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 (pO2), consumption, and delivery in crystalloid normoperfused (perfusion pressure>70 mmHg) and hypoperfused (perfusion pressure approximately 50 mmHg) constant flow isolated rat hearts. EPR oximetry with lithium phthalocyanine was used to measure myocardial pO2. Baseline myocardial pO2 (means +/- SE) was 185 +/- 13 mmHg (normoperfused) and 162 +/- 14 mmHg (hypoperfused). Myocardial pO2 fell to < 1 mmHg during no-flow ischemia. After recovery from repetitive ischemia, myocardial pO2 and coronary resistance increased significantly in all hearts; oxygen consumption and left ventricle work decreased in normoperfused hearts, although not significantly compared with controls, and did not change significantly in hypoperfused hearts. Increased myocardial pO2 in the normoperfused group may be due to decreased oxygen consumption and/or increased local delivery, while increased myocardial pO2 in the hypoperfused hearts is due to increased local oxygen delivery.