ASTM F2504-05
(Practice)Standard Practice for Describing System Output of Implantable Middle Ear Hearing Devices
Standard Practice for Describing System Output of Implantable Middle Ear Hearing Devices
SIGNIFICANCE AND USE
IMEHDs are alternatives to air conduction hearing aids. They are similar to air conduction hearing aids in that they process incoming sound by applying frequency shaping and compression to create an analog, vibratory audio frequency output. IMEHDs differ from hearing aids in that they do not create an airborne acoustical output signal with an electroacoustical output transducer in the external ear canal, but rather a mechanical stimulation that results in the vibration of the cochlear fluid. Therefore, the IMEHD output signal is not readily accessible after implantation in the way hearing aid output is accessible with real-ear probe microphone measurements. Different devices will use different methods of coupling to the ossicular chain or cochlea. This makes it difficult to design a uniform model of the middle ear in the way the 2-cm3 coupler is used as a model of the external ear canal with conventional hearing aids.
This practice provides uniformity of data collection practices, thus allowing IMEHD in vitro performances to be evaluated and readily compared. Once clinical data are available, the performance specifications can be augmented with corresponding transfer functions or results from measurements in patients.
The temporal bone is a well-accepted model that relates closely to the biomechanics of the living middle ear, which is readily relatable to hearing level. Laser Doppler vibrometry provides accurate velocity measurements in the ranges required for human hearing.
SCOPE
1.1 This practice defines means for describing system performance (ex vivo) and, in particular, system output of an implantable middle ear hearing device (IMEHD) by measuring a physical quantity that is relevant to the insertion gain and output level of the IMEHD when implanted in the patient.
1.2 This practice is similar to headphone calibration on an artificial ear in which the sound pressure level (in decibel sound pressure level (SPL)) measured in the artificial ear can be converted to patient hearing level (in decibel hearing level (HL)) using a known transfer function, as defined by ANSI 3.7. These measurements can then be used to predict system parameters relevant for patient benefit such as functional gain, maximum output, and variability. Measurements defined in this practice should be useful for patients, clinicians, manufacturers, investigators, and regulatory agencies in making comparative evaluations of IMEHDs.
1.3 The values given in SI units are to be considered the standard.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Standards Content (Sample)
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Designation: F2504 − 05
StandardPractice for
Describing System Output of Implantable Middle Ear
Hearing Devices
This standard is issued under the fixed designation F2504; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2 In the following definitions, these symbols are used for
physical quantities:
1.1 This practice defines means for describing system per-
3.2.1 E=electrical drive signal (voltage or current)
formance (ex vivo) and, in particular, system output of an
3.2.2 p=sound pressure
implantablemiddleearhearingdevice(IMEHD)bymeasuring
3.2.3 v=vibration velocity
a physical quantity that is relevant to the insertion gain and
output level of the IMEHD when implanted in the patient.
3.3 Alltransferfunctionsaredenotedbythesymbol H,with
1.2 This practice is similar to headphone calibration on an
the following subscripts indicative of the type of transfer
artificial ear in which the sound pressure level (in decibel
function:
sound pressure level (SPL)) measured in the artificial ear can
3.3.1 A=IMEHD-aided
be converted to patient hearing level (in decibel hearing level
3.3.2 E=electrical
(HL))usingaknowntransferfunction,asdefinedbyANSI3.7.
3.3.3 H=hearing level
These measurements can then be used to predict system
3.3.4 S=sound field sound pressure
parameters relevant for patient benefit such as functional gain,
3.3.5 T=tympanic membrane (ear drum) sound pressure
maximumoutput,andvariability.Measurementsdefinedinthis
3.3.6 U=unimplanted
practice should be useful for patients, clinicians,
3.3.7 V=vibration of stapes
manufacturers, investigators, and regulatory agencies in mak-
ing comparative evaluations of IMEHDs.
3.4 Definitions:
3.4.1 coupling, n—points and methods of attachment.
1.3 The values given in SI units are to be considered the
standard.
3.4.2 displacement, n—integral of velocity measured in
1.4 This standard does not purport to address all of the nanometres.
safety concerns, if any, associated with its use. It is the
3.4.3 ear-canal sound pressure, p ,n—sound pressure pro-
T
responsibility of the user of this standard to establish appro-
duced in the ear canal, at the tympanic membrane, by a sound
priate safety and health practices and determine the applica-
field stimulus, specified in units of pascals.
bility of regulatory limitations prior to use.
