Pure-tone audiometry

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Pure tone audiometry
HumanEar.jpg
Diagram of the human ear
ICD-9-CM 95.41
MeSH D001301

Pure-tone audiometry is the main hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss [1] [2] and thus providing a basis for diagnosis and management. Pure-tone audiometry is a subjective, behavioural measurement of a hearing threshold, as it relies on patient responses to pure tone stimuli. [3] Therefore, pure-tone audiometry is only used on adults and children old enough to cooperate with the test procedure. As with most clinical tests, standardized calibration of the test environment, the equipment and the stimuli is needed before testing proceeds (in reference to ISO, ANSI, or other standardization body). Pure-tone audiometry only measures audibility thresholds, rather than other aspects of hearing such as sound localization and speech recognition. However, there are benefits to using pure-tone audiometry over other forms of hearing test, such as click auditory brainstem response (ABR). [3] Pure-tone audiometry provides ear specific thresholds, and uses frequency specific pure tones to give place specific responses, so that the configuration of a hearing loss can be identified. As pure-tone audiometry uses both air and bone conduction audiometry, the type of loss can also be identified via the air-bone gap. Although pure-tone audiometry has many clinical benefits, it is not perfect at identifying all losses, such as ‘dead regions’ of the cochlea and neuropathies such as auditory processing disorder (APD). [4] [5] [6] This raises the question of whether or not audiograms accurately predict someone's perceived degree of disability.

Contents

Pure-tone audiometry procedural standards

The current International Organization for Standardization (ISO) standard for pure-tone audiometry is ISO:8253-1, which was first published in 1983. [7] The current American National Standards Institute (ANSI) standard for pure-tone audiometry is ANSI/ASA S3.21-2004, prepared by the Acoustical Society of America.

In the United Kingdom, The British Society of Audiology (BSA) is responsible for publishing the recommended procedure for pure-tone audiometry, as well as many other audiological procedures. The British recommended procedure is based on international standards. Although there are some differences, the BSA-recommended procedures are in accordance with the ISO:8253-1 standard. The BSA-recommended procedures provide a "best practice" test protocol for professionals to follow, increasing validity and allowing standardisation of results across Britain. [8]

In the United States, the American Speech–Language–Hearing Association (ASHA) published Guidelines for Manual Pure-Tone Threshold Audiometry in 2005.

Variations

There are cases where conventional pure-tone audiometry is not an appropriate or effective method of threshold testing. Procedural changes to the conventional test method may be necessary with populations who are unable to cooperate with the test in order to obtain hearing thresholds. Sound field audiometry may be more suitable when patients are unable to wear earphones, as the stimuli are usually presented by loudspeaker. A disadvantage of this method is that although thresholds can be obtained, results are not ear specific. In addition, response to pure tone stimuli may be limited, because in a sound field pure tones create standing waves, which alter sound intensity within the sound field. Therefore, it may be necessary to use other stimuli, such as warble tones in sound field testing. [9] There are variations of conventional audiometry testing that are designed specifically for young children and infants, such as behavioral observation audiometry, visual reinforcement audiometry and play audiometry. [10] [11]

Conventional audiometry tests frequencies between 250 hertz (Hz) and 8 kHz, whereas high frequency audiometry tests in the region of 8 kHz-16 kHz. Some environmental factors, such as ototoxic medication and noise exposure, appear to be more detrimental to high frequency sensitivity than to that of mid or low frequencies. Therefore, high frequency audiometry is an effective method of monitoring losses that are suspected to have been caused by these factors. It is also effective in detecting the auditory sensitivity changes that occur with aging. [12]

Cross hearing and interaural attenuation

Interaural attenuation with bone conduction BONE CONDUCTION.jpg
Interaural attenuation with bone conduction

When sound is applied to one ear the contralateral cochlea can also be stimulated to varying degrees, via vibrations through the bone of the skull. When the stimuli presented to the test ear stimulates the cochlea of the non-test ear, this is known as cross hearing. Whenever it is suspected that cross hearing has occurred it is best to use masking. This is done by temporarily elevating the threshold of the non-test ear, by presenting a masking noise at a predetermined level. This prevents the non-test ear from detecting the test signal presented to the test ear. The threshold of the test ear is measured at the same time as presenting the masking noise to the non-test ear. Thus, thresholds obtained when masking has been applied, provide an accurate representation of the true hearing threshold level of the test ear. [13]

