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Auditory fatigue

auditory fatigue, auditory fatigue definition
Auditory fatigue is defined as a temporary loss of hearing after exposure to sound This results in a temporary shift of the auditory threshold known as a temporary threshold shift TTS The damage can become permanent permanent threshold shift, PTS if sufficient recovery time is not allowed for before continued sound exposure1 When the hearing loss is rooted from a traumatic occurrence, it may be classified as noise-induced hearing loss, or NIHL

There are two main types of auditory fatigue, short-term and long-term2 These are distinguished from each other by several characteristics listed individually below

Short-term fatigue

  • full recovery from TTS can be achieved in approximately two minutes
  • the TTS is relatively independent of exposure duration23
  • TTS is maximal at the exposure frequency of the sound

Long-term fatigue

  • recovery requires a minimum of several minutes but can take up to several days
  • dependent on exposure duration and noise level23


  • 1 Physiology
    • 11 Affected anatomy
    • 12 Affected mechanisms
      • 121 Traveling wave theory
        • 1211 Classical passive system
        • 1212 Active process
      • 122 Excessive vibrations
      • 123 Recovery
    • 13 Protective measures
      • 131 Toughening and energy spread
      • 132 Substances
        • 1321 Furosemide
        • 1322 Salicylic acid
        • 1323 Antioxidants
        • 1324 Limitations
  • 2 Risk increasing factors
  • 3 Experimental studies
  • 4 References


Affected anatomyedit

Human ear anatomy

Note: The complete anatomy of the ear is extensive, and can be divided into the inner ear and outer ear The remainder of this article mainly references the cochlea, outer hair cells, and organ of Corti

In general, structural damages to any anatomical part of the ear can cause hearing-related problems Usually, minor bending of the stereocilia of the inner ear is associated with temporary hearing loss and is involved in auditory fatigue Complete loss of the stereocilia causes permanent hearing damage and is more associated with noise-induced hearing loss and other auditory diseases

The outer hair cells, or OHCs, can be thought of as microamplifiers that provide stimulation to the inner hair cells The OHCs are the most fragile of the hair cells, hence their involvement in auditory fatigue and other hearing impairments

Location of anatomical parts
Inner ear showing cochlea Cochlea showing organ of Corti Organ of Corti showing hair cells

Affected mechanismsedit

Traveling wave theoryedit

Temporary threshold shifts related to auditory fatigue are related to the amplitude of a stimulus-driven traveling wave4 This is believed to be true because the vibration propagated by the active process is not usually at the center of the maximum amplitude of this wave Instead, it is located much further down and the differences associated between them explain the shift in threshold2 The TTS that is experienced is the exhaustion of the active system located at the locus of the traveling wave driven by the cochlear amplifier described below4 Auditory fatigue can be explained by the relative activity of the active process at low-level stimulation <30 dB2

Classical passive systemedit

There are two different systems associated with the mechanics of the cochlea: the classical passive system and an active process The passive system works to stimulate the inner hair cells directly and works at levels above 40 dB4 At stimulation levels that prevent the excitation of the passive system, prolonged noise exposure results in a decrease in the loudness heard over time, even when the actual intensity of the noise has not changed2 This is caused by the exhaustion of the active process

Active processedit

The active process is also known as the cochlear amplifier This amplification increases vibrations of the basilar membrane through energy obtained from the Organ of Corti4 As the stimulation increases, it is assumed that basilar membrane displacement, caused by the traveling wave, becomes continually more basal in regards to the cochlea5 A sustained low-level stimulus can cause an energetic exhaustion of the active system which in turn prevents the passive system from activating

Excessive vibrationsedit

Currently it is believed that auditory fatigue and NIHL are related to excessive vibrations of the inner ear which may cause structural damages678 Metabolic activity is required in order to maintain the electrochemical gradients used in mechano-electrical and electro-mechanical transduction during noise exposure and sound recognition6 The metabolic activity is associated with active displacements which are components of the sound-induced vibration involving prestin, a motor protein that causes OHC motility6 Excess vibrations require increased metabolic energy

