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Biomedical subjects

M S Redfern

Publications and source records attributed to M S Redfern.

34 records · Page 2Linked to original sources
PubMed1998

Postural control, attention and sleep deprivation.

We investigated the effect of sleep deprivation on postural control during a simple reaction time task (SRT), during a task requiring the intermittent inhibition of a reaction (IRT), and in the absence of a concurrent information processing task. Postural sway, i.e. changes in center of pressure on a force platform, was recorded in three increasingly difficult standing conditions (fixed platform, sway-referenced platform and sway-referenced platform with sway-referenced visual scene) during the three information-processing task conditions. Five healthy subjects performed the tasks either after normal sleep or following 24 h of sustained wakefulness. As hypothesized, sleep deprivation significantly increased postural sway only in the IRT condition. Within the IRT condition, sleep deprivation significantly increased sway across all postural conditions.

Adult↗
PubMed1998

Visual-induced postural sway in children with and without otitis media.

Children with otitis media with effusion (OME) have been shown to have a significantly higher velocity of sway than normal children. To further evaluate the effect of OME on balance, we studied visual dependency for balance by investigating the influence of optic flow on postural sway. The results of this preliminary study suggest that children with OME may be more visually dependent for balance than healthy age-matched controls. This was particularly evident for higher-frequency stimulus conditions (0.25 Hz) as opposed to lower-frequency stimulus conditions (0.10 Hz). These findings indicate that OME may affect vestibular function in children, thereby causing excessive reliance on other, nonvestibular sensory cues to maintain balance. Further studies are needed to define the role of vestibular function in the management of children with OME.

Child↗
PubMed1997

Functional stability limits while holding loads in various positions.

Stability of the body during manual material handling is an important issue in the prevention of falls and over-exertion injuries. This research investigated stability limits while standing and holding loads in different positions relative to the body. Theoretically, the stability region is the full base of support defined by the perimeter of the foot contact area. However, the functional stability region may be smaller. The purpose of this study was to locate functional stability limits with respect to the base of support. Fifteen male subjects leaned as far as possible in four directions in the sagittal and frontal planes. Their center of gravity location at these extremes determined the stability limit. The results showed that functional stability limits reached only about 60% of the distance to the maximum base of support limits under the conditions of this study. The sway angles reached at the stability limits averaged 9.2 degrees anteroposteriorly and 15.3 degrees laterally. External load positions which lowered the center of gravity of the body-and-load system extended those stability limits. This study provides a postural stability perspective of load-holding which may be applied in establishing safe lifting and reach limits.

Accident Prevention↗
PubMed1997

The influence of flooring on standing balance among older persons.

This study investigated the effects of flooring on balance during quiet standing in healthy young and older participants. Seven flooring conditions were examined, including a hard tile floor and combinations of low-pile and high-pile carpet with urethane foam and rubber padding. The resulting floors provided a variety of compliant surfaces, ranging from very soft to hard. Participants stood during three separate visual conditions: eyes open, eyes closed, and looking at a moving visual surround. Three measures of postural sway were calculated using center of pressure recordings during the trails. The results showed that the amplitude of sway was higher in the older than in the younger participants, particularly in the moving visual surround condition. Flooring compliance was found to have an effect on sway during moving visual environments, with the largest effects found among the older participants. Softer floors increased the amount of sway in the older participants. These results suggest that floor compliance influences standing postural stability in older people, particularly in destabilizing visual environments.

Adult↗
PubMed1996

Galvanic-induced postural movements as a test of vestibular function in humans.