A reduction or loss of energy occurs with cross hearing, which is referred to as interaural attenuation (IA) or transcranial transmission loss. [13] IA varies with transducer type. It varies from 40 dB to 80 dB with supra-aural headphones. However, with insert earphones it is in the region of 55 dB. The use of insert earphones reduces the need for masking, due to the greater IA which occurs when they are used (See Figure 1). [14]

Air conduction results in isolation, give little information regarding the type of hearing loss. When the thresholds obtained via air conduction are examined alongside those achieved with bone conduction, the configuration of the hearing loss can be determined. However, with bone conduction (performed by placing a vibrator on the mastoid bone behind the ear), both cochleas are stimulated. IA for bone conduction ranges from 0-20 dB (See Figure 2). Therefore, conventional audiometry is ear specific, with regards to both air and bone conduction audiometry, when masking is applied.

Pure-tone audiometry thresholds and hearing disability

Pure-tone audiometry is described as the gold standard for assessment of a hearing loss [15] but how accurate pure-tone audiometry is at classifying the hearing loss of an individual, in terms of hearing impairment and hearing disability is open to question. Hearing impairment is defined by the World Health Organization (WHO) as a hearing loss with thresholds higher than 25db in one or both ears. The degree of hearing loss is classified as mild, moderate, severe or profound. [16] The results of pure-tone audiometry are however a very good indicator of hearing impairment.

Hearing disability is defined by the WHO as a reduction in the ability to hear sounds in both quiet and noisy environments (compared to people with normal hearing), which is caused by a hearing impairment. [17] Several studies have investigated whether self-reported hearing problems (via questionnaires and interviews) were associated with the results from pure-tone audiometry. The findings of these studies indicate that in general, the results of pure-tone audiometry correspond to self-reported hearing problems (i.e. hearing disability). However, for some individuals this is not the case; the results of pure-tone audiometry only, should not be used to ascertain an individual's hearing disability. [18] [19]

Figure 10: Speech recognition threshold (SRT) with noise. To aid explanation of this concept the CHL and the SNHL have the same magnitude of hearing loss (50 dBHL). The horizontal part of the curves is where the noise is inaudible. Thus, there is no masking effect on the SRT. The horizontal portion of the curve for the SNHL and CHL extends further than that for a normal hearing person, as the noise needs to become audible to become a problem. Thus, more noise has to be applied, to produce a masking effect. At the right hand side of the graph, to identify 50% of the speech correctly, the speech needs to much more intense than in the quiet. This is because at this end of the graph, the noise is very loud whether the person has a hearing loss or not. There is a transition between these two areas described. Factor A is a problem only in low noise levels, whereas Factor D is a problem when the noise level is high. Speech recognition threshold in noise2.jpg
Figure 10: Speech recognition threshold (SRT) with noise. To aid explanation of this concept the CHL and the SNHL have the same magnitude of hearing loss (50 dBHL). The horizontal part of the curves is where the noise is inaudible. Thus, there is no masking effect on the SRT. The horizontal portion of the curve for the SNHL and CHL extends further than that for a normal hearing person, as the noise needs to become audible to become a problem. Thus, more noise has to be applied, to produce a masking effect. At the right hand side of the graph, to identify 50% of the speech correctly, the speech needs to much more intense than in the quiet. This is because at this end of the graph, the noise is very loud whether the person has a hearing loss or not. There is a transition between these two areas described. Factor A is a problem only in low noise levels, whereas Factor D is a problem when the noise level is high.

