Auditory brainstem responses to middle- and low-frequency tone pips

Occupational noise exposure and its association with incident hyperglycaemia: a retrospective cohort study

Noise pollution is reported to be associated with diabetes, but few studies have elucidated the associations between noise frequency characteristics. We aimed to evaluate the relationships between different noise frequency components and incident hyperglycaemia. An industry-based cohort of 905 volunteers was enrolled and followed up to 2012. Octave-band frequencies of workstation noise and individual noise levels were measured in 2012 to classify subjects' exposures retrospectively. We applied Cox regression models to estimate the relative risk (RR) of hyperglycaemia. An increased RR for hyperglycaemia of 1.80 (95% confidence interval [CI]: 1.04, 3.10) was found among subjects exposed to ≥ 85 A-weighted decibels (dBA) compared with those exposed to < 70 dBA. The high-exposure groups at frequencies of 31.5, 63, 125, 250, 500, 1000, and 2000 Hz had a significantly higher risk of hyperglycaemia (all p values < 0.050) than the low-exposure groups. A 5-dB increase in noise frequencies at 31.5, 63, 125, 250, 500 Hz, and 1000 Hz was associated with an elevated risk of hyperglycaemia (all p values < 0.050), with the highest value of 1.27 (95% CI: 1.10, 1.47) at 31.5 Hz (p = 0.001). Occupational noise exposure may be associated with an increased incidence of hyperglycaemia, with the highest risk observed at 31.5 Hz.

Perceptual Encoding in Auditory Brainstem Responses: Effects of Stimulus Frequency

PURPOSE

A central question about auditory perception concerns how acoustic information is represented at different stages of processing. The auditory brainstem response (ABR) provides a potentially useful index of the earliest stages of this process. However, it is unclear how basic acoustic characteristics (e.g., differences in tones spanning a wide range of frequencies) are indexed by ABR components. This study addresses this by investigating how ABR amplitude and latency track stimulus frequency for tones ranging from 250 to 8000 Hz.

METHOD

In a repeated-measures experimental design, listeners were presented with brief tones (250, 500, 1000, 2000, 4000, and 8000 Hz) in random order while electroencephalography was recorded. ABR latencies and amplitudes for Wave V (6-9 ms) and in the time window following the Wave V peak (labeled as Wave VI; 9-12 ms) were measured.

RESULTS

Wave V latency decreased with increasing frequency, replicating previous work. In addition, Waves V and VI amplitudes tracked differences in tone frequency, with a nonlinear response from 250 to 8000 Hz and a clear log-linear response to tones from 500 to 8000 Hz.

CONCLUSIONS

Results demonstrate that the ABR provides a useful measure of early perceptual encoding for stimuli varying in frequency and that the tonotopic organization of the auditory system is preserved at this stage of processing for stimuli from 500 to 8000 Hz. Such a measure may serve as a useful clinical tool for evaluating a listener's ability to encode specific frequencies in sounds.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.6987422.

Occupational Noise Frequencies and the Incidence of Hypertension in a Retrospective Cohort Study

Occupational noise exposure is associated with cardiovascular disease, but little is known about the contributions of noise frequency components. This retrospective study investigated the relationship between exposure to different noise frequencies and the incidence of hypertension. A cohort of 1,002 volunteers from 4 machinery and equipment manufacturing companies in Taichung, Taiwan, was followed from 1973 to 2012. Personal noise measurements and environmental octave-band analyses were performed to divide subjects into different exposure groups. Cox regression models were used to estimate the relative risk of hypertension. Participants exposed to ≥80 A-weighted decibels (dBA) over 8 years had a higher relative risk of hypertension (relative risk = 1.38, 95% confidence interval: 1.02, 1.85) compared with those exposed to <75 dBA. Significant exposure-response patterns were observed between incident hypertension and stratum of noise exposure at frequencies of 250 Hz, 1 kHz, 2 kHz, 4 kHz, and 8 kHz. The strongest effect was found at 4 kHz; a 20-dBA increase in noise exposure at 4 kHz was associated with a 34% higher risk of hypertension (relative risk = 1.34, 95% confidence interval: 1.01, 1.77). Occupational noise exposure may be associated with an increased risk of hypertension, and the 4 kHz component of occupational noise exposure may have the strongest relationship with hypertension.

