British journal of audiology最新文献

Evidence-based medicine is the use of current best evidence in making decisions about individual patients. It involves formulating a question, searching for information, appraisal of the literature, implementation and subsequent audit. Two case studies involving a non-linear hearing aid and cochlear implantation are used to illustrate the process. Critical appraisal of the evidence-based medicine in the general literature shows little sign that the approach is effective and indicates that further rigorous evaluation is a priority. It is suggested that systematic reviews and clinical practice guidelines should be a high priority for audiologists and that a working group of audiologists should form to promote their production.

Electrical impedance measurements can give useful information about the status of individual electrodes of a cochlear implant. Impedances within the normal range (when measured in the common ground mode of stimulation) suggest that current flow occurs in the tissue and fluid of the cochlea. Low impedance measurements may suggest that particular electrodes are short circuiting, whereas high impedances might be due to a broken electrode wire or an electrode only in contact with air. In the case discussed, low impedance measurements were recorded intra-operatively from a child with Mondini dysplasia on electrodes 1-13 of a Nucleus CI24M device. Post-operatively the impedances had returned to the expected range and were comparable with other patients implanted with the CI24M device. Possible reasons for this are discussed. It was thought that impedances were low intra-operatively due to a larger-than-normal proportion of fluid surrounding the electrode array, rather than short circuits occurring along the array, as suggested by the dps7 software.

The cross-sectional population sample studied here was randomly selected from the population register of northern Finland. The subjects comprised 10 different age groups between 2 and 75 years of age. Pure tone averages over the frequencies of both 0.5, 1 and 2 kHz and 0.5, 1, 2 and 4 kHz - i.e. better ear hearing levels (BEHL) of BEHL0.5-2kH and BEHL0.5-4kHz - were calculated. The prevalence of various grades of hearing impairment was investigated among the 3518 people who participated in audiometric measurements. Two different classifications were used to grade the hearing impairment. According to the World Health Organization (WHO) classification (1991), 94.3% of the subjects had normal hearing, whereas 3.8% had mild hearing impairment, 1.3% had moderate impairment, 0.4% severe impairment and 0.1% profound impairment. When the more recent EU definition (1996) was used, 85.3% of the subjects had normal hearing. Mild impairment was found in 11.5% of the subjects, moderate impairment in 2.8%, severe impairment in 0.3%, and profound in 0.1%. The difference between the two definitions mentioned above (resulting in different prevalence figures of hearing impairments) is clear. The WHO classification reveals the need for rehabilitation and can thus be used as a basis of resource allocation, whereas the EU proposal reveals even the mildest hearing impairments and hence better illustrates the real prevalence of impairment. The need for the current and future audiological services may be estimated from the prevalence rates of hearing impairments. The proportion of the Finnish elderly - the people most frequently using health services - is expected to increase from today's 15% to 23% within the next 20 years. The same phenomenon is to be expected in other Western societies.

The aim of this study was to provide statistical information on otoacoustic emission (OAE) measurements in new-born infants, which could be useful in the interpretation of results and could add some clinical parameters that might be used for future objective and automatic response evaluations. Transient evoked OAEs (TEOAEs) using maximum length sequences (MLS) were recorded in 129 full-term new-born infants between 48 and 72 hours of age. The use of MLS enabled stimulus rates of up to 2000/sec to be utilized. The analysis comprised five main issues: (1) signal to noise ratio (S/N); (2) derived non-linear responses; (3) a combination of derived non-linear emissions called compound non-linear emissions; (4) time/frequency analysis and (5) signal power analysis. The result of the analysis were as follows. (1) The largest S/N ratio was obtained when more than 60% of the recordings were rejected. (2) The derived non-linear emissions comprised level non-linear and rate non-linear responses, the latter obtained by subtraction of recordings at fixed stimulus level, but at different stimulus rates. The rapid suppression of emission amplitude as the stimulus rate increases is the basis for this non-linear response which also features stimulus cancellation. (3) The compound non-linear emissions, consisting of a sum of derived non-linear responses may prove efficient by proper selection of stimulus parameters, but did not in the present form show the expected improvements of amplitude and stimulus cancellation. (4) The time/frequency analysis, however, based on calculations of the instantaneous frequency as a function time after stimulus onset, showed a consistent tendency of falling frequency versus time after stimulus onset as a basic characteristic feature of OAE. (5) The analysis of the emission power as a function of time after stimulus onset showed that linear recordings in new-born infants are reliable, with stimulus ringing fully decayed 3 ms after the stimulus onset. The findings may prove useful in future attempts to develop screening equipment with automatic response evaluation for new-born infants. From a clinical point of view the MLS technique was successful when measuring emissions in neonates, owing to the fast recording time and the utilization of an efficient noise rejection paradigm.

Recording and quantifying eye movement is the basis of audiologic balance testing. The ability to record and quantify eye movement is a key part of the electronystagmography (ENG) test battery. With computerization, eye movements can be more accurately detected and analysed--testing the limits of the standard recording technique. In response to this, manufacturers are introducing alternative recording protocols. Specifically, infra-red video technology allows an accurate and sophisticated recording and analysis of eye motion in response to balance-related stimuli. The purpose of this technical note is to discuss the limitations of the EOG recording method and discuss the advantages that video-oculography offers.

Thirty patients undergoing open heart surgery under induced hypothermia had transient evoked otoacoustic emissions (TEOAE) recorded during cooling to 26.07 degrees C (standard deviation (SD) 4.25 degrees C) vesically measured temperature and 24.86 degrees C (SD 4.7 degrees C) nasopharyngeally measured temperature respectively. Subsequently tè patients were rewarmed until normal body temperature was reached again. There was a clear influence of body temperature on the amplitudes and reproducibilities of the TEOAE. The relationship of temperature and amplitude or reproducibility during the cooling phase was significantly different from that during rewarming. No TEOAE were measurable during cooling at a mean temperature lower than 33.41 degrees C (SD 2.04 degrees C) vesical temperature and 30.16 degrees C (SD 3.0 degrees C) nasopharyngeal temperature respectively. During rewarming the echoes became recognizable again at a mean temperature of 28.75 degrees C (SD 3.38 degrees C) vesical temperature and 27.49 degrees C (SD 2.99 degrees C) nasopharyngeal temperature. These results suggest a hysteresis in the relationship between the amplitude of TEOAE and temperature, similar to the well-established relationship between evoked potentials and temperature.

Transiently evoked otoacoustic emissions (TEOAE) and auditory brainstem response (ABR) tests were used in parallel to screen 862 neonates with risk factors for hearing loss. Seven neonates (0.81%) passed on TEOAE screen yet failed on ABR in one ear (six neonates) or both ears (one neonate). This combination of results has been termed 'anomalous'. Examination of audiometric results obtained on follow-up shows that in one ear of one neonate the result was consistent with the later confirmed audiogram shape. The explanation for the anomalous results in the remaining ears is unclear although neural maturation and the effects of hyperbilirubinaemia are possibilities. There were no instances of progressive or retrocochlear hearing loss identified. None of the seven neonates had better ear hearing loss of > or = 40 dB on long term follow-up.

This paper presents a study in which five cochlear implantees were asked to discriminate the timbre of stimuli with temporally asymmetric envelopes. Stimuli were damped and ramped sinusoids presented acoustically. They were transformed by the speech processor of the implant and were presented through one electrode. All cochlear implantees could discriminate the damped and ramped sinusoids when the half-life was 4 ms, the carrier frequency was 400 Hz, and the period of the envelope was 50 ms. In a second experiment, timbre discrimination performance was measured as a function of half-life for two cochlear implantees. Both showed that timbre discrimination was possible over the range 1-24 ms. In normal-hearing listeners, the range is 1-64 ms and in cochlear implantees, stimulated directly without the speech processor, the range is 1-300 ms. At long half-lives, the decrease in discrimination performance observed with the speech processor appears to be due to the amplitude compression applied by the device. The present results suggest that it may be important to ensure that cochlear implants do not restrict temporal asymmetry unduly when applying compression to control level.