What we claim is our invention
1. A cardiac disaster alarm system for use with a central alarm console comprising in combination at least one portable unit, each unit including a transmitter having a source of power, circuits which may be operatively connected to a ptient for monitoring cardiac function, means for actuating said transmitter to transmit coded alarm signals when predetermined high or low levels of said cardiac function are exceeded, a receiver within radio range of said transmitter operatively connected to the associated central alarm console, said alarm being connected to said alarm console, means in said receiver for decoding the alarm signals and causing said alarm signals are received, means for controlling and turning off said alarm, said console and receiver also including means to identify the location transmitting the alarm by the coding of the transmitted signal, means for transmitting, receiving and decoding an intermittent "Operating" signal for automatically checking the operation of said system, and means in said receiver for operating said alarm when said intermittent Operating signal is absent.
2. A cardiac disaster alarm system for use with a central alarm console comprising in combination at least one portable unit, each unit including a transmitter having a source of power, circuits which may be operatively connected to a patient for monitoring cardiac function, means for actuating said transmitter to transmit coded alarm signals when predetermined high or low levels of said cardiac function are exceeded, a receiver within radio range of said transmitter operatively connected to the associated central alarm console, said alarm being connected to said alarm console, means in said receiver for decoding the alarm signals and causing said alarm to indicate when said alarm signals are received, means for controlling and turning off said alarm, said console and receiver also including means to identify the location transmitting the alarm by the coding of the transmitted signal, and means for periodically transmitting, receiving and decoding coded pulses representing the heart rate of the patient being monitored, the periodicity of said coded pulses automatically checking the operation of said system, and means in said receiver for operating said alarm when said coded pulses are absent.
BACKGROUND OF THE INVENTION
This invention relates to new and useful improvements in cardiac disaster alarms.
Patients with acute myocardial infarction are routinely kept under observation in a coronary care unit and monitored for the first 72 hours when the incidence of potentially fatal arrhythmias is greatest. Then the patients are transferred to a regular medical ward for 14 to 21 days. However, they cannot be kept under constant observation while on a regular ward an it is found that a small but disturbing number of these patients die suddenly and unexpectedly, presumably due to undetected fatal arrhythias. Irrespective of the cause of an arrhythia, lives can be saved if the staff could be warned of a cardiac catastrophe when it occurs, and so immediately incur resuscitation.
Cardiac monitors in current use are relatively large, and require specially trained staff since they are designed for constant visual observation. Such equipment is useless on a regular ward since the ordinary ward staff are not trained in their use. Further, the entire ECG is continuously transmitted. A simple type of monitor is needed for this use to immediately warn of trouble by giving an alarm if the heart rate is too slow or too fast. The Cardiac Disaster Alarm has been devised to fulfill this need.
SUMMARY OF THE INVENTION
The cardiac disaster alarm is a small, portable instrument, worn by a patient, which senses the heart's activity and transmits an alarm signal if the patient's heart rate deviates beyond preset limits. In addition to the alarm signal, the instrument can also be made so as to transmit an "Operating O.K." which provides a check on the operation of the entire monitor-alarm system, and, in another embodiment, this O.K. signal could be coded so as to transmit the value of the patient's heart rate.
This device will give an alarm should the heart rate become too high or too low (tachycardia and brachycardia respectively), the particular rates at which the alarm is triggered may be set to the needs of each individual patient. The alarm can also identify the patient and give his location so that the necessary action may be taken.
A pulsed, coded alarm signal can be transmitted or a periodic coded Operating O.K. signal can be transmitted. The bandwidth and signal handling requirements are greatly reduced over alternate methods which transmit the electrocardiogram on a continuous basis. This method uses much less power than usual telemetry.
With the considerations and inventive objects herein set forth in view, and such other or further purposes, advantages or novel features as may become apparent from consideration of this disclosure and specification, the present invention consists of the inventive concept which is comprised, embodied, embraced or included in the method, process, construction, composition, arrangement or combination of parts, or new use of any of the foregoing, herein exemplified in one or more specific embodiments of such concept, reference being had to the accompanying Figures in which:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of one embodiment of the invention.
FIG. 2 is a schematic diagram of a suitable circuit for the patient unit.
FIG. 3 is a schematic diagram of a suitable circuit for the room receiver transmitter.
FIG. 4 is a schematic diagram of a suitable circuit for the central console (and alarm system).
FIG. 5 is a schematic block diagram of the nonfail-safe embodiment.
FIG. 6 is a schematic block diagram of one version of a fail-safe circuit.
FIG. 7 is a view similar to FIG. 6 but showing an alternative circuit.
