Transcript A combined hearing protection device and communication

Outer Hair Cell functionality and
new models for noise damage
NTAF’s etterutdanningskurs
Hell, October 2007
Olav Kvaløy
SINTEF ICT
ICT
1
’State of the Art’ of understanding
of damage risk
 At levels from 85dBA to <130dBA:
Damage = dBlevel * time (dose)
 At higher levels >150dB instantaneous damage
(legislation states max 130dBCpeak)
 Our model works on the continuous noise integration
ICT
2
’State of the Art’ understanding of OHC
 OHC is damaged by continuous high noise
 OHC hearing loss is often accompanied by hyperacusis
 OHC represents +57dB gain at threshold (Moore)
 OHC is not active above 90dB (Moore)
ICT
3
’State of the Art’ questioned
Why is OHC damaged at high levels
if they are inactive above 90dB?
We is know these are the dangerous levels.
ICT
4
Beyond ’State of the Art’
 OHC is damaged by high noise
 OHC hearing loss is often accompanied by hyperacousis
 OHC represents +57dB gain at threshold
New hypothesis:
 OHC is active above 90dB
ICT
5
OHC, Gain and Protection
If OHC work against or dampen the movement at high
levels this would explain:
 Why OHC are damaged at high levels
(they work harder!)
 Hyperacousis when OHC damage
(no OHC to restrict the level)
ICT
6
Recruitment and
Outer Hair Cells (OHC)
ICT
7
‘Diffusion’ model for HOC damage
Assumptions in the model:
 OHC work to protect cochlea during high noise and are
‘worn out’ by to much work
 Some substance ‘X’ is needed for the cells to work
 Some substance ‘Y’ needs to be carried away from cells
 If the X or Y concentration goes beyond certain limits the
cells will be damaged
 These substances must be transported to / fro the cells by
diffusion
ICT
8
The Cochlea
http://en.wikipedia.org/wiki/Image:Cochlea-crosssection.png
ICT
9
The Cochlea with diffusion model
Vg
Iros
http://en.wikipedia.org/wiki/Image:Cochlea-crosssection.png
ICT
10
Diffusion model of HOC damage
 Literature shows that Reactive Oxygen Specimen (ROS)
is produced in the cells and will destroy them
 Antioxidants protect the ear against noise
(Vitamin C will reduce ROS concentration and protect)
 The model will give credit to resting periods between noise
 Literature shows destructive levels start <70dB if no rest
ICT
11
Diffusion model of HOC damage
x(t) is instantaneous sound pressure
h(t) is the ROS production function
Vg is antioxidant source
We assume TTS is a sign increased ROS concentration
(by this we can calibrate the model)
ICT
12
Thank you for listening
ICT
13
How to prove OHC hypothesis?
ICT
14
Protocol for OHC hypothesis test:
 Gather young healthy subjects (students?)
 Expose them to high noise (produce TTS)
concerts or brass-band practice as exposure source (students own choice!)
 Measure Threshold and UnComfortable Level (UCL)
before and after sound exposure
 Threshold levels and/or OAE to document OHC activity
 ’Loudness Scaling’ and/or ’Reflex Measurement’ used to measure
UCL
 Lower OHC activity and lower UCL after exposure proves hypothesis
 Main Problem:
Ethics in exposing subjects to potentially hazardous sound levels
ICT
15