An inexpensive Herman San
portable
ECG transmitter
N. Uhley, M.D.
Francisco,
Calif.
Within the past few years, the clinician has witnessed the rapid evolution of the field of electrical monitoring of the heart.’ Continuous electrical monitoring in coronary and intensivecare units has been extended to more sophisticated forms of automatic electrical monitoring on the general hospital floor.“.:l Long-term monitoring with a Holter tape recorder has become increasingly popular for outpatient use. Telemetry has also been widely applied to transmit ECG information from patients to a remote observer. Such applications include radio transmissions from ambulances,‘,6 ambulatory patient radio transmission within the hospital, telephone transmission of arrhythmias,’ and telephone transmission of information relating to a pacemaker function. Virtually all of the techniques described require bulky or costly equipment limiting widespread application. It is the purpose of this paper to demonstrate how modern electronic technology may be used to construct an inexpensive small ECG transmitter which may be used in conjunction with commonly available demodulators and an ECG recorder for long-distance transmission of ECG information over the telephone, In addition, the varying tone of the device may serve as a bedside indicator of ECG activity. ECG transmitter
The transmitter converts the ECG signal into an audio tone (Fig. 1). It is made up of three sections: an amplifier (IC l), a voltage-control oscillator (IC 2), and an audio output transformer and speaker (Fig. 2). Conventional monitor adhesive electrodes are
From the Department Center, San Francisco, Received
for publication
of Medicine, Calif.
Mount
Zion Hospital
and Medical
Oct. 10, 1974.
Reprint requests to: Herman N. Uhley, M.D., Mount Zion Hospital and Medical Center, P.O. Box 7921, San Francisco, Calif. 94120.
November,
1975, Vol. 90, No. 5, pp. 607-610
Table
I. Components
of the ECG transmitter
R,, R:
500 Kohms 44 Mohms 1.8 Mohms 100 Kohms pot. 1.5 Kohms 10 Kohms 0.02 pfd 200 pfd 0.001 ,ufd 47 pfd miniature audio output I ransformer 200 Ohm primary 8 Ohm secondary S 8 Ohm miniature speakw IC, and socket /LA 776 Fairchild ICI and socket NE 566 Signetics Batteries 2-l! Volt AA cells l-9 Volt transistor hatter? Battery holders and connectors Slide switches 2-SPDT Electrodes, electrode wires, wire. case, and circuit hoard. resistors are ‘C uvatt. R,, R, R-, R. R7 R,, R.. c, Cd C., G T
All
placed on the chest wall in the vicinity of the heart. The electrodes are generally kept close to each other since large DC skin potential differences may interfere with the operation of the oscillator. The electrodes feed an operational amplifier (IC 1) which has a high input impedance. The ECG signal is amplified and sent through a large capacitor to a voltage-controlled oscillator (IC 2). The voltage-control oscillator is an integrated circuit which develops an audio tone suitable for transmission over telephone lines. The frequency varies with the amplitude of the output of the operational amplifier-integrated circuit. A coupling condenser and audio output transformer carry the frequency-modulated signal to a small speaker which is held in close proximity to the telephone mouthpiece for transmission of the tone to a demodulator-ECG recorder.
American
Heart
Journal
607
Uhley
Fig.
1. The
components
of the ECG
Fig. 2. Schematic
transmitter
diagram
The audio tone generated by the transmitter provides the clinician with some information about the heart beat at the bedside. While there is no substitute for palpation of the pulse, the device leaves the physician’s hands free for procedures, e.g., carotid sinus massage. In addition the difference in sound of wide QRS complexes, such as due to ventricular premature beats, as compared to the normal duration QRS complex, may be easily detected by the ear. Thus, in practice, the device has some value for use at the bedside as well as for transmission of the signal over the telephone. Subsequent voice communication with an interpreter after sending the signal over the telephone
608
are contained
of the ECG
within
a small
plastic
box.
transmitter.
provides the sender transmission.
