Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to electronically assisted
stet:hoscopes, and more particularly to electronic conver~
sion units for converting a conventional stethoscope into
a phonostethoscope whose authenticity of sound amplifica-
tion and ease of operation are within range of those direct-
ly and indirectly involved with the medical field.
It is common procedure during the work up of a patient
to include electrocardiogram recordings in the patient's
chart. Such a recording provides evidence of important
cardiac functions; rate, rhythm, axis hypertrophy, and,
miscellaneous drugs effects. Unfortunately the attempt
to solve problems of cardiac defects, valvular hernodynamics,
and other physiological abnormalities are often limited
by the individuals acoustic capacity and memory.
Specialized equipment is available to aid this aural
registering, including a variety of electronic recording
and analysis devices. However, these devices are often
expensive, n~n-mobile and require the servicesof trained
personnel.
Conventional stethoscopes often employ a resonant
peak within their frequency response characteristics this peak
often falling nominally between 50 Hz and 200 Hz. Certain
stethoscope models exhibit peaks in their response at
1500 Hz to 3000 Hz. These characteristics are determined
by a number of factors. Among the major contributors to
resonant peaks are chestpiece chamber volume and diaphragm
thickness/mass ratio. These resonant peaks axe often highly
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useful in that they are utilized by physicians to accentu-
ate certain commonly encountered sounds.
Electronic stethoscopes have been available for
many years but they have not gained wide acc~ptance by medic-
al practitioners because of their inconveniences in use,
their high cost, high weight and bulk, difficulty in attach-
ment, and often lack of easy mobility. Additionally, and
perhaps more importantly, the electronic stethoscopes previous-
ly available have imposed a burden on the user in the form
of a highly unnatural sounding instrument, or at best, an
instrument to which the user has not been attuned. Repre-
sentative prior art includes Slosberg et al, U. S. Patent
3,846,585, Keesee,U. S. Patent 3,539,724, Minsky, U. S.
Patent 2,385,221, Cefaly et al,U. S. Patent 3,247,324,
Clark et al, U. S. Patent 3,182,129, Croslin, U. S. Patent
3,233,041 and Andries et al, U. S. Patent 3,160,708, each
of which fails to recognize the importance of providing a
light weight transducer assembly easily mountable and located
at the earpiece locations which is the terminal point of
exit of the sound from the air column.
The prior art devices may be viewed as utilizing
techniques of basically three general types. The first
type utilizes an electronic input sensor and amplification
device at the chestpiece location, and thereafter employs
purely passive acoustic means throughout the length of the
vibrating air column and into the earpieces. A second
type utilizes a combined electronic input sensor and
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407
amplification means at some intermediate point in the
vibrating air column; while the input sensor and the
output means are of conventional acoustic configurations.
The third type utilizes electronic amplification techniques
at both the chestpiece and at some intermediate point within
the vibrating air column, while the earpieces remain con-
ventional.
I have discovered that the location of the amplifica-
tion and frequency controls in the prior art devices has not
resulted in optimal positioning of the devices and in turn
have often created additional problems.
Considering the stethoscope and the human body as
an integral unit for transmission of sounds, it becomes
apparent that whatever form of amplification, or frequency
response shaping that interrupts the sound flow along
its route from origin to exit of the stethoscope, it will
invariably cause alterations in sound characteristics.
More importantly, it often alters the character of the per-
ceived sound as the physician has been trained to recogn~ze
it. To alleviate this situation, this invention utilizes
the concept of placing the amplifier unit and frequency
response shaping elementsat the final exit of the sound
from the stethoscope (i.e., earpieces) resulting in sub-
stantially unaltered sound flow, and a highly natural
sounding electronically assisted stethoscope.
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It will become obvious that this new combination.and
configuration has advantages over existing electronically
aided stethoscopes and may be of significant aid in
diagnostic and teaching situations when utilized in conjunc-
tion with a specific recording format and presently exist-
ing medical procedures.
It is therefore a primary object of an embodiment
of the instant invention to overcome the disadvantages of
the prior art by providing the benefits of electronic
assistance to existing, conventional air-column actuated
stethoscopes in the form of conversion units adaptable to
most stethoscope models in widespread use.
It is another object of an embodiment of this
invention to provide an electronically assisted stethoscope,
hereinafter referred to as a phonostethoscope, that combines
the advantages of conventional acoustic listening with
those obtainable via electronic amplification and frequency
response shaping.
