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Biomedical subjects

R J Peterka

Publications and source records attributed to R J Peterka.

At least 19 recordsLinked to original sources
PubMed1998

Effect of altered sensory conditions on multivariate descriptors of human postural sway.

Multivariate descriptors of sway were used to test whether altered sensory conditions result not only in changes in amount of sway but also in postural coordination. Eigenvalues and directions of eigenvectors of the covariance of shnk and hip angles were used as a set of multivariate descriptors. These quantities were measured in 14 healthy adult subjects performing the Sensory Organization test, which disrupts visual and somatosensory information used for spatial orientation. Multivariate analysis of variance and discriminant analysis showed that resulting sway changes were at least bivariate in character, with visual and somatosensory conditions producing distinct changes in postural coordination. The most significant changes were found when somatosensory information was disrupted by sway-referencing of the support surface (P = 3.2 x 10(-10)). The resulting covariance measurements showed that subjects not only swayed more but also used increased hip motion analogous to the hip strategy. Disruption of vision, by either closing the eyes or sway-referencing the visual surround, also resulted in altered sway (P = 1.7 x 10(-10)), with proportionately more motion of the center of mass than with platform sway-referencing. As shown by discriminant analysis, an optimal univariate measure could explain at most 90% of the behavior due to altered sensory conditions. The remaining 10%, while smaller, are highly significant changes in posture control that depend on sensory conditions. The results imply that normal postural coordination of the trunk and legs requires both somatosensory and visual information and that each sensory modality makes a unique contribution to posture control. Descending postural commands are multivariate in nature, and the motion at each joint is affected uniquely by input from multiple sensors.

Adult↗
PubMed1995

Role of somatosensory and vestibular cues in attenuating visually induced human postural sway.

The purpose of this study was to determine the contribution of visual, vestibular, and somatosensory cues to the maintenance of stance in humans. Postural sway was induced by full-field, sinusoidal visual surround rotations about an axis at the level of the ankle joints. The influences of vestibular and somatosensory cues were characterized by comparing postural sway in normal and bilateral vestibular absent subjects in conditions that provided either accurate or inaccurate somatosensory orientation information. In normal subjects, the amplitude of visually induced sway reached a saturation level as stimulus amplitude increased. The saturation amplitude decreased with increasing stimulus frequency. No saturation phenomena were observed in subjects with vestibular loss, implying that vestibular cues were responsible for the saturation phenomenon. For visually induced sways below the saturation level, the stimulus-response curves for both normal subjects and subjects experiencing vestibular loss were nearly identical, implying (1) that normal subjects were not using vestibular information to attenuate their visually induced sway, possibly because sway was below a vestibular-related threshold level, and (2) that subjects with vestibular loss did not utilize visual cues to a greater extent than normal subjects; that is, a fundamental change in visual system "gain" was not used to compensate for a vestibular deficit. An unexpected finding was that the amplitude of body sway induced by visual surround motion could be almost 3 times greater than the amplitude of the visual stimulus in normal subjects and subjects with vestibular loss. This occurred in conditions where somatosensory cues were inaccurate and at low stimulus amplitudes. A control system model of visually induced postural sway was developed to explain this finding. For both subject groups, the amplitude of visually induced sway was smaller by a factor of about 4 in tests where somatosensory cues provided accurate versus inaccurate orientation information. This implied (1) that the subjects experiencing vestibular loss did not utilize somatosensory cues to a greater extent than normal subjects; that is, changes in somatosensory system "gain" were not used to compensate for a vestibular deficit, and (2) that the threshold for the use of vestibular cues in normal subjects was apparently lower in test conditions where somatosensory cues were providing accurate orientation information.

Adult↗
PubMed1992

Relation between perception of vertical axis rotation and vestibulo-ocular reflex symmetry.

Subjects seated in a vertical axis rotation chair controlled their rotational velocity by adjusting a potentiometer. Their goal was to null out pseudorandom rotational perturbations in order to remain perceptually stationary. Most subjects showed a slow linear drift of velocity (a constant acceleration) to one side when they were deprived of an earth-fixed visual reference. The amplitude and direction of this drift can be considered a measure of a static bias in a subject's perception of rotation. The presence of a perceptual bias is consistent with a small, constant imbalance of vestibular function that could be of either central or peripheral origin. Deviations from perfect vestibulo-ocular reflex (VOR) symmetry are also assumed to be related to imbalances in either peripheral or central vestibular function. We looked for correlations between perceptual bias and various measures of vestibular reflex symmetry that might suggest a common source for both reflexive and perceptual imbalances. No correlations were found. Measurement errors could not account for these results since repeated tests in the same subjects of both perceptual bias and VOR symmetry were well correlated.