Galvanic stimulation produces a postural sway and eye movements in humans. Since galvanic currents are thought to exert their effect at the trigger zone of the vestibular nerve, an intact vestibular nerve should be necessary to produce a response. We have used galvanic stimulation in humans to test the hypothesis that intact vestibular nerve fibers are required to obtain a postural away response. Experimental subjects included normal subjects, patients who had undergone resection of an acoustic neuroma, and patients who had undergone vestibular neurectomy and surgical labyrinthectomy. Our results support the hypothesis that an intact vestibular nerve is necessary to produce a response. Moreover, two patients with recurrent vertigo following vestibular neurectomy and labyrinthectomy, who had absent ice-water caloric test responses in the operated ears, were found to have a positive galvanic response. This result suggested that their recurrent vertigo was based on intact residual vestibular nerve fibers. Although previous research has not yielded a routine clinical use for galvanic stimulation, our results suggest that galvanic stimulation of the vestibular system can provide unique and valuable diagnostic information.

Aged↗
PubMed1996

Time-varying characteristics of visually induced postural sway.

To study potential time-varying dynamics of postural sway as measured via center-of-pressure (COP) under the feet, we applied time-frequency analysis to COP data from ten vestibularly impaired subjects and 13 nonimpaired controls, during quiet stance and in response to visual perturbation. This analysis revealed that 1) the spectral characteristics of COP change over time; 2) there are time-dependent and frequency-dependent differences in COP between impaired and nonimpaired populations during visual perturbation, and 3) there is no difference in COP during quiet stance (eyes opne) between impaired and nonimpaired populations for the parameters investigated. A novel finding of this research is that controls appear to adapt to constant frequency visual perturbation, while vestibularly impaired subjects do not. This difference could not have been observed with conventional Fourier analysis, which is commonly used in COP data analysis, because time is not a parameter of the spectrum and adaptation is, by nature, a time-varying process. These results suggest that time-frequency analysis of COP data is useful for studying temporal dynamics of postural control, and in particular the differences between vestibularly impaired subjects and healthy controls during visual perturbation.

Adult↗
PubMed1995

Time-frequency analysis of postural sway.

Postural sway during quiet stance has been used to characterize the postural control system. Most studies have used center of pressure (COP) measurements and have assumed stationarity, however, recent research has indicated that COP is not stationary. The purpose of this study is to introduce and demonstrate a nonstationary spectral estimation technique to examine the time-varying nature of postural sway. Data from two experiments were used to verify the usefulness of the spectral estimator for the analysis of COP. The first data set contains COP recorded from normal subjects swaying about their ankles in response to a metronome as it was gradually changed from 2 to 1 Hz. The time-frequency distribution reveals time-varying spectral changes corresponding to frequency changes made by the subjects. The second set consists of COP from normal subjects and vestibularly impaired patients standing quietly on a force plate with eyes closed for 100 s. The time-frequency distributions for the COP were estimated for both sets of data. The COP's appear to be nonstationary with the energies at a given frequency modulating through time.

Computer Simulation↗
PubMed1994

A model of foot placement during gait.

Foot placement is known to affect balance during gait; however, how foot placements are chosen is unknown. Objectives of this research were to analyze swing trajectories of the foot during gait with respect to the pelvis, and to propose a model of foot placement control which provides a stable base of support. Effects of gait speed and vision on this model of foot placement were then examined. Foot trajectories were analyzed using spherical coordinates referenced to the pelvis, termed the pelvic spherical coordinates (PSCs). A model was developed based on this coordinate system which predicts foot placement in terms of position and velocity with respect to the pelvis. It is proposed that foot placements are chosen to minimize the sum of PSC coordinates of the stance and swing feet. Foot velocity at heel contact is proposed to minimize the sum of the PSC stance and swing angular velocities. Experimental data were collected to test this model during walking trials of different speeds, both with and without vision. Results showed that sums of stance and swing feet PSCs were very close to zero at heel contact, supporting the positional control hypothesis. Sums of PSC velocities, however, were not zero at heel contact. Rather, individual swing leg PSC velocities were zero at heel contact, suggesting independent swing leg velocity control. Vision did not have an effect on position or velocity variables at heel contact. Gait speed did have an effect, particularly on PSC velocities at heel contact.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Visual influences on balance.

