Heterogeneity of local myocardial flow and oxidative metabolism

Abstract

In mammalian hearts, local myocardial flow (LMF) varies between 20 and 200% of the mean. It is not clear whether oxidative metabolism has a similar degree of heterogeneity. Therefore, we investigated the relation between LMF and local oxidative metabolism in isolated rabbit hearts. Buffer oxygenation with 18O2 resulted in labeled myocardial oxidation water (H2 18O). In four hearts, myocardial oxygen consumption (MV˙o 2) was calculated from the H2 18O production and compared with that calculated according to Fick. In eight additional hearts, LMF was measured using microspheres. Coronary venous H2 18O kinetics and local H2 18O residues were determined and analyzed by mathematical modeling. MV˙o 2 recovery from H2 18O was >93% compared with that according to Fick. LMF ranged from 1.91 to 11.24 ml · min−1 · g−1, and local H2 18O residue ranged from 0.41 to 1.04 μmol/g. Both variables correlated ( r = 0.62, n = 64, P < 0.001). Measurements in nine hearts were fitted by modeling using capillary permeability-surface area products ( PS c) from 2 to 10 ml · min−1 · g−1. With flow-proportional PS c, a 3.33-fold difference in LMF was associated with a 6.45-fold difference in local MV˙o 2. Both LMF and local oxidative metabolism are spatially heterogeneous, and they correlate to one another.