US3774594A

US3774594A - Apparatus for telemetering of ekg signals from mobile stations

Info

Publication number: US3774594A
Authority: US
Inventors: R Huszar
Original assignee: Pioneer Medical Systems Inc
Current assignee: Pioneer Medical Systems Inc
Priority date: 1972-01-06
Filing date: 1972-01-06
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27

Abstract

A system for the radio transmission of EKG signals to a hospital from an ambulance. After an initial limited transmission of EKG waves, no further signals are transmitted unless the EKG (R-R) rate departs significantly from the initial rate. The EKG signals modulate a voltage controlled oscillator. A code is associated with the transmission to identify patient, rescue vehicles and hospital.

Description

United States Patent [1 Huszar APPARATUS FOR TELEMETERING OF EKG SIGNALS FROM MOBILE STATIONS Inventor: Robert J. Huszar, Hartford, Conn.

Pioneer Medical Systems, Inc., New Britain, Conn.

Filed: Jan. 6, 1972 Appl. No.: 215,890

Related US. Application Data Continuation of Ser. No. 819,226, April 25, 1969, abandoned.

Assignee:

US. Cl. 128/2.06 R, l28/2.1 A Int. Cl A6lb 5/04 Field of Search 128/2.05 P, 2.05 R, 128/205 T, 2.06 A, 2.06 F, 2.06 R, 2.1 A; 340/248 A, 248 R, 279

References Cited UNITED STATES PATENTS 5/1970 Finch et a] 128/206 R EKG JEKG

SIGNAL SQUARING CIRCUIT [111 3,774,594 1 Nov. 27, 1973 FOREIGN PATENTS OR APPLlCATIONS 1,008,027 10/1965 Great Britain l28/2.l A 1,264,680 3/1968 Germany 128/206 F Primary Examiner-William E. Kamm Att0rneyThomas J. Greer, Jr.

6 Claims, 8 Drawing Figures TRANSMITTER RAMP GENERATOR Patented Nov. 27, 1973 3 Sheets-Sheet 2 m J m E: m5 E5: :5: im 0 2 3 Sheets-Sheet 5 waif ATTORNEYS Patented Nov. 27, 1973 R w a: R m m H n E M H R M m W28 2% Ex 28:50 em 5; Y 5235:

$28: as 2 GE 5222 M22 APPARATUS FOR TELEMETERING OF EKG SIGNALS FROM MOBILE STATIONS This is a continuation of application Ser. No. 819,226, filed Apr. 25, 1969, and now abandoned.

This invention relates totelemetering and more particularly to the transmission from rescue vehicles of information correlated to a physiological parameter. According to the invention, a system is provided for the monitoring and transmitting of electrocardiogram signals (EKG) from ambulances or other rescue vehicles while a heart attack victim is en route to hospitals. The invention comprehends the transmission of still other parameters, such as respiration rate, blood pressure, and the like.

A great number (estimated at 400,000) of persons die in the United States each year of heart attacks. Of this number, it is estimated that approximately fiveeighths of such deaths occur outside of a hospital and after one hour of the initial attack. It is further estimated that perhaps three-fourths of these deaths would be preventable, provided proper diagnosis and medical attention could be made available rapidly enough. Considering those instances where medical attention is obtained, the victim must be brought from the locale of the attack to a hospital for treatment. Such treatment requires expert analysis of the particular heart condition before proper ameliorative procedures can be administered. The more rapid the analysis of the heart condition, the more rapidly treatment can be provided. In the past, monitoring of the hearts EKG signals was generally not possible until the victim arrived at a hospital. If cardiac arrhythmias (heart standstill or fibrillation) occurred during ambulance transit, they remained undetected until arrival. By the practice of the present invention, EKG signals are radioed for analysis by a physician at the hospital. In severe cases, the doctor can then radio the ambulance and direct the attendants in emergency external heart massage in order to keep blood flowing and prevent brain damage or death due to oxygen starvation.

