F. Jung, G. Pindur, B. Hiebl, R. P. Franke
[Applied Cardiopulmonary Pathophysiology 14: 229-235, 2010]
Under physiological conditions, tissue oxygen tension depends mainly on oxygen convection in the flowing blood and on oxygen consumption of the cells in the surrounding tissue. Below a certain limit velocity, 50 % of the cells in a Krogh cylinder do not receive enough oxygen to survive and cell death may occur. For a given capillary geometry, such a limit velocity can be calculated by finding numerical solutions to coupled partial differential equations.
The results show that the risk of tissue ischemia depends very strongly on capillary architecture and the velocity of capillary blood flow. When capillary erythrocyte velocity falls below 0.26 mm/s, there will be an insufficient blood supply to the region supplied by the distal venous branch of a capillary of 1 mm length, whereas in short capillaries this will occur only when velocities fall below 0.024 mm/s.
It seems that regions with a high metabolic demand, for example the retina or the myocardium, have short capillaries with rapid blood flow. This means that they have a greater blood flow reserve before an ischemic event can occur.
Key words: capillary dimension, ischemia, hypoperfusion
Prof. Friedrich Jung, M.D.
Center for Biomaterial Development and Berlin-Brandenburg Center for Regenerative Therapies (BCRT)
Centre for Materials and Costal Research