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An update on falls.

PURPOSE OF REVIEW: Falls among elderly persons create immense social problems because of their association with physical decline, serious psychosocial consequences, negative impact on the quality of life, and markedly reduced survival. In addition, falls pose high costs to the public health service. For these reasons, falls remain a popular topic for research. Here, we review several interesting developments that have been published during the past year. RECENT FINDINGS: Considerable attention has been focused on early identification of fallers and prevention strategies for falls or injuries. A remaining challenge is to implement such strategies into daily clinical practice, at acceptable costs and with good acceptance. New evidence has been generated to suggest the importance of high-level processing for postural control, but it remains difficult to predict falls based upon a simple dual tasking test. Neuroimaging studies are now beginning to provide new insights into the role of cortical structures in balance regulation, and how cortical dysfunction might contribute to falls. Posturography studies using multidirectional moving platforms or computer models of balance have provided new insights into falling mechanisms, in particular the role of abnormal protective responses (stepping or grasping) and the negative effects of stiffening. Other studies have shown how a fear of falling, a common sequel to falls, may lead to secondary degeneration of postural control, thus completing a vicious loop. SUMMARY: While these examples illustrate that falls research is very much ongoing, one cannot speak of true progress until the scientific evidence can be implemented into real life, with falls being prevented effectively in individual cases.

Accidental Falls↗

Test-retest reliability of lower extremity functional instability measures.

OBJECTIVES: 1) To evaluate the test-retest reliability of lower extremity functional instability measures involving testing situations of varying complexity, and 2) To evaluate the interrelationships among performances observed during these tests and a maximal single-limb forward hop for distance. DESIGN: A repeated measures design, repeated on two occasions. SETTING: Postural control laboratory. PARTICIPANTS: Thirty young healthy subjects (23.5 +/- 2.0 years). MAIN OUTCOME MEASURES: Subjects performed single-limb standing balance and forward hop tests on two occasions completed within 1 week and at least 24 hours apart. Standing balance was assessed using a force platform and the following four progressively complex test situations: 1) standing on the stable platform with eyes open, 2) standing on a foam mat placed over the platform with eyes open, 3) standing on the stable platform with eyes closed, and 4) standing on the stable platform after landing from a maximal single-limb forward hop. RESULTS AND CONCLUSIONS: Intraclass correlation coefficients were moderate to excellent (0.41 to 0.91) suggesting that the standing balance tests are appropriate for distinguishing among group performances. Standard errors of measurement and associated 95% confidence intervals suggested that a change in an individual's standing balance performance of approximately 10-30% would be necessary in order to confidently state that a true change had occurred. Stronger relationships were observed between hop distance and standing balance tests performed with eyes closed (r = -0.63, p < 0.001) and after landing from a maximal hop (r = -0.53, p = 0.003), suggesting that tests that challenge postural control to a greater extent are more representative of functional performance.

Adult↗

Does impulse noise induce vestibular disturbances?

The effect of impulse noise on postural stability was evaluated in 54 subjects from the Finnish army, who were suffering from acute hearing loss caused by exposure to firearms noise. For referents we used 20 non-exposed army recruits and 39 civilian volunteers. The effects of vision, pressoreceptor function and proprioception were stepwise excluded or altered, leaving mainly the vestibular guidance of postural control intact. Since the postural perturbation was fairly smooth during these instances we assume that the condition evaluates mainly the function of the otolith organs in guiding stance. We found no difference in any of the test conditions used, between normal controls, army controls and impulse noise exposed subjects. Furthermore, there was no dose response with body sway and severity of hearing loss. The results indicate that impulse noise may not be the cause of significant functional changes in the vestibular system that can account for noise-induced postural instability.

Adult↗

The polymodal sensory cortex is crucial for controlling lateral postural stability: evidence from stroke patients.

In modern literature, internal models are considered as a general neural process for resolving sensory ambiguities, synthesising information from disparate sensory modalities, and combining efferent and afferent information. The polymodal sensory cortex, especially the temporoparietal junction (TPJ), is thought to be a nodal point of the network underlying these properties. According to this view, a pronounced disruption of the TPJ functioning should dramatically impair body balance. Surprisingly, little attention has been paid to this possible relationship, which was the subject of investigation in this study. Twenty-two brain-damaged patients and 14 healthy subjects were subjected to a self-regulated lateral balance task, performed while sitting for 8 s on a rocking platform. Their lateral body balance was analysed both with and without vision (darkness). Support displacements in the frontal plane were recorded by means of an accelerometer. Two criteria were taken into account to evaluate body stability in each trial: the number of aborted trials due to balance loss and the angular dispersion of the supporting surface. Lesions involving the temporoparietal junction were found to markedly increase body instability, both with and without vision. Therefore, the temporoparietal junction plays a pivotal role in lateral body stabilisation, irrespective of the sensory condition in which the task is performed. This suggests that body stability is controlled throughout internal model(s).

