Related Website Stereophonic Stethoscope
A Virtual Round-Table Talk
All about the Stethoscope
(The entire content of this virtual round-table talk is based on true comments by actual people.)
Present at this talk are:
Dr. A Male resident
Dr. B Male resident
Dr. C Female resident
Dr. H Faculty (cardiologist)
Dr. R Faculty (pulmonologist)
Dr. S Heart surgeon at a national hospital
Mr. M Engineer of a stethoscope manufacturer
Dr. X Inventor of the stereophonic stethoscope
Dr. A: I am beginning my first-year of residency training. As for a stethoscope, I was using
one I bought at a low price as a student. However, now I would like to get a really good one.
Please tell us some hard facts about the stethoscope.
Dr. B: Some of my senior residents advise us to be cautious when choosing stethoscopes,
while some other residents say that all the stethoscopes are much the same.
Dr. H: Surely at one time in the past there were not much difference in acoustic performance
among different stethoscopes. However, at present there are a variety of stethoscopes with
their own characteristics you need to be aware of when using. Accordingly, you should
understand all those differences before you choose one for yourself.
Dr. C: What makes the difference among all those stethoscopes?
Mr. M: Generally speaking, the larger and heavier a stethoscope is, the more efficiently
auscultatory sounds are picked up by your ears, while the smaller and lighter, the easier its
handling is. To fulfill these opposing ends, stethoscopes come in different designs.
Dr. A: How come the larger and heavier a stethoscope is, the more efficiently auscultatory
sounds are picked up?
Dr. R: First of all, the chest piece of a stethoscope is put on the body to pick up sounds from
within. The larger the area of the chest piece that comes in contact with the body surface
is, the better sounds are picked up. This is because the sound-conveying channels is wider
when the chest piece is larger. However, if the chest piece is too large, it looses contact
with the body surface, because the latter is curved outward in configuration. In this case,
sounds are not only picked up inefficiently but sounds are actually lost through the openings
between the chest piece and the body surface.
Mr. M: Currently the chest piece of a stethoscope is almost uniformly between 45 and 50 mm
in diameter irrespective of manufacturers.
Dr. H: The material comprising the chest piece plays an important role in efficiency of
picking up sounds. Sounds propagate within the air or materials, and eventually disappear as
they are converted into thermal energy. The fact is, sounds are not attenuated within heavy
metals, while they are easily attenuated within light metals and plastics.
Mr. M: It is our policy to use stainless steel and titanium for the chest piece of stethoscopes
priced high, and to use aluminum and plastics for those priced low. Manufacturing cost is
also taken into consideration when choosing materials for the stethoscope.
Dr. H: The binaural tubing is also important in terms of efficiency of the stethoscope. The
larger its internal diameter is, the shorter and the thicker walled it is, the better the
efficiency of a stethoscope is. However, these factors must be considered taking practicality
into account.
Dr. B: What is the difference between the open-bell and the diaphragm microphones?
Dr. R: The open-bell microphone is the starting point of the stethoscope. The stethoscope
was first conceived by Laenneck of France in 1816. His stethoscope was of the open-bell
type. The open bell microphone picks up sounds of the whole frequency range. It should be put
on the body with only a light pressure. Naturally, the diameter of the open-bell microphone is
limited, because if it is too large, its outer margin looses contact with the body surface. The
diaphragm microphone, on the other hand, is the one covered with a plastics membrane. The
menbrane cuts off sounds of low frequnecy, namely sounds of 200 Hz and lower, and by so
doing makes the microphone more sensitive to sounds of higher frequency. It should be put on
the body with a little heavier pressure. Naturally, the diameter of the diaphragm microphone
can be made larger than the open-bell microphone. Therefore, the volume of sounds heard
with the diaphragm microphone is louder than that heard with the open-bell microphone.
Dr. H: In auscultation of the heart, the first and second sounds and majority of systolic
murmurs are heard well with the diaphragm microphone, because these sounds and murmurs
belong to high-frequency sounds. However, the third and fourth sounds, and the diastolic
rumbling murmur of mitral stenosis fall into the low-frequency range. Therefore, the
open-bell microphone is fit for auscultation of these low-pitched sounds and murmurs.
Dr. R: The diaphragm microphone is the choice for auscultating pulmonary sounds because
both normal and abnormal sounds heard in the lungs belong to higher-frequency sounds.