Adult↗
PubMed1992

Surgical management of perilymphatic fistulas: a Portland experience.

A comprehensive review of our series of surgical perilymphatic fistula (PLF) repairs, as well as a review of published results from other otologists, suggested an unacceptably high rate of postoperative PLF recurrence. Some recurrences were related to specific events (i.e., coughing, strenuous activity, Valsalva-type maneuvers). However many cases had no apparent cause. Rather, the patients' symptoms recurred spontaneously, and at reoperation the graft was seen to have not "taken," suggesting graft failure rather than "patient failure." After a critical evaluation of current PLF surgical procedures and state-of-the-art concepts of wound healing, we developed a new surgical technique for PLF closure. Combining the use of laser graft-site preparation, an autologous fibrin glue "buttress," and a program of postoperative activity restriction, the new procedure allowed us to achieve statistically significant improvements in graft retention and surgical outcome, with recurrences dropping from 27 percent to 8 percent. In addition, complete resolution or significant symptomatic improvement occurred in 89 percent of patients with vertigo and/or dizziness and in 84 percent with disequilibrium. We conclude that this new surgical technique is an important addition to the otologic surgeon's arsenal for PLF management.

Adolescent↗
PubMed1991

Surgical management of perilymph fistulas. A new technique.

A wide range of recurrence rates (21% to 47%) for perilymph fistula repairs have been reported in the otology literature. An improved surgical technique developed at the Portland (Ore) Good Samaritan Hospital and Medical Center Neurotology Department was used to repair perilymph fistulas in 58 patients from October 1986 to October 1988. Our recurrence rate was reduced from 27% in a 1982-1985 study to 8% in our study. At 1 year postoperatively, improvements in disequillibrium, dizziness, and vertigo were comparable with results of older surgical techniques. Functional outcomes were also good: 83% of patients returned to normal activities of daily living, and 71% also returned to school or resumed gainful employment outside the home.

Adolescent↗
PubMed1990

The dynamic posturographic pressure test for the presumptive diagnosis of perilymph fistulas.

A diagnosis of perilymph fistulas (PLFs) can be made only by identification of repeated accumulation of crystal-clear fluid from an otic capsule defect or labyrinthine window at tympanotomy. It would be highly desirable to base a decision to operate for the diagnosis and management of PLFs on a database that includes quantitative test data, which confirms, with a high probability, a clinical suspicion of PLF. This article reviews progress in the development of a test of the vestibular response to external auditory canal pressure changes as recorded by dynamic posturography. Based on results to date, it appears that a fistula test with dynamic posturography is more sensitive than those based on VOR responses. This may be due to the ability of dynamic posturography to isolate vestibular from both visual and somatosensory influences on motor responses during external canal pressure changes.

Ear Diseases↗
PubMed1989

Effects of unilateral loss of vestibular function on the vestibulo-ocular reflex and postural control.

Long-term recovery from surgically induced unilateral loss of vestibular function was studied in 14 patients. Seven patients underwent surgical extirpation or section of the vestibular nerve, and seven patients underwent labyrinthectomy without vestibular nerve section. The vestibulo-ocular reflex (VOR) and postural control were evaluated preoperatively and monitored for up to 4 years postoperatively with use of pseudorandom rotation (combined sinusoidal frequencies from 0.009 to 1.5 Hz) and moving platform posturography. Immediately following surgery all patients showed minimal reductions in the VOR gain constant, but marked reduction in the time constant, and marked increase in slow eye velocity bias. Bias returned to normal values within about 10 days, but time constants never returned to normal values. Results of standard Romberg tests in these patients were normal throughout the preoperative and postoperative periods. However, all patients showed marked postural control abnormalities in tests of the ability to maintain balance in unusual sensory environments in the immediate postoperative period. Seventy-five percent of the patients eventually recovered normal postural control. Postural control returned to near baseline performance with a time course similar to that of the VOR bias. However, postural control also continued to improve after the recovery of VOR bias was complete.

Adolescent↗
PubMed1987

Quantitative diagnostic test for perilymph fistulas.

Clinically, the definitive diagnosis of perilymph fistulas can only be made by tympanotomy. Results of various fistula tests based upon the vestibulo-ocular reflex have not correlated well with findings during tympanotomy. A new fistula test has been developed based upon vestibulo-spinal responses. By systematic removal of both visual and support-surface orientation references from the subject--leaving only vestibular control of postural reflexes--patients with perilymph fistulas demonstrated an increased (sometimes phase-locked) postural sway in response to sinusoidal changes in external auditory canal pressures. Results from 100 consecutively operated ears (64 patients)--77 of whom underwent preoperative and postoperative moving-platform fistula tests--indicate that the test sensitivity is 97 percent for this highly selective patient population. Absolute specificity could not be determined because, on patients without clinical indications for surgery, tympanotomy is contraindicated.

