Changes in Balance and Falls

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Balance or stable physical equilibrium can be studied clinically, as with gait, by simply observing individuals as they rise from a chair, stand, walk, or turn. Do the subjects examined sway, sweep, and stagger when performing these movements? In the elderly, the fear of falling and pain, or limitation of joint movement, are all reflected in their carriage (21-24). The main adaptation to a balance disorder is the shortening of step length accompanied by slowing of gait and increasing of time between steps. This pattern is particularly noticeable in people who have fallen repeatedly, and indeed, it is called "post-fall syndrome" or "3 Fs syndrome" (fear of further falling) (23).

The immediate consequence of a worsening in balance is an increased frequency of falls. There is a good deal of reserve in the postural system, and young adults can fairly well tolerate

BOX 1 Pyramidal and Extrapyramidal Motor Pathways

Skilled movements (e.g., fine finger movements) are regulated in the brain by nerve fibers that originate in the motor cortex and form the "pyramids" in the medulla, hence the term pyramidal tracts. Grosser movements and posture are regulated by central nervous system (CNS) areas (e.g., basal ganglia) other than those connected with the pyramidal tracts, hence, by exclusion, the term extrapyramidal pathways. Coordination, adjustment, and smoothing of movements are regulated by the cerebellum, which receives impulses from several sensory receptors. Impulses from all of these brain structures ultimately determine the pattern and rate of discharge of the spinal motor neurons and neurons in motor nuclei of cranial nerves, thereby controlling somatic motor activity. Axons from these neurons form motor nerves that travel from the spinal cord to the various skeletal muscles throughout the body. Once the muscle has been reached, motor nerves synapse at the myoneural junction and transmit the nerve impulse to the muscle fibers. Contraction or relaxation of muscles will, in turn, direct bone and joint movements to maintain posture and promote mobility.

experiments in which they are tested in moving platforms with sensory input (primarily vision) absent. The elderly are much less tolerant of any loss or decline of sensory input (such as vision) (15,24). Falls of the elderly occur when engaging in ordinary activities, most often indoors. Trips and accidents account for the largest number of falls. It is to be noted that the incidence of falls declines with further aging, probably due to the reduced mobility of the very old. Some falls occur without any external cause and may be due to impaired peripheral (ocular, vestibular, and proprioceptive) and central (cerebellar and cortical) coordination (24) or, especially in postmenopausal women, to bone fractures due to osteoporosis (21) (Chapters 10 and 20).

Falls are often fatal in the elderly, but even the nonfatal falls have serious consequences, including

■ physical injury,

■ fear (the 3 Fs syndrome, "fear of further falling"),

■ functional deterioration, and

■ institutionalization (23).

Performance-oriented evaluation of falls shows that their occurrence may be related to impaired central information processing (e.g., decrements in selective attention and choice reaction time as in central processing) as well as in sensory input (e.g., vision) and motor activity (e.g., muscles).

Women are at greater risk for falls and the consequences thereof than men because of a number of factors, including (21)

■ more severe osteoporosis and bone fragility, especially after menopause (Chapter 10),

■ less muscle strength,

■ more sedentary, physically less strenuous way of life (Chapters 20 and 24), and

■ greater degree of comorbidity and disability (Chapter 3).

Comparison among ethnic groups in the United States indicates few differences in the increasing frequency and severity of motor disabilities, fractures, and falls with old age. Mexican-American women present a profile similar to that of non-Hispanic Caucasian women (25). However, Japanese women (in Hawaii) (26) and African-American women (27) have lower rates of falls and fractures than Caucasian women of the same age. These differences seem, in the main, to depend on a better neuromuscular performance in Japanese women and on lower incidence of osteoporosis in African-American women.

■ Get Up and Move: A Call to Action for Older Men and Women

There is considerable overall functional reserve in the locomotor system: hence, the loss of one of the sources of control of postural maintenance may be of little consequence (28). However, in elderly individuals, in whom impairment tends to occur simultaneously at several functional levels, this reserve is easily depleted. It is not difficult to understand why a fall is the consequence of the simultaneous involvement of two major factors: neurologic (e.g., extrapyramidal damage) and extraneurologic or environmental (e.g., drugs, cardiovascular, skeletal, and social). As our methods for measuring gait and balance become more sophisticated and quantitative, the close examination of these two factors—neurologic and environmental—becomes increasingly more important as a means of providing a comprehensive picture of the physiologic or pathologic condition of the older individual. At the same time, improving the mobility of the old individual, if not vital for survival, will considerably increase the well-being and overall health of the elderly (29).