In the drawings like characters of reference indicate corresponding parts in the different figures.
Referring now to the drawings by reference characters, there is shown in FIG. 1 the layout of the nonfail-safe system. Carried by either ambulatory or stationary patients are the patient units 10, described in detail below, which are of vest pocket size. Should the heart rate of a patient reach a predetermined alarm condition, a small transmitter in the unit is switched on automatically. The waveform of the output of this transmitter is modulated in a manner characteristic of that particular patient (though patients served by different room units may have transmitters with the same modulation). This signal is sent through the room to a room receiver 11, which may actuate a local alarm 12. Alternatively, under favourable transmission conditions, this signal could go directly to the central station. The room receiver unit then changes the carrier frequency to one suitable for sending throughout the building either by power supply mains, hard wire connections or telemetry. The characteristic modulating waveform remains unaltered by this process. The room receiver units in each ward may send out a different carrier frequency which will serve to identify the location of the patient. When the central console 13, picks up this frequency an alarm 14 is sounded and from the information received, the patient and his location is automatically identified. Alternatively, the receiver may be incorporated in the central station or alarm circuits may be incorporated in the room receiver.
FIG. 2 is a schematic diagram showing a suitable conventional circuit for the patient unit. The important sections of the circuit shown are 15, balanced input to dual differential amplifiers; 16, waveform filters; 17, trigger level setting; 18, monostable circuit; 19, an integrator; 20, upper and lower level detectors; 21, power supply gate; 22, tone oscillator; 23, radio frequency oscillator; 24, R.F. modulator; and 25, R.F. amplifier.
The device operates in the following manner:
Electrodes 27 are connected to the patient as for an electrocardiogram. The output from the first stage therefore, at 28, is the voltage waveform developed across the heart, plus some interfering signals which are weaker than the desired signal pulse due to filtering action.
With each input pulse the monostable circuit gives a fixed voltage output for a pre-set length of time, before dropping back to zero. Interfering signals as well as the desired ones may trigger this circuit, and to prevent this happening, a trigger level setting device 29 may be adjusted so that only the strongest signals operate the monostable circuit. A fast heart rate gives a greater mark to space ratio in the rectangular-wave output than a slow one. When these pulses are fed into the integrator, the steady output voltage is higher, the faster the heart rate. This is developed at 30 and then fed into upper and lower level detectors.
Should the voltage level at 30 reach certain pre-set upper or lower limits, the power supply gate will be closed and the transmitter made operative. The upper and lower level detactors may be adjusted by means of variable resistors 31 and 32 so that alarm is transmitted when certain heart rates are reached, these limits being determined by the condition of each individual patient. Alternatively, these may be pre-set and, for simplicity, these fixed alarm settings are preferred.
Under normal conditions, all the stages after the power supply gate are inoperative, ensuring economic battery usage. When an alarm condition is reached, the power supply gate is closed and the final stages are made operative. The transmitter may be made to operate in a pulsed fashion, if desired, to increase range and conserve power. The tone oscillator A, radio frequency oscillator B, modulator C and amplifier D, all function in the normal manner. The modulating signal is made different for each patient unit in a particular ward. The modulated wave is then transmitted from the portable antenna 32A to be picked up by the room receivers.
FIG. 3 is a schematic diagram showing a suitable conventional circuit for the room receiver.
As this device operates in a conventional way, only a brief description will be entered into here. The signal from the patient unit is received on an antenna 36, and amplified as at 37. This is then fed into the mixer 38, where it is mixed with another frequency produced by the oscillator 39, the difference in frequency being the intermediate frequency. The room receivers in each ward may have a different intermediate frequency or other indentifying characteristics. This signal is picked out and amplified. It is modulated by the waveform characteristic of the patient whose alarm is operative.
By means of the tuned circuits at point 33 this signal is fed into the power supply mains or other communicating link, through which it is conducted to the central console. An automatic gain control cirucit 40, is also included so that the circuits are not overloaded by strong signals. Reference character 41 indicates an I.F. amplifier circuit and 42 the I.F. power amplifier circuit.
FIG. 4 is a schematic diagram showing a suitable circuit for the central console. The important sections of the circuit shown are (1) radio frequency amplifiers (2) tone frequency (audio frequency) amplifier and filter 44 (3) automatic gain control 45 and (4) self latching alarm system 46.
The device shown here is only capable of receiving one intermediate frequency, though only minor modifications are needed to take more. It operates in the following manner:
The desired signals are removed from the mains by tuned circuits at point 34. These signals are then amplified in several stages, automatic gain control being applied to one of them. The modulating audio frequency is detected and amplified.