with
information
on the
Discussion
Several years ago a multitude of individual components would have been required to construct an ECG transmitter. These numerous components added to the size and cost of the total unit. In the mid-sixties, the electronics industry developed integrated assemblies of components which were combined to form complete circuits, called integrated circuits. The integrated circuit, or “ICY, may be very small and may contain hundreds of separate electronic components. Two
November,
1975, Vol. 90, No. 5
Fig. 3. Examples of ECG transmissions from the portable telephone transmitter. Top strip is a transmision New York to San Francisco. Middle strip shows the conversion of a paroxysmal atria1 tachycardia to sinus with a Valsalva maneuver. Bottom strip shows a demand pacemaker transmission (left) and the subsequrol recording with a conventional ECG recorder at the bedside for comparison (right).
low-cost IC’s (approximately $4.50 each) and a few miscellaneous electronic components (Table I) are used in this device. The small number of components involved make it possible for individuals with minimal experience in electronics to construct the transmitter. The integrated circuits used in this device are physically small as well as inexpensive, and equivalent to many electronic components. For example, the operational amplifier in the transmitter is 0.370 inch in diameter and 0.185 inch high. It contains 24 transistors, eight resistors, and a capacitor. The total cost of the transmitter is less than $20.00. Many hospitals are already equipped with demodulators for converting ECG signals transmitted from various remote sources such as
American
Heart
Journal
irom rhl thtrr tiirt1r.t
ambulances. In such instances the small portable transmitter described may be tuned (R,,C,) to the frequency of the demodulator and can be incorporated in the existing system. In the examples shown (Fig. 3), an Electrobiometrics Demodulator” was used and the transmitter R!,C! values did not need to be changed. The frequency response of the entire system (transmitter to ECG strip recorder) was 0.5 to 40 Hertz. Widespread use of telephone transmission of ECG signals can be of considerable assistance to the practicing physician (Fig. 3). Patients suspected of having various arrhythmias (jr syncopal problems may have a signal transmit ted at a time of distress. Likewise, pacemakers with potential problems may be analyzed via the telephone as the time for replacement nears. It is also possible
609
Uhley
to record with tone from the transmitter with a small casette tape recorder for subsequent replay.
2.
3.
Summary A small, easy-to-construct, pocket-sized ECG telephone transmitter utilizing few components and costing less than $20.00 is described. The tone produced varies with the ECG signal and may be transmitted over the telephone system to a demodulator and ECG recorder for permanent records and interpretation, as well as serving as an indicator of the ECG signal at the bedside. This simple device provides useful information on patients with various clinical problems.
4.
5.
6.
7.
8. REtERENCES 1.
610
Uhley, patients,
H.
N.: Electrical Geriatics 25:145,
monitoring 1970.
of the
acutely
ill
Uhley, H. N., Brown, A. E., Friedman, M., et al.: Automatic surveillance of rate, rhythm and T wave contour: The concept of monitoring large number of patients, Am. J. Cardiol. 26:375, 1970. Uhley, H. N.: Automatic monitoring for all patients, J. Am. Hosp. Assoc. 41 :lOl, 1973. Bleifer, S. B., Karpman, H. L., Sheppard, J. J., et al.: Relation between premature ventricular complexes and development of ventricular tachycardia, Am. J. Cardiol. 3 1:400, 1973. Nagel, E. L., Hirschman, J. L., Nassenfeld, S. R., et al.: Telemetry-medical command in coronary and other mobile emergency care systems, J. A. M. A. 214:332-338, 1970. Uhley, H. N.: Electrocardiographic telemetry from ambulances. A practical approach to mobile coronary units, AM. HEART J 80:838, 1970. Peter, T., Harper, R., Luxton, M., et al.: Personal telephone electrocardiogram transmitter, Lancet 2( #7838):1110, 1973. Escher, D. J. W.: Follow-up of the patient with an implanted cardiac pacemaker, Mod. Concepts Cardiovast. Dis. 43~77. 1974.
