Biomedical subjects

Heidi Sveistrup

Publications and source records attributed to Heidi Sveistrup.

7 recordsLinked to original sources

PubMed2005

Age-related changes in postural responses to externally- and self-triggered continuous perturbations.

This is a cross sectional study of eight healthy young (age 22+/-2 years) and eight healthy older (age 70+/-5 years) adults who participated in an experiment in which they had to keep their balance while standing on a platform moving in the anterior/posterior direction. The 20 cm peak-to-peak platform movements were sinusoidal at increasing frequencies up to 0.61 Hz. The frequency increases were either sudden and unpredictable (externally-triggered perturbations) or controlled by the subjects themselves (self-triggered perturbations). To maintain balance, all subjects used anticipatory adjustments such as early postural muscle activation, leading to fewer steps being taken, tighter coupling of the center of pressure (COP) and the platform movements, and small COP excursions. These adjustments were found to be lacking for externally-triggered perturbations in older subjects; in these subjects the COP range was larger and more often in less safe regions at the boundaries of the base of support.

Adult↗

PubMed2005

Postural stabilization from fingertip contact II. Relationships between age, tactile sensibility and magnitude of contact forces.

In the present report, we extend our previous observations on the effect of age on postural stabilization from fingertip contact (Exp Brain Res 157 (2004) 275) to examine the possible influence of sensory thresholds measured at the fingertip on the magnitude of contact forces. Participants (young, n=25, 19-32 years; old, n=35, 60-86 years) underwent psychophysical testing of the right index finger to determine thresholds for spatial acuity, pressure sensitivity and kinesthetic acuity. Spatial acuity was determined from the ability to detect gaps of different widths, while Semmes-Weinstein monofilaments were used for pressure sensitivity. Kinesthetic acuity was determined by asking participants to discriminate plates of different thicknesses using a thumb-index precision grip. These tests were selected on the basis that each reflected different sensory coding mechanisms (resolution of spatial stimuli, detection of mechanical forces and integration of multi-sensory inputs for hand conformation) and thus provided specific information about the integrity and function of mechanoreceptive afferents innervating the hand. After log transformation, thresholds were first examined to determine the influence of age (young and old) and gender (male, female) on tactile acuity. Sensory thresholds were then entered into multiple linear regression models to examine their ability to predict fingertip contact forces (normal and tangential) applied to a smooth surface when subjects stood with eyes closed on either a firm or a compliant support surface. As expected, age exerted a significant effect (p<0.01) on all three thresholds, but its impact was greater on spatial acuity than on pressure sensitivity or kinesthetic acuity. Gender had a marginal impact on pressure sensitivity thresholds only. The regression analyses revealed that tactile thresholds determined at the index fingertip accounted for a substantial proportion of the variance (up to 30%) seen in the contact forces deployed on the touch-plate, especially those exerted in the normal direction. The same analyses further revealed that much of the variance explained by the models arose from inter-individual differences in tactile spatial acuity and not from differences in pressure sensitivity or in kinesthetic acuity. Thus, of all three tests, the spatial acuity task was the most sensitive at detecting differences in hand sensibility both within and between age groups and, accordingly, was also better at predicting the magnitude of fingertip forces deployed for postural stabilization. Since spatial acuity is critically dependent upon innervation density, we conclude that the degree of functional innervation at the fingertip was likely an important factor in determining the capacity of older participants to use contact cues for stability purposes, forcing the most affected individuals to exert unusually high pressures in order to achieve stabilization in the presence of reduced tactile inputs arising from contact with the touched surface.

Adult↗

PubMed2004

Motor rehabilitation using virtual reality.

Virtual Reality (VR) provides a unique medium suited to the achievement of several requirements for effective rehabilitation intervention. Specifically, therapy can be provided within a functional, purposeful and motivating context. Many VR applications present opportunities for individuals to participate in experiences, which are engaging and rewarding. In addition to the value of the rehabilitation experience for the user, both therapists and users benefit from the ability to readily grade and document the therapeutic intervention using various systems. In VR, advanced technologies are used to produce simulated, interactive and multi-dimensional environments. Visual interfaces including desktop monitors and head-mounted displays (HMDs), haptic interfaces, and real-time motion tracking devices are used to create environments allowing users to interact with images and virtual objects in real-time through multiple sensory modalities. Opportunities for object manipulation and body movement through virtual space provide frameworks that, in varying degrees, are perceived as comparable to similar opportunities in the real world. This paper reviews current work on motor rehabilitation using virtual environments and virtual reality and where possible, compares outcomes with those achieved in real-world applications.

Journal Article↗

PubMed2004

Postural stabilization from fingertip contact: I. Variations in sway attenuation, perceived stability and contact forces with aging.