Hearing impairment (based on the audiogram) and auditory handicap (based on speech discrimination in noise) data was reviewed by Reinier Plomp [ who? ]. This led to the formulation of equations, which described the consequences of a hearing loss on speech intelligibility. The results of this review indicated that there were two factors of a hearing loss, which were involved in the effect on speech intelligibility. These factors were named Factor A and Factor D. Factor A affected speech intelligibility by attenuating the speech, whereas Factor D affected speech intelligibility by distorting the speech. [20]

Speech recognition threshold (SRT) is defined as the sound pressure level at which 50% of the speech is identified correctly. For a person with a conductive hearing loss (CHL) in quiet, the SRT needs to be higher than for a person with normal hearing. The increase in SRT depends on the degree of hearing loss only, so Factor A reflects the audiogram of that person. In noise, the person with a CHL has the same problem as the person with normal hearing (See Figure 10). [20]

For a person with a Sensorineural hearing loss (SNHL) in quiet, the SRT also needs to be higher than for a person with normal hearing. This is because the only factor that is important in quiet for a CHL and a SNHL is the audibility of the sound, which corresponds to Factor A. In noise, the person with a SNHL requires a better signal-to-noise ratio to achieve the same performance level, as the person with normal hearing and the person with a CHL. This shows that in noise, Factor A is not enough to explain the problems of a person with a SNHL. Therefore, there is another problem present, which is Factor D. At present, it is not known what causes Factor D. Thus, in noise the audiogram is irrelevant. It is the type of hearing loss that is important in this situation. [20]

These findings have important implications for the design of hearing aids. As hearing aids at present can compensate for Factor A, but this is not the case for Factor D. This could be why hearing aids are not satisfactory for a lot of people. [20]

Audiograms and hearing loss

The shape of the audiogram resulting from pure-tone audiometry gives an indication of the type of hearing loss as well as possible causes. Conductive hearing loss due to disorders of the middle ear shows as a flat increase in thresholds across the frequency range. Sensorineural hearing loss will have a contoured shape depending on the cause. Presbycusis or age-related hearing loss for example is characterized by a high frequency roll-off (increase in thresholds). Noise-induced hearing loss has a characteristic notch at 4000 Hz. Other contours may indicate other causes for the hearing loss.

See also

Related Research Articles

Otosclerosis Condition characterized by an abnormal bone growth in the middle ear

Otosclerosis is a condition of the middle ear where one or more foci of irregularly laid spongy bone replace part of normally dense enchondral layer of bony otic capsule in the bony labyrinth. This condition affects one of the ossicles resulting in hearing loss, tinnitus, vertigo or a combination of symptoms. The term otosclerosis is something of a misnomer. Much of the clinical course is characterized by lucent rather than sclerotic bony changes, so the disease is also known as otospongiosis.

Hearing test

A hearing test provides an evaluation of the sensitivity of a person's sense of hearing and is most often performed by an audiologist using an audiometer. An audiometer is used to determine a person's hearing sensitivity at different frequencies. There are other hearing tests as well, e.g., Weber test and Rinne test.

Acoustic reflex Small muscle contraction in the middle ear in response to loud sound

The acoustic reflex is an involuntary muscle contraction that occurs in the middle ear in response to loud sound stimuli or when the person starts to vocalize.

Conductive hearing loss Medical condition

Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles). If a conductive hearing loss occurs in conjunction with a sensorineural hearing loss, it is referred to as a mixed hearing loss. Depending upon the severity and nature of the conductive loss, this type of hearing impairment can often be treated with surgical intervention or pharmaceuticals to partially or, in some cases, fully restore hearing acuity to within normal range. However, cases of permanent or chronic conductive hearing loss may require other treatment modalities such as hearing aid devices to improve detection of sound and speech perception.

Sensorineural hearing loss Hearing loss caused by an inner ear or vestibulocochlear nerve defect

Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ or the vestibulocochlear nerve. SNHL accounts for about 90% of reported hearing loss. SNHL is usually permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat.

An otoacoustic emission (OAE) is a sound that is generated from within the inner ear. Having been predicted by Austrian astrophysicist Thomas Gold in 1948, its existence was first demonstrated experimentally by British physicist David Kemp in 1978, and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear. Studies have shown that OAEs disappear after the inner ear has been damaged, so OAEs are often used in the laboratory and the clinic as a measure of inner ear health.

Audiometry is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or distinguish speech from background noise. Acoustic reflex and otoacoustic emissions may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear, and often make use of an audiogram.

Auditory neuropathy (AN) is a hearing disorder in which the outer hair cells of the cochlea are present and functional, but sound information is not transmitted sufficiently by the auditory nerve to the brain. Hearing loss with AN can range from normal hearing sensitivity to profound hearing loss.

