Vasomotor coronary oscillations: A model to evaluate autoregulation

A simple model was proposed to characterise the oscillatory and nonoscillatory pattern of canine coronary circulation responses induced by a small dose of a vasodilator adenosine or the Ca²⁺-channel blocker diltiazem. This model consists of two differential equations describing the interaction of dilating (D) and constricting (C) resistance components. With the assumption that the rate constants associated with (D) were dependent on adenosine concentration and those associated with (C) were a function of Ca²⁺ channels, the model predicted: a) a damped oscillation of resistance to flow at low dose of adenosine, b) a predominant vasodilation at high dose of adenosine, and c) a sustained vasodilation in response to diltiazem. Parameters characterising the coronary resistance were evaluated by fitting the model results to calculated resistance from measured coronary flow and aortic pressure. As well, the model predicted accurately the peak resistance to great cardiac and coronary sinus venous flow in patients. This study indicates that the oscillation frequency of coronary resistance induced by a low dose of adenosine (0.01 mg/kg) is indicative of the uptake rate of adenosine by the heart and the coronary resistance provides considerable information on vasomotor control of the coronary circulation.