Derived-band auditory brain-stem response estimates of traveling wave velocity in humans: II. Subjects with noise-induced hearing loss and Meniére's disease.

Abstract

Estimates of cochlear traveling wave velocity (TWV) were computed from derived-band auditory brain-stem response (ABR) latencies in subjects with noise-induced hearing loss (NIHL) or Meniére's disease (MD). ABR wave V latencies were determined for each of six derived frequency bands (unmasked-8 kHz, 8-4 kHz, 4-2 kHz, 2-1 kHz, 1 kHz-500 Hz, and 500-250 Hz). Representative frequencies were assigned to the derived bands by estimating their energy midpoints, and cochlear positions corresponding to these frequencies were determined using Greenwood's (1961) place-frequency function for humans. An exponential function of the form I = A + BeCd was fitted to each subject's latency-by-distance data using a least-squares algorithm, and a TWV function was generated by taking the reciprocal of the derivative of the latency function with respect to distance [v = 1/(BCeCd)]. Expected values for subjects' TWV functions were compared to normative data from Donaldson and Ruth (1993) at five cochlear loci. NIHL subjects' TWV estimates fell within normal limits at all cochlear loci, and no relation between severity of high-frequency hearing loss and TWV could be discerned. MD subjects with good low-frequency hearing sensitivity generally yielded normal TWV estimates, whereas MD subjects with low-frequency hearing loss yielded either normal or elevated TWVs. MD subjects' data generally support the hypothesis that endolymphatic hydrops results in increased TWV or, alternatively, a basalward shift in the peak of the traveling wave, in cochleas with presumed normal basilar membrane elasticity.