US2363686A - Acoustic Stethoscope - Google Patents

Acoustic Stethoscope Download PDF

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Publication number
US2363686A
US2363686A US43713942A US2363686A US 2363686 A US2363686 A US 2363686A US 43713942 A US43713942 A US 43713942A US 2363686 A US2363686 A US 2363686A
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stethoscope
diaphragm
acoustic
impedance
sounds
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English (en)
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Harry F. Olson
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B7/00—Instruments for auscultation
    • A61B7/02—Stethoscopes

Definitions

  • This invention relates to acoustic pickup devices and more particularly to an acoustic stethoscope.
  • the physieians stethoscope is one of the most useful instruments which he has in diagnosing a patients condition. To be most useful, this instrument should reproduce accurately and eiliciently the body sounds which it picks up.
  • This instrument should reproduce accurately and eiliciently the body sounds which it picks up.
  • the primary object of my present invention is to provide an improved stethoscope which is not subject to the aforementioned defects and limitations characteristic of prior art stethoscopes.
  • Another object of my present invention is to provide an improved acoustic stethoscope as aforesaid which has a much wider frequency range than similar stethoscopes heretofore used.
  • Still another object of my present invention is to provide an improved stethoscope as aforesaid which has a smooth response over its entire working range.
  • a further object of my present invention is to provide an improved acoustic stethoscope which will not pick up sounds o'r noises extraneous to the subject under study.
  • Still a further object of my present invention is to provide an improved acoustic stethoscope which is freefrom transition losses.
  • the acoustic impedance of each ear canal is approximately the same as the surge acoustic impedance of a tube filled with air having an area of about ⁇ 0.2 square centi meter.
  • the acoustic impedance of both ear canals is approximately the same as the surge acoustic impedance of a tube having an area of 0.3 square centimeter, or a diameter of about V1 inch.
  • the pickup diaphragm must be 300 times that of a tube V4 inch in diameter, or about 41A inches. This is entirely too large for a stethoscope because it would be impossible to localize sounds with a stethoscope having a pickup diaphragm of 4V4 inches in diameter.
  • stethoscopes have been provided with diaphragms of about .1V2 to 2 inches in diameter, with a resultant mismatch of about 8 to 1 for the 1V2 inch diameter and about i1/2 to 1 for the 2 inch diameter. This is bad mismatch and represents a sizable loss. Moreover, even a 1V2 to 2 inch diameter diaphragm is still too large. About the maximum tolerable diameter for the pickup end of a stethoscope is 1 inch. To match this diaphragm in contact with the body to air in a tube, the diameter of the tube would be slightly less than inch.
  • I use a tapered tube to match the relativelyhigh impedance atthe pickup end of a stethoscope with a 1 inch diaphragm to the relatively low impedance of the ear.
  • I can employ a small diaphragm which is most useful in localizing the source of sounds and at the same time match the relatively high impedance of the body to the relatively low impedance of the ear canal.
  • the spacing back of the diaphragm must be large in order to obviate closure of the tube by the diaphragm when the stethoscope is pressed to the body.
  • the spacing introduces a shunt acoustic capacitance which, when large, shunts out the high frequencies.
  • this type of diaphragm will transmit high frequencies without attenuation because the spacing between the diaphragm and back plate is small, which, in turn, means that the shunt lacoustic impedance is large because the shunt acoustic capacitance is small.
  • the stethoscope designed in accordance with my present invention exhibits a uniform response over a frequency range of from about to about 4000 cycles. Furthermore, the sensitivity of my improved stethoscope is about 15 decibels greater than that of the conventional open bell type stethoscope and about 6 decibels greater than that of existing diaphragm type stethoscopes.
  • Figure 1 is a chart showing the range of various sounds generated in the human body, the frequency range of the fundamentals being shown in solid bars and the frequency range of the harmonies being indicated by the sectioned bars;
  • Figure 2 is an elevational view, partly in section, of an acoustic stethoscope constructed in accordance with this invention
  • Figure 3 is a schematic cross-sectional view of the acoustic system of my improved stethoscope shown applied to the body and the ear;
  • Figure 4 is a wiring diagram of the equivalent electrical circuit of the acoustic system shown in Fig. 3;
  • Figure 5 shows a set of curves representing the resistive and reactive components of the acoustic impedance looking into the ear canal
  • Figure 6 is a set of response curves showing, by way of comparison, the responses of (I) the conventional open bell type stethoscope, (II) the conventional diaphragm type stethoscope, and (III) my improved stethoscope; and
  • Figure 7 is a plan view, partly broken away, of the backing member constituting a part of the pickup device of my improved stethoscope.
  • the fundamental sounds of systolic and diastolic murmurs range from 300 to 800 cycles.
  • the overtones in certain cases can be observed up to 2000 or 3000 cycles.
