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Web Posted on: August 24, 1998


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Modeling and Simulation in Gerontechnology

Jan A.M. Graafmans, Tom L. Harrington

Center for Biomedical and Health Care Technology

Institute for Gerontechnology

Eindhoven University of Technology

POB 513, 5600MB Eindhoven, the Netherlands

tel: +31 40 247 2008, fax: +31 40 244 3335, email: j.a.m.graafmans@bmgt.tue.nl

1 Summary

Physical simulations can be developed and used to generate data about ageing that can either be experienced first hand or can in turn be used in mathematical modeling. In gerontechnology we need a high level of simulation for a number of applications. Most of them are still in the future. However, there are some simpler approaches that we are working on now. For example, we can simulate systems such as bank machines and ticket machines (Rudinger, 1992) and a host of tasks so that older people who are not familiar with them can gain experience. We can modify driving and flight simulators to measure performance and to retrain the elderly. And, we can even simulate ageing itself, so that individuals associated with aged people, such as designers, family members, school children, scientists and others can feel what it is like to age (Moore, 1986). This paper gives two examples of simulating ageing processes. The first example deals with reduced tactile feedback of the footsoles and the second adresses the consequences of essential tremor.



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2 Introduction

Several experiments in the simulation of ageing are being conducted in the laboratory of the Institute for Gerontechnology. It was found, by comparing the data on gait patterns and balance control from artificially impaired students with data from actual older people to validate the simulation, that it is possible to allow a younger person to experience the losses of joint mobility and sensory input that some older people experience (Harrington et al, 1997). The experimental subjects had been hobbled with knee braces, partially blinded with special glasses, and deprived of both cutaneous sensibility and stable footing by a carpet made from sponge. The results of the experiment have led to a follow-up study into the optimization of the mechanical quality of insoles and shoe soles for older people.

A second set of simulations deals with the degrees and types of disabilities that come with essential tremor in older people. A number of simulations of tremor and a number of representative tasks have been devised, such as a slowly pulsing vibrator attached to the wrist with an experimental subject who is required to turn the pages of a book, thread a needle, spoon liquid and so on. Results showed that tremor does not manifest itself only as a purely motor disturbance (Jacobs, in press). For example in the page turning tasks very fine cutaneous discrimations were disrupted by the vibration. The first results are now implemented on a PC with a vibrating cursor and mouse allowing for collecting mathematical data in a perfect form for mathematical modeling of the performance characteristics of older people with tremor.



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3. Simulating gait pattern and balance control

The gait pattern as well as balance control change a lot with increasing age. Balance control is influenced by many factors. Three systems are of interest: the vestibular system, the somatosensoric system and the visual system. Along these three systems, posture is very important in maintaining balance. Decreased control of balance may result in disturbances in the gait pattern.

The purpose of this project was to simulate four aspects of aging: decreased range of motion of the knees, diminished peripheral field of vision, forward bended head and decreased ankle-foot proprioception. Knee braces were used to inhibit complete extension. Glasses from which the sides were taped black diminished the peripheral field of vision. Glasses from which the lower part was taped black made people bend their head. A foam rubber mat made the ankle-foot proprioception unreliable.

Balance and gait pattern were examined to compare the effects of the simulations. Balance was measured with a force platform which records sway. Subjects walked with special shoes which recorded velocity and relative stance time. Step length and heart rate were also measured. 18 Young women performed the experiment with eight different combinations of the simulations. 17 Old women served as controls. The experiments with the old subjects were executed at another location.

All four simulations influenced the balance and the gait pattern of young subjects. The foam rubber surface deteriorated balance more than aging does and overruled the effect of the other simulations. In the cases where foam rubber was used the sway had a value of about 500 mm, which is doubled compared to the situations where no foam rubber was involved. The mean sway of the old subjects was 300 mm. The step length of the young subjects with different combinations of simulations varied from 0.71 m to 0.77 m. The old subjects walked with a mean step length of 0.59 m. Three old subjects repeated the experiment at the same location as the young subjects. This time they walked with a mean step length of 0.66 m. Combining the simulations seemed to have largest effect on free walking velocity. The velocity declined from 1.43 m/s to 1.34 m/s from the situation without simulations to the situation with all simulations. The mean velocity of the elderly was 1.10 m/s and at the other location 1.26 m/s.

Sway increases and both step length and velocity decrease when young women are restricted with the simulations. The effects of all simulations together on step length and free walking velocity of young subjects appear to resemble the effect of aging. With a better composition of foam rubber balance is also simulated best by using all simulations. It may be concluded that the four aspects of aging chosen are of major importance for the deterioration in gait pattern and balance.

A new project is well under way, investigating the relationship between the firmness of the foot support material and balance control. It is expected that an S-curve will show a sharp decrease in balance control when using gradually softer materials for foot support. This then will enable us to choose materials that will maximize the amount of required tactile feedback and minimize the impact on joints, such as ankle, knee and hip, when walking.



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4. Simulating age-associated tremor

Essential tremor was found in the literature as the most common age-related tremor among older people. Essential tremor is characterized by a postural or action tremor, which is absent at rest. The frequency of essential tremor ranges from 4 to 8 Hz and the tremor may involve many parts of the body, although the hands are most commonly affected. The onset of the disease may occur at any age with no obvious gender or racial differences. The tremor may progress over time, but the process is usually slow and nonfatal. Therefore, essential tremor is generally considered a 'benign' condition. However, as its name implies, the etiology of essential tremor remains unknown.

The aim of the experiment, described here, is to simulate a tremor associated to ageing. This tremor has been simulated in two different ways. First, a commercially available vibrating pencil with high frequency and low amplitude was used to find out if tremor has any effect on some activities of daily life. Second, a rotating cam was developed with a natural tremor amplitude and frequency. The subjects, between 20 and 30 years of age, performed five tasks associated to activities of daily life. On the basis of these tasks, the effect of trembling has been examined. It can be concluded from the results of the experiments that essential tremor is of major importance for the deterioration in the performance of activities of daily life.

All five tasks have been influenced by tremor. Tremor deteriorates especially the very fine task, such as threading needle, more than the other tasks. The protocol that addresses this task shows that tremor has a big influence on the performance of the task. It can be concluded that people affected by tremor are disabled in their activities of daily life foremost in those activities that require fine motor control and good tactile feedback.

At present, a new project has been started to investigate a wider range of frequencies and amplitudes in the tremor in combinations with other activities of daily life in order to collect more realistic data on the disabling effects of tremor.



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5. References

Harrington, T.L., Graafmans, J.A.M., Hermens, Y., de Weerd, W. Shade tree psychophysics, models, mathematical and concrete for the simulation of ageing. In: J. Graafmans, V. Taipale and N. Charness (Eds). Gerontechnology, a sustainable investment in the future. IOS Press, Amsterdam, 1997.

Jacobs, C. The simulation of tremor associated with ageing. MSc-thesis report. Institute for Gerontechnology, Eindhoven (in press).

Moore, P. Disguished: a true story. Word books, London, 1986.

Rudinger, G., Espey, J., Neuf, H., Simon, U. Technology and aging: Using ticket machines. In: H. Bouma and J.A.M. Graafmans (Eds), Gerontechnology, Studies in Health Technology and Informatics, Vol. 3. IOS Press, Amsterdam, 1992.



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