MRI quantification of the role of the reflected pressure wave on coronary and ascending aortic blood flow

Abstract

The respective roles of the windkessel effect, which is related to the vessel compliance, and of the returning pressure wave, which is reflected off peripheral resistances, in generating the total diastolic blood flow in the ascending aorta (VT: coronary + flow through the upper part of the ascending aorta) were assessed under physiological conditions. In ten healthy young men (21–30 years), magnetic resonance phase mapping was used to assess non-invasively both blood flow and vessel cross-sectional area (CSA) at the upper part of the ascending aorta. Measurements of blood flow velocities and CSAs were carried out over complete cardiac cycles, with a 30 ms resolution time. The total diastolic blood flow volume (VT was significantly greater than the diastolic blood flow volume related to the windkessel effect (Vw). Consequently, since the windkessel effect could not account for the whole diastolic blood flow volume, the difference was attributed to the diastolic blood flow volume related to the reflected pressure wave (Vpw). The mean and SD of Vw and Vpw were estimated to be 4.34 ± 1.94 ml/cycle and 6.80 ± 2.40 ml/cycle (n = 10), respectively, for a measurement slice placed at 5.12 cm (on average) from the aortic valve and a mean coronary diastolic blood flow volume assumed to be equal to 4 ml/cardiac cycle in all subjects. The present non-invasive MR phase mapping study indicates that the windkessel effect and the reflected pressure wave might play a similar role in generating the total diastolic blood flow in the ascending aorta, under physiological conditions. Furthermore, pathophysiologic implications are discussed.