  • Prestolic murmurs are usually of a low frequency, ranging from about 60 to about 200 cycles.
  • the overtones range up to about 1000 cycles. Above this frequency, the overtones are masked by the body sounds.
  • the fundamental of peristaltic sounds has a tremendous range in both frequency and intensity. Fundamentals up to 2000 cycles are quite common.
  • the overtones in the case of very intense sounds extend beyond 4000 cycles. ⁇
  • the fundamental frequency of respiratory squeaks, rales, crackles, and groans ranges from 40 cycles to 1000 cycles. Respiratory sounds such as wheezes and the rushing of air are of a random nature and do not possess true fundamentals. The components of these sounds are scattered over the entire audible spectrum.
  • Fig. 2 shows a pickup device I adapted to be placed against the human body or other subject to be studied.
  • the pickup device I comprises a supporting plate 2 having a hollow stem 3 exresponding parts throughout, Fig. 1 shows the 75 tending from its back face, a bore or opening 5 being formed in .the supporting plate 2 in communication with the hollow stem 3.
  • the backing member I Secured to the front face of the plate 2 is a backing member l having an opening 3 in communication with the opening 5 and having a plurality of forwardly extending projections II thereon.
  • the backing member I may be of any suitable material, but I-prefer to make it of an elastic material, such as rubber.
  • the proj tions Il may be of any suitable shape, such as conical, pyramidal, or the like, being shown as small pyramids with curved sides or faces as one example of the type of projections found satisfactory.
  • a mem rancus diaphragm I3 of thin, sheet rubber o the like is carried by the supporting plate 2 wi its rear or inner surface in engagement with ⁇ e apices of the projections II.
  • the projections II ⁇ are spaced from each other on the backing member 1 and are distributed over the entire area of the diaphragm I3, the spacing of the projections being such as to provide a plurality of intersecting and intercommunicating passageways I4 which communicate with the openings l and 5 and the hollow stem 3.
  • a flexible tube I5 of rubber or the like which connects the pickup device I to a Y connector I1, the latter connecting the tube I5 to a pair of ear tubes I9 terminating in a pair of ear pieces 2
  • the tube I5 is provided with a tapered passage 23 the stem. fto the connector I'I.
  • the Adlapln-agm II is ot the order-.of one inch in diameter whereby its-areaisofthe order of scuare inchA and thefidiameter of the en o 'o at the stem I -is 'approximately inch whereby its cross sectionalarea-at stemt is of the order of f., 1024 K square inch.
  • the impedance of'the area of the human body covered by the diaphragm I3,when in lcontact therewith matches the surge acoustic impedance of the air in the passageway 23 at its smaller-end. Since, however, this does not match the impedance o1' the ear canals,
  • the clearance or space behind the diaphragm I3 represented by the intersecting passageways I4 is very small.
  • the diaphragm has small inherent stiffness and therefore will transmit low frequencies without attenuation, while at the same time transmitting high frequencies without attenuation because the space between the diaphragm and the backing member 'I is small.
  • Fig. 3 shows a simplified acoustic system of the body B which is under study or examination and has a sound source S, a stethoscope according to my present invention, and the ear E.
  • Fig. 4 shows a wiring diagram of the analogous electrical system or circuit.
  • ZAB represents the impedance of the body B
  • ZAE represents the impedance of the ear canals
  • M is the mass of the diaphragm I3
  • CAD is the capacitance of the diaphragm
  • Cile isthe capacitance of the resilient projections II
  • CAA represents the capacitance of the air chamber between the diaphragm I3 and the resilient projections or supports II
  • p being the acoustic pressure applied to the diaphragm I3.
  • tapered passage or line 23, 25, 21 acts as an acoustic transformer, being expandingly tapered all the Way from the pickup device I to the ear piece 2I and the ear E.
  • This tapered line is represented by the block 30 in Fig. ⁇ 4 representing a transformer.
  • the measured frequency response characteristics of conventional stethoscopes and of my improved stethoscope are shown by the curves of Fig. 6, the dash line curve I representing the response of the conventional bell type stethoscope, the dot and dash line curve II representing the response of the conventional diaphragm type' stethoscope, and the solid line curve III representing the response of my improved stethoscope.
  • the output of my asoaese 3 winch expands muuuy andunirormiy from improved stethOwODe is about I2 decibels higher than the conventional bell type stethoscope and about 8 decibek higher than the conventional diaphragm type stethoscope in its most sensitive region.
  • my novel stethoscope has considerably greater high frequency and low frequencyv ranges than do existing stethoscopes. Whereas existing stethoscopes cut ofi' at around 1500 cycles, the high frequency response of my improved stethoscope is maintained to about 4000 cycles. It will further be noted that the response of my improved stethoscope is quite uniform, whereas the curves I and -II show that the response of prior art stethoscopes is non-uniform. The peaks" and dips" in the response frequency characteristic of each of the bell type and diaphragm type stethoscopes of the prior art indicate frequency discrimina.- tion.
