Middle Ear Muscle Contractions in Response to Non-Acoustic Stimuli: The Role of Voluntary Motor Activity

Details

• Personal Author:
  Ahroon WA ; Deiters KK ; Flamme, Gregory A. ; Greene NT ; Jones HG ; Murphy, William J. ; Smith MV ; Tasko SM
• Description:
  Background: Middle ear muscle contractions (MEMCs), which are activations of the stapedius and/or tensor tympani muscles, can be elicited by a range of acoustic and non-acoustic stimuli. MEMCs can increase the impedance of the middle ear system, reducing the efficiency of sound energy transmission to the cochlea. As a result, some damage risk criteria (DRC), which estimate hearing damage from noise exposure, have assmned a protective role for MEMCs. Inclusion in DRC implies that MEMCs are pervasive within the exposed population, exhibit magnitudes sufficient to provide protection, and presence and magnitude should not be substantially altered by other variables. Studies characterizing MEMCs have largely focused on responses to acoustic stirnuli for auditory diagnosis (i.e. the acoustic reflex), while studies examining the role of nonacoustic elicitors, such as rnotor activity, are few. DRC are irnplemented in operational environments that place a range of situational and behavioral demands on the warfighter. These activities will engage motor systerns that may influence the presence and rnagnitude of MEMCs, and therefore the warfighter's noise exposure. The overall goal of this project was to examine relations between voluntary facial rnuscle activity and MEMCs. Purpose: The purpose of this study was to (1) examine the occunence rates of MEMCs in response to voluntary eye closure; (2) assess if eye closure effort influences occunence rates; and (3) assess the association between MEMC occunence rates and demographic and clinical factors in a large participant group with excellent hearing sensitivity and normal middle ear function. Background: Middle ear muscle contractions (MEMCs), which are activations of the stapedius and/or tensor tympani muscles, can be elicited by a range of acoustic and non-acoustic stimuli. MEMCs can increase the impedance of the middle ear system, reducing the efficiency of sound energy transmission to the cochlea. As a result, some damage risk criteria (DRC), which estimate hearing damage from noise exposure, have assumed a protective role for MEMCs. Inclusion in DRC implies that MEMCs are pervasive within the exposed population, exhibit magnitudes sufficient to provide protection, and presence and magnitude should not be substantially altered by other variables. Studies characterizing MEMCs have largely focused on responses to acoustic stimuli for auditory diagnosis (i.e. the acoustic reflex), while studies examining the role of non-acoustic elicitors, such as motor activity, are few. DRC are implemented in operational environments that place a range of situational and behavioral demands on the warfighter. These activities will engage motor systems that may influence the presence and magnitude of MEMCs, and therefore the warfighter's noise exposure. The overall goal of this project was to examine relations between voluntary facial muscle activity and MEMCs. Purpose: The purpose of this study was to (1) examine the occurrence rates of MEMCs in response to voluntary eye closure; (2) assess if eye closure effort influences occurrence rates; and (3) assess the association between MEMC occurrence rates and demographic and clinical factors in a large participant group with excellent hearing sensitivity and normal middle ear function. Methods: A group of 190 participants performed unilateral voluntary eye closure at different effort levels while the status of the ipsilateral ear was monitored using an otoacoustic emissions (OAE) probe. Eye closure was quantified using electromyographic (EMG) recordings of the orbicularis oculi muscle. A broad band click was delivered into the ear canal by the OAE probe at 50 ms intervals. Eye closure related changes in root-mean-square amplitude of the clicks relative to an average baseline click indicated the presence of middle ear muscle activity. A panel of judges independently identified MEMCs from a 25th percentile trace of the distribution of replicates for each participant at each eye closure effort level. Occurrence rates were estimated from these judgements and logistic regression was used to determine how experimental and participant factors influenced the likelihood of observing MEMCs. Conclusions: MEMCs were commonly observed during EMO-verified eye closure gestures. Voluntary eye EMG activity was a potent elicitor of MEMCs. MEMC occurrence rates at even moderate levels of eye muscle activity are much greater than are observed for impulse-like acoustic stimuli and MEMCs were very common at maximum levels of eye muscle activity. In conclusion, eye-related motor activity is a powerful elicitor of MEMCs that can serve as a confounding factor for auditory exposure studies. These results also complicate the interpretation of impulsive noise DRC that assume MEMCs serve as a consistent, uniform protective factor. [Description provided by NIOSH]
• Subjects:
  Ear Eye Hearing Musculoskeletal System Noise Noise, Occupational Occupational Health Safety Sense Organs
• Keywords:
  Ears Eyes Impulse Noise Muscle Contraction Muscle Function Noise Exposure
• Publisher:
  U.S. Army Aeromedical Research Laboratory (USAARL)
• Document Type:
  Text
• Funding:
  Contract
• Genre:
  Report
• Place as Subject:
  Alabama ; Ohio ; OSHA Region 4 ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DFSE - Division of Field Studies and Engineering
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-28
• NIOSHTIC Number:
  nn:20062070
• Citation:
  Fort Rucker, AL: U.S. Army Aeromedical Research Laboratory (USAARL), Technical Report 2020-44, 2020 Sep; :1-28
• Federal Fiscal Year:
  2020
• Peer Reviewed:
  False
• Source Full Name:
  Middle ear muscle contractions in response to non-acoustic stimuli: the role of voluntary motor activity
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:3dc330195d59303154ef8fe841e84bc1bcc22b74b4db34647b99f32dc8fe0cae9823fac76d070771ecc3dd877e9bca34f24390ed66a883aba5dd8e74c7deb912
• Download URL:
  https://stacks.cdc.gov/view/cdc/225388/cdc_225388_DS1.pdf
• File Type:
  [PDF - 1.90 MB ]