Subjective visual vertical (SVV) patterns obtained using different translation times during unilateral centrifugation (UC) testing.

Abstract

Unilateral centrifugation (UC) is a test of utricular function that involves the eccentric displacement of a patient while undergoing high velocity rotation. These off-center placements permit evaluation of utricles as only one organ is subjected to linear stimulation. Currently, several different protocols are used for translation times between positions (e.g., Clarke et al, 1996; Wuyts et al, 2003). This study examined the effects of different translation times between eccentric and centric positions during UC on an individual's perceived subjective visual vertical (SVV). A prospective repeated measures design was used in this study. Forty-three young adults with no history or complaints of vestibular or neurological disorders participated in this study. All testing was performed on a Neuro Kinetics Inc. (Pittsburgh, PA) Neuro-Otologic Test Center (NOTC) rotational chair at the Bloomsburg University of Pennsylvania Vestibular Clinic. Each participant completed six SVV trials in the static condition (sSVV) as a baseline of function. In addition, each participant completed UC trials using a rotational velocity of 300°/sec with 4 cm eccentric lateral displacements that were maintained for 60 sec per position. Translations of 5, 10, 15, 20, 25, and 30 sec were randomized. The maximum velocity was maintained for 90 sec prior to the eccentric placement. Multiple estimations of dynamic subjective visual vertical (dSVV) were performed for each position. dSVV data yielded several trends. At 5 sec translations, dSVV values had greater variability and required longer for participant responses to stabilize. Regardless of UC translation time, initial trial values were often quite different from the remaining trials. Shorter UC translation times were associated with more eccentric dSVV values outside of the clinical norms. While not statistically significant, more variance was associated with the shortest UC translation times, while 15 and 25 sec translation data demonstrated the best correlations and lowest variances. Findings suggest that incorporating sSVV data to normalize dSVV data should be considered to reduce the influence of the underlying baseline static otolithic function on the UC results. The presence of a clear tendency for shorter UC translation times to be associated with larger numbers of clinically abnormal findings may indicate that very short UC translation times may not be ideal for clinical applications. This is supported by our finding that longer UC translation times elicited more consistent SVV results and less response variability. While some of these findings were not statistically significant, the results do suggest that clinical UC testing may benefit from optimization of translation time as well as inclusion of sSVV in response interpretation.