Plantar cutaneous sensory stimulation improves single-limb support time, and EMG activation patterns among individuals with Parkinson's disease.

Parkinson's disease is a chronic neurological disorder that results in gait and posture impairment. There is increasing evidence that these motor impairments may be partially due to deficits within the sensory system. In this study, the effects of a facilitatory insole that provides increased plantar sensory stimulation, was evaluated during gait, in a group of individuals with Parkinson's disease in comparison with healthy age-matched controls. Spatial-temporal parameters of gait were evaluated using an instrumented carpet, and muscle activation patterns were evaluated using surface EMG. All participants were tested with both a facilitatory (ribbed) insole and a conventional (flat) insole while walking 20 feet. Results indicated that the use of the facilitatory insole produced a significant increase in single-limb support time. Additionally, the muscle activation sequence of the tibialis anterior was normalized by the facilitatory insole, at the time of initial ground contact. These changes may lead to an overall improvement in gait pattern and stability, and suggest that the use of this type of facilitatory insole may be a useful treatment strategy for improving the gait of individuals with Parkinson's disease. This also provides support for the role of facilitation of the sensory system in improving motor output in individuals with Parkinson's disease.

Contribution of vision and cutaneous sensation to the control of centre of mass (COM) during gait termination.

This study employed manipulation of sensory inputs (vision and plantar-surface cutaneous sensation) during gait termination to elicit insight into the roles played by these sensory systems in the control of gait termination. Attenuation of cutaneous sensation was achieved through hypothermic anesthesia. Visual information was occluded using special glasses. The subjects were asked to walk along an 8 m walkway and during randomly selected trials (25% of trials) to terminate their gait in a predetermined area. The centre of mass (COM) was obtained in order to provide an indication of the efficiency and stability during termination when sensory inputs were manipulated. Lack of visual information delayed the initiation of the slowing down of the COM forward progression and increased the step length of the last step of termination. Additionally, lack of vision resulted in the COM moving closer to the base of support (BOS) during double support and more variability, in the COM, when attempting to achieve a final stable position. Insensitivity of the plantar-surface mechanoreceptors led to a longer second step and a more variable foot placement of the first step, and increased the loading rate during the final two steps of termination. Additionally when vision and cutaneous information were absent the resolution of the final stable position was not as effectively controlled. The results demonstrated that visual information about self-motion and object-motion and sensation from the plantar surface of the foot play phase-specific roles in the control of COM during gait termination.

The role of plantar cutaneous mechanoreceptors in the control of compensatory stepping reactions evoked by unpredictable, multi-directional perturbation.

The role of plantar pressure sensation in controlling compensatory stepping was explored via hypothermic anesthesia of the foot soles, in 10 healthy young adults. Stepping reactions were evoked by unpredictable platform translation in forward, backward and lateral directions. The findings suggest three specific direction- and phase-dependent roles for the plantar cutaneous afferents: (1) sensing posterior stability limits during initiation of backward steps, (2) sensing and controlling heel-contact and subsequent weight transfer during termination of forward steps, and (3) maintaining stability during the prolonged swing phase of lateral crossover steps.

Thresholds for step initiation induced by support-surface translation: a dynamic center-of-mass model provides much better prediction than a static model.

The need to initiate a step in order to recover balance could, in theory, be predicted by a static model based solely on displacement of the center of mass (COM) with respect to the base of support (BOS), or by a dynamic model based on the interaction between COM displacement and velocity. The purpose of this study was to determine whether the dynamic model provides better prediction than the static model regarding the need to step in response to moving-platform perturbation. The COM phase plane trajectories were determined for 10 healthy young adults for trials where the supporting platform was translated at three different acceleration levels in anterior and posterior directions. These trajectories were compared with the thresholds for step initiation predicted by the static and dynamic COM models. A single-link-plus-foot biomechanical model was employed to mathematically simulate termination of the COM movement, without stepping, using the measured platform acceleration as the input. An optimization routine was used to determine the stability boundaries in COM state space so as to establish the dynamic thresholds where a compensatory step must be initiated in order to recover balance. In the static model, the threshold for step initiation was reached if the COM was displaced beyond the BOS limits. The dynamic model showed substantially better accuracy than the static model in predicting the need to step in order to recover balance: 71% of all stepping responses predicted correctly by the dynamic model versus only 11% by the static model. These results support the proposition that the central nervous system must react to and control dynamic effects, i.e. COM velocity, as well as COM displacement in order to maintain stability with respect to the existing BOS without stepping.