This paper discusses the impact of vision on balance and orientation in patients with vestibular disorders and in anxiety patients with space and motion discomfort (SMD). When the vestibular system is impaired, vision has a greater influence on standing postural control, resulting in greater sway when individuals are presented with erroneous or conflicting visual cues. Studies have shown that individuals with other motion sensitivities, such as motion sickness, also tend to rely on vision for balance and do not disregard erroneous visual cues. Recently, patients with anxiety disorders that include SMD also have been shown to have increased postural sway in conflicting visual environments, similar to patients with vestibular disorders. Thus, while specific vestibular deficits are not always directly associated with SMD, data regarding the impact of vision on balance suggest that some patients with SMD may have an underlying balance disorder.

Anxiety↗
PubMedDate not supplied

Psychological factors influencing recovery from balance disorders.

This article reviews evidence for three mechanisms whereby psychological factors may aggravate dizziness and retard recovery from balance disorders. Firstly, a common behavioral response to dizziness is to avoid activities and environments that provoke symptoms, yet such avoidance deprives the individual of the exposure necessary to promote psychological and neurophysiological adaptation. Secondly, anxiety arousal and hyperventilation may add to, amplify, and disinhibit the somatic symptoms induced by balance disorder. Thirdly, attention and cognitive load may influence the central processing of information required for the perception and control of orientation. The need to combine physiotherapy for dizziness with psychotherapy is discussed.

Anxiety↗
PubMedDate not supplied

The influence of flooring on standing comfort and fatigue.

Many occupations require standing for extended periods of time, resulting in complaints of musculoskeletal fatigue and pain. One intervention method to reduce this problem has been to alter the flooring on which workers stand by using "antifatigue" mats. This article reviews the published research on the influence of flooring on people during long-term standing. Most studies have used subjective ratings of fatigue and discomfort experienced while standing in controlled laboratory settings. Some have included objective measures, such as electromyography, leg volume changes, and postural movements. Studies in the literature report mixed and sometimes conflicting results. There are methodological differences across the studies that could have led to many of the conflicting results, with the foremost variable being duration of testing. Generally, softer floors result in reduced discomfort as compared with a hard floor, particularly for the lower extremities and the lower back. Objective measures have been less conclusive, with no consensus about the influence of flooring on any physiological or biomechanical measures. Investigations of the influence of flooring characteristics on discomfort suggest that elasticity, stiffness, and thickness play roles. Further research is needed on underlying physiological causes of standing discomfort and fatigue as well as the influence of flooring properties on subjective and objective measures.

Electromyography↗
PubMedDate not supplied

Visual-vestibular interaction during OVAR in the elderly.

This study assessed visual-otolith interaction in healthy older humans and compared responses from older subjects to those of younger subjects. Using off-vertical axis rotation (OVAR) to stimulate the otolith organs, eye movement responses, measured using electro-oculography, were recorded during rotation in the dark, rotation with an earth-fixed lighted visual surround, and rotation with a subject-fixed fixation target. Results indicated that older subjects, like young subjects, exhibit a modulation component that was as large during rotation with a lighted earth-fixed visual surround as that seen in the dark and a modulation component during rotation with a subject-fixed visual target that was incompletely suppressed. The modulation component was, in general, larger in the older subjects. This study confirms findings from a previous study of visual-otolith interaction in young subjects and suggests that older subjects, like young subjects, have difficulty visually suppressing the modulation component induced by off-vertical axis rotation.

Adult↗
PubMedDate not supplied

Postural sway of patients with vestibular disorders during optic flow.

