INTRODUCTION

Profound deafness is a deficit that affects personality, relationships and the whole lifestyle of subjects. There are different etiologies, both congenital and acquired, sometimes causing severe sensorial loss that disables the subject to communicate normally and even to listen to simple environmental sounds such as traffic noise, sirens and alarms that comprise warning signs in our daily lives. These subjects are unable to listen to their own voices and therefore they do not modulate speech, producing aesthetically poor voices.

Since it does not require mandatory notification before public agencies, the estimate of deafness incidence is uncertain in the country. In 1995, World Health Assembly (WHA) estimated 120 million as the number of hearing impaired people and 2.2% as the prevalence of deafness in the world population 1.

Conventional hearing aids are effective in managing hearing loss at different levels, including severe losses. However, since it is a sound amplifier, hearing aid requires sufficient cochlear reserve to generate good sound and speech perception for the patient. Some subjects, however, present such a significant auditory dysfunction that even a powerful hearing aid would not help them. Patients that do not reach discrimination levels higher than 40% in sentence recognition tests in open-set presentation, with the best amplification possible, are candidates to second rehabilitation alternative of hearing loss by cochlear implant.

In 1990, thanks to the joint initiative of the Discipline of Clinical Otorhinolaryngology, Hospital das Clínicas, and Division of Bioengineering, Instituto do Coração, University of Sao Paulo, the monochannel cochlear implant FMUSP-1 was developed. It aimed at training staff and developing national technology 2. Based on this initiative, the Cochlear Implant Group, HC-FMUSP, was created comprising a multidisciplinary team with ENT physicians, audiologists and psychologists directed to training and rehabilitating hearing impaired subjects.

Our objective in the present study was to assess auditory results of patients with bilateral severe or profound loss implanted with multichannel cochlear implant by the Group of Cochlear Implant, Discipline of Otorhinolaryngology, Medical School, University of Sao Paulo.


MATERIAL AND METHOD

One hundred and twelve patients were implemented with multichannel cochlear implants between April 1999 and November 2003, at Hospital das Clínicas, Medical School, University of Sao Paulo.

Inclusion criteria were continuous use of cochlear implants for 6 months in adult patients: 58 patients aged 17 to 77 years. Three patients had monochannel cochlear implant FMUSP-1 and had changed the system to the same ear. The time of use of implant in these patients was considered only after replacement for multichannel system. We excluded 7 patients with ossifying labyrinthitis implanted with Double Array (Cochlear Co) and 27 children. These patients will be discussed in other specific studies.

Patients started speech processor programming 30 days after surgery in the Cochlear Implant Group, Discipline of Otorhinolaryngology, HC-FMUSP. Audiological assessment was conducted by the team of audiologists in the group. It comprised the following tests:

1- Pure tone Audiometry

2- Vowel recognition in open-set presentation (%) 3

3- Recognition of monosyllables in open-set presentation (%) 4

4- Recognition of three syllable-words in close-set presentation 5

5- Medial consonants (%) 5

6- Recognition of sentences in open-set presentation (%) 6
Tests were applied with CD recording technology at 70dB sound pressure level.

Table 1 describes the studied group, duration of deafness, speech processor activation date, implant model used and strategy for speech processor in use.

RESULTS

We compared the results after six months of speech processor programming. Pure tone threshold mean was 38.7 dB SPL (36-50 dB SPL). The mean for sentence recognition in open-set presentation was 71.3%, vowels 86.5%, monosyllables was 52.6%, medial consonant was 52.6% and three-syllable words was 95.15%. Most of the patients were capable of using the phone.

Auditory results of patients in different recognition tests with words and sentences are synthesized in Table 2.

DISCUSSION

Assessment of auditory benefits received by deaf subjects through cochlear implant is essential for the correct clinical guidance of patients candidates to cochlear implant and to determine new alternatives for deafness management. The great variability among patients candidates for cochlear implants in terms of age, deafness characteristics, duration of hearing deprivation, speech production and communication skills and also the different implant models already used in the routine of many different centers are a problem for the selection of the best method to assess hearing after use of implant. The main objective of cochlear implants in adult patients with post-lingual deafness is acquisition of speech perception and recognition of words. The tests that assess this objective, therefore, should allow assessment of different aspects of communication, obeying a hierarchy of skills that range from vowel and consonant recognition to complete speech understanding. Ideally, the same test battery should be used by different researchers to allow comparison of results of different research centers and cochlear implant models. Despite the fact that there is some standardization of auditory assessment in English language for patients that are implanted, there is wide variability of parameters used in each research center in Brazil, hindering the comparison of absolute results among different studies.

