Speech intelligibility in aircraft noise as a function of altitude.

UNLABELLED: Few studies have addressed physiological effects of altitude and noise combined, although these two factors are inherent parts of all aviation. Altitude effects on hearing function have mainly been studied using gas mixtures with reduced oxygen content. The results have been inconclusive. HYPOTHESIS: The present study was designed to assess the effect of altitude on speech intelligibility in aircraft noise. The primary hypothesis was that exposure to altitude would produce a detrimental, hypoxic effect on speech intelligibility in noise. METHODS: Eight male subjects with normal hearing were fitted with an aviation headset specially adapted for use with the audiometer. Pure-tone audiometry, as well as speech audiometry in noise, were performed at 0, 10,000, 13,000, and 16,000 ft simulated altitudes in a hypobaric chamber. The four test altitudes were performed double blind with respect to audiometry operator and test subject. Arterial blood gases where measured using an intra-arterial catheter. Tympanometric measurements verified full middle ear equilibration. Noise levels where monitored and logged throughout all experiments. RESULTS AND CONCLUSION: A substantial increase in speech intelligibility in noise due to altitude was evident in our study. The physical effect of barometric pressure on noise causing an increased signal-to-noise ratio was found to greatly outweigh any possible hypoxic detrimental effect.

Static magnetic field and the inner ear. A functional study of hearing and vestibular function in man after exposure to a static magnetic field.

The sensory cells of the inner ear are vulnerable to several agents (aminoglycosides, cytostatics, ionizing irradiation). The effect of strong magnetic fields occurring in industries with production based on electrolytic processes and with medical magnetic resonance equipment is unknown. The aim of this study was to clarify the effect of strong static magnetic fields on the inner ear, by exposing 11 healthy men to a magnetic field with flux density of 2-7 mT for 9 h. No damage was found to the acoustic or vestibular system.

The effect of a headset leakage on speech intelligibility in helicopter noise.

INTRODUCTION: Speech intelligibility tests in recorded helicopter noise were performed on 10 subjects with normal hearing, using a Peltor aviation headset. The subjects acted as their own controls, a pair of sunglasses being the only variable factor. METHODS: Noise levels were also measured at the tympanic membrane in one of the test subjects for 7 consecutive fittings of the headset, with and without glasses. RESULTS: Results showed a substantial decrease in speech intelligibility when wearing glasses, being most marked for critical signal-to-noise ratios and the most difficult speech material. Changes were statistically highly significant. Average speech intelligibility scores decreased from 68% to 29% for one-syllable words when wearing glasses at critical signal-to-noise ratios. Noise measurements at the tympanic membrane in one subject showed a low-frequency leakage varying between consecutive fittings. CONCLUSION: Our findings show that even small leakages due to fitting of the headset or helmet should be avoided, particularly in noisy aircraft with communication-demanding mission profiles.

Patient performance with two types of multiple electrode intracochlear implant.

The functional results of 9 persons implanted with the Symbion Ineraid and 8 persons implanted with the Nucleus cochlear implant with the F0, F1, F2 coding strategy are reported. All patients were postlingually totally deaf, the patients implanted with the Symbion Ineraid were all above 40 years of age, while the Nucleus patients were with one exception under 40 years of age. The CID Everyday Sentences Test, the Helen Test and the Speech Tracking Test showed that all patients improved their communication skills when sound through the implant was added to lip-reading. The patients' ability to understand without lip-reading was tested with the CID everyday sentences test, with the Helen test, with spondees, with three-choice vowels and with a consonant confusion test. These showed that all 9 Symbion Ineraid patients achieved some degree of open speech understanding. Four of the 8 Nucleus patients achieved some degree of open speech understanding. Difference limen tests for intensity and frequency indicated that 2 of the Nucleus patients who did not achieve open speech understanding probably had extensive cochlear nerve damage, while the remaining 2 Nucleus patients without open speech understanding had good frequency and intensity discrimination.

Personal cassette players ('Walkman'). Do they cause noise-induced hearing loss?

Playing selected types of music on five different personal cassette players (PCPs) and using different gain (volume) settings, A-weighted maximum and equivalent sound pressure levels (SPLs) were measured on KEMAR (Knowles Electronics Manikin for Acoustic Research). The octave band SPLs were measured on KEMAR ear and transformed to field values in order to compare measured values with the Norwegian noise risk criteria. Temporary threshold shifts (TTS) measured in 6 subjects after listening to two different pop music cassettes on one PCP in two separate sessions, are presented. Based upon these studies we conclude that the risk of acquiring permanent noise-induced hearing loss (NIHL) from use of PCP is very small for what we found to be normal listening conditions.

A study of the possibility of acquiring noise-induced hearing loss by the use of personal cassette players (walkman).

