Ever since Richard W. Eckstein reported evidence of anastomoses, or the fusion of previously detached blood vessels in the body, researchers have sought to explain the exact mechanisms that allow this phenomenon to occur (Eckstein, 1957). When a patient experiences ischemia, there is often a biological response to deliver oxygenated blood to the myocardial region being cut-off through an alternate pathway by means of collateral circulation, or more specifically in this case, coronary collateral circulation. If this alternate route did not exist, the cardiac tissue would die (Seiler, 2003).
New blood vessels can be formed from preexisting ones in collateral circulation pathways through the process of angiogenesis. It is thought that in order …show more content…
Arteriogenesis is the conversion of pre-existing anastomoses to functioning arteries through the induction of shear fluid stress. When looking at coronary collateral circulation, arteriogenesis plays a role in the 20-fold enlargement of existing collateral arterioles once the major supply artery is obstructed and a collateral circulation method of blood supply is crucial. Once this occurs, endothelial cells express monokines and monocyte adhesion molecules, which help break down the pre-existing vessels and prompt the re-growth of smooth muscle cells and vessel expansion. Interestingly, this theory is confirmed by a study that demonstrates that arteriogenesis is impaired in mice that lack macrophage colony-stimulating factors and placental growth factors (PLGF) because these substances are thought to promote collateral growth and smooth muscle cell growth by increasing monocyte recruitment (Heil et al., 2006; Carmeliet, …show more content…
In dogs and pigs, it is thought that hypoxia and peripheral wall stress induce the coronary collateral vasculature to expand and enlarge through active growth processes. Long-term exercise has the potential to alter chemical and physical factors involved in these processes such as platelet-derived growth factors and hypertrophy of left ventricular wall thickness due to training. Pigs have vasculature that is more similar to humans and have demonstrated increases in the intricate anastomotic network of coronary collateral blood vessels after participating in exercise programs, demonstrating that it is possible that the human heart may respond to exercise in the same way with similar cardiac adaptations (Roth et al., 1990; Bloor et al.,