US3195535A

US3195535A - Miniature radiating electrocardiograph

Info

Publication number: US3195535A
Application number: US118605A
Authority: US
Inventors: Joseph F Westermann
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1961-06-21
Filing date: 1961-06-21
Publication date: 1965-07-20
Anticipated expiration: 1982-07-20

Description

July 20, -1965 .|.IF. wEsTERMANN MINIATURE RADIATI-NG ELECTROCARDIOGRAPH INVENTOR ATTORNEYSy Filed June 21, 1961 @g BY fm, WML-4 United States Patent O 3,195,535 MHNATURE RADIA'HNG ELECTRO- CARDHOGRAPH .oseph i?. Westermann, Abington, Pa., assigner, by mesne assignments, to United Aircraft orporation, a corporation of llielaware Filed .lune 21, 1961, Ser. No. 11%,605 3 Claims. (Ci. 12S- 2.06)

This invention generally relates to electrocardiographs and is particularly concerned with miniature battery powered electrocardiograph apparatus adapted to be carried by or attached to the patient and to continuously monitor the patient and transmit the information obtained over radio waves to a remote receiving station.

It is accordingly a principal object of the invention to provide a radio transmitting electrocardiograph apparatus for providing dynamic measurements of the patient while the patient is experiencing the stresses of normal Work and other activities.

Another object of the invention is to provide a portable radio beam generating electrocardiograph adapted to be Worn by the patient whereby the patient is completely unrestrained in his activities while diagnostic measurements of the heart are being made.

A further object is to provide such apparatus in miniature size and weight adapted to be easily carried or worn by the patient without impeding his normal activities or body exercises and without being externally observable by others so as to cause discomfort or embarrassment to the patient.

A more specific object is to provide a radio electrocardiograph transmitter system comprised completely of battery powered transistor circuitry that is adapted to be worn in close proximity to the patients body, yet is substantially unalfected by body heating or variations in voltage of the powering battery.

A still further object is to provide such a system for transmitting a frequency modulated carrier radio beam proportional to the patients cardiac responses that is extremely stable in operation despite variations in temperature, battery voltage, and other external inlluences or body generated extraneous signals.

Other objects and additional advantages will be more readily comprehended by those skilled in the art after a detailed consideration of the following specification taken with the single accompanying drawing illustrating, partially in block diagram form and partially in electrical schematic diagram form, one preferred embodiment of the invention.

Referring now to the single drawing, there is shown one complete radio electrocardiograph apparatus adapted to be worn by the patient and to transmit by means of a frequency modulated radio Wave, the electroeardiograph data to a remote radio receiver (not shown) that may be located at `a hospital, a doctors oflice or elsewhere at some distance from the patient.

As shown, the system generally includes a pair of electrodes or sensors 8 and 9, illustrated within dotted enclosure 10, adapted to be attached to closely spaced positions on the patients body, a pair of small diameter flexible electrical conductors 11 and 12 for connection to the electrodes for the purpose of conveying the electrical body generated signals, and a complete radio transmitter 3,195,535 Patented July 20, 1965 ICC and antenna system, including components generally designated 16, 1S, 2t) and 21 for responding to the desired signals from the body and for producing and radiating a frequency modulated radio wave to convey the cardiac information to a remote receiver (not shown).

All of the apparatus depicted in the drawing with the exception of the electrodes 8 yand 9 and the connecting wires 11 and 12 is adapted to be contained within a single miniature housing approximating the size of a cigarette package whereby this housing may be easily concealed in a pocket of the wearers clothing or suitably strapped to the body without being externally noticeable to others. The apparatus is also adapted to be completely powered for operation by means of a single small secondary battery, such as a cadmium nickel battery 57 or other as is presently available on the open market.

According to the invention, the body electrodes S and 9 are adapted to be continuously attached to the patients body for a relatively long period of time and to maintain low electrical resistance coupling to the body despite various changes in body movement and body curvature occurring while the patient is performing a variety of activities. The preferred electrodes are also quite small in size and easily attached to the body without awkward 7 straps or fastening means whereby they may be worn by the patient without impeding or interfering in any substantial measure with his activities, or causing him any discomfort. A preferred electrode construction providing these characteristics is disclosed in a copending application 4of Richard Berman and Bernard Schwartz, Serial No. 116,586, led June 12, 1961, and assigned to the same assignee, now Patent No. 3,085,577.

