EFFECT OF REPETITIVE ISCHEMIA ON MYOCARDIAL OXYGEN-TENSION IN ISOLATED-PERFUSED AND HYPOPERFUSED RAT HEARTS

The objective of this study was to determine the effects of repetitive ischemia on myocardial oxygen tension (pO(2)), consumption, and deliv ery in crystalloid normoperfused (perfusion pressure >70 mmHg) and hyp operfused (perfusion pressure similar to 50 mmHg) constant flow isolat ed rat hearts, EPR oximetry with lithium phthalocyanine was used to me asure myocardial pO(2). Baseline myocardial pO(2) (means +/- SE) was 1 85 +/- 13 mmHg (normoperfused) and 162 +/- 14 mmHg (hypoperfused). Myo cardial pO(2) fell to <1 mmHg during no-flow ischemia, After recovery from repetitive ischemia, myocardial pO(2) and coronary resistance inc reased significantly in all hearts; oxygen consumption and left ventri cle work decreased in normoperfused hearts, although not significantly compared with controls, and did not change significantly in hypoperfu sed hearts, Increased myocardial pO(2) in the normoperfused group may be due to decreased oxygen consumption and/or increased local delivery , while increased myocardial pO(2) in the hypoperfused hearts is due t o increased local oxygen delivery.