Coronary driving pressure and vasomotor tonus as determinants of coronary blood flow.

AS GENERALLY agreed, the magnitude . of coronary flow is determined by the pressure head at the coronary ostia, the vasomotor tonus of the coronary vessels, and the compression exerted upon the intramural vessels by the beating heart muscle (not considering here: blood viscosity, coronary venous pressure, and certain other factors). Coronary flow is usually more than sufficient to supply the heart muscle with oxygen; the metabolic needs of the myocardium are dictated by its mechanical activity. The mechanisms that coordinate cardiac oxygen supply and consumption are not clear. Whenever coronary flow changes, it has been difficult to separate the role of coronary vasomotor tonus from passive variations of the coronary lumen resulting from alterations of intraluminal or extracoronary pressures. A method is described here whereby the three determinants of coronary flow, i.e., the active vasomotor state of the coronary vessel smooth muscle, and the intravascular and extravascular mechanical factors, can be separated and quantitated under different dynamic states.