Temporary and Permanent Noise-induced Threshold Shifts

Abstract

Objective To review basic and clinical findings relevant to defining temporary (TTS) and permanent (PTS) threshold shifts and their sequelae. Data Sources Relevant scientific literature and government definitions were broadly reviewed. Data Synthesis The definitions and characteristics of TTS and PTS were assessed and recent advances that expand our knowledge of the extent, nature and consequences of noise-induced hearing loss were reviewed. Conclusions Exposure to intense sound can produce TTS, acute changes in hearing sensitivity that recover over time, or PTS, a loss that does not recover to pre-exposure levels. In general, a threshold shift ≥10 dB at 2, 3 and 4 kHz is required for reporting purposes in human studies. The high-frequency regions of the cochlea are most sensitive to noise damage. Resonance of the ear canal also results in a frequency region of high noise sensitivity at 4–6 kHz. A primary noise target is the cochlear hair cell. While the mechanisms that underlie such hair cell damage remain unclear, there is evidence to support a role for reactive oxygen species, stress pathway signaling and apoptosis. Another target is the synapse between the hair cell and the primary afferent neurons. Large numbers of these synapses and their neurons can be lost after noise, even though hearing thresholds may return to normal. This affects auditory processing and detection of signals in noise. The consequences of TTS and PTS include significant deficits in communication that can impact performance of military duties or obtaining/retaining civilian employment. Tinnitus and exacerbation of post-traumatic stress disorder are also potential sequelae.

Effects of noise exposure on auditory brainstem response and speech-in-noise tasks: a review of the literature

“…Hearing loss that occurs after exposure to loud sound may recover, in which case it is a temporary threshold shift (TTS) or the hearing loss may not resolve, in which case it is a permanent threshold shift (PTS) (for review, see Ryan et al 2016). The classic literature on human TTS includes the measurement of TTS 2 minutes after the end of the noise exposure (TTS 2 ) (Yates, Ramsey, and Holland 1976;Stephenson and Wall 1984).…”

Otoprotectants: From Research to Clinical Application

“…Although there is not yet good consensus around clinical test paradigms and primary outcomes, active discussions and efforts to derive consensus are underway. [135][136][137] NIHL and DIHL are clinically significant issues, and given the number of agents of interest with positive preclinical supporting data, there is good reason to hope that one or more otoprotective agents will ultimately be effective in clinical testing and approved by the FDA. Because some of the active agents discussed in this review can be purchased over the counter (OTC) as dietary supplements (i.e., b-carotene, vitamins C and E, magnesium, NAC, coenzyme Q10, L-met), some patients may question whether they should take dietary supplements.…”

The Role of Powered Surgical Instruments in Ear Surgery: An Acoustical Blessing or a Curse?

“…The vast majority of studies have focused on noised-induced hearing loss, which is a clear subcategory of sensorineural hearing loss, while vibrations, or more precisely, skull vibrations, have garnered much less attention until recently and deserve further study and consideration. Such hearing loss is measured based on the degree to which the hearing threshold sensitivity has risen and is classified as either a permanent threshold shift or a temporary threshold shift [2]. Most sensorineural hearing loss caused by powered surgical instruments fortunately falls into the temporary threshold shift category.…”