Hearing impairment pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief:

Overview

Sound waves vary in amplitude and frequency. Amplitude is that the sound wave's peak pressure variation. Frequency is that the number of cycles per second of a sinusoidal component of a wave. Loss of the power to detect some frequencies, or to detect low-amplitude sounds, that an organism naturally detects, may be termed as a hearing disorder. Hearing sensitivity is indicated by the quietest sound that a person can detect, termed the hearing threshold. The normal hearing threshold is not the same for all frequencies of sounds. Long-term exposure to environmental noise, Genetics, Disease or illness, Medications[1], and Physical trauma are different biological mechanisms for hearing loss.

Pathophysiology

  • Sound waves vary in amplitude and frequency. Amplitude is that the sound wave's peak pressure variation. Frequency is that the number of cycles per second of a sinusoidal component of a wave. Loss of the power to detect some frequencies, or to detect low-amplitude sounds, that an organism naturally detects, may be termed as a hearing disorder.[2]

Loudness, frequency, and discrimination deficiencies[3]

  • Hearing sensitivity is indicated by the quietest sound that a person can detect, termed the hearing threshold. This threshold is often accurately measured by a behavioral audiogram, in humans and a few animals. A record is formed of the quietest sound that consistently prompts a response from the listener. The test is administered for sounds of various frequencies. There also are some electrophysiological tests that will be performed without requiring a behavioral response of the individual.
  • The normal hearing threshold is not the same for all frequencies of sounds. If different frequencies of sound are played at an equivalent amplitude, some are going to be loud, quiet, or completely inaudible. Generally, if the amplitude is increased, a sound is more likely to be heard. Ordinarily, when animals use sound to speak, hearing therein sort of animal is most sensitive for the frequencies produced by calls, or, within the case of humans, speech. This tuning of hearing exists at many levels of the sensory system, all the way from the physical characteristics of the ear, to the nerves, and tracts that convey the auditory impulses to the portion of the brain that is sensitive to hearing sounds.[4]
  • A hearing disorder exists when a person isn't sensitive to the sounds normally heard by its kind. The term hearing impairment is usually reserved for folks that have relative insensitivity to sound within the speech frequencies. The severity of hearing impairment is defined as; how much louder a sound must be made over the usual levels before the listener can perceive it. In profound deafness, even the loudest sounds which will be produced by the instrument wont to measure hearing like an audiometer, might not be detected.
  • There is a rare sort of hearing impairment that affects speech discrimination alone. There is another aspect to hearing that involves the quality of a sound instead of amplitude and frequency. This quality of sound is typically measured by tests of speech discrimination. These tests require that the sound isn't only detected but understood.

Different biological mechanisms

Long term exposure to environmental noise[5][6]

  • Populations of individuals living near airports or freeways are exposed to levels of noise typically > 65 dB. If the lifestyle of a person includes significant outdoor activities, these exposures over time can degrade hearing. Various states have set noise standards to guard people against these adverse sound risks.
  • The EPA has identified the extent of 70 DB for twenty-four-hour exposure because of the level necessary to guard the general public against deafness (EPA, 1974).
  • Noise-Induced deafness (NIHL) typically is centered at 4000 Hz.
  • The louder the noise is, the shorter is the safe amount of exposure. Normally, the safe amount of exposure is reduced by an element 2 for each additional 3 dB. for instance, the safe daily exposure amount at 85 dB is 8 hours, while the safe exposure at 91 dB is merely 2 hours. Sometimes, an element 2 per 5 dB is employed.
  • Personal electronic audio devices, like iPods, can produce powerful enough sound to cause significant Noise-Induced deafness, iPods often reaching 115 decibels or higher, as long as lesser intensities of even 70 dB also can cause deafness.

Genetic[7][8]

  • Hearing loss is often inherited. Both dominant and recessive genes exist which may cause mild to profound impairment. If a family features a gene for deafness it'll persist across generations because it'll happen within the offspring albeit it's inherited from just one parent. If a family had a genetic hearing disorder caused by a gene it'll not always be apparent because it will need to be passed onto offspring from both parents Dominant and recessive hearing disorders are often syndromic or non-syndromic. Recent gene mapping has identified dozens of non-syndromic dominant and recessive sorts of deafness.
  • The most common sort of congenital hearing disorder in developed countries is non-syndromic recessive, also referred to as Connexin 26 deafness.

