The Human Cardiovascular System - Computational Hemodynamics: Theory, Modelling and Applications - page 39

in other non-major arteries can result in pain in the areas of the body deprived of
oxygen, which can lead to cell death.
Medical devices such as heart stents or artificial heart valves used for cardiovas-
cular treatments are complicated by thrombosis formation and fatal haemorrhage.
These issues are partially linked with the bio-fluid dynamics phenomena within
the heart and arteries. For example blood cell damage leading to trauma of the
erythrocytes is caused by excessive turbulence; and blood clot formation incurred
by stagnant flow. Hemolysis or rupture of erythrocyte membrane due to high shear
flow also aggravates platelet activation. Furthermore, platelets in a high shear flow
have a higher chance of activation, leading to thrombus formation. At the same
time, high shear stress is necessary for preventing the activated platelets from ad-
hering to the artificial surface of an implanted medical device and forming platelet
aggregation. It should be noted that a layer of adsorbed plasma protein accumulates
onto an artificial surfaces rapidly when it comes into contact with blood, and this
forms an interface for the platelets. Therefore, platelet activation and adhesion have
to be balanced in terms of viscous shear stress, which significantly complicates the
design of an artificial device.

2.3.5 Stroke

Haemorrhagic stroke develops when bleeding is present within the brain of a patient
diagnosed with aneurysm in the cerebral arteries. It is a common cause of death by
cardiovascular disease and affects 15 % of stroke patients in the world's population
(AIHW Board 2008). Its onset has been linked to diabetes, obesity, alcoholism, to-
bacco use and copper deficiency (Valencia et al. 2008). Patients who die from such
a medical condition exhibit copper deficiency of approximately a quarter quantity
of a normal person. Tobacco and alcohol intake diminishes the copper content with-
in the body, resulting in the progression of aneurismal growth (Utter and Rossmann
2007).
As mentioned in Sect. 2.3.4, a blood clot can travel to the cerebral artery with-
in the brain of a patient and block the blood supply to result in ischemic stroke.
In a similar manner, when plaque in the atherosclerotic region of a carotid artery
ruptures, debris of the vulnerable plaque may result. This debris flows with the
blood and blocks the narrow vessels downstream of the artery (Fig. 2.19 ). Another
means of a complete arterial occlusion is by tearing of the tunica intima at the arte-
rial wall which results in an arterial dissection of the carotid arteries, causing blood
clots to enter between the inner and outer layers of the vessel. Ischemic and haemor-
rhagic stroke conditions account for 85 % and 15 % of cases respectively.
Blockage of cerebral arteries in the brain can give rise to a condition known as
cerebral thrombosis. This can cut off blood supply to the brain in the micro-scale
arteries. When the smaller diseased vessels rupture and bleed, cerebral haemor-
rhage occurs. Both these events are known as cerebrovascular disease of which the
most common is stroke. A stroke results in numbness or paralysis, affecting speech,
swallowing, vision, body balance and coordination. Stroke is a growing epidemic