Biomedical Engineering Reference
In-Depth Information
Figure 5
. The effect of autonomic blockade with atropine and propranolol on RR interval
dynamics in a healthy human subject.
connectivity are lost, resulting in a less complex output signal. This loss of com-
plexity is associated with a decline in functional ability. Finally, late in life,
physiologic inputs are diminished to the extent that the output becomes periodic
or random, and the individual crosses a frailty threshold. At this point the ability
to adapt to stress is lost and relatively minor perturbations such as new medica-
tions, a viral illness, or emotional trauma may result in serious disability and
death.
6.
INTERVENTIONS TO RESTORE COMPLEXITY IN
PHYSIOLOGIC SYSTEMS
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. Some single interventions that have multiple system effects
have already shown to improve functional ability in older individuals. These
include exercise (18), which can improve physical and mental function, and
medications such as beta-blockers, which reverse many of the physiologic con-
sequences of congestive heart failure. Other multifactorial interventions that
address the multiple systems that are impaired in individuals with syndromes
such as falls (19) or delirium (20) have also proven useful in clinical trials. Re-
cently, Dr. Collins and colleagues demonstrated that low levels of mechanical or
electrical noise can be used to enhance somatosensation and thus improve pos-
tural control in healthy elderly subjects and patients with diabetic neuropathy or
stroke (21). New dynamic drug delivery systems provide more physiologic drug