The low voltage level signals being obtained from these electrodes are directed over iiexible insulated conductors 11 and 12, and through suitable low frequency pass electrical lters in each conductor line, including capacitor 13 in line 11 and inductor 14 and capacitor 15 in line i2, to a pair of separate input terminals of a differential amplifier 16. In the differential amplifier 16, the pair of low voltage level electrode signals are filtered and combined in such manner as to eliminate any extraneous cornmon mode signal that is transduced by both electrodes in common, thereby to produce a single signal representing the desired cardiac information. This single signal is ampliiied by a ratio of about 200 to 30() to one and thence conveyed over an input line 17 to frequency modulate the preferred radio transmitter shown within the dotted enclosure designated 18.

Due to the fact that the `complete miniature transmitting system is adapted to be battery powered by a small secondary battery and is adapted to be strapped to or carried close to the patients body, it is subjected to variations in the voltage of the battery as well as changes in temperature resulting from body heat and ambient temperature variations. For `this reason, the differential amplifier 16 is compensated t-o prevent such variations from affecting the characteristics of the amplified cardiac signals produced over line 17 since otherwise, the transmitted signals would be subject to error and would not accurately reflect the condition of the patient. One preferred differential amplifier 16 providing the functions described and being compensated against such extraneous influences is disclosed in the copending application of Lyman Bethke, Serial No. 115,711, tiled lune 8, 1961,

lated carrier is then directed over output line 19 toV alow pass filter to remove any extraneous higher frequency as will bev of eliminating any extraneous signals" from entering the i transmitter ,18. The capacitorv22 is aA high capacity signals and is then passed outwardly over line 21 leading Y to la radiating antenna means whereby the, radiol beam may be propagated to a remote receiving and monitoring station (not shown). Y

At the remote receiving station, which may'belocated at a distanthospital, doctors .office .or the like, the frequency modulated radio beam is received and Vdetected to reproduce the intelligence signal and enable the heart wave signals to be recorded and displayed cna recording oscilloscope or other recorder as is well Vknown in theart.

It is `preferred to minimize the number of external leads and connection `wires so that the apparatus may be installed and put into use by doctors and medically trained technicians without the need for special electronic training Ain the use of the equipment. For vthis reason the externalfexible connector `12, interconnecting theV body electrode 8 with the differential amplifier 16, is also preferably employed as` the radiating antenna for the system by being connected to the radio output line' 21'.'

trodes 8 and 9 to thek miniature lhousing forthesys'tem` e'lectrolytic type capacitor for providing a low reactance to the passage of the `desired low frequency intelligence signals while at the same time blocking the passage of any extraneous direct current signals that may be carried over line 17. The inductor 24, on the other hand,V provides a large reactanceY to prevent the passage of any undesired higher frequency signals to and from line 17 to the transmitter butpermitsthe lower frequency intelligence signals to pass through to the transmitter. Since the overall circuit is adapted to be miniaturized in size, it is preferred that the capacitor 22 be a titanium electrolytic lcapacitor for providing-the desired high capacity neededtand being obtainable in a very smallsize unit.

Y After beingfilter'ed, the Vintelligencesignal is applied across a voltagev'ariable capacitance diode V26 whose alternating current capacitance is .varied in proportion to theV amplitude of the low frequencyintellligence signal. This variable capacitance diode effectively functions `as part of,the..modulator whereby the variations in the capacitance of this `diodef26 are employed to vary the frequency Vof the oscillatoras will bemore fully dis- `cus-sed below. l l

