Impulse noise injury prediction based on the cochlear energy

Abstract

The current impulse noise criteria for the protection against impulse noise injury do not incorporate an objective measure of hearing protection. A new biomechanically-based model has been developed based on improvement of the Auditory Hazard Assessment Algorithm for the Human (AHAAH) using the integrated cochlear energy (ICE) as the damage risk correlate (DRC). The model parameters have been corrected using the latest literature data. The anomalous dose-response inversion behavior of the AHAAH model was eliminated. The modeling results show that the annular ligament (AL) parameters are the dominant cause of the non-monotonic dose-response behavior of AHAAH. Based on parametric optimization analysis, a 40% reduction of the AL compliance from the AHAAH default value removed the dose-response inversion problem, and this value was found to be within the physiological range when compared with experimental data. The transfer functions from the new model are in good agreement with those of the human ear. A dose-response curve based on ICE was developed using the human walk-up temporary threshold shift (TTS) data. Furthermore, the ICE values calculated for the German rifle noise tests show excellent comparison with the injury outcomes, hence providing a significant independent validation of the improved model. The ICE was found to be the best DRC to both large weapons and small arms noise injury data, covering both protected and unprotected exposures, respectively. The new AHAAH model with ICE as the dose metric is adequate for use as a medical standard against impulse noise injury.

Intracochlear pressure measurements during acoustic shock wave exposure

“…These results thus support the AHAAH assumption that middle ear motion saturates at high levels (Price et al, 1991), derived from earlier measurements in cat (Price, 1974a), but suggest that this saturation occurs at a higher sound pressure level than predicted by the AHAAH model (Greene et al, 2017). This result is consistent with the approach pursued by a recent attempt at an update to the AHAAH model (Zagadou et al, 2016), which decreased both annular ligament resistance and cochlear input resistance, thereby eliminating the anomalous dose-response inversion observed in AHAAH responses. Note, however, that while cochlear input impedance does not appear to vary with exposure level, it does vary (by an order of magnitude) across frequency (Greene et al, 2017; Nakajima et al, 2009).…”

“…In other words, no dose-response inversion was observed with increasing sound pressure level, despite the sound levels increasing above levels at which middle-ear components (particularly the SAL) limit ossicular chain motion. The responses observed here thus support a correction to the SAL compliance similar to that proposed by Zagadou et al (2016) that eliminates this anomalous behavior in the AHAAH model.…”

“…Two main nonlinearities are included in AHAAH: the first involves contraction of middle ear muscles either in response, or in anticipation of a noise exposure, and is the subject of two recent studies exploring this phenomena in humans (Flamme et al, 2017; Jones et al, 2017); the second, which we have explored recently (Greene et al, 2017), and was the focus of this study, involves the frequency and level dependence of middle ear motion in response to high level noise exposure. One recent report attempted to address several of the concerns, including updating several parameters with more recent parameters derived from human cadavers (particularly an alteration to SAL compliance that eliminates the dose-response inversion), and introduction of a new damage risk correlate (integrated cochlear energy, ICE) (Zagadou et al, 2016); however, this attempt to modify the model met with controversy, and both the model’s authors (Price et al, 2017), and the article’s authors (Zagadou et al, 2017) have published commentary.…”

“…Additionally, the differential pressure (i.e. the pressure difference across the basilar membrane), along with the volume velocity of the basilar membrane, make up the inputs to the newly proposed damage risk correlate, ICE (Zagadou et al, 2016). Furthermore, this method allows for testing of hearing protective devices at much higher levels than methods involving human performance (e.g.…”

“…In support of such a result, reports have provided evidence in support of a compressive nonlinearity in the ossicular chain motion (Price et al, 2017). Others, however, have suggested that while the displacement limitation is present, the implementation in the AHAAH model is overly-compressive, and that reduction (but not elimination) of the SAL compliance eliminates this behavior (Smoorenburg, 2003; Zagadou et al, 2016). The controversy surrounding the dose-response inversion (in addition to other controversial aspects) of the AHAAH model have been discussed previously (Wightman et al, 2010), and have been the subject of a recent exchange in the literature (Price et al, 2017; Zagadou et al, 2016; Zagadou et al, 2017).…”