Auditory thresholds detected for our patients synthesized one of the most important benefits of cochlear implant and what differentiates it from hearing aids. Even though we hardly have symmetrical improvement of auditory thresholds of subjects with profound hearing loss who use conventional hearing aids, especially in high frequencies, cochlear implant provides a possibility of hearing threshold that is equivalent in all frequencies, given that it is artificially reached by increasing or decreasing the intensity of electrical current in each electrode. The mean of hearing thresholds obtained with hearing aids in our patients was 84.8 dB SPL (73-100 dB SPL). Cochlear implant allowed considerable improvement in all patients, with mean thresholds of 38.7 dB SPL (36-50 dB SPL). This result is comparable to results described in the literature 7, 8 and allows patients to have speech and environmental sound perception. The duration of hearing deprivation and etiology or presence of residual hearing did not influence hearing thresholds obtained in our patients.

Vowel recognition tests used by us were presented to patients in closed-set format with 5 alternatives six months after implantation and presented average result of 86.5%. This result is comparable to that found by authors using both system Nucleus and speech processing strategies CIS and SAS in systems Med EL and Clarion 8,9,10,11. Because it is a relatively easy test, its importance is to follow up patients that do not have good discrimination in more complex tests.

Information about speech signal can be understood through auditory and visual information. Subjects use cochlear implant to present distinct performance when tested in situations that are only auditory in relation to concomitant use of visual information. Speech perception tests can be administered to patients in exclusively auditory, exclusively visual or auditory-visual situations. The results of this independent and combined test modality provide to researchers information about how effectively sounds are perceived by the patients through the cochlear implant, and how much it is improved with visual clues added. Auditory-visual performance is the one that is the closest to real life conditions of the patients, given that lip reading takes place automatically in a normal conversation. The mean recognition rate for monosyllables found in our patients was 54.10% in exclusively auditory mode. If visual cues were added (lip reading), the mean went up to 77.6%. The importance of lip reading as a complementary factor for communication of deaf subjects with cochlear implants can be analyzed based on these results. Patients with poor performance when tested only with cochlear implant rely on lip reading to help them reach results similar to the others, when tested in auditory-visual situations, found in real life.

Most of the tests used in the assessment of cochlear implant use lists of words and sentences in open and closed-set presentation provided to patients in exclusively auditory presentation. Tests in open-set presentation are those in each the listener has a number of infinite responses. That is, repeats what is heard without a closed-set of possibilities. Tests in closed-set presentation restrict the listener to a set of closed responses, such as for example a multiple-choice test or vowel recognition. Open-set presentation tests have the advantage of simulating real communication conditions and are influenced by cognitive processing of patients. General knowledge, vocabulary and intelligence of patients influence the results of these tests, as well as communication skills of patients in their everyday lives. The mean of correct answers in sentences presented in open-set format among our patients was 71.30%. This result was similar to the ones found in the literature, but for methodology reasons (different lists of sentences and different level of difficulty) the comparison of tests conducted in different languages have relative value. WITHIFORD (12) found 49.5% in sentence recognition with SIT and when the same patients were tested with CUNY sentences, results reached 75.7%. KIEFER (13) also changed significantly the results by changing methodology and reaching 100% as the best result in sentence recognition when using Innsbrucker list and only 55% with Gottingen sentences.

Tests in closed-set presentation are part of a set of tests, such as sentences in closed context, used when we want to follow up the progression of patients with little or no recognition skills in open-set tests. The mean recognition of three-syllables in closed-set context was 95.15%. This result demonstrates that this test should be used only to assess and follow up patients with poor results, since it proved to be too easy for the other patients.


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* Associate Professor

** Ph.D., Assistant Physician

*** Assistant Physician

§ Ph.D., Audiologist in the group of cochlear implant

§§ Audiologist in the group of cochlear implant.

Discipline of Otorhinolaryngology, University of Sao Paulo

Fundação Otorrinolaringologia

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Rubens de Brito Neto

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