HF DPOAEs were repeatable across four test trials for all three paradigms measured in a group of CF patients. These results are encouraging for the measurement of HF DPOAEs to be monitored in those exposed to ototoxic agents.

These findings suggest that preventive measures may be warranted to prevent a future increase of clinically relevant NIHL among heavy users of PLDs.

Ipsilateral suppression characteristics of transiently evoked otoacoustic emissions (TEOAEs) are described in relation to psychoacoustic threshold at 4000 Hz and the presence or absence of spontaneous otoacoustic emissions in 41 adults with normal hearing. TEOAE amplitudes were measured in response to 4000-Hz tonebursts presented in linear blocks at 40 and 50 dB SPL while puretone suppressors were introduced at a variety of frequencies and levels ipsilateral to and simultaneously with the tonebursts. Suppressors close to the toneburst frequency were most effective in decreasing the amplitude of the TEOAEs, while those more remote in frequency required significantly greater intensity for a similar amount of suppression. Consequently, characteristic tuning curve shapes were obtained. Tuning-curve tip levels were closely associated with the level of the toneburst and tip frequencies occurred at or above the toneburst frequency. Tuning-curve widths (Q10), however, varied significantly across subjects with similar psychoacoustic thresholds in quiet determined by a two-alternative forced-choice method. The results suggest that a portion of that variability may be explained by the presence or absence of spontaneous otoacoustic emissions in an individual ear.

In adult cystic fibrosis patient populations, gram-negative bacteria, particularly Pseudomonas aeruginosa, frequently require aggressive therapy including systemic antibiotics, bronchodilators and airway clearance techniques. Aminoglycosides including tobramycin are used frequently to control these chronic airway infections. They, however, cause important nephrotoxic and ototoxic effects that can significantly alter the quality of life. We investigated the genetic predisposition to aminoglycoside ototoxicity in a typical unscreened North American cystic fibrosis population by screening for variants in mitochondrial 12S ribosomal RNA and noted several polymorphisms occurred at higher frequencies than expected and were associated with clinically significant cases of hearing loss. In the population studied, both patients possessing the 1555A>G transition exhibited profound ototoxicity after nontoxic dosing of tobramycin. We also identified new homoplasmic genetic variations in the mitochondrial 12S ribosomal RNA, several of which occurred in highly conserved regions of the gene and were present in patients with moderate-to-severe ototoxicity after exposure to aminoglycosides.

The majority of adult patients with CF are (often repeatedly) exposed to parenteral aminoglycosides and lose hearing at a rate that far exceeds that predicted from aging alone.