Re-Thinking Adverse Noise Effects and Interactions with Other - - PDF document

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Re-Thinking Adverse Noise Effects and Interactions with Other Exposures

Dimitri Palilis, Au.D. Director of Audiology, MedEvals of Calfornia

Disclosure:

 I am a co-owner of Innovative Hearing Designs, a research lab which specializes in custom hearing protection.  There are no financial disclosures to speak of because the company doesn’t make any money.  Don’t worry – I won’t try and sell you anything that I manufacture as I’m not setup for that.

Agenda

 How effective is OSHA?  Synergistic Effects  Specific Interactions  Tinnitus  Problems within my patient populations  Alternative approaches  How to setup a proactive HCP

(And a boatload of sidetracks)

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Metrics

 Audiometric screening is a weak metric – we need to find something that is more effective  OSHA regulations result in a 29% rate of hearing loss  NIOSH recommendations result in 9% rate of hearing loss  All metrics are currently based on annual testing to show change – reactive process  What does audiometric testing show us?  Sensorineural vs. conductive HL  Symmetry  Gross abnormalities

 i.e.: acoustic neuroma, otitis media, cholesteatoma

 Diagnostically useful, Functionally irrelevant

 Cochlear mapping could indicate function  Cochlear mapping via audiometric threshold testing requires over 300 frequencies

Audiometric Testing:

 Functionally useless?! Wait, why? We’ve been doing it this way from the beginning of the development of audiology!  BECAUSE WE’VE BEEN DOING IT THIS WAY FROM THE BEGINNING OF AUDIOLOGY!  APD, Adult onset APD, Subclinical (or hidden hearing loss) and a variety

• f other functional difficulties keep making their way into the world

 Everything we do revolves around threshold testing and matching that to speech in quiet  Shocker – almost 90% of people will achieve 90% or better speech understanding in quiet when 2kHz is made audible. We don’t measure functionality.  Speech in noise testing needs to be part of the new test battery as it stresses the system significantly more so than speech in quiet.

Damaging Doses:

 OSHA  90dB(A) TWA 5dB exchange rate  Example = 100dB measurement is safe unprotected for 2 hours  NIOSH is OSHA’s gold standard  85dB(A) TWA 3dB exchange rate  Example = 100dB measurement is safe unprotected for 15 minutes  Age correction is an archaic way of doing things but it adds a correction factor to the calculation per tone.  Reduces the stringency of the STS criteria so that agencies are not held accountable for damages incurred while patient is employed

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OSHA vs. NIOSH Quick SideTrack!

 We talked about OSHA’s risk criteria, but what is it based

• n?!

 The A-Weighted dB measurement system.  Isn’t the A-Weighted dB system based off of equal loudness contours? – Yes it is, thank you!

Loudness Contours:

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Synergistic Effects:

 Ototoxic Medications  Chemical interactions  Aromatic Solvents  Toluene and Xylene are amongst the strongest correlated with hearing loss  Heavy metal toxicity  High blood lead levels

 Increases ROS leads to poorer hearing than in matched samples

 Vascular issues  Inner ear is highly vascularized and we often see poorer thresholds with vascular disease despite not having a clear understanding as to why  Bleeding disorders – ISSHL – let’s stop relying 100% on intratympanic steroids with an approximate 50% success rate  Prothrombin and Leiden  Metabolic disorders  Increased BMI shown to have poorer thresholds 10

Cochlear Vascular System Specific Interactions:

 Heavy Metal Toxicities  Aromatic Solvents  Systemic interactions

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Heavy Metal Toxicity

 Welders, Miners, Refinery Workers, Plumbers among others  Several studies indicate the ototoxicity of lead and Mercury  Ototoxocity via neurotoxic mechanism of action  Weird fact: Beethoven had an alcohol dependency and cheap wine in his era had high lead content. There is at least one piece in the literature that suggests that his hearing loss may have been exacerbated, if not entirely caused, by lead.

Aromatic Solvents:

 Toluene

 Found in Adhesives, Paints, Lacquers, Varnishes and many

• ther sources

 Styrene

 Found during manufacturing of plastics, rubbers and glass

 Mechanism of action appears to be different based on long/short term exposures. Acute exposure appears to be cochleotoxic affecting cells within the Organ of Corti while long-term exposures lead to ROS and cell apoptosis.

Multi-System Effects of noise:

 Hypertension

 Employees working on the flight line  Police/Military Rangemasters/Tac teams

 Cardiovascular disease  Tinnitus

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Tinnitus

 Often a side effect of noise exposure

 Approximately 10% of the normal hearing population have it  Almost 23% of noise exposed groups have it

 Sleep disturbances in approximately 84% of people who experience the disorder  This often leads to concentration difficulties, increased irritation levels as well as general drowsiness during the day.

Patient Problems with HPD’s:

 Reduced situational awareness  Gardeners, Military, Police  Remember to look at the dosimetry results – maximum hearing protection is rarely necessary!  Uncomfortable  Lack of availability  Motorcycle PD assigned to construction site after leaving the station  Inconsistency of fit  This is why there are correction factors for the NRR that must be utilized  Customs lead to the most consistent fit and over time, end up being less expensive than single fit “foamies”  PRIMARY PROBLEM: Minimal effort has been placed on determining the most effect type of HPD based on job class. We are essentially forced to provide patients with what is manufactured, not what they need.

Moving from Reactionary to Proactive

 Currently waiting for problems to show up audiometrically, which can take years. In addition, it is a subjective examination.  Change in abilities to perform speech in noise tasks have been shown to be an early predictor of damage due to noise exposure  High Frequency audiometry  Otoacoustic Emissions as a physiologic measure of cochlear function

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Proactive Approaches:

 Measure cochlear function pre/post exposure

 Literature has not investigated correlation between percent change in otoacoustic emissions and temporary threshold shifts

 Job class specific exposures

 Don’t forget, not everyone needs maximum hearing protection  Worn hearing protection is better than no hearing protection

Otoacoustic Emissions

 Bi-product of the non-linearity of the cochlear amplifier  Spontaneous versus Elicited  Extremely quiet  Essentially caused by hair cell stimulation  Obviously negatively affected by middle ear status  Calculated by a specific ratio of 2f1 – f2  Increasing the resolution of the test protocol can potentially be used for cochlear mapping in less than 1 minute  Not specific enough to measure threshold, however, can be used to measure amplitude changes  Don’t we use these for newborn screenings? Yes but just because William Shatner has stepped foot on every planet from here to the end of the universe, doesn’t mean he can’t do the occasional travel commercial. What I’m getting at is we have a very powerful tool that has been typecast and should be used in additional manners.

Pre/Post Exposure Example:

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Use of OAE’s as a predictive measure of HPD effectiveness Proactive Hearing Conservation

 Determine job class specific hearing protection devices  Determine effective hearing protection devices based off cochlear function  Add high frequency audiometry  Add speech in noise testing  Enforce routine audiometric monitoring

Questions:

1. Heavy Metal Toxicity operates by the following mechanism of action:

1. Acute exposure appears to be cochleotoxic affecting cells within the Organ of Corti while long-term exposures lead to ROS and cell apoptosis. 2. Via neurotoxicity 3. By reducing ABR amplitude 4. By stiffening the ossicular change and creating a conductive component to the hearing loss

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Questions:

 2. Tinnitus can:

1. Lead to reduced performance at work due to sleep disturbances 2. Cause

Questions:

 Otoacoustic emissions are:

1. Audible to other people around you 2. Beethoven’s next masterpiece 3. Capable of showing cochlear change caused by high doses

• f noise exposures