Postural Control in Elderly Subjects ILMARI PYYKKO, PIRKKO JANTTI, HEIKKI AALTO
The postural stability of 23 subjects aged 85 years or over was studied with a force platform. The sensory function of the lower limbs was disturbed with small vibrators placed on both calf muscles and/or by placing the subjects on a platform covered with foam plastic. When compared with a group (n= 100) of 50-60-year-old subjects, the elderly subjects had significantly higher sway velocities even during nonperturbed conditions. The perturbation of muscle spindles with vibration and/or pressoreceptor function with foam plastic did not increase the postural instability of the elderly subjects. Visual deprivation had a significant effect on postural stability, and the visual influx contributed about 50% of the postural stability. Postural control is reduced as a result of loss of sensory cues of pressoreceptors and also deterioration in function of stretch reflexes initiated from muscle spindles. The very elderly seem to rely on visual control of posture; this is slow, which can be one reason for susceptibility to falls.
Introduction
has been evaluated to identify people liable to fall [12-15]. The afferent influxes from three Falls are one of the main problems afflicting main sensory modes are involved in postural elderly people. In the USA, accidental falls are control: the proprioceptive endings; vision and one of the leading causes of death among the vestibular organs. Under natural conditions, elderly population, surpassing even the death the rank order of the receptive system and its rate due to car accidents [1]. Falls are also availability determine the afferent influx used in responsible for numerous minor injuries of the the organization of the movement to maintain bones and soft tissues requiring nursing facili- balance [16]. This may change during ageing ties for prolonged periods [2]. Finland has a [15]. Eye closure reduces the availability of population of 220000 senior citizens (aged 65 visual information and shifts postural mechanyears or more); approximately 1.5% of these isms towards vestibular and proprioceptive suffer a fracture of the proximal femur in a year control, which may be unfavourable to the postural control of elderly subjects [17]. [3]. The mechanisms leading to injuries have In sudden body perturbation, the hierarchibeen extensively studied. In Finland, for exam- cal ordering of different receptor systems ple, 35% of senior citizens suffer from disequi- changes to prevent falls. T h e stretch reflexes librium which is also a major handicap interfer- seem to operate in the early prevention of falls, ing with daily activities. Vertigo linked to a if these do not function the protective responses defective vestibular system may be one reason will be incomplete [16]. Functional stretch for the postural instability and accidental falls of reflexes are employed to achieve full control. It elderly people [4]. Other factors related to falls has been suggested that vestibular influx govare medication [5], altered mental ability [6], erns 65% of the body sway during sudden level of physical activity [7, 8] and muscle perturbation, and 3 5 % is accounted for by strength [9], poor vision [10] and a defective visual and proprioceptive influx [18]. The cosensorimotor system [11]. activation of functional stretch reflexes appears The function of the postural control system to be defective in aged subjects [11, 15]. Age and Ageing 1990:19:215-221
Downloaded from http://ageing.oxfordjournals.org/ at University of California, San Fransisco on September 5, 2014
Summary
216
I. PYYKKO ET AL.
The purpose of the present study was to evaluate the postural control mechanism of elderly subjects. Specifically, we aimed to study the functioning of this different receptor mechanism in order to gain insight into the postural synergy changes associated with ageing. Subjects and Methods
Results Bare surface: When the elderly subjects stood with their eyes open on a firm surface, their sway velocity (23 mm/s) was nearly three times as high as that of the control subjects (9 mm/s) (Figure 2). The vibration of calf muscles with increasing frequencies increased body sway,
40Hz 80Hz
60
20Hz 60Hz 100Hz
90
120
150 Time (s)
Figure 1. Computer display of posturography measurement: uppermost tracing—stimulus; middle tracing—fore-aft sway; lowest tracing—lateral sway; ordinate—centre point of force (CPF); abscissa— time.
