COMPONENTS OF POSTURAL DYSCONTROL IN THE ELDERLY A REVIEW PDF

Request PDF on ResearchGate | Components of postural dyscontrol in the elderly: A review | The concept of a generalized aging effect on a generalized. Printed in the U.S.A. /89 $ + REVIEW Components of Postural Dyscontrol in the Elderly: A Review F A Y B. H O R A K, 1 C H A R L O T T E L. The effects of Parkinson’s disease, hemiplegia, cerebellar degeneration, peripheral vestibular loss, and other disorders on the components of postural control.

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Components of postural dyscontrol in the elderly: a review. – Semantic Scholar

Components of postural dyscontrol in the elderly: Printed in the U. Components ofpostural dyscontrol in the elderly: Neural dysclntrol components of normal postural control mechanisms dyscobtrol identified and discussed.

The effects of Parkinson’s disease, hemiplegia, cerebellar degeneration, peripheral vestibular loss, and other disorders on the components of postural control are summarized. Quantitative posturography is advocated to detect preclinical manifestation of multiple musculoskeletal and neuromus- cular pathologies and reduced compensatory abilities dyscojtrol posturally unstable elderly adults. However, superimposed aging adult.

One-third to one-half of the population aged 65 years upon a small decrease in postural stability due to age alone is the and older fall each year, and these falls can result in serious injury, increased probability posturao the elderly of developing specific pathol- and even death 26, 27, 29, 39, 52, 96, In this model, the probability with which population as a whole, a small proportion of the elderly enjoy good a given pathology will develop is dyyscontrol to each rebiew, and postural stability well into advanced age 26, 96, Also, the therefore the pattern of postural instability and the type of falls will majority of elderly individuals, who have at least occasional also be unique to each individual.

In this view, measurable trouble with balance, have many different patterns of falls and declines in postural control in an individual actually reflect difficulties with postural control.

Neurophysiological models of sensorimotor control of posture A wealth of scientific research into postural stability in the and movement are evolving rapidly, but few have been applied to elderly has produced evidence consistent with both of these views. Any model of the effect of age on postural have documented deficits in many physiologic systems critical for control must account both for the increased instability commonly postural control, including: One processing 52, 3 neural pathways for motor control commonly accepted model is shown in Fig.

Components of postural dyscontrol in the elderly: a review.

Since postural 93,elderlyy 4 musculoskeletal integrity 78,12 l. The results of instability is so common, it is considered, in this model, an such studies are often interpreted as evidence that age alone can inevitable ” a g i n g ” effect resulting from widespread degeneration account for significant changes in neural and musculoskeletal of the musculoskeletal, neuromuscular, and sensory systems.

The function which lead to postural imbalance in the ostensibly normal increase in elderlyy in postural stability in elderly subjects elderly population For example, Belal and Gorig 4 have results, in this model, from an increase in variability about the used the term “presbyastasis'” to describe disequilibrium due, mean age-related decrease in neural function, due perhaps to presumably, to age alone in the elderly without clear signs of differences in lifestyle and genetic traits.

An alternative model of the effect of age on postural control is However, there is also evidence that disequilibrium in the shown in Fig.

According to this model, the effect of age, per ostensibly normal elderly is not a simple function of age. Dow Neurological Sciences Institute, N. Examples of generalized measures of increasing postural instabil- AGE 65 yrs ity with age.

A Ratio of sway energy with eyes closed to sway energy with eyes open as a function of age. B Estimated sway area as a function of age for stance with eyes open and eyes closed [adapted from ].

Subjects stood on reciew fixed surface and wore a harness bearing a — NORMAL stylus which traced the sway path on grid paper 10 squares revisw the inch.

Both figures show sway with eyes closed increasing with age more quickly than sway with eyes open. Changes in these measures are also not well correlated with an FIG. Schematic representations of two models of the effect of increased tendency to fall or the perception of instability 30, 51, age-related changes in neural function on postural stability.

A Neural function solid line declines as a function of age only. Shaded area shows Furthermore, generalized measures of postural control cannot the degree of decline necessary to produce observable postural instability.