The transistor in the first stage of `the transmitter isf connected'ina Hartleyoscillator type configuration with its base electrode being connected in series-with a piezoelectric crystal 31 to theupper terminal ofl a feedback tank circuit,.including capacitor 28and inductor 29, and

with `a tap or terminal on inductor 29 being connected through a resistor34 to the emitter electrode.y The collector electrode ,of transistor 35 is Vconnected to the upper tive terminal vof the battery 57 and alternating current to serve as both Yinput leads from the electrodes andas a radiating antenna for the system. Y n l v The preferredftran'smitter shown within the dotted'` enclosure designated 18 is preferably comprised of three` signal over line 17 to produce a variable frequency al-j ternating current signal, in the low radiofrequency brand, across its output tank circuit, including parallel connected capacitor 364 4and inductor 37. t

In the second stage, this` variable frequency radio signal is proportionally lincreased in frequencyby a factor coupled to the positive terminal lat groundv through a capacitor39. It is Vto be noted atthis point, however, that the complete portablesystem is adapted to be carried by thepatient andnis not connected to actual ground at any position, and that the ground symbols on Vthe drawing,

t therefore, signify only the positive terminal of the portable of about two'to one to double the frequency ofthe.

oscilla-tor, and in the third stage,` the resulting radio signal is further multiplied in frequency by a factor of.

The purpose vof providing this rather high ratio of frequency multiplication in the transmitter is vto provide a wide range of frequency devi-ation inthe output radio signal Ain response'to Athe incoming intelligence signals" originating frorn the electrodes Stand 9, or in other words, to provide a highly sensitive transmitting system wherein a small change'in the amplitude Mof the Velectrode signals produces a relatively large variation in the frequency of thepropagated radio beam.

Returning vnow to the drawing and tracing through the prefenred vtransmitter circuit 18, the incoming intel-'- ligence signal from` the amplifier V16 and vover line 17 is first directed through a filter including a series connected capacitor 22,resistor 23 and inductor 24 for the purpose battery.` It will also be notedpthat throughout lthe transmitter, alternating current by-pass capacitors 39,` 46 and 55 are-employed to prevent the alternating current signals Y from passing'through the battery terminals.

' Returning to the first stage oscillator, the lower terminal of the input tank circuit is alternating current coupled toA the lower terminal of the output tank'circuit through capacitor 39 andthe direct current battery potentialis applied across these terminals. Forproviding direct current biasing of the base electrode, avoltage divider comprising resistors 32 and 33-,isl energizedacross the terminals of the battery and the junction of .these resistorsl isV connected to the base electrode ofY transistor 35. y

Inoperation, the resonant frequency of the tank circuit comprising the rvoltage variable diode capacitor 26,l fixed capacitor 28and inductor 29, operatingwith the crystal 31, normally determinesthe Ystablev frequency of oscillation Vof the first stage and this oscillating signal, together with its harmonics, is produced across the `output tank circuit comprising capacitor 36 and inductor 37. The'incoming low frequency intelligence signal over v,line 17 'varies the capacity ofthe voltage variable diode 26 and, therefore,

t the oscillator signal from -being transmitted backwardly` changesV the resonant frequency offthis tank circuit thereby to vary ther oscillation frequency. This xlowfrequency modulating signal over line 17 is blocked from reaching the ybase electrode of transistor .35 by the couplingcapacitor 27 which serves to couplethe higher Voscillator frequency to the variable capacitordiode 26 but decouples the modulating signal fromvtransistor 35. The series connected inductor 24 on the other hand prevents to the amplifier 16.

Thus the oscillator frequency in the first stage is varied in proportion to the amplitude of the incoming intelligence signal over line 17. This variable frequency oscillator signal is produced across the output tank circuit, comprising capacitor 36 and inductor 37, which tank circuit is tuned to resonance over a narrow band at the second harmonic frequency of the oscillator. The variable oscillator signal is thus doubled in frequency at the output of the first stage.

To provide an oscillator signal that is rich in the higher frequency harmonics, a resistor 34 is placed in the emitter circuit of transistor whereby the oscillator stage functions in the class C region to provide the necessary harmonics for the frequency multiplication stages.