November, 1975, Vol. 90, No. 5
portable
ECG transmitter
N. Uhley, M.D.
Francisco,
Calif.
Within the past few years, the clinician has witnessed the rapid evolution of the field of electrical monitoring of the heart.’ Continuous electrical monitoring in coronary and intensivecare units has been extended to more sophisticated forms of automatic electrical monitoring on the general hospital floor.“.:l Long-term monitoring with a Holter tape recorder has become increasingly popular for outpatient use. Telemetry has also been widely applied to transmit ECG information from patients to a remote observer. Such applications include radio transmissions from ambulances,‘,6 ambulatory patient radio transmission within the hospital, telephone transmission of arrhythmias,’ and telephone transmission of information relating to a pacemaker function. Virtually all of the techniques described require bulky or costly equipment limiting widespread application. It is the purpose of this paper to demonstrate how modern electronic technology may be used to construct an inexpensive small ECG transmitter which may be used in conjunction with commonly available demodulators and an ECG recorder for long-distance transmission of ECG information over the telephone, In addition, the varying tone of the device may serve as a bedside indicator of ECG activity. ECG transmitter
The transmitter converts the ECG signal into an audio tone (Fig. 1). It is made up of three sections: an amplifier (IC l), a voltage-control oscillator (IC 2), and an audio output transformer and speaker (Fig. 2). Conventional monitor adhesive electrodes are
From the Department Center, San Francisco, Received
for publication
of Medicine, Calif.
Mount
Zion Hospital
and Medical
Oct. 10, 1974.
Reprint requests to: Herman N. Uhley, M.D., Mount Zion Hospital and Medical Center, P.O. Box 7921, San Francisco, Calif. 94120.
November,
1975, Vol. 90, No. 5, pp. 607-610
Table
I. Components
of the ECG transmitter
R,, R:
500 Kohms 44 Mohms 1.8 Mohms 100 Kohms pot. 1.5 Kohms 10 Kohms 0.02 pfd 200 pfd 0.001 ,ufd 47 pfd miniature audio output I ransformer 200 Ohm primary 8 Ohm secondary S 8 Ohm miniature speakw IC, and socket /LA 776 Fairchild ICI and socket NE 566 Signetics Batteries 2-l! Volt AA cells l-9 Volt transistor hatter? Battery holders and connectors Slide switches 2-SPDT Electrodes, electrode wires, wire. case, and circuit hoard. resistors are ‘C uvatt. R,, R, R-, R. R7 R,, R.. c, Cd C., G T
All
placed on the chest wall in the vicinity of the heart. The electrodes are generally kept close to each other since large DC skin potential differences may interfere with the operation of the oscillator. The electrodes feed an operational amplifier (IC 1) which has a high input impedance. The ECG signal is amplified and sent through a large capacitor to a voltage-controlled oscillator (IC 2). The voltage-control oscillator is an integrated circuit which develops an audio tone suitable for transmission over telephone lines. The frequency varies with the amplitude of the output of the operational amplifier-integrated circuit. A coupling condenser and audio output transformer carry the frequency-modulated signal to a small speaker which is held in close proximity to the telephone mouthpiece for transmission of the tone to a demodulator-ECG recorder.
American
Heart
Journal
607
Uhley
Fig.
1. The
components
of the ECG
Fig. 2. Schematic
transmitter
diagram
The audio tone generated by the transmitter provides the clinician with some information about the heart beat at the bedside. While there is no substitute for palpation of the pulse, the device leaves the physician’s hands free for procedures, e.g., carotid sinus massage. In addition the difference in sound of wide QRS complexes, such as due to ventricular premature beats, as compared to the normal duration QRS complex, may be easily detected by the ear. Thus, in practice, the device has some value for use at the bedside as well as for transmission of the signal over the telephone. Subsequent voice communication with an interpreter after sending the signal over the telephone
608
are contained
of the ECG
within
a small
plastic
box.
transmitter.
provides the sender transmission.
