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Regional coronary venous oxygen saturation and myocardial oxygen tension (PO 2 ) in isolated dog hearts were measured using two different methods--a new technique of microscopic oximetry and an improved oxygen electrode. Both methods yielded similar results. In studies of the isolated perfused dog heart developing a constant left ventricular systolic pressure, mean coronary venous oxygen saturation of blood in the subendocardial veins of the left ventricle was significantly lower than that in the subepicardial veins. Following abrupt increases in systolic pressure, subendocardial coronary venous saturations fell to even lower levels. Following abrupt decreases in systolic pressure, the mean subendocardial coronary venous oxygen saturation increased to levels above those in the blood of the subepicardial veins. These findings agree with the hypothesis that transient underperfusion and overperfusion of the subendocardial layers of the left ventricle occur with abrupt increases and decreases in ventricular pressure, respectively.
Gamble et al. (Wed,) studied this question.