Device For The Audible Reproduction Of A Cardiogram With Speech-like Sounds

Abstract

A device for the audible reproduction of electrophysiological signals, which includes a serially connected sine wave generator and pulse shaper in which these signals are reproduced in the form of speech-like sound signals, and a pair of band pass filters of which one is frequency tunable to vary the monotonic signals from the pulse shaper in response to deviations in the electrophysiological signals so that the deviations are reproduced as speech-like deviations in these sound signals.

Description

The invention relates to a device for the audible reproduction of electrophysiological signals such as, for example, electrical signals produced by the action of the heart.

Such a device is known from U. S. Pat. No. 3,650,264 dated Mar. 21, 1972. The device described therein modulates an audio-frequency carrier wave both in frequency and in amplitude, in accordance with an applied electrical signal. Variations in a signal to be detected appear as variations of the pitch and as variations of the volume of the sound.

The invention has for its object to reproduce said electrical signal in a more directly appealing audible signal, in particular by reproducing a cardiogram in a speech-like sound. A device of the kind set forth is characterized according to the invention in that electronic means are provided to convert electrophysiological signals into speech-like sounds.

Such a device offers the advantage that a normal cardiogram is reproduced as a readily recognizable speech-like sound and that deviations in the cardiograms result in deviations in the reproduced speech-like sound which correspond with speech sounds. The human ear is very sensitive to tone differences in a speech sound, so that slight deviations in a cardiogram will also be quickly noticed. The response of the cardiogram thus obtained is particularly suitable for verbal transfer. By choosing, for example, the sound produced by a generally known physical phenomenon as a standard sound, the sound signal can be defined by standardizing all relevant circumstances.

In order that the invention may be readily carried into effect, one embodiment thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which:

FIG. 1 is a diagrammatic circuit arrangement of a device according to the invention, and

FIG. 2 is an embodiment of a device according to the invention in the form of a portable cardiogram recording apparatus.

With the aid of, for example, three input electrodes 1, 2 and 3, electrical signals produced by the action of the heart are recorded and supplied, via a preamplifier 4, to a voltage-controlled sinewave generator 5 on the one hand, and to a frequency filter 6 on the other hand. As an input signal an electrocardiogram recorded directly on a patient may be used, which recording may also be made with more or less than three electrodes. As an input signal may also be used a cardiogram signal recorded elsewhere, for example, a voltage signal supplied by a recorder, in which case the preamplifier 4 is superfluous. Signals to be supplied by the voltage-controlled sinewave generator, the frequency of which varies monotonously with the cardiogram voltage, are supplied to a pulse generator 7. A maximum pulse duration thereof is, for example, 0.1 ms. This pulse duration is not critical and may be arbitrarily chosen with a maximum duration of about 1 ms within given limits. The repetition frequency of the pulse generator 7 determines the pitch of the sound to be produced. A choice has to be made for the average repetition frequency. For this frequency, for example, 200 Hz may be chosen. The sound then lies at the level of a high male voice (tenor) and a low female voice (alto), respectively. In order to make the sound to be produced ultimately resemble speech-like sounds, it is desirable to give the signal a tone pitch swing. The choice therefore is rather arbitrary. In a preferred embodiment attempts have been made to avoid a machine-like sound as much as possible. Consequently, a tone pitch swing of approximately 50 percent is introduced for conditions producing maximum deflection in the cardiogram. For the device of the pitch swing, a pitch rise is chosen at the beginning and a pitch drop at the end of the vowel to be reproduced, which is again in accordance with natural articulations. The voltage-controlled generator 5 and the pulse generator 7 together act as an artificial larynx. A mouth cavity acts as an acoustic filter and the corresponding filter 6 acts as a simulation thereof. This filter is composed of a first filter 8 and a second filter 9. In the mouth cavity two low-pass bands or formant regions act as band-pass filters for the reproduction of vowels. These two formants are simulated by the two band-pass filters 8 and 9. These filters have a Q-value of, for example, approximately 10 to 15. The filter 8 preferably has a permanently adjusted frequency which may lie, for example, between approximately 200 Hz and 1,000 Hz, corresponding to the intermediate frequency of the last formant. The filter 9 is electrically tunable, the frequency at the low-frequency side having about the value of the band-pass frequency of the filter 8, and extending at the high-frequency side to, for example, approximately 3,000 Hz. The tuning frequency varies monotonically between these values with the cardiogram signal which is supplied to the frequency filter via the conductor 10. A frequency of approximately 1,200 Hz is chosen as the basic adjustment of the frequency filter 9, this choice being arbitrary and giving the best possible adaptation to speech-like sounds. By such an adjustment, the condition representing maximum deflection in the cardiogram is reproduced by a fast sound transition, for example, as a j-like sound. The signals to be supplied by the filter are supplied via an amplifier 11 to a loudspeaker 12 or to another device for the conversion of electrical signals into sound signals, for example, to a stetoscope.

In the embodiment shown in FIG. 2 the various components are accommodated in an envelope 13 of a suitable synthetic resin, the design of which is slightly adapted to the manner in which the apparatus is used. In order to provide a satisfactory electrical contact between the electrodes 1, 2 and 3, and a physical surface, such as the thorax in the case of an examination of the heart, contact arms 14, 15 and 16 are provided on the envelope 13. These arms may be mounted on the envelope 13 in a movable and/or resilient manner.

The envelope is furthermore provided with a toggle switch 17 by means of which the apparatus can be switched on and off. The volume of the sound departing, for example, through slots 19 can be controlled with the aid of a sliding knob 18.

Claims

What is claimed is:

1. A device for the audible reproduction of electrophysiological signals comprising first means for producing said electrophysiological signals from the action of the heart, second means for converting said electrophysiological signals to speechlike sounds including means for converting deviations of said electrophysiological signals into corresponding speech sounding deviations whereby said electrophysiological signal is reproduced as a speech-like sound with deviations in said electrophysiological signal reproduced as deviations in said speech-like sound so that the human ear being more sensitive to tonal differences in a speech sound will quickly detect the slightest deviation of said action of the heart.

2. The device of claim 1 wherein said second means converts said electrophysiological signals to sounds having a frequency of about 200 hertz.

3. The device of claim 1 wherein said means for converting deviations comprises means for producing a tonal pitch swing to said speech-like sounds which tonal pitch swing rises at the beginning and drops at the end of a vowel to be reproduced whereby said deviations in said electrophysiological signal are reproduced in accordance with natural articulations.

4. The device of claim 1 wherein said second means comprises a voltage controlled sine wave generator for producing a monotonically variable frequency signal corresponding to said electrophysiological signal and a pulse generator for receiving said sine wave generator signal and producing pulse signals having a maximum pulse duration of approximately 1 millisecond.

5. The device of claim 4 wherein said second means further includes a first and second band pass filter means to simulate the mouth cavity function of acting as an acoustic filter for the sounds produced by the larynx, said filter means receiving the signal produced by said pulse generator and said second band pass filter means being electrically tunable and receiving the signal produced by said first means which signal tunes said second band pass filter.

6. The device of claim 5 which includes transducer means for converting electrical signals to audible signals, said means receiving the output of said first and second band pass filter means.

7. The device of claim 6 which further includes envelope means adapted to enclose said first and second means and is shaped in the form of a T with a plurality of slots therein for the audible transmission of audible signals from the means of claim 6 and a plurality of contact arms mounted on said envelope means, said contact arms being resilient for contact with portions of the human body and wherein said means for producing physiological signals are disposed in said contact arms.