Since the transistor 35 is subject to variation with temperature change as may result from the body heat of the patient or other external temperature variation, the present invention provides compensation for this effect to insure that the oscillator frequency remains stable and varies only according to the intelligence signal as desired. This compensation is provided by employing a capacitor 28 in the tank circuit possessing a negative temperature coeicient whereby its capacity decreases with increase in temperature. Since this capacitor 28 serves as one parameter in controlling the frequency, and it functions in opposition to the temperature changes in transistor 35, the oscillator frequency is stabilized against undesired variations due to temperature variations.

From the output tank circuit of the first stage oscillator, the frequency modulated radio signal is coupled to the second stage by a secondary winding 3S that is inductively coupled to inductor winding 37, as shown. From the secondary winding 38, the radio signal passes through a coupling capacitor 4f? and is applied between the emitter and base electrodes of transistor 43. The transistor 43 is connected in a common base configuration, with the base electrode being connected directly to the positive terminal of the battery and the collector electrode being energized by the negative terminal thereof through a resonant tuned circuit comprising a capacitor 44 shunted by an inductor winding 45. Direct current biasing is applied between the base and emitter by means of a series connected resistor 4Z and inductor 41 connecting these electrodes, with the inductor #il being in circuit to prevent the radio signal from affecting the direct current biasing of the transistor.

This common base configuration of the second stage transistor 43 'provides maximum amplification at the high radio frequency involved due to the more favorable interelectrode capacities of the transistor being provided with the transistor in this configuration. it also provides optimum stability despite variation in the potential of the battery voltage as well as improved frequency response for the frequency variable radio signal being conveyed.

The output tuned circuit comprising capacitor d4 and inductor 4S is made resonant at the third harmonic frequency to provide an additional frequency multiplication of the radio signal.

rEhe third or final stage of the transmitter, and including transistor 5l., is essentially in the same circuit conguration as is the second stage with the transistor 51 being connected in -a common base conguration to provide optimum gain compatible with the desired frequency response and stability of the circuit despite variations .in the potential of the battery. The input and output circuits thereof are provided with tuned tank circuits to provide additional frequency multiplication of the radio signal as is desired. Thus the output radio signal being produced by the transmitter over line 19 is a frequency modulated radio signal having a wide range of frequency deviation in proportion to the cardiac intelligence signal obtained from the electrodes.

As generally discussed above, the frequency modulated radio signal over line 19 is then passed by a low pass filter Ztl to remove any extraneous higher frequency noise and finally directed over line 21 to the radiating antenna input connecter 12 Where it is propagated as a radio beam to a remotely located frequency modulation receiver.

Although but one preferred embodiment of the invention has been illustrated and described, many variations may be made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, this invention should be considered as being limited only by the following claims.

What is claimed is:

1. In a portable self-contained radio electrocardiograph apparatus adapted to be completely carried hy the patient and free of external electrical wiring interconnecting the patient with a fixed location for monitoring the patients heart characteristics in a dynamic fashion while the patient is subjected to stresses encountered by unrestrained activity, ransducer electrodes adapted to be bonded to the patients skin and being iiexible to maintain low resistance contact with the same location on the body despite variations in body curvature, and transmitter means producing a carrier radio-frequency responsive to electrical signals obtained from the electrodes to produce a frequency modulated ultra high frequency radiation to be detected at a remote location, said transmitter means comprising a battery, a radio frequency oscillator powered by the battery, and a housing containing said oscillator and battery and adapted to be carried by the patient during unrestrained activity in intimate heat transferring relationship with the patients body and means for stabilizing said transmitter means to prevent heating by bo-dy temperature and variations in battery potential from producing spurious variations in the radiation, said stabilizing means including a temperature sensitive electrical component in said oscillator for varying the oscillator frequency in opposition to the change normally produced by heat.

2. ln a self-contained electrocardiograph system adapted to be completely carried by the patient and having no external electrical wiring interconecting the patient with a fixed location, small electro-des for attachment to the patients skin and providing substantially constant low electrical resistance with the same skin locations despite variations in body curvature with unrestrained movement of the patient, and a battery powered radio transmitter operating in the ultra high frequency bandwidth, said transmitter being modulatable according to the electrode produced signals to vary its frequency of radio transmission, and means for compensating said transmitter against spurious variations, said transmitter including a lower frequency crystal controlled oscillator and frequency multiplier stages for proportionately increasing the frequency of the oscillator for transmission in the ultra high frequency bandwidth, and means for varying the frequency oflthe oscillator according to the electrode produced signa s.

