Electrical audio signal processing systems and devices – Stethoscopes – electrical
Patent
1997-02-28
2000-10-17
Lee, Ping
Electrical audio signal processing systems and devices
Stethoscopes, electrical
A61B 704
Patent
active
061343315
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electronic stethoscope of the type comprising a vibration transducer, an amplifier, and a headphone arrangement.
Stethoscopes are used by physicians to listen to sounds from the organism, in particular heart and lungs. The phenomena listened for emit sounds with frequencies from below 16 Hz to about 8 kHz, but a serious low pass filtering occurs during the passage of tissue and skin. The skin acts like a transmitter of those signals which are subsequently accessible. The construction of the stethoscope ascertains that only a small area of the skin is listened to at a time, and that sounds in the room outside are dampened, and thus the signal-to-noise ratio is somewhat improved. Physicians train actively in the use of stethoscopes, and thereby their ability to distinguish signals in the surrounding noise may rise by about 15 dB. This occurs the world over, and one might say that a stethoscope is a universal tool. However, its value and/or performance to the users have fallen, due to the technical development of society. The increased machine noise, in particular in hospitals, in practice causes the signals to lie below or at the most at the lower limit of human hearing. To this may be added that more and more young persons suffer from hearing loss at the time they may embark on a medical education, and hence the acoustic stethoscope has in practice reached its limit of performance.
It has long been realized that a traditional acoustic stethoscope introduces many linear distortions in its signal transmission, in particular because of the possibility for standing waves in the long tubes. This may be expressed differently by stating that the bad impulse response causes a strong distortion of the temporal reproduction of the signals. Traditionally, there are various constructions of stethoscopes, and they each have their individual characteristic transfer function, and one may to a certain degree, by changing acoustical stethocscope, obtain a more distinct representation of a given acoustic phenomenon. However, the physician's reliability in using stethoscopes is generally so large, in particular when using the stethoscope they have become used to, that the impulse response problem has not been regarded as a bar to the use of acoustic stethoscopes.
For this reason it has not been attractive to use an electronic stthoscope, even though it gives the possibility of active amplification to any desired degree. Even though there are furthermore very improved possibilities for adapting the sensitivity of a vibration transducer to the body being measured upon, and even though headphones with a high damping may act as better insulators against surrounding noise than ordinary earpieces of a traditional stethoscope, an electronic stethoscope still meets resistance, in particular because it does not "sound like they used to", due to the wider frequency band and the consequent larger content of noise. The ability to distinguish phenomena which has laboriously been learnt by the physician does not help any longer.
It has been recognized that there is a need for amplifying certain frequency areas relative to those which are effectively reproduced by an acoustic stethoscope. A known construction of an electronic stethoscope is described in U.S. Pat. No. 5,003,605 which electronically performs a lifting of these wider frequency areas and performs a frequency conversion for very low frequency areas. In this way certain phenomena are given an improved clarity. Furthermore the stethoscope is connected to electrodes and electrocardiographic circuits for the recognition of the QRS complex in order that signals representing the electrical activity of the heart may be brought to the ear simultaneously with the heart sounds so that the temporal relationship of the sounds in relation to the heart cycle may be evaluated.
It has been recognized in the invention that it will be possible to obtain a considerably improved stethoscope which has both the advantage of a larger amplification and of knowledgeable analy
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patent: 4598417 (1986-07-01), Deno
patent: 5481615 (1996-01-01), Eatwell et al.
patent: 5539831 (1996-07-01), Harley
patent: 5602924 (1997-02-01), Durand et al.
Bang & Olufsen Technology A/S
Lee Ping
Safran David S.
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