P8.12 Arterial Distension-Pressure Loop Analysis in Hypertensive Rats: Advantages, Pitfalls and Possibilities

Arterial wall viscosity (AWV) of central arteries, as well as distensibility, is important to properly buffer systolic ejection pressure. AWV is measured either by the area within the hysteresis of distension-pressure (DD-P) loop, defined as the viscous energy (AWV=Ve) or the ratio of Ve/Ve+energy stored during systole (=AWV%). We record DD-P loop via echotracking; averaged over 30 cardiac cycles, AWV and AWV% are calculated via MatLab software. Here we perform a post analysis of the DD-P loop in 12 groups of rats (n=5–8): normo- or hypertensive, with and without arterial remodeling, at different operating blood pressures (BP), using different compounds. AWV decreases and DD-P loop is flattened with increased BP; moreover it is differently altered if pulse pressure (PP) is altered and remains low at any operating BP in models with vascular wall remodeling. However in all conditions the ratio AWV% is poorly modified. Our results suggest that the AWV as the Ve (hysteresis loop area) is the most relevant in defining the viscous properties of the artery; they indicate that mean operating BP, PP and structural distensibility independently participate in modifying the shape of the loop which is largely dependent on the delay between peak systolic pressure and peak systolic diameter, apparent in the higher BP of the loop. This suggests that isobaric distensibility cannot be compared in the lower and upper part of the loop but only at a similar mean BP. Further studies will aim to confirm these suggestions and determine how to improve loop hysteresis evaluation