3.4.4 equivalent hearing level, L ,n—ratio of an equivalent
H
2. Referenced Documents sound pressure, p , relative to the sound field pressure,
Q
2 p , at 0° incidence that is just detectable monaurally by a
RETSPL
2.1 ANSI Standards:
normally hearing individual, as defined inANSIS3.6, Table9,
ANSI 3.6Specification for Audiometers
expressed in decibels: L = 20·log (p /p ).
H 10 Q RETSPL
ANSI 3.7Method for Coupler Calibration of Earphones
3.4.5 equivalent sound pressure, p ,n—unimplanted input
ANSI 3.22Specification of Hearing Aid Characteristics
Q
sound field pressure needed to produce a stapes velocity equal
3. Terminology
to that produced by a specified IMEHD input in the IMEHD-
aided condition: p = E · H .
3.1 RefertotheblockdiagramofFig.1foraclarificationof Q ES
the mathematical notations used in this section. 3.4.5.1 Discussion—The equivalent sound pressure is the
productoftheequivalentsoundpressuretransferfunction,H ,
ES
and the IMEHD output transducer electrical input E: p = E ·
Q
ThispracticeisunderthejurisdictionofASTMCommitteeF04onMedicaland
H . The equivalent sound pressure can be expressed as
ES
Surgical Materials and Devices and is the direct responsibility of Subcommittee
equivalent sound pressure level in units of decibels, SPL ,
F04.37 on Implantable Hearing Devices (IHDs). eq
-5
Current edition approved Nov. 1, 2005. Published November 2005. DOI: calculated as 20·log (p /2·10 Pa).
10 Q
10.1520/F2504-05.
3.4.6 equivalent sound pressure level, L ,n—logarithmic
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., Q
4th Floor, New York, NY 10036. representationofequivalentsoundpressure, L =20·log (p ).
Q 10 Q
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2504 − 05
FIG. 1 Signal Flow in the Unimplanted and IMEHD-Aided Middle Ear
3.4.7 hearing level (HL), L, n—ratiooftheinputsoundfield 3.4.16 maximum equivalent sound pressure, p ,
E,max
pressure, p , relative to the sound field pressure p at 0° n—equivalentsoundpressurethatcorrespondstothemaximum
S RETSPL
incidence that is just detectable monaurally by a normally electricaloutput E oftheimplantelectronics, p = E ·
max E,max max
hearingindividual,asdefinedinANSIS3.6,Table9,expressed H .
ES
in decibels as: L = 20·log (p /p ).
10 S RETSPL 3.4.17 maximum equivalent sound pressure level, L ,
E,max
n—logarithmic representation of the maximum equivalent
3.4.8 IMEHD electrical input at threshold E ,
threshold
-5
sound pressure L = 20·log (p /2·10 Pa).
n—electrical input to the IMEHD output transducer at thresh-
E,max 10 E,max
old of audibility.
3.4.18 sound pressure at threshold, p ,n—stimulus
threshold
sound field pressure at the threshold of audibility.
3.4.9 IMEHD harmonic distortion, n—harmonic distortion
3.4.19 stapes velocity (IMEHD-aided), v ,n—translational
ofthestapesvelocityIMEHD-aidedanalogoustoANSIS3.22,
A
velocity of the stapes when driven by the IMEHD output
Section 6.11S, from sinusoidal inputs of the frequencies 500,
transducer, specified in units of mm/s.
800, and 1600 Hz; input levels shall be E −20dB.
max
3.4.20 stapes velocity (unimplanted), v ,n—translational
U
3.4.10 IMEHD output transducer, n—electromechanical
velocityofthestapeswhendrivenbysoundinputtothemiddle
output transducer of the IMEHD.
ear specified in units of mm/s.
3.4.11 IMEHDoutputtransducerfrequencyrange, n—using
the equivalent sound pressure transfer function, H , draw a Transfer Function
ES
horizontal line at the average for 1000, 1600, and 2500 Hz,
3.4.21 acousto-electric transfer function, H ,n—electrical
SE
then subtract 20 dB, or divide by 10; the lower and the upper
input to the IMEHD output transducer E produced by a sound
bounds of the frequency response range are where the average
field, divided by the input sound field pressure p : H = E/p .
