1 Departamento de Implante Coclear Fundación Arauz
Buenos Aires, Argentina
2 Facultad de Ingeniería, Universidad Nacional de
Entre Ríos 
Entre Ríos , Argentina
september 2002

ABSTRACT

Aims:
The first purpose of this study is, to know how the impedance values (Z) change with cochlear implant use and the second one is to determine if there is a correlation between maximum perceptual levels and impedance values in order to adjust maximum hearing levels in very young children.

Method:
Longitudinal telemetric measurements (Z) in children implanted with the Combi 40+ systems were performed at the first fitting and every three months up to 24 months of using the system. The correlation coefficient R between Z and the Maximum Comfortable Levels MCL, (RZMCL) was calculated at the same period of time, as well as the linear estimation.
Fifty-nine patients divided in 4 groups participated in this study: Group I: 12 patients from 2 to 4 years old; Group II: 16 patients from 4 to 6 years old; Group III: 18 patients from 6 to 9 years old and Group IV: 13 patients from 9 to 14 years old.

Results:
A good correlation RZMCL was found in most of the patients, especially those belonging to groups III and IV. An increasing correlation was observed over time in most of the patients, indicating a better MCL determination.
The values of MCL where modified to increase the correlation value. All the changes where previously tested in the patients to ensure comfortable perception.
Loudness balance and vowels discrimination were tested in several old children before and after the maps were modified. The scores of vowel discrimination improved with the use of such modified maps, perhaps indicating a better loudness balance at MCL.

Patients
62 children divided in 4 groups
Group I: 15 children 2 to 4,6 years old
Group II: 16 children 4,6 to 7,6 years old
Group III: 18 children 7,6 to 9,6 years old
Group IV: 13 children 9,6 to 11 years old

Impedance over time

TRENDLINES
RZC = 0.6212 6 months use

RZC = 0.8942 12 months use

RZC = 0.778 18 months use

RZC = 0.848 24 months use

Conclusions

Impedances decrease the first 3 to 4 months
after the switch-on. From then on values remain stable

RZC improved over time in about 82% of the children studied

For Group I no RZC was observed

For Groups II, III and IV, RZC reached high values

When RZC improved, a better vowel balance was
always observed

The method seems to be useful to determine the Maximum Comfortable Levels in very young children and consequently, to reach a better loudness balance at those levels which in time produce better auditory conditions for language acquisition.