Presbycusis, or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although differentiating the individual effects of distinct causes of hearing loss can be difficult.

Audiogram Graph showing audible frequencies

An audiogram is a graph that shows the audible threshold for standardized frequencies as measured by an audiometer. The Y axis represents intensity measured in decibels and the X axis represents frequency measured in hertz. The threshold of hearing is plotted relative to a standardised curve that represents 'normal' hearing, in dB(HL). They are not the same as equal-loudness contours, which are a set of curves representing equal loudness at different levels, as well as at the threshold of hearing, in absolute terms measured in dB SPL.

Audiometer Machine used to evaluate hearing acuity

An audiometer is a machine used for evaluating hearing acuity. They usually consist of an embedded hardware unit connected to a pair of headphones and a test subject feedback button, sometimes controlled by a standard PC. Such systems can also be used with bone vibrators, to test conductive hearing mechanisms.

Hearing range Range of frequencies that can be heard by humans or other animals

Hearing range describes the range of frequencies that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, although there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. Sensitivity also varies with frequency, as shown by equal-loudness contours. Routine investigation for hearing loss usually involves an audiogram which shows threshold levels relative to a normal.

The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors.

Auditory masking occurs when the perception of one sound is affected by the presence of another sound.

Hearing Sensory perception of sound by living organisms

Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory science.

Bone-conduction auditory brainstem response or BCABR is a type of auditory evoked response that records neural response from EEG with stimulus transmitted through bone conduction.

Visual reinforcement audiometry (VRA) is a key behavioural test for evaluating hearing in young children. First introduced by Liden and Kankkunen in 1969, VRA is a good indicator of how responsive a child is to sound and speech and whether the child is developing awareness to sound as expected. Performed by an audiologist, VRA is the preferred behavioral technique for children that are 6 – 24 months of age. Using classic operant conditioning, a stimulus is presented, which is followed by a 90 degree head turn from midline by the child, resulting in the child being reinforced with an animation. The child is typically seated in a high chair or on a parent's lap while facing forward. A loud speaker or two are situated at 45 or 90 degrees from the child. As the auditory stimulus is presented, the child will naturally search for the sound source, resulting in a head turn and reinforcement is followed shortly after through an animated toy or video next to the speaker where the auditory stimulus was presented. Using VRA, an audiologist can obtain minimal hearing thresholds ranging in frequencies from 250 Hz - 8000 Hz using speakers, headphones, inserts earphones or through a bone conduction transducer and plot them on an audiogram. The results from the audiogram, paired with other objective measures such as a Tympanogram, Otoacoustic emissions testing and/or Auditory Brainstem Response testing can provide further insight into the child's auditory hearing status as well as future treatment plans if deemed necessary. VRA works well until about 18–24 months of age. Above 18–24 months of age, children need more interesting tasks to hold their attention, which is when audiologists introduce Conditioned Play Audiometry.

Tone decay test

The tone decay test is used in audiology to detect and measure auditory fatigue. It was developed by Raymond Carhart in 1957. In people with normal hearing, a tone whose intensity is only slightly above their absolute threshold of hearing can be heard continuously for 60 seconds. The tone decay test produces a measure of the "decibels of decay", i.e. the number of decibels above the patient's absolute threshold of hearing that are required for the tone to be heard for 60 seconds. A decay of between 15 and 20 decibels is indicative of cochlear hearing loss. A decay of more than 25 decibels is indicative of damage to the vestibulocochlear nerve.

Acoustic trauma is the sustainment of an injury to the eardrum as a result of a very loud noise. Its scope usually covers loud noises with a short duration, such as an explosion, gunshot or a burst of loud shouting. Quieter sounds that are concentrated in a narrow frequency may also cause damage to specific frequency receptors. The range of severity can vary from pain to hearing loss.

Diagnosis of hearing loss

Identification of a hearing loss is usually conducted by a general practitioner medical doctor, otolaryngologist, certified and licensed audiologist, school or industrial audiometrist, or other audiometric technician. Diagnosis of the cause of a hearing loss is carried out by a specialist physician or otorhinolaryngologist.

