Threshold-distance functions predict speech recognition with cochlear implants

Area of Science:

• Neurosurgery
• Audiology
• Biomedical Engineering

Background:

• Cochlear implantation outcomes vary due to factors like auditory nerve degeneration.
• Assessing the auditory nerve's functional state is crucial for optimizing cochlear implant performance.

Purpose of the Study:

• To investigate the relationship between electrode-modiolus distance and electrically-evoked compound action potentials (eCAPs).
• To determine if the slope of the eCAP threshold-distance function can predict speech understanding variability.

Main Methods:

• Monopolar stimulation was used in human subjects with cochlear implants.
• Electrode-modiolus distance was quantified using fluoroscopy and cone-beam computed tomography.
• eCAP thresholds were measured and correlated with electrode position.

Main Results:

• Electrode-modiolus distance explained up to 91% of the variability in eCAP thresholds.
• A linear relationship was observed between eCAP threshold and distance from the modiolus for individual electrodes.
• The slope of this relationship explained up to 67% of the variability in speech understanding.

Conclusions:

• The slope of the eCAP threshold-distance function is a potential marker for the functional state of spiral ganglion cells.
• This metric may aid in assessing individual patient status and optimizing cochlear implant rehabilitation.