Biomedical Engineering Reference
In-Depth Information
7.3
AGING AS A PROCESS OF
COMPLEXITY LOSS
Lewis A. Lipsitz
The Hebrew Rehabilitation Center for the Aged,
Beth Israel Deaconess Medical Center, and
Harvard Medical School, Boston
Healthy physiologic function requires the integration of complex networks of control sys-
tems and feedback loops that operate on multiple scales in space and time. When meas-
ured continuously, the output of physiologic systems is highly complex, resulting in
dynamic behavior that can be described using techniques derived from fractal analysis.
These fractal-like physiologic processes enable an organism to adapt to the exigencies of
everyday life. During normal human aging the degeneration of various tissues and or-
gans, and the interruption of communication pathways between them, results in a loss of
complexity of physiologic systems and, consequently, a reduced capacity to adapt to
stress. Therefore, relatively minor perturbations such as new medications, a viral illness,
or emotional trauma may result in serious disability and death. Fortunately, a number of
novel interventions may be able to restore healthy dynamics in elderly individuals and
enhance their ability to adapt to a variety of external stimuli.
1.
INTRODUCTION
Classical research in the field of aging has been largely reductionistic, de-
fining the process of aging as a linear decline in many organs and physiol-
ogic systems until functional disability results (Figure 1) (1). However, aging
is a nonlinear, multidimensional process that is associated not only with
changes in individual systems but, probably more importantly, alterations in the
Address correspondence to: Lewis A. Lipsitz, MD, Hebrew Rehabilitation Center for the Aged,
1200 Centre Street, Boston, MA 02131 (Lipsitz@mail.hrca.harvard.edu).
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