  • a pick-up device having an impedance substantially equal to that of a given area of a subject to be examined, and an acoustic coupling line connected at one end to said pick-up device and adapted to be connected at its other end to a detector having a different impedance than said first named lmpedance, said line having a passage of gradually varying cross section and the ends of said passage having impedances which match said first and second named impedances, respectively, whereby said coupling line transmits acoustical energy without substantial loss.
  • a pick-up device having a relatively high impedance equal substantially to that of a given area of a subject to be examined, and an acoustic coupling line connected at one end to said pick-up device and adapted to be connected at its other end to a detector having a relatively low impedance, said line having a tapered passage between its ends which expands gradually from said pick-up device to its detector end, and the ends of said passage having impedances which match said high and low impedances, respectively, whereby said coupling line transmits acoustical energy without substantid attenuation.
  • a pick-up device including a relatively limp, exible vibratory member adapted to engage a given area of a subjectto be examined, said subject area having a relatively high impedance, and an acoustic coupling line connected to said pick-up device and adapted to be connected at its other-end to a detector having a relatively low impedance, said line having a tapered passage between its ends which expands gradually from said pickup device to its detector end, and the ends of said passage having irnpedances which match saidhigh and low impedances, respectively, whereby said coupling line transmits acoustical energy without substantial attenuation.
  • a pick-up device including a relatively limp, flexible vibratory member adapted to engage a given area of a subject to be examined and a backing member having a plurality of projections in engagement with said vibratory member, said subject area having a relatively high impedance, and an acoustic coupling line connected to said pick-up device and adapted -to be connected at its other end to a. detector having a relatively low impedance, said line having atapered passage between its ends which expands gradually from said pickup to its detector end, and the ends of said passage having impedances which match said high and low impedances, respectively, whereby said coupling line transmits acoustical energy without substantial attenuation.
  • An acoustical piek-up device comprising a supporting member,v a backing member o! yieldable material carried by said supporting member and having a plurality of projections thereon, andra diaphragm on said supporting member having one surface thereof vin engagement with said projections, said projections being distributed over the area of said surface and being spaced from each other to provide a. plurality of intersecting, intercommunicating passageways therebetween.
  • An acoustical pick-up device characterized in that said backing member is made of an elastic material.
  • An acoustical pick-up device according t0 claim 11 characterized in that said backing member is made of rubber.
  • said vibratory member is constituted 4o each other to provide intercommunicating acoustic passageways therebetween and are distributed over the area of said member, and characterized further in that said intercommunicating passageways have communication with said tapered passage.
  • An acoustic stethoscope comprising a pickup element matched in impedance to the subject to be explored thereby, an ear piece element matched in impedance to the ear canals, and means providing a tapered passageway constituting an acoustic transmission path coupling said elements, said passageway being of smallest cross sectional area at the pick-up element end thereof and of largest cross sectional area at the ear piece element end thereof, and said passageway having an impedance at each end, looking into the respectively associated elements, of substantially the same magnitude as said respective elements throughout the range of sounds to be transmitted thereby.
  • An acoustical pick-up device characterized in that said projections are substantially pyramidal in shape, and characterized further in that their apices are in engagement with said diaphragm.
  • each of said projections is tapered to substantially a point, and characterized further in that the pointed ends of said projections are in engagement with said diaphragm.l 16.
  • An acoustical pick-up device according to -claim l1 characterized in thatsaid diaphragm is constituted by a thin, rubber membrane in substantially unstretched condition.
  • An acoustical pick-up device characterized in that said diaphragm has an area of the order of 0 way coupled at one end to said diaphragm and adapted to be connected at its other end to a detector having a different impedance from that of said source, said means constituting an acoustic transformer which matches the impedance of s said source to the impedance of said detector whereby said transformer is capable of transmitting acoustical energy from said source to said detector without substantial attenuation.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Molecular Biology (AREA)
  • Surgery (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Medical Informatics (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
  • Headphones And Earphones (AREA)
  • Details Of Audible-Bandwidth Transducers (AREA)
US43713942 1943-10-29 1942-04-01 Acoustic Stethoscope Expired - Lifetime US2363686A (en)