This signal is then fed into resonant circuits corresponding to the various modulation waveforms of the different patient units. Only the one that corresponds to the signal being received will be activated, and this will then set off an alarm. An advantage of the circuit shown is that it is self latching, i.e. regardless of the signals received the alarm 35 will sound until re-set by a push button 35' or the like.
Semi-conductor types, component values and apparatus designations are given solely by way of example, and not in a limiting sense. The invention is not limited solely to sending an alarm for heart rates, this being given as an example. The system is capable of giving a warning of many abnormalities, e.g. biological processes, blood pressure, temperature, malfunction of the equipment and the like. While tone-modulated coding is used in this example, digital coded signals (pulses) could also be used.
Summarizing, our device is capable of signal processing at the source, transmission of coded alarm signals, transmission via remote receiver transmitters to central monitor or identifying the location of a malfunction or disaster as well as identification of the malfunction or disaster.
FIG. 5 shows a schematic block diagram of the nonfail-safe version in which the amplifier is indicated by 15 and includes a rate meter 47 which in turn is connected to alarm limit circuitry 48 as hereinbefore described. The transmitter control 49 operates transmitter 56 and receiver 13 operates alarm circuits 14. In FIG. 5, corresponding reference characters of the previous embodiments are shown in parenthesis.
In this embodiment, only alarm signals are transmitted as hereinbefore described.
FIGS. 6 and 7 show schematic block diagrams of preferred embodiments and dealing first with FIG. 6, the amplifier 15, rate meter 47, and alarm limit circuits 48 are similar to those shown in FIG. 5. An alarm modulator 50 connects to the transmitter control 49 which operates the transmitter 56 and receiver 13 feeds to decoding circuits 31 which in turn are connected to an operating indicator 52 for locating the source of the signal and to alarm signals 14. Corresponding reference characters of the previous embodiments are shown in parenthesis.
An operating signal and modulator circuit shown by reference character 53 connects to the transmitter control and is adapted to periodically transmit an operating signal thus allowing the operator to check on the fact that the circuit is in operating condition. When an alarm is triggered, then of course the circuit operates in a manner similar to that hereinbefore described. A similar or different kind of alarm will be sounded if the decoding circuits (51) do not sense the periodic "Operating" signal (53).
FIG. 7 shows a modification in which the amplifier 15 and rate meter 47 are similar to those hereinbefore described. A sampler and modulator circuit 54 connects to the transmitter control 49 and hence to the transmitter 56 with the receiver 13 being connected to a location indicator 52 and to a rate meter with alarm shown by reference character 55. This particular version periodically transmits rate data so that a continuous monitoring can be kept on the patient and at the same time of course if the high or low levels that have been pre-set, are exceeded, then the alarm signals will also show. Also cessation of the coded rate data will cause an alarm.
The basic difference between the present invention and previous types of electrocardiographic monitors is that in the present device, pulsed signals are transmitted, while in ordinary telemetry the entire ECG is continuously transmitted. The present device has the advantage that the signals are easier to handle in this form so that it should be significantly less expensive than existing apparatus.
As mentioned previously, the invention can take two forms, either fail-safe or nonfail-safe. The simplest form shown schematically in FIGS. 1 to 5 inclusive, is nonfail-safe. In this form, the monitor senses the heart rate in the patient-transmitter but only broadcasts an alarm signal. Therefore there is no assurance that the system is working and capable of an alarm but it is the least expensive approach so far as the receiver is concerned.
The fail-safe versions will automatically monitor the operation of the patient-transmitter and sound an alarm if the system malfunctions, as well as if the heart rate limits are exceeded. The two methods described and shown in FIGS. 6 and 7 can be used to implement this version.
The first method shown in FIG. 6 indicates that the patient-transmitter can broadcast an intermittent operating signal in addition to the alarm signal. The absence of several operating pulses would then be an alarm condition showing malfunction of the device.
In FIG. 7, instead of a simple operating signal, the patient-transmitter periodically transmits coded pulses representing the heart rate and the rate alarm circuitry may be located at the receiver. This coded, intermittent rate signal may serve the same purpose as the operating signal described in reference to FIG. 6.
By appropriate coding, either type of pulsed signal can of course be used to identify and locate the patient.
In any version of the disaster alarm hereinbefore described, because the heart rate is computed in the patient unit the transmitted signal can be intermittent or pulsed, and can be coded for ease of handling and identification.
This provides a distinct advantage over prior methods which required the continuous high-fidelity transmission of the ECG to the receiver/rate meter.
Since various modifications can be made in our invention as hereinabove described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.