Double hearing protection and speech intelligibility-room for improvement.

INTRODUCTION: Double hearing protection is used in many air forces around the world for protection in noisy aircraft environments, particularly in helicopters. The usual combination is foam ear plugs under headset or helmet muffs. Much of the research that spurred the introduction of foam earplugs indicated little change in speech intelligibility in persons with normal hearing. However, aircrew often complain about having to maximize intercom volume for speech understanding, causing a situation with no reserve volume and bad sound quality. In recent years, further developments have included so-called hi-fi plugs and custom made ear plugs which are claimed to improve speech communication. The aim of the present project was to investigate different types of ear plugs and their effect on speech intelligibility in helicopter noise. METHODS: Each of nine normal-hearing pilot subjects were placed in an environment of recorded helicopter noise from a BO-105 helicopter. Speech audiometry was performed under four different conditions: headset only, and three different ear plugs worn under the headset. Fitting of the ear plugs was performed by an ear, nose and throat specialist to ensure similar conditions. The sequence of test conditions was randomized and double-blind. In addition, a subjective rating scale was used. RESULTS: Wearing foam ear plugs under the headset decreased speech intelligibility dramatically. The "hi-fi" plug was somewhat better than foam plugs, and the custom made ear plug provided a speech intelligibility close to the headset-only situation. Subjective rating scores coincided with these findings. DISCUSSION: In helicopter noise, custom made ear plugs may provide a much improved speech intelligibility over conventional plugs when worn under a headset, while maintaining improved noise protection over the headset-alone situation. Custom made ear plugs might therefore be a good alternative to other forms of enhanced noise protection in helicopters.

Effects of active noise reduction on noise levels at the tympanic membrane.

BACKGROUND: Active noise reduction (ANR) is an electronic system that works by continuous sampling of noise inside the earshell of the headset with a small microphone. This signal is inverted in phase through the headset speaker, thus reducing noise levels by destructive interference of the acoustic field. The system provides good low-frequency noise attenuation, but aircrew differ in their subjective opinion of ANR. The present study is an attempt to provide an objective assessment of the effect of ANR on noise levels at the tympanic membrane. METHODS: There were 7 subjects with normal ears who were placed in an environment of recorded noise from a BO-105 helicopter. A microphone probe was inserted to within 5 mm of the tympanic membrane of each subject's right ear. Noise levels in the ear were measured without a headset and with two different ANR headsets. Measurements were performed with and without the ANR system on, and with and without white noise through the headset communication system. The white noise was used to simulate aircraft communication noise. RESULTS: The two headsets tested had differing levels of passive and active attenuation. The ANR system produced a substantial low-frequency attenuation. However, noise levels in the mid frequencies increased somewhat when the ANR system was switched on. This effect was augmented when white noise in the communications system was introduced, particularly for one of the two headsets. Low-frequency noise attenuation of ANR systems is substantial, but an increased mid- and high-frequency noise level caused by the ANR may affect both communication and overall noise levels. Our data provide advice on what factors should be taken into account when ANR is evaluated for use in an aviation operational environment.

Transient evoked otoacoustic emissions as screening for hearing losses at the school for military training.

The present study was designed to investigate the applicability of transient evoked otoacoustic emissions (TEOAEs) as a method of screening for hearing losses among recruits attending obligatory military service. TEOAEs, tympanometry and puretone audiometry were recorded in 95 male recruits. Sixty-one recruits were tested after a 2-month period of gunfire exposure in order to document any permanent change in cochlear function. Screening by pure-tone audiometry showed an unexpectedly high prevalence of hearing losses > 20 dBHL, probably due to technical reasons. Thresholds were corrected using lower thresholds obtained at the end of service or by ENT specialists. The accuracy with which normal and impaired ears could be identified with TEOAEs analysed in frequency bands was determined by decision theory. Impairment was defined as mean hearing thresholds > or = 30 dBHL averaged from three neighbouring frequencies. Adequate accuracy was obtained in the middle frequencies. Further improvement of the technique is needed before it can be deemed suitable for detecting hearing losses at low and high frequencies. TEOAEs are quicker to measure and offer greater objectivity than pure-tone audiometry. A small decrease in TEOAE level was found after the training period. The TEOAEs were highly repeatable and had a higher sensitivity than pure-tone audiometry to detection of small changes in cochlear function under conditions normally found when testing recruits.

Topical levocabastine compared with orally administered terfenadine for the prophylaxis and treatment of seasonal rhinoconjunctivitis.

BACKGROUND: This study was designed to compare the efficacy and tolerability of a new topical (nasal spray and eye drops) H1-receptor antagonist, levocabastine, with that of orally administered terfenadine for the prophylaxis and treatment of seasonal allergic rhinoconjunctivitis. METHODS: A total of 115 patients with documented birch pollen allergy were enrolled in this randomized, double-blind, double-dummy, parallel-group trial. Treatment was initiated immediately before the birch pollen season started and continued for a total of 8 weeks. Xylometrazoline (Otrivin) nasal spray was permitted as rescue medication. RESULTS: The investigator's evaluation of symptoms showed similar effects for levocabastine and terfenadine. Both the patients' and the investigator's global evaluations of ocular and nasal symptoms disclosed a somewhat higher percentage of good or excellent results for levocabastine, but the differences were not statistically significant. Visual analog scale ratings from the patients' diaries showed better results for levocabastine. Levocabastine was significantly more effective than terfenadine in relieving sneezing, rhinorrhea, lacrimation, itch, and burning sensation (p < 0.05). For some symptoms, levocabastine was significantly more effective than terfenadine on days when the pollen count was high. There were no statistically significant differences in the use of rescue medication or in the incidence of adverse reactions reported in each treatment group. CONCLUSIONS: In the present study topical levocabastine was frequently more effective than orally administered terfenadine for the treatment of seasonal allergic rhinoconjunctivitis. Both drugs were well-tolerated.

Attenuation of hearing protectors at 85 dB SPL investigated by commercial "insertion gain" method.

Attenuation of hearing protectors is conventionally measured as the difference between the subject's pure-tone hearing threshold with, and without, hearing protection under free field conditions (loudspeaker) in a sound attenuated (an-echoic) room. This REAT procedure is not objective as it involves the response of a subject. The attenuation can not be measured at noise hazard levels: > 85 dB SPL. Commercial computerized "insertion gain" equipment has recently been developed to improve the individual fitting of hearing aids. By "insertion gain" method a slender silicone probe-tube connected to an outside microphone, is inserted in the ear canal, registering the sound pressure level in front of the tympanic membrane. Thus one can objectively register the sound pressure level difference (gain) obtained close to the tympanic membrane with a given hearing aid in a non-attenuated room. We wanted to study whether the same procedure could be used to assess the attenuation of hearing protectors at noise hazard levels with acceptable measurement variability. With a commercial computerized "insertion gain" equipment (IGO-HAT 1000. Madsen Electronics) we registered the "insertion loss", the difference in sound pressure level measured < 5 mm in front of the tympanic membrane for 20 consecutive sessions (fittings) in the same subject with versus without the same hearing protector. Below 6000 Hz standard deviations were remarkably low--around 2 dB--for the two protectors tested.