Accordingly, the main purpose of the present invention is to reduce the time required for initial analysis of a heart condition. This is achieved by initiating transmission of EKG data from an ambulance to a hospital immediately upon placing the victim in the ambulance, as opposed to the general practice of having to wait until the patient is in the hospital before conducting EKG tests. Because of the great demand for limited space in the wireless spectrum, continuous transmission from a large number of rescue vehicles is not practical. The present invention, accordingly, permits the minimum time use of the airways for a single emergency. This in turn enables a greater number of (ambulance) transmission stations to use the same band for transmission.

IN THE DRAWINGS FIG. 1 is a schematic view of the major portions of the transmission system of the invention.

FIG. 2 is a detailed schematic view showing the automatic transmission system of the invention, located in an ambulance.

FIG. 3 represents a normal potential v. time EKG.

FIG. 4 represents the potential v. time curve in a certain line in the system of FIG. 2.

FIG. 5 represents a voltage generated by a portion of the system of FIG. 2.

FIG. 5a represents the voltage applied to the base of transistor O in FIG. 2.

FIG. 6 shows the face of the meter M of FIG. 2.

FIG. 7 illustrates the receiving equipment located in a hospital.

Referring now to FIG. 1 of the drawings, the illustration relates to the taking of an electrocardiogram of a patient either immediately before or immediately after he has been placed into an ambulance or other rescue vehicle for transfer to a hospital. An electrocardiogram may be defined as the amplification and pictorialization of a naturally occurring flmv potential generated in a tissue adjacent the heart. It is often taken by coupling the left leg to the common terminal of a differential amplifier and connecting the remaining two leads, respectively, to the right and left arms. After being amplified by amplifier A, the EKG information is fed to a radio transmitter whenever switch SW is closed. As indicated in FIG. 1, the EKG signals modulate the output (carrier) of a voltage controlled oscillator. The thus modulated VCO oscillator signal passes to switch SW. The other portion of the EKG is fed to a signal squaring circuit. The output from the square wave generator actuates two relays, RL, and RL The former relay is coupled to a ramp generator and functions to ground the potential generated by the ramp generator whenever the relay is actuated, resetting it to zero. The latter relay RL maintains its associated switch closed during the major portion of the EKG signals, and becomes deenergized to thereby open the switch upon the QRS portions of the EKG signals. When closed, a voltage +V is shunted to ground by the RL switch. Relay RI. controls a normally open switch which shunts +V to ground whenever the voltage generated by the ramp generator exceeds a predetermined amount, here four volts. A fourth relay RL, actuates radio transmission with SW whenever either one of two conditions occur. The first condition occurs when the voltage generated by the ramp generator exceeds a predetermined amount, here 6 volts. In the second condition neither of the switches associated with relays RL or RL are closed to thereby shunt +V to ground and +V then actuates RL By this arrangement, as will be apparent from the more detailed discussion to follow, the EKG is only transmitted (during the automatic transmission mode of operation of the system) whenever the EKG heart rate departs from an initial rate. The initial rate is whatever heart rate the victim had when the EKG was first taken. The subsequent rate is any later rate the victim displays while en route in the ambulance to the hospital. It will be appreciated that this journey occurs during the initial and often the most critical portion of the heart attack.

Referring now to FIG. 2 of the drawings, the patient is connected to the system through three integrated circuit linear amplifiers (A A A connected in a modified differential amplifier, voltage follower configuration. The construction of such amplifiers A A A is well known and forms no part of the invention. The amplified EKG signals are applied over wire 1 to a voltage controlled oscillator (VCO). The EKG modulates, hole by frequency modulation, the VCO output over a 1,400 Hertz (Hz. band between 600 and 2,000 Hz.

The VCO converts the EKG signal to an FM subcatrier compatible with the transmission capabilities of the radio transmitter. The VCO is a complimentary symmetry astable multivibrator which is driven directly from the output of the EKG amplifier. The transistors Q16, Q17 adjust the base bias voltage of the transistors Q14, Q18. This adjustment alters the voltage at which the transistors switch, hence the duration of their ON- OFF cycle, hence the multivibrators frequency. Two adjustments are provided: R, for zero input or center frequency, the other, R adjusts the slope of the VCO transfer function, input voltage to output frequency. These controls are not independent. The VCO square wave output is filtered by a single pi section to remove high frequency harmonics.

