1、Designation: F 2504 05Standard Practice forDescribing System Output of Implantable Middle EarHearing Devices1This standard is issued under the fixed designation F 2504; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice defines means for describing system per-formance (ex vivo) and, in particular, system output of animplant
3、able middle ear hearing device (IMEHD) by measuringa physical quantity that is relevant to the insertion gain andoutput level of the IMEHD when implanted in the patient.1.2 This practice is similar to headphone calibration on anartificial ear in which the sound pressure level (in decibelsound pressu
4、re level (SPL) measured in the artificial ear canbe converted to patient hearing level (in decibel hearing level(HL) using a known transfer function, as defined byANSI 3.7.These measurements can then be used to predict systemparameters relevant for patient benefit such as functional gain,maximum out
5、put, and variability. Measurements defined in thispractice should be useful for patients, clinicians, manufactur-ers, investigators, and regulatory agencies in making compara-tive evaluations of IMEHDs.1.3 The values given in SI units are to be considered thestandard.1.4 This standard does not purpo
6、rt to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ANSI Standards:2ANSI
7、 3.6 Specification for AudiometersANSI 3.7 Method for Coupler Calibration of EarphonesANSI 3.22 Specification of Hearing Aid Characteristics3. Terminology3.1 Refer to the block diagram of Fig. 1 for a clarification ofthe mathematical notations used in this section.3.2 In the following definitions, t
8、hese symbols are used forphysical quantities:3.2.1 E = electrical drive signal (voltage or current)3.2.2 p = sound pressure3.2.3 v = vibration velocity3.3 All transfer functions are denoted by the symbol H, withthe following subscripts indicative of the type of transferfunction:3.3.1 A = IMEHD-aided
9、3.3.2 E = electrical3.3.3 H = hearing level3.3.4 S = sound field sound pressure3.3.5 T = tympanic membrane (ear drum) sound pressure3.3.6 U = unimplanted3.3.7 V = vibration of stapes3.4 Definitions:3.4.1 coupling, npoints and methods of attachment.3.4.2 displacement, nintegral of velocity measured i
10、nnanometres.3.4.3 ear-canal sound pressure, pT, nsound pressure pro-duced in the ear canal, at the tympanic membrane, by a soundfield stimulus, specified in units of pascals.3.4.4 equivalent hearing level, LH, nratio of an equivalentsound pressure, pQ, relative to the sound field pressure,pRETSPL, a
11、t 0 incidence that is just detectable monaurally by anormally hearing individual, as defined in ANSI S3.6, Table 9,expressed in decibels: LH= 20log10(pQ/pRETSPL).3.4.5 equivalent sound pressure, pQ, nunimplanted inputsound field pressure needed to produce a stapes velocity equalto that produced by a
12、 specified IMEHD input in the IMEHD-aided condition: pQ= E HES.3.4.5.1 DiscussionThe equivalent sound pressure is theproduct of the equivalent sound pressure transfer function, HES,and the IMEHD output transducer electrical input E: pQ= E HES. The equivalent sound pressure can be expressed asequival
13、ent sound pressure level in units of decibels, SPLeq,calculated as 20log10(pQ/210-5Pa).3.4.6 equivalent sound pressure level, LQ, nlogarithmicrepresentation of equivalent sound pressure, LQ= 20log10(pQ).3.4.7 hearing level (HL), L, nratio of the input sound fieldpressure, pS, relative to the sound f
14、ield pressure pRETSPLat 0incidence that is just detectable monaurally by a normallyhearing individual, as defined inANSI S3.6, Table 9, expressedin decibels as: L = 20log10(pS/pRETSPL).1This practice is under the jurisdiction ofASTM Committee F04 on Medical andSurgical Materials and Devices and is t
15、he direct responsibility of SubcommitteeF04.37 on Implantable Hearing Devices (IHDs).Current edition approved Nov. 1, 2005. Published November 2005.2Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbo
16、r Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.4.8 IMEHD electrical input at threshold Ethreshold,nelectrical input to the IMEHD output transducer at thresh-old of audibility.3.4.9 IMEHD harmonic distortion, nharmonic distortionof the stapes velocity IMEHD-aided analogous to
17、ANSI S3.22,Section 6.11S, from sinusoidal inputs of the frequencies 500,800, and 1600 Hz; input levels shall be Emax20dB.3.4.10 IMEHD output transducer, nelectromechanicaloutput transducer of the IMEHD.3.4.11 IMEHD output transducer frequency range,nusing the equivalent sound pressure transfer funct
18、ion, HES,draw a horizontal line at the average for 1000, 1600, and 2500Hz, then subtract 20 dB, or divide by 10; the lower and theupper bounds of the frequency response range are where theaverage line crosses the transfer function curve.3.4.12 IMEHD output transducer input, E, nelectricalinput to th
