USEFULNESS AND LIMITATIONS OF THE POSITIVE PROTOSYSTOLIC PEAK OF CORONARY ARTERIAL BLOOD-FLOW AS AN INDEX OF EPICARDIAL ARTERIAL COMPLIANCE

The aim of the study was to investigate the physiological meaning of t he positive peak which appears at the onset of ventricular ejection on traces of blood flow in the left coronary artery. It was proposed tha t the protosystolic peak could represent systolic charging of epicardi al coronary arterial compliance, i.e. the compliance which is not sque ezed by myocardial contraction and which resides in superficial corona ry arteries. To verify this hypothesis, blood flow was recorded from t he left circumflex coronary artery in five anesthetized open-chest dog s and the protosystolic peak was identified by visual analysis or on t he basis of zero-crossing of the first derivative. An index of epicard ial compliance (DELTAV/DELTAP) was derived by dividing the peak area ( DELTAV) by the aortic pulse pressure (DELTAP). Under basal conditions, the estimate of epicardial compliance, amounting to 0.2 71 +/- 0.149 x 10(-3) ml/mmHg (2.04 +/- 1.12 x 10(-12) m4s2kg-1; mean +/-SD), fell in the lower part of the range of values found by different authors an d increased during hemorrhagic hypotension, due to nonlinearities of c ompliance in general. Similar values of epicardial compliance were obt ained when a lumped resistance-capacitance parallel model was fitted t o systolic coronary blood flow. Unexpectedly, however, the protosystol ic peak was greatly decreased during coronary reactive hyperemia, We c onclude that the protosystolic peak can be used as an index of epicard ial compliance, but only at basal coronary vasomotor tone.