Regional O2 consumption in canine left ventricular myocardium in experimental acute aortic valvular insufficiency

Moderate and severe acute aortic valvular insufficiency (AVI) were produced for 30 min in anesthetised, open-chest dogs, in order to measure O2 consumption in subepicardial (EPI) and subendocardial (ENDO) regions of the left ventricular free wall. Regional O2 consumption (MVO2) was determined from regional O2 extraction and blood flow data determined by absorbence microspectrophotometry and radioactive microspheres. In all groups, venous saturations were lower and O2 extractions higher in the ENDO than in the EPI. Oxygen extractions increased in both regions in both severities of AVI, but more so with severe AVI. The ENDO became perfused relative to the EPI with increasing severity of AVI. Left ventricular MVO2 increased with AVI; however, ENDO MVO2 increased less than EPI MVO2. ENDO/EPI blood flow ratios decreased from 1.21 to 0.93 in moderate AVI and to 0.76 in severe AVI. ENDO/EPI MVO2 ratio decreased from 1.44 in controls to 0.94 in moderate and 0.54 in severe AVI. The ENDO/EPI MVO2 ratios began to decrease when DPTI/SPTI was less than 0.4 to 0.5. We conclude that AVI increases MVO2, but the ENDO cannot maintain its MVO2 relative to EPI because of proportionately less ENDO flow, and maximal O2 extraction.