Paul Y Ertel Merle Lawrence Richard K Brown And Aaron-Books Pdf

PAUL Y ERTEL MERLE LAWRENCE RICHARD K BROWN and AARON
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Stethoscope Acoustics, II Transmission and Filtration Patterns. By PAuL Y ERTEL M D MERLE LAWRENCE PH D, RICHARD K BROWN PH D AND AARON M STERN M D. T HERE are no reliable acoustical data scopes since the means have been available. to aid physicians in their selection or to perform calibrated studies. use of a stethoscope Yet the sole medical The American Standards Association was. utility of any stethoscope is derived from its established as the organ through which acous. acoustical performance It is the purpose of tical test methods became standardized Test. this paper to provide clinicians with objec procedures were set up for the evaluation. tive acoustical performance data on intact of many acoustical devices 7 earphones mi. and current stethoscopes crophones and loudspeakers but no standard. Frederick and Dodge first recognized that method has been adopted as yet for the testing. the stethoscope was deserving of acoustical of stethoscopes We developed a new acous. study in 1924 They studied the intact stetho tical test method8 specifically designed to. scope but their data understandably reflected obtain calibrated response curves on intact. the limitations of acoustical test instruments of stethoscopes It provided the means of testing. the time In 1940 Johnston and Kline2 made the instruments while they were actually being. an objective acoustical study of stethoscope worn by physicians It was observed that the. components Their test method was physio acoustics of human ears became an integral. logically oriented and employed a sound part of the acoustics of stethoscopes In short. source implanted within a cadaver heart They human ears alter the performance of a stetho. concluded that the design of the chestpiece scope Thus in order to standardize the test. was an important determinant in shaping the ing of stethoscopes it is necessary to incorpo. response of a stethoscope Rappaport and rate standard ears into the test system There. Sprague3 4 studied stethoscope tubing They is no such thing as an unvarying standard. interpreted their data to indicate that the human ear but the acoustical contributions. physical properties of tubing had considerable of such a hypothetical ear are now known. influence on stethoscope efficiency Groom5 6 We employed a mechanical analog ear9. investigated stethoscope performances through which has the same influence upon the acous. well executed subjective studies He called tics of a stethoscope as does the calculated. attention to the importance of well fitting ear average normal human ear This paper will. pieces and cited the impairment of stethoscope describe the properties of the analog ear and. performances caused by air leaks and ambient the acoustical response patterns of a sampling. noise levels However we have been unable of currently available stethoscopes All data. to find any fully calibrated objective data in this paper are objective. published on the acoustics of intact stetho Method. The test method is identical in all respects to, From the Department of Pediatrics and Communi method B described in the preceding paper8. cable Diseases The University of Michigan Medical, Center Ann Arbor Michigan Laboratory facilities. were provided by the Kresge Hearing Research In This test method is being employed in further. stitute acoustical studies For the purpose of clarity it will. This investigation was supported by a grant from be referred to as the MHA Stethoscope Test System. the Michigan Heart Association and a National In It is named for the Michigan Heart Association whose. stitutes of Health General Research Support Grant support made possible its development. Circulation Volume XXXIV November 1966 899, Downloaded from circ ahajournals org by on October 16 2007.
900 ERTEL ET AL, see fig 5 part I page 892 of this issue except Stethoscopes Studied. that stethoscope earpieces are terminated into Twenty eight unaltered commercial stethoscopes. artificial ears rather than into human ears Sound were tested against the artificial ears This sam. input to the stethoscope chestpiece is held constant pling included the more popular models currently. throughout the test frequency range from 20 to available in this country plus a number of imports. 3 000 cps Stethoscope outputs are measured by and lesser known instruments We have not. the probe technique at the earpiece auditory attempted a complete cataloging of all stetho. canal junction as in humans Both the input scopes past and present. signal and the stethoscope output are recorded Each instrument was fully assembled and. on a synchronized oscillator recorder system All checked for air leaks Several were found to. tests were carried out in a sound proof room have air leaks in their chestpieces although they. The entire test system was fully calibrated in were new and unused These were replaced with. absolute units air tight ones The earpieces of each stethoscope. The Average Human Ear were inserted into a pair of artificial ears in. Data obtained from the preceding studies of the same fashion as they would be worn by. stethoscopes and humans were utilized to deter humans fig 2 The probe was positioned at. mine the acoustical influence of the average, the earpiece auditory canal junction either by. insertion through the wall of the artificial ear, normal ear upon the acoustics of a reference fig 1 or through a hole drilled in the stetho. stethoscope Variations in the response of this scope earpiece fig 2 Identical responses were. instrument were determined in a series of 20 seen with either insertion and the route selected. subjects with proven normal hearing The mean was usually the former as a matter of convenience. response curve was arithmetically calculated from, A silastic cushion held stethoscope earpieces in. these data at frequency points pertinent to the place and assured air tight seals The chestpiece. response curve of the stethoscope This was, was clamped to the sound stage of the test.
taken as the standard curve representing the apparatus as in method B fig 2 A petroleum. response of the reference stethoscope coupled, with the average human ear Artificial ears were jelly sealant prevented air leaks at the contact. then designed to duplicate the average human surface Through the use of support rings dia. curve with the reference stethoscope, phragms were not permitted contact with the. sound stage This prevented any damping from, The Artificial Ear Mechanical Ear Analog nonvibratory contact. The artificial ear is in the form of an im Presentation of Data. pedance chamber consisting of a series of inter The intensity level of the input signal was held. connected air cavities fig 1 The dimensions constant at 80 db referenced to 0 0002 dyne cm 2. of these cavities were based upon calculations For the purpose of comparing the output of a. kindly supplied us by Josef Zwislocki personal stethoscope to its input it is convenient to desig. communication 1963 of Syracuse University nate the constant input signal at the 0 db level. The cavities are bored from solid aluminum The Thus whenever stethoscope output response. distal end of the artificial ear is closed and its. proximal end contains the opening which receives, the stethoscope earpiece The proximal cavity is ACOUSTICAL EAR ANALOG. connected to a distal cavity through a minute, passage 1 mm in diameter The proximal cavity.