Downloaded from http://ageing.oxfordjournals.org/ at University of California, San Fransisco on September 5, 2014
Thirteen women and four men aged 85 years or more were studied at the Geriatric Department of the City Hospital of Tampere. All subjects were outpatients living on their own whose informed consent to the study was obtained in writing. As controls, we had 100 subjects (aged 50-60 years, 46 women and 54 men) assessed in connection with a cohort study and living in different parts of Finland. The health of the subjects was assessed by one of the authors (P.J.). In addition to general examination, vibration sensitivity in the extremities was tested with a tuning fork and a careful evaluation of stretch reflexes was made. A force platform constructed on the strain gauge principle [19] was employed. Vertical force distribution over the platform surface was measured and the co-ordinates of the centre point of the force (CPF) in fore-aft and lateral directions were recorded during the test and stored electronically for later analysis. Postural perturbation was induced by stimulating the calf muscles of each leg with vibrations, delivered in pseudo-random fashion at various frequencies. This activates the tonic vibration reflex through the muscle spindles. The stimulator unit was controlled by a microcomputer (Hewlett Packard 75 C) and the vibrations were produced by rotatory shakers giving a 0.4 mm peak-to-peak amplitude at all frequencies. The posturography measurement lasted for 180 s. Figure 1 shows a computer display of posturography measurement for one of the most stable elderly subjects. The uppermost trace indicates the timing and strength of the stimulus, and the middle and lowest tracings show the body position (CPF) on the platform surface referred to the geometrical centre of the surface. For calculation of position shift the new position is referred to baseline values. The middle tracing shows the body position in anteroposterior (A and P) direction. The lowest tracing shows the body position in right (R) and (L) directions. The posturography signal was fed to a microcomputer (Hewlett Packard 9000 series 300 for analysis). The data were sampled at a frequency of 33.3 Hz and were filtered with a non-linear 3-point median filter to eliminate artefacts and smoothed with linear moving average filters of 3 and 5 points to remove
random noise. The passband limit (-3 dB) was at 3.3 Hz and the stop-band attenuation was more than 32 dB (over 6.3 Hz). All filters were non-recursive and did not cause phase shift at frequencies below 6.6 Hz. The program calculated, among other parameters, sway velocity during stimulation-free as well as at various stimulation conditions. A detailed description of the measuring procedure [19] and data calculation [20] is provided elsewhere. The test was conducted in four conditions: on a firm bare surface (a) with visual control and (b) without visual control; on a foam plastic covered surface (c) with visual control, and (d) without visual control. The posturographic testing lasted for 1 hour. To eliminate environmental noise and to standardize the state of alertness, the subjects wore headphones and they listened to music during the test. Wilcoxon's signed rank test was used for statistical comparison of the different test conditions, and the Mann-Whitney U test was used for comparison between younger and old subjects. Statistical significance was pre-defined as p < 0.05.
POSTURAL CONTROL IN ELDERLY SUBJECTS EYES OPEN, RIGID SURFACE
EYES OPEN, FOAM SURFACE
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BASE 40 60 80 100 Stimulation frequency (Hz)
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Figure 2. Posturography results from elderly subjects (•) and from younger control subjects (A) under different visual and support surface conditions. Means and standard errors of means are given. Abscissa—stimulation frequency; ordinate— sway velocity. reaching an average sway velocity of 34 mm/s at 80 Hz. The differences between vibration periods at 60, 80 and 100 Hz and the baseline condition were not statistically significant. The difference between the elderly subjects and the control subjects was statistically highly significant at all vibration frequencies and in the baseline values (p < 0.001). The postural control of the elderly subjects was severely impaired when they stood on the bare surface without visual control (Figure 2). In quiet stance the average sway velocity was 48 mm/s, exceeding normal values (12 mm/s) by a factor of four. Vibration only slightly increased
their body sway, and at 80 Hz an average sway velocity of 56 mm/s was reached. No significant differences were found between the different frequencies of vibration and the baseline value in the elderly subjects. Nevertheless, they differed highly significantly from the controls at all stimulation frequencies and at baseline values (p< 0.001). Foam plastic covered surface: With their eyes open, the elderly subjects displayed almost identical body sway on the foam plastic covered surface as on the bare surface. Thus, in the baseline condition their sway velocity averaged 30 mm/s and reached an average sway velocity
Downloaded from http://ageing.oxfordjournals.org/ at University of California, San Fransisco on September 5, 2014
vay veloc ty (mm/
CO
e 40
w
217
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I. PYYKKO ET AL.
