Clinical Trial: Effects of Infrasound Exposure on Measures of Endolymphatic Hydrops

Study Status: Not yet recruiting
Recruit Status: Not yet recruiting
Study Type: Observational

Official Title: Effects of Infrasound Exposure on Measures of Endolymphatic Hydrops

Brief Summary: Persons exposed to infrasound - frequencies below 20 Hz - describe a variety of troubling audiovestibular symptoms, but the underlying mechanisms are not understood. Recent animal studies, however, provide evidence that short-term exposure to low frequency sound induces transient endolymphatic hydrops. The existence of this effect has not been studied in humans. The long-term objective of this research is to identify a possible mechanism to describe the effects of infrasound on the human inner ear. The central hypothesis of the proposed study is that short-term infrasound exposure induces transient endolymphatic hydrops in humans. This will be tested by performing electrophysiologic tests indicative of endolymphatic hydrops among normal hearing individuals before and immediately after a period of infrasound exposure. Recordings of infrasound generated by wind turbines in the field have been established and calibrated by this team of engineers, otologist, and hearing and balance scientists. An infrasound generator reproduces the acoustic signature based on these field recordings. Aim 1: Determine the effect of infrasound on the summating potential to action potential (SP/AP) ratio on electrocochleography (ECoG). Hypothesis 1: Infrasound exposure will cause a reversible elevation of the SP/AP ratio. Aim 2: Determine the effect of infrasound on the threshold response curves of ocular and cervical vestibular evoked myogenic potentials. (oVEMP and cVEMP). Hypothesis 2: Infrasound exposure will cause elevation of the oVEMP and cVEMP thresholds at the frequency of best response. Successful completion of the aims will provide evidence for a possible mechanism of the effect of infrasound on the inner ear. This understanding will benefit individuals exposed to environmental infrasound and those in regulatory, research, and advocacy roles when crafting interventions and future policy.

Detailed Summary:

Infrasound is generated within the human body by processes such as respiration and myocardial contraction. External sources include those produced naturally, such as wind and earthquakes, and those that are human-made, such as automobile engines and heavy machinery. Wind turbines are known to emit infrasound with a fundamental frequency of 1 Hz with intensities approaching 100 decibels (dB), depending on wind speed. Over 75,000 wind turbines have been deployed between 2003 and 2015 in the U.S. alone. As environmental infrasound exposure has increased in prevalence and intensity with the advent of technologies such as large-scale wind turbines, renewed attention has been directed to the effects of infrasound on exposed individuals.

As it falls below audible thresholds, conventional wisdom would dictate that infrasound does not affect humans. However, some individuals living in proximity to wind turbines experience increased levels of annoyance and sleep disturbance in a dose-response fashion. Other reported symptoms from infrasound exposure include aural fullness, tinnitus, dizziness, and vertigo. Some researchers hypothesize that these otologic symptoms are related to the infrasonic component of wind turbine noise affecting inner ear function. However, since the mechanism or causal role have yet to be established, others attribute such symptoms to a psychosomatic or "nocebo" effect (i.e. worsening symptoms produced by negative expectations). As wind farms and other infrasound-generating sources become widespread, there is now a critical need to determine the effects of infrasound on inner ear function.

Studies conducted in humans have confirmed that infrasound has measurable effects within the cochlea. Hensel et al presented infrasound tones of 6 and 12 Hz at 130 dB sound pressure level (SPL) while simultaneously
Sponsor: University of Minnesota - Clinical and Translational Science Institute

Current Primary Outcome:

  • Measure the effects of infrasound exposure on the SP/AP ratio of electrocochleography [ Time Frame: Test measurements at time -10, 10, and 20 minutes ]
    A baseline ECoG recording will be obtained and the waveform's SP/AP ratio will be calculated and recorded (time "-10"). A 10-minute infrasound stimulus will ensue. Immediately following cessation of the stimulus (time 10), a repeat ECoG test run will be performed. A 10-minute recovery period will take place followed by a final ECoG test run (time 20). S/P ratios will be recorded for each test run and percent change will be calculated.
  • Measure the effects of infrasound exposure on the threshold tuning curve of cVEMP [ Time Frame: Test measurements at time -10, 10, and 20 minutes ]
    A baseline cVEMP tuning curve will be obtained and recorded (time "-10"). A 10-minute infrasound stimulus will ensue. Immediately following cessation of the stimulus (time 10), thresholds will be repeated. A 10-minute recovery period will take place followed by a final threshold measurement (time 20). Thresholds will be recorded for each test run and average change in threshold in dB will be calculated.
  • Measure the effects of infrasound exposure on the threshold tuning curve of oVEMP [ Time Frame: Test measurements at time -10, 10, and 20 minutes ]
    A baseline oVEMP tuning curve will be obtained and recorded (time "-10"). A 10-minute infrasound stimulus will ensue. Immediately following cessation of the stimulus (time 10), thresholds will be repeated. A 10-minute recovery period will take place followed by a final threshold measurement (time 20). Thresholds will be rec

    Original Primary Outcome: Same as current

    Current Secondary Outcome:

    Original Secondary Outcome:

    Information By: University of Minnesota - Clinical and Translational Science Institute

    Dates:
    Date Received: March 9, 2017
    Date Started: July 2017
    Date Completion: June 2018
    Last Updated: April 25, 2017
    Last Verified: April 2017