Road traffic noise frequency and prevalent hypertension in Taichung, Taiwan: a cross-sectional study

BACKGROUND

Epidemiological studies have reported the association between hypertension and exposure to road traffic noise, but the association between noise frequency characteristics is not clear. This study investigated the association between exposure to different frequency components of road traffic noise and the prevalence of hypertension in central Taiwan.

METHODS

We recruited 820 residents living near main roads for more than 3 years. Frequency components of traffic noise and traffic flow rates during 0900-1700 on weekdays were measured simultaneously in 2008. Multiple logistic regressions were conducted to estimate odds ratios (ORs) for diagnosed hypertension, adjusting for potential confounders and the total traffic flow rate.

RESULTS

The high-exposure group (≥ the median of noise levels [decibels, dB]) at 63 Hz, 125 Hz and 1000 Hz had ORs for hypertension of 2.77 (95% confidence interval [CI]: 1.17-6.52), 4.08 (95% CI: 1.57-10.63) and 1.98 (1.00-3.92) (95% CI: 1.00-3.92), respectively, compared to the low-exposure group (< the median of noise levels [dB]). There was an increasing trend in the prevalence of hypertension by exposure to road traffic noise at 63, 125 and 1000 Hz in all subjects and in men. Total subjects exposed to ≥ 51 dB at 125 Hz had an OR of 4.65 (95% CI = 1.46-14.83) compared to those exposed to < 47 dB.

CONCLUSIONS

With the possible bias of exposure misclassification and a bias from using diagnosed hypertension, these results suggest that exposure to road traffic noise at low and hearing-sensitive frequencies may be associated with hypertension and exposure to noise at 125 Hz may have the greatest risk for hypertension.

On the dual structure of the auditory brainstem response in dogs

OBJECTIVE

To use the over-complete discrete wavelet transform (OCDWT) to further examine the dual structure of auditory brainstem response (ABR) in the dog.

METHODS

ABR waveforms recorded from 20 adult dogs at supra-threshold (90 and 70dBnHL) and threshold (0-15dBSL) levels were decomposed using a six level OCDWT and reconstructed at individual scales (frequency ranges) A6 (0-391Hz), D6 (391-781Hz), and D5 (781-1563Hz).

RESULTS

At supra-threshold stimulus levels, the A6 scale (0-391Hz) showed a large amplitude waveform with its prominent wave corresponding in latency with ABR waves II/III; the D6 scale (391-781Hz) showed a small amplitude waveform with its first four waves corresponding in latency to ABR waves I, II/III, V, and VI; and the D5 scale (781-1563Hz) showed a large amplitude, multiple peaked waveform with its first six waves corresponding in latency to ABR waves I, II, III, IV, V, and VI. At threshold stimulus levels (0-15dBSL), the A6 scale (0-391Hz) continued to show a relatively large amplitude waveform, but both the D6 and D5 scales (391-781 and 781-1563Hz, respectively) now showed relatively small amplitude waveforms.

CONCLUSIONS

A dual structure exists within the ABR of the dog, but its relative structure changes with stimulus level.

SIGNIFICANCE

The ABR in the dog differs from that in the human both in the relative contributions made by its different frequency components, and the way these components change with stimulus level.

Sound-evoked neurogenic responses with short latency of vestibular origin

OBJECTIVE

In ABR recording, a large negative deflection with a latency of 3 ms (N3) has been recorded in patients with peripheral profound deafness. It has been suggested that N3 might be of vestibular origin. So far, N3 has been recorded only in patients with peripheral profound deafness. If we can record N3 potentials in subjects with preserved hearing, recording N3 potentials might be a new clinical test of the vestibular system. To record neurogenic potentials (N3) of vestibular origin in healthy volunteers and patients with vestibular disorders.

