Electrical audio signal processing systems and devices – Stethoscopes – electrical
Reexamination Certificate
1999-04-16
2001-04-17
Mei, Xu (Department: 2644)
Electrical audio signal processing systems and devices
Stethoscopes, electrical
C181S131000, C600S528000
Reexamination Certificate
active
06219424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for electrical, stereophonic amplification of sound signals. The present invention is described hereinafter with reference to a stereophonic stethoscope, however, it will be appreciated that the invention does have broader applications.
BACKGROUND OF THE INVENTION
Commonly available stethoscopes provide a monaural sound in that the sound is received in a single sound accumulator such as bell type accumulators or diaphragm type accumulators from which it is “mechanically” provided to ear pieces via ear tubes. A person using such a conventional, monophonic stethoscope will not be able to perceive any directionality of spatiality of the sounds heard. This is because the sound is transmitted to both ear tubes from the one sound accumulator, which acts as the transducer of the sound and therefore becomes a single, intermediate source, in which the sounds generated by the true sources are superimposed.
The perception of directionality and spatiality of the sounds in stethoscopes would allow a differentiation between sounds. E.g cardiac murmurs which are the result of a turbulence of the blood flow in the heart and thus the origins of sounds associated with cardiac murmurs are widely spread whereas the closing and opening clicks of cardiac valves originate from a point source.
To enable perception of directionality and spatiality of sound obtained from a stethoscope, each ear must be provided with sounds transduced by separate sound accumulators and consequently two sound channels must be provided to realise a stereophonic stethoscope.
Stethoscopes providing a stereo signal mechanically have been produced and tested, e.g. reference is made to S. Kazama, “A new Stereophonic Stethoscope”, Jpn. Heart J, Vol. 31/6, November 1990.
On the other hand, the use of the conventional, mechanical stethoscope principle has limitations in that sounds can only be heard live in the sense that typically only one person is listening to the sounds and bases his or her diagnosis on his perception of the sounds. To obtain a second opinion of another person, this person must also perform an examination of the patient with the stethoscope therefore the patient is required for a longer time and discomfort may be imposed onto the patient. Therefore, the use of electronic stethoscopes can enable an easy and direct way to record the sounds in one examination which can be replayed to other persons at any time and without further examination of the patient. Further, the electronic audio signal can be more readily made available to more than one person during the examination by transducing the audio signal via speakers. An electronic stethoscope in which a microphone is connected to one precordial stethoscope probe or esophageal probe to monitor a monophonic sound accumulated in the bell or probe electronically via a high quality amplifier is described by J. H. Philip et al in “An electronic stethoscope is judged better than conventional stethoscopes for anaesthesia monitoring”, Journal of Clinical Monitoring, Vol. 2/3, July 1986. Previous electronic stethoscopes have employed electronic frequency filtering to selectively amplify sound in the range 37.5-1000 Hz where most heart and lung sounds occur 1, e.g. a bandpass frequency of 0.7-5000 Hz with selectable bass and treble boost/cut circuitry. Other electronic stethoscopes use an upward frequency shift of the entire audio band, aiming to allow improved detection of low frequency sounds. However, the electronic manipulation involved makes for complex and expensive circuitry, as well as increased size, particularly if two units are to be employed for stereophonic stethoscopes. It also requires a significant degree of retraining as the familiar heart and lung sounds may be quite altered.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention there is provided a device for use in a stethoscope, the device including two diaphragm type sound accumulator chambers, one microphone located in each accumulator chamber, one amplification stage connected to each microphone for electronically amplifying audio signals received by the microphones, and an output connector for outputting the amplified audio signals, wherein the amplification sages are connected to one common earth potential and the output connector is arranged in a manner such that the negative inputs of sound transducers which are in use connected to the connector are connected to the common earth potential via an impedance. The positioning of the microphones within the diaphragm type sound accumulator chambers can effect a mechanical filtering means for sounds received by the microphones wherein the filter characteristics can be easily adjusted by varying a pressure on the diaphragms. This can be done by e.g. varying the pressure with which the diaphragm type sound accumulators are pressed against the chest of a patient during examination of a patient.
This can improve a perception of spatiality of the amplified audio signals. In one embodiment the impedance is chosen to be substantially the same as the impedances of the sound transducers which are in use connected to the output connector. Advantageously, the impedance is a resistor, although e.g. an inductive coil can also be used.
Preferably, each amplification stage includes a variable gain control. In one embodiment, the variable gain controls of the amplification stages can be adjusted simultaneously and in a manner such that the variation is the same for each amplification stage. In another embodiment, the variable gain control of each amplification stage is independently adjustable.
Preferably, the accumulator chambers are located on a housing and separated by a distance wherein the diaphragms of the accumulators are facing outwardly from the housing.
In one embodiment the distance is a fixed distance whereas in another embodiment the distance can be variable.
Further, the amplification stages can be located within the housing and an the output connector can be located on the housing.
In one embodiment the device further includes two speakers which are each in use connected to one of the amplification stages via the connector, to transduce the amplified audio signal as a sound signal. Preferably, the two speakers are incorporated in headphones.
Preferably, the device is battery powered.
Advantageously, the device includes a power-on indicator which includes a high brightness blue light emitting diode (L.E.D.). This can provide a light source to e.g. elicit a pupillary response if required as part of accompanying neurological examination.
In accordance with a second aspect of the present invention there is provided a stethoscope, the stethoscope including two diaphragm type sound accumulator chambers, a microphone located in each accumulator chamber, an amplification stage connected to each microphone for electronically amplifying audio signals received by the microphone, and a transducer connected to each amplification stage for transducing the amplified audio signals as a sound signal, wherein the amplification stages are connected to one common earth potential and the negative inputs of the transducers are connected to the common earth potential via an impedance.
In one embodiment the impedance is chosen to be substantially the same as the impedances of the transducers. Advantageously the impedance is a resistor, although e.g. an inductive coil can also be used.
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Shigeru Kazama, M.D.,A New Stereophonic Stethoscope
Fulwider Patton Lee & Utecht LLP
Hunter Area Health Service
Mei Xu
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