A two-dimensional Doppler ultrasonic probe for flow measurement.

The use of a single-transducer pulsed-Doppler ultrasound system in clinical practice has been severely limited, not only by the effects of acoustics and physiologic parameters, but also by inaccuracy because the Doppler angle between the transducer axis and the flow velocity is unknown. In this study, a dual-transducer pulsed-Doppler ultrasound system was used because the Doppler angle could be directly calculated for more accurate determination of the fluid flow velocity vector. From the velocity estimate and velocity profiles, other flow characteristics such as volume flow rates and shear stress can also be estimated. Experimental results indicated that the new transducer model could increase the accuracy of fluid flow velocity measurement and thereby improve the ability to estimate the characteristics of turbulent fluid flow for research and diagnostic purposes.

Effects of amrinone and dopamine on uterine blood flow and vascular responses in the gravid baboon.

Amrinone is a bipyridine derivative with positive inotropic and vasodilator properties. We investigated its effects on uterine and iliac artery blood flow, blood pressure, and heart rate in 10 acutely instrumented gravid baboons. Amrinone was compared with dopamine, infused systemically or regionally via the common iliac artery. When given intravenously at a constant rate of 40 micrograms/kg/min, amrinone produced a slight increase in iliac artery blood flow but did not significantly alter mean arterial pressure, heart rate, or uterine artery blood flow. Dopamine at an intravenous dose of 40 micrograms/kg/min produced a mean (+/- SD) 49.2% +/- 18.7% increase in mean arterial pressure (p less than 0.01) and a 84.2% +/- 56.1% increase in uterine vascular resistance (p less than 0.01), but caused no changes in heart rate, uterine artery blood flow, or iliac artery blood flow. Regional infusion of amrinone at the rate of 25 micrograms/kg/min produced a significant increase in iliac artery blood flow (p less than 0.01) without changing uterine artery blood flow, heart rate, or mean arterial pressure. Regional infusion of dopamine at concentrations of 2.5 to 25 micrograms/kg/min produced decreases in flow (p less than 0.01) and increases in resistance (p less than 0.01) in the uterine and iliac vascular beds. We conclude that amrinone dilates the vascular bed of the external iliac artery, but has no remarkable effect on the uterine vascular bed. Dopamine increases uterine vascular resistance and may impair uteroplacental perfusion.