The efficacy of head immobilization techniques during simulated vehicle motion.

STUDY DESIGN: Laboratory experiment. OBJECTIVE: To compare the efficacy of different head immobilization techniques during motion simulating ambulance transport. BACKGROUND: A significant number of neurologic injuries associated with cervical spine fractures arise or are aggravated during emergency extrication or patient transport. Previous studies have not addressed the effect of head immobilization on the passive motion that could occur across the neck during transport. METHODS: Three different head-immobilization methods were compared in six healthy young adults by using a computer-controlled moving platform to simulate the swaying and jarring movements that can occur during ambulance transport. In all tests, the trunk was secured by means of a commonly used "criss-cross" strapping technique. Efficacy of head immobilization was evaluated using measures of head motion and neck rotation. RESULTS: None of the three immobilization techniques was successful in eliminating head motion or neck rotation. Movement of the trunk contributed substantially to the lateral bending that occurred across the neck. A new product involving the placement of wedges underneath the head provided some small, but statistically significant improvements in fixation of the head to the fracture board; however, there was no improvement in terms of the relative motion occurring across the neck. CONCLUSIONS: Somewhat improved fixation of the head to the fracture board can be achieved by placing wedges under the head; however, the benefits of any fixation method, in terms of cervical spine immobilization, are likely to be limited unless the motion of the trunk is also controlled effectively. Future research and development should address techniques to better control head and trunk motion.

Effect of facilitation of sensation from plantar foot-surface boundaries on postural stabilization in young and older adults.

BACKGROUND: One of the more pervasive effects of aging is loss of cutaneous sensation, which appears to correlate with impaired postural control and increased risk of falling. This study examined the potential for compensating for the destabilizing effects of reduced cutaneous sensitivity by placing a raised edge underneath the perimeter of the plantar foot surface, so as to facilitate sensation from the stability boundaries of the base of support. METHODS: The main experiment involved 14 healthy older adults (aged 65-73) selected because they were known, from a previous study, to have moderate plantar cutaneous insensitivity. We also report results of an initial experiment involving 7 healthy young adults (aged 23-31). In both experiments, we studied effects of the plantar facilitation on control of rapid stepping reactions evoked by unpredictable postural perturbation, applied via sudden platform movement in forward, backward, and lateral directions. We also studied effects on "feet-in-place" responses evoked by continuous pseudorandom platform motion in mediolateral and anteroposterior directions. Subjects were blindfolded in all tests. RESULTS: Plantar facilitation reduced the incidence of "extra" limb movements, beyond the initial step, during forward-step reactions in the older adults. There also appeared to be an improved ability to control feet-in-place reactions: young subjects were better able to recover balance without stepping when falling backward (given instructions to "try not to step"), and both young and older subjects reduced the extent to which the center of foot pressure approached the posterior foot boundary during continuous anteroposterior platform motion. CONCLUSIONS: This study provides evidence that mechanical facilitation of sensation from the boundaries of the plantar surface of the foot can improve the efficacy of certain types of stabilizing reactions evoked by unpredictable postural perturbation. The results may be directly transferable to the design of special footwear insoles to reduce instability and risk of falling in older adults.

The use of expandable metallic stents for acute tracheal stenosis in the growing lamb.

