Pressure but not angiotensin II-induced increases in wall mass or tone influences static and dynamic aortic mechanics

Objective To distinguish between static (due to slow changes in pressure) a nd dynamic (due to pressure pulsatility) components of aortic compliance ov er a large pressure range in vivo and to examine the effects of increased v ascular mass and smooth muscle tone on these components, Methods Using ultrasound wall tracking, aortic lumen area-pressure curves w ere generated in anaesthetized rats over a broad range of pressures by alte ring blood volume. The compliance coefficient calculated at each mean press ure was considered the dynamic compliance at that pressure; the slope of th e diastolic lumen area - pressure curve represents static compliance. Exper iments were performed in control rats and rats treated with angiotensin II( ANG II) acutely (500 ng/kg per min intravenously) to modify vascular tone o r chronically (250 ng/kg per min subcutaneously for 2 weeks) to modify vasc ular mass. Results The dynamic compliance-pressure curve approximated a parabola, Maxi mal dynamic compliance (0.272 +/- 0.026 mm(2)/kPa in control rats) was achi eved at near-normotensive pressure (+/- 105 mmHg), The diastolic lumen area -pressure curve showed an exponential relationship within a physiological r ange (30-130 mmHg), ANG II-induced increases in aortic wall mass or smooth muscle tone did not modify the relationship between static or dynamic compl iance and pressure. Conclusions These findings demonstrate that static and dynamic mechanics of the rat thoracic aorta depend differently on blood pressure. Static compli ance increases slightly with pressure in a physiological range, while dynam ic compliance is auto-regulated around normotensive pressures, Neither stat ic nor dynamic compliance of the rat thoracic aorta are influenced by ANG I I-induced increases in aortic wall mass or smooth muscle tone. J Hypertens 1999, 17:1109-1116 (C) Lippincott Williams & Wilkins.