US3639907A - Interrogated telemetry alarm system for physiological monitoring - Google Patents

Abstract

Apparatus for monitoring from a single station a physiological condition of each of a plurality of remotely located patients. A radio transmitter at the station generates sequentially a plurality of tone signals, one for each patient and each of a different frequency, on a common carrier. A radio receiver with each patient has a band pass corresponding to a particular one of the tone signals. Each receiver when addressed activates a radio transmitter with the patient for transmitting to a single receiver at the station a coded signal indicative of the physiological state of the patient, derived from signal generating means operatively connected to the patient. The signals received at the station are sequentially routed, decoded, and applied to suitable indicators.

Description

United States Patent Greatbatch Feb. 1, 1972 INTERROGATED TELEMETRY ALARM SYSTEM FOR PHYSIOLOGICAL MONITORING Attorney-Christel and Bean [72] lnventor: Wilson Greatbatch, Clarence, NY. [73] Assignee: Mennen-Greatbatch Electronic, Inc., [57] ABSTRACT Clarence, N.Y. Apparatus for monitoring from a single station a physiological condition, of each of a plurality of remotely located patients. A [22] filed Sept radio transmitter at the station generates sequentially a plu- [21] Appl. No.: 854,582 rality of tone signals, one for each patient and each of a different frequency, on a common carrier. A radio receiver with each patient has a band pass corresponding to a particular one 340/150 346/33 5g of the tone signals. Each receiver when addressed activates a l 58] Field ME radio transmitter with the patient for transmitting to a single 1 1 A 2 05 receiver at the station a coded signal indicative of the physiological state of the patient, derived from signal generating means operatively connected to the patient. The signals [56] References cued received at the station are sequentially routed, decoded, and

UNITED STATES PATENTS applied to suitable indicators.

3,253,588 5/1966 Vuilleumier et al. ..340/1 83 X I 4 Claims, 2 Drawing Figures PATIENT PATIENT 3 RECElVER TRANsMrrTeR l l 37 k I 56 1-470 57 l g cormuuous I READOUT CODING CONTROL 8 4 7 l 39 V 55 -49 I @i 57 I PREAMPLIFlER DECISION COMMAND I INTERROGATED TELEMETRY ALARM SYSTEM FOR PHYSIOLOGICAL MONITORING BACKGROUND OF THE INVENTION dition of each of a large number of patients by the telemetry.

Physiological monitoring of a large number of patients by automatic means is becoming increasingly necessary as shortages of hospital personnel increaseand as hospital activities expand and become more highly specialized. Upon leaving intensive care units, patients are in hospital areas which often are relatively less rigidly observed, and in such areas automatic physiological monitoring can reduce the mortality rate from cardiac arrest and fibrillation. As hospital care progresses from its present state, additional intensive care units, each of a more specialized nature, are envisioned and will augment the need for automatic physiological monitoring. Automatic physiological monitoring by telemetry hasbeen proposed and isparticularly advantageous because of the ability to continuously monitor an ambulatory patient.

I-le'retofore, the number of patients that could be accommodated economically by telemetry was limited to about patients due to equipment and frequency spectrum limitations. For example, there must be interference-free reception from one patient about 200 feet from a receiving antenna and delivering only 2 or 3 microvolts of signal tothe receiver, and yet another patient on an adjacent telemetry channel and positioned only about 10 feet from the same antenna must not contribute any crosstalk. Otherwise, an alarm might be received from the wrong patient. In addition, the channel separations must be unequal so as to avoid unwanted modulation products from mixed transmitter signals, from mixed receiver local oscillators and from various I.F. signals traveling through the system.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide apparatus for continuouslymonitoring the physiological condition of each of a large number of patients, such as about 100, by telemetry.

lt is a further object of this invention toprovide such apparatus which is readily usable with ambulatory patients.

It is an additional object of this invention to provide such apparatus which provides a rapid indication of the type of patient disorder giving rise to an alarm, deferred access to stored physiological data, and continuous readout of data from apatient inalarm.