S SE S
line crosses the transfer function curve.
3.4.21.1 Discussion—H willdependontheparticulargain
SE
settings used, for example, full-on gain or minimal gain. The
3.4.12 IMEHD output transducer input, E, n—electrical
gainshouldbereportedwheneverthattransferfunctionisused.
input to the IMEHD output transducer, specified in volts or
amperes, as appropriate for the particular device.
3.4.22 acousto-vibrational transfer function (IMEHD
aided), H —stapes velocity (IMEHD aided) divided by the
SVA
3.4.13 IMEHD system frequency range, n—using the inser-
input sound field pressure: H =v /p .
SVA A S
tion gain transfer function (velocity), H , draw a horizontal
VV
3.4.22.1 Discussion—This quantity can be measured di-
line at the average for 1000, 1600, and 2500 Hz, then subtract
rectly or computed from the product of the electro-vibrational
20 dB, or divide by 10; the lower and the upper bounds of the
transfer function, H , and the acousto-electric transfer
EV
frequency response range are where the average line crosses
function, H ,measuredintheIMEHD-aidedcondition:H =
SE SVA
the transfer function curve.
v /p .
A S
3.4.14 input sound field pressure, p,n—sound stimulus
S
3.4.23 acousto-vibrational transfer function (unimplanted),
measuredinthefreefieldandpresentedtothelistenerineither
H ,n—stapes velocity (unimplanted) when driven by the
SVU
the IMEHD-aided or unimplanted condition, specified in units
input sound field, divided by the input sound field pressure:
of pascals.
H = v /p .
SVU U S
3.4.15 maximum electrical transducer input, E , 3.4.23.1 Discussion—This quantity can be measured di-
max
n—maximum electrical output of the sound signal processor, rectly or computed from the product of the middle-ear transfer
specified as peak-to-peak or root mean square value, specified function, H , and the ear-canal transfer function, H , mea-
TV ST
in volts or amperes, as appropriate for the particular device. sured in the unimplanted condition: H = v /p = H · H .
SVU U S ST TV
F2504 − 05
3.4.24 ear-canal pressure transfer function, H ,n—ear 3.5.1 IHD—implantable hearing device
ST
canal sound pressure, p , produced by the input sound field
T
3.5.2 IMEHD—implantable middle-ear hearing device
pressure, p , in the unimplanted case, divided by that input
S
3.5.3 LDV—laser Doppler vibrometry
sound field pressure: H = p /p ; this quantity is unitless (1,
ST T S
2).
3.5.4 SPL—sound pressure level
3.4.25 electro-vibrational transfer function, H ,n—stapes
EV
velocity (IMEHD-aided) when driven by the IMEHD output
4. Summary of Practice
transducer, divided by the transducer input: H = v /E.
EV A
4.1 This practice involves the use of human temporal bones
3.4.26 equivalent sound pressure transfer function, H ,
ES
and laser Doppler interferometry measurements of middle ear
n—unimplanted sound field pressure needed to produce a
structures velocities, to test for the ex-vivo performances of
stapes velocity equivalent to that produced by an electrical
IMEHD. Once a procedure for measuring system output has
IMEHD input in the IMEHD-aided condition, divided by the
been defined, several characteristics of the IMEHD can be
IMEHD input.
specified. Detailed instructions for measuring and reporting
3.4.26.1 Discussion—If the electrical IMEHD input pro-
these characteristics are given below. The important character-
duces a linear change in stapes velocity with a change in input
istics are:
electrical stimulus, the equivalent sound pressure transfer
4.1.1 For Transducers:
function, H , can be computed as the quotient between the
ES
vibro-electric transfer function (IMEHD-aided), H , and the
4.1.1.1 Equivalent sound pressure transfer function,
EV
vibro-acoustic transfer function (unimplanted), H : H =
SVU ES
4.1.1.2 IMEHD output transducer frequency range, and
(v/E)/(v/p)= H /H .
