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Sci. Aging Knowl. Environ., 21 April 2004
Vol. 2004, Issue 16, p. pe16
[DOI: 10.1126/sageke.2004.16.pe16]


Physiological Complexity, Aging, and the Path to Frailty

Lewis A. Lipsitz

Lewis A. Lipsitz is at the Hebrew Rehabilitation Center for Aged, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, MA 12131, USA. E-mail: Lipsitz{at}

Key Words: complexity • variability • fractal • power law • heart rate • frailty

Abstract: Healthy physiological processes require the complex interaction of multiple control systems operating over multiple time scales. The output of these processes (for example, heart rate, blood pressure, hormonal rhythms, or postural sway) demonstrates complex variability that can be quantified using the concept of fractals, derived from the field of nonlinear dynamics. Complex physiological dynamics enable an organism to rapidly respond to the internal and external perturbations of everyday life. Aging and disease are associated with a loss of complexity in the dynamics of many physiological systems. This loss of complexity may reduce the ability to adapt to stress and lead to the syndrome of frailty.

Citation: L. A. Lipsitz, Physiological Complexity, Aging, and the Path to Frailty. Sci. Aging Knowl. Environ. 2004 (16), pe16 (2004).

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Science of Aging Knowledge Environment. ISSN 1539-6150