Biomedical Engineering Reference
In-Depth Information
to an obstruction of a blood vessel, occurring in approximately 85 percent of the
cases. A hemorrhagic stroke is due to a rupture of a blood vessel, which occurs in
approximately 15 percent of the cases (Rosamond 2008).
10.2.2 Impairments
Due to blood deficiency, as a direct consequence of the stroke, brain tissue is
destructed. This can result in a variety of sensory, motor, cognitive and psycholog-
ical impairments. This includes sensory loss, hemispatial neglect, aphasia, mus-
cle weakness, spasticity, limited movement coordination, attention and memory
deficits, depression and behavioral changes (Speach 1995).
Concerning the motor domain, a stroke often leads to damage of descending
nerve pathways from the brain to the spinal cord, and of neural communication
between brain areas. A reduction in integration of sensory and motor information
combined with altered nerve signals, limits the selective activation of muscles.
Coupled activation of muscles is often observed, such as shoulder abduction and
elbow flexion, called muscle synergies. Without selective and voluntary control
of muscles, arm and hand functionality is impaired, causing serious limitations in
activities of daily living (Dewald 1995, Beer 1999).
Weakness is a common impairment of the upper extremity in 77 percent of the
patients with a first-ever stroke (Lawrence 2001). Even after six months, 60 percent
of stroke survivors have a hemiparetic arm which remains without function, due
to for example weakness, synergistic coupling or spasticity in the arm (Kwakkel
2003).
10.2.3 Recovery
Spontaneous neurological recovery occurs after stroke. This involves short-term
and long-term (from six months onward) physiological mechanisms in the brain
(Kwakkel 2004). The extent of the neurological recovery varies among patients.
Though, the recovery of motor functions follows a stereotypical sequence (Kreisel
2006).
When damage in the brain is detected, enhancement of active brain tissue
surrounding the damaged area (infarct) occurs. Within days the swelling from
excessive accumulation of plasma fluid in the tissue surrounding the infarct is re-
duced. Therefore reperfusion of the blood deprived brain area around the infarcted
area can occur and the ischemic penumbra is resolved. Also the diaschisis, which
is a malfunction of remote brain areas due to lack of neural input, is diminished.
Due to these short-term mechanisms related brain areas can regain their neural
communication (Speach 1995, Krakauer 2005).
A longer-term mechanism involved in natural neurological recovery is neural
plasticity: cortical representations of, for example motor actions change during
recovery. Cortical reorganization can occur in areas adjacent to and remote from
the infarcted area, both in the infarcted (ipsilesional) and opposite (contralesional)