S EV SVU
4.1.1.3 IMEHD harmonic distortion.
3.4.27 insertion gain transfer function (sound field), H ,
SS
4.1.2 For the System:
n—ratio of the equivalent sound pressure produced in the
4.1.2.1 Maximum insertion gain transfer function (sound
IMEHD-aidedcasewithagivenelectricalinputtotheIMEHD
field) (see full-on gain in ANSI S3.22, paragraph 3.7),
output transducer and the input sound field pressure used as
4.1.2.2 Maximum equivalent sound pressure level (see
input in the IMEHD-aided case required to produce the same
OSPL90 in ANSI S3.22, paragraph 3.5), and
IMEHD output transducer electrical input: H = p /p ; this
SS E S
4.1.2.3 IMEHD system frequency range.
ratio is unitless.
3.4.27.1 Discussion—With a linear sound signal processor,
the insertion gain (sound field) can be computed from the 5. Significance and Use
productoftheequivalentsoundpressuretransferfunction,H ,
ES
5.1 IMEHDs are alternatives to air conduction hearing aids.
and the electro-acoustic transfer function, H : H = p /p =
SE SS E S
They are similar to air conduction hearing aids in that they
H · H . H willdependontheparticulargainsettingsused,
SE ES SS
process incoming sound by applying frequency shaping and
for example, full-on gain or minimal gain. The gain should be
compression to create an analog, vibratory audio frequency
reported whenever that transfer function is used.
output. IMEHDs differ from hearing aids in that they do not
3.4.28 insertion gain transfer function (velocity), H ,
Vv
create an airborne acoustical output signal with an electroa-
n—ratio of the stapes velocity (IMEHD-aided) and the stapes
coustical output transducer in the external ear canal, but rather
velocity (unimplanted) produced by a given input sound field:
a mechanical stimulation that results in the vibration of the
H = v /v ; the ratio is unitless and can be expressed in
VV A U
cochlear fluid. Therefore, the IMEHD output signal is not
decibels as 20·log (H ).
10 Vv
readily accessible after implantation in the way hearing aid
3.4.28.1 Discussion—With a linear sound signal processor
output is accessible with real-ear probe microphone measure-
and IMEHD, that is, a processor whose electrical output E is
ments.Differentdeviceswillusedifferentmethodsofcoupling
proportional to the input sound field pressure, p , and an
S
to the ossicular chain or cochlea. This makes it difficult to
IMEHD whose vibrational output is proportional to its electri-
designauniformmodelofthemiddleearinthewaythe2-cm
cal output, the insertion gain (sound field), H , will equal the
SS
coupler is used as a model of the external ear canal with
insertion gain transfer function (velocity), H .
VV
conventional hearing aids.
3.4.29 maximum insertion gain transfer function (sound
5.2 This practice provides uniformity of data collection
field), H ,n—maximum insertion gain transfer function
SS,max
practices, thus allowing IMEHD in vitro performances to be
(sound field) that can be achieved with the implant electronics.
evaluated and readily compared. Once clinical data are
3.4.30 middle-ear transfer function, H ,n—stapesvelocity
TV
available, the performance specifications can be augmented
(unimplanted) produced by an ear-canal sound pressure, di-
with corresponding transfer functions or results from measure-
vided by the ear-canal sound pressure, in units of mm/s/Pa:
ments in patients.
H = v /p .
TV U T
5.3 The temporal bone is a well-accepted model that relates
3.5 Acronyms:
closely to the biomechanics of the living middle ear, which is
readily relatable to hearing level. Laser Doppler vibrometry
3 providesaccuratevelocitymeasurementsintherangesrequired
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. for human hearing.
F2504 − 05
6. Procedure of the figure depict the experimental temporal bone. The filled
boxesdepictthemeasuringandIMEHDoutputtransducersand
6.1 Procedure Setup—The basic procedure is to define a
instrumentation. All measurement instrumentation shall be
method for the measurement of the insertion gain and maxi-
calibrated at least annually.
mum output of the IMEHD based on temporal bone measure-
6.2.2.2 A signal generator/analyzer produces a swept or
ments of sound-induced stapes velocity before implantation
multitone signal that drives the speaker and creates a sound in
and measurements of IMEHD-induced stapes velocity after
the auditory ear canal to allow sound-induced velocity mea-
implantation.
surements of the middle-ear transfer
...
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