As a result, generalized balance information function with increasing age. B The effect of age alone on neural function permits neither a differential diagnosis nor a specific treatment for is represented by the solid line. The effect of any given pathology or postural instability in a given elderly individual. While the effect of age and If the security and mobility of the elderly population are to be either pathology alone is not sufficient to result in observable postural enhanced substantially, a different approach to the study of instability, the combined effect of all factors produces disequilibrium.

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Measures of postural control which characterize the pattern of postural abnor- malities unique to each elderly individual must be developed. In the studies cited above tested a relatively unselected elderly this paper, we propose that this goal can be achieved by dividing population.

For example, some researchers have defined the postural control into a set of functional components based on normal elderly as anyone over 60 years of age 51, Others recent studies of the neurophysiology of postural control.

We also have tried to restrict their definition of the normal elderly to give specific examples of the effect of well-defined neural pathol- individuals of a certain age, but also free of pathology.

However, elferly, including hemiplegia, Parkinson’s disease, cerebellar de- when Gabell and Nayak 33 screened eeview group of 1, individuals generation, and somatosensory and vestibular loss, on postjral 65 years and over, they found only who were free of functional components of postural control.

Problems unique to the musculoskeletal or neurologic abnormalities and who had no elderly, such as the high probability of abnormalities in several history of fails. The older adults in this elite group performed as physiological systems and the reduced ability to adaptively com- well as younger fhe on the measures of gait used in this study. Gabell and Nayak therefore concluded that age-related changes in gait are due primarily to pathology.

Figure 2 gives thought to result from activation of reflex pathways by information two examples of generalized balance deficits as a function of age, from sensory receptors 67, 69, In this view, shown by an increased amount of energy expended Fig. Although this reflex model of postural Studies which employ generalized balance measures provide control adequately describes changes in limb and head position in important information. It is critical for both health care profes- response to externally imposed perturbations in reduced animal sionals and human factors experts to understand that balance may preparations, postural control in a behaving human is a highly be compromised even in an elderly population without obvious complex behavior.

Coordination of postural movement patterns Dissatisfaction with reflex models of postural control has led to Latency to postural response the development of a different approach or ” s y s t e m s ” model Scaling the postural response to the stimulus Motor learning In this model, the CNS maps the location of the body’s center of Biomechanics gravity and adaptively dysfontrol its response to disequilibrium by centrally preprogramming postural sensorimotor strategies or plans Sensory Components for action 7, 35, 41, Based on the body’s biomechanical Detection of peripheral sensory stimuli constraints, the available sensory information, the environmental Central selection and weighting of sensory information Sense posturak stability limits context, and prior od, the CNS activates an appropriate Sensorimotor integration motor ” s y n e r g y ” a group lf muscles acting as a functional unit to correct center of gravity position or prevent its movement.

In The list of proposed functional components of postural control in Table this systems approach, sensory inputs play a role not only in 1 is not exhaustive.

Rather, it oc the more important components of the detecting a stimulus and triggering a postural response, but also in postural response which have been identified in recent studies of basic postural control mechanisms. Also, the functional components are arbi- developing an internal representation of the position of the center trarily divided into motor and sensory categories, although it is clear that of gravity and the characteristics of the environment 36, 64, For example, The functional component approach to the study of disequilib- disequilibrium could result from pathology either in the traditional “sen- rium in the elderly is based on the systems model of postural sory” or “motor” nervous systems.

Further, a sensory disorder is likely to control. In this approach, the postural response is broken down have an impact on a motor component and vice versa. In the following sections we will define each component of postural control, summarize studies of patients with pathologies which the body’s center of gravity over its base of support both during elverly each component, and discuss the relevance of these regiew stance and during active movement, both in response to studies to postural stability in both the normal and the posturally externally imposed perturbations and to destabilizing forces result- unstable elderly.

In the final section of the paper eldedly show how the ing from voluntary movements. Postural control also requires the ELDERLY ydscontrol to select and finely adapt a corrective or protective response, and to execute that response within the biomechanical Motor Components constraints of the body and the physical constraints of the environment.

