. Receiver 52 demodulates the signal
to provide, on an output line 53, the 2 kHz subcarrier, modulated by the
baseband information from patient 13. Line 53 is connected to a phase
locked loop discriminator 54 which recovers the baseband signal from the
subcarrier signal on line 53.
A conventional phase locked loop discriminator has two outputs, here
indicated as appearing on lines 55 and 56. The output on line 55 is the
demodulated output signal which, in this case, is in the DC to 150 Hz
range, which signal may be applied via a filter 57 to output tap 34, which
is then available in room 14 for connection to a monitor to view the
hearbeat of patient 13. The other output of discriminator 54, on line 56,
is the same modulated subcarrier signal on line 53 which has been
substantially filtered, since the frequency is eminating from a pure phase
locked oscillator within discriminator 54. This recreated subcarrier
signal, having the baseband information thereon, is applied to an FM
oscillator 60, which is also preferably crystal controlled for purposes of
stability. For present purposes, oscillator 60 is chosen to operate within
the range of 18 to 24 megacycles, a frequency band which is high enough to
conveniently pass through all of the network-type elements that exist in
master antenna systems and yet low enough not to interfere with the normal
broadcast channels. As was the case with patient unit 22, the oscillators
60 in different wall units 31 would be spaced in frequency by
approximately 200 kHz so as to provide the required degree of separation
between the channels of multiple units 31.
The output of oscillator 60 is applied to a low pass/high pass
combiner/filter 61, a conventional off-the-shelf element having a common
port 62, a low frequency port 63, and a high frequency port 64. If the
output of oscillator 60 is applied to low frequency port 63, it emanates
from common port 62, but not from high frequency port 64. Thus, by
connecting common port 62 via line 33 to MATV wall tap 19, the output of
oscillator 60 may be coupled directly to cable 18. The television signals
coming down cable 18, on the other hand, which are at much higher
frequencies and enter common port 62, emanate form high frequency port 64
where they may be connected via line 32 to television set 20. Thus,
oscillator 60 will not interfere with the normal operation of television
set 20.
Referring now to FIG. 4, the signals from all oscillators 60, which have
been applied to cable 18, appear at the head end of cable 18, at the
output of amplifier 17. Cable 18, at the output of amplifier 17, is broken
for insertion of directional coupler 35. The signals coming up cable 18
from all oscillators 60 are relatively weak and emanate into line 36 and
the line connected to the output of amplifier 17. Since amplifier 17 is
operating at a different frequency and since the signals are relatively
weak, they do not affect the operation of amplifier 17.
The portion of the signals from cable 18 emanating on line 36 is applied to
the common port 67 of a low pass/high pass separator/filter 68, which is
identical to unit 61, and has a low frequency port 69 and a high frequency
port 70. The low frequency signal entering common port 67 exits low
frequency port 69 where it is conducted to a broadband converter 71, which
also receives the signal from a local oscillator 72. Broadband converter
71 is a conventional device for receiving a band of frequencies and for
converting them to a different band of frequencies, dependent upon the
frequency of local oscillator 72. The result is that the signals applied
to broadband converter 71, which may be 10, 20, 30, or more, frequencies
confined within the 18 to 24 MHz range, exit from converter 71, converted,
by way of example, to the 82 to 88 megacycle range. This frequency range
is chosen because it corresponds to channel 6, which is an unassigned
channel in the Los Angeles metropolitan area. Obviously, in different
localities, the frequency of local oscillator 72 would be adjusted to
utilize an available, unused channel.
The output of broadband converter 71 is applied to a power amplifier 73
where the signal strength is amplified and applied to high frequency port
70 of separator/filter 68. This high frequency signal finds its way back
to common port 67 and then via lead 36 and directional coupler 35 back to
cable 18. Power amplifier 73 adjusts the gain of the signal output from
converter 71 so that it is now of a signal strength similar to what is
currently emanating from amplifier 17 that is delivering the remaining
channels of television to hospital 11.
Referring now to FIG. 5, the amplified signal from broadband converter 71
and amplifier 73 is now conducted throughout hospital 11 by cable 18.