Dr. C: Then we need both the open-bell and the diaphragm microphones, don't we?
Drs. H and R: Definitely yes.
Dr. A: There are stethoscopes with single tubing and other ones with dual tubings. How are
they different?
Mr. M: There are three different tubings. The first one is a single tubing. The second is dual
tubing, the third is dual tubing forming one tubing in outlook.
Dr. H: In theory, the dual tubing system is more efficient than the single tubing system, but
in practice, the two systems are much the same in efficiency, at least concerning the
conventional stethoscopes.
Dr. R: It is more important to make a good fit of the ear pieces with your ears. When the
fitting is bad, auscultatory sounds leak out, and at the same time ambient noises come in,
making diagnostic auscultation difficult.
Dr. H: The size and the component material of the ear piece, and the force of the spring all
play roles in making a good fit with the examiner's ears. You must choose an ear piece that
fits best to your ears, since the size of the meatus varies according to individuals. As to the
component material of the ear piece, hard materials are superior to soft materials because
the latter absorb and attenuate auscultatory sounds.
Mr. M: Each of our stethoscopes is provided with two or three different optional ear pieces
so that each customer can find the best one for himself.
Dr. H: The firm spring generally offers a good fit of the ear pieces to the ear, but one should
be warned that a too firm spring causes pain in the ear.
Dr. R: The directional relationship between the ear piece and the meatus is also important.
The meatus opens not at exactly 90 degrees to the side, but a little backwards. Therefore,
the ear pieces should be directed a little bit forward. In almost all the stethoscopes the ear
pieces can be rotated on their long axis to change their direction.
Dr. B: I think we have come to a very good understanding about the stethoscope. There are so
many different stethoscopes available on the market today. What stethoscope should we
choose?
Dr. H: Some of the existing stethoscopes are shown on another pages. There are still some
other stethoscopes that are not shown here. These eight stethoscopes possess different
configurations, and therefore, different efficiency and characteristics in acoustic
performance. But it should not be difficult to choose stethoscopes for yourself , if you take
into consideration the points we have discussed so far. In short, you should choose one with
both the open-bell and the diaphragm microphones, with little plastic as a component
material, and with dual tubings.
Dr. R: The one shown in figure 4 is equipped with three microphones. Two of them are
diaphragm microphones with different frequency responses. One of dual tubings of the
stethoscope shown in figure 5 is longer than the other. This tubing configuration is claimed
to enhance acoustic performance. The one shown in figure 6 is basically a diaphragm type
stethoscope, but in this one only the projection in the center and the outer rim come in
contact with the patient's body. The diaphragm itself does not touch the body. This
configuration is also claimed to enhance acoustic performance.
Dr. H: The one shown in figure 7 possesses only the diaphragm microphone. But its frequency
response can be varied by changing the pressure on the chest piece.
Dr. R: When you judge acoustic performance of a stethoscope, you should judge it by hearing
faint sounds, not hearing loud sounds. For instance, loud sounds such as the first and second
heart sounds, and normal bronchial sounds can be heard quite well with almost all
stethoscopes. But faint sounds such as early-stage valvular murmurs and alveolar sounds
can be heard only with efficient stethoscopes. Acoustic performance of a stethoscope should
be judged by whether faint but important abnormal sounds can be picked up or not.
Mr. M: At this point I would like to introduce our new stethoscope, the stereophonic
stethoscope.
Dr. C: What is it, the stereophonic stethoscope?
Mr. M: It is shown in figure 8. Its over-all size and configuration are much the same as those
of conventional stethoscopes. But its microphones, both the open-bell and the diaphragm
microphones, are divided into two microphones, and each microphone is connected to an
independent tubing. Thus there are two channels - left and right channels - in this
stethoscope. The conventional stethoscopes are one-channel stethoscopes, because heir
binaural tubings are connected to a single microphone. These are monaural stethoscopes in
essence, and you hear only volume and tonal characteristics of auscultatory sounds. On the
other hand, this new stethoscope can pick up time delay and phase shift between the right and
left channels as well as volume and tonal characteristics. Auscultatory sounds picked up by
this new stethoscope are rendered stereophonic. Therefore, you can hear with this
stereophonic stethoscope not only sound volume and tonal characteristics but spatial
spreading, movement and direction of auscultatory sounds. Switching the open-bell and the
diaphragm microphones is done in the same manner as the conventional stethoscopes.
