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Biomedical subjects

M E Lutman

Publications and source records attributed to M E Lutman.

71 records · Page 4Linked to original sources
PubMed1984

The relationship between acoustic reflex threshold and air-bone gap.

Neither air-bone gap nor acoustic reflex presence/absence gives an unequivocal indication of abnormality in middle-ear sound transmission. In the present study, a stratified population sample was investigated to examine the interrelationships between these and other parameters of middle-ear status. Of a total of 1725 ears, 1450 had both normal acoustic reflex threshold (ART less than or equal to 100 dB; see text) and air-bone gap (ABG less than or equal to 15 dB); 70 had both abnormal ART and ABG; 160 had abnormal ART but normal ABG; 45 had abnormal ABG but normal ART. Examination of data on tympanic membrane appearance and middle-ear pressure in the latter two groups suggests that ART is a considerably more sensitive indicator than ABG of hearing loss involving middle-ear abnormality, with only a marginally higher rate of false positives. However, a more comprehensive clinical picture is obtained when both ART and ABG are measured.

Acoustic Impedance Tests↗
PubMed1983

Microcomputer-controlled psychoacoustics in clinical audiology.

Several commonly used psychoacoustical procedures for the evaluation of auditory function can only be carried out practically when a computer is used to control stimulus presentation. In particular, there are several procedures, such as gap detection and non-simultaneous masking, which require accurate and adaptable timing of signals which could not be conveniently carried out using manually operated or hard-wired equipment. This paper describes the development of a practical system for clinical research which is capable of carrying out a wide range of psychoacoustical procedures. The development has involved three stages: (a) General design of the system so that it is suited to the procedures envisaged; (b) design of the hardware to meet acoustical constraints such as linearity and signal-to-noise ratio; and (c) software development to provide a means for the non-expert of producing control programs with a minimum of effort. Although the system is still being improved, it is now in practical use and it is possible to produce new working control programs within a few minutes.

Audiometry↗
PubMed1982

Validation of a screening oto- admittance instrument.

A within-subject comparison between an American Electromedics 85R screening tympanometer and a Grason-Stadler 1723 clinical otoadmittance meter indicated equivalent results for middle-ear pressure. Tympanometer admittance readings needed to be rescaled to concur with the oto-admittance meter. Screening by acoustic reflex response using the single-intensity stimulus of the tympanometer was problematic and gave many misleading results.

Acoustic Impedance Tests↗
PubMed1980

Ipsilateral acoustic reflex artefacts measured in cadavers.

Ipsilateral acoustic reflex eliciting stimuli were presented via the probes of six impedance meters to cadaver ears to determine the minimum stimulus levels at which apparent impedance changes occurred. These artefactual indications of impedance change were detected in all but one instrument within the range of intensities available for all frequencies tested. The remaining instrument employs a pulsed stimulus technique which attempts to avoid the artefact problem, and this device only produced artefacts at one frequency and at relatively higher levels than the other instruments. Attempts were made to increase the minimum intensities at which artefacts occurred by introducing various pressure differentials across the tympanic membrane. Generally only small (< 10 dB) increases in the artefact threshold were obtained in this way, although with one instrument there were somewhat larger increases.

Acoustic Impedance Tests↗
PubMed1980

Real-ear calibration of ipsilateral acoustic reflex stimuli from five types of impedance meter.

The Hearing Level scale has been established in national and international standards for tones presented via supra-aural earphones. However, the standards do not encompass stimuli from the probes of ipsilateral impedance meters. This study transfers the calibration of standardised earphones to the probes of five types of impedance meter and therefore enables the intensities of their ipsilateral stimuli to be defined in terms of Hearing Levels. The method used for transfer of calibration is based on equality of acoustic reflex responses elicitied by the impedance meter probe and by a standardised earphone. Ten subjects were tested with all five instruments to ensure comparability between instruments. The resultant calibration data are expressed in terms of Reference Equivalent Threshold Sound Pressure Levels measured in both 2 cc and Zwislocki couplers. The results indicate a considerable variation amongst instruments emphasising the need for a set of calibration data for each design of probe. This variation is less marked for the Zwislock coupler than for the 2 cc coupler.

