General Notes on Coronary Circulation

•Flow determined by myocardial Oxygen requirement (myocardial metabolism rate)

•O₂ extraction is normally very high, so this is not important in increasing O₂ supply

•At rest there is pronounced basal tone in precapillary resistance vessels of heart

-This is NOT due to neural input

-Vessels are autoregulated… low O₂ in vessel triggers automatic vasodilation

•Catecholamines effects on coronary vessels:

-Indirect action of coronary vasodilation due to incr. O₂ demands of myocardium

-Direct action of decreasing flow to subendocardium

•this effect can be independent of changes in total coronary flow

•Diastole is the major time of coronary blood flow

-Systole only accounts for about 20-30% of coronary blood flow

-this percentage decreases with increased cardiac activity

Category: Physiology Notes