\ It is a further object of the present invention-to provide such apparatus which can monitor a large number of patients at a relatively-fast rate, for-example the total' number of patients every 10 or seconds. 5

The present invention provides physiological monitoring apparatus including a radio receiver 'with'each patient. and

connected in controlling relation to a correspondingradio transmitter with each patient, each receiver havinga different i The foregoing and'additionaladvantages and characterizing features of the present invention-willbecome clearly apparent upon a reading of theensuing *detail description of an illustrative embodiment together with theincluded drawing depicting the same.

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. I is a schematic block diagram of physiological monitoringapparatus in accordance with the present invention; and

FIG. 2 isa schematic block diagram showing in more detail a portion of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Ina preferredarrangement of physiological monitoring apparatus constructed in accordance with the present invention,

the equipment designated generally at 10 on the left hand side of FIG. lis stationary, being in a fixed location relative to the patients being monitored. For convenience hereafter, the components .in this portion of the apparatus will be designated with the .term, station. The nursess station on a hospital floor or the central monitoring station in an intensive care unit are examples of wherestation apparatus 10 can be located.

Station apparatus l0comprises a radio transmitter 11 having a radiatingantenna 12 which transmitter functions, briefly, to generate a radiofrequency signal consisting of a plurality of coded tones on a common carrier. There would be generated, more specifically, a different tone or a combination of different tones :for each patient, and the tones would be transmitted sequentially. A sequencing means l3'suitable for this purpose is operatively connected through a line 14 to transmitter 11.Station apparatus 10 further comprises aradio receiver 15 having a receiving antenna 16 which receiver functions,:briefly, toreceive radiofrequency signals on a different channel relative to that of transmitter 11. More specifically,receiver 15 responds to signals received from patients being monitored which signals indicate the physiological condition of each patient.Receiver 15 is operatively connected through aline 17 to a decoding circuit 18 which also is operatively connected to sequencing means 13 through aline 19. The purpose of this arrangement is to route properly a received and decoded signal to a particular one of a plurality ofindicators 20, one for each patient, which are connected to the outputof decoder 18 through lines designated 21.Indicators 20 preferably are lamps or other visual devices which tell the observer immediately when a particular patient is experiencing a physiological disorder, as willbe described in more detail hereafter.

25 preferably is of a size and construction readily adapted to be carried by an ambulatory patient and for this reason will be referred to as being patient-carried. Each patient-carried unit includes, briefly, a radio receiventhe antenna of which is designated 26 inFIG. 1, adapted to respond to a particular one of the coded tones generated by transmitter 11 at station .l0..Each.unit 25 further includesa radio transmitter conrnected in controlled relation tothe receiver and which functions, whenwactivated, to transmit from anantenna 27,

radiofrequency signals indicative of that patients's physiological condition. These signals are received byreceiver 15 at station I0. .Eachunit25 further includesinput terminals 28, 29

for receivingv electrical signals indicative of the patients physiological condition. For example whenthe apparatus of 'thepresent invention isused to monitorthe cardiac behavior of each of a: number of patients, input-terminals 28, 29 are connected directly to the patient, being placed in or on his chest in a conventional manner, and the'voltages thereon indicative of cardiac behavior are amplified andprocessed by cadditionalcircuitry incomponent 25 as will be described hereafter; Alternatively,terminals 28, 29 may be connected to the output of an appropriate transducer operatively connected to the'patient.

FIG. 2 shows in more detail a preferred form of each patient-carried unit especially suitable for monitoring cardiac behavior. A radio receiver is operatively connected toantenna 26 and has a particular frequency passband which permits reception of a particular one of the coded tones from station transmitter 11.Receiver 30 is connected through a line 31 in controlling relation to aradio transmitter 32 which, in turn, is operatively connected toantenna 27. By virtue of this arrangement,receiver 30 when addressedby one of the coded tones from station transmitter 11 activatestransmitter 32 which, in turn, radiates from antenna 27 a coded signal indicative of that patient's physiological condition, in this particular example a signal coded in terms of cardiac behavior.