Adult↗

Gender affects sympathetic neurovascular control during postural stress.

Sympathetic outflow increases during head-up tilt (HUT) to stabilize blood pressure in the presence of decreases in venous return and stroke volume (SV). Otherwise, orthostatic hypotension would develop. Gender differences in orthostatic tolerance have been noted but the mechanisms are still uncertain. More recently, Waters et al. reported in a limited sample, greater susceptibility of women to demonstrate orthostatic intolerance following space flight. Therefore, it is important to understand gender differences in reflex blood pressure regulation. Recently, we reported smaller increments in muscle sympathetic nerve activity (MSNA) in healthy women during graded HUT and a non-baroreflex cold pressor test. The purpose of this report is to examine the hypothesis that gender differences in blood pressure control during HUT are related to important variations in MSNA discharge patterns.

NASA Discipline Neuroscience↗

Dynamics of human cardiorespiratory responses to standing on one leg with eyes closed.

The postural control system has been extensively studied in terms of somatic motor function but little is known about its connection with human autonomic function. The purpose of this study was to determine the cardiorespiratory changes in response to the 1-min balance test that was performed by standing on one leg with eyes closed (SOLEC) or eyes open (SOLEO) in 12 healthy young women [mean age 20.7 (SD 3.3) years]. Heart rate (HR), respiratory rate (RR), duration of inspiration and expiration, tidal volume (VT), and oxygen uptake (VO2) were measured during the test. The SOLEC test produced rapid increases in HR at the onset. There were significant increases in HR later during the test (P < 0.05). Metabolic rate (VO2) showed a gradual increase during the SOLEC test, indicating that the late responses could have been partly due to metabolic changes. The RR increased significantly at the onset of the test (P < 0.05), and remained elevated until the end of the test. The early responses were considered to be mediated neurally through the postural control system which receives the afferent inputs arising from the vestibular system and from muscle proprioceptors of the leg. In contrast, SOLEO caused small insignificant changes in HR, RR, VT and VO2, suggesting that a visual input is essential for balancing a postural change. The SOLEC test may have potential as a test of autonomic function.

Adolescent↗

Cardiorespiratory changes when balancing one's whole body on one leg with eyes closed.

Postural control system has been extensively studied in terms of somatic motor function, but little is known about its connection with human autonomic function. The purpose of this study was to determine the cardiorespiratory changes in response to the 3-min load that was performed by balancing one's whole body on one leg with eyes closed (SOLEC load) or eyes open (SOLEO load) in 11 healthy young subjects (5 males and 6 females, mean age 20.8 +/- 1.9 year). Blood pressure (BP), heart rate (HR), respiratory rate (RR), inspiratory and expiratory duration (Ti and Te), tidal volume (VT), and oxygen uptake (VO2) were measured before, during, and after the load. The SOLEC load produced significant increases in HR and systolic BP within 1 min. There were further increases in systolic and diastolic BP during the late period of the load. Metabolic rate (VO2) showed a gradual increase during the SOLEC load, indicating that the late responses would be partly due to metabolic alteration. The early responses are considered to be mediated neurally through the postural control system which receives the afferent inputs arising from vestibular system and from muscle proprioceptors of the leg. In contrast, SOLEO load caused small insignificant changes in BP, HR, VT, and VO2, suggesting that a visual input is essential for balancing a postural change. The balance test with eyes closed may have value in a clinical neurological rehabilitation setting.

Adult↗

Posturographic findings in patients with idiopathic cervical dystonia before and after local injections with botulinum toxin.

