ARTERIAL ADAPTATION TO INCREASED WALL SHEAR-STRESS

The timing and magnitude of arterial dilation in response to increased flow velocities and the effect on wall shear stress were evaluated in a chronic nonatherogenic animal model. A 7 mm femoral arteriovenous f istula was constructed in one groin in 10 mongrel dogs, the other groi n serving as a control. Duplex ultrasound was used at regular interval s to make bilateral measurements of systolic and diastolic luminal dia meters, peak systolic velocity, and volume flows to allow estimation o f wall shear stress and any vasodilation; measured systemic pulse pres sure was used to calculate compliance. Data were acquired at baseline; immediately postoperatively; at one and two weeks, and at one, three, five, and seven months. There were no significant changes from baseli ne in control vessels at any time interval in blood flow (135 +/- 56 m l/min), lumen diameter (4.4 +/- 0.4 mm), wall shear stress (8.8 +/- 4. 3 dynes/cm(2)), or compliance (0.14 +/- 0.04 %/mmHg). In the experimen tal vessels, baseline values were not significantly different from tho se seen on the control side. Immediate postoperative fistula flow was 1590 +/- 295 ml/minute, and these flow values were maintained througho ut the study. Immediately postoperatively the luminal diameter increas ed to 5.6 +/- 0.5 mm with a calculated shear stress of 49.8 +/- 14.1 d ynes/cm(2) (P < 0.001 compared with baseline). This increase in lumina l diameter and the resulting shear stress remained essentially constan t throughout the study, with values of 5.8 +/- 0.3 mm and 47.0 +/- 11. 5 dynes/cm(2), respectively, at seven months. No significant changes i n compliance were seen during the study. The authors conclude that inc reased blood flow alone causes early moderate arterial dilation but wi ll not produce a complete normalization of wall shear stress. For that to occur, additional mechanisms may be involved relating increased sh ear stress and dysfunctional vascular endothelium, such as occurs in h ypercholesterolemia.