could be said to approximate the external auditory Probe 2 Omm I D. canal The 1 0 mm passage acoustically repre Silicone Rubber Seal Steel Wool. sents the impedance of the middle ear structures, and the distal cavity approximates the acoustics. of the inner ear Precise anatomic correlations, were not attempted nor are they pertinent The. purpose of the ear analog is to duplicate the, overall terminus acoustics of the average human. ear within the stated frequency range, The stethoscope selected as the reference instru Stethoscope earpiece seats firmly into a silastic sili. ment was the Army Ford s It possesses a regularity cone rubber grommet Its outlet lumen is flush to. in its response curve which facilitated the frequency opening of artificial ear Microphone probe inserts. location of data points in calculating the mean re to the midpoint of this junction Steel wood grade 00. sponse fills proximal cavity and functions as damping material. Circulation Volume XXXIVJ November 1966, Downloaded from circ ahajournals org by on October 16 2007.
STETHOSCOPE ACOUSTICS 901, presented on the same graph The transmission. acoustics are indicated by a superimposed, tracing as a dotted line and the filtration acous. tics are indicated by solid line curves All solid, line curves shown are photographs of the original. graphic recordings taken directly from the re, corder A complete listing of all stethoscopes. tested appears in the appendix to this paper, Stethoscopes are assigned numbers in the listing.
which correspond to their response curves if, included in the results section of the text. Human Response Variations, A composite of 40 response curves obtained. with human subjects wearing the reference, stethoscope is shown in part I see fig 11. page 895 of this issue The mean response was, then mathematically calculated at the frequen. cy points where peaks and troughs occurred, in the overall response pattern These points.
established the average response of normal, ears at these selected frequencies and are. indicated by white dots superimposed on the, composite graph. Response of the Artificial Ears, Figure 3 shows the response of the refer. Figure 2 ence stethoscope when worn by the artificial. The test system A Artificial ears B probe tube, ears Superimposed on this curve are the cal. C output microphone D input microphone E, stethoscope chestpiece bell F sound stage and.
G sound source headphone ZA210 11, exceeds its input amplification has occurred and w. its amplitude is indicated by db Where at m 1 I0, tenuation has occurred it is indicated by db. The actual recording of the input signal appears as LiJ. a flat line at 0 db onall graphs Its maximum, I 20 I I11 W. deviation from a true flat response is less than z. 0 5 db The decibal scale appears along the a, ordinate and the test frequencies appear along w. the abscissa This practice will apply to all data, presented in this paper.
Curves obtained from bell type chestpieces, represent their transmission acoustics Diaphragm 10 20 50 100 200 500 1000 3000. type chestpieces present two different acoustical FREQUENCY CYCLES PER SECOND. patterns Their transmission acoustics are obtained Figure 3. with the diaphragm removed Though this is, not their condition when in actual use their Response of artificial ear Straight line at 0 db indi. transmission patterns are presented to delineate cates input signal direct measure Solid line curve. the acoustical contribution of the diaphragm itself is the measured response of reference stethoscope. When the diaphragm is in place sound passing obtained with artificial ear Closed circles show mean. through it is filtered and this pattern is desig response with human ears same data points as in. nated as filtration acoustics Both curves are white dots in fig 11 part I page 895 of this issue. Circulation Volume XXXIV November 1966, Downloaded from circ ahajournals org by on October 16 2007. 902 ERTEL ET AL, culated data points indicating the calculated 20 1. response pattern of the same stethoscope, coupled to average normal ears The maxi iI.
mum deviations in the response of the artificial, ears from the response of average human ears 0. are 1 5 db to 3 db This pattern was re w, producible within 0 5 db on five repeat testings u 10. with the artificial ears z, Objective Stethoscope Comparisons 1 w 20. The Transmission Patterns of Bell Chestpieces, As stated in Methods the response pat 30 t. terns of diaphragm chestpieces are considered 10 20 50 100 200 500 1000 3000. separately from bell type chestpieces The fol FREQUENCY CYCLES PER SECOND. lowing group of curves illustrate the trans, mission patterns of stethoscopes terminated Figure 5.
by a bell either singly or as a component Response of stethoscope no 1 bell chestpiece. of a combination chestpiece There are four group I double tubing trumpet bell. basic variations in the design of these in, struments These basic design features are others Two stethoscopes have been selected. diagrammed in figure 4 Bells were either to represent each group. deep and trumpet shaped or shallow and, bowl shaped The tubing and bell outlets were Group I Double Tubing Trumpet Bell. either single or double The response patterns Stethoscope No 1 Fig 5 The combination. of all instruments within a given design group of this particular trumpet shaped bell with. are characteristic of that group though no double tubing design resulted in the greatest. two of them are identical There are many range of amplification at the high frequencies. subtle design variations which produce less of all stethoscopes tested There are narrow. significant response variations tubing length troughs of attenuation at 500 1 000 and. and material bell height and diameter and 2 500 cps but its peaks of amplification extend. beyond 3 000 cps No other stethoscope was, found to amplify beyond 3 000 cps. 30 il tM 1, 10 20 50 100 200 500 1000 3000, FREQUENCY CYCLES PER SECOND. Stethoscope Acoustics II Transmission and Filtration Patterns By PAuL Y ERTEL M D MERLE LAWRENCE PH D RICHARD K BROWN PH D AND AARON M STERN M D

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