The reflex model does not adequately account for As discussed revieww, adequate postural control depends on the FIG. Left shows an ankle strategy in a healthy elderly man asked to sway lbrward to his limits of stability. Middle shows a hip strategy in a posturally tbe woman asked to sway forward to her stability limits. When asked to sway backwards right this subject used a stepping strategy. Thus, any knee and hip.

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In this section, some of the effects of neuromuscular and In addition, elderly subjects show a significant increase in postural musculoskeletal pathologies common in the elderly on compoments responses in antagonist muscles, which are not typically activated components of postural control are discussed.

Coordination o f postural movement patterns. Three discrete Latency to postural response.

Adequate control of the position patterns of postural movements have been described for correction of the center of gravity depends on the timely initiation of of anterior-posterior sway in normal adults: Postural responses are initiated in hip strategy, and a stepping or stumbling strategy 23, 47, 79, 86, two different ways. First, postural reactions occur in response to The ankle strategy shown in Fig.

In commonly used postural movement pattern. This strategy shifts normal subjects, muscle responses are initiated within the body’s center of gravity by rotating the body about the ankle msec following an unexpected perturbation, regardless of the joints with minimal movement of hip or knee joints. A hip strategy strategy used to correct sway These automatic responses, Fig. A stepping strategy Fig. However, the majority of posturat responses are initiated in a In normal adults, the use of a particular strategy depends on the different way.

Postural adjustments also occur in anticipation of configuration of the support surface and on the size of the voluntary movements and act to prevent losses of balance which perturbation. The ankle strategy is normally used in response to could result from the destabilizing forces associated with self- slow, small perturbations on a firm, wide surface capable of initiated body movements 5, 15, 34, The hip strategy is normally In order for postural responses to unexpected perturbations to used in response to larger, faster perturbations and when the be executed quickly enough to prevent a fall, the perturbation’s support surface is compliant or smaller than the feet.

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The hip direction and amplitude must be encoded and the appropriate strategy cannot be used on slippery surfaces, since hip sway response must be selected and initiated within a very short time. The stepping Thus, postural responses to unexpected perturbations could be strategy is normally used when ankle and hip strategies are delayed by pathologies which slow nerve conduction time in inadequate, usually in response to very fast or large perturbations.

Anticipatory postural adjustments could also be dycsontrol. When the support surface characteristics are suddenly delayed by pathologies which slow central processing time or changed, normal adults continue to use the dyscomtrol strategy initially, nerve conduction time in efferent pathways. The latency to and gradually switch to the new strategy, showing a mixture of anticipatory postural reaction has also been shown to depend on two strategies before finally adopting the most efficient strategy the speed of the voluntary movement: Normal coordination of these postural strategies depends on Thus, pathologies which slow voluntary movements may also correct sequential timing relationships among the onsets of the result in delayed postural responses.

Figure Studies of postural control in normal young subjects have 4 illustrates schematically three normal EMG activation patterns shown in some cases that the latencies of postural responses to and two abnormal patterns in response to backward surface perturbations can be delayed by experimentally induced losses of perturbations. The normal ankle strategy Fig.

For normal postural subjects distal-to-proximal muscle burst activations, with msec standing on a flat, firm surface, eye closure has little effect on delays between ankle, thigh, and trunk muscles In contrast, response latency 57, Loss of ankle and foot joint and for the same direction of sway, the hip strategy Fig.

A mixed ankle-hip pattern is shown in Fig. Patients with bilateral vestibular stroke. Posturally unstable patients with Parkinson’s disease show loss have also been reported to show longer response componwnts to a pattern of muscle activation resembling a normal ankle and some types of perturbations, especially with eyes closed [ 57 ; but normal hip strategy, but activated simultaneously, instead of see also 85 and ].

This results in Studies of postural control in the ostensibly normal elderly stiff coactivation around all joints, and the patients fall in response have shown increased latencies both in postural responses to to displacements without appearing to activate a postural response unexpected perturbations and in postural adjustments prior dyscontrpl 49, Many supposedly normal elderly individuals show mild voluntary movements.