Clinical examination and management of the dizzy patient.

Dizziness is the commonest reason for a GP appointment over the age of 75 years and many dizzy patients will end up in hospital. This article introduces the range of vestibular disorders commonly seen in hospital practice with a symptom-based approach and discusses the range of treatments that might be considered.

The effect of electrode positioning on the ocular vestibular evoked myogenic potential to air-conducted sound.

OBJECTIVE: To assess the effect of electrode position on the amplitude and latency of ocular vestibular evoked myogenic potentials (oVEMPs) produced by air-conducted (AC) sound with a view to optimisation of the recording paradigm. METHODS: Eight otologically normal subjects (16 ears) were stimulated by 500 Hz AC tone bursts at 95 dBnHL; oVEMP traces were recorded below the eye contralateral to the acoustic stimulation. Five independent oVEMP measurements were recorded with the active electrode in equally spaced positions in the infra-orbital plane relative to a reference electrode positioned 2 cm below the lower lid in the orbital midline. These measurements included the accepted standard-montage in which the electrodes were positioned vertically above and below each other in the orbital midline. A further recording was made using a belly-tendon montage with reference to the inferior oblique muscle. RESULTS: Of the six recording paradigms tested the largest amplitude oVEMP response was found using the belly-tendon montage with an n10 average of 5.67 ± 3.42 µV (sd). This was significantly larger than the amplitude recorded using the standard-montage (p < 0.01). With the reference electrode in the orbital midline, the position of the active electrode in the infra-orbital plane was found to significantly alter the response magnitude. As the active electrode was moved laterally the response reduced in amplitude, however when moved medially the response polarity reversed indicating the existence of a null-point at which no response was present. CONCLUSIONS: The location of oVEMP recording electrodes significantly alters the response amplitude. Whilst the standard-montage provides a reasonable method for recording oVEMPs, the belly-tendon montage results in a significantly larger amplitude response. Furthermore medial and lateral variations in the position of the active electrode using the standard-montage significantly affect the magnitude and polarity of the response. SIGNIFICANCE: The standard-montage used for recording oVEMPs is sensitive to the placement of the active electrode. Small variations in position result in significant changes in the n(10) amplitude and this may account for the variability reported in the literature. Using the belly-tendon montage, larger amplitude responses can be elicited which may improve the robustness with which oVEMPs can be collected. However this enhancement in response amplitude must be balanced against the increased possibility of signal contamination from neighbouring extraocular muscles.

Altered frequency dynamics of cervical and ocular vestibular evoked myogenic potentials in patients with Ménière's disease.

OBJECTIVE: To measure the frequency dynamics of cervical and ocular vestibular evoked myogenic potentials in healthy subjects and patients with Ménière's disease. STUDY DESIGN: A prospective cohort study. SETTING: A university teaching hospital. SUBJECTS: Eight healthy volunteers (16 ears) and 12 adult patients with unilateral Ménière's disease (8 with definite disease and 4 with probable disease) by American Academy of Otolaryngology - Head and Neck Surgery diagnostic criteria. INTERVENTIONS: Cervical and ocular vestibular evoked myogenic potentials generated by tone bursts at 250, 500, 750, 1,000, 1,500, 2,000, 3,000, and 4,000 Hz were measured in both groups. MAIN OUTCOME MEASURES: The frequency sensitivity of both the cervical and ocular vestibular evoked myogenic potentials, as evaluated by p13-n23 and n10 amplitudes in healthy ears and in ears affected and not affected by Ménière's disease. RESULTS: Cervical and ocular vestibular evoked myogenic potentials were present in all ears tested. In the healthy volunteers, the acoustic stimulus frequency at which the response amplitudes were largest was 500 Hz. This shifted to higher frequencies in patients with definite Ménière's disease for both measurements, with the effect being more pronounced for ocular vestibular evoked myogenic potentials. The shift was less marked in the probable Ménière's group and was absent in the unaffected ears of the Ménière's patients. CONCLUSION: Ménière's ears display alterations in cervical and ocular vestibular evoked myogenic potentials tuning responses with changes in the latter being more prominent. These findings indicate that the disease process affects both the otolith organs but may have an enhanced effect on the utricle. We propose that this more dominant affect may relate to the anatomical configuration of the utricle.

TRANSDUCER FIELD IMAGING USING ACOUSTOGRAPHY.

A common current practice for transducer field mapping is to scan, point-by-point, a hydrophone element in a 2D raster at various distances from the transducer radiating surface. This approach is tedious, requiring hours of scanning time to generate full cross-sectional and/or axial field distributions. Moreover, the lateral resolution of the field distribution image is dependent on the indexing steps between data points. Acoustography is an imaging process in which an acousto-optical (AO) area sensor is employed to record the intensity of an ultrasound wavefield on a two-dimensional plane. This paper reports on the application of acoustography as a simple but practical method for assessing transducer field characteristics. A case study performed on a commercial transducer is reported, where the radiated fields are imaged using acoustography and compared to the corresponding quantities that are predicted numerically.