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US50821543 US2389868A (en) 1943-10-29 1943-10-29 Acoustic Stethoscope

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US2363686A true US2363686A (en) 1944-11-28

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US50821543 Expired - Lifetime US2389868A (en) 1943-10-29 1943-10-29 Acoustic Stethoscope

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BE (2) BE474567A (xx)
FR (2) FR1018260A (xx)
GB (2) GB568128A (xx)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2573438A (en) * 1946-09-18 1951-10-30 Rca Corp Electroacoustic transducer set
DE1049046B (de) * 1954-12-28 1959-01-22 Belge D Optique Et D Instr De Abhoervorrichtung fuer AErzte
US2933145A (en) * 1951-12-12 1960-04-19 Dictaphone Corp Headphone device
US3493075A (en) * 1967-12-26 1970-02-03 Us Navy Single tubing stethoscope
US20050033198A1 (en) * 2001-04-18 2005-02-10 Georges Kehyayan Device for assistance in the analysis of adventitious sounds
US9404829B1 (en) * 2013-10-02 2016-08-02 Andrew Tien Stethescope based leak detection apparatus with interchangeable heads
USD814631S1 (en) 2015-09-21 2018-04-03 3M Innovative Properties Company Stethoscope with one-piece tubing, chest piece and diaphragm-rim
US10667782B2 (en) 2015-05-15 2020-06-02 3M Innovative Properties Company Stethoscope

Families Citing this family (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2632521A (en) * 1953-03-24 Frequency selector
US3314499A (en) * 1967-04-18 Instrument for quantitating sound intensities
BE518558A (xx) * 1952-03-20
DE1026480B (de) * 1955-01-24 1958-03-20 Dr Emmanuel Roy Bier Atemkanuele mit Atemgeraeuschverstaerker
US3294195A (en) * 1965-01-25 1966-12-27 Telex Corp Compressional wave signaling apparatus
US3690404A (en) * 1971-07-30 1972-09-12 Bio Data Inc Selective frequency stethoscope structure
US4270627A (en) * 1979-07-02 1981-06-02 Hill Raymond R Stethoscope with probe sound pick-up and resonant cavity amplification
US4246776A (en) * 1979-09-25 1981-01-27 Cornell Thompson Leak scope for detecting leaks in plumbing equipment
US4387784A (en) * 1981-10-06 1983-06-14 Hill Raymond R Stethoscope with improved resonant cavity amplification
US4763753A (en) * 1984-07-05 1988-08-16 Etymotic Research, Inc. Insert earphones for audiometry
US4633971A (en) * 1985-11-06 1987-01-06 Minnesota Mining And Manufacturing Company Stethoscope with high frequency filter
US5492129A (en) * 1993-12-03 1996-02-20 Greenberger; Hal Noise-reducing stethoscope
US5530212A (en) * 1995-05-12 1996-06-25 Baffoni; Frank A. Multiple phase stethoscope
US6119806A (en) * 1997-06-24 2000-09-19 Baffoni; Frank A. Multiple phase acoustic systems
KR101637830B1 (ko) * 2015-04-30 2016-07-07 서울시립대학교 산학협력단 헬름홀츠 공명을 이용한 청진기, 그 제어방법 및 그 제조방법
KR101697424B1 (ko) * 2015-06-02 2017-01-17 서울시립대학교 산학협력단 헬름홀츠 공명을 이용한 청진기와 연결되는 휴대단말 시스템, 그 제어방법 및 그 제조방법

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2573438A (en) * 1946-09-18 1951-10-30 Rca Corp Electroacoustic transducer set
US2933145A (en) * 1951-12-12 1960-04-19 Dictaphone Corp Headphone device
DE1049046B (de) * 1954-12-28 1959-01-22 Belge D Optique Et D Instr De Abhoervorrichtung fuer AErzte
US3493075A (en) * 1967-12-26 1970-02-03 Us Navy Single tubing stethoscope
US20050033198A1 (en) * 2001-04-18 2005-02-10 Georges Kehyayan Device for assistance in the analysis of adventitious sounds
US9404829B1 (en) * 2013-10-02 2016-08-02 Andrew Tien Stethescope based leak detection apparatus with interchangeable heads
US10667782B2 (en) 2015-05-15 2020-06-02 3M Innovative Properties Company Stethoscope
USD814631S1 (en) 2015-09-21 2018-04-03 3M Innovative Properties Company Stethoscope with one-piece tubing, chest piece and diaphragm-rim

Also Published As

Publication number Publication date
FR989229A (xx) 1951-09-06
BE474930A (xx) 1947-08-30
GB596787A (en) 1948-01-21
US2389868A (en) 1945-11-27
GB568128A (en) 1945-03-20
BE474567A (xx) 1947-08-30
FR1018260A (xx) 1953-01-05

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