Quantitative determination of regional oxygen consumption in the dog heart

A micro-Fick method has been developed to measure the O2 consumption of different regions of an organ. The method was tested in isolated dog gracilis muscle and consisted of microspectrophotometric determination of arterial and venous O2 saturation in quick frozen tissue to determine O2 extraction and flow measured with 85Sr-labeled microspheres, with O2 consumption calculated from the product. This was compared to electromagnetically measured flow and O2 extraction determined by Van Slyke or CO-oximeter. The accuracy of the new measurement was at worst 8.7% for O2 consumption over the range tested in a single muscle. In the hearts of anesthetized open-chest dogs, right ventricular O2 consumption, 7.1 +/- 0.9 ml O2/min per 100 g, was significantly lower than left, 11.0 +/- 0.4. This gradient was related to a blood flow difference. Right ventricular base had a 51% lower O2 consumption than right ventricular apex. In the left ventricle, subepicardial O2 consumption, 9.5 +/- 0.7, was lower than that of the subenocardium, 12.1 +/- 0.7. This difference was related to a difference in O2 extraction.