Hemodilution is an accepted modality for the conduct of
cardiopulmonary bypass. The degree of
hemodilution clinically employed has been in the range of 20 per cent of the initial hematocrit levels. This study was designed to evaluate the effects of
hemoglobin levels and
oxygen content on the reversibility of the damaged or altered ultrastructure of the endocardial layer of the ventricle and the possible role of the
no-reflow phenomenon. Two series of mongrel dogs were subjected to
cardiopulmonary bypass at normothermic levels and a standard period of ischemic arrest. One series was with
hemoglobin levels between 5 and 10 grams (mean 7.25 grams) designated as moderate
hemodilution (MH). The second series was of
hemodilution with less than 5 grams of
hemoglobin (mean 4.8 grams) designated as severe
hemodilution (SH). The ultrastructural alteration gradient (UAG) between the epicardium and endocardium was studied with its relationship to reversibility of myocardial function and animal survival. The study demonstrated a definitive relationship between
oxygen content and the reversibility of myocardial damage under normothermic conditions and anoxic arrest. The poor survival results in the SH group; two of 12 are attributed to the low
oxygen availability possibly triggering the
no-reflow phenomenon which prevents reversibility of the myocardial ultrastructural damage and ultimately the functional integrity of the ventricle.