Playing various types of music on five selected personal cassette players (PCPs), A-weighted sound pressure levels (SPLs), together with octave band spectrum, were measured on KEMAR (Knowles Electronics Manikin for Acoustic Research). Maximum and equivalent SPLs were measured for various types of music, PCPs and for different gain (volume) settings. The measured SPL-values on KEMAR ear were transformed to field values outside the ear canal by means of corrections based on KEMAR's ear canal resonance curve--in order to compare measured values with the Norwegian national noise risk criteria. Temporary threshold shift (TTS) was measured after listening to PCP music for one hour in order to obtain additional information about possible risk of hearing damage. TTS values are presented for six subjects when playing two different pop music cassettes on one type PCP. Our analysis indicates that the risk for permanent noise-induced hearing loss from listening to PCP is very small for normal listening conditions.

[Care of hearing in the elderly in Akershus. Use of hearing aids]. / Hørselomsorg blant eldre i Akershus. Bruksfrekvens av høreapparat.

The daily use of hearing aids was investigated in two groups of persons over 70 years of age. One group received only initial instruction in the use of the hearing aid. In this group only six of the 35 patients used their hearing aid every day or on most days. In the other group, which received a further audiopedagogical follow-up, the corresponding figure was 48 out of 61. Better cooperation between the primary health care and ear-nose-and throat-departments/specialists may lead to a better audiopedagogical follow-up of these patients.

[Care of hearing in the elderly in Akershus. Needs and provisions]. / Hørselomsorg for eldre i Akershus. Behov og behovsdekning.

543 persons over 70 years of age and living in Akershus county near Oslo were offered a hearing test at the local health centre. 495 (91%) were tested. The test revealed that 111 (22.4%) needed a hearing aid. 52 (10.5%) of these already had a hearing aid. Most of those who required a hearing aid (97.3%) belonged to the group with subjective hearing problems. It is concluded that good health care for the elderly also includes a hearing test for persons with a hearing problem, and provision of a hearing aid if necessary. It is important that also this part of the health care is provided locally.

Acoustic brain stem response in diagnosis of acoustic neuroma.

The aim of the present investigation is to throw light upon the following question: Is recording of click-evoked brain stem responses (ABR) a more sensitive and reliable test than the oto-neurological and conventional audiological tests in selecting patients for computerized tomography (CT)? Thirty-three patients were examined. They all presented case histories and otoneurological findings indicating a tumor in te cerebellopontine angle. In all cases CT was carried out. A tumor was found in 16 patients, normal findings in 17. The results obtained by audiological and oto-neurological tests were compared to those obtained by ABR recording. It is concluded that recording of ABR and the caloric vestibular test are the most reliable examinations in selecting patients for CT. These examinations alone, are, however, not sufficient to secure a completely reliable selection, and should be supplemented by other audiological tests.

A comparison between auditory and visual evoked responses in multiple sclerosis.

Sixteen patients, 6 males and 10 females, all fullfilling the criteria of clinically definite multiple sclerosis, were examined. All but one patient presented anamnestic data or clinical findings suggesting a previous or present brain stem lesion. The result obtained by visual (VER) and auditory evoked responses (ABR) were compared. In all cases abnormal VER were observed. Abnormal ABR were only recorded in 9 of the 16 patients. Consequently VER is the method of choice in establishing the multiple sclerosis diagnosis.

Auditory brain stem responses (ABR) in cat. Latency as a function of stimulus polarity, intensity and acoustic waveform.

ABR from cats were measured by use of standard EEG surface electrodes and ERA Madsen-74 equipment. A method for recording the waveform of the stimulus at the ear drum is demonstrated. ABR to both phases of three different stimuli was compared. In four out of five cats the ABR latency for rarefaction clicks was shown to be shorter than for condensation clicks at high stimulus levels. This effect of stimulus polarity was most pronounced for stimuli with few and broad peaks in the acoustic waveform. At lower stimulus intensities no differences in ABR latency could be demonstrated by reversing stimulus polarity. It is suggested that the first negative deflection in the acoustic waveform is mainly responsible for the ABR at high stimulus level. At lower stimulus level not only the onset but a greater part of the acoustic signal is responsible for the response.

Impedance changes elicited by tactile and electrocutaneous stimulation.

In each of 24 randomly selected outpatient the size of the impedance changes elicited by touching the skin in the ipsilateral cavum conchae with cotton wool were compared with those elicited by electrical stimulation of the same skin area. Pulse trains of 0.5 s duration, consisting of individual squarewave constant current pulses of frequency 200 Hz and duration 1 ms, were used. In all ears a current of 0.5-1 mA produced impedance change of about the same size as the tactile stimulus. Therefore, in testing the middle ear function observation of impedance changes elicited by tactile as well as electrical stimulation can be used. Electrical stimulation, however, has the following advantages: 1) Artifacts produced by accidently touching the probe tip are avoided. 2) The electrical stimulus is well defined and reproducible.