A new look into the microscope: proliferation and regression of myocardial capillaries.

The key to understanding the mechanics of capillary proliferation probably lies in comprehension of the normal capillary growth during the early postnatal period when most of the terminal vessels in mammalian hearts are being formed. Similarly, stimulated cardiac growth is accompanied mainly, but not exclusively, by capillary proliferation if it takes place in the young, growing organism. The opposite situation, decreased capillarization of the heart, is commonly found in several experimental and clinical situations. The cause of lower capillary density is more often due to the growth of capillaries which is slower than the rate of growth of the remaining tissue, rather than to a disappearance of the existing capillaries. This brief review is followed by the discussion of how to evaluate the myocardial capillary supply based on the theoretical analysis of the effect of alterations in capillary surface density on myocardial PO2. The final part deals with confusing teminology in the field, with the following terms discussed in depth: diffusion distance, maximal diffusion distance and hexagonal array.