Transmitter 32 is provided with information concerning the patients cardiac behavior by the following arrangement.input terminals 28, 29 are connected to the input of a preamplifier 33 which is designed to have an amplification factor of about 1,000 when the apparatus is employed in cardiac monitoring. In this particular situation the signals onterminals 28, 29 indicative of the patients heartbeat will have an amplitude of only about 2-3 microvolts. The amplified signals appearing at the output of preamplifier 33 are applied through aline 34 to the input of a decision circuit 35, the purpose of which is to determine whether the signals are indicative of normal or abnonnal physiological behavior. For example, in monitoring of cardiac activity, the repetition rate of signals applied to circuit 35 is the information parameter. Circuit 35, which can include standard frequency responsive and logic networks, in this particular example makes a comparative determination as to whether the rate is normal, indicating that the cardiac condition of the patient is satisfactory, too fast indicating tachycardia/fibrillation, or too slow indicating bradycardia/arrest. The frequency parameter on the input signal to circuit 35 can be converted therein to an amplitude or pulse width parameter on the output thereof. For example, circuit 35 can be constructed to provide no output when the rate is normal but to provide an output or alarm signal when either of the abovementioned disorders is detected, the particular one being determined by output signal amplitude, duration or even.

polarity.

There is also included a command circuit 36, the input of which is connected through a line 37 to the output of decision circuit 35. The output of command circuit 36 is applied through aline 38 to a coding means 39, operatively connected totransmitter 32 through a line 40. The purpose of command circuit 36 is to transfonn the signals received from decision circuit 35, indicative of the patients condition, into corresponding signals which are suitable to command operation of coding means 39 to generate a coded signal corresponding to the particular condition of the patient. Coding means 39 can have several known forms, depending upon the manner in which the output signal oftransmitter 32 is to be modulated in terms of information concerning the physiological condition of the patient. The signal fromtransmitter 32 can, for example, be a coded tone in a one of three code indicating patient satisfactory, bradycardial/arrest alarm or tachycardia/arrest alarm. A fourth state might be added to the code indicating no signal from the transmitter so that the particular patients equipment can be repaired or replaced. Instead of coded tones, other types of modulation, for example pulse width, might be employed.

It is apparent, therefore, that command circuit 36 can have several known forms depending upon the nature of coding means 39 and the type of signals required to operate it. In certain applications it also may be possible to incorporate the function of command circuit 36 into either or both of decision circuit 35 and coding means 39.

The patient-carriedapparatus 25 also includes a tape-loop recorder, designated generally at 45, for providing deferred access to stored physiological data, for example about 10 minutes of recorded ECG activity. The output of preamplifier 33 accordingly is connected bylines 46 and 47 to a recording head 48 oftape recorder 45. Tape recorder would be placed in operation at the patients location whenever it is desired that recording begin. Preferably, alarm activation would stop the tape so as to store the previous ten minutes of data preceding the event and to this end the output of decision circuit 35 is connected by a line 49 to a controlled tape drive means 50.

The physiological monitoring apparatus of the present invention operates in the following manner. It is, in effect, an interrogation system, and is somewhat similar to the [FF system (Identification, Friend or Foe) used in military aircraft. The patient-carried radio transmitters, such astransmitter 32, all operate at the same frequency but transmit only when interrogated. ln monitoring of cardiac behavior, the response modulation can be one of four audio tones, one for no alarm," the second for bradycardia/arrest alarm, the third for "tachycardia/fibrillation alarm," and the fourth for no signal alarm."

Station transmitter 11 together with the patient-carried receivers, one of which isreceiver 30, constitute an interrogator. Transmitter 11 operates on a frequency different from that on which patient-carriedtransmitters 32 operate so that the overall system uses only two radiofrequency channels. The coded tones provided by transmitter 11, one for each patient, are generated sequentially under control of sequencer 13 which in one form can be a two-gang stepping switch. One gang provides sequencing of code generation by transmitter 11, represented schematically by line 14, and the other gang controls routing of signals fromreceiver 15 through decoder 18 to the particular one of thepatient indicator 20. Since only a tone is elicited from eachpatient transmitter 32 in response to interrogation, i.e., the correspondingpatient receiver 30 being addressed by the particular coded tone from transmitter 11, the patient scanning rate is very fast, sampling patients every 10 or 20 seconds.