Other objects and features of the invention will
become more readily understood from the following detailed
description when read in conjunction with the accompanying
drawings in which like reference numerals designate like
parts throughout the figures thereof, and wherein;
Figure 1 is an overall view of a stethoscope showing
the interconnections of the electronic conversion units of
the instant invention;
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Figure 2 illustrates the general mechanical
configuration and internal arrangement of an electronic
conversion unit;
Figure 3 illustrates the electronics amplifying
circuitry in functional block form;
Figure 4 shows the amplitude/frequency response
curves associated with various stethoscope configurations
disclosed herein; and
Figure 5 illustrates the phonostethoscope being
used in conjunction with permanent recording means.
Referring to Figure 1, a preferred embodiment of an
electronically assisted stethoscope is indicated generally
at 10. The assembly includes an acoustic chestpiece mem-
ber 12, a flexible tubular connecting member 14, a neck
region 16 which provides for sound division and trans-
mission to two ear branch tubular members 18a and 18b.
Each ear branch member 18a terminates in an output aperture
20a (shown in Figure 2A). Hereinafter the "a" branch is
described, the "b" branch is identical. For a conventional
stethoscope the variations in sound pressure level induced
- in the chestpiece due to the physiological phenomena under
investigation are conducted via the air columns within
the flexible tubular connecting member 14 and the two ear
branch tubular members 18A and 18B into the ear of the
user physician for analysis and interpretation. In addition
to the conventional passive, vibrating air column stethoscope,
a pair of electronic conversion units 22a and 22b are con-
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nected to each of the two ear branches thus providing binaural,
electronically assisted representation of the physiological
sounds of interest. The output of the electronic conversion
units 22a and 22b are routed to the user's ears via eartip
pieces 24a and 24b respectively.
Figures 2A-2C illustrate the mechanical configuration
of the electronic conversion unit 22a in greater detail. As
shown in Figure 2A, a preferred embodiment of the present in-
vention allows for the rapid conversion of a conventional
stethoscope merely by the removal of the earpiece tip 24a,
connection of an electronic conversion unit 22a onto the
output aperture 2Oa of an ear branch member 18a, and the
reconnection of the earpiece tip 24a onto the threaded output
aperture of the electronics conversion unit 22a. Obviously,
the above steps may be accomplished in a more or less
permanent manner by use of adhesives of various degrees
of permanence thereby rendering the resulting instrument an
integrated phonostethoscope rather than a convertible device.
Figure 2B shows a cross sectional view of the electronic con-
version unit 22a, and more particularly the internalarrangement of selected portions of the electronics. A
collection of discrete components comprising the amplifying
circuitry (shown in functional block form in Figure 3)
are housed on a printed circuit board so as to occupy a
volume nominally that of an elongated annulus, as indicated
by a region designated E. Included in this collection of
components are a plurality of components (shown in
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generalized form in Figure 2C)consisting of: transistors,
diodes, resistors, capacitors, batteries, switches and
other elements to implement the conventional amplifier and
feedback networks as are well known to those skilled in the
electronics instrumentation art. An input microphone M is
located adjacent to the sound channel and receives its stimu-
lus via a plurality of vent slots S in the portion of the
electronic conversion unit 22a which constitutes a uniform
continuation of the stethoscope air column, the primary
air column 26a, fed by the output aperture 2Oa. A
sound baffle B is located so as to provide a movable blockage
of the primary air column as described below. Earpiece
driver D is lcoated so as to also communicate with the air
column but in a position beyond the sound baffle B into a
secondary air column 28a. The acoustic output of earpiece
driver D is delivered into the secondary air column 28a
via a plurality of holes designated as H. Figure 2C is a
cross sectional view of electronics conversion unit 22a,
taken along the lines -2C-, to illustrate the operation
and function of sound baffle B. The sound baffle B, a
flat, rigid member, is activated through a 70 degree arc
25 to substantially block the primary air column when the
electronically assisted capability is in use. The sound
baffle B is shown first in the unblocked position where
it is restrained by a stop pin 23. At this location, a
circular aperture 21a in sound baffle B is aligned with the
continuation of aperture 20a of earpiece member 18a so as
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to provide unimpeded sound transmission to the ear of the user
via primary air column 26a, secondary air column 28a and ear-
tip piece 24a. The sound baffle s is also shown in phantom
lines in the blocked position, after it has been actuated
through the arc 25 (nominally 70) where it is restrained
by a stop pin 27. As shown, the aperture 21a in sound
baffle B no longer aligns with aperture 20a, and the solid
portion of sound baffle B blocks the air column, thereby
producing the substantially independent and acoustically
isolated secondary air column 28a. The baffle actuation is
coupled to an on/off microswitch (not shown) so as to
energize the electronics circuitry whenever the sound
transmission path is divided into the primary and secondary
air columns 26a and 28a. This arrangement provides the
required input/output isolation, thus precluding unwanted
electronic oscillations. Such features as an access cover
for battery replacement, means for the selection, via
discrete switch positions and/or continuously variable con-
trol means, of amplifier gains and frequency response, and an
output connection for recording purposes are not discussed
as they are in common usage in the electronic art.