In this posturographic study, whole-body postural control was impaired in more than 75% of patients with idiopathic cervical dystonia (ICD) before local injections with botulinum toxin type A (BTX-A) and the impairment was independent of the direction of the torticollis. Six weeks after therapy with BTX-A, the number of pathological posturographic parameters had decreased by almost 30%, and the improvement reached statistical significance for sway path, sway area and anteroposterior sway during stance on foam with eyes closed. From a pathophysiological point of view, this improvement may be explained - at least in part - by a reduction of abnormal proprioceptive input from the neck. Accordingly, it seems possible that neck proprioceptive input plays a role in whole-body postural control in ICD patients, even though previous studies suggested that the neck input is relatively ignored in these patients.

Adult↗

Physical therapy management of peripheral vestibular dysfunction: two clinical case reports.

We describe the treatment of two patients with peripheral vestibular dysfunction using a novel, staged exercise program. Response to treatment was documented. The first patient, a 62-year-old woman with unilateral vestibular dysfunction (UVD) and a 6-month history of disequilibrium following herpes zoster oticus resulting in damage to the right inner ear, was treated with an 8-week course of vestibular physical therapy. During the 8 weeks, the patient attended weekly physical therapy sessions and was trained to perform vestibular adaptation exercises on a daily basis at home. The second patient, a 53-year-old woman with progressive disequilibrium secondary to profound bilateral vestibular hypofunction (BVH), was treated with a 16-week course of vestibular physical therapy. During the first 8 weeks, the patient attended weekly physical therapy sessions and was trained to perform vestibular adaptation and substitution exercises on a daily basis at home. During the second 8 weeks, the patient continued performing vestibular physical therapy exercises at home independently. Vestibular function (sinusoidal vertical axis rotation testing), postural control (clinical tests and posturography), stability during the performance of selected activities of daily living (ADLs), and self-perception of symptoms and handicap were measured prior to and at the conclusion of treatment for both patients and at the midpoint of treatment for the patient with BVH. After 8 weeks of treatment, both patients reported improvements in self-perception of symptoms and handicap and demonstrated objective improvements in clinical balance tests, posturography, and several kinematic indicators of stability during the performance of selected ADLs. Further improvements were noted in the patient with BVH after 16 weeks of treatment. Improvements in postural control were noted after 8 weeks of treatment for the patient with UVD and after 16 weeks for the patient with BVH. Vestibular function improved during the course of treatment for the patient with UVD only. These case reports describe two different individualized treatment programs and document self-reported and laboratory-measured functional improvements in two patients with vestibular deficients--one with unilateral damage and one with bilateral damage.

Activities of Daily Living↗

Intrinsic risk factors for inversion ankle sprains in females--a prospective study.

Ankle sprains are extremely common. However, very little is known about the variables that predispose individuals to these injuries. The purpose of this study was to examine prospectively intrinsic risk factors for inversion sprains in a young physically active female population. One hundred and fifty-nine female physical education students were evaluated for several possible intrinsic risk factors for inversion sprains at the beginning of their academic study. The evaluated intrinsic risk factors included anthropometrical and physical characteristics, ankle joint position sense, isokinetic ankle muscle strength, lower leg alignment characteristics, postural control and muscle reaction time during a sudden inversion perturbation. All sports injuries were registered during 1-3 years and exposure to sport was recorded (mean: 15.33+/-4.33 h a week). Thirty-two (20%) of the 159 females sprained their ankle. The number of ankle sprains per 1000 h of sports exposure was 0.75. The Cox regression analysis revealed that females with less accurate passive joint inversion position sense [hazard ratio (HR): 1.08, 95% confidence interval (CI): 1.02-1.14 for absolute error at 15 degrees inversion], a higher extension range of motion at the first metatarsophalangeal joint (HR: 1.03, 95% CI: 1.00-1.06) and less coordination of postural control (HR: 0.96, 95% CI: 0.93-1.00 for endpoint excursion; HR: 0.94, 95% CI: 0.89-0.99 for maximal endpoint excursion) are at greater risk of an ankle sprain. The findings of this study suggest that effective prevention and conservative rehabilitation of ankle inversion sprains should include attention to these variables.

Adolescent↗

Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits.

