Upright balance is believed to be maintained through active and passive mechanisms, both of which have been shown to be impacted by aging. A compensatory balance response often observed in older adults is increased co-contraction, which is generally assumed to enhance stability by increasing joint stiffness. We investigated the effect of aging on standing balance by fitting body sway data to a previously developed postural control model that includes active and passive stiffness and damping parameters. Ten young (24 +/- 3 years) and seven older (75 +/- 5 years) adults were exposed during eyes-closed stance to perturbations consisting of lateral pseudorandom floor tilts. A least-square fit of the measured body sway data to the postural control model found significantly larger active stiffness and damping model parameters in the older adults. These differences remained significant even after normalizing to account for different body sizes between the young and older adult groups. An age effect was also found for the normalized passive stiffness, but not for the normalized passive damping parameter. This concurrent increase in active stiffness and damping was shown to be more stabilizing than an increase in stiffness alone, as assessed by oscillations in the postural control model impulse response.
Abstract The goal of this study was to quantify the association between sensory integration abilities relevant for standing balance and disease stage in glaucoma. The disease stage was assessed using both functional (visual field deficit) and structural (retinal nerve fiber layer thickness) deficits in the better and worse eye. Balance was assessed using an adapted version of the well-established Sensory Organization Test (SOT). Eleven subjects diagnosed with mild to moderate glaucoma stood for 3 min in 6 sensory challenging postural conditions. Balance was assessed using sway magnitude and sway speed computed based on center-of-pressure data. Mixed linear regression analyses were used to investigate the associations between glaucoma severity and balance measures. Findings revealed that the visual field deficit severity in the better eye was associated with increased standing sway speed. This finding was confirmed in eyes open and closed conditions. Balance was not affected by the extent of the visual field deficit in the worse eye. Similarly, structural damage in either eye was not associated with the balance measures. In summary, this study found that postural control performance was associated with visual field deficit severity. The fact that this was found during eyes closed as well suggests that reduced postural control in glaucoma is not entirely attributed to impaired peripheral visual inputs. A larger study is needed to further investigate potential interactions between visual changes and central processing changes contributing to reduced balance function and increased incidence of falls in adults with glaucoma.
In this paper we demonstrate a new method to quantify direction and magnitude of sway in response to periodic inputs. The postural sway response was modeled as an ellipse, allowing the determination of angle of heading as well as the resultant magnitude. To demonstrate this methodology, center of pressure data obtained from a subject receiving sinusoidal (0.25 Hz, 1.2 mA peak-to-peak) galvanic vestibular stimulation in both the binaural-bipolar and binaural-monopolar configurations were analyzed. The binaural-bipolar and binaural-monopolar stimuli elicited sway patterns that were oriented at 4° and 97° to the medial-lateral axis, respectively. In addition, the binaural-monopolar stimulus generated twice as much sway as the binaural-bipolar stimulus. We propose that this method can be applied to sway obtained from sinusoidal inputs to the sensory systems controlling balance. Estimation of the direction and magnitude of postural sway will become an important tool for understanding postural control mechanisms for disturbances to balance that do not occur in a cardinal direction.
Previous studies of vestibulo-ocular function in patients with anxiety disorders have suggested a higher prevalence of peripheral vestibular dysfunction compared to control populations, especially in panic disorder with agoraphobia. Also, our recent companion studies have indicated abnormalities in postural control in patients with anxiety disorders who report a high degree of space and motion discomfort. The aim of the present study was to assess the VOR, including the semicircular canal-ocular reflex, the otolith-ocular reflex, and semicircular canal-otolith interaction, in a well-defined group of patients with anxiety disorders. The study included 72 patients with anxiety disorders (age 30.6 +/− 10.6 yrs; 60 (83.3% F) and 29 psychiatrically normal controls (age 35.0 +/minus; 11.6 yrs; 24 (82.8% F). 25 patients had panic disorder; 47 patients had non-panic anxiety. Patients were further categorized based on the presence (45 of 72) or absence (27 of 72) of height phobia and the presence (27 of 72) or absence (45 of 72) of excessive space and motion discomfort (SMD). Sinusoidal and constant velocity earth-vertical axis rotation (EVAR) was used to assess the semicircular canal-ocular reflex. Constant velocity off-vertical axis rotation (OVAR) was used to assess both the otolith-ocular reflex and static semicircular canal-otolith interaction. Sinusoidal OVAR was used to assess dynamic semicircular canal-otolith interaction. The eye movement response to rotation was measured using bitemporal electro-oculography. Results showed a significantly higher VOR gain and a significantly shorter VOR time constant in anxiety patients. The effect of anxiety on VOR gain was significantly greater in patients without SMD as compared to those with SMD. Anxiety patients without height phobia had a larger OVAR modulation. We postulate that in patients with anxiety, there is increased vestibular sensitivity and impaired velocity storage. Excessive SMD and height phobia seem to have a mitigating effect on abnormal vestibular sensitivity, possibly via a down-weighting of central vestibular pathways.
Injuries and deaths are often the result of slips/falls. The perceived danger of slipping affects gait biomechanics. This paper investigated the effect of having a-priori knowledge of the floor's contaminant condition on the biomechanics of slips. Five healthy young male subjects donned a safety harness and walked across a walkway, while ground reaction forces and whole body motion were recorded bilaterally at 60 Hz. Slips on soapy floors occurred under 3 “knowledge” conditions: (1) unexpected slips, (2) slips when uncertain of the contaminant condition, and (3) slips when walking onto known contaminated floors. in (2) and (3), i.e. anticipation of slippery surfaces, subjects generated proactive reactions (reduced stance duration and foot angle at heel contact as well as greater hip flexion) compared to unexpected conditions in (1). Those reactions reduced slip potential but also minimized gait disturbances (reduced slip distance and sliding velocity of the heel) when a slip occurred.
To obtain normative longitudinal vestibulo-ocular and balance test data in children from ages three to nine years with normal middle ear status.Prospective, longitudinal cohort.Tertiary care pediatric hospital.Three-year-old children were entered and tested yearly. Subjects underwent earth vertical axis rotation testing using sinusoidal and constant velocity stimuli and performed the Sensory Organization Test.One hundred forty-eight children were entered, and usable data were collected on 127 children. A linear increase in the vestibulo-ocular reflex gain as children aged was found, without a change in the phase of the response. An age-related linear increase in equilibrium scores, indicating reduced postural sway, was also observed.These normative data can be used in the evaluation of dizziness and balance disorders in children.
The evaluation and prevention of slips and falls require methods of quantifying the slipperiness of floors. The concept of coefficient of friction (COF) has been and continues to be commonly used as one such method. The objective of this paper is to present some results from investigations into the effects of vertical force and velocity on COF measures for different types of floors. Tests involving both static COF (SCOF) and dynamic COF (DCOF) measurements were performed under various conditions. It was found that the SCOF changed as a function of the vertical force used. Generally, the SCOF increased as the vertical force was increased. This was not true, however, for tile floors. It was also found that there was a significant first order interaction effect on the SCOF between vertical weight and the condition of the floor (wet or dry). The dynamic tests showed that velocity of the shoe material with respect to the floor had a large effect on the DCOF values obtained. The velocity effect was dependent on the shoe material and the conditions tested. Possible reasons for these findings and ramifications on slip testing are presented.
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