The repeatability of oVEMP in response to low-frequency vibration against the vertex and forehead.

BACKGROUND: The measurement of ocular Vestibular Evoked Myogenic Potentials (oVEMP) is a novel method for investigating vestibular function. Stimulus and recording techniques vary in the literature. A standardized test procedure is desirable in order to ensure repeatable results. OBJECTIVE: To investigate the magnitude and repeatability of the asymmetry ratio (AR) of oVEMPs in response to low-frequency bone conducted vibration (BCV) applied to the forehead and vertex in a healthy population. METHODS: 20 healthy subjects were tested three times by stimulating with 125 Hz BCV at the forehead and the vertex. The first two tests were performed with the subject remaining in the examining room and the electrodes in place. After a short break, a third test was performed with a new set of electrodes. The AR was calculated for each test based on the evoked oVEMPs responses from the left and the right side. The AR magnitude, variance and repeatability coefficients were evaluated to determine which of the two stimulus sites is best suited in clinical use. RESULTS: Stimulation at the forehead resulted in a statistically significant lower median AR compared to the vertex. The forehead had lower repeatability coefficients, and statistically significantly lower variances. CONCLUSIONS: This study indicates that the forehead is a better stimulation site than the vertex for low-frequency BCV in clinical use.

Disequilibrium in patients with posterior fossa arachnoid cysts.

BACKGROUND: Arachnoid cysts (AC) are benign, congenital malformations of the leptomeninges. In our experience, dizziness and vertigo are common complaints in patients with such cysts. OBJECTIVE: To quantify dizziness and imbalance in patients with arachnoid cysts in the posterior fossa using the Dizziness Handicap Inventory (DHI), Vertigo Symptom Scale Short-Form (VSS-SF) and Computerized Dynamic Posturography (CDP). We also wanted to investigate whether any dizziness and imbalance are reversible after surgical cyst decompression. METHODS: The study includes four patients with AC in the posterior fossa (two in the cerebellopontine angle and two supracerebellar in the midline) and 15 control subjects undergoing ENT surgery for benign lesions of the larynx (n = 10) or the parotid glands (n = 5). All participants answered the DHI and VSS-SF and underwent CDP the day before, and at follow-up after surgery. The AC patients also graded their dizziness through the use of a Visual Analogue Scale (VAS). RESULTS: Preoperatively, cyst patients scored higher than controls on subjective symptoms (DHI, VSS-SF A and VSS-SF V) and had a lower score on postural sway (CDP). Symptom scores decreased after surgery; the cyst patients improved in the subjective tests (DHI, VAS and VSS-SF), and three of the patients improved their CDP scores. In the controls, symptom and CDP scores were unchanged after surgery. CONCLUSION: Patients with fossa posterior cyst had a significant preoperative impairment compared with the controls, and they exhibited post-operative improvement in their subjective dizziness.

Pre- and post-operative dizziness and postural instability in temporal arachnoid cyst patients.

OBJECTIVES: Arachnoid cysts (AC) are benign, congenital malformations of the leptomeninges, with a predilection for the temporal fossa. In our clinical experience, patients with temporal AC often complain of dizziness and imbalance. However, these symptoms and the effect of surgery on them have not been studied before. MATERIALS AND METHODS: Dizziness and imbalance in patients with temporal AC were quantified before and after surgical cyst decompression, using the Dizziness Handicap Inventory (DHI), Vertigo Symptom Scale - Short-Form (VSS-SF) and computerized dynamic posturography (CDP). The study includes 16 patients with temporal AC and 15 control subjects undergoing surgery for benign lesions of the larynx (n = 10) or the parotid glands (n = 5). All participants answered the DHI and VSS-SF and underwent CDP the day before and 3-6 months after surgery. The patients with AC also graded their dizziness through the use of a visual analogue scale (VAS). RESULTS: Preoperatively, cyst patients scored higher than controls on subjective symptoms (DHI, VSS-SF A and VSS-SF V), but not on postural sway (CDP). Symptom scores decreased after surgery; the cyst patients improved significantly in the subjective tests (DHI, VAS and VSS-SF), while CDP scores did not. In the controls, symptom and CDP scores were unchanged after surgery. CONCLUSIONS: Patients with temporal AC have a significant preoperative impairment and post-operative improvement in their subjective dizziness, but not in postural sway as measured by CDP.

Short-term information pattern in optokinetic nystagmus amplitude time series.

In this paper we analyzed optokinetic nystagmus (OKN) signals for underlying information patterns. Fourteen OKN signals were recorded in five healthy subjects. First, we tested the correlation between nystagmus slow and fast phases. Previously, it has been suggested that the correlation is higher between the amplitude of the slow phase and the following fast phase, compared to the correlation between the fast phase and the following slow phase. However, we found no such difference. This is in agreement with the view that the saccade performed by the eye is not determined by the previous slow phase, but is free to move voluntarily in order to focus on an object of interest. Second, we analyzed the information entropy contained in the sequence of optokinetic nystagmus amplitudes, and found a short-term information pattern. Further analysis of these patterns could eventually lead to more knowledge about the vestibular and oculomotor systems.

Postural control in a simulated saturation dive to 240 msw.

INTRODUCTION: There is evidence that increased ambient pressure causes an increase in postural sway. This article documents postural sway at pressures not previously studied and discusses possible mechanisms. METHODS: Eight subjects participated in a dry chamber dive to 240 msw (2.5 MPa) saturation pressure. Two subjects were excluded due to unilateral caloric weakness before the dive. Postural sway was measured on a force platform. The path length described by the center of pressure while standing quietly for 60 seconds was used as test variable. Tests were repeated 38 times in four conditions: with eyes open or closed, while standing on bare platform or on a foam rubber mat. RESULTS: Upon reaching 240 msw, one subject reported vertigo, disequilibrium and nausea, and in all subjects, mean postural sway increased 26% on bare platform with eyes open (p < 0.05) compared to predive values. There was no significant improvement in postural sway during the bottom phase, but a trend was seen toward improvement when the subjects were standing with eyes closed on foam rubber (p = 0.1). Postural sway returned to predive values during the decompression phase. DISCUSSION: Postural imbalance during deep diving has been explained previously as HPNS possibly including a specific effect on the vestibulo-ocular reflex. Although vertigo and imbalance are known to be related to compression rate, this study shows that there remains a measurable increase in postural sway throughout the bottom phase at 240 msw, which seems to be related to absolute pressure.