ASTM F2504-05(2014)
(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
5.1 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.
5.2 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.
5.3 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.
1.4 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)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: F2504 − 05 (Reapproved 2014)
Standard Practice for
Describing System Output of Implantable Middle Ear
1
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
2.1 ANSI Standards: RETSPL
normally hearing individual, as defined inANSIS3.6, Table9,
ANSI 3.6Specification for Audiometers
expressed in decibels: L = 20·log (p /p ).
ANSI 3.7 Method for Coupler Calibration of Earphones H 10 Q RETSPL
ANSI 3.22Specification of Hearing Aid Characteristics
3.4.5 equivalent sound pressure, p ,n—unimplanted input
Q
sound field pressure needed to produce a stapes velocity equal
3. Terminology
to that produced by a specified IMEHD input in the IMEHD-
3.1 RefertotheblockdiagramofFig.1foraclarificationof
aided condition: p = E · H .
Q ES
the mathematical notations used in this section.
3.4.5.1 Discussion—The equivalent sound pressure is the
productoftheequivalentsoundpressuretransferfunction,H ,
ES
1
ThispracticeisunderthejurisdictionofASTMCommitteeF04onMedicaland
and the IMEHD output transducer electrical input E: p = E ·
Q
Surgical Materials and Devices and is the direct responsibility of Subcommittee
H . The equivalent sound pressure can be expressed as
ES
F04.37 on Implantable Hearing Devices (IHDs).
equivalent sound pressure level in units of decibels, SPL ,
Current edition approved March 1, 2014. Published April 2014. Originally eq
-5
approved in 2005. Last previous edition approved in 2005 as F2504 – 05. DOI: calculated as 20·log (p /2·10 Pa).
10 Q
10.1520/F2504-05R14.
2 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, http://www.ansi.org. 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
1
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F2504 − 05 (2014)
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
in
...
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