Interaction between Gregg's phenomenon and coronary flow control: a model study.

Coronary perfusion pressure, Pp, affects coronary arterial resistance, Ra, (autoregulation) as well as myocardial oxygen consumption, MVO2 (Gregg's phenomenon). The interaction between the effects of Pp and MVO2 on coronary flow control was investigated using a coronary flow control model. Model analysis predicts that response of the pressure-flow ratio, p/q(t), following a change in Pp depends on the sensitivity of Ra to a change in tissue oxygen concentration (tone sensitivity) and on the sensitivity of MVO2 to a change in capillary pressure (Gregg's sensitivity). At high tone sensitivity Gregg's effect is small, whereas at high Gregg's sensitivity autoregulation is attenuated. In experiments glibenclamide decelerated the p/q(t) in response to a pressure step by a factor of four. However, the proposed model demonstrates that this is compatible with a reduction in rate of change of Ra by a factor of ten. This is due to the interaction of negative and positive feedback gains in the model. Model analysis demonstrates that autoregulation and Gregg's phenomenon compete with each other in controlling coronary flow.