In addition, these extra vibrations can cause the formation of free radicals known as reactive oxygen species or ROS910 Elevated levels of ROS continue to increase the metabolic demands of the system These increasing demands fatigue the system and eventually lead to structural damages to the Organ of Corti611


In all cases of auditory fatigue, sufficient recovery time should allow full correction of the hearing impairment and return threshold levels to their baseline values2 There is currently no way to estimate the amount of time needed to recover from auditory fatigue because it is not usually detectable until after the injury has already occurred Studies that measured recovery time have noted that the time required is related to the magnitude of the initial hearing loss12 The most significant recovery was found to occur during the first 15 minutes following cessation of the noise exposure1314 When sufficient recovery time is not allotted, the effects become permanent, resulting in acquired noise-induced hearing loss12 Up to 120 minutes of recovery time can be required of noises of only 95 dB12 For comparison, common items that can produce noise at this level are motorcycles and subways15

Protective measuresedit

Toughening and energy spreadedit

Two protective measures have been investigated related to the amount of noise exposure and the duration of that exposure Although these would be hard to regulate in spontaneous occurrences, they could have a positive effect on work conditions if guidelines could be set for machining times or for other systems that produce loud noises over a long period of time The toughening effect is put in place by increasing the system's resistance to noise over time16 Currently, the specific mechanisms that cause the cochlear toughening are not known However, the OHCs and related processes are known to play a role17 The other toughening measure is to spread a given amount of energy to the system over a longer amount of time This would allow recovery processes to take place during the quiet interludes that are gained by increasing the exposure duration16 So far, studies have not shown a direct correlation between the amount of toughening and the amount of threshold shift experienced16 This suggests that even a toughened cochlea may not be completely protected


Both furosemide and salicylic acid are considered ototoxic at certain doses Research has been done to determine their ability to protect against auditory fatigue and permanent damage through toughening phenomena, a state described by reduced active cochlear displacements Although limited research has been done with these two substances in terms of protective drug regimes because of their associated risks, both have shown positive results in reducing auditory fatigue by the decrease in ROS formation through individual mechanisms described below618


Furosemide injections prior to noise exposure have been shown to decrease the endocochlear potential19 This decrease results in a reduction of active cochlear displacements and it is believed that the protection by furosemide stems from the limitation of excessive vibrations while the cochlear amplifier is depressed20

Salicylic acidedit

Salicylic acid competitively interferes with anion binding to OHC prestin which thereby reduces motility This reduction in active displacement is again associated with depression of the cochlear amplifier which decreases the excessive vibrations experienced during noise-exposure78911


Vitamins A, C and E have been shown to be 'free radical scavengers' by studies looking for protective tendencies of antioxidants21 In addition, NAC, or N-acetyl-L-cysteine acetylcysteine, has been shown to reduce ROS formation associated with the excessive vibrations induced by the noise exposure102223


Although auditory fatigue and NIHL protective measures would be helpful for those who are constantly exposed to long and loud noises, current research is limited due to the negative associations with the substances6 Furosemide is used in congestive heart failure treatments because of its diuretic properties Salicylic acid is a compound most frequently used in anti-acne washes, but is also an anticoagulant Further uses of these substances would need to be personalized to the individual and only under close monitoring Antioxidants do not have these negative effects and therefore are the most commonly researched substance for the purpose of protecting against auditory fatigue6 However, at this time there has been no marketed application In addition, no synergistic relationships between the drugs on the degree of reduction of auditory fatigue have been discovered at this time24