The interrogator portion of the apparatus of the present invention can comprise one of several interrogation systems commercially available, modified so as to be coded with respect to the patients being monitored. One is an induction coupled, low frequency variety whereinstation antenna 12 would comprise a wire surrounding the patients being monitored andantennae 26, 26, etc., each with a particular patient, would be induction-coupled to the wire in a manner similar to the coupling between transformer secondary and primary coils. A second variety is of the radiofrequency type, operating in the range of about 27 to about 54 megacycles, and including vibrating needs in the receivers for decoding.

Decoder 18 at themonitoring station 10 would include standard radio receiver detector circuitry, the exact nature depending upon the type of modulation employed in thepatient transmitters 32. It is contemplated that the speed of operation of sequencer 13 in relation to the time needed for a radio signal to travel fromstation 10 and for a response signal to return is such that one response signal will be properly routed to apatient indicator 20 before sequencer l3 advances to the next step for generation of the next coded tone in transmitter 11. The output of decoder 18, routed to theparticular line 21, could be one of three voltage levels depending upon the nature of the alarm received. Eachindicator 20 could include three lamps differentiated by color or by indicia according to the nature of the alarm, and there would be included also suitable voltage level responsive circuitry for energizing the lamps.

The alarm signals generated bypatient transmitters 32 rather than being coded tones could be microsecond duration pulses. In this case, three radio receivers instead of asinglestation receiver 15, could be employed to locate the particular patient by vector resolution techniques. Such techniques are well known, for example Loran, and in this particular situation three receivers measure the time difference in arrival of a signal from a single transmitter (patient transmitter 32) rather than three transmitters sending signals to a single receiver which is the usual case.

The apparatus of the present invention advantageously provides continuous monitoring of a large number, for example about 100, ambulatory patients. Monitoring is done at an extremely fast rate, such as the total number of patients every or 20 seconds. Moreover, the patient-carriedtransmitters 32 operate only upon interrogation, in a time-sharing mode, thereby reducing battery drain and permitting less frequent battery replacement. All patient transmitters are identical units and only the coding elements in thepatient receivers 30 are different so transmitter construction and tuning is advantageously quite simple.

The apparatus of the present invention can include an additional arrangement whereby in response to the occurrence of an alarm, a continuous readout of the patients ECG signal automatically is transmitted to the station. To this end line 46, on which the ECG signal is available from the output of preamplifier 33, is connected by a line 55 to the input of a component designated 56 in FIG. 2 for controlling the operation oftransmitter 32 in this continuous readout mode.Component 56 is to operate only in response to the occurrence of an alarm signal provided by decision circuit 35, and for thisreason component 56 is connected in controlled relation through aline 57 and line 49 to the output of decision circuit 35.Circuit 56 is connected by aline 58 totransmitter 32 whereby the carrier thereof is modulated with the patients ECG signal.Circuit 56 in addition would be constructed to provide an additional tone which when transmitted to station 10 would stop sequencing of transmitter 11 and hold it on the particular channel where the alarm had been received. To this end a frequency-responsive circuit, designated 60 in FIG. 1, is connected to the output of receiver by a line 61 and adapted to respond to this particular tone.Circuit 60, in turn, is connected to sequencing means 13 by aline 62 to command stopping thereof.

Thereceiver 15 atstation 10 then would receive continuous ECG data from the patient and would ignore all other patients on the system until that particular patients transmitter had been cleared whereupon the system would again start sequencing through the total number of patients. Readout and possibly also storage of the particular patients continuous ECG signal is performed by conventional equipment, designated 65, connected to the output ofreceiver 15.