In this study, we compared the ability of young (n=10, 19-32 years) and older subjects (n=35, 60-86 years) to use fingertip contact as a balance aid during quiet stance under various conditions to determine whether aging would influence contact strategies. Experimental trials (duration, 60 s) included two visual conditions (vision; no vision), three fingertip contact conditions (no touch; smooth touch; rough touch) and two support surface conditions (firm; foam). In trials with contact, participants were required to maintain a light contact with their right index fingertip on an instrumented touch-plate. Subjects were not constrained to exert minimal contact force, although they were aware that the touch-plate was not designed for physical support. From displacements of the centre of foot pressure (COP), mean sway amplitude (MSA) was computed in the anterior-posterior (COP(AP)) and medio-lateral (COP(ML)) directions. Subjective estimates of stability were also obtained by asking participants to rate perceived stability on a visual analog scale in each condition. Mean normal force (FN) and mean resultant tangential force (F(TAN)) were computed from contact force data applied on the touch plate. In both age groups, touch conditions had a substantial effect on MSA in the AP direction under both support surface conditions, with reductions averaging between 40-55% when touch was allowed. Reductions in the ML direction, though less important (8-12% on average), were nevertheless highly significant, especially in the older subjects when standing on the foam. In the two groups, vision and texture had only marginal impact on MSA computed on both support surfaces. Contrasting with sway measurements, stability ratings were highly influenced by visual conditions in both age groups. Only in conditions of deficient support (foam surface) and absent vision did the perceived effect of touch exceed that of vision. Age had a major impact, however, on contact forces deployed during trials with touch. While individuals in the young group typically produced forces of <1 N (mean FN, 0.32+/-0.15 N) to achieve postural stabilization, older subjects tended to use higher, though not too excessive, contact forces (mean FN, 1.21+/-0.75 N) under the same conditions. From these findings, we conclude that the ability to use contact cues from the fingertip as a source of sensory information to improve postural stability is largely preserved in healthy older adults. The increase in contact force deployed by older individuals to achieve postural stabilization is interpreted as a compensatory strategy to help overcome age-related loss in tactile sensation, an issue that will be further addressed in a companion paper.

Adult↗

PubMed2003

Experimental studies of virtual reality-delivered compared to conventional exercise programs for rehabilitation.

This paper presents preliminary data from two clinical trials currently underway using flat screen virtual reality (VR) technology for physical rehabilitation. In the first study, we are comparing a VR-delivered exercise program to a conventional exercise program for the rehabilitation of shoulder joint range-of-motion in patients with chronic frozen shoulder. In the second study, we are comparing two exercise programs, VR and conventional, for balance retraining in subjects post-traumatic brain injury. Effective VR-based rehabilitation that is easily adapted for individuals to use both in inpatient, outpatient and home-based care could be used as a supplement or alternative to conventional therapy. If this new treatment approach is found to be effective, it could provide a way to encourage exercise and treatment compliance, provide safe and motivating therapy and could lead to the ability to provide exercises to clients in distant locations through telehealth applications of VR treatment. VR is a new technology and the possibilities for rehabilitation are only just beginning to be assessed.

Brain Injuries↗

PubMed2003

The effect of two types of virtual reality on voluntary center of pressure displacement.

Voluntary movements result in internal perturbations of balance and equilibrium. One variable regulated during movement is the position of the center of pressure (COP). Sensory information from the visual, vestibular and somatosensory systems is used in establishing relevant frames of reference for postural control. In this study, we were interested in determining whether different limitations of COP movement occur when different approaches to delivering virtual environments are used and when visual information incoherent with vestibular and somatosensory information is provided. Eighteen healthy adults completed voluntary lateral reaches under three conditions: continuous lateral reach (CLR), flatscreen virtual reality (FS), and head-mounted display virtual reality (HMD). Reaching behavior was indexed by force plate measures of maximum anterior-posterior and lateral displacement of the COP. The COP movement decreased in the lateral direction in the HMD condition relative to the FS. The maximum range of COP movement in the anterior-posterior direction increased as a function of reaching task with HMD realizing the greatest amount of movement. The lack of an exocentric frame of reference in HMD coherent with information from other sensory systems results in limiting COP movement within the base of support (BOS) in order to decrease the challenge to the postural control system.

Adult↗

PubMed2002

The development of coordination for reach-to-grasp movements in children.

When adults reach to grasp stationary targets, movement kinematics (endpoint trajectories, interjoint coordination) are highly stereotyped and stable. The emergence of an optimal coordination for reaching involves mastering the redundant number of degrees of freedom while the body grows. Reaching has been well studied in healthy children under the age of 3 years. We characterised the development of coordination during reaching in children over the age of 3 years and identified age ranges in which stable patterns emerge. A random sample of 38 healthy children aged 4-11 years and nine adults participated in the study. They reached from the seated position with the dominant arm and grasped a cone placed at three distances in the forward sagittal plane in front of the body. Kinematic data from markers placed on the arm, head and trunk were recorded at 100 Hz (Optotrak Motion Analysis System). Immature patterns of reaching were characterised by increased variability in younger compared to older children. Hand trajectories became smoother and less variable with age. Interjoint coordination became more consistent, while trunk displacement and variability decreased with age. Only children between 8 and 10 years old had variability similar to adults. Our data suggest that different aspects of movement kinematics mature at different rates. However, our data do not support the idea of a sequential maturation of different biomechanical variables.

Adult↗