Risk increasing factorsedit

  • Physical exercise
  • Heat exposure
  • Workload
  • Ototoxic chemicals

There are several factors that may not be harmful to the auditory system by themselves, but when paired with an extended noise exposure duration have been shown to increase the risk of auditory fatigue This is important because humans will remove themselves from a noisy environment if it passes their pain threshold12 However, when paired with other factors that may not physically recognizable as damaging, TTS may be greater even with less noise exposure One such factor is physical exercise Although this is generally good for the body, combined noise exposure during highly physical activities was shown to produce a greater TTS than just the noise exposure alone2526 This could be related to the amount of ROS being produced by the excessive vibrations further increasing the metabolic activity required, which is already increased during physical exercise However, a person can decrease their susceptibility to TTS by improving their cardiovascular fitness overall12

Heat exposure is another risk factor As blood temperature rises, TTS increases when paired with high-frequency noise exposure12 It is hypothesized that hair cells for high-frequency transduction require a greater oxygen supply than others, and the two simultaneous metabolic processes can deplete any oxygen reserves of the cochlea27 In this case, the auditory system undergoes temporary changes caused by a decrease in the oxygen tension of the cochlear endolymph that leads to vasoconstriction of the local vessels28 Further research could be done to see if this is a reason for the increased TTS during physical exercise that is during continued noise-exposure as well

Another factor that may not show signs of being harmful is the current workload of a person Exposure to noise greater than 95 dB in individuals with heavy workloads was shown to cause severe TTS12 In addition, the workload was a driving factor in the amount of recovery time required to return threshold levels to their baselines12

There are some factors that are known to directly affect the auditory system Contact with ototoxic chemicals such as styrene, toluene and carbon disulfide heighten the risk of auditory damages12 Those individuals in work environments are more likely to experience the noise and chemical combination that can increase the likelihood of auditory fatigue1029 Individually, styrene is known to cause structural damages of the cochlea without actually interfering with functional capabilities10 This explains the synergistic interaction between noise and styrene because the cochlea will be increasingly damaged with the excessive vibrations of the noise plus the damage caused by the chemical itself Specifically, noise damage typically damages the first layer of the outer hair cells The combined effects of styrene and noise exposure shows damages to all three rows instead, reinforcing previous results10 Also, the combined effects of these chemicals and the noise produce greater auditory fatigue than when an individual is exposed to one factor immediately followed by the next10

It is important to understand that noise exposure itself is the main influential factor in threshold shifts and auditory fatigue, but that individuals may be at greater risk when synergistic effects take place during interactions with the above factors12

Experimental studiesedit

Studies have been carried out in humans,3031 marine mammals dolphins,32 harbour porpoises33 and harbour seals33 rodents mice,3435 rats,10 guinea pigs36373839 and chinchillas16 and fish40