References

  1. ↑ Audiology Pure-Tone Testing at eMedicine
  2. ↑ Roeser, Ross J. (2013). Roeser's audiology desk reference (2nd ed.). New York: Thieme. ISBN   9781604063981. OCLC   704384422.
  3. 1 2 Handbook of clinical audiology. Katz, Jack., Burkard, Robert, 1953-, Medwetsky, Larry. (5th ed.). Philadelphia: Lippincott Williams & Wilkins. 2002. ISBN   0683307657. OCLC   47659401.{{cite book}}: CS1 maint: others (link)
  4. ↑ Moore, BC (April 2004). "Dead regions in the cochlea: conceptual foundations, diagnosis, and clinical applications". Ear and Hearing. 25 (2): 98–116. doi:10.1097/01.aud.0000120359.49711.d7. PMID   15064655.
  5. ↑ Moore BCJ (2001). "Dead Regions in the Cochlea: Diagnosis, Perceptual Consequences, and Implications for the Fitting of hearing aids". Trends Amplif. 5 (1): 1–34. doi:10.1177/108471380100500102. PMC   4168936 . PMID   25425895.
  6. ↑ Landegger, LD; Psaltis, D; Stankovic, KM (May 2016). "Human audiometric thresholds do not predict specific cellular damage in the inner ear". Hearing Research. 335: 83–93. doi:10.1016/j.heares.2016.02.018. PMC   5970796 . PMID   26924453.
  7. ↑ "ISO 6189:1983" . Retrieved 18 November 2019.
  8. ↑ Recommended Procedure: Pure-tone air-conduction and bone-conduction threshold audiometry with and without masking (PDF). Bathgate, UK: British Society of Audiology. 2011. Retrieved 18 November 2019.
  9. ↑ http://www.emedicine.com/ent/topic311.htm [Accessed on 27/02/07]
  10. ↑ http://michiganotoplasty.com/understanding-deafness-pta-testing/ Archived 2015-07-22 at the Wayback Machine [Accessed on 07/18/15].
  11. ↑ "Hearing Testing and Screening in Young Children". patient.info. Retrieved 16 November 2014.
  12. ↑ Monteiro de Castro Silva, I; Feitosa, MA (2005). "High-frequency audiometry in young and older adults when conventional audiometry is normal". Brazilian Journal of Otorhinolaryngology. 72 (5): 665–72. doi: 10.1590/S0034-72992006000500014 . PMID   17221060.
  13. 1 2 Katz J. Clinical Handbook of Audiology. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2002.
  14. ↑ Bagatto, M; Moodie, S; Scollie, S; Seewald, R; Moodie, S; Pumford, J; Liu, KP (2005). "Clinical protocols for hearing instrument fitting in the Desired Sensation Level method". Trends in Amplification. 9 (4): 199–226. doi:10.1177/108471380500900404. PMC   4111495 . PMID   16424946.
  15. ↑ Sindhusake D, Mitchell P, Smith W, Golding M, Newall P, Hartley D, et al. Validation of self-reported hearing loss. The Blue Mountains Hearing Study. Int. J. Epidemiol. 2001;30:1371-78.
  16. ↑ "Deafness and hearing loss Fact sheet N°300". WHO (World Health Organization). Retrieved 16 November 2014.
  17. ↑ "Sound Advice". Sound Advice Safety and Health Ltd. Retrieved 10 May 2016.
  18. ↑ Hietamen A, Era P, Henrichsen J, Rosenhall U, Sorri M, Heikkinen E. Hearing among 75-year old people in three Nordic localities: A comparative study. Int. J. Audiol. 2004;44:500-08.
  19. ↑ Uchida Y, Nakashima T, Ando F, Niino N, Shimokata H. Prevalence of Self-perceived Auditory Problems and their Relation to Audiometric Thresholds in a Middle-aged to Elderly Population. Acta. Otolaryngol. 2003;123:618-26.
  20. 1 2 3 4 Plomp, R (February 1978). "Auditory handicap of hearing impairment and the limited benefit of hearing aids". The Journal of the Acoustical Society of America. 63 (2): 533–49. doi:10.1121/1.381753. PMID   670550.
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