Does the human immunodeficiency virus influence the vestibulocollic reflex pathways? A comparative study.

BACKGROUND: This study compared vestibulocollic reflex and vestibulo-ocular reflex functioning in subjects with and without human immunodeficiency virus. It also described test results throughout progression of the disease and compared the results of human immunodeficiency virus positive subjects who were receiving antiretroviral therapies with those not receiving this treatment. METHODS: Subjects comprised 53 adults with human immunodeficiency virus (mean age 38.5 ± 4.4 years) and 38 without human immunodeficiency virus (mean age 36.9 ± 8.2 years). Clinical examinations included cervical vestibular-evoked myogenic potential and bithermal caloric testing. RESULTS: Abnormal cervical vestibular-evoked myogenic potential and caloric results were significantly higher in the human immunodeficiency virus positive group (p = 0.001), with an odds ratio of 10.2. Vestibulocollic reflex and vestibulo-ocular reflex involvement increased with progression of the disease. There were more abnormal test results in subjects receiving antiretroviral therapies (66.7 per cent) than in those not receiving antiretroviral therapies (63.6 per cent), but this difference was insignificant. CONCLUSION: Human immunodeficiency virus seems to influence vestibulocollic reflex pathways. Combining cervical vestibular-evoked myogenic potential and caloric testing may be useful to detect early neurological involvement in human immunodeficiency virus positive subjects.

Evaluation of the rotatory vestibular test: exploration of stimulus parameters.

OBJECTIVES: The aim of this study was to construct a rotational test protocol after exploring the stimulus parameters of the rotatory vestibular test. METHODOLOGY: Twenty-four normal subjects were submitted to three different rotational paradigms: the sinusoidal harmonic acceleration test (SHAT), the pseudorandom rotation test (PRRT), and the velocity step test (VST). We investigated the influence of frequency and velocity on gain, phase and asymmetry values for the SHAT and the PRRT. In the case of the VST, we examined the influence of velocity and deceleration on gain, slow component velocity at deceleration, time constant, nystagmus preponderance, and time constant asymmetry. RESULTS: Frequency affected the SHAT response parameters, with significant phase differences between the frequencies 0.01, 0.02, 0.05, 0.1, and 0.2 Hz, while velocity, if kept below 150 degrees/s, had no influence on the results. In the case of the VST, responses were influenced by stimulus velocity and not by stimulus deceleration, with significantly higher gain values for the velocities 50 and 250 degrees/s. CONCLUSIONS: A velocity of 50 degrees/s tested at the frequencies 0.01, 0.02, 0.05, 0.1, and 0.2 Hz was suggested for the SHAT and PRRT protocol, whereas a velocity of 100 degrees/s with a deceleration of 200 degrees/s2 was preferred for the VST. The relevance of this rotational protocol has yet to be established from patient data.

Sensitivity of transient evoked and distortion product otoacoustic emissions to the direct effects of noise on the human cochlea.

Measurement of otoacoustic emissions (OAEs) has been proposed as a sensitive test to reliably assess the effects of noise exposure. The present study in humans was designed to evaluate the sensitivity and applicability of transient evoked OAEs (TEOAEs) and 2f1-f2 distortion product OAEs (DPOAEs) as quantitative indices of the functional integrity of the outer hair cells (OHC) during growth of and recovery from temporary threshold shift (TTS). This was examined in two different groups of volunteers by measuring the per- and post-stimulatory effects of a one hour BBN and an on-site five hour exposure to loud music from a discotheque. The results of both experiments show consistent growth and recovery patterns for both DPOAEs and TEOAEs. For TEOAEs, both the reproducibility scores and signal to noise ratio values for the 4 kHz frequency band exhibited the greatest sensitivity. The DPOAEs, on the other hand, showed the greatest sensitivity between 2 and 5.5 kHz. Thus, both the TEOAEs and DPOAEs have a great potential in the detection of TTS after noise exposure.

Multi-variant analysis of otoacoustic emissions and estimation of hearing thresholds: transient evoked otoacoustic emissions.

Evaluation of cochlear hearing loss by means of transiently evoked otoacoustic emissions is already established in clinical practice. However, accurate prediction of pure-tone thresholds is still questioned and is still regarded as troublesome. Both click- and tone-burst-evoked otoacoustic emissions at several intensity levels were measured and analysed in 157 ears from normally hearing and 432 ears from patients with different degrees of pure sensory hearing loss using the ILO88/92 equipment. Results of otoacoustic emissions (OAE), elicited by clicks and tone-bursts at centre frequencies from 1 to 5 kHz, were analysed using two different statistical methods. Both multivariate discriminant analysis and forward multiple regression analysis were used to determine which OAE variables were most discriminating and best at predicting hearing thresholds. We found that a limited set of variables obtained from both tone-burst and click measurements can accurately predict and categorize hearing loss levels up to a limit of 60 dB HL. We found correct classification scores of pure-tone thresholds between 500 and 4000 Hz up to 100 per cent when using combined click and tone-burst otoacoustic measurements. Prediction of pure-tone thresholds was correct with a maximum estimation error of 10 dB for audiometric octave frequencies between 500 and 4000 Hz. Measurements of multiple tone-bursts OAEs have a significant clinical advantage over the use of clicks alone for clinical applications, and a good classification and prediction of pure-tone thresholds with otoacoustic emissions is possible.

Distortion product otoacoustic emissions: a normative study.

Distortion product otoacoustic emissions (DPOAEs) were quite recently introduced as a new objective auditory screening technique, having a unique potential because of their ability to analyze the micromechanical functions of the cochlea in a frequency-specific way. In 1992, Kemp and Bray released the commercially available Otodynamics Analyzer ILO92, which enabled investigators and audiological centres to perform DPOAE measurements in different populations, but without any relationship to normative data. The purpose of this study was to describe the normative aspects of 2f1-f2 DPOAEs obtained with the ILO92 from 101 normal ears of 101 healthy young adults. The DPOAEs were obtained automatically by means of two data-collection protocols on the ILO92 in the form of DP-gram and DP-growth functions. These data were statistically processed to form a normative database which has the potential of serving as a basis of for further research aimed at determining the utility of DPOAE testing in evaluating ear pathology.