METHODS

Twelve healthy volunteers (10 men and two women, aged 23-37 years) and 12 patients with vestibular disorders (6 men and 6 women, aged 29-71 years) were enrolled in this study. To record responses, surface electrodes were placed on the ipsilateral mastoid and the vertex. An electrode on the nasion served as the ground. Recording was performed using an auditory evoked potential recording system with a mini-mixer and a stereo-amplifier. Signals at the vertex to the ispilateral mastoid were amplified and bandpass filtered (100-3000 Hz). One thousand-hertz short tone bursts (1 kHz STB; rise/fall time=0.5 ms, plateau time=1 ms) were presented to either ear through a headphone with or without white noise (WN) ipsilateral to the stimulated ear. The stimulation rate was 10 Hz, and the analysis time was 10 ms. The responses to 500 stimuli were averaged twice.

RESULTS

When 1 kHz STB (95 dBnHL, equivalent to 130 dBSPL) were presented with 100 dBSPL WN (ipsilateral to the stimulated ear), a negative peak with 3-4 ms latency (N3) was observed in 23 of the 24 ears (95.8%) with reproducibility in healthy subjects. Without WN, N3 was observed in 17 of the 24 ears (70.8%). The threshold of N3 was 90.2 dBnHL on the average. The presence of N3 in the patients was in agreement with the presence of the VEMP, which were also recorded.

CONCLUSIONS

Using techniques of WN exposure ipsilateral to the stimulated ear, we recorded N3 in healthy subjects and in vestibular disorder patients with preserved hearing. This negative peak is likely to be of vestibular origin.

SIGNIFICANCE

N3 may be measured from subjects who cannot contract neck muscles due to their ages, mental states, or consciousness disorders. In other words, N3 may be measured from subjects from whom VEMP cannot be recorded. In combination with VEMP, N3 may be useful for the detection of lesion sites.

Audiogram Construction Using Frequency-Specific Auditory Brainstem Response (ABR) Thresholds

Brainstem evoked response audiometry (ABR) permits auditory pathway assessment without the need for voluntary response. Brainstem responses are unaffected by attention, drugs, and most other confounding conditions. Consequently, if ABR could be used to determine hearing threshold in the speech frequencies, it would have great value for patients who are unable or unwilling to respond accurately during behavioral audiometric testing. Utilizing broad band clicks, one can only estimate hearing sensitivity in the frequency range of 2,000 to 4,000 Hz. This is inadequate for medical or legal purposes in which hearing in the speech frequencies must be assessed. Consequently, we have developed a modified ABR technique that permits a more accurate determination of hearing threshold at 500, 1,000, 2,000 and 3,000 Hz, as illustrated in tests on 27 normal ears. This technique has great potential value for neonatal and mentally handicapped populations, as well as for individuals involved in hearing loss litigation.

Hearing threshold investigations in infants and children

The influence of age on the auditory brainstem responses (ABRs) of 39 normal infants (aged less than 6-18 months) and children (aged 19 months to 3.5 years) was investigated. While the ABR threshold of infants (mean value: 9.3 dB nHL) is still slightly higher than that of normal-hearing adults, children show a distribution which corresponds approximately to that of adults. The mean I-V interpeak interval of the ABRs of these children is slightly longer (4.1 ms) compared with a normal value in the range of 3.95 ms. Furthermore, a comparison was made between the threshold values measured by brainstem-evoked response audiometry and conditioned orientation reflex audiometry in 115 children of between 6 months and 3.5 years of age who were suspected to be hearing impaired. In the case of normally configurated ABRs there was an 86% agreement of thresholds (within the limits of +/- 10 dB) while it amounted to 66% in the case of ABR changes, which indicates brainstem lesions.

