US 3650264 A
A medical diagnostic apparatus for producing an audible indication of the nature of electric signals produced in the human body by the action of the heart. An audio frequency carrier wave is modulated both in frequency and in amplitude in accordance with the aforesaid applied electric signals. The level of the fundamental tone normally remains below the limit of audibility. This limit is exceeded only when an electric heartbeat signal occurs.
Description (OCR text may contain errors)
United States Patent J anssen [451 Mar. 21, 1972  APPARATUS FOR ELECTRO-MEDICAL 3,338,234 8/1967 Kleinerman et aL. ...128/2.06 R INVESTIGATION 3,426,150 2/ 1969 Tygart ...l28l2.06 R 3,413,546 11/1968 Riehl et a1. ..l28/2.06 R  Inventor: Frits Jacques Janssen, Emmasingel, Eindhoven, Netherlands FOREIGN PATENTS OR APPLICATIONS 73 Assignee; Philips Corporation, New York, NY 250,557 11/1966 Austria 128/206 R  Filed: 2, 1969 Primary Examiner-William E. Kamm 21 Appl. No.: 881,462 Tnfa"  Foreign Application Priority Data  ABSTRACT Dec. 4, 1968 Netherlands ..6817326 I A medical diagnostic apparatus for producing an audible indication of the nature of electric signals produced in the human  U.S. Cl. ..128/2.06 A y y h ion f h heart- An audio frequency carrier [51 1111.01. ..A61l5/04 wave is modulated both in qu n y a d in mplitude in ac- 53 Field 01 Search 1 28/206 A, 2.06 F, 2.06 R, eerdenee with the aforesaid pp electric eignele- The level 123/2 1 A, 2 5 T of the fundamental tone normally remains below the limit of audibility. This limit is exceeded only when an electric heart- References Cited j fw fifi fi occurs W A UNITED STATES PATENTS 2,918,054 12 1959 Qoolltasian ....128/205 T 4 Claims 2 Drawing 4 SJ 9 10 11 5 FM AM MOD PATENTEDMAR21 I972 -55 AMP AMP 6 FM MOD) AM MOD AF osc 7\J;
T flgJ INVENTOR. FRITS JACQUES JANSSEN BY (K M /K v ENT APPARATUS FOR ELECTRO-MEDICAL INVESTIGATION This invention relates to an apparatus for providing an audible indication of the strength of electro-physiological signals produced in the human body, for example, electrical voltages and currents produced by the action of the heart. Such apparatus are known in which an audiofrequency carrier wave is used whose frequency is modulated by the applied signals, while signal strength alterations become manifest by variations of the pitch of the tone. In this manner deviations from the normal course of given physiological phenomena may be assessed before other apparatus particularly designed for such an examination is available, particularly in emergency cases, when a quick assessment of deviations may be decisive of the manner of treatment of a patient, useful indications can be obtained. It has been found that the size and the weight of apparatus of this kind, which are energized by batteries, may be readily restricted to such an extent that they can be added without any objection to the portable instruments required for a medical examination.
Like the electrocardiograph such an apparatus can pick up the electrical signals from the heart, which are then reproduced in the form of a sound varying in pitch. The constantly audible fundamental tone makes the distinction of the separate heart complexes difficult so that auscultation is a fatiguing strain.
There has been employed a suppressed carrier wave which provides at each pulse an audible tone as a result of the electrocardiogram signals, said tone having a given frequency and a very short duration. The sound in the pulse intervals is thus reduced to a level below the limit of audibility, but the perceptible sound does not contain information about the signal strength.
The invention has for its object to avoid said disadvantages and to facilitate quick recognition of the most lethal cardiac diseases such as fibrillation, arrest and arrhythmia. According v to the invention the audiofrequency carrier wave is modulated in accordance with the applied electrical signal both in frequency and in amplitude. The amplitude modulation may be adjusted so that the sound level of the nonaudible audiofrequency tone is raised in the presence of a signal until the limit of audibility is transgressed, after which alterations of the signals become manifest in differences of pitch and strength. In this case the sound level of the fundamental tone may be reduced to a value below the limit of audibility without the desired information getting lost or being markedly weakened.
The invention will be described in greater detail by means of the following description of a preferred embodiment thereof in conjunction with the accompanying drawing, in which:
FIG. 1. is a simplified circuit diagram of the apparatus in accordance with the invention, and
FIG. 2. relates to one embodiment of the apparatus.
By means of the input electrodes 1, 2 and 3, electrical signals produced by the heart beat in the human body are derived and applied to a simple electrocardiogram amplifier 4, in which the derived signals are combined in known manner into a single signal voltage. This signal voltage is applied to an audiofrequency oscillator 5, the frequency of which is modulated by the signal voltage so that, e.g., an increase in signal voltage may result in a rise of frequency and hence the pitch of the fundamental tone is raised. By means of the switch 6 the DC current source 7, preferably formed by dry cell batteries or a different easily manipulated current source of small size, is put in or out of operation. The signal supplied by the amplifier 4 is applied via the rectifier 8 to the amplitude modulator 9 which modulates the amplitude of the frequency-modulated signal coming out of the audiofrequency oscillator 5 in accordance with the strength of the signal from the amplifier 4. An amplifier 10 with gain control supplies the signal to the sound reproducing device 11 in which it is converted into an audible tone.
The required parts of the circuit described are accommodated in a housing 12 composed of a suitable synthetic resin. The shape of the housing [8 to some extent adapted to the manner in which the apparatus is employed. For establishing the electric connection between the input electrodes 1, 2 and 3 and the body surface, that is to say, the patients thorax in the case of an examination of the heart, the required number of contact arms 13, 14 and 15 are provided on the housing 12. These arms may, if necessary, be movably fastened in order to allow some relative displacement. The housing is furthermore provided with a rocker 16 for actuating the switch 6. The gain of the amplifier 10 is adjusted by means of a rotatable or slidable knob 17. A plurality of slots 18 in the housing 12 provide an outlet for the produced sound.
What is claimed is:
1. An apparatus for providing an audible indication of the strength of electric signals produced in the human body by heart activity comprising, means for generating an audiofrequency carrier wave, means for modulating the frequency thereof in accordance with the strength of the electric signals, and means for amplitude modulating the frequency modulated carrier wave so as to vary the tone strength of the carrier wave in accordance with the strength of the electric signals applied to the apparatus.
2. A device for the audible observation of heart activity comprising, at least two electrodes adapted to derive electric signals from the body produced by the action of the heart, means for generating an audio frequency carrier wave, amplifier means having an input coupled to said electrodes, means for coupling the output of said amplifier means to an input of said audio frequency generating means whereby the carrier wave is frequency modulated in accordance with said electric signals, means coupled to the output of said amplifier means and to the output of said audio frequency generating means for amplitude modulating the frequency modulated carrier wave in accordance with said electric signals derived from the human body, and means responsive to the amplitude and frequency modulated carrier wave for producing an audible indication thereof.
3. A device as claimed in claim 2 further comprising rectifier means connected between the output of said amplifier means and an input of said amplitude modulating means.
4. A device as claimed in claim 2 further comprising means for suppressing the audio frequency carrier wave whenever the electric signals are below a given threshold level.