absence of vision. The old subjects were affected only slightly by muscle vibration having proprioceptive quotients of 0.84. The subjects aged from 40 to 60 years had a proprioceptive quotient of about 0.51. Together with absent or weak tendon reflexes these figures indicate (with simplified interpretation) that aged subjects have poor proprioception and unsatisfactory functioning of stretch reflexes. The difference between the younger and old subjects was statistically significant (p
The postural stability of 23 subjects aged 85 years or over was studied with a force platform. The sensory function of the lower limbs was disturbed with small vibrators placed on both calf muscles and/or by placing the subjects on a platform covered with foam plastic. When compared with a group (n= 100) of 50-60-year-old subjects, the elderly subjects had significantly higher sway velocities even during nonperturbed conditions. The perturbation of muscle spindles with vibration and/or pressoreceptor function with foam plastic did not increase the postural instability of the elderly subjects. Visual deprivation had a significant effect on postural stability, and the visual influx contributed about 50% of the postural stability. Postural control is reduced as a result of loss of sensory cues of pressoreceptors and also deterioration in function of stretch reflexes initiated from muscle spindles. The very elderly seem to rely on visual control of posture; this is slow, which can be one reason for susceptibility to falls.
Introduction
has been evaluated to identify people liable to fall [12-15]. The afferent influxes from three Falls are one of the main problems afflicting main sensory modes are involved in postural elderly people. In the USA, accidental falls are control: the proprioceptive endings; vision and one of the leading causes of death among the vestibular organs. Under natural conditions, elderly population, surpassing even the death the rank order of the receptive system and its rate due to car accidents [1]. Falls are also availability determine the afferent influx used in responsible for numerous minor injuries of the the organization of the movement to maintain bones and soft tissues requiring nursing facili- balance [16]. This may change during ageing ties for prolonged periods [2]. Finland has a [15]. Eye closure reduces the availability of population of 220000 senior citizens (aged 65 visual information and shifts postural mechanyears or more); approximately 1.5% of these isms towards vestibular and proprioceptive suffer a fracture of the proximal femur in a year control, which may be unfavourable to the postural control of elderly subjects [17]. [3]. The mechanisms leading to injuries have In sudden body perturbation, the hierarchibeen extensively studied. In Finland, for exam- cal ordering of different receptor systems ple, 35% of senior citizens suffer from disequi- changes to prevent falls. T h e stretch reflexes librium which is also a major handicap interfer- seem to operate in the early prevention of falls, ing with daily activities. Vertigo linked to a if these do not function the protective responses defective vestibular system may be one reason will be incomplete [16]. Functional stretch for the postural instability and accidental falls of reflexes are employed to achieve full control. It elderly people [4]. Other factors related to falls has been suggested that vestibular influx govare medication [5], altered mental ability [6], erns 65% of the body sway during sudden level of physical activity [7, 8] and muscle perturbation, and 3 5 % is accounted for by strength [9], poor vision [10] and a defective visual and proprioceptive influx [18]. The cosensorimotor system [11]. activation of functional stretch reflexes appears The function of the postural control system to be defective in aged subjects [11, 15]. Age and Ageing 1990:19:215-221
Downloaded from http://ageing.oxfordjournals.org/ at University of California, San Fransisco on September 5, 2014
Summary
216
I. PYYKKO ET AL.
The purpose of the present study was to evaluate the postural control mechanism of elderly subjects. Specifically, we aimed to study the functioning of this different receptor mechanism in order to gain insight into the postural synergy changes associated with ageing. Subjects and Methods
Results Bare surface: When the elderly subjects stood with their eyes open on a firm surface, their sway velocity (23 mm/s) was nearly three times as high as that of the control subjects (9 mm/s) (Figure 2). The vibration of calf muscles with increasing frequencies increased body sway,
40Hz 80Hz
60
20Hz 60Hz 100Hz
90
120
150 Time (s)
Figure 1. Computer display of posturography measurement: uppermost tracing—stimulus; middle tracing—fore-aft sway; lowest tracing—lateral sway; ordinate—centre point of force (CPF); abscissa— time.
