Biomedical Engineering Reference
In-Depth Information
Figure 1
. Age-related decrements in physiologic performance from Shock et al., the Baltimore
Longitudinal Study on Aging (1). Classical research in aging examined the mean values of
various physiologic functions in different age groups or over time, thus failing to recognize the
complex dynamics of these processes.
connections and interactions between system components. The complex mecha-
nisms by which these components interact to enable an organism to perform a
variety of functions necessary for survival is the subject of physiology.
Healthy physiologic processes require the integration of complex networks
of control systems and feedback loops that operate on multiple scales in space
and time (2). For example, physiologic systems exist at molecular, subcellular,
cellular, organ, and systemic levels of organization. Continuous interplay be-
tween the electrical, chemical, and mechanical components of these systems
ensures that information is constantly exchanged, even as the organism rests.
These dynamic processes give rise to a highly adaptive, resilient organism that is
prepared to respond to internal and external perturbations.
Recognition of the dynamic nature of regulatory processes challenges the
concept of homeostasis, which is taught by physiologists as a function of all
healthy cells, tissues, and organs to maintain static or steady-state conditions in
their internal environment (3). However, with the introduction of techniques that
can acquire continuous data from physiologic processes such as heart rate, blood
pressure, nerve activity, or hormonal secretion, it has become apparent that these
systems are in constant flux, even under so-called steady-state conditions. Dr.
Eugene Yates introduced the term
homeodynamics
to convey the fact that the
high level of bodily control required to survive depends on a dynamic interplay
of multiple regulatory mechanisms rather than constancy in the internal envi-
ronment (4).