OBJECTIVE: To quantify changes in balance parameters and ranges of postural control at the ankle after isokinetic fatigue. DESIGN: Before-after trials, with a 5 x 6 repeated-measures design. SETTING: General community. PARTICIPANTS: Twenty-four men (age, 24.9 +/- 3.92y; height, 177.79 +/- 6.36cm; weight, 80.78 +/- 13.22kg) without ankle trauma within 2 years. INTERVENTIONS: Fatigue of the plantarflexors and dorsiflexors was induced by isokinetic contractions. Balance was assessed by using a unilateral test (15-s quiet stance, 10-s lean test) on a force platform immediately before and at 0 (T0), 10 (T10), 20 (T20), and 30 (T30) minutes postfatigue. MAIN OUTCOME MEASURE: Mediolateral (ML) and fore-aft (FA) sway as well as ML and FA displacement were analyzed by analysis of variance with repeated measures for time (alpha =.05). RESULTS: In quiet stance, ML sway was greater at T0, whereas total sway increased at all time points postfatigue (P < .05). For the lean test, FA sway increased at T0 and T10, and total sway increased at all time points (P < .05). Both ML and FA displacement significantly differed at T0 (P < .05). All sway parameters returned to baseline within 20 minutes. CONCLUSIONS: Isokinetic fatigue of ankle plantarflexors and dorsiflexors significantly influences sway parameters and ranges of postural control in healthy young men. These perturbations are transient, and recovery occurs within 20 minutes.

Adult↗

VEMPs and dynamic posturography after intratympanic gentamycin in Menière's disease.

In this study, we investigated whether vestibular evoked myogenic potentials (VEMPs) and dynamic posturography (DP) are useful in the evaluation of the vestibular function in patients affected by active monoaural Menière's disease (MD) treated with intratympanic gentamycin. Twelve subjects affected by monoaural MD were treated with weekly intratympanic injections of 0.5 ml of gentamycin at a concentration of 20 mg/ml. VEMPs were used to test saccular function, while postural control was analyzed by DP. The results obtained with these two techniques were compared with those obtained by using bithermal caloric test. The mean follow-up was 15.3 months (6--28 months). Therapy resulted in complete absence of the caloric response in six subjects (50) and in caloric test-induced asymmetry in the remaining individuals, ranging from 83 to 27. At follow-up, eleven patients (91.6%) were free of vertigo, while one patient had two vertigo spells 9 months after treatment. Before treatment, VEMPs were present in the affected ear of eleven patients. After treatment VEMPs were absent in all the patients. At the end of follow-up, reappearance of VEMPs was observed in two patients, with no changes in latency values and amplitude ratio. DP demonstrated a reduction of the Composite Score (CS) one week after therapy, with a prevalent reduction of the vestibular component. After 6 months, there was an improvement of the CS and, in particular, of the vestibular component. The present study demonstrates that bithermal caloric test and VEMPs allow for the functional evaluation of both the horizontal semicircular canal and the sacculus, suggesting that these techniques might be used together to monitor the efficacy of intratympanic gentamycin therapy. In addition, our data indicate that DP might provide important information on compensation phenomena and show that intratympanic gentamycin can improve postural control in MD patients.

Adult↗

Determinants and predictors of the maximum walking speed during computer-assisted gait training in hemiparetic stroke patients.

OBJECTIVE: To investigate biomechanical determinants and predictors of walking speed in early gait training after stroke. DESIGN: Prospective. SETTING: Physical therapy room of Tohoku University Hospital. PARTICIPANTS: Thirty-four male hemiparetic stroke patients received 8 weeks of computer-assisted gait training (CAGT), which was initiated within approximately 3 months after stroke onset. MAIN OUTCOME MEASUREMENTS: The time and the number of steps required to walk 10m at the fastest possible speed (maximum walking speed [MWS]), the sway path of the center of feet pressure (CFP) in the upright posture, the change in CFP when shifting the body weight either left to right or back and forth, and the maximal isokinetic muscle strength during extension of both knees were measured at the start and at 4 and 8 weeks. Stepwise regression procedures were performed to analyze determinants and predictors of the MWS using the MWS as the dependent variable and personal characteristics, standing balance, and the muscle strength of both knees as the independent variables. RESULTS: The MWS significantly increased from 40.4 to 76.5m/min on average after 8 weeks. The determinant of MWS at the start was the postural control of shifting to the left and right (coefficient of determination of 45.4%). The determinant of MWS at 4 and 8 weeks was the muscle strength during knee extension on the affected side (coefficient of determination of 62.9% and 54.5%, respectively). The predictors of MWS at 4 weeks were the MWS at the start of CAGT, followed by muscle strength during knee extension on the affected side and the time from stroke onset to the start of CAGT (total variance of 84.3%). The predictors at 8 weeks were the MWS at the start, followed by the muscle strength during knee extension on the affected side (total variance of 73.4%). CONCLUSIONS: After 4 weeks, the biomechanical determinant of MWS had changed from the postural control of weight-shifting from left to right to the muscle strength during knee extension on the affected side. The MWS at 4 and 8 weeks could be predicted by the initial MWS, the initial muscle strength during knee extension on the affected side, and the time since stroke onset, with high coefficients of determination.