Disease or illness[9]

  • Autoimmune disease has only recently been recognized as a possible cause of cochlear damage. Although probably rare, autoimmune processes can focus on the cochlea specifically, without symptoms affecting other organs. Wegener's granulomatosis is one of the autoimmune conditions which will precipitate deafness.
  • Presbycusis is deaf thanks to the loss of perception to high tones, mainly within the elderly people. It is caused by some to be a degenerative processes within the inner ear, although there is no proven link to aging.[10]
  • AIDS patients frequently experience sensory system anomalies.
  • Chlamydia may cause deafness in newborns to whom the disease has been passed at birth through the birth canal during normal vaginal delivery.
  • Syphilis is usually transmitted from pregnant women to their fetuses, and a few thirds of the infected children will eventually become deaf.

Medications[1]

See also Ototoxicity
  • Extremely heavy Vicodin and OxyContin abuse are understood to cause hearing disorders.

Physical trauma

  • There is often external damage either to the ear itself or to the brain centers that process the aural information conveyed by the ears.
  • People who sustain head injury are especially susceptible to deafness or tinnitus, either temporary or permanent.
  • Exposure to very bang (90 dB or more, like jet engines at close range) can cause progressive deafness. Exposure to one event of extreme bang (such as explosions) also can cause deafness. A typical source of acoustic trauma may be a too-loud music concert.

References

  1. 1.0 1.1 Lanvers-Kaminsky C, Zehnhoff-Dinnesen AA, Parfitt R, Ciarimboli G (2017). "Drug-induced ototoxicity: Mechanisms, Pharmacogenetics, and protective strategies". Clin Pharmacol Ther. 101 (4): 491–500. doi:10.1002/cpt.603. PMID 28002638.
  2. Nieman CL, Oh ES (2020). "Hearing Loss". Ann Intern Med. 173 (11): ITC81–ITC96. doi:10.7326/AITC202012010. PMID 33253610 Check |pmid= value (help).
  3. Beechey T, Buchholz JM, Keidser G (2020). "Hearing Impairment Increases Communication Effort During Conversations in Noise". J Speech Lang Hear Res. 63 (1): 305–320. doi:10.1044/2019_JSLHR-19-00201. PMID 31846598.
  4. Moser T, Starr A (2016). "Auditory neuropathy--neural and synaptic mechanisms". Nat Rev Neurol. 12 (3): 135–49. doi:10.1038/nrneurol.2016.10. PMID 26891769.
  5. Hammer MS, Swinburn TK, Neitzel RL (2014). "Environmental noise pollution in the United States: developing an effective public health response". Environ Health Perspect. 122 (2): 115–9. doi:10.1289/ehp.1307272. PMC 3915267. PMID 24311120.
  6. Carroll YI, Eichwald J, Scinicariello F, Hoffman HJ, Deitchman S, Radke MS; et al. (2017). "Vital Signs: Noise-Induced Hearing Loss Among Adults - United States 2011-2012". MMWR Morb Mortal Wkly Rep. 66 (5): 139–144. doi:10.15585/mmwr.mm6605e3. PMC 5657963. PMID 28182600.
  7. Meena R, Ayub M (2017). "Genetics Of Human Hereditary Hearing Impairment". J Ayub Med Coll Abbottabad. 29 (4): 671–676. PMID 29331002.
  8. Ahmed S, Sheraz S, Malik SA, Ahmed NR, Malik SA, Farooq S; et al. (2018). "Frequency Of Congenital Hearing Loss In Neonates". J Ayub Med Coll Abbottabad. 30 (2): 234–236. PMID 29938425.
  9. Paul A, Marlin S, Parodi M, Rouillon I, Guerlain J, Pingault V; et al. (2017). "Unilateral Sensorineural Hearing Loss: Medical Context and Etiology". Audiol Neurootol. 22 (2): 83–88. doi:10.1159/000474928. PMID 28738350.
  10. Fischer N, Weber B, Riechelmann H (2016). "[Presbycusis - Age Related Hearing Loss]". Laryngorhinootologie. 95 (7): 497–510. doi:10.1055/s-0042-106918. PMID 27392191.