Changes of external ear resonance before and after surgery in chronic otitis media / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: External ear resonance (EER) can normally increase the sound pressure level at the tympanic membrane by as much as 20 dB at the frequency between 2 and 4 kHz. Perforation of tympanic membrane (TMP) may alter the resonance characteristics. Surgical modifications of the external auditory canal by tympanoplasty may also change the EER features. We aimed to analyze the EER of patients with the TMP before and after surgery. MATERIALS AND MEHTOD: This study comprised of 130 patients (135 ears) with chronic otitis media. We checked EERs before and after the surgery. The preoperative group was divided into two groups according to perforation size. Postoperatively, the EER was checked at 3, 6, 9, 12 months or after 15 months. We compared these data with the control group which comprised of 96 adult ears. RESULTS: In the preoperative group, the peak resonant gain and the frequency were not different from the control's and the peculiar negative peaks appeared around 1500 Hz in half of the cases. No significant differences were found in the first peak gains according to the perforation size. The negative peaks appeared deeper in the larger perforation group. After tympanoplasty, the gain markedly increased. As time passed, the gain tended to decrease, but did not equalize with the control's data. CONCLUSION: Additional gain should be considered in the frequency of around 1 kHz for hearing aid users with the TMP. We could expect alterations of EER after tympanoplasty, suggesting that these changes should be considered at the time of fitting hearing aids.

Improvement of Speech Intelligibility in Patients with Sensorineural Hearing Loss Using Noise Reduction Algorithms / 대한이비인후과학회지

BACKGROUND & OBJECTIVES: Speech intelligibility is significantly decreased in noisy environments in patients with sensorineural hearing loss (SNHL) compared to those without hearing loss. It is caused by increased hearing threshold, recruitment, and decreased frequency selectivity. The hearing threshold and recruitment could be grossly controlled by the hearing aid with a compression circuit. It has been well established that various techniques can be used to trigger the signal to increase the noise ratio (SNR), such as noise reduction algorithms, in order to compensate for decreased speech intelligibility in noisy environments. These algorithms are incorporated into some of the commercially available digital hearing aids. This study was designed to measure the effect of noise in speech intelligibility of patients with sensorineural hearing loss and the effect of reducing the background noise with a noise reduction algorithm. MATERIALS AND METHODS: Twenty-one ears with sensorineural hearing loss were selected for this study. Speech reception thresholds (SRTs) and speech discrimination scores (SDSs) were checked with or without noise, and after removal of noise using a noise reduction algorithm. RESULTS: SRTs were increased in noise compared with a quiet environment. By reducing noise using the algorithm we prepared, SRTs were decreased by 4.6 dB, 4.2 dB, and 4.9 dB at +6, 0, -6 dB SNRs, respectively, in comparison with those who didn't use the algorithm in noise. It was observed that SDSs were decreased by 24-50% in noise and patients partially recovered hearing loss when noise was reduced. CONCLUSION: Speech intelligibility deteriorated in noise but partially improved with a noise reduction algorithm. A further study on the development of the noise reduction algorithm is needed to improve SNRs.

Hearing Impairment Simulation for the Performance Evaluation of Hearing Aid / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: With the advent of high speed digital signal processing chips, many digital techniques have been introduced to hearing aids. Generally, subject-based clinical tests are needed to verify the performance of hearing aids, which required both time and cost. A hearing impairment simulation (HIS) system is developed in real-time system which is aimed to simulate the sensorineural hearing impairment. In this paper, we present an indirect method to evaluate and predict the performance of hearing aid systems without the help of actual subjects. MATERIALS AND METHODS: The system is developed based on the model constructed from auditory test results and nonlinear behaviors of sensorineural hearing impaired persons. To verify the proposed system, signals processed were presented to normal listeners and their auditory data modified by the system were measured and compared with those of the impaired models. RESULTS: The auditory data of models were closely simulated to normal listeners by HIS system in all frequencies especially to those with hearing loss of more than 60 dB. CONCLUSION: HIS System can be used clinically in developing new digital hearing aid algorithm.