  1. ^ Barbara A Bohne; Gary W Harding June 14, 1999 "Noise & Its Effects on the Ear" Noise-induced Hearing Loss Dept of Otolaryngology, Washington University School of Medicine, St Louis, MO Retrieved July 5, 2016 Parameters of Noise Which Affect Its Damage Potential 
  2. ^ a b c d e f g Charron, S, & Botte, M C 1988 Frequency-selectivity in loudness adaptation and auditory fatigue Article Journal of the Acoustical Society of America, 831, 178-187
  3. ^ a b Hirsh IJ, Bilger RC, Burns W Auditory-Threshold Recovery after Exposures to Pure Tones The Journal of the Acoustical Society of America 1955;275:1013-1013
  4. ^ a b c d Davis H An active process in cochlear mechanics Hearing Research 1983;91:79-90
  5. ^ McFadden D, Plattsmier H Exposure-induced loudness shifts and threshold shifts New Perspectives in Noise-induced Hearing Loss 1982:363-374
  6. ^ a b c d e f g Adelman, C, Perez, R, Nazarian, Y, Freeman, S, Weinberger, J, & Sohmer, H 2010 Furosemide Administered Before Noise Exposure Can Protect the Ear Article Annals of Otology Rhinology and Laryngology, 1195, 342-349
  7. ^ a b Ou HC, Bohne BA, Harding GW Noise damage in the C57BL/CBA mouse cochlea Hearing Research 2000;1451-2:111-122
  8. ^ a b Wang Y, Hirose K, Liberman MC Dynamics of Noise-Induced Cellular Injury and Repair in the Mouse Cochlea JARO - Journal of the Association for Research in Otolaryngology 2002;33:248-268
  9. ^ a b Ohlemiller KK, Wright JS, Dugan LL Early Elevation of Cochlear Reactive Oxygen Species following Noise Exposure Audiology and Neurotology 1999;45:229-236
  10. ^ a b c d e f g Chen GD, Henderson D 2009 "Cochlear injuries induced by the combined exposure to noise and styrene" Hearing Research 254 1-2: 25–33 ISSN 0378-5955 doi:101016/jheares200904005 
  11. ^ a b Henderson D, Bielefeld E, Harris K, Hu B The role of oxidative stress in noise-induced hearing loss Ear Hear 2006;27:1 - 19
  12. ^ a b c d e f g h i j Chen C-J, Dai Y-T, Sun Y-M, Lin Y-C, Juang Y-J Evaluation of Auditory Fatigue in Combined Noise, Heat and Workload Exposure Industrial Health 2007;454:527-534
  13. ^ Ward WD Temporary threshold shift and damage-risk criteria for intermittent noise exposures Journal of the Acoustical Society of America 197048:561-574
  14. ^ Ward WD Recovery from high values of temporary threshold shift Journal of the Acoustical Society of America 197032:497-500
  15. ^ <"Archived copy" Archived from the original on 2010-12-14 Retrieved 2010-12-05 >
  16. ^ a b c d <Hamernik RP, Ahroon WA Interrupted noise exposures: Threshold shift dynamics and permanent effects The Journal of the Acoustical Society of America 1998;1036:3478-3488
  17. ^ Zheng X-Y, Henderson D, McFadden SL, Hu B-H The role of the cochlear efferent system in acquired resistance to noise-induced hearing loss Hearing Research 1997;1041-2:191-203
  18. ^ Adelman C, Freeman S, Paz Z, Sohmer H Salicylic acid injection before noise exposure reduces permanent threshold shift Audiol Neurootol 2008;13:266 - 272
  19. ^ Ruggero M, Rich N Furosemide alters organ of corti mechanics: evidence for feedback of outer hair cells upon the basilar membrane J Neurosci 1991;11:1057 - 1067
  20. ^ Ikeda K, Morizono T Effect of albumin-bound furosemide on the endocochlear potential of the chinchilla Alleviation of furosemide-induced ototoxicity Arch Otolaryngol Head Neck Surg 1989;115:500 - 502
  21. ^ Le Prell CG, Hughes LF, Miller JM Free radical scavengers vitamins A, C, and E plus magnesium reduce noise trauma Free Radical Biology and Medicine 2007;429:1454-1463
  22. ^ Bielefeld E, Kopke R, Jackson R, Coleman J, Liu J, Henderson D Noise protection with N-acetyl-l-cysteine NAC using a variety of noise exposures, NAC doses, and routes of administration Acta Otolaryngol 2007;127:914 - 919