19、e IMEHD output transducer, specified in volts oramperes, as appropriate for the particular device.3.4.13 IMEHD system frequency range, nusing the inser-tion gain transfer function (velocity), HVV, draw a horizontalline at the average for 1000, 1600, and 2500 Hz, then subtract20 dB, or divide by 10;
20、the lower and the upper bounds of thefrequency response range are where the average line crossesthe transfer function curve.3.4.14 input sound field pressure, pS, nsound stimulusmeasured in the free field and presented to the listener in eitherthe IMEHD-aided or unimplanted condition, specified in u
21、nitsof pascals.3.4.15 maximum electrical transducer input, Emax,nmaximum electrical output of the sound signal processor,specified as peak-to-peak or root mean square value, specifiedin volts or amperes, as appropriate for the particular device.3.4.16 maximum equivalent sound pressure, pE,max,nequiv
22、alent sound pressure that corresponds to the maxi-mum electrical output Emaxof the implant electronics, pE,max=Emax HES.3.4.17 maximum equivalent sound pressure level, LE,max,nlogarithmic representation of the maximum equivalentsound pressure LE,max= 20log10(pE,max/210-5Pa).3.4.18 sound pressure at
23、threshold, pthreshold, nstimulussound field pressure at the threshold of audibility.3.4.19 stapes velocity (IMEHD-aided), vA, ntranslationalvelocity of the stapes when driven by the IMEHD outputtransducer, specified in units of mm/s.3.4.20 stapes velocity (unimplanted), vU, ntranslationalvelocity of
24、 the stapes when driven by sound input to the middleear specified in units of mm/s.Transfer Function3.4.21 acousto-electric transfer function, HSE, nelectricalinput to the IMEHD output transducer E produced by a soundfield, divided by the input sound field pressure pS: HSE= E/pS.3.4.21.1 DiscussionH
25、SEwill depend on the particular gainsettings used, for example, full-on gain or minimal gain. Thegain should be reported whenever that transfer function is used.3.4.22 acousto-vibrational transfer function (IMEHDaided), HSVAstapes velocity (IMEHD aided) divided by theinput sound field pressure: HSVA
26、=vA/pS.3.4.22.1 DiscussionThis quantity can be measured di-rectly or computed from the product of the electro-vibrationaltransfer function, HEV, and the acousto-electric transfer func-tion, HSE, measured in the IMEHD-aided condition:HSVA=vA/pS.3.4.23 acousto-vibrational transfer function (unimplante
27、d),HSVU, nstapes velocity (unimplanted) when driven by theinput sound field, divided by the input sound field pressure:HSVU= vU/pS.3.4.23.1 DiscussionThis quantity can be measured di-rectly or computed from the product of the middle-ear transferfunction, HTV, and the ear-canal transfer function, HST
28、, mea-sured in the unimplanted condition: HSVU= vU/pS= HST HTV.3.4.24 ear-canal pressure transfer function, HST, nearcanal sound pressure, pT, produced by the input sound fieldpressure, pS, in the unimplanted case, divided by that inputsound field pressure: HST= pT/pS; this quantity is unitless (1,2
29、).33.4.25 electro-vibrational transfer function, HEV, nstapesvelocity (IMEHD-aided) when driven by the IMEHD outputtransducer, divided by the transducer input: HEV= vA/E.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.FIG. 1 Signal Flow in the Unimplan
30、ted and IMEHD-Aided Middle EarF25040523.4.26 equivalent sound pressure transfer function, HES,nunimplanted sound field pressure needed to produce astapes velocity equivalent to that produced by an electricalIMEHD input in the IMEHD-aided condition, divided by theIMEHD input.3.4.26.1 DiscussionIf the
31、 electrical IMEHD input pro-duces a linear change in stapes velocity with a change in inputelectrical stimulus, the equivalent sound pressure transferfunction, HES, can be computed as the quotient between thevibro-electric transfer function (IMEHD-aided), HEV, and thevibro-acoustic transfer function
32、 (unimplanted), HSVU: HES=(v/E)/(v/pS)=HEV/HSVU.3.4.27 insertion gain transfer function (sound field), HSS,nratio of the equivalent sound pressure produced in theIMEHD-aided case with a given electrical input to the IMEHDoutput transducer and the input sound field pressure used asinput in the IMEHD-
33、aided case required to produce the sameIMEHD output transducer electrical input: HSS= pE/pS; thisratio is unitless.3.4.27.1 DiscussionWith a linear sound signal processor,the insertion gain (sound field) can be computed from theproduct of the equivalent sound pressure transfer function, HES,and the
34、electro-acoustic transfer function, HSE: HSS= pE/pS=HSE HES. HSSwill depend on the particular gain settings used,for example, full-on gain or minimal gain. The gain should bereported whenever that transfer function is used.3.4.28 insertion gain transfer function (velocity), HVv,nratio of the stapes
