Outer hair cells (OHC) are thought to act like piezoelectric transducers that amplify low sounds and hence enable the ear's exquisite sensitivity. Distortion product otoacoustic emissions (DPOAE) reflect OHC function. The present study investigated potential effects of electromagnetic fields (EMF) of GSM (Global System for Mobile Communication) cellular phones on OHCs by means of DPOAEs. DPOAE measurements were performed during exposure, i.e., between consecutive GSM signal pulses, and during sham exposure (no EMF) in 28 normally hearing subjects at tone frequencies around 4 kHz. For a reliable DPOAE measurement, a 900-MHz GSM-like signal was used where transmission pause was increased from 4.034 ms (GSM standard) to 24.204 ms. Peak transmitter power was set to 20 W, corresponding to a specific absorption rate (SAR) of 0.1 W/kg. No significant change in the DPOAE level in response to the EMF exposure was found. However, when undesired side effects on DPOAEs were compensated, in some subjects an extremely small EMF-exposure-correlated change in the DPOAE level (< 1 dB) was observed. In view of the very large dynamic range of hearing in humans (120 dB), it is suggested that this observation is physiologically irrelevant.

There is a large amount of knowledge about the different components of the organ of Corti (OC), but little is known about how these components act together in vivo. To clarify the complex mechanical behavior of the OC, anatomic results are carefully analyzed and used to develop a finite element model of a short section of OC, which includes 8 outer hair cells (OHC) and their supporting structures. The modal analysis shows the frequency-dependent phase reversal of the radial stereocilia displacement. The transient computation confirms the amplification of OC displacements when the ability of the OHC to contract and elongate is considered. The inclusion of a nonlinear function describing the mechanoelectrical transduction in OHC amplifies and distorts the displacement of the OC when it is stimulated by a sinusoidal input pressure function. These results are in agreement with other psychoacoustic, electrophysiologic and otoacoustic measurements.