Amplified EKG signals are also applied over wire 2 to the base of transistor 0,. The combination of Q, and Q with resistors R,-R -R is proportioned such that Q, is completely out off while Q conducts fully. The drop across R provides the cut-off level of Q,.

The QRS portion of the EKG wave is quite large as compared to the rest of the complex, note FIG. 3. This portion causes Q, to start to turn on which in turn lowers the base and emitter currents of Q The regenerative action then switches Q, into strong conduction until the peak recedes; then Q, switches off and Q switches on providing a sharp square wave across R and R for the period when the peak exceeds the value of voltage across R This action produces square waves in the lower conductor 2a, note FIG. 4.

Elements D,,, R,,, C Q, and R, provide an integrator fed from source V, whose period is adjustable by R The output of this integrator is linear. The integrator is a ramp generator whose output is a potential which is employed as a reference potential.

When the square wave voltage across R, and R,, changes, condenser C, differentiates this voltage (FIG. 5a) to provide a sharp positive pulse across R to fire O, which discharges C to reset the ramp to zero.

Diode D, conducts the ramp voltage over wire 3 to condenser C which retains the last peak voltageobtained from the ramp. Transistors Q and Q,, are Darlington connected to provide an emitter follower to operate meter M which indicates the last peak voltage of the integrator.

When the patient is first connected to the system, an operator holds push button PB,, PB, open to prevent the relay RL, from becoming energized. Radio transmission is thus precluded. He then adjusts R so that the patients heart rate (RR) causes the meter M (initial heart rate) to read 5 volts. This should only require several EKG signals. PB, and PB, are released after which PB, is depressed. This causes monostable multivibrator MMV to start up, the action of which is to throw normally open transistor 0,, into conduction for about 1 minute. Radio transmission takes place for this initial timed period. During this time, the EKG is recorded at the hospital receiving station. After this time, with no change in RR rate, the system is quiescent. P8,, 0,, Q,,, and 0,, form a 1 minute initial transmit circuit. When the circuit has not been operated for some time, 0, is full ON due to bias current through R,,,. The low collector voltage of Q,,, prevents Q,, from receiving bias current so it is OFF. The ratio of R and R is such that Q, does not receive bias current and it is OFF. Capacitor C is charged to the supply voltage through R,,. Depression of PB, connects C to the base of Q,,. C discharges providing bias current for Q, turning it ON. The collector voltage of 0 drops, C couples this drop to the base of 0, and it turns off. The collector voltage of Q, rises toward the supply voltage and Q,,

turns on. Collector current of Q,, flows through wire 8 connected to relay RL,. Relay RL, turns on operating the radio transmitter. Capacitor C charges through R,,,. When the voltage on C reaches the emitter voltage of Q,,,, 0,, turns ON. The collector voltage of Q,,,

drops turning off Q,,. When 0,, turns OFF, relay RL,

turns OFF and the transmitter turns OFF. Q10 turning On also turns OFF 0,. The circuit is ready for the next depression of P8,.

During quiescent operation the rise time of the first EKG pulse fires Q, and the square wave voltage in line 2a and across R, and R falls, producing a negative pulse on the base of O, which is already cut off. When the EKG pulse falls, Q, cuts off, Q, fires and a positive pulse is applied to the base of O to reset the ramp to zero by shunting its voltage to ground.

If the R-R period between each succeeding EKG pulse remains substantially constant (permissible deviation to be described later) the ramp voltage will arrive at approximately 5 volts after each integrating period.

Two actions should be observed: 1) should the heart rate increase from the preset normal, the ramp voltage will reset to zero before it reaches 5 volts; and (2) should the heart rate decrease, the ramp voltage will build up and exceed 5 volts prior to the next R peak.

The ramp voltage is applied over wire 4 to two Zener diodes, Z, and 2,, rated at 4 volts and 6 volts. This difference defines a zone within which the R--R rate can fluctuate without activating automatic transmission. Zener Z, conducts the ramp voltage to R, when the ramp exceeds 4 volts (a heart rate of per minute). Zener Z conducts the ramp to R,, when the ramp exceeds 6 volts (a heart rate of 30 per minute).