Dr. H: I have already used the stereophonic stethoscope, and I have found it to be a
fabulous, epoch-making stethoscope.
Dr. R: As I said earlier, the stethoscope was invented by Laenneck of France in 1816, and he
named it as stethoscope (steth=chest, scope=finder). It was first used in auscultation of lung
diseases, then in heart diseases. Before Laenneck's invention, physicians put their ears
directly on the body of the patient (direct auscultation). Laenneck's stethoscope was an
open-bell type in the form of a wooden cylinder (the cover photo), but soon the stethoscope
underwent numerous modifications to enhance efficiency of auscultation. First,
trumpet-shaped stethoscopes of various configurations appeared, and these types were used
subsequently for over 100 years. Leerd of the U.S. invented a stethoscope with Y-shaped
binaural tubings in 1851. This binaural stethoscope was exceedingly easier to use, and
quickly became very popular in North America. In 1894, Bowles of the U.S. introduced the
diaphragm stethoscope. This stethoscope cuts off sounds in the low frequency range, and
makes itself more sensitive to medium and high-frequency sounds, as I explained earlier.
Finally in 1926 Sprague of the U.S. invented a stethoscope that is equipped with both an
open-bell and a diaphragm microphone. This Sprague stethoscope has become the standard in
the art of the stethoscopes.
Dr. H: A number of improvements have been made in design and component materials of the
stethoscopes since then, but no significant progress has been seen concerning the basic
principle of the stethoscope. However, the stereophonic stethoscope, an entirely new
stethoscope, appeared in Japan in 1991, to my greatest surprise. I guess I have been thinking
that the stethoscope had already come to the end of its development.
Dr. R: I feel the same way. We have here with us Dr. X, the inventor of the stereophonic
stethoscope. Dr. X, please tell us how you came to conceive the stereophonic stethoscope.
Dr. X: Well, first of all, I liked the stethoscope and auscultation very much as a resident. I
have tried number of stethoscopes, both domestic and imported, to find out which was the
best stethoscope. But it seemed to me that there was not very much difference between all
the available stethoscopes. And I began to think whether there was not any way to improve
the stethoscope. One day it came to me two-channelization might be able to improve
acoustic performance of the stethoscope. Conventional stethoscopes are equipped with
binaural tubings, but these tubings are connected to a single microphone. Therefore,
conventional stethoscopes are in reality monaural stethoscopes, and we can hear only
monaural sounds with them. What happens if there are two independent microphones in the
chest piece, each of them provided with an independent ear tubing? That will be a totally
two-channelized stethoscope, and will we not be able to hear stereophonic sounds with it?
Records and FM broadcasting were in the monaural mode at the beginning, but afterwards
they were turned into the stereophonic mode with two-channelization of the recording and
reproducing systems. How do pulmonary and cardiac sounds sound like in stereophonic
auscultation? With the stereophonic stethoscope can't we better hear faint sounds that are
hard to hear with the monaural stethoscope? I had these questions and expectations in mind
when I began to work on the idea of the stereophonic stethoscope.. First, I took two
stethoscopes apart,and out of these parts I assembled a stethoscope which had two
independent microphones and two ear tubings. I gave this two-channel stethoscope a try,
and immediately found out that only strange sounds were heard. My right and left ears heard
different sounds, which was no more than annoying auscultation. The further the two
microphones were placed on the patient's body, the stranger and more annoying the
auscultatory sounds became. Even when the two chest pieces were placed closely side by
side, the sounds were still strange and annoying. I concluded that this two-channel
stethoscope does not bring stereophonic sounds; it has no practical value. Moreover, I found
in the literature that Alison of Ireland had already introduced the two-channel stethoscope
of this type as the differential stethoscope in 1858 .
It has since been almost totally forgotten, probably because it had no practical value. But it
should be pointed out that at the present time some pulmonologists still use this stethoscope
for comparing lung sounds at different locations. I surmised that the reason why the
above-mentioned two channel stethoscope cannot work as a stereophonic stethoscope is that
the distance between the two microphones was too large for stereophonic auscultation. The
left and right microphones should come very close together for stereophonic effects to be
perceived. Therefore, in the true stereophonic stethoscope there must be two microphones
built in one chest piece. It took about 10 years for this proposed stereophonic stethoscope to
make its appearance, because the work on it was very difficult. What resulted from trying
out this new stethoscope was exactly what I expected, or more than I expected.