Low-level 0.5 and 1 kHz auditory brainstem responses. A search for the low-frequency point in the two-point ABR audiogram

We have compared the auditory brainstem responses (ABRs) to 0.5 and 1 kHz tone burst stimuli with high-pass noise masking in 10 normal-hearing adults. The overall quality of the low-level responses was poor, but a two-point ABR audiogram is feasible by using the summation technique described. The 1 kHz stimulus gave slightly better responses than 0.5 kHz, and a correction factor of 30-40 dB seems necessary. Our data indicate that these low-level, low-frequency responses are frequency-specific.

Auditory brainstem responses in noise-induced permanent hearing loss

Fifty-four patients (108 ears) with presumed noise-induced hearing loss, were subjected to tonal and speech audiometry, impedance tests and measurements of auditory brainstem responses (ABR), in order to check for possible retrocochlear involvement. ABR data indicated that latency values of waves I, III and V, as well as III-I, V-III and V-I intervals fell within the normal range in all cases (M +/- 2 SD), even for fast repetition rates (51 stim/s). Poor waveform resolution of early components, particularly of wave I, was found in 12 ears (11.1%) and a total absence of evoked potentials not always related to the hearing loss, occurred in 5 ears (4.6%).

Low-frequency auditory brainstem response threshold

Auditory brainstem thresholds have been determined in 35 non-cooperative, anaesthetized children using a 'two-point audiogram' paradigm. The high-frequency point was found with a 2 kHz tone-burst without masking, and the low-frequency with a 0.5 kHz tone-burst together with 1 kHz high-pass noise masking. Great variability was found in the low-frequency thresholds, and only 3 of 18 ears with normal high-frequency thresholds had low-frequency thresholds below 70 dB nHL. It is concluded that the 0.5 kHz tone-burst with 1 kHz high-pass noise masking is not a reliable method for routine assessment of low-frequency auditory threshold at the brainstem level.

Auditory brain-stem (ABRs) and middle latency auditory responses (MLRs) in the prognosis of severely head-injured patients

Auditory brain-stem responses (ABRs) were studied in 66 subjects with severe head trauma. Middle latency responses (MLRs) were also recorded in 22 of them. Patients were carefully selected to avoid conditions such as pre-existing or acute deafness, hypothermia or ethanol intoxication. In order to evaluate the usefulness of potentials in predicting recovery, patients were classified according to the Glasgow Coma Scale (GCS). ABR tracings were classified into 5 groups and MLR into 2 groups. The recovery was good in the presence of a type 1 ABR, poor in the presence of types 3, 4 and 5. Concerning type 2 ABR, the outcome is related to the MLR type, and to the presence of an electrophysiological improvement within the first 3 months following trauma. The reliability of ABR and MLR in predicting the outcome of severe head injury appears to be greater than other usually considered clinical and instrumental data (age, GCS, CT scan, EEG).

Effects of stimulus repetition rate on slow and fast components of auditory brain-stem responses

Effects of stimulus repetition rate on the slow and fast components of the auditory brain-stem response (ABR) were investigated in 10 adult subjects with normal hearing. The ABRs were recorded with click stimuli at repetition rates of 8, 13.3, 23.8, 40 and 90.9/sec and at an intensity level of 55 dB nHL. Power spectral analysis of the averaged responses was performed. Then the responses were divided into a slow component (0-400 Hz) and a fast component (400-1500 Hz) by using digital filtering technique. The magnitude of the slow component was little affected with increasing stimulus rate from 8/sec to 90.9/sec, while successive waves of the fast component, including wave V, decreased in amplitude as stimulus rate was increased. The latency of the slow component and each wave of the fast component was prolonged with increasing click rates. The shift of latency became longer in the later waves than in the earlier waves.