35、velocity (IMEHD-aided) and the stapesvelocity (unimplanted) produced by a given input sound field:HVV= vA/vU; the ratio is unitless and can be expressed indecibels as 20log10(HVv).3.4.28.1 DiscussionWith a linear sound signal processorand IMEHD, that is, a processor whose electrical output E ispropo
36、rtional to the input sound field pressure, pS, and anIMEHD whose vibrational output is proportional to its electri-cal output, the insertion gain (sound field), HSS, will equal theinsertion gain transfer function (velocity), HVV.3.4.29 maximum insertion gain transfer function (soundfield), HSS,max,
37、nmaximum insertion gain transfer function(sound field) that can be achieved with the implant electronics.3.4.30 middle-ear transfer function, HTV, nstapes velocity(unimplanted) produced by an ear-canal sound pressure, di-vided by the ear-canal sound pressure, in units of mm/s/Pa:HTV= vU/pT.3.5 Acron
38、yms:3.5.1 IHDimplantable hearing device3.5.2 IMEHDimplantable middle-ear hearing device3.5.3 LDVlaser Doppler vibrometry3.5.4 SPLsound pressure level4. Summary of Practice4.1 This practice involves the use of human temporal bonesand laser Doppler interferometry measurements of middle earstructures v
39、elocities, to test for the ex-vivo performances ofIMEHD. Once a procedure for measuring system output hasbeen defined, several characteristics of the IMEHD can bespecified. Detailed instructions for measuring and reportingthese characteristics are given below. The important character-istics are:4.1.
40、1 For Transducers:4.1.1.1 Equivalent sound pressure transfer function,4.1.1.2 IMEHD output transducer frequency range, and4.1.1.3 IMEHD harmonic distortion.4.1.2 For the System:4.1.2.1 Maximum insertion gain transfer function (soundfield) (see full-on gain in ANSI S3.22, paragraph 3.7),4.1.2.2 Maxim
41、um equivalent sound pressure level (seeOSPL90 in ANSI S3.22, paragraph 3.5), and4.1.2.3 IMEHD system frequency range.5. Significance and Use5.1 IMEHDs are alternatives to air conduction hearing aids.They are similar to air conduction hearing aids in that theyprocess incoming sound by applying freque
42、ncy shaping andcompression to create an analog, vibratory audio frequencyoutput. IMEHDs differ from hearing aids in that they do notcreate an airborne acoustical output signal with an electroa-coustical output transducer in the external ear canal, but rathera mechanical stimulation that results in t
43、he vibration of thecochlear fluid. Therefore, the IMEHD output signal is notreadily accessible after implantation in the way hearing aidoutput is accessible with real-ear probe microphone measure-ments. Different devices will use different methods of couplingto the ossicular chain or cochlea. This m
44、akes it difficult todesign a uniform model of the middle ear in the way the 2-cm3coupler is used as a model of the external ear canal withconventional hearing aids.5.2 This practice provides uniformity of data collectionpractices, thus allowing IMEHD in vitro performances to beevaluated and readily
45、compared. Once clinical data are avail-able, the performance specifications can be augmented withcorresponding transfer functions or results from measurementsin patients.5.3 The temporal bone is a well-accepted model that relatesclosely to the biomechanics of the living middle ear, which isreadily r
46、elatable to hearing level. Laser Doppler vibrometryprovides accurate velocity measurements in the ranges requiredfor human hearing.6. Procedure6.1 Procedure SetupThe basic procedure is to define amethod for the measurement of the insertion gain and maxi-mum output of the IMEHD based on temporal bone
47、 measure-ments of sound-induced stapes velocity before implantationand measurements of IMEHD-induced stapes velocity afterimplantation.6.2 Components of the Test System:6.2.1 Test ModelHuman Temporal Bone:6.2.1.1 Temporal Bone Pre-SelectionFresh or fresh-frozen temporal bones shall be used. Fresh te
48、mporal bonesshall be kept moist and used within seven days of harvesting orbe frozen within 24 h of harvesting for later testing (3).Thawedbones shall be used within six days. Fresh or thawed temporalbones shall be stored at 5C in isotonic saline with 1:10 000thimerosal (or antibacterial equivalent)
49、. Once removed fromstorage, all measurements, including qualification, shall bemade within one 8-h period. The middle and inner ears shall beF2504053inspected to be morphologically intact and with normal-appearing tympanic membrane and middle ear. Diseased earsor overtly abnormal structures or evidence of a conductivedefect, or combination thereof, shall disqualify bones fromtesting. Temporal bones with indicated leaks of perilymph alsoshall not be used in the study. Microscopic visual inspection,surgical observation, or phy