It is therefore apparent that the present invention accomplishes its intended objects. While a single specific embodiment thereof has been described in detail, this is done for the purpose of illustration without thought of limitation.

lclaim:

1. Apparatus for monitoring from a single station a physiological condition of each of a plurality of remotely located patients comprising:

a. a radio receiver with each patient and each receiver having a different frequency passband;

b. a radio transmitter with each patient and connected in controlled relation to said receiver;

c. a signal producing means adapted to be operatively connected to each patient for providing electrical signals having a parameter which varies in accordance with changes in a physiological characteristic of the particular patient;

d. decision circuit means with each patient and having an input coupled to the output of said signal producing means, said decision circuit means comparing the variations in said parameter with a predetermined normal value and providing an output alarm signal in response to abnormal variations in said parameter;

e. coding means with each patient coupled to said decision circuit means and to said transmitter whereby the radiofrequency signal generated by each transmitter is coded in terms of the alarm state of the physiological characteristic of the particular patient;

f. a radio transmitter at said station for generating sequentially a plurality of signals, the number being equal to the total number of patients being monitored and the frequency of each one corresponding to a particular passband of one of said receivers whereby said transmitter with each patient is periodically interrogated;

g. a radio receiver at said station for receiving signals from said transmitter with each patient;

h. decoding means connected to the output of said station receiver and operative sequentially in synchronism with said station transmitter for decoding the physiological state signal from each patient; and

i. a plurality of indicating means, one for each patient,

operatively connected to said decoding means.

2. Apparatus as defined in claim 1 wherein each signal producing means comprises:

a. an input terminal adapted to be operatively connected to the particular patient for sensing electrical signals indicative of cardiac behavior; and

b. an amplifier having an input connected to said terminal and an output; and

c. decision circuit means having an input connected to the output of said amplifier, and wherein said decision circuit provides output alarm signals in response to an abnormal rate of signals applied to the input thereof.

3. Apparatus as defined in claim 2 further including magnetic tape recording means, the recording element of which is connected to the output of said amplifier and the drive means of which is connected in controlled relation to the output of said decision circuit for stopping said tape recording means in response to an alarm signal.

4. Apparatus as defined in claim 2 further including means connected in controlled relation to the output of said decision circuit for coupling the output of said amplifier directly to said patient transmitter in response to an alarm signal.

"una-

Claims (4)

1. Apparatus for monitoring from a single station a physiological condition of each of a plurality of remotely located patients comprising: a. a radio receiver with each patient and each receiver having a different frequency passband; b. a radio transmitter with each patient and connected in controlled relation to said receiver; c. a signal producing means adapted to be operatively connected to each patient for providing electrical signals having a parameter which varies in accordance with changes in a physiological characteristic of the particular patient; d. decision circuit means with each patient and having an input coupled to the output of said signal producing means, said decision circuit means comparing the variations in said parameter with a predetermined normal value and providing an output alarm signal in response to abnormal variations in said parameter; e. coding means with each patient coupled to said decision circuit means and to said transmitter whereby the radiofrequency signal generated by each transmitter is coded in terms of the alarm state of the physiological characteristic of the particular patient; f. a radio transmitter at said station for generating sequentially a plurality of signals, the number being equal to the total number of patients being monitored and the frequency of each one corresponding to a particular passband of one of said receivers whereby said transmitter with each patient is periodically interrogated; g. a radio receiver at said station for receiving signals from said transmitter with each patient; h. decoding means connected to the output of said station receiver and operative sequentially in synchronism with said station transmitter for decoding the physiological state signal from each patient; and i. a plurality of indicating means, one for each patient, operatively connected to said decoding means.

2. Apparatus as defined in claim 1 wherein each signal producing means comprises: a. an input terminal adapted to be operatively connected to the particular patient for sensing electrical signals indicative of cardiac behavior; and b. an amplifier having an input connected to said terminal and an output; and c. decision circuit means having an input connected to the output of said amplifier, and wherein said decision circuit provides output alarm signals in response to an abnormal rate of signals applied to the input thereof.

3. Apparatus as defined in claim 2 further including magnetic tape recording means, the recording element of which is connected to the output of said amplifier and the drive means of which is connected in controlled relation to the output of said decision circuit for stopping said tape recording means in response to an alarm signal.

4. Apparatus as defined in claim 2 further including means connected in controlled relation to the output of said decision circuit for coupling the output of said amplifier directly to said patient transmitter in response to an alarm signal.

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