Stereophonic effects in auscultatory sounds such as spatial spreading, direction, and
movement of lung and heart sounds were clearly heard. There were no strange or annoying
quality in the sounds picked up by this stethoscope. Certain faint cardiac murmurs and
prosthetic valve sounds, which were frequently inaudible with the conventional stethoscopes,
became easier to hear. My impression was that a truly new stethoscope was born. Patents
were granted in Japan, the U.S., and Germany, and the present manufacturer began producing
this stereophonic stethoscope.
Mr. M: The stereophonic stethoscope was hard to come by not only as a trial product but as
merchandise because there were a number of technical difficulties. We started working on it
in 1988, and we got it out as a finished product in 1991.
Dr. X: We named the product "Stereophonette" which sounds somewhat like French, because
we wanted to pay respect to Laenneck, the French physician who invented the stethoscope.
Dr. H: I still clearly remember my astonishment when I first used the stereophonic
stethoscope. Heart sounds came in totally differently from the way they did with the old
stethoscope. It is easier to understand this by simply using it than by being explained orally.
The best example is auscultation of aortic valve diseases. The murmur of aortic
insufficiency, which is written as a to-and-fro murmur in the textbook, is really heard to
move from right to left, and left to right, as if one were listening to a stereophonic audio
system. Without using the so-called inching technique you can easily determine the point of
the maximal intensity of a heart murmur, since you can hear the direction where the
murmur is coming from. Auscultation of pulmonary and tricuspid diseases have been made a
lot more accurate, as well as mitral valve diseases. You feel as if your ears were blocked
with stoppers when you use the conventional stethoscopes after having used the stereophonic
stethoscope.
Dr. R: I think that in auscultation of pulmonary disease, sounds picked up by the
stereophonic stethoscope are really clear. In the case of pulmonary fibrosis, fine crackles,
which are a sound specific to this particular condition, are heard emanating from all over the
lung. It is rather astonishing to be able to realize that each of those fine crackles has its
own location of origin different from the other. As I got used to this stethoscope, I feel like I
can determine the depth of each pulmonary sound.
Dr. S: I have become to really enjoy auscultation since I acquired the stereophonic
stethoscope. In the case of tetralogy of Fallot, for example, you can hear really well how
different the murmurs of pulmonary stenosis and ventricular septal defect are from each
other. I feel as if I were in the different world when I think of those days I was using the old
stethoscope. The stereophonic stethoscope is also excellent for hearing prosthetic valve
sounds, and for making differential diagnosis based on auscultation.
Mr. M: The stereophonic stethoscope is now being used by many physicians overseas, and
commended uniformly. Dr. William Pierce, Professor of Surgery at Pennsylvania State
University, Hershey, says "I and my colleagues are most impressed with it." Dr. Lawrence
Tierney, Professor of Medicine at University of California, San Francisco, says "I enjoy using
the Stereophonette greatly. There is no question in my mind that it is superior to the
instrument that I have been accustomed to using." Dr. Antonio de Leon, Medical Director at the
St. John Cardiovascular Institute, Tulsa, Oklahoma, says "I believe that you have come up with
wonderful contribution to clinical auscultation. I think that if medical students start out
with your stethoscope and get used to how both heart and breath sounds sound like from the
stereophonic stethoscope, that they would not be willing to switch to a monaural
stethoscope." Dr. Mathius Borst at the Faculty of Medicine of Heidelberg Univesity, Germany,
says "In comparison with other high-class stethoscopes, the Stereophonette possesses superb
acoustic qualities both in the auscultation of heart sounds and murmurs and in pulmonary
auscultation. Therefore I should thoroughly recommend this stethoscope to any cardiologist or
pulmonologist." Dr. Fletcher, Professor of Medicine at Harvard Medical School, Boston, tells
"Your stethoscope has introduced an entirely new dimension into listening to the chest.
Suzanne Fletcher, who directs the physical diagnosis course at Harvard Medical School, has
the same impression." Dr. Henry Seidel,Professor of Pediatrics at John's Hopkins University,
Baltimore, "I have enjoyed using yourstethoscope. We will in the new edition of our textbook,
which should be out sometime towardsthe end of the year, indicate the availability of the
stereophonic stethoscope. I know that I hearwell and with clarity when I use it." Dr. Robert
Hall, Director of Cardiology Education at the Texas Heart Institute, Houston, says "I have
greatly enjoyed testing your stethoscope. Thus far, I am impressed with the clarity of sound
transmission, which I find to be superior to other stethoscopes I have used." There are many
other overseas doctors who have expressed their admiration for the stereophonic stethoscope.
