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Doubal, Stanislav (3)
Year of Publication
Visco-elastic response of human skin and aging
The changes in visco-elastic properties of skin belong to the most conspicuous manifestations of cutaneous aging. In spite of apparent simplicity, the measurement of mechanical parameters of skin in vivo presents both theoretical and practical problems. Reproducibility, standardization, duration of measurement, discomfort for experimental subjects are the main complications. Measurement and analysis of transient deformation response to pressure stress provides theoretically consistent and practically applicable methodology.
Experiment: The transient deformation response of skin was measured in two groups consisting of 15 healthy men and 17 healthy women. The range of age interval was 20 to 58 years. The deformation response was measured as reaction of skin on sudden change of pressure stress between two levels of loading on skin surface.
Results: Transient response of human skin consists of sum of two exponential curves. A “rapid” exponential curve has time constant typically of order 10 ms, while “slow” exponential curve has a time constant of order 0.1 to 1s. Both time constants increase with chronological age. Time for drop of deformation on 12.5% of full deformation proved to be a simple and sensitive criterion of skin aging, with strong correlation with chronological age.
Main advantage of the method: Measurement is quantitative and reproducible. Procedure is easy to repeat. Its average duration is approx. 2 minutes and it does not represent any discomfort for test subjects.
Gompertz — A program for evaluation and comparison of survival curves
Principles, properties and use of a program for evaluation of survival curves are described. Parameters of Gompertzian mortality curves are computed from survival data of two populations by help of nonlinear regression. The differences in parameters of both curves are evaluated statistically. This method evaluates effectively even survival data of very small populations. The results are presented in numeric, verbal and graphic forms. Finally, reading of the results is offered to distinguish changes corresponding to altered aging rate from changes caused by influences not affecting the basic mechanism of aging. Program GOMPERTZ in the form of Microsoft Excel workbook equipped with Visual Basic procedures is offered free through e-mail (email@example.com).
Practical methodology of evaluation of mortality curves and detection of aging-related interventions
A practical and simple method of direct proof of occurrence of changes in the aging rate is suggested. The aging rate is defined here according to the pacemaker concept of the control of aging as the rate of pace of the inner aging clock. The principle of the method consists of the analysis of relationships between mortality curves. The methodology makes it possible to distinguish the changes in mortality caused by direct intervention in the basic mechanism of the control of aging processes (the pacemaker) from changes caused by intervention in other systems of an organism. As mortality curves are often difficult to obtain directly in experimental gerontology, a method of transformation of survival data into mortality curves is demonstrated. The general purpose of this study is to derive more information from experimental data and from demographic studies, and contribute to a more exact methodology of verification in gerontology.
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