Acoustic Impedance Tests↗
PubMed1979

Calibration of ipsilateral acoustic reflex stimuli. A comparison of loudness balance and equal reflex response methods.

Hearing levels for ipsilateral impedance probes have not yet been established. This study compares two techniques for "transfer of threshold" from the standardised TDH-39 earphone to the unstandardised probe. Ten normal hearing subjects participated, using both a loudness balance technique and a reflex measurement technique. The reflex measurement technique involved comparing the intensity required from each transducer to produce an equal reflex response, whereas the loudness balance technique compared the intensity required from each transducer for equal loudness. The two techniques were found to differ significantly in terms of the Hearing Level values which they produced. Differences between techniques amounted to approximately 3 dB at 1000 Hz, 11 dB at 2000 Hz, and 7 dB at 3000 Hz. As a comparison of the two techniques, the day to day variances were statistically estimated. The reflex measurement technique was shown to be more reliable than the loudness balance technique.

Acoustic Impedance Tests↗
PubMedDate not supplied

Note on identification and rectification of the "overshoot" observed with the Grason-Stadler otoadmittance meter during acoustic reflex measurements.

Acoustic reflexes measured with the Grason-Stadler 1720 otoadmittance meter exhibit an artefactual overshoot due to the transient response characteristics of the instrument. Additional circuitry has been developed to overcome this problem. It allows the temporal characteristics of the acoustic reflex to be recorded accurately without this artefact.

Bone Conduction↗
PubMedDate not supplied

The distribution of hearing threshold levels in the general population aged 18-30 years.

Hearing threshold levels at audiometric frequencies between 0.25 and 8 kHz were obtained by manual audiometry using 5-dB steps in adults aged 18-30 years, as part of a large random survey of hearing in the UK. After screening to ensure otological normality, including careful analysis of any noise exposure history, the median thresholds of the 241 screened subjects deviated from audiometric zero by an average of 4.3 dB over the frequencies from 0.5 to 4 kHz in the direction of poorer hearing. Even greater deviations were evident at 0.25, 6 and 8 kHz, consistent with the discrepancies between normal hearing threshold and ISO 389 standard reference zero that have been reported previously. Within the age band from 18 to 30 years, age did not influence hearing threshold levels. Socio-economic status defined by occupational group (manual or non-manual) had a significant effect at frequencies up to 2 kHz, with those in non-manual occupations having better hearing than those in manual occupations by an average of 2.4 dB, despite screening for middle-ear disease, noise exposure and other possibly confounding factors. In a screened sample, males had better hearing threshold levels than females, but this difference was sensitive to screening criteria. The unscreened sample had median hearing threshold levels that were at most 2 dB worse than the screened sample across the frequency range.

Adolescent↗
PubMedDate not supplied

Reduced àudiogram ripple' in normally-hearing subjects with weak otoacoustic emissions.

Correspondence between spectral patterns in otoacoustic emissions (OAE) and the fine structure of the pure-tone audiogram has often been noted, but the link is by no means clearly understood nor complete in all subjects. This paper presents part of a broader study focusing on individuals with normal hearing but anomalously weak OAEs, the primary purpose of which was to determine the reasons for the weak OAEs. Subjects were selected from an exhaustive search of some 400 ears of highly co-operative adults, and comprised a test group of subjects with normal hearing thresholds but weak OAEs, and a control group of normals from the same sample. Reported here are data on audiogram fine structure measured in the two groups of subjects. The basic finding is that the subjects with weak OAEs also exhibited significantly less audiogram fine structure than the controls, as evaluated by analysing the periodicity in the respective threshold curves as well as by identifying and quantifying individual peaks in the curves. These findings first provide further evidence of an underlying link between the fine structure of the audiogram and OAEs, as proposed by Kemp in his original work. Second, assuming that the degree of fine structure would be largely unaffected by minor middle ear alterations, our findings suggest that predominantly cochlear rather than middle ear factors are responsible for the low levels of OAEs in the normal subjects of our test group. Finally, the results presented suggest that, like OAEs, audiogram fine structure measurements provide information on the auditory system that is not available in the conventional pure-tone audiogram.