The voltage across R, and R during the peak of the QRS wave is reduced to the point that Q, cuts off. Current now flows from +V, through R over wire 5 to 0,. However, since the voltage on the ramp (from the last QRS to QRS period) exceeds 4 volts, Zener Z, conducts current through wire 7 to R,,, and through R, and C and the base of Q, holding it conducting. Condenser C, provides a slight delay before Q, cuts off. When the EKG main pulse (QRS) decays, Q conducts, pulling current on wire 6 below the conduction point of D The rise of the square wave on R, and R is differentiated by C, to apply a positive pulse to the base of O, which now resets the ramp to zero. Zener Z, opens and Q, cuts ofi. Thus, during quiescent operation, either Q, or Q, bleeds V, to ground, preventing it from triggering the gate of SCR,.

Should an EKG pulse (QRS) appear prior to the ramp attaining the 4 volt level (quickening of the heart rate) Q, conducts on the rise of the QRS complex causing Q, to reduce the voltage across R, and R cutting off 0,. Zener Z, has not yet conducted and hence Q, is cut off. Current now flows from +V, through R wire 6, through D,, through R through P8,, to R,,,, and to the gate of SCR,, which now fires and stays conducting. SCR, conduction operates the transmitter relay RL, to close switch SW turning on the transmitter.

If the RR period lengthens, due to a slowing or failure of the heart to produce a normalQRS (cardiac standstill), the ramp will continue to build up until Zener Z, fires at 6 volts which immediately places the ramp voltage through R,, to the gate of SCR,, which fires and initiates radio transmission.

The meter M provides visual means for monitoring the heart rate and also setting into the system the initial heart rate in accordance with the patients cardiac status. When the heart rate departs from the preset value, it is extremely urgent that the hospital to which the ambulance is proceeding be immediately alerted, advised of the ambulance identity code and start receiving the EKG pattern. At this crucial period, time does not permit coding transmission. Therefore, this invention provides for simultaneous transmission of the EKG signals and identity codes. SW provides the option for continuous (C) or automatic (A) EKG transmission. Small bypass capacitors C of 2.3 mf placed, as indicated in FIG. 2, served to improve operation by shunting radio frequency oscillations to ground.

The audio spectrum may be divided into several bands, 300 Hertz to 600 Hertz, for identity coding, and the band from 600 to 2,000 Hertz for the EKG modulation. Q and Q operate a code oscillator circuit. Code 1 in FIG. 2 designates a code for, say, a particular rescue vehicle, while Codes 2 and 3 (of corresponding circuitry) designate the hospital and the patient. Q and Q form a high gain amplifier. Voltage fed from the collector of through R is in phase with the signal at the base of 0 The tuned circuit formed by L and C, provide the necessary frequency selection to cause oscillation. R is a resistor whose resistance changes with its power dissipation. This provides ambient temperature compensation of the oscillator frequency, D R R form bias adjustment circuit that provides automatic output amplitude compensation.

A tone generator and a lamp connected in parallel and Q provides an audible and visual signal synchronous with each QRS complex.

FIG. 6 illustrates one layout of the meter dial. Three zones are provided to facilitate initial set in and rapid readout.

Referring now to FIG. 7 of the drawings, the receiver/demodulator is shown. This device, which is usually located in the hospital, consists of a demodulator which recovers the EKG signal from the carrier and provides an output compatible with standard EKG monitoring devices. The demodulator input is a two-stage (Q Q high gain, saturating amplifier. The amplifier output is a square wave at the input frequency. The square wave is differentiated (C R and rectified (D,,) to produce a positive pulse train. These pulses trigger a monostable multivibrator (Q Q Q of 100 microsecond duration.

The monostable multivibrator output is integrated by a 200 Hertz low pass filter (F The filter output drives a differential amplifier (Q Q Q The amplifier output is attenuated 1,000 times to permit the use of standard EKG monitors. The inverting input to the differential amplifier transistor Q is used to adjust (R the output voltage to zero when the subcarrier frequency is at the EKG zero input value (center frequency).

Control of the monostable multivibrator pulse duration is also provided (R This control adjusts the slope of the demodulator transfer function, input frequency to output voltage. These two controls are not independent.

