Varied walking velocities and dynamic visual acuity during locomotion

P84

OtolaryngologyHead and NeckSurgery August T999

Research Forum--Monday

Poster 20

An Analysis of Vestibular Decruitment JAMES JOHN BOUZOUKISMD (presenter); ARVIND KUMAR MD; Chicago IL

Problem: Vestibular decruitment (VD) is a paradoxical response to stimulation of the ear with the 2 strengths of the Torok monothermal caloric test. The culmination frequency (CF) value of the weaker of the 2 stimuli is equal to or greater than the strong stimulus response. Vestibular decruitment has been shown to be associated with brain stem and cerebellar lesions. However, the underlying neurophysiology of VD is not known. The purpose of this study is to attempt an understanding of VD by analyzing the CF values obtained from a normal group of subjects and comparing the results from a patient cohort who had MRI confirmed brain stem/cerebel!ar lesions. Methods: From our database of patients, we randomly selected 70 patients who had both MRI-confirmed posterior fossa lesions and VD. In 35 patients VD was unilateral, and in the rest it was bilateral. Normative data were obtained prospectively from 27 patients. The CF values from each of these groups were statistically compared and analyzed. Results: Patients with bilateral VD displayed an average CF of 40.9 with the 10-mL stimulus and 40.6 with the 100-mL stimulus. The latter values showed no statistical difference from CF values of normal subjects. However the 10-mL CF values in patients were significantly higher than CF values of normal subjects. Statistical analysis of CF values of unilateral VD showed similar results. Conclustion: Although this study does not explain the underlying neurophysiological mechanisms of VD, statistical analysis of the data shows that in VD it is an increase in the weaker stimulus CF value that results in the paradoxical response rather than a decrease in the strong stimulus responses. This information could form the basis for further experimental studies. Poster 21

Varied Walking Velocities and Dynamic Visual Acuity during Locomotion DIANE M SHIRLEYMD (presenter); JACOB J BLOOMBERG PHD; AJiTKUMAR MULAVARA PHD; LAUREN A MERKLE PHD; HELEN S COHEN EDD; Houston TX

Problem: The maintenance of functional visual acuity during activities of daily living demands that gaze be stabilized during body motion. The ability to read during locomotion requires integration of various vestibular and locomotor reflexes. Change in any system leads to altered dynamic visual acuity (DVA) during locomotion. Testing DVA during locomotion serves as a global indicator of the integration of events responsible for locomotion. The Locomotor Dynamic Visual Acuity Test (LDVA) identifies deficits that may result in functional limitations. This test can indicate potential functional

changes in crew members, evaluate labyrinthine-deficient patients, and document rehabilitation progress. Methods: The LDVA protocol constrained subjects by walking at a single velocity, 6.4 km/hour. Our goal was to improve the test by examining results across a range of walking velocities. Eight normal subjects and 4 patients with bilateral vestibular dysfunction read numerals of different font sizes displayed on a computer while walking at varied velocities: 3.2, 4.0, 4.8, 5.6, 6.4, 7.2, and 8.0 km/hour. Three labyrinthinedeficient patients (LD) were evaluated while walking at 3.2, 4.0, 4.8, and 5.6 km/hour. One patient walked at 2.4, 3.2, and 4.0 km/hour only. Head and trunk kinematic data were collected using a video-based motion analysis system. Results: Normal subject DVA scores were significantly decreased at the faster walking velocities, 5.6 to 8.0 km/hour. Preliminary data analysis showed that the LD scores were worse across all velocities tested. The trend in the kinematic data demonstrated that, in comparison to the normal subjects, the LD subjects had lower magnitudes at the predominant frequency of motion of the head, in the pitch, roll, and yaw planes at the varied walking speeds. The magnitudes at the lower frequencies increased. Conclusion: We conclude that these results indicate an increase in the efficacy of the LDVA test by evaluating scores across a range of walking velocities. The preliminary kinematic results indicate a trend showing that the LD patients relied a greater amount on voluntary mechanisms for head stabilization in comparison with the normal subjects, who relied predominantly on the reflex mechanisms of head stabilization in the plane of progression during walking. This may contribute to the decrease in gaze stabilization in the LD patients resulting in the worsening of their DVA scores. Clinical Significance: DVA is a global indicator of sensorimotor integration. The LDVA test is an easily administered, sensitive test of crew member neurologic function on return from spaceflight. It takes approximately 30 minutes to administer and serves as a guide for flight surgeons in determining the readiness of crew members to return to their activities of daily living such as flying, driving, and operating machinery. It also has an extension into clinical medicine and is currently being evaluawxtas a test to follow the progression of rehabilitation in labyrinthine-deficientpatients. In the above-stated situations, it offers a viable alternative to the more traditional, time-consuming vestibular testing. (Supported by Baylor College of Medicine [D.M.S.], National Research Council [L.A.M.], and the Clayton Foundation for Balance Disorders [H.S.C.].) Poster 22

GABA Transporter mRNAs in the Mammalian Vestibular End Organs MANU GUJRATI (presenter); ALAN ROBINSON PHD; DIMITRI PITOVSKI MD; Chicago IL

Problem Addressed: In the vertebrate vestibular periphery