Micro Flows in the Cardiopulmonary System: A Surgical Perspective - Bioanalysis Advanced Materials Methods and Devices - page 69

Fig. 5.1 Coronary artery stents

Atherosclerotic disease primarily affects the large conductance vessels of the
heart. The hemodynamic effect that a coronary artery stenosis has upon blood flow
may be considered in terms of Poiseuille's law, which describes the resistance ( R )
of a viscous fluid to laminar flow through a cylindrical tube. Resistance is inversely
proportional to the fourth power of the radius ( r ) and directly proportional to
the length ( L ) of the narrowing, and viscosity of the fluid ( m ). By Poiseuille's law
a 1-cm, 80% stenosis has a resistance that is 16 times as high as the resistance of a
1-cm, 60% stenosis. Similarly, if this stenosis progresses to a 90% stenosis, the
resistance is 256 times as great as the resistance of a 60% stenosis [ 6 , 10 ]

=p r 4

R 8 m L

¼

Placement of coronary artery stents (Figs. 5.1 and 5.2 ) or coronary artery bypass
(Fig. 5.3 ) reestablish the coronary blood flow and decrease the probability of
myocardial infarction. However, this approach is only addressing the patency of
large vessels and there is increasing evidence that the microcirculation plays a very
relevant role in the pathophysiology of myocardial perfusion states with increased
flow resistance.