A transmitter which has been found satisfactory is GE model Royal Professional, 30 w. solid state. Similarly, a suitable commercially available receiver is GE model DM76KCU.

A tone actuated relay and tape recorder are coupled to the receiver as illustrated at FIG. 7. A Bramco multichannel reed relay device is satisfactory. The various reeds are resonant to several distinct frequencies and are accordingly well suited to respond to the codes sent with the EKG information. It will be recalled that the filtered VCO (FIG. 2) output consists of square waves whose spacing (frequency) is determined by the EKG signals, When received, these waves contain the audio frequencies corresponding to the EKG signals, the output at R R-, of the demodulator being the fully reconstructed EKG, such as shown at FIG. 3.

What is claimed is:

l. A telemetering system for transmission of physiological parameters having normal periods, such as EKG signals having QRS portions, including:

a. means for amplifying signals from a physiological parameter having a period,

b. means for converting said signals into pulses of varying width,

c. an fm radio transmitter,

d. the output of said converting means (b) modulating said transmitter,

e. means for measuring the period of the parameter and switch means for controlling the transmission by said radio of said signals,

f. means for actuating said transmitter switch when a subsequent value of the periodicity of said parameter departs greater than a predetermined amount from an initial periodicity of said parameter,

g. a ramp generator,

h. a reference periodic voltage being generated by the ramp generator,

i. means for diminishing to zero said ramp voltage with a period initiating change in said parameter,

j. a first Zener diode in a path between said ramp generator and switch means for conducting said ramp voltage to actuate said switch means, when a subsequent periodicity of the parameter increases beyondthe reference periodicity,

k. means for supplying an operating potential apart from the ramp generator to actuate said switch means,

1. means for shunting said operating potential to ground, said means including a second Zener diode, having a lower breakdown voltage than said first Zener, which is in a line defining a first shunt to ground,

m. a second shunt means to ground, parallel with said first shunt to ground, said second shunt being normally closed and opened only upon a period initiating change in the parameter.

2. The system of claim 1 wherein,

a. said means (e) includes means for supplying a potential for actuating said radio switch means, a first switch normally shunting said potential to ground but which opens and fails to shunt upon a period initiating change in the parameter, and a second switch normally open but which shunts said potential to ground when said reference voltage exceeds a predetermined value. a

3. A telemetering system for transmission of physiological parameters having periods, such as EKG signals having QRS portions, including:

a. means for generating a periodic reference voltage corresponding to an initial periodicity value of said parameter,

b. a radio transmitter having a radio transmission switch,

c. means for energizing the radio transmission switch by said periodic reference voltage when it exceeds a first predetermined value,

d. a second voltage source for energizing said radio transmission switch,

e. means shunting to ground said second voltage source except upon period initiating changes in said parameter,

f. means for shunting to ground said second voltage source when said periodic reference voltage exceeds a second and lower predetermined value,

g. whereby the radio transmission switch is energized and signals corresponding to the physiological parameter are trans-mitted when subsequent periodicity values of the parameters depart from initial periodicity values by an amount greater than half of the difference between the first and second predetermined values.

4. The system of claim 3 including,

a. means for visually presenting the periodic reference voltage.

5. A telemetering system for transmission of physiological parameters having normal periods, such as EKG signals having QRS portions, including:

a. means for amplifying signals from a physiological parameter having a period,

b. means for converting said signals into an audible frequency, of variable pitch, in the range 600 to 2000 Hz,

c. an fm radio transmittter,

d. the output of said converting means (b) modulating said transmitter,

f, means for actuating said transmitter switch when a g. a first Zener diode in a path between said ramp generator and switch means for conducting said ramp voltage to actuate said switch means, when a subsequent periodicity of the parameter increases beyond the reference periodicity,

h. means for supplying an operating potential apart from the ramp generator to actuate said switch means,

'. means for shunting said operating potential to ground, said means including a second Zener diode, having a lower breakdown voltage than said first Zener, which is in a line defining a first shunt to ground,

j. a second shunt means to ground, parallel with said first shunt to ground, said second shunt being normally closed and opened only upon a period initiating change in the parameter.