Patients with vestibular orders often complain of sensitivity to moving visual environments, leading to dizziness and imbalance. This study investigated standing postural sway of healthy adults and patients with vestibular disorders in response to optic flow in the central field. Visual conditions of varying properties were presented monocularly with a 60 degrees viewing field. The conditions included: eye open-no flow, eye closed, sinusoidal expansions/contractions at 0.3 Hz, a constant flow giving the appearance of tunnel, and a vertically translating checkerboard. Postural sway, defined in this study as movement of the center of pressure, was recorded using a force platform during presentation of the visual stimuli. Patients with vestibular disorders were found to have a significantly higher magnitude of postural sway than control subjects while viewing central optic flow stimuli. Sinusoidally expanding and contracting optic flow induced postural sway at the stimulus frequency in both the patients and controls; patients, however, had a much larger increase in sway at frequencies near the stimulus frequency. These results suggest that postural control in patients with vestibular disorders is particularly affected by optic flow stimuli to the central region of the visual field.

Adult↗
PubMedDate not supplied

Functional reach and single leg stance in patients with peripheral vestibular disorders.

The purpose of this study was to compare functional reach distance and right single leg stance time in patients who had peripheral vestibular disease. Twenty-eight patients (15 female, 13 male) between the ages of 35 and 84 were asked to perform 3 trials each of functional reach (FR) and right single leg stance (SLS). SLS times were measured by a Kistler static force platform on line with a Caspar personal computer. FR distance was measured by using a free-standing 147-cm rule. In addition, each subject filled out the Dizziness Handicap Inventory (DHI). Trials were randomized to prevent fatigue or practice effects. A Pearson product-moment correlation was performed between FR and SLS (r = 0.59, P = 0.001). Post hoc analyses of the first, the best, and the average scores highlighted the importance of using means for comparison in a population as variable as the vestibularly impaired. Post hoc analyses showed no correlation between the DHI score and either functional reach distance or single leg stance time. However, when the subjects were divided into groups based on DHI score (group 1 with DHI < or = 49/100, group 2 with DHI > or = 50/100) and a pooled two-sample t-test was performed, a significant difference (P = 0.05) was found in functional reach distance; the subjects who reported less perception of handicap reached farther than those who reported more perception of handicap. No difference was found between the two DHI groups in single leg stance time. Post hoc correlations of functional reach and single leg stance time. Post hoc correlations of functional reach and single leg stance within the two DHI groups showed a higher correlation in group 1 (DHI < or = 49/100), with r equals 0.65 (P < or = 0.01), than in group 2 (DHI > or = 50/100), with r equals 0.38 (P = 0.20). The study found a highly significant, moderate correlation between functional reach distance and single leg stance times in patients with peripheral vestibular disease. These results support the use of FR as an additional assessment tool with patients who have peripheral vestibular disease.

Adult↗
PubMedDate not supplied

Clinical evidence that the vestibular system participates in autonomic control.

The vestibular system, including both the peripheral vestibular system, that is, the labyrinth, and the central vestibular system, is known to influence autonomic function in several ways that have clinical implications. This paper discusses evidence for vestibular influences on autonomic control from normal human subjects, evidence for vestibular influences on autonomic control from patients, clinical implications of vestibulo-autonomic regulation, and speculations regarding possible clinical implications of vestibulo-autonomic control. Situations that provoke vestibular-induced autonomic responses in normal subjects include vestibular laboratory testing, vehicular motion, simulators, and, possibly, exposure to microgravity. Patients with peripheral and central vestibular abnormalities manifest both symptoms and signs of autonomic dysfunction presumably via vestibulo-autonomic connections. Vestibulo-autonomic regulation impacts vestibular diagnostic testing, clinical diagnosis of balance disorders, and treatment of balance disorders. In addition to well-recognized peripheral and central vestibular disorders, anxiety disorders have recently been linked to vestibular dysfunction in a subset of patients. In particular, vestibular dysfunction has been linked to panic disorder and agoraphobia. Vestibular-autonomic connections may form a basis for an association between vestibular dysfunction and panic attacks. The importance of vestibulo-autonomic regulation in the clinical arena is not fully known. Two speculative areas discussed in this paper include vestibular-induced orthostatic intolerance and the role of vestibular-respiratory pathways on sleep apnea.

Autonomic Nervous System↗