Adolescent↗
PubMed1987

Vestibular reflex changes following aminoglycoside induced ototoxicity.

The effects of aminoglycoside-induced changes on the vestibular system were evaluated in three subjects who suffered significant damage over the course of treatment. Measurements of vestibulo-ocular reflex (VOR) function were made using sinusoidal and pseudorandom rotational stimuli between 0 to 5 days after initiation of drug therapy, during drug therapy, and up to 579 days following drug administration. All subjects tested at baseline evaluations had normal VOR function. During aminoglycoside therapy there was a precipitous drop in both the VOR time and gain constants. The decline in VOR function was larger at lower stimulus frequencies compared to high frequencies, resulting in a relative preservation of function in the high frequencies. Over a period of about a year, VOR high frequency gains recovered to within normal limits. However, the VOR time constants showed only a modest recovery and remained well below the normal range.

Aminoglycosides↗
PubMed1987

Optokinetic and vestibulo-ocular reflex responses to an unpredictable stimulus.

Horizontal plane optokinetic (OKR) and vestibulo-ocular reflex (VOR) eye movements were obtained from normal subjects in response to pseudorandom rotational stimulation. Results showed large intersubject variability in OKR responses. Typical OKR responses had approximately constant gain (Mean 0.65) over 0.02-1.5 Hz. Response phase was near zero below 0.1 Hz with increasing phase lags as frequency increased consistent with time delays of 180 ms (Mean value). Variations in OKR responses included declining gains with increasing frequency and phase lags consistent with time delays of 90 to 268 ms. Significant interactions of visual and vestibular motion information were detected at the highest stimulus frequency at which both were tested (1.5 Hz). Results suggested that visual motion information could be significant in the control of eye movements up to 6.1 Hz. Pseudorandom optokinetic stimulation induced motion sickness symptoms in approximately 20% of 213 subjects tested. Pseudorandom vestibular stimulation of twice the amplitude and duration did not initiate motion sickness symptoms in any subject.

Humans↗
PubMed1985

Neural modeling and model identification.

The complexity of the nervous system poses challenging experimental and theoretical problems to the investigator. While experimental studies have provided a broad understanding of the physiological and anatomical role of neural elements, a comprehensive description of how the nervous system acquires and processes information is still lacking. Neural modeling addresses itself to the quantitative interpretation of neurophysiological experiments, to the assimilation of diverse experimental results into unified theories, and to the investigation of mechanisms of information-processing units, codes, and networks and their relation to capabilities of living systems. This review will emphasize neural models which can be tested by physiological or psychophysical experiments and will include the identification of model parameters based on experimental measurements. An overview of neural firing models, neural interaction models, neural variability and coding, design of input-output experiments for model identification, and description of small network interactions through multiunit and gross potential recording will be included.

Action Potentials↗
PubMed1984

Differences between cats in response properties of horizontal semicircular canal primary afferents.

The response properties of cat horizontal canal afferents (N = 81) were characterized by three parameters: their long time constants (tau), low frequency gain constants (G1), and middle frequency gain constants (Gm). An average value of each of these parameters was calculated for each of eight animals and comparisons were made across animals. There were significant differences between individual animals in their average values of tau and Gm. There was also a significant negative correlation between tau's and Gm's. An animal with a larger average tau tended to have a smaller average Gm. We also used anatomic data on membranous canal duct diameter from the literature to independently estimate the potential effect of interanimal anatomic variability on the predicted range of tau and Gm values in a population. We then compared the data from our 81 afferents with the predictions from the anatomic data.

Animals↗
PubMed1981

Responses to head tilt in cat eighth nerve afferents.

Responses to head tilt were recorded from eighth nerve axons in barbiturate anesthetized cats. The maximally excitatory head tilt (polarization vector), a zero-force discharge rate, and tilt sensitivity were measured for each cell. In one population of afferents, the maximum discharge frequency was obtained by aligning the saccular plane with gravity. The response properties of these saccular afferents were compared with a second population arising from the utriculus. Both the resting discharge rate and the response sensitivity were lower for saccular than utricular afferents in the cat. The average resting discharge was about 20% lower and the sensitivity about 15% higher in the cat than in the squirrel monkey.

Afferent Pathways↗