6. The system of claim 5 wherein, a. said means (e) includes means for supplying a po tential for actuating said radio switch means, a first switch normally shunting said potential to ground but which opens and fails to shunt upon a period initiating change in the parameter, and a second switch normally open but which shunts said potential to ground when said reference voltage exceeds a predetermined value.

Claims

1. A telemetering system for transmission of physiological parameters having normal periods, such as EKG signals having QRS portions, including: a. means for amplifying signals from a physiological parameter having a period, b. means for converting said signals into pulses of varying width, c. an fm radio transmitter, d. the output of said converting means (b) modulating said transmitter, e. means for measuring the period of the parameter and switch means for controlling the transmission by said radio of said signals, f. means for actuating said transmitter switch when a subsequent value of the periodicity of said parameter departs greater than a predetermined amount from an initial periodicity of said parameter, g. a ramp generator, h. a reference periodic voltage being generated by the ramp generator, i. means for diminishing to zero said ramp voltage with a period initiating change in said parameter, j. a first Zener diode in a path between said ramp generator and switch means for conducting said ramp voltage to actuate said switch means, when a subsequent periodicity of the parameter increases beyond the reference periodicity, k. means for supplying an operating potential apart from the ramp generator to actuate said switch means, l. means for shunting said operating potential to ground, said means including a second Zener diode, having a lower breakdown voltage than said first Zener, which is in a line defining a first shunt to ground, m. a second shunt means to ground, parallel with said first shunt to ground, said second shunt being normally closed and opened only upon a period initiating change in the parameter.

2. The system of claim 1 wherein, a. said means (e) includes means for supplying a potential for actuating said radio switch means, a first switch normally shunting said potential to ground but which opens and fails to shunt upon a period initiating change in the parameter, and a second switch normally open but which shunts said potential to ground when said reference voltage exceeds a predetermined value.

3. A telemetering system for transmission of physiological parameters having periods, such as EKG signals having QRS portions, including: a. means for generating a periodic reference voltage corresponding to an initial periodicity value of said parameter, b. a radio transmitter having a radio transmission switch, c. means for energizing the radio transmission switch by said periodic reference voltage when it exceeds a first predetermined value, d. a second voltage source for energizing said radio transmission switch, e. means shunting to ground said second voltage source except upon period initiating changes in said parameter, f. means for shunting to ground said second voltage source when said periodic reference voltage exceeds a second and lower predetermined value, g. whereby the radio transmission switch is energized and signals corresponding to the physiological parameter are trans-mitted when subsequent periodicity values of the parameters depart from initiAl periodicity values by an amount greater than half of the difference between the first and second predetermined values.

4. The system of claim 3 including, a. means for visually presenting the periodic reference voltage.

5. A telemetering system for transmission of physiological parameters having normal periods, such as EKG signals having QRS portions, including: a. means for amplifying signals from a physiological parameter having a period, b. means for converting said signals into an audible frequency, of variable pitch, in the range 600 to 2000 Hz, c. an fm radio transmittter, d. the output of said converting means (b) modulating said transmitter, e. means for measuring the period of the parameter and switch means for controlling the transmission by said radio of said signals, f. means for actuating said transmitter switch when a subsequent value of the periodicity of said parameter departs greater than a predetermined amount from an initial periodicity of said parameter, said (f) means including a ramp generator, a reference periodic voltage being generated by the ramp generator, means for diminishing to zero said ramp voltage with a period initiating change in said parameter, g. a first Zener diode in a path between said ramp generator and switch means for conducting said ramp voltage to actuate said switch means, when a subsequent periodicity of the parameter increases beyond the reference periodicity, h. means for supplying an operating potential apart from the ramp generator to actuate said switch means, i. means for shunting said operating potential to ground, said means including a second Zener diode, having a lower breakdown voltage than said first Zener, which is in a line defining a first shunt to ground, j. a second shunt means to ground, parallel with said first shunt to ground, said second shunt being normally closed and opened only upon a period initiating change in the parameter.

6. The system of claim 5 wherein, a. said means (e) includes means for supplying a potential for actuating said radio switch means, a first switch normally shunting said potential to ground but which opens and fails to shunt upon a period initiating change in the parameter, and a second switch normally open but which shunts said potential to ground when said reference voltage exceeds a predetermined value.