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Biomedical subjects

S W Wade

Publications and source records attributed to S W Wade.

6 recordsLinked to original sources
PubMed1999

Time constant of nystagmus slow-phase velocity to yaw-axis rotation as a function of the severity of unilateral caloric paresis.

OBJECTIVE: Complete unilateral loss of vestibular function results in a phase advance (reduced time constant) of the horizontal slow-phase nystagmus response to yaw-axis rotation. The objective of this study was to determine whether partial losses of lateral semicircular canal function would result in proportional reductions in the time constant. SETTING AND STUDY DESIGN: This was a retrospective study of consecutive patients' records at two tertiary referral centers for vestibular disorders. PATIENTS: Four hundred fifty-four patients who presented for evaluation of vertigo or imbalance or both and who were found to have partial or complete unilateral canal paresis on caloric testing. MAIN OUTCOME MEASURES: In 372 patients, the gain and time constant of the horizontal nystagmus response was measured using a 5-second velocity ramp of constant yaw-axis acceleration. Caloric responses to standard bithermal irrigations at 30 degrees and 44 degrees were obtained using an open-loop irrigation system. In a second group of 82 patients, the gain and time constant of the horizontal vestibulo-ocular reflex were measured using a sum-of-sines (pseudorandom) yaw-axis acceleration. The caloric response was measured using a closed-loop system. RESULTS: In both groups, the peak gain of the nystagmus response was independent of the level of the canal paresis. However, the time constant of the response both toward and away from the lesioned side decreased proportionally with increasing canal paresis. CONCLUSION: This result supports the hypothesis that bilateral symmetrical peripheral vestibular input is a necessary condition for the mechanisms or processes underlying normal horizontal slow-phase velocity storage.

Caloric Tests↗
PubMed1997

The effect of ocular torsional position on perception of the roll-tilt of visual stimuli.

Perceived postural orientation during whole-body roll-tilt is commonly inferred from settings of a visual line to the perceived gravitational horizontal or vertical. This inference assumes that the change in ocular torsional position (ocular counterrolling) which occurs during roll-tilt has no effect on the perceived orientation of the visual stimulus. We investigated this assumption by measuring, during whole body roll-tilt stimulation, settings of a visual line and a somatosensory bar to the perceived gravitational horizontal and comparing the difference in these settings to the objectively measured ocular torsional position for each subject. Two stimulus paradigms were used: one where the subject was given a roll-tilt stimulus and the eye torted, the other where there was eye torsion without a roll-tilt stimulus. In both paradigms there was a very close relationship in magnitude and direction between the difference in the settings of the two perceptual indicators to gravitational horizontal and the objectively measured ocular torsion. We conclude that change in ocular torsional position alone changes the perceived orientation of a visual line. The corollary is that settings of a visual line cannot be used to infer perceived postural orientation directly.

Adult↗
PubMed1996

What is the minimal vestibular function required for compensation?

Living with an uncompensated, abnormal vestibular system requires oppressive modification of life style and often prevents return to work and activities of daily living. Patients with vestibular abnormalities were studied to determine the minimal residual vestibular function required to achieve compensation. Three groups of patients with (a) complete unilateral loss of vestibular function with normal horizontal canal-vestibulo-ocular (HCVOR) function in the opposite ear, (b) complete unilateral loss with abnormal HCVOR function in the opposite ear, and (c) bilateral reduction of vestibular function from aminoglycoside toxicity underwent vestibuloocular (VOR), optokinetic (OKN), visual-VOR (VVOR), and computerized dynamic posturography (CDP) tests before and after therapeutic procedures. Results suggest that a minimal VOR response amplitude must be present for compensation of VVOR function to occur. The roles of VOR and OKN phase shifts in vestibular compensation are more complicated and require further study. Compensation of vestibulospinal function does not necessarily accompany VOR or VVOR compensation. Ascending and descending vestibular compensatory mechanisms may involve different spatial sensory inputs. Results of these studies have important implications for the diagnosis and treatment of patients with vestibular disorders, including selection and monitoring of patients for therapeutic regimens such as vestibular nerve section and streptomycin therapy.

Humans↗
PubMed1995

Ocular torsion position and the perception of visual orientation.

Previous studies have shown that in patients with unilateral vestibular deafferentation (UVD) there is a close relationship between the change in ocular torsional position consequent on the UVD, and the visually perceived orientation of short dim lines in an otherwise darkened room (1). However that result may have been confounded because the UVD may have affected both ocular torsion and sensory information about head position re gravity which must be used in making the visual perceptual judgement. Therefore we have sought a means of testing the relationship between ocular torsional position and the visual perception of orientation which was not confounded by the possible effect of changes in perceived head position.

Afferent Pathways↗
PubMed1994

An evaluation of Duke University's LIVE FOR LIFE health promotion program on changes in worker absenteeism.

The effect of an employer-sponsored health promotion program on worker absenteeism is examined over a 4-year period in a group of 4972 Duke University hourly employees. Program participants experienced an average of 4.6 fewer absentee hours in the third year of program availability than did nonparticipants, after controlling for baseline absenteeism, gender, race, education, and age. These results suggest that employer-sponsored health promotion initiatives can have a favorable influence on absenteeism.

Absenteeism↗