Benefits of physical exercise versus a sedentary life are discussed in Chapter 24. A regimen of regular physical activity is recommended for all ages; when it is started at a young age and continued throughout life, it may confer significant benefits on health and longevity. Among these benefits, not least are those promoting better neurologic and mental activity in old age, as suggested by the impact of running in "boosting" neural cell number. Studies in mutant mice affected by a rare neurodegenerative disease (ataxia telangiectasia, characterized by a progressive loss of brain cells, first in the cerebellum and then throughout the brain), with consequent loss of motor control show that when these mice are placed on running wheels, the miles they log correlate directly with the increase in the number of brain cells; in contrast, in nonrunning control mice, most brain cells continue to die (30,31). In humans, the growth of new cells also occurs in adults and elderly under specific conditions, including physical exercise and learning (32,33) (Chapters 6 and 24).

■ CHANGES IN SLEEP AND WAKEFULNESS

■ Biologic Clocks and Sleep Cycles

Changes in several cyclic functions with aging may be ascribed to changes in so-called biologic clocks—the biological timepieces that govern the rhythm of several functions, such as the 24-hour (circadian) hormonal rhythms (Chapters 9-13) and several behaviors (34-36). The cessation of menstrual cycles and of ovarian function at menopause (Chapter 10) exemplifies alterations occurring in one such rhythmically recurring event. Cyclic functions are thought to depend on specific signals located primarily in the brain and coordinated by the

Diagram Demonstrating Sleep Stages Eeg

FIGURE 1 Diagrammatic representation of an eight-hour sleep period. The dark areas represent REM sleep. The EEG recordings (on the left side of the diagram) show the different rhythms that accompany each sleep stage. Abbreviations: REM, rapid eye movement; EEG, electroencephalogram.

suprachiasmatic nucleus in the hypothalamus, the so-called circadian pacemaker. These signals are required for the clock to progress through the synthesis of gene-regulated molecules (e. g., RNA, proteins, and neurotransmitters).

The most usual change with aging in the biological rhythmic systems is a reduction in the amplitude of circadian rhythms (36). Usually, the level of motor activity and the amplitude of the activity rhythm are greatly reduced with advancing age as are learning and memory (37) as well as blood pressure, heart rate, and temperature regulation (38,39). The deteriorating activity rhythm of old hamsters may be rejuvenated by a surgical implantation of fetal tissue from the same hypothalamic area that contains the circadian pacemaker; the brain grafts not only would restore the amplitude of the activity rhythm but also increase the longevity of the animals (40).

A prime example of a neural cyclic function is the circadian sleep/wake cycle, which undergoes characteristic changes with aging, including phase advancement (a shifting of the circadian rhythm to an earlier period). With respect to the changes in sleep, this "phase advancement" means that older people tend to go to bed earlier and to wake up earlier in the morning (41). A precise delineation of sleeping changes intrinsic to normal aging is still lacking. However, the incidence of chronic sleep-related abnormalities (e.g., poor sleep efficiency, frequent and prolonged nocturnal arousals, and day sleepiness) becomes increasingly prevalent in old age (42-44) and does not show significant differences among ethnic groups (44). Changes in sleep patterns have been viewed as part of the normal aging process; they are often associated with altered responses to external (light) (45) or internal (body temperature) (46) cues. Many of these common disturbances may also be related to the development of pathological processes that disturb sleep (47,48).

As we all know, sleep is a regular and necessary phenomenon of our daily lives. Lack of sleep leads to a desire for sleep. The pressure to sleep is strongest at night, particularly in the early hours of the morning. Yet, the mechanisms and purpose of sleep still elude us. Researchers have identified genes upregulated specifically during sleep; expression of such genes would vary depending on the state of sleep and of wakefulness (49). A popular assumption is that sleep provides a quiescent period during which the body recovers from the strains of the waking hours and that it represents a descent to a lower level of consciousness, but such a hypothesis remains to be proved. There are, however, certain facts that are recognized:

n Sleep is closely related to the electrical activity of the brain, as measured by the electroencephalogram (EEG), which records the variations in brain electrical activity. n Sleep is also closely associated to whole-body visceral manifestations such as changes in heart rate, respiration, basal metabolic rate, endocrine function, etc. n There are two kinds of sleep: the rapid eye movement (REM) sleep, with an EEG resembling the alert, awake state and a four-phase, non-REM or slow-wave (SW) sleep with unique EEG patterns (Fig. 1). Each sleep phase has its EEG pattern.

Sleep patterns change during growth and development as well as in old age (50). In old age, major changes include n decrease in total sleep time (TST), n increase in length of slow wave (SW) stages 1 and 2 sleep, n decrease in length of SW stages 3 and 4 sleep, n essentially unchanged rapid eye movement (REM) sleep time, and n possibly modified sleep patterns in neuropsychiatric disorders and by the administration of psychotropic drugs (see below) (Chapter 22).

FIGURE 1 Diagrammatic representation of an eight-hour sleep period. The dark areas represent REM sleep. The EEG recordings (on the left side of the diagram) show the different rhythms that accompany each sleep stage. Abbreviations: REM, rapid eye movement; EEG, electroencephalogram.

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