Summary and Conclusions Summary and Conclusions

164 In the present thesis we have investigated heterogeneous local blood flow in the left ventricle of the heart, and compared this to local oxygen consumption measured in the same tissue sample at the same time point. For many years it has been known that blood flow can be very heterogeneous, but the relation with local oxygen demand was unclear. From previous studies it was known that there was likely an adaptation of local supply to demand in the heart, but because oxygen consumption could not be measured at sufficiently small spatial resolution at the same time as oxygen delivery, this point was not proven. In all studies described in this thesis, we compared oxygen consumption per heart estimated by NMR spectroscopy to oxygen consumption as calculated from blood gas data to validate our method. In all studies a rather good correlation was found, which, in our opinion, at least means that the NMR-based method is quite robust. A disadvantage of the method is the destructive character. In our experiments the animal was sacrificed because it was necessary to freeze-clamp the heart at the end of the experiment, in order to stop metabolism as quickly as possible. Further, we can only estimate local oxygen consumption at one time point, i.e. at the end of the experiment, while we can measure local blood flow at various moments. However, in the control group, blood flow was quite stable over time. With other techniques, especially positron emission tomography, it might be possible to get the same results, but the resolution is still less than for our method. Better spatial resolution with our 13 C method may be possible if metabolites are measured with mass spectrometry. Discrepancy between different groups may be caused by experimental procedures. Basal blood flow in the control group was lower than in the ischemia group before occlusion was applied. A possible reason might be that we manipulated the left anterior descending artery by applying a partial occluder around the artery, causing a difference in blood flow distal to the occluder. However, we have no reason to believe that blood flow heterogeneity is different in this group. We know that measurement of blood flow by microspheres has relative errors of about 5%, and the 13 C NMR method has even larger errors. For the NMR method the error margins depend on the parameters that are analysed. For the estimation