Pulse Wave Velocity Measured at End-Diastole Underestimates Aortic Stiffness

Introduction: Aortic stiffness (AS) is assessed using pulse wave velocity (= distance (D) between two aortic sites / foot-to-foot transit time of pressure or velocity pulse (ffPTT) between the sites ) which is considered as “gold standard”. But, PWV varies with cyclic pressure in the normal aorta and PWV measured at end-diastole underestimates AS. This underestimation is greatest when aorta is the stiffest. Hypothesis: We hypothesize that PWV measured at diastole is lower than that measured at systole and that PWV should be measured over the entire cardiac cycle for better representation of AS. Methods: We measured pressures invasively with a dual sensor catheter (0.46 mm dia) at two descending aortic sites (25 mm apart) in normal rats. We measured blood velocities noninvasively with two Doppler probes placed at aortic arch and abdominal aorta. The pressure and blood velocity signals were acquired simultaneously (at baseline & post-esmolol admin). From the two pressure signals we measured PWVsp (at dicrotic notch; end-systolic fiducial marker) and PWVdp (at end-diastole; foot fiducial marker). PWVd (end-diastole; foot) was measured from the two blood velocity signals. Results & Conclusions: We plotted the PWV versus blood pressure. We found that the slope of aPWVsp > the slope of aPWVdp indicating that PWV varies with blood pressure within the cardiac cycle. We also found that slope of aPWVd < aPWVdp because, D used to calculate PWVdp is fixed at 25mm, whereas D used to calculate aPWVd was estimated as the distance between Doppler probe tips on the surface of the skin (aortic arch curvature was not accounted for). In conclusion, a more representative AS can be assessed through 1. PWV measurement at systole & diastole within the cardiac cycle of a noninvasively measured vessel wall motion (a pressure signal surrogate) where the systolic and diastolic fiducial points can be identified, and 2. use of two aortic sites on the straight part of the descending aorta for better estimating of D.