Frequency specificity of the auditory brainstem responses. A derived-band study

Auditory brainstem responses evoked by both clicks and 0.5 kHz tone-bursts were recorded using the derived-band paradigm in 10 normal-hearing subjects. The derived-band analyses showed a similar distribution of activity with both stimuli, the largest contributions coming from the 2-4 and 4-8 kHz bands. Neither the click nor the 0.5 kHz tone-burst is a frequency-specific stimulus, and both would appear to be unsuitable for brainstem response audiometric evaluation of the apical cochlea.

Altered peripheral and brainstem auditory function in aged rats

A technique for conducting free-field brainstem auditory evoked potential (BAEP) audiometry in unanesthetized, unrestrained rats revealed a non-recruiting 18 dB elevation of click threshold in aged rats. BAEPs were first recorded in young and aged rats to clicks of equal intensity (80 dB SPL). Compared to the young group, aged animals exhibited longer wave I and wave IV latencies with no difference seen in the I-IV central conduction time. The prominent negative wave (No) following wave IV was also delayed and the I-No and IV-No conduction times increased in the aged group. When BAEPs were recorded to clicks with intensities adjusted to 35 dB above individual threshold, no differences in wave I or wave IV latencies or in the I-IV central conduction time were found between groups. However, the No component was delayed and the I-No and IV-No conduction times remained prolonged in the aged group. The results suggest that in addition to changes in peripheral auditory structures, changes in the rostral auditory brainstem accompany age-related hearing loss in rats.

Frequency specificity of the auditory brainstem responses in the cat

The auditory brainstem responses evoked by click, noise-burst and tone-bursts have been recorded in the cat, and octave-wide derived bands obtained at 20 and 50 dB RL intensity levels. At near-threshold intensity both the 2 and 4 kHz tone-bursts are frequency specific, while the click and noise-burst ABR contain no contributions below 2 kHz. The principal contribution to the 1 kHz ABR comes from the 2-4 kHz band, while at 0.5 kHz almost the entire response is generated basally. Higher stimulus intensity produces a spread of activity into other bands. Low frequency cochlear function cannot be assessed by this technique.

Auditory brainstem responses of the cat: on- and off-responses

The auditory brainstem on- and off-responses evoked by tone and noise bursts have been studied in the cat. The number and amplitude of the off-response waves are proportional to the frequency specificity of the on-response, being greatest for the 4-kHz tone burst and smallest for the noise burst. The threshold of the 0.5-kHz off-response is lower than that of the on-response, but the amplitude of the former does not increase at higher stimulus levels. Derived-band studies show that at 4 kHz the on-and off-responses have identical frequency content, the 0.5-kHz off-response is restricted to the 2- to 8-kHz frequency band, while the noise burst off-response is entirely high frequency. The off-response is an on-response and is evoked by acoustic transients from the loudspeaker transducer.

Middle-latency auditory components in response to clicks and low- and middle-frequency tone pips (0.5-1 kHz)

Middle-latency auditory components (MLC) in response to clicks and tone pips have been recorded in 20 normal subjects, aged between 26 and 32 years, in order to verify their reliability in response to frequency-specific stimuli (0.5 and 1kHz). The results indicate a good reliability of MLC obtained when using tone pips. The responses show the conventionally labeled Po, Na, Nb, Pb waves. The latencies of these waves tend to be greater than those of the corresponding waves elicited by clicks and their amplitudes are smaller. This is probably due to an asynchrony of the responses. The Po and Pa waves are the most resistant to decreasing stimulus intensity, as both are clearly detectable down to 20 dB nHL, but Po is the best threshold index because at 20 dB it has a more clear-cut shape than Pa. According to the latency values obtained for MLC elicited by both clicks and tone pips, the Po wave is probably generated at the inferior colliculus level. The latency shift towards the click-elicited Jewett wave V is mainly due to the different filter settings employed. The morphology of MLC elicited by tone pips is less affected by changes in stimulus frequency than that of corresponding auditory brainstem responses. Thus, MLC are a reliable indicator for defining low- and middle-frequency auditory thresholds.