3. in a self-contained electrocardiograph system adapted to be completely carried by the patient and having no external electrical wire interconnecting the patient with a fixed location, small electrodes for attachment to the patients skin and providing substantially constant low electrical resistance with the same skin locations despite variations in body curvature with unrestrained movement of the patient, and a battery powered radio transmitter operating in the ultra high frequency bandwidth, said transmitter being modulatable according to the electrode produced signals `to vary its frequency of radio transmission, and means for compensating said transmitter against spurious variations, said transmitter including a lower frequency crystal controlled oscillator and frequency multiplie-r stages for proportionately increasing the frequency of the oscillator for transmission in the ultra high frequency bandwidth, and means for varying the frequency of the oscillator according to the electrode produced signals, said means including a voltage variable capacitor diode.

eferencc-s on following page) Y References Cite by Ehe Examiner y Y 'Y V 3,051,896 8/ 62 Begani i.- 324-71 2756741 Ugmsm PATENTS ,128 '2 05 ji if?? Y:23:11:31:*S 2,827,040,l v3/58 GillrfI-ln- 128:2:05 5 Y .QTHER REFERENCES 2,484,992 g/58 pigeon Y1259.105V v Barr, The M111tary Surgon, February 1954, pgs. 79-83.

i j: 'i RICHARD A- GAUDE'T Pffmafy Emmen 2,981,911 4/ 61 Warnick 12S-2.05 XR RICHARD ,.T.V HOFFMAN, JORDAN FRANKLIN, 3,029,808 4/62 Kagan 12S-206 1() A Y -Y Y 1 Examiners. Y

Claims

1. IN A PORTABLE SELF-CONTAINED RADIO ELECTROCARDIOGRAPH APPARATUS ADAPTED TO BE COMPLETELY CARRIED BY THE PATIENT AND FREE OF EXTERNAL ELECTRICAL WIRING INTERCONNECTING THE PATIENT WITH A FIXED LOCATION FOR MONITORING THE PATIENT''S HEART CHARACTERISTICS IN A DYNAMIC FASHION WHILE THE PATIENT IS SUBJECTED TO STRESSES ENCOUNTERED BY UNRESTRAINED ACTIVITY, TRANSDUCER ELECTRODES ADAPTED TO BE BONDED TO THE PATIENT''S SKIN AND BEING FLEXIBLE TO MAINTAIN LOW RESISTANCE CONTACT WITH THE SAME LOCATION ON THE BODY DESPITE VARIATIONS IN BODY CURVATURE, AND TRANSMITTER MEANS PRODUCING A CARRIER RADIO-FREQUECY RESPONSIVE TO ELECTRICAL SIGNALS OBTAINED FROM THE ELECTRODES TO PRODUCE A FREQUENCY MODULATED ULTRA HIGH FREQUENCY RADIATION TO BE DETECTED AT A REMOTE LOCATION, SAID TRANSMITTER MEANS COMPRISING A BATTERY, A RADIO FREQUENCY OSCILLATOR POWERED BY THE BATTERY, AND A HOUSING CONTAINING SAID OSCILLATOR AND BATTERY AND ADAPTED TO BE CARRIED BY THE PATIENT DURING UNRESTRAINED ACTIVITY IN INTIMATE HEAT TRANSFERRING RELATIONSHIP WITH THE PATIENT''S BODY AND MEANS FOR STABILIZING SAID TRANSMITTER MEANS TO PREVENT HEATING BY BODY TEMPERATURE AND VARIATIONS IN BATTERY POTENTIAL FROM PRODUCING SPURIOUS VARIATIONS IN THE RADIATION, SAID STABILIZING MEANS INCLUDING A TEMPERATURE SENSITIVE ELECTRICAL COMPONENT IN SAID OSCILLATOR FOR VARYING THE OSCILLATOR FREQUENCY IN OPPOSITION TO THE CHANGE NORMALLY PRODUCED BY HEAT.