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Biomedical subjects

C W Stockwell

Publications and source records attributed to C W Stockwell.

At least 19 recordsLinked to original sources
PubMed1994

Interlaboratory variability of rotational chair test results. Interlaboratory Rotational Chair Study Group.

Test-retest reliability of rotational chair testing for a single facility has previously been examined by others. The actual data analysis methods, however, have received far less attention. The variety of both hardware and software currently used theoretically may affect the results for a given subject tested at different facilities. The purposes of this study were, first, to quantify the amount of variability in the analysis of identical raw data files at multiple rotational chair testing facilities by using automated analysis; second, to evaluate the effect of operator intervention on the analysis; and third, to identify possible sources of variability. Raw data were collected from 10 normal subjects at 0.05 Hz and 0.5 Hz (50 degrees per second peak velocity). Diskettes containing raw electro-oculogram data files were then distributed to eight participating laboratories for analysis by two methods: (1) using automated analysis algorithms and (2) using the same algorithms but allowing operator intervention into the analysis. Response parameters calculated were gain and phase (re: velocity). The SD of gain values per subject for automated analysis ranged from 0.01 to 0.32 gain units and of phase values from 0.4 to 13.7 degrees. For analysis with operator intervention, the SD of gain values ranged from 0.02 to 0.10 gain units and of phase values from 0.4 to 4.4 degrees. The difference between automated analysis and analysis with operator intervention was significant for gain calculations (p < 0.02) but not for phase calculations (p > 0.05). This study demonstrates significant variability in automated analysis of rotational chair raw data for gain and phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Rehabilitation therapy for patients with disequilibrium and balance disorders.

Vestibular rehabilitation is based on the use of adaptive and compensatory mechanisms already existing in the human brain. Research using animals provides a great deal of information on the neural mechanisms responsible for these functions and suggests strategies that should be helpful in rehabilitation of patients with disequilibrium and balance disorders. Research in animals and human beings suggests that rehabilitation should be specifically designed, depending on the patients' deficits. It also suggests that to be effective it needs to be started soon after impairment and that vestibulosuppressive medication may reduce recovery. Studies are now underway to evaluate the effectiveness of vestibular rehabilitation on several groups of patients and to answer some fundamental questions about the mechanisms and the effectiveness of these treatment methods. Current information suggests that vestibular rehabilitation is an effective method of therapy for many patients with disequilibrium and balance disorders and that for some patients it is the best therapy available.

Animals↗
PubMed1989

Evaluation of the monothermal caloric test.

In 1970, Torok reported that patients with labyrinthine disease showed vestibular recruitment and that patients with retrolabyrinthine disease showed vestibular decruitment on the monothermal caloric test. Other investigators have failed to confirm these findings; however, their studies did not precisely replicate Torok's test procedure. Following Torok's procedure exactly, the monothermal caloric test was administered to normal individuals and to patients with well-documented vestibular lesions. Nine of ten normal persons showed normal responses and one person showed borderline decruitment. Six of eight patients who had lesions of the vestibular nerve or central vestibular pathways showed decruitment. Two patients with active Meniere's disease showed recruitment and one showed asymmetry. Two patients with Meniere's disease who had undergone endolymphatic sac operations showed normal responses. These findings support Torok's claim that the monothermal caloric test discriminates between labyrinthine and retrolabyrinthine vestibular pathology.

Adult↗
PubMed1988

The influence of active versus passive head oscillation, and mental set on the human vestibulo-ocular reflex.

We compared passive (manual) whole body, and active head oscillation in normal human subjects attempting mentally to influence the vestibulo-ocular reflex (VOR). Our objective was to establish simple procedural guidelines for vestibular test procedures in clinical settings. Using a head-fixed target, both methods of oscillation yielded virtually zero gain. Using an Earth-fixed target, active oscillation gain was unity, while passive gain was slightly less than 1. Using an imagined Earth-fixed target in the dark, both active and passive gains were reduced considerably, but passive gain was reduced more. Using an imagined head-fixed target in the dark, VOR gain was near zero at low frequencies but increased as frequency increased. Again, passive gain was less than active gain. At frequencies above 1 Hz, VOR gain in all conditions approached a value between 0.7 and 0.9. We conclude that active and manual passive rotation are simple and effective methods to test the VOR, but emphasize that visual and mental influences must be carefully controlled.

Adult↗
PubMed1978

Reliabilities of air and water caloric responses.

Air is a safer and more convenient caloric-irrigating medium than water, but many otologists are reluctant to use it because they suspect that it yields less reliable nystagmus responses. To compare reliabilities of air and water caloric responses, we subjected eight normal persons to 12 irrigations each of 50 degrees C air, 44 degrees C water, 24 degrees C air, and 30 degrees C water. Standard caloric-testing conditions were used, and nystagmus responses were recorded by the method of electronystagmography. We found that the reliabilities of air and water caloric responses were not significantly different. A single observation permitted estimation of response strength within approximalely +/- 5 degrees/sec (95% confidence level), regardless of whether air or water was used as the irrigating medium.

Adult↗
PubMedDate not supplied

Computer simulation of fixation suppression of vestibular nystagmus in normal persons.

Fixation suppression of vestibular nystagmus was tested in normal humans during passive, nonperiodic angular rotation. The eye movement responses of the subjects were simulated using a simple mathematical model of visual-vestibular interaction. Agreement between observed and simulated responses was reasonably close, indicating that the model is a realistic representation of the physiologic mechanisms involved. The model was then used to assess the relative contributions of the pursuit and optokinetic systems to fixation suppression. It showed that, under these testing conditions, fixation suppression is mediated almost entirely by the pursuit system.

Acoustic Stimulation↗
PubMedDate not supplied

A method for evaluating vestibular control of posture.

Tests that measure the patient's ability to control his posture generally have failed to yield clinically useful information about vestibular function. The primary reason for this failure is that postural control does not depend on vestibular function when visual and proprioceptive cues are available. To test vestibular function, one should use a procedure that forces the patient to rely on vestibular cues by eliminating cues from these other sensory systems. Such a procedure is described. Vision is eliminated by eye closure, and proprioceptive cues are minimized by rotating the supporting surface to null changes in ankle angle. Data are presented which show that postural responses are complex, but that they appear to conform to the pattern originally observed by Nashner. A method potentially capable of separately evaluating semicircular canal and otolith function is described.

Ankle Joint↗
PubMedDate not supplied

Posturography.

Posturography is a method of measuring a patient's ability to control his balance. Currently available testing techniques may be useful to otologists, although they have not been shown to yield information beyond that obtained from other diagnostic procedures. More powerful techniques are under development, but methodologic problems remain, and none is yet ready for routine clinical use.

Cerebellum↗