with
information
on the
Discussion
Several years ago a multitude of individual components would have been required to construct an ECG transmitter. These numerous components added to the size and cost of the total unit. In the mid-sixties, the electronics industry developed integrated assemblies of components which were combined to form complete circuits, called integrated circuits. The integrated circuit, or “ICY, may be very small and may contain hundreds of separate electronic components. Two
November,
1975, Vol. 90, No. 5
Fig. 3. Examples of ECG transmissions from the portable telephone transmitter. Top strip is a transmision New York to San Francisco. Middle strip shows the conversion of a paroxysmal atria1 tachycardia to sinus with a Valsalva maneuver. Bottom strip shows a demand pacemaker transmission (left) and the subsequrol recording with a conventional ECG recorder at the bedside for comparison (right).
low-cost IC’s (approximately $4.50 each) and a few miscellaneous electronic components (Table I) are used in this device. The small number of components involved make it possible for individuals with minimal experience in electronics to construct the transmitter. The integrated circuits used in this device are physically small as well as inexpensive, and equivalent to many electronic components. For example, the operational amplifier in the transmitter is 0.370 inch in diameter and 0.185 inch high. It contains 24 transistors, eight resistors, and a capacitor. The total cost of the transmitter is less than $20.00. Many hospitals are already equipped with demodulators for converting ECG signals transmitted from various remote sources such as
American
Heart
Journal
irom rhl thtrr tiirt1r.t
ambulances. In such instances the small portable transmitter described may be tuned (R,,C,) to the frequency of the demodulator and can be incorporated in the existing system. In the examples shown (Fig. 3), an Electrobiometrics Demodulator” was used and the transmitter R!,C! values did not need to be changed. The frequency response of the entire system (transmitter to ECG strip recorder) was 0.5 to 40 Hertz. Widespread use of telephone transmission of ECG signals can be of considerable assistance to the practicing physician (Fig. 3). Patients suspected of having various arrhythmias (jr syncopal problems may have a signal transmit ted at a time of distress. Likewise, pacemakers with potential problems may be analyzed via the telephone as the time for replacement nears. It is also possible
609
Uhley
to record with tone from the transmitter with a small casette tape recorder for subsequent replay.
2.
3.
Summary A small, easy-to-construct, pocket-sized ECG telephone transmitter utilizing few components and costing less than $20.00 is described. The tone produced varies with the ECG signal and may be transmitted over the telephone system to a demodulator and ECG recorder for permanent records and interpretation, as well as serving as an indicator of the ECG signal at the bedside. This simple device provides useful information on patients with various clinical problems.
4.
5.
6.
7.
8. REtERENCES 1.
610
Uhley, patients,
H.
N.: Electrical Geriatics 25:145,
monitoring 1970.
of the
acutely
ill
Uhley, H. N., Brown, A. E., Friedman, M., et al.: Automatic surveillance of rate, rhythm and T wave contour: The concept of monitoring large number of patients, Am. J. Cardiol. 26:375, 1970. Uhley, H. N.: Automatic monitoring for all patients, J. Am. Hosp. Assoc. 41 :lOl, 1973. Bleifer, S. B., Karpman, H. L., Sheppard, J. J., et al.: Relation between premature ventricular complexes and development of ventricular tachycardia, Am. J. Cardiol. 3 1:400, 1973. Nagel, E. L., Hirschman, J. L., Nassenfeld, S. R., et al.: Telemetry-medical command in coronary and other mobile emergency care systems, J. A. M. A. 214:332-338, 1970. Uhley, H. N.: Electrocardiographic telemetry from ambulances. A practical approach to mobile coronary units, AM. HEART J 80:838, 1970. Peter, T., Harper, R., Luxton, M., et al.: Personal telephone electrocardiogram transmitter, Lancet 2( #7838):1110, 1973. Escher, D. J. W.: Follow-up of the patient with an implanted cardiac pacemaker, Mod. Concepts Cardiovast. Dis. 43~77. 1974.
November, 1975, Vol. 90, No. 5
