Hybrid 10 clinical trial: preliminary results

Abstract

Acoustic plus electric (electric-acoustic) speech processing has been successful in highlighting the important role of articulation information in consonant recognition in those adults that have profound high-frequency hearing loss at frequencies greater than 1500 Hz and less than 60% discrimination scores. Eighty-seven subjects were enrolled in an adult Hybrid multicenter Food and Drug Administration clinical trial. Immediate hearing preservation was accomplished in 85/87 subjects. Over time (3 months to 5 years), some hearing preservation was maintained in 91% of the group. Combined electric-acoustic processing enabled most of this group of volunteers to gain improved speech understanding, compared to their preoperative hearing, with bilateral hearing aids. Most have preservation of low-frequency acoustic hearing within 15 dB of their preoperative pure tone levels. Those with greater losses (>30 dB) also benefited from the combination of electric-acoustic speech processing. Postoperatively, in the electric-acoustic processing condition, loss of low-frequency hearing did not correlate with improvements in speech perception scores in quiet. Sixteen subjects were identified as poor performers in that they did not achieve a significant improvement through electric-acoustic processing. A multiple regression analysis determined that 91% of the variance in the poorly performing group can be explained by the preoperative speech recognition score and duration of deafness. Signal-to-noise ratios for speech understanding in noise improved more than 9 dB in some individuals in the electric-acoustic processing condition. The relation between speech understanding in noise thresholds and residual low-frequency acoustic hearing is significant (r = 0.62; p < 0.05). The data suggest that, in general, the advantages gained for speech recognition in noise by preserving residual hearing exist, unless the hearing loss approaches profound levels. Preservation of residual low-frequency hearing should be considered when expanding candidate selection criteria for standard cochlear implants. Duration of profound high-frequency hearing loss appears to be an important variable when determining selection criteria for the Hybrid implant.

Fig. 1

Change in low-frequency thresholds compared to percentage point improvement in CNC word scores in the combined mode (9- and 12-month follow-ups combined; n = 68). Changes were measured in reference to preoperative low-frequency thresholds and preoperative CNC word scores with 2 hearing aids. Different colors and symbols indicate the degree of postoperative low-frequency hearing loss in the implanted ear. Two subjects, with mild to moderate hearing thresholds up to 750 Hz in both ears, preferred to use their natural low-frequency hearing in both ears, rather than hearing aids, with the Hybrid implant and were tested in this listening mode. These 2 subjects were still considered to be using combined electric and acoustic hearing.

Fig. 2

Improvement in CNC word recognition and speech reception thresholds for the BKB-SIN test for 61 subjects who have 9–12 months experience with their implant in the combined mode for both test measures (n = 61). Different colors and symbols indicate the degree of postoperative low-frequency hearing loss in the implanted ear. Points that fall within vertical dotted lines indicate no significant pre- to postoperative changes on the CNC word test, based on binomial (95%) comparisons. Points that fall within horizontal dotted lines indicate no significant pre- to postoperative changes for the BKB-SIN test, based on the critical difference (±3.1 dB) for the test as administered (BKB-SIN Test Manual, 2005). Seven of the subjects shown in figure 1 were not assessed on the BKB-SIN test and not included in this figure.

Fig. 3

SRT for the recognition of spondees in competing talkers as a function of the low-frequency average pure tone thresholds. The 2 dashed lines at the top represent the average long-electrode SRT values for the large unselected group (n = 20) and the smaller matched group (n = 11).