PURPOSE: Expandable metallic stents (Palmaz stents) have been used in the treatment of tracheobronchial obstruction in children and adults. The authors investigated their utility in the management of acute airway stenosis in a growing animal model. METHODS: A model for tracheal stenosis was developed in young lambs (mean age, 4 weeks; mean weight, 8.6 kg). Via an anterior tracheotomy, a circumferential mucosal injury to the trachea was produced with electrocautery in 31 lambs. In the control group (n = 10) no further intervention was used. In the treatment groups, either serial balloon dilatation of the stricture was performed (n = 6), or expandable metallic stents were inserted across the stricture (n = 15). All animals were monitored daily for signs of respiratory distress. Body weights, fluoroscopic airway measurements and rigid bronchoscopy were performed at least weekly. RESULTS: The average weekly rate of airway growth was 8.2% +/- 5.5% of the tracheal cross-sectional area (CSA). All animals displayed severe stenosis (mean, 90.2% +/- 7.5% of CSA) within 13.1 +/- 4 days after the injury. All animals in the control group had severe respiratory distress, weight loss and died within 14.6 +/- 2.8 days after injury. Serial balloon dilatation of the stricture alone failed to relieve symptoms in all six animals in this group, who died within 20 +/- 1 days after the injury, despite two to three dilatations each. With placement of expandable metallic stents, only 3 of 15 lambs died (two of pneumonia, one of iatrogenic perforation). The remaining 12 remained symptom-free and gained weight during a 2-month follow-up period. However, fluoroscopic examination showed partial collapse of the stents in all of these animals (mean, 44.7% +/- 21.6% of CSA) requiring an average of 2 +/- 0.7 bronchoscopic dilatations. Pathological evaluation showed more pronounced granulation tissue in the stented animals. CONCLUSIONS: The authors conclude that expandable metallic stents provide an effective tool in the management of acute tracheal stenosis. However, airway growth, tissue reaction, and the mechanical properties of the stent require close monitoring and stent adjustment.

Influence of lateral destabilization on compensatory stepping responses.

Previous studies of compensatory stepping, in response to postural perturbation, have focussed on forward or backward stepping; however, the ability to step in other directions is of equal functional importance, since the perturbations encountered in daily life may often include a lateral component. The primary objective of this study was to determine how lateral destabilization affects the compensatory stepping response, in terms of: (1) swing-leg selection, (2) preparatory unloading of the swing leg, and (3) spatial and temporal characteristics of the swing trajectory. A novel multi-directional moving platform was used to apply transient perturbations in eight horizontal directions, in 10 healthy young adults. Perturbation magnitude was varied unpredictably over a wide range and subjects were instructed to try not to step, so as to discourage preplanned 'volitional' foot movement. The predominant strategy, seen in 96% of stepping responses to lateral destabilization, was to swing the leg that was unloaded by the perturbation. This strategy allowed a much more rapid foot-lift but required a longer and more complex swing trajectory, compared to responses where the perturbation-loaded leg was swung. When compared to forward and backward steps, the addition of a lateral component to the perturbation led to a 20% (90 ms) reduction in time to foot-off, a 20% (7 cm) increase in step length and a 70% (110 ms) increase in swing duration, on average. The results clearly demonstrate that compensatory stepping responses to non-sagittal perturbations are strongly influenced by biomechanical constraints and affordances that do not affect the forward and backward stepping behaviour that has been studied traditionally. These findings underscore the need to assess postural responses in multiple directions, in order to understand more fully how balance is maintained in the exigencies of everyday life.

Influences of inversion/eversion of the foot upon impact loading during locomotion.

Pronation of the foot is believed to be one of the mechanisms used during locomotion to attenuate the loading experienced by the body at ground contact. The purpose of this study was to quantify the changes in loading induced by modifications to the normal pronation of the foot during walking and running. Impact loading in 10 subjects was determined using ground reaction force and tibial acceleration. The results indicated that impact loading was increased when normal pronation was prevented during running. However, there was no reduction in impact loading when normal pronation was exaggerated. RELEVANCE: Orthotic corrections are commonly prescribed to control excessive foot pronation in patients who experience knee pain. The findings of the present paper demonstrate that pronation modifications can affect the magnitude of the impact experienced by the body during locomotion. It was also found that the loading responses to pronation modifications were not consistent between walking and running. Thus care should be exercised when orthotics that will be used for both walking and running are prescribed. Furthermore, patients should be informed that their orthotics may be activity specific.