Acceleration↗

Locust local nonspiking interneurons which tonically drive antagonistic motor neurons: physiology, morphology, and ultrastructure.

Local nonspiking interneurons have been implicated in the control of behavior. We have characterized the physiology of two local nonspiking interneurons in the locust and subsequently examined the neurons in the light and electron microscopes. Physiologically the two interneurons have opposite effects upon antagonistic motor neurons and are tonically releasing transmitter at their "resting potentials." This combination of tonic release and reciprocal driving of antagonistic motor neurons by single interneurons provides a hitherto undescribed means of controlling posture. One interneuron (DCVII, 4) excites flexor tibiae and inhibits the slow extensor tibiae motor neurons when depolarized. The other interneuron (DCVII, 5) inhibits the flexor tibiae and excites the slow extensor tibiae motor neurons when depolarized. In both cases, when the interneurons are hyperpolarized, they have the opposite effects upon the same motor neurons. Intracellular staining of these neurons confirms that they are local interneurons. Furthermore, an examination of sectioned material shows that the neurons are unique and can be identified as such in a population of locust neurons. Ultrastructurally, we find synapses only on the smaller (less than 2 micrometers) branches. These neurons may form the presynaptic element in either of two configurations, these being the discrete density (one presynaptic) and the dense bar (one presynaptic, two postsynaptic) type of configurations. The functional implications of these findings for neurons controlling posture are discussed.

Animals↗

The use of viewing posture to control visual processing by lateralised mechanisms.

Chicks were trained and tested to run to a dish and feed from it under one of four conditions. In three of these, the dish was covered by a light lid that the chicks readily learned to remove. The square lid (SL) had slightly protruding corners, so that it could be removed by a blow of the bill at a range of positions. A round lid (UL), which fitted snugly, could best be removed by inserting the bill into a medial U-shaped indentation. A round lid (STR), which fitted all the way round to the edge of the dish, could be removed by grasping and tugging a centrally placed piece of string. The final dish had no lid (NOL). The dish and the layout of the arena were otherwise identical under all conditions. Chicks trained and tested with lids predominantly fixated the dish during approach with the right eye and showed leftward deviation from the direct line of approach (which facilitated right eye use). NOL chicks fixated with the left eye and deviated rightwards. The right eye is thus used when a motor plan has to be set up and sustained. The use of the left eye is expected when topographical information has to be used. Here, the approach was so simple and practised that the assumption of left eye viewing is likely to be a default condition. It would facilitate detection of any change in layout. A standard set of head positions were used, particularly by SL and NOL chicks, showing that the head was aligned with some reference point, perhaps the centre of the dish. These fell into two series (used by both eyes), and in both the peaks of frequent use were 10 degrees apart. One (20 degrees, 10 degrees ) was probably generated by head saccades ending with the bill pointing directly at the dish (0 degrees ). The other (35 degrees, 25 degrees, 15 degrees ) is best explained by slight divergence of the optic axes. The 25 degrees right eye position was consistently used by STR chicks at the beginning of approach. The STR condition requires the most difficult manipulation, and the manipulandum is most obvious from a distance. This is consistent with right eye use during establishment of a motor plan. Head postures consistent with divergence were also used when close to the dish under conditions where choice between targets was necessary. This was clear in the NOL condition, where the chick could see the food grains as it approached. Here, it is likely that both eyes are used in independent search. If so, it may be that divergence is used as a strategy during establishment of a motor plan (as in STR chicks) to increase the independence of the right eye system.

Animals↗

Dynamic role of vision in the control of posture in man.

The influence of moving visual surround on the manitenance of upright posture has been studied in man during combined motion of a platform (cart) on which subjects were standing. The normal visual surround was either moving together with the cart, or with a velocity equal to cart velocity either in the same or in the opposite direction of car motion (cart acceleration was either 0.2 m/s2 or 0.05 m/s2). The changes in body pitch observed under these three conditions of visual surround motion were in the same direction as those observed when visual surround motion was given in isolation. However, their amplitude was greater, particularly when visual surround motion was in conflict with body motion.

Acceleration↗