Biomedical Engineering Reference
In-Depth Information
Figure 9
. Systems-medicine conceptual framework: intertwined Man (Patient)-Machine
(Sensors/Devices) and Patient-Clinician interaction and communication. The confluence of
complexity and systems robustness gives rise to a mutually reinforcing state of fragility and
risk.
and that can give rise to highly coordinated and optimized behavior. The com-
plex adaptive behavior of global-level structures that emerges is a consequence
of nonlinear spatiotemporal interactions of local-level processes or subsystems
(see Figure 10). This form of nested cooptation (across levels of organization) is
evident in isolated cells, organisms, societies, and ecologies. Systems of this
type are nonlinear, nonstationary, nonequlibrium, and nonreductionist, and are
governed by universal principles of adaptation and self-organization in which
control and order are emergent rather than predetermined.
From a system-theory standpoint, a system that is endowed with a greater
number of degrees of freedom is more robust and has a greater ability to ac-
commodate imposed disturbances. In general, biological systems, independent
of hierarchical organization (molecular to multicellular), normally operate such
that a finite number of regulatory modes can be invoked. Chaotic systems are
extremely susceptible to changes in initial conditions, i.e., small changes in a
parameter of a chaotic system can produce a large change in the output, i.e.,
poised at the "edge of chaos" (18). This ability allows the system to switch
quickly from one state to another. It may be that the chaotic regime enables a
subsystem to exert its function such that regulatory changes can be achieved
with minimal external input, reminiscent of self-organized criticality seen in
other physical phenomena. From a standpoint of economy of performance (en-
ergy use, responsiveness), some upper limit must be set on the number of active
degrees of freedom (control variables) that can or need be summoned. Most
