Cochlear Duct Length Research Articles

Real Human Hearing: Damage Detection and Monitoring of the Treatment Effectiveness

Hearing loss is determined by the diapason change of perceived ear sound frequencies and intensity. Cochlear tonotopicity represents the relationship between stimulation frequency f and place ℓ along the cochlea by the equation of the acoustic-wave hearing model at before-receptors stage ℓ(f) = Lo.22log(f/fmo), where Lo = 32 mm – the cochlear duct length, fmo = 20 kHz – maxima frequency of audible sound. Age-related frequencies standards can be represented by f(t)=fmoe–rt, where r=0.01 year–1 – high-frequency loss factor sound. Using both relations together, we get the length of the cochlear duct for T years LT = Lo.22log(fT/fmo). Destruction of the cochlear duct is exposed apex experiencing cyclical exposure to sound, which represents a decline of frequency fmo. The real length of the cochlear duct LR determined by the same ratio at a frequency fT = fmaxR, established audiometric. Treatment (pharmacological or physical therapy) causes a change in the physical and audiometric properties of inner ear structures. Daily monitoring of the upper frequency sound (fmaxX) determines the effective (useful) the length of the cochlear duct LX. Value LX/LR can be a criterion of treatment effectiveness: LX/LR →1 when the treatment is effective.

Depth of Electrode Insertion and Postoperative Performance in Humans with Cochlear Implants: A Histopathologic Study

The depth of electrode insertion of a multichannel cochlear implant has been suggested as a clinical variable that may correlate with word recognition using the implant. The current study evaluates this relationship using the human temporal bone collection at the Massachusetts Eye and Ear Infirmary. Twenty-seven temporal bones of subjects with cochlear implants were studied. Temporal bones were removed at autopsy, fixed and prepared for histological study by standard techniques. Specimens were then serially sectioned, and reconstructed by two-dimensional methods. Three measures of length were made from each subject’s reconstruction: (1) depth of insertion (DI) of the cochlear implant electrode array, from the round window to the array’s apical tip; (2) inserted length (IL) from the cochleostomy to the apical tip of the array, and (3) cochlear duct length (CDL) from the round window to the helicotrema. The active electrode length (AEL) was defined as the distance between the most apical and most basal electrodes of the array. Stepwise regression was used to identify whether subsets of six metrics associated with insertion depth (DI, DI/AEL, DI/CDL, IL, IL/AEL and IL/CDL), duration of deafness, sound-processing strategy, potential for central impairment and age at implantation accounted for significant across-subject variance in the last recorded NU-6 word score measured during each subject’s life. Age at implantation and potential for central impairment account for significant percentages of the across-subject variance in NU-6 word scores for the 27 subjects studied. None of the insertion metrics accounted for significant performance variance, even when the variance associated with the other variables was controlled. These results, together with those of previous studies, are consistent with a relatively weak association between electrode insertion depth and speech reception.

Postnatal development of the rat organ of Corti. II. Hair cell receptors and their supporting elements.

The development of cochlear receptor cells and their supporting elements was studied by means of semi-thin and ultra-thin sections during the first postnatal weeks in the rat. The temporal and spatial patterns of the receptor cell development were investigated between the 4th and 24th days after birth. At approx. ten equidistant positions along the entire cochlear duct length of inner and outer hair cells, width of outer hair cell triad and stereocilia-length of the outer hair cells were quantitatively analyzed. Striking maturational changes take place before the 12th day after birth, that is, when the onset of hearing occurs. These changes are the formation of the tunnel of Corti, of the Nuel spaces, the appearance of filaments within the supporting elements and the change in cell shape of the hair cells. Between 4 days and 20 days after birth the maturation of outer hair cells is characterized by a decrease of organelles in the cytoplasm and establishment of the subsurface cistern. The quantitative analysis revealed a unique developmental pattern of the length of the outer hair cells, the width of the outer hair cell triad and the stereocilia length of the outer hair cells. Shortly after birth these structures have an almost constant size along the whole cochlear duct, but with increasing age the structures shorten at the cochlear base and enlarge at the apex. This pattern results in the establishment of a baso-apical gradient of the above mentioned structures. We assume that this baso-apical gradient is of central importance for the frequency representation.

Postnatal changes in the size of the avian cochlear duct.

The length of the cochlear duct was measured in chicks aged embryonic day 14 to post-hatch day 469. Chicks were anesthetized, decapitated and their cochlear ducts exposed under an operating microscope. Because of the very thin bone and cartilage surrounding the relatively straight tube of the papilla the entire cochlear duct could rapidly be exposed and measured without fixation or removal from the head. The length of the duct was measured using a computer based Zeiss Videoplan Image Analysis System. A total 41% increase in length was seen from embryonic day 14 to post-hatch day 469; 20% of this increase occurred after hatching. It is suggested that this increase in cochlear duct length could influence basilar membrane properties important to frequency coding mechanisms during development.