Downloaded from http://ageing.oxfordjournals.org/ at University of California, San Fransisco on September 5, 2014
Thirteen women and four men aged 85 years or more were studied at the Geriatric Department of the City Hospital of Tampere. All subjects were outpatients living on their own whose informed consent to the study was obtained in writing. As controls, we had 100 subjects (aged 50-60 years, 46 women and 54 men) assessed in connection with a cohort study and living in different parts of Finland. The health of the subjects was assessed by one of the authors (P.J.). In addition to general examination, vibration sensitivity in the extremities was tested with a tuning fork and a careful evaluation of stretch reflexes was made. A force platform constructed on the strain gauge principle [19] was employed. Vertical force distribution over the platform surface was measured and the co-ordinates of the centre point of the force (CPF) in fore-aft and lateral directions were recorded during the test and stored electronically for later analysis. Postural perturbation was induced by stimulating the calf muscles of each leg with vibrations, delivered in pseudo-random fashion at various frequencies. This activates the tonic vibration reflex through the muscle spindles. The stimulator unit was controlled by a microcomputer (Hewlett Packard 75 C) and the vibrations were produced by rotatory shakers giving a 0.4 mm peak-to-peak amplitude at all frequencies. The posturography measurement lasted for 180 s. Figure 1 shows a computer display of posturography measurement for one of the most stable elderly subjects. The uppermost trace indicates the timing and strength of the stimulus, and the middle and lowest tracings show the body position (CPF) on the platform surface referred to the geometrical centre of the surface. For calculation of position shift the new position is referred to baseline values. The middle tracing shows the body position in anteroposterior (A and P) direction. The lowest tracing shows the body position in right (R) and (L) directions. The posturography signal was fed to a microcomputer (Hewlett Packard 9000 series 300 for analysis). The data were sampled at a frequency of 33.3 Hz and were filtered with a non-linear 3-point median filter to eliminate artefacts and smoothed with linear moving average filters of 3 and 5 points to remove
random noise. The passband limit (-3 dB) was at 3.3 Hz and the stop-band attenuation was more than 32 dB (over 6.3 Hz). All filters were non-recursive and did not cause phase shift at frequencies below 6.6 Hz. The program calculated, among other parameters, sway velocity during stimulation-free as well as at various stimulation conditions. A detailed description of the measuring procedure [19] and data calculation [20] is provided elsewhere. The test was conducted in four conditions: on a firm bare surface (a) with visual control and (b) without visual control; on a foam plastic covered surface (c) with visual control, and (d) without visual control. The posturographic testing lasted for 1 hour. To eliminate environmental noise and to standardize the state of alertness, the subjects wore headphones and they listened to music during the test. Wilcoxon's signed rank test was used for statistical comparison of the different test conditions, and the Mann-Whitney U test was used for comparison between younger and old subjects. Statistical significance was pre-defined as p < 0.05.
POSTURAL CONTROL IN ELDERLY SUBJECTS EYES OPEN, RIGID SURFACE
EYES OPEN, FOAM SURFACE
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m/s,
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BASE 40 60 80 100 Stimulation frequency (Hz)
30 2010—i
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1—>
BASE 40 60 80 100 Stimulation frequency (Hz)
Figure 2. Posturography results from elderly subjects (•) and from younger control subjects (A) under different visual and support surface conditions. Means and standard errors of means are given. Abscissa—stimulation frequency; ordinate— sway velocity. reaching an average sway velocity of 34 mm/s at 80 Hz. The differences between vibration periods at 60, 80 and 100 Hz and the baseline condition were not statistically significant. The difference between the elderly subjects and the control subjects was statistically highly significant at all vibration frequencies and in the baseline values (p < 0.001). The postural control of the elderly subjects was severely impaired when they stood on the bare surface without visual control (Figure 2). In quiet stance the average sway velocity was 48 mm/s, exceeding normal values (12 mm/s) by a factor of four. Vibration only slightly increased
their body sway, and at 80 Hz an average sway velocity of 56 mm/s was reached. No significant differences were found between the different frequencies of vibration and the baseline value in the elderly subjects. Nevertheless, they differed highly significantly from the controls at all stimulation frequencies and at baseline values (p< 0.001). Foam plastic covered surface: With their eyes open, the elderly subjects displayed almost identical body sway on the foam plastic covered surface as on the bare surface. Thus, in the baseline condition their sway velocity averaged 30 mm/s and reached an average sway velocity
Downloaded from http://ageing.oxfordjournals.org/ at University of California, San Fransisco on September 5, 2014
vay veloc ty (mm/
CO
e 40
w
217
2l8
I. PYYKKO ET AL.
absence of vision. The old subjects were affected only slightly by muscle vibration having proprioceptive quotients of 0.84. The subjects aged from 40 to 60 years had a proprioceptive quotient of about 0.51. Together with absent or weak tendon reflexes these figures indicate (with simplified interpretation) that aged subjects have poor proprioception and unsatisfactory functioning of stretch reflexes. The difference between the younger and old subjects was statistically significant (p
![[Postural control in the elderly].](/assets/img/hold.png)