Therefore, the only thing left to be done is to receive it, and this may
be done adjacent any MATV wall tap 19. Accordingly, at central monitoring
station 12, line 41 is connected to wall tap 19 and then to a unit 40
which includes an FM receiver and discriminator 75, which is similar to FM
receiver and demodulator 52, except that it is tuned to one of the
frequencies from converter 71, the one that corresponds to the particular
patient unit 22 desired. The output of receiver and discriminator 75,
which is the subcarrier of 2 kHz, is conducted to a phase locked loop
discriminator 76, which operates identically to discriminator 54 to
provide the baseband information on a line 77 which is passed through a DC
to 150 Hz filter 78 to an output tap 79. By connecting a conventional
monitor 43 to tap 79, the ECG information from patient 13 may be viewed.
Assuming there were ten patients in hospital 11 provided with ten patient
units 22 operating at ten different frequencies and ten wall units 31
operating at ten corresponding different frequencies, ten units 40 would
be provided at central monitoring station 12 for simultaneously monitoring
all patients 13. But in the cardiologist's office, or the like, it is not
necessary to simultaneously monitor all patients. Therefore, the
cardiologist's office may be provided with a single unit 40 having a tuner
80 coupled to FM receiver and discriminator 75. Tuner 80 would be similar
to the tuner in a conventional television receiver. Under such
circumstances, if the nurse at station 12 sees that patient numberr three
is having a problem, she can call the cardiologist who can tune
discriminator 75 to channel number three and immediately view the ECG
information from patient number three. Or, if a patient was admitted to
the emergency room and a problem occurred, the cardiologist could tune to
the channel assigned to the emergency room and, from his office, view the
problem there. By providing a channel in an operating room, the
cardiologist could look in on a patient undergoing an operation without
having to leave his office.
It can therefore be seen that according to the present invention, there is
provided a remote ECG monitoring and telemetry system which solves the
problems encountered heretofore. With the present system, each patient to
be monitored is provided with a portable transmitter unit 22 which permits
a certain freedom of movement in relation to the receiver unit 31 mounted
in the patient's room 14. Unit 22 may have sufficient power and unit 31
may have sufficient sensitivity so that patient 13 can move around
relatively freely, without affecting the signal from patient 13, provides
an output plug 34 which is always available and adapted to receive a
low-cost, non-isolated monitor which can be plugged in at any time to
immediately view the patient's heartbeat, right in his room, without
altering the connections to him.
After retransmission by unit 31 and conversion and amplification by unit
37, the information from all patients within hospital 11 is simultaneously
available on cable 18. With such an arrangement, one can go to any wall
tap 19 within hospital 11 and couple a receiver/demodulator unit 40
thereto to receive and demodulate the baseband information. Furthermore,
multiple monitors can be provided in different locations in hospital 11
for monitoring by different personnel.
With system 10, a trained nurse or ECG observer can effectively monitor ECG
and other patient information from widely scattered locations within
hospital 11, at a single monitoring station. This being the case, it is
unnecessary to put a patient in intensive care to monitor critical life
support functions. When a patient is in trouble, the nurse knows exactly
where he is and a portable monitor can be immediately attached to receiver
unit 31 for monitoring instantaneous ECG information. System 10 can be
installed in a conventional hospital without any rewiring or modification
thereof, other than the installation of the various units and the
connection thereof to the conventional master antenna wall taps 19.
While the invention has been described with respect to a preferred physical
embodiment constructed in accordance therewith, it will be apparent to
those skilled in the art that various modifications and improvements may
be made without departing from the scope and spirit of the invention. For
example, while specific frequency ranges have been given for the various
units within system 10, by way of example only, it will be evident to
those skilled in the art that a wide variety of frequency ranges may be
used, depending on the circumstances and local transmitting regulations.
Furthermore, while the present system has been described as applicable for
the remote monitoring of patient ECG signals, it will be evident to those
skilled in the art that the present system may be used to monitor other
types of information. Accordingly, it is to be understood that the
invention is not to be limited by the specific illustrative embodiment,
but only by the scope of the appended claims.
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