Exercise training-induced increase in coronary transport capacity.

The objective of this study was to measure effects of exercise training on coronary flow heterogeneity, microvascular transport, and hemodynamics. Five miniature swine were trained on a treadmill (ET) for 16 wk; five control pigs (C) were confined to cages for the same period. At the end of that period we used the multiple indicator dilution method to measure permeability-surface area product (PS) to EDTA over a range of flow (F) in an anesthetized, open-chest preparation. We found that the heterogeneity of flow as measured by microspheres decreased with increasing F, but that ET had no clear effect on heterogeneity. We evaluated PS from the indicator concentration curves, taking into account flow heterogeneity and variations in capillary recruitment throughout the bed. In both C and ET pigs we observed an increase in PS with F until a maximum value of PS was reached at full recruitment. This relationship between PS and F was unaltered by ET. However, hemodynamic resistance was significantly reduced by ET, and F was higher at a given perfusion pressure after training. Since PS increases with F, ET pigs had higher PS values at typical coronary artery pressures.