  23. ^ Kopke RD, Jackson RL, Coleman JKM, Liu J, Bielefeld EC, Balough BJ NAC for noise: From the bench top to the clinic Hearing Research 2007;2261-2:114-125
  24. ^ Tamir S, Adelman C, Weinberger J, Sohmer H Uniform comparison of several drugs which provide protection from noise induced hearing loss Journal of Occupational Medicine and Toxicology 2010;51:26
  25. ^ Lindgren F, Axelsson A The Influence of Physical Exercise on Susceptibility to Noise-Induced Temporary Threshold Shift Scandinavian Audiology 1988;171:11-17
  26. ^ <Miani C, Bertino G, Francescato M, di Prampero P, Staffieri A Temporary Threshold Shift Induced by Physical Exercise Scandinavian Audiology 1996;253:179-186
  27. ^ Miller J, Ren T, Dengerink H, Nuttall A Cochlear blood flow changes with short sound stimulation Scientific Basis of Noise-Induced Hearing Loss 1996:95-109
  28. ^ Axelsson A, Vertes D, Miller J Immediate Noise Effects on Cochlear Vasculature in the Guinea Pig Acta Oto-Laryngol 1981;911-6:237-246
  29. ^ Mizoue T, Miyamoto T, Simizu T Combined effect of smoking and occupational exposure to noise on hearing loss in steel factory workers Occupational and Environmental Medicine 2003; 60:56-59
  30. ^ Lin, C Y, Wu, J L, Shih, T S, Tsai, P J, Sun, Y M, & Guo, Y L 2009 Glutathione S-transferase M1, T1, and P1 polymorphisms as susceptibility factors for noise-induced temporary threshold shift Hearing Research, 2571-2, 8-15 doi:101016/jheares200907008
  31. ^ Melnick, W 1991 HUMAN TEMPORARY THRESHOLD SHIFT TTS AND DAMAGE RISK Journal of the Acoustical Society of America, 901, 147-154
  32. ^ Finneran, J J, & Schlundt, C E 2010 Frequency-dependent and longitudinal changes in noise-induced hearing loss in a bottlenose dolphin Tursiops truncatus L Journal of the Acoustical Society of America, 1282, 567-570 doi:101121/13458814
  33. ^ a b Kastelein, R, Gransier, R, van Mierlo, R, Hoek, L, & de Jong, C 2011 Temporary hearing threshold shifts and recovery in a harbor porpoise Phocoena phocoena and harbor seals Phoca vitulina exposed to white noise in a 1/1‐octave band around 4 kHz The Journal of the Acoustical Society of America, 129, 2432
  34. ^ Groschel, M, Gotze, R, Ernst, A, & Basta, D 2010 Differential Impact of Temporary and Permanent Noise-Induced Hearing Loss on Neuronal Cell Density in the Mouse Central Auditory Pathway Article Journal of Neurotrauma, 278, 1499-1507 doi:101089/neu20091246
  35. ^ Housley GD et al, "ATP-gated ion channels mediate adaptation to elevated sound levels" Proc Natl Acad Sci U S A 2013 Apr 30; 11018:79=494-9
  36. ^ Fetoni, A R, Mancuso, C, Eramo, S L M, Ralli, M, Piacentini, R, Barone, E, et al 2010 IN VIVO PROTECTIVE EFFECT OF FERULIC ACID AGAINST NOISE-INDUCED HEARING LOSS IN THE GUINEA-PIG Neuroscience, 1694, 1575-1588 doi:101016/jneuroscience201006022
  37. ^ Gourevitch, B, Doisy, T, Avillac, M, & Edeline, J M 2009 Follow-up of latency and threshold shifts of auditory brainstem responses after single and interrupted acoustic trauma in guinea pig Brain Research, 1304, 66-79 doi:101016/jbrainres200909041
  38. ^ Chen, Y S, Tseng, F Y, Lin, K N, Yang, T H, Lin-Shiau, S Y, & Hsu, C J 2008 Chronologic Changes of Nitric Oxide Concentration in the Cochlear Lateral Wall and Its Role in Noise-Induced Permanent Threshold Shift Laryngoscope, 1185, 832-836 doi:101097/MLG0b013e3181651c24
  39. ^ Yamashita, D, Minami, S B, Kanzaki, S, Ogawa, K, & Miller, J M 2008 Bcl-2 genes regulate noise-induced hearing loss Journal of Neuroscience Research, 864, 920-928 doi:101002/jnr21533
  40. ^ Popper, A N, Halvorsen, M B, Miller, D, Smith, M E, Song, J, Wysocki, L E, & Stein, P 2005 Effects of surveillance towed array sensor system SURTASS low frequency active sonar on fish The Journal of the Acoustical Society of America, 117, 2440

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