Referring now to Figure 3, a circuit for providing
the required electronic amplification and frequency response
shaping is illustrated. The circuit has as its input trans-
ducer the microphone M for the conversion of incident sound
pressure variations into corresponding electrical analog
voltages. The output of microphone M is applied via an
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input node Il to the input of a preamplifier Gl and in
turn via an input node I2 to the input of a power amplifier
G2. A feedback network H2 is connected from the output
of power amplifier G2 back to input node I2 to provide a
frequency selective return path. The feedback network
H2 functions to shape the overall system frequency response so
as to produce the three characteristic frequency response
curves which will be described below in connection with
Figure 5. A second feedback network Hl is connected from
the output of power amplifier G2 back to the input of pre-
amplifier Gl via input node I1. This second feedback
network functions to establish the overall amplification
provided by the electronic amplifier unit. An adjustment
control G is provided to select overall system amplification
by altering elements in the network Hl, and an adjustment
control F performs a similar function in concert with the
network H2 for overall system frequency response. These
adjustments are substantially independent, are well known
in the electronics arts, and are described in more func-
tional detail hereinbelow. An output of power amplifier G2is routed to the ear piece driver D thereby providing an
acoustical output representative of the lower level acoustic
input as sensed by microphone M. A further output from
power amplifier G2 is applied to an auxiliary output terminal
A for use with recording devices or other external equipment.
Referring now to Figure 4, a number of amplitude-
frequency response curves are shown for a single electronics
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cha;nnel. The curves represent the overall acoustic
res,ponse of a conventional stethoscope equipped with the
electronic conversion units, for various operating modes~
A curve 40 illustrates the response of the system with
the electronic units inoperative. This is substantially
the same as would be encountered in a basic unequipped
stethoscope and is expressed in decibels (db) where the
zero db level has been arbitrarily selected to facilitate
comparisons with other curves. The curve 40 shows a fairly
broad resonant peak in the vicinity of 100-200 Hz, the
output drops off sharply thereafter with increasing frequency.
A curve 42 shows the overall response of the electronically-
assisted stethoscope when the unit is operating with "FLAT"
amplification. Curve 42 is nominally 15-20 db greater than
the BASIC system and is flat within - 1 db for the frequency
range of 10 Hz to 1,000 Hz. Curves 44 and 46 show the re-
sulting responses when the electronics conversion units
are adjusted in frequency to provide "PEAKED" amplifica-
tion. The curve 44 shows a "LOW PEAK" response nominally
6-8 db greater than the "FLAT" curve, with the peak
located in the 20-70 Hz region; while curve 46 shows a
similar peak, the "HIGH PEAX," in the 140 Hz region.
Both peaked responses fall off sharply with increasing
frequency beyond their peaked regions.
Curves 42-46 should be considered only representa-
tive in the sense that they show only one each of entire
families of amplitude-frequency responses available for the
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stethoscope user. For example: other "FLAT" response
curves similar to curve 42, are also selectable as dis-
cussed above by user selection of alternate gain adjust-
ments of element Hl, shown in Figure 3, by means of control
G. These additional "FLAT" curves would be everywhere
parallel to curve 42 but might be typically adjustable in
3 db steps within some limited range. By way of further
illustration, a three discrete position selection by control
G of elements comprising Hl could produce the curve 42 as
its MID gain position, with a HIGH gain position 3 db higher
than that shown, and a LOW gain position 3 db lower than
that shown. In addition, the location of the maximum
frequency response peaks are also adjustable to meet the
criteria of best enhancement of the corporeal sound of
interest at the moment; or optimum compensation for loss
of frequency acuity in the particular ear, or ears, of the
user. For the illustrative modes described - three
discrete gain positions (HIGH, MID and LOW), and three
discrete frequency responses (FLAT, LOW PEAK and HIGH PEAK)-
a total of nine distinct responses are available at eachear.
Figure 5 illustrates a conventional two channel
recording device 30 electronically coupled to output A of
electronics conversion unit 22a via an interconnecting
cable 32, and to a further electronic conversion unit (not
shown) via an interconnecting cable 34.
While a particular embodiment has been described
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and illustrated in detail it will be understood that the
description and drawings are merely illustrative of and
not restrictive on the broad invention, and that various
departures and modifications may be made without departing
from the spirit and scope of the appended claims.
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