Dr. A: The stereophonic stethoscope seems to have established a substantial reputation. How
many units have already been delivered?
Mr. M: Since its introduction in 1991, approximately 8,000 units have been delivered in Japan,
and 2,000 more units overseas.
Dr. B: Is it not difficult in any way to use ?
Dr. H: Absolutely not, there are no difficulties in using the stereophonic stethoscope. You just
use it in the same way as you use the conventional stethoscopes. Moreover, you may
eventually find some new specific usage of it, one you have never experienced with
conventional stethoscopes.
Dr. C: Is it suitable for residents?
Dr. R: The stereophonic stethoscope is most suitable for residents. It would help
understanding of the underlying pathophysiology of the cardiac or pulmonary status which
gives rise to specific murmurs and sounds.
Dr. A: I feel that stereophonic stethoscopes are a bit expensive.
Mr. M: The first stereophonic stethoscope was a high-class, high-priced model. But
afterwards an inexpensive model has been added to the list, so that everybody can choose
according to one's need.
Dr. H: The physician is a professional among the professionals. He should always acquire the
best instrument available in the market to fullfill his professional duty. One of my friends is
a professional photographer, who uses only the best therefore the most high-priced
equipments to make his photos. He has to invest as much as he can in order to survive as a
professional in the ongoing competition in which he is posed. In the same way, professional
violinists do not play "cheap" violins, and racing drivers do not drive "cheap" machines.
Dr. B: I think I have to agree. Then the stereophonic stethoscope is the most advanced
stethoscope at the present time?
Dr. R: Certainly it is. The conventional monaural stethoscopes will eventually be replaced by
the stereophonic stethoscope. The stereophonic stethoscope will be every physician's
stethoscope in the future.
Dr. C: I understand there are several different models of the stereophonic stethoscope.
Mr. M: Yes. Model 171 is the first model of the Stereophonette, the stereophonic stethoscope.
Its chest piece is made of ultra-hard stainless steel, and therefore it is rather high-priced.
Model 171 Gold is plated with gold. Model 172 is priced lower by using zinc for its chest
piece. Model 753 is for pediatric use, and Model 333 is for nurses.
Dr. A: Which model should we choose?
Dr. S: Actually you should have a few stethoscopes, not just one. You use them according to
time, place, and occasion. I myself have two, one for adult patients, and the other for
children.
Dr. H: I use a Model 171 in my university hospital, but I bring a Model 172 with me when I go
to the affiliated hospital. However, one stethoscope would be enough for a resident at first.
Dr. R: If you choose one model, Model 171 is the best choice. Its acoustic performance is the
best among Stereophonettes. Since you can use a stethocope for 10 years at least, Model 171
will never disappoint you, particularly if you wish to specialize in internal medicine, and lung
and heart surgery.
Dr. H: I might have squeezed you up a little too tight earlier, but I admit the price is an
important factor. Model 171 is superior to Model 172, but their difference in acoustic
performance is small. In fact, if you compare Model 172 with conventional stethoscopes, 172
is much, much better. It is very wise for a resident to choose the Model 172.
Dr. C: Is there any particular model for female physicians?
Mr. M: Model 333's come in pink, blue and gray in their tubing color, since they are intended
for nurses. There are no particular female models among the other ones.
Drs. A, B, C: We all thank you for teaching us about the stethoscopes, beginning from the
Laenneck's invention to the latest stereophonic stethoscope. We believe we have understood
what to consider when we get stethoscopes for ourselves. We will certainly choose the best
one for ourselves by taking into account all that you have taught us.
References
1. Kazama, S. A new stereophonic stethoscope. Japanese Heart Journal vol.31, pp.837-843, 1990
2. Seidel, H.M. (Editor). Mosby's Guide to Physical Examination. 3rd Edition. Mosby-Yearbook Inc., St. Louis, U.S.,1995, p.69
Edited by Shigeru Kazama, M.D.
Department of Cardiothoracic Surgery
Kitasato University School of Medicine
Sagamihara, Kanagawa, Japan