Adult↗
PubMedDate not supplied

Correspondence amongst microstructure patterns observed in otoacoustic emissions and Békésy audiometry.

Similar patterns of microstructure have been reported in normal ears for Békésy threshold recordings and various forms of otoacoustic emissions (OAE). It has been suggested that they have a common origin associated with the amplifying function of the outer hair cell system and wave interactions occurring within cochlear mechanics. Fine-frequency Békésy audiometry was conducted in ten normal ears and its microstructure was compared with that recorded using two OAq techniques: stimulus frequency (SFOAE) and distortion product (DPOAE). All sweeps encompassed the frequency range from 992 to 2000 Hz in 16-Hz steps. The same probe was used for all Békésy and OAE recordings to eliminate transducer effects. SFOAEs were obtained with stimulus intensities of 0, 3, 6 and 9 dB. DPOAEs were obtained for 2F1-F2 with primary levels (L1/L2) of 40/30, 45/35, 50/40 and 55/45 dB. Reliable microstructure was recorded in all ears. Mean values of microstructure peak spacing ranged from 5.6 to 9.3 per cent amongst methods, consistent with published data. Microstructure was similar within each OAE method for different stimulus intensities for each subject. However, comparisons between Békésy and OAEs, or between OAE methods, did not show the strong correspondence that would be expected if there were a simple common origin to the microstructure. There was weak support for the expected correspondence between Békésy and SFOAE, but no support for any correspondence between Békésy and DPOAE. It is concluded that the various forms of microstructure cannot be explained by a simple common origin.

Adult↗
PubMedDate not supplied

Methods for early identification of noise-induced hearing loss.

An ideal test for identifying shifts in cochlear function would be highly repeatable and sensitive to minor damage. Three types of otoacoustic emission (OAE) test and pure-tone audiometry were evaluated for this purpose. They were compared in terms of test-retest repeatability within subjects and sensitivity to differences between subjects. The OAE measures were transiently evoked either conventionally (TEOAE) or using maximum length sequences (TEOAE-MLS), or continuously evoked as distortion products (DPOAEs). Several stimulus conditions were evaluated for each type. Thirty eight subjects with normal hearing or mild hearing losses were tested on all measures. Test-retest repeatability was rescaled according to the sensitivity of each measure to differences in hearing threshold level, thus allowing a direct comparison across methods. The most repeatable method thus defined was TEOAE-MLS which gave a rescaled standard deviation of 1.8 dB on replication. This was followed by TEOAE and DPOAE which gave rescaled standard deviations of 2.9 and 3.1 dB, respectively. All were more reliable than pure-tone audiometry which had a standard deviation of 4.9 dB. It is concluded that the various OAE measures have the potential to distinguish small changes in cochlear function from measurement uncertainty, and hence show promise for monitoring cochlear function in ears exposed to noise or other hazards.

Acoustic Stimulation↗
PubMedDate not supplied

Transient-evoked otoacoustic emissions in a representative population sample aged 18 to 25 years.

Transient-evoked otoacoustic emissions (TEOAEs) were obtained from 688 ears of a group of 345 young adults aged 18 to 25 years, using the Otodynamics ILO88 in the standard, non-linear mode. Normative data for TEOAEs obtained from 186 otologically normal (ON) ears are presented. In 5 ON ears, there was no recordable response, despite hearing threshold levels better than 20 dB. The main factors affecting the TEOAE level were (1) gender, where females had larger responses on average than males; (2) tympanometric measures, where ears with entirely normal tympanometric measures had larger responses than those with minor tympanometric abnormalities; (3) click stimulus intensity measured in the ear canal, which correlated positively with TEOAE level; and (4) hearing threshold level at 0.5 kHz, which correlated negatively with amplitude. There was also a small effect of social noise exposure in the 2-kHz region of the TEOAE, where the response was lower in those subjects exposed to significant social noise.

Acoustic Impedance Tests↗