Effects of Vasoactive Agents

Vasoactive drugs are known to affect impedance (pressure/flow) and vessel wall motion in arteries. The nonlinear theory of oscillatory flow in straight elastic vessels indicates that wall shear rate is affected by changes in impedance phase angle and wall motion. To test whether wall shear rate depends on impedance phase angle and wall motion in vivo, wall shear rate was measured in the abdominal aorta of anesthetized dogs by using a flush-mounted hot-film anemometer, and the hemodynamic state was characterized by pressure, flow, and vessel dimension measurements. Vasodilators (nitroprusside and isoproterenol) and vasoconstrictors (angiotensin II and norepinephrine) were administered acutely, and the responses of wall shear rate and hemodynamics were determined. In the control state (no drugs), peak wall shear rate was 1835+153 s-1 (mean±SEM). The vasodilators induced large increases in impedance phase angle and wall motion concomitant with large increases in peak wall shear rate (62.4+20.4% for nitroprusside and 68.9±28.3% for isoproterenol), which were not predicted accurately by Womersley's theory of oscillatory flow in a rigid vessel or the nonlinear theory of oscillatory flow in an elastic vessel, with measured flow and vessel dimension used as inputs. The vasoconstrictors induced small decreases in impedance phase angle and wall motion and small changes in peak wall shear rate (increase, 30.5+8.0% for norepinephrine; decrease, 18.2±7.1% for angiotensin II), which were predicted accurately by Womersley's theory. The present study shows that vasoactive drugs, particularly vasodilators, can have significant effects on wall shear rate (stress) in the abdominal aorta that appear to be related to changes in impedance phase angle and vessel wall motion. However, the effects on wall shear